diff --git a/.ghci b/.ghci
new file mode 100644
--- /dev/null
+++ b/.ghci
@@ -0,0 +1,1 @@
+:set -Wall
diff --git a/COPYING b/COPYING
new file mode 100644
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,674 @@
+ GNU GENERAL PUBLIC LICENSE
+ Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc.
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+ Preamble
+
+ The GNU General Public License is a free, copyleft license for
+software and other kinds of works.
+
+ The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works. By contrast,
+the GNU General Public License is intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users. We, the Free Software Foundation, use the
+GNU General Public License for most of our software; it applies also to
+any other work released this way by its authors. You can apply it to
+your programs, too.
+
+ When we speak of free software, we are referring to freedom, not
+price. Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+them if you wish), that you receive source code or can get it if you
+want it, that you can change the software or use pieces of it in new
+free programs, and that you know you can do these things.
+
+ To protect your rights, we need to prevent others from denying you
+these rights or asking you to surrender the rights. Therefore, you have
+certain responsibilities if you distribute copies of the software, or if
+you modify it: responsibilities to respect the freedom of others.
+
+ For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must pass on to the recipients the same
+freedoms that you received. You must make sure that they, too, receive
+or can get the source code. And you must show them these terms so they
+know their rights.
+
+ Developers that use the GNU GPL protect your rights with two steps:
+(1) assert copyright on the software, and (2) offer you this License
+giving you legal permission to copy, distribute and/or modify it.
+
+ For the developers' and authors' protection, the GPL clearly explains
+that there is no warranty for this free software. For both users' and
+authors' sake, the GPL requires that modified versions be marked as
+changed, so that their problems will not be attributed erroneously to
+authors of previous versions.
+
+ Some devices are designed to deny users access to install or run
+modified versions of the software inside them, although the manufacturer
+can do so. This is fundamentally incompatible with the aim of
+protecting users' freedom to change the software. The systematic
+pattern of such abuse occurs in the area of products for individuals to
+use, which is precisely where it is most unacceptable. Therefore, we
+have designed this version of the GPL to prohibit the practice for those
+products. If such problems arise substantially in other domains, we
+stand ready to extend this provision to those domains in future versions
+of the GPL, as needed to protect the freedom of users.
+
+ Finally, every program is threatened constantly by software patents.
+States should not allow patents to restrict development and use of
+software on general-purpose computers, but in those that do, we wish to
+avoid the special danger that patents applied to a free program could
+make it effectively proprietary. To prevent this, the GPL assures that
+patents cannot be used to render the program non-free.
+
+ The precise terms and conditions for copying, distribution and
+modification follow.
+
+ TERMS AND CONDITIONS
+
+ 0. Definitions.
+
+ "This License" refers to version 3 of the GNU General Public License.
+
+ "Copyright" also means copyright-like laws that apply to other kinds of
+works, such as semiconductor masks.
+
+ "The Program" refers to any copyrightable work licensed under this
+License. Each licensee is addressed as "you". "Licensees" and
+"recipients" may be individuals or organizations.
+
+ To "modify" a work means to copy from or adapt all or part of the work
+in a fashion requiring copyright permission, other than the making of an
+exact copy. The resulting work is called a "modified version" of the
+earlier work or a work "based on" the earlier work.
+
+ A "covered work" means either the unmodified Program or a work based
+on the Program.
+
+ To "propagate" a work means to do anything with it that, without
+permission, would make you directly or secondarily liable for
+infringement under applicable copyright law, except executing it on a
+computer or modifying a private copy. Propagation includes copying,
+distribution (with or without modification), making available to the
+public, and in some countries other activities as well.
+
+ To "convey" a work means any kind of propagation that enables other
+parties to make or receive copies. Mere interaction with a user through
+a computer network, with no transfer of a copy, is not conveying.
+
+ An interactive user interface displays "Appropriate Legal Notices"
+to the extent that it includes a convenient and prominently visible
+feature that (1) displays an appropriate copyright notice, and (2)
+tells the user that there is no warranty for the work (except to the
+extent that warranties are provided), that licensees may convey the
+work under this License, and how to view a copy of this License. If
+the interface presents a list of user commands or options, such as a
+menu, a prominent item in the list meets this criterion.
+
+ 1. Source Code.
+
+ The "source code" for a work means the preferred form of the work
+for making modifications to it. "Object code" means any non-source
+form of a work.
+
+ A "Standard Interface" means an interface that either is an official
+standard defined by a recognized standards body, or, in the case of
+interfaces specified for a particular programming language, one that
+is widely used among developers working in that language.
+
+ The "System Libraries" of an executable work include anything, other
+than the work as a whole, that (a) is included in the normal form of
+packaging a Major Component, but which is not part of that Major
+Component, and (b) serves only to enable use of the work with that
+Major Component, or to implement a Standard Interface for which an
+implementation is available to the public in source code form. A
+"Major Component", in this context, means a major essential component
+(kernel, window system, and so on) of the specific operating system
+(if any) on which the executable work runs, or a compiler used to
+produce the work, or an object code interpreter used to run it.
+
+ The "Corresponding Source" for a work in object code form means all
+the source code needed to generate, install, and (for an executable
+work) run the object code and to modify the work, including scripts to
+control those activities. However, it does not include the work's
+System Libraries, or general-purpose tools or generally available free
+programs which are used unmodified in performing those activities but
+which are not part of the work. For example, Corresponding Source
+includes interface definition files associated with source files for
+the work, and the source code for shared libraries and dynamically
+linked subprograms that the work is specifically designed to require,
+such as by intimate data communication or control flow between those
+subprograms and other parts of the work.
+
+ The Corresponding Source need not include anything that users
+can regenerate automatically from other parts of the Corresponding
+Source.
+
+ The Corresponding Source for a work in source code form is that
+same work.
+
+ 2. Basic Permissions.
+
+ All rights granted under this License are granted for the term of
+copyright on the Program, and are irrevocable provided the stated
+conditions are met. This License explicitly affirms your unlimited
+permission to run the unmodified Program. The output from running a
+covered work is covered by this License only if the output, given its
+content, constitutes a covered work. This License acknowledges your
+rights of fair use or other equivalent, as provided by copyright law.
+
+ You may make, run and propagate covered works that you do not
+convey, without conditions so long as your license otherwise remains
+in force. You may convey covered works to others for the sole purpose
+of having them make modifications exclusively for you, or provide you
+with facilities for running those works, provided that you comply with
+the terms of this License in conveying all material for which you do
+not control copyright. Those thus making or running the covered works
+for you must do so exclusively on your behalf, under your direction
+and control, on terms that prohibit them from making any copies of
+your copyrighted material outside their relationship with you.
+
+ Conveying under any other circumstances is permitted solely under
+the conditions stated below. Sublicensing is not allowed; section 10
+makes it unnecessary.
+
+ 3. Protecting Users' Legal Rights From Anti-Circumvention Law.
+
+ No covered work shall be deemed part of an effective technological
+measure under any applicable law fulfilling obligations under article
+11 of the WIPO copyright treaty adopted on 20 December 1996, or
+similar laws prohibiting or restricting circumvention of such
+measures.
+
+ When you convey a covered work, you waive any legal power to forbid
+circumvention of technological measures to the extent such circumvention
+is effected by exercising rights under this License with respect to
+the covered work, and you disclaim any intention to limit operation or
+modification of the work as a means of enforcing, against the work's
+users, your or third parties' legal rights to forbid circumvention of
+technological measures.
+
+ 4. Conveying Verbatim Copies.
+
+ You may convey verbatim copies of the Program's source code as you
+receive it, in any medium, provided that you conspicuously and
+appropriately publish on each copy an appropriate copyright notice;
+keep intact all notices stating that this License and any
+non-permissive terms added in accord with section 7 apply to the code;
+keep intact all notices of the absence of any warranty; and give all
+recipients a copy of this License along with the Program.
+
+ You may charge any price or no price for each copy that you convey,
+and you may offer support or warranty protection for a fee.
+
+ 5. Conveying Modified Source Versions.
+
+ You may convey a work based on the Program, or the modifications to
+produce it from the Program, in the form of source code under the
+terms of section 4, provided that you also meet all of these conditions:
+
+ a) The work must carry prominent notices stating that you modified
+ it, and giving a relevant date.
+
+ b) The work must carry prominent notices stating that it is
+ released under this License and any conditions added under section
+ 7. This requirement modifies the requirement in section 4 to
+ "keep intact all notices".
+
+ c) You must license the entire work, as a whole, under this
+ License to anyone who comes into possession of a copy. This
+ License will therefore apply, along with any applicable section 7
+ additional terms, to the whole of the work, and all its parts,
+ regardless of how they are packaged. This License gives no
+ permission to license the work in any other way, but it does not
+ invalidate such permission if you have separately received it.
+
+ d) If the work has interactive user interfaces, each must display
+ Appropriate Legal Notices; however, if the Program has interactive
+ interfaces that do not display Appropriate Legal Notices, your
+ work need not make them do so.
+
+ A compilation of a covered work with other separate and independent
+works, which are not by their nature extensions of the covered work,
+and which are not combined with it such as to form a larger program,
+in or on a volume of a storage or distribution medium, is called an
+"aggregate" if the compilation and its resulting copyright are not
+used to limit the access or legal rights of the compilation's users
+beyond what the individual works permit. Inclusion of a covered work
+in an aggregate does not cause this License to apply to the other
+parts of the aggregate.
+
+ 6. Conveying Non-Source Forms.
+
+ You may convey a covered work in object code form under the terms
+of sections 4 and 5, provided that you also convey the
+machine-readable Corresponding Source under the terms of this License,
+in one of these ways:
+
+ a) Convey the object code in, or embodied in, a physical product
+ (including a physical distribution medium), accompanied by the
+ Corresponding Source fixed on a durable physical medium
+ customarily used for software interchange.
+
+ b) Convey the object code in, or embodied in, a physical product
+ (including a physical distribution medium), accompanied by a
+ written offer, valid for at least three years and valid for as
+ long as you offer spare parts or customer support for that product
+ model, to give anyone who possesses the object code either (1) a
+ copy of the Corresponding Source for all the software in the
+ product that is covered by this License, on a durable physical
+ medium customarily used for software interchange, for a price no
+ more than your reasonable cost of physically performing this
+ conveying of source, or (2) access to copy the
+ Corresponding Source from a network server at no charge.
+
+ c) Convey individual copies of the object code with a copy of the
+ written offer to provide the Corresponding Source. This
+ alternative is allowed only occasionally and noncommercially, and
+ only if you received the object code with such an offer, in accord
+ with subsection 6b.
+
+ d) Convey the object code by offering access from a designated
+ place (gratis or for a charge), and offer equivalent access to the
+ Corresponding Source in the same way through the same place at no
+ further charge. You need not require recipients to copy the
+ Corresponding Source along with the object code. If the place to
+ copy the object code is a network server, the Corresponding Source
+ may be on a different server (operated by you or a third party)
+ that supports equivalent copying facilities, provided you maintain
+ clear directions next to the object code saying where to find the
+ Corresponding Source. Regardless of what server hosts the
+ Corresponding Source, you remain obligated to ensure that it is
+ available for as long as needed to satisfy these requirements.
+
+ e) Convey the object code using peer-to-peer transmission, provided
+ you inform other peers where the object code and Corresponding
+ Source of the work are being offered to the general public at no
+ charge under subsection 6d.
+
+ A separable portion of the object code, whose source code is excluded
+from the Corresponding Source as a System Library, need not be
+included in conveying the object code work.
+
+ A "User Product" is either (1) a "consumer product", which means any
+tangible personal property which is normally used for personal, family,
+or household purposes, or (2) anything designed or sold for incorporation
+into a dwelling. In determining whether a product is a consumer product,
+doubtful cases shall be resolved in favor of coverage. For a particular
+product received by a particular user, "normally used" refers to a
+typical or common use of that class of product, regardless of the status
+of the particular user or of the way in which the particular user
+actually uses, or expects or is expected to use, the product. A product
+is a consumer product regardless of whether the product has substantial
+commercial, industrial or non-consumer uses, unless such uses represent
+the only significant mode of use of the product.
+
+ "Installation Information" for a User Product means any methods,
+procedures, authorization keys, or other information required to install
+and execute modified versions of a covered work in that User Product from
+a modified version of its Corresponding Source. The information must
+suffice to ensure that the continued functioning of the modified object
+code is in no case prevented or interfered with solely because
+modification has been made.
+
+ If you convey an object code work under this section in, or with, or
+specifically for use in, a User Product, and the conveying occurs as
+part of a transaction in which the right of possession and use of the
+User Product is transferred to the recipient in perpetuity or for a
+fixed term (regardless of how the transaction is characterized), the
+Corresponding Source conveyed under this section must be accompanied
+by the Installation Information. But this requirement does not apply
+if neither you nor any third party retains the ability to install
+modified object code on the User Product (for example, the work has
+been installed in ROM).
+
+ The requirement to provide Installation Information does not include a
+requirement to continue to provide support service, warranty, or updates
+for a work that has been modified or installed by the recipient, or for
+the User Product in which it has been modified or installed. Access to a
+network may be denied when the modification itself materially and
+adversely affects the operation of the network or violates the rules and
+protocols for communication across the network.
+
+ Corresponding Source conveyed, and Installation Information provided,
+in accord with this section must be in a format that is publicly
+documented (and with an implementation available to the public in
+source code form), and must require no special password or key for
+unpacking, reading or copying.
+
+ 7. Additional Terms.
+
+ "Additional permissions" are terms that supplement the terms of this
+License by making exceptions from one or more of its conditions.
+Additional permissions that are applicable to the entire Program shall
+be treated as though they were included in this License, to the extent
+that they are valid under applicable law. If additional permissions
+apply only to part of the Program, that part may be used separately
+under those permissions, but the entire Program remains governed by
+this License without regard to the additional permissions.
+
+ When you convey a copy of a covered work, you may at your option
+remove any additional permissions from that copy, or from any part of
+it. (Additional permissions may be written to require their own
+removal in certain cases when you modify the work.) You may place
+additional permissions on material, added by you to a covered work,
+for which you have or can give appropriate copyright permission.
+
+ Notwithstanding any other provision of this License, for material you
+add to a covered work, you may (if authorized by the copyright holders of
+that material) supplement the terms of this License with terms:
+
+ a) Disclaiming warranty or limiting liability differently from the
+ terms of sections 15 and 16 of this License; or
+
+ b) Requiring preservation of specified reasonable legal notices or
+ author attributions in that material or in the Appropriate Legal
+ Notices displayed by works containing it; or
+
+ c) Prohibiting misrepresentation of the origin of that material, or
+ requiring that modified versions of such material be marked in
+ reasonable ways as different from the original version; or
+
+ d) Limiting the use for publicity purposes of names of licensors or
+ authors of the material; or
+
+ e) Declining to grant rights under trademark law for use of some
+ trade names, trademarks, or service marks; or
+
+ f) Requiring indemnification of licensors and authors of that
+ material by anyone who conveys the material (or modified versions of
+ it) with contractual assumptions of liability to the recipient, for
+ any liability that these contractual assumptions directly impose on
+ those licensors and authors.
+
+ All other non-permissive additional terms are considered "further
+restrictions" within the meaning of section 10. If the Program as you
+received it, or any part of it, contains a notice stating that it is
+governed by this License along with a term that is a further
+restriction, you may remove that term. If a license document contains
+a further restriction but permits relicensing or conveying under this
+License, you may add to a covered work material governed by the terms
+of that license document, provided that the further restriction does
+not survive such relicensing or conveying.
+
+ If you add terms to a covered work in accord with this section, you
+must place, in the relevant source files, a statement of the
+additional terms that apply to those files, or a notice indicating
+where to find the applicable terms.
+
+ Additional terms, permissive or non-permissive, may be stated in the
+form of a separately written license, or stated as exceptions;
+the above requirements apply either way.
+
+ 8. Termination.
+
+ You may not propagate or modify a covered work except as expressly
+provided under this License. Any attempt otherwise to propagate or
+modify it is void, and will automatically terminate your rights under
+this License (including any patent licenses granted under the third
+paragraph of section 11).
+
+ However, if you cease all violation of this License, then your
+license from a particular copyright holder is reinstated (a)
+provisionally, unless and until the copyright holder explicitly and
+finally terminates your license, and (b) permanently, if the copyright
+holder fails to notify you of the violation by some reasonable means
+prior to 60 days after the cessation.
+
+ Moreover, your license from a particular copyright holder is
+reinstated permanently if the copyright holder notifies you of the
+violation by some reasonable means, this is the first time you have
+received notice of violation of this License (for any work) from that
+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
+
+ Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License. If your rights have been terminated and not permanently
+reinstated, you do not qualify to receive new licenses for the same
+material under section 10.
+
+ 9. Acceptance Not Required for Having Copies.
+
+ You are not required to accept this License in order to receive or
+run a copy of the Program. Ancillary propagation of a covered work
+occurring solely as a consequence of using peer-to-peer transmission
+to receive a copy likewise does not require acceptance. However,
+nothing other than this License grants you permission to propagate or
+modify any covered work. These actions infringe copyright if you do
+not accept this License. Therefore, by modifying or propagating a
+covered work, you indicate your acceptance of this License to do so.
+
+ 10. Automatic Licensing of Downstream Recipients.
+
+ Each time you convey a covered work, the recipient automatically
+receives a license from the original licensors, to run, modify and
+propagate that work, subject to this License. You are not responsible
+for enforcing compliance by third parties with this License.
+
+ An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations. If propagation of a covered
+work results from an entity transaction, each party to that
+transaction who receives a copy of the work also receives whatever
+licenses to the work the party's predecessor in interest had or could
+give under the previous paragraph, plus a right to possession of the
+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
+
+ You may not impose any further restrictions on the exercise of the
+rights granted or affirmed under this License. For example, you may
+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
+
+ 11. Patents.
+
+ A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based. The
+work thus licensed is called the contributor's "contributor version".
+
+ A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version. For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
+this License.
+
+ Each contributor grants you a non-exclusive, worldwide, royalty-free
+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
+
+ In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement). To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
+
+ If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients. "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
+
+ If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
+
+ A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License. You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+ Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+ 12. No Surrender of Others' Freedom.
+
+ If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License. If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all. For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+ 13. Use with the GNU Affero General Public License.
+
+ Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work. The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
+
+ 14. Revised Versions of this License.
+
+ The Free Software Foundation may publish revised and/or new versions of
+the GNU General Public License from time to time. Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+ Each version is given a distinguishing version number. If the
+Program specifies that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation. If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+ If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+ Later license versions may give you additional or different
+permissions. However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+ 15. Disclaimer of Warranty.
+
+ THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+ 16. Limitation of Liability.
+
+ IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+ 17. Interpretation of Sections 15 and 16.
+
+ If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+ END OF TERMS AND CONDITIONS
+
+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+
+ Copyright (C)
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+
+Also add information on how to contact you by electronic and paper mail.
+
+ If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+ Copyright (C)
+ This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+ You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+.
+
+ The GNU General Public License does not permit incorporating your program
+into proprietary programs. If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library. If this is what you want to do, use the GNU Lesser General
+Public License instead of this License. But first, please read
+.
diff --git a/Postmaster.hs b/Postmaster.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster.hs
@@ -0,0 +1,44 @@
+{- |
+ Module : Postmaster
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+
+ The Postmaster ESMTP Server. See
+ for an
+ introduction.
+ -}
+
+module Postmaster
+ ( module Postmaster.Base
+ , module Postmaster.FSM
+ , module Postmaster.IO
+ , module Postmaster.Main
+ , module Control.Monad.RWS
+ , module Data.Typeable
+ , module Network
+ , module ADNS
+ , module Text.ParserCombinators.Parsec.Rfc2821
+ , module System.Posix.Syslog
+ )
+ where
+
+import Network ( PortID(..) )
+import Control.Monad.RWS hiding ( local )
+import ADNS hiding ( Debug, queryMX, queryA, queryPTR )
+import Data.Typeable
+import Text.ParserCombinators.Parsec.Rfc2821 hiding ( path )
+import System.Posix.Syslog
+import Postmaster.Base
+import Postmaster.FSM
+import Postmaster.IO
+import Postmaster.Main
+
+-- ----- Configure Emacs -----
+--
+-- Local Variables: ***
+-- haskell-program-name: "ghci -ladns -lcrypto" ***
+-- End: ***
diff --git a/Postmaster/Base.hs b/Postmaster/Base.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/Base.hs
@@ -0,0 +1,208 @@
+{-# LANGUAGE Rank2Types, DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.Base
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.Base
+ ( module Postmaster.Base
+ , module Postmaster.Env
+ )
+ where
+
+import Prelude hiding ( catch )
+import Foreign
+import System.IO
+import Network.Socket hiding ( listen, shutdown )
+import Control.Exception
+import Control.Monad.State
+import Control.Monad.RWS hiding ( local )
+import Control.Concurrent
+import Data.Typeable
+import Text.ParserCombinators.Parsec.Rfc2821 hiding ( path )
+import Postmaster.Env
+
+-- * The @Smtpd@ Monad
+
+type GlobalEnv = MVar Env
+type SmtpdState = Env
+type Smtpd a = RWST GlobalEnv [LogMsg] SmtpdState IO a
+
+-- |@say a b c msg = return ('reply' a b c [msg])@
+--
+-- The 'SmtpReply' codes returned the event handler returns
+-- determine what Postmaster will do:
+--
+-- [@1xx@, @2xx@, @3xx@] make the 'SessionState' transition
+-- determined determined by 'smtpdFSM'.
+--
+-- [@4xx@, @5xx@] Do /not/ make the transition.
+--
+-- [@221@, @421@] Drop the connection after this reply.
+--
+-- The reply for the 'Greeting' event (the first event
+-- triggered when a session starts up) is interpreted as
+-- follows: @2xx@ accepts the connection, everything else
+-- refuses the connection.
+
+say :: Int -> Int -> Int -> String -> Smtpd SmtpReply
+say a b c msg = return (reply a b c [msg])
+
+-- ** Environment
+
+global :: EnvT a -> Smtpd a
+global f = do
+ mv <- ask
+ liftIO . modifyMVar mv $ return . swap . runState f
+ where swap (a,e) = (e,a)
+
+local :: EnvT a -> Smtpd a
+local f = do
+ (a, st) <- gets (runState f)
+ put st
+ return a
+
+type SmtpdVariable = forall a. Typeable a => (Variable -> EnvT a) -> Smtpd a
+
+defineLocal :: String -> SmtpdVariable
+defineLocal n = \f -> local (f (mkVar n))
+
+defineGlobal :: String -> SmtpdVariable
+defineGlobal n = \f -> global (f (mkVar n))
+
+-- ** Generating Unique Identifiers.
+
+type ID = Int
+
+-- |Produce an unique 'ID' using a global counter.
+
+getUniqueID :: Smtpd ID
+getUniqueID = global $ tick (mkVar "UniqueID")
+
+-- |Provides an unique 'ID' for every (TCP) session.
+
+mySessionID :: Smtpd ID
+mySessionID = do
+ let key = mkVar "SessionID"
+ sid' <- local $ getVar key
+ case sid' of
+ Just sid -> return sid
+ _ -> do sid <- getUniqueID
+ local $ setVar key sid
+ return sid
+
+-- ** Event Handler
+
+type EventHandler = Event -> Smtpd SmtpReply
+
+type EventT = EventHandler -> EventHandler
+
+-- ** Data Handler
+
+type ByteCount = Word16
+type Capacity = Word16
+data Buffer = Buf !Capacity !(Ptr Word8) !ByteCount
+ deriving (Eq, Show, Typeable)
+
+type DataHandler = Buffer -> Smtpd (Maybe SmtpReply, Buffer)
+
+-- ** Logging
+
+data LogMsg = LogMsg ID SmtpdState LogEvent
+ deriving (Show)
+
+-- |Given a log event, construct a 'LogMsg' and write it to
+-- the monad's log stream with 'tell'. Every log event
+-- contains the current 'SmtpdState' and the \"SessionID\".
+
+yell :: LogEvent -> Smtpd ()
+yell e = do
+ sid <- mySessionID
+ st <- get
+ tell [LogMsg sid st e]
+
+data LogEvent
+ = Msg String
+ | StartSession
+ | EndSession
+ | Input String
+ | Output String
+ | AcceptConn SockAddr
+ | DropConn SockAddr
+ | UserShutdown
+ | CaughtException Exception
+ | CaughtIOError IOException
+ | StartEventHandler String Event
+ | EventHandlerResult String Event SmtpCode
+ | CurrentState
+ | AssignMailID ID
+ deriving (Show)
+
+-- * Exception Handling
+
+-- |Run a computation and fall back to the second if the
+-- first throws an exception. The error is logged. An
+-- exception in the second computation will propagate.
+
+fallback
+ :: Smtpd a -- ^ computation to run
+ -> Smtpd a -- ^ fallback function
+ -> Smtpd a
+fallback f g = do
+ cfg <- ask
+ st <- get
+ (r, st', w) <- liftIO $ catch
+ (runRWST f cfg st)
+ (\e -> runRWST (yell (CaughtException e) >> g) cfg st)
+ tell w
+ put st'
+ return r
+
+-- |Like bracket, but only performs the final action if
+-- there was an exception raised by the in-between
+-- computation. GHC 6.5 provides this function in
+-- "Control.Exception".
+
+bracketOnError
+ :: IO a -- ^ computation to run first (\"acquire resource\")
+ -> (a -> IO b) -- ^ computation to run last (\"release resource\")
+ -> (a -> IO c) -- ^ computation to run in-between
+ -> IO c -- returns the value from the in-between computation
+bracketOnError before after thing =
+ block (do
+ a <- before
+ catch
+ (unblock (thing a))
+ (\e -> do { after a; throw e })
+ )
+
+-- * Resource Management
+
+-- |Convert 'bracket'-style resource management to
+-- allocate\/free style. We need this, because we have to
+-- acquire resources that leave the scope in which they were
+-- allocated. Yeah, callback-driven I\/O does that to
+-- functional programs. Anyway, the resource will be /gone/
+-- once you empty the 'MVar' (or when it falls out of
+-- scope). So use only 'withMVar' and friends to access the
+-- value.
+
+acquire :: ((a -> IO b) -> IO b) -> IO (MVar a)
+acquire f = do
+ sync <- newEmptyMVar
+ let hold r = do putMVar sync r
+ yield
+ putMVar sync r
+ return undefined
+ forkIO (f hold >> return ())
+ return sync
+
+-- |Let go of a resource allocated with 'acquire'.
+
+release :: MVar a -> IO ()
+release a = takeMVar a >> yield >> return ()
diff --git a/Postmaster/Env.hs b/Postmaster/Env.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/Env.hs
@@ -0,0 +1,112 @@
+{- |
+ Module : Postmaster.Env
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+
+ A generic environment.
+-}
+
+module Postmaster.Env where
+
+import Control.Monad.State
+import Control.Monad.Reader
+import Data.Char
+import Data.Dynamic
+import Data.ByteString.Char8 ( ByteString, pack )
+import qualified Data.Map as FM
+
+-- |Variables are stored in all-uppercase internally. Thus,
+-- the environment is case-less.
+
+newtype Variable = Var ByteString
+ deriving (Eq, Ord)
+
+instance Show Variable where
+ showsPrec _ (Var str) = shows str
+
+-- |Construct a variable.
+
+mkVar :: String -> Variable
+mkVar = Var . pack . map toUpper
+
+-- |An environment maps from 'Variable's to any 'Typeable'
+-- value. The 'toDyn' and 'fromDynamic' casts are done by
+-- the /environment/; the API does not expose 'Dynamic'.
+
+type Env = FM.Map Variable Dynamic
+
+-- |The empty environment.
+
+emptyEnv :: Env
+emptyEnv = FM.empty
+
+-- |The environment is accessed through a monadic interface.
+
+type EnvT a = State Env a
+
+-- |Test whether a variable is set.
+
+isVar :: Variable -> EnvT Bool
+isVar = gets . FM.member
+
+-- |Set a variable.
+
+setVar :: (Typeable a) => Variable -> a -> EnvT ()
+setVar key val = unsetVar key >> modify (FM.insert key (toDyn val))
+
+-- |Erase an entry from the environment.
+
+unsetVar :: Variable -> EnvT ()
+unsetVar = modify . FM.delete
+
+-- |This function does not distinguish between the two
+-- potential cases of failure we have: (1) value does not
+-- exist and (2) value does exist but 'fromDynamic' failed.
+-- Accurate type signatures should prevent the latter case
+-- from happening anyway.
+
+getVar :: (Typeable a) => Variable -> EnvT (Maybe a)
+getVar key = do
+ res <- gets $ FM.lookup key
+ case res of
+ Nothing -> return Nothing
+ Just a -> return (fromDynamic a)
+
+-- |Wrapper that will 'fail' when the variable is unset.
+
+getVar_ :: (Typeable a) => Variable -> EnvT a
+getVar_ key = getVar key >>= maybe badluck return
+ where badluck = fail ("variable " ++ show key ++ " is unset!")
+
+-- |Wrapper that will return a default when the variable is
+-- unset.
+
+getVarDef :: (Typeable a) => Variable -> a -> EnvT a
+getVarDef key def = getVar key >>= return . maybe def id
+
+-- |Modify a variable in the environment and return it.
+-- 'Nothing' may signify that the value wasn't set or that
+-- conversion from 'Dynamic' failed; it's not
+-- differentiated.
+
+modifyVar :: (Typeable a) => Variable -> (Maybe a -> (b, a)) -> EnvT b
+modifyVar key f = do
+ (b, a) <- fmap f (getVar key)
+ setVar key a
+ return b
+
+-- |Variant that returns @()@. Comes in handy on the occasion.
+
+modifyVar_ :: (Typeable a) => Variable -> (Maybe a -> a) -> EnvT ()
+modifyVar_ key f = getVar key >>= setVar key . f
+
+-- |Convenience wrapper to implement counters. Starts
+-- counting with @0@ in case the variable doesn't exist or
+-- doesn't contain an 'Int'.
+
+tick :: Variable -> EnvT Int
+tick key = modifyVar key (maybe (0, 1) (\i -> (i, i+1)))
diff --git a/Postmaster/FSM.hs b/Postmaster/FSM.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM.hs
@@ -0,0 +1,118 @@
+{- |
+ Module : Postmaster.FSM
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM
+ ( mkEvent
+ , announce
+ , queryA, queryPTR, queryMX
+ , feed
+ , isEhloPeer
+ , trigger
+ , myHeloName
+ , getMailFrom
+ , getMailID
+ , getPeerAddr
+ , getPeerHelo
+ , getSessionState
+ )
+ where
+
+import Network ( HostName )
+import Postmaster.Base
+import Postmaster.FSM.Announce
+import Postmaster.FSM.DNSResolver
+import Postmaster.FSM.DataHandler
+import Postmaster.FSM.EhloPeer
+import Postmaster.FSM.EventHandler
+import Postmaster.FSM.HeloName
+import Postmaster.FSM.MailFrom
+import Postmaster.FSM.MailID
+import Postmaster.FSM.PeerAddr
+import Postmaster.FSM.PeerHelo
+import Postmaster.FSM.SessionState
+import Postmaster.FSM.Spooler
+import Text.ParserCombinators.Parsec.Rfc2821
+
+-- |Generate the standard ESMTP event handler. The
+-- parameters are the path to the spool directory and our
+-- @HELO@ name.
+
+mkEvent :: HostName -> FilePath -> EventHandler
+mkEvent heloname spooldir
+ = announce "PIPELINING"
+ . initHeloName heloname
+ . handleMailID
+ . handleMailFrom
+ . handleEhloPeer
+ . handlePeerHelo
+ . handlePayload spooldir
+ $ event
+
+-- |The Standard Bad-Ass Event Handler
+
+event :: EventHandler
+
+event Greeting = do
+ whoami <- myHeloName
+ say 2 2 0 (showString whoami " Postmaster ESMTP Server")
+
+event Shutdown = do
+ whoami <- myHeloName
+ say 2 2 1 (showString whoami " closing connection")
+
+event NotImplemened =
+ say 5 0 2 "command not implemented"
+
+event (Unrecognized _) =
+ say 5 0 0 "unrecognized command"
+
+event (SyntaxErrorIn cmd) =
+ say 5 0 1 (showString "syntax error in parameters or arguments of " cmd)
+
+event (SayOK) =
+ say 2 5 0 "Massive system failure. Just kidding ... ok."
+
+event (NeedHeloFirst) =
+ say 5 0 3 "You should say HELO first."
+
+event (NeedMailFromFirst) =
+ say 5 0 3 "What MAIL are you talking about?"
+
+event (NeedRcptToFirst) =
+ say 5 0 3 "Care to tell me where I should send it to?"
+
+event (ResetState) =
+ say 2 5 0 "state reset"
+
+event (SeeksHelp []) =
+ say 5 0 2 "Why don't you ask about something specific?"
+
+event (SeeksHelp _) =
+ say 5 0 4 "I don't implement HELP with parameters."
+
+event (SayHelo _) = do
+ trigger ResetState
+ whoami <- myHeloName
+ say 2 5 0 (showString whoami " Postmaster; pleased to meet you.")
+
+event (SayEhlo peer) = event (SayHelo peer)
+event (SayHeloAgain peer) = event (SayHelo peer)
+event (SayEhloAgain peer) = event (SayHelo peer)
+
+event (SetMailFrom mbox) = do
+ trigger ResetState
+ say 2 5 0 (mbox `shows` " ... sender ok")
+
+event (AddRcptTo mbox) =
+ say 5 5 3 (mbox `shows` " ... unknown recipient")
+
+event StartData = event NotImplemened
+
+event Deliver = event NotImplemened
diff --git a/Postmaster/FSM/Announce.hs b/Postmaster/FSM/Announce.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/Announce.hs
@@ -0,0 +1,28 @@
+{- |
+ Module : Postmaster.FSM.Announce
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+
+ Announce ESMTP Capability.
+ -}
+
+module Postmaster.FSM.Announce where
+
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+
+-- |Append the given ESMTP keyword to the reply produced
+-- during 'SayEhlo'.
+
+announce :: String -> EventT
+announce keyword f e@(SayEhlo _) = do
+ Reply rc msg <- f e
+ let msg' = msg ++ [keyword]
+ case rc of
+ Code Success _ _ -> return (Reply rc msg')
+ _ -> return (Reply rc msg)
+announce _ f e = f e
diff --git a/Postmaster/FSM/DNSResolver.hs b/Postmaster/FSM/DNSResolver.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/DNSResolver.hs
@@ -0,0 +1,42 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving, DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.FSM.DNSResolver
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.DNSResolver where
+
+import Control.Monad.RWS hiding ( local )
+import ADNS
+import Data.Typeable
+import Postmaster.Base
+import Control.Monad.Trans
+
+newtype DNSR = DNSR Resolver
+ deriving (Typeable)
+
+dnsResolver :: Variable
+dnsResolver = mkVar "dnsresolver"
+
+setDNSResolver :: Resolver -> EnvT ()
+setDNSResolver f = setVar dnsResolver (DNSR f)
+
+getDNSResolver :: Smtpd Resolver
+getDNSResolver = do
+ DNSR f <- local (getVar dnsResolver)
+ >>= maybe (global $ getVar_ dnsResolver) return
+ return f
+
+queryA :: HostName -> Smtpd (Maybe [HostAddress])
+queryA h = getDNSResolver >>= \r -> liftIO $ ADNS.queryA r h
+
+queryPTR :: HostAddress -> Smtpd (Maybe [HostName])
+queryPTR h = getDNSResolver >>= \r -> liftIO $ ADNS.queryPTR r h
+
+queryMX :: HostName -> Smtpd (Maybe [(HostName, HostAddress)])
+queryMX h = getDNSResolver >>= \r -> liftIO $ ADNS.queryMX r h
diff --git a/Postmaster/FSM/DataHandler.hs b/Postmaster/FSM/DataHandler.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/DataHandler.hs
@@ -0,0 +1,30 @@
+{-# LANGUAGE DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.FSM.DataHandler
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.DataHandler where
+
+import Data.Typeable
+import Postmaster.Base
+
+newtype DH = DH DataHandler
+ deriving (Typeable)
+
+dataHandler :: SmtpdVariable
+dataHandler = defineLocal "datahandler"
+
+setDataHandler :: DataHandler -> Smtpd ()
+setDataHandler f = dataHandler (`setVar` DH f)
+
+getDataHandler :: Smtpd DataHandler
+getDataHandler = dataHandler getVar_ >>= \(DH f) -> return f
+
+feed :: DataHandler
+feed buf = getDataHandler >>= ($ buf)
diff --git a/Postmaster/FSM/EhloPeer.hs b/Postmaster/FSM/EhloPeer.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/EhloPeer.hs
@@ -0,0 +1,31 @@
+{- |
+ Module : Postmaster.FSM.EhloPeer
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.EhloPeer where
+
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+
+-- |Local Variable: @EHLOPEER :: 'Bool'@
+
+ehloPeer :: SmtpdVariable
+ehloPeer = defineLocal "ehlopeer"
+
+handleEhloPeer :: EventT
+handleEhloPeer f e = do
+ r <- f e
+ case (e, isSuccess r) of
+ (SayEhlo _, True) -> ehloPeer (`setVar` True)
+ (SayHelo _, True) -> ehloPeer (`setVar` False)
+ (_, _) -> return ()
+ return r
+
+isEhloPeer :: Smtpd Bool
+isEhloPeer = ehloPeer (`getVarDef` False)
diff --git a/Postmaster/FSM/EventHandler.hs b/Postmaster/FSM/EventHandler.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/EventHandler.hs
@@ -0,0 +1,39 @@
+{-# LANGUAGE DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.FSM.EventHandler
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.EventHandler where
+
+import Data.Typeable
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+
+newtype EH = EH EventHandler
+ deriving (Typeable)
+
+-- |This variable /must/ be initialized in the global
+-- environment or Postmaster won't do much.
+
+eventHandler :: Variable
+eventHandler = mkVar "eventhandler"
+
+setEventHandler :: EventHandler -> EnvT ()
+setEventHandler = setVar eventHandler . EH
+
+getEventHandler :: Smtpd EventHandler
+getEventHandler = do
+ EH f <- local (getVar eventHandler)
+ >>= maybe (global $ getVar_ eventHandler) return
+ return f
+
+-- |Trigger the given event.
+
+trigger :: Event -> Smtpd SmtpReply
+trigger e = getEventHandler >>= ($ e)
diff --git a/Postmaster/FSM/HeloName.hs b/Postmaster/FSM/HeloName.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/HeloName.hs
@@ -0,0 +1,35 @@
+{- |
+ Module : Postmaster.FSM.HeloName
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.HeloName where
+
+import Control.Monad
+import Network ( HostName )
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+
+-- |Local Variable: @HELONAME :: 'HostName'@
+
+heloName :: SmtpdVariable
+heloName = defineLocal "heloname"
+
+-- |Initialized during the 'Greeting' event; will not
+-- overwrite the variable if it does exist already.
+
+initHeloName :: HostName -> EventT
+initHeloName n f e = do
+ when (e == Greeting) (heloName (`modifyVar_` maybe n id))
+ f e
+
+-- |Will 'fail' when @HELONAME@ is not set.
+
+myHeloName :: Smtpd HostName
+myHeloName = heloName getVar_
+
diff --git a/Postmaster/FSM/MailFrom.hs b/Postmaster/FSM/MailFrom.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/MailFrom.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving, DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.FSM.MailFrom
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.MailFrom where
+
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+import Data.Typeable
+
+newtype SmtpMailbox = SMB Mailbox
+ deriving (Typeable)
+
+-- |Local Variable: @MAILFROM :: 'Mailbox'@
+
+mailFrom :: SmtpdVariable
+mailFrom = defineLocal "mailfrom"
+
+handleMailFrom :: EventT
+handleMailFrom f e = do
+ r <- f e
+ case (e, isSuccess r) of
+ (SetMailFrom x, True) -> mailFrom (`setVar` (SMB x))
+ (ResetState, _) -> mailFrom unsetVar
+ (_, _) -> return ()
+ return r
+
+getMailFrom :: Smtpd Mailbox
+getMailFrom = mailFrom getVar_ >>= \(SMB x) -> return x
diff --git a/Postmaster/FSM/MailID.hs b/Postmaster/FSM/MailID.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/MailID.hs
@@ -0,0 +1,36 @@
+{- |
+ Module : Postmaster.FSM.MailID
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.MailID where
+
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+
+-- |Local Variable: @MAILID :: 'ID'@
+
+mailID :: SmtpdVariable
+mailID = defineLocal "mailid"
+
+-- |Set when 'SetMailFrom' succeeds; unset during
+-- 'ResetState'.
+
+handleMailID :: EventT
+handleMailID f e = do
+ r <- f e
+ case (e, isSuccess r) of
+ (SetMailFrom _, True) -> getUniqueID >>= \x -> mailID (`setVar` x)
+ (ResetState , _ ) -> mailID unsetVar
+ (_, _) -> return ()
+ return r
+
+-- |Will 'fail' when @MailID@ is not set.
+
+getMailID :: Smtpd ID
+getMailID = mailID getVar_
diff --git a/Postmaster/FSM/PeerAddr.hs b/Postmaster/FSM/PeerAddr.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/PeerAddr.hs
@@ -0,0 +1,23 @@
+{- |
+ Module : Postmaster.FSM.PeerAddr
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.PeerAddr where
+
+import Postmaster.Base
+import Network.Socket ( SockAddr )
+
+peerAddr :: Variable
+peerAddr = mkVar "peeradr"
+
+setPeerAddr :: SockAddr -> EnvT ()
+setPeerAddr = setVar peerAddr
+
+getPeerAddr :: Smtpd (Maybe SockAddr)
+getPeerAddr = local (getVar peerAddr)
diff --git a/Postmaster/FSM/PeerHelo.hs b/Postmaster/FSM/PeerHelo.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/PeerHelo.hs
@@ -0,0 +1,37 @@
+{- |
+ Module : Postmaster.FSM.PeerHelo
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.PeerHelo where
+
+import Control.Monad
+import Network ( HostName )
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+
+-- |Local Variable: @PEERHELO :: 'HostName'@
+
+peerHelo :: SmtpdVariable
+peerHelo = defineLocal "peerhelo"
+
+-- |Set when 'SayHelo' or 'SayEhlo' succeed.
+
+handlePeerHelo :: EventT
+handlePeerHelo f e = do
+ r <- f e
+ case (e, isSuccess r) of
+ (SayEhlo peer, True) -> peerHelo (`setVar` peer)
+ (SayHelo peer, True) -> peerHelo (`setVar` peer)
+ (_, _) -> return ()
+ return r
+
+-- |Will 'fail' when @PEERHELO@ is not set.
+
+getPeerHelo :: Smtpd HostName
+getPeerHelo = peerHelo getVar_
diff --git a/Postmaster/FSM/SessionState.hs b/Postmaster/FSM/SessionState.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/SessionState.hs
@@ -0,0 +1,30 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving, DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.FSM.SessionState
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.SessionState where
+
+import Postmaster.Base
+import Text.ParserCombinators.Parsec.Rfc2821
+import Data.Typeable
+
+newtype SmtpSessionState = SSST SessionState
+ deriving (Typeable)
+
+-- |Local Variable: @SESSIONSTATE :: 'SessionState'@
+
+sessionState :: SmtpdVariable
+sessionState = defineLocal "sessionstate"
+
+setSessionState :: SessionState -> Smtpd ()
+setSessionState sst = sessionState (`setVar` (SSST sst))
+
+getSessionState :: Smtpd SessionState
+getSessionState = sessionState (`getVarDef` (SSST Unknown)) >>= \(SSST sst) -> return sst
diff --git a/Postmaster/FSM/Spooler.hs b/Postmaster/FSM/Spooler.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/FSM/Spooler.hs
@@ -0,0 +1,123 @@
+{-# LANGUAGE DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.FSM.Spooler
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.FSM.Spooler where
+
+import Foreign
+import Control.Exception
+import Control.Concurrent.MVar
+import Control.Monad.State
+import System.Directory
+import System.IO
+import Postmaster.Base
+import Postmaster.IO
+import Postmaster.FSM.EventHandler
+import Postmaster.FSM.SessionState
+import Postmaster.FSM.DataHandler
+import Postmaster.FSM.MailID
+import Text.ParserCombinators.Parsec.Rfc2821 hiding ( path )
+import OpenSSL.Digest
+import Data.Typeable
+
+data Spooler = S (Maybe FilePath) (Maybe WriteHandle) DigestState
+ deriving (Typeable)
+
+spoolerState :: SmtpdVariable
+spoolerState = defineLocal "spoolerstate"
+
+getState :: Smtpd (MVar Spooler)
+getState = spoolerState getVar_
+
+setState :: MVar Spooler -> Smtpd ()
+setState st = spoolerState (`setVar` st)
+
+-- |The Standard Bad-Ass Payload Handler. Needs the path to
+-- the spool directory.
+
+handlePayload :: FilePath -> EventT
+
+handlePayload _ f Greeting = do
+ liftIO (newMVar (S Nothing Nothing (DST nullPtr))) >>= setState
+ setDataHandler feeder
+ f Greeting
+
+handlePayload spool _ StartData =
+ do st <- getState
+ mid <- getMailID
+ let path = spool ++ "/temp." ++ show mid
+ liftIO . modifyMVar_ st $ \(S p' h' (DST c')) ->
+ assert (p' == Nothing) $
+ assert (h' == Nothing) $
+ assert (c' == nullPtr) $
+ Postmaster.Base.bracketOnError
+ (openBinaryFile path WriteMode)
+ (hClose)
+ (\h -> Postmaster.Base.bracketOnError ctxCreate ctxDestroy $ \ctx -> do
+ hSetBuffering h NoBuffering
+ when (ctx == nullPtr) (fail "can't initialize SHA1 digest context")
+ md <- toMDEngine SHA1
+ when (md == nullPtr) (fail "can't initialize SHA1 digest engine")
+ rc <- digestInit ctx md
+ when (rc == 0) (fail "can't initialize SHA1 digest")
+ return (S (Just path) (Just h) (DST ctx)))
+ say 3 5 4 "terminate data with ."
+ `fallback`
+ say 4 5 1 "requested action aborted: error in processing"
+
+handlePayload spool _ Deliver =
+ do st <- getState
+ sha1 <- liftIO $
+ modifyMVar st $ \(S (Just p) (Just h) ctx@(DST c)) ->
+ assert (c /= nullPtr) $ do
+ hClose h
+ sha1 <- fmap (>>= toHex) (evalStateT final ctx)
+ let fname = spool ++ "/" ++ sha1
+ renameFile p fname
+ return (S Nothing Nothing ctx, sha1)
+ say 2 5 0 (sha1 ++ " message accepted for delivery")
+ `fallback`
+ say 4 5 1 "requested action aborted: error in processing"
+
+handlePayload _ f ResetState = clearState >> f ResetState
+handlePayload _ f Shutdown = clearState >> f Shutdown
+handlePayload _ f e = f e
+
+feeder :: DataHandler
+feeder buf@(Buf _ _ 0) = return (Nothing, buf)
+feeder buf@(Buf _ ptr n) = do
+ xs <- liftIO (peekArray (fromIntegral n) ptr)
+ let theEnd = map (toEnum . fromEnum) "\r\n.\r\n"
+ (eod, i) = case strstr theEnd xs of
+ Nothing -> (False, max 0 (n - 4))
+ Just j -> (True, fromIntegral (j-3))
+ i' = fromIntegral i
+ st <- getState
+ buf' <- liftIO . withMVar st $ \(S _ (Just h) ctx@(DST c)) ->
+ assert (c /= nullPtr) $ do
+ hPutBuf h ptr i'
+ execStateT (update' (ptr, i')) ctx
+ flush i buf
+ if not eod then return (Nothing, buf') else do
+ r <- trigger Deliver
+ trigger ResetState -- TODO: this doesn't really
+ setSessionState HaveHelo -- belong here
+ return (Just r, buf')
+
+clearState :: Smtpd ()
+clearState = do
+ st <- getState
+ liftIO . modifyMVar_ st $ \(S path h (DST ctx)) -> do
+ let clean Nothing _ = return ()
+ clean (Just x) f = try (f x) >> return ()
+ clean h hClose
+ clean path removeFile
+ when (ctx /= nullPtr) (ctxDestroy ctx)
+ return (S Nothing Nothing (DST nullPtr))
diff --git a/Postmaster/IO.hs b/Postmaster/IO.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/IO.hs
@@ -0,0 +1,230 @@
+{-# LANGUAGE DeriveDataTypeable #-}
+{- |
+ Module : Postmaster.IO
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+ -}
+
+module Postmaster.IO where
+
+import Data.List
+import Data.Maybe
+import Data.Dynamic ( Typeable )
+import Control.Concurrent ( forkIO )
+import Control.Exception
+import Control.Monad.RWS hiding ( local )
+import System.IO
+import System.IO.Error
+import System.Timeout
+import Network ( listenOn, PortID(..) )
+import Network.Socket
+import Text.ParserCombinators.Parsec.Rfc2821
+import Foreign
+import Postmaster.Base
+
+-- * Static Buffer I\/O
+
+type ReadHandle = Handle
+type WriteHandle = Handle
+
+-- |Run the given computation with an initialized, empty
+-- 'Buffer'. The buffer is gone when the computation
+-- returns.
+
+withBuffer :: Capacity -> (Buffer -> IO a) -> IO a
+withBuffer 0 = fail "BlockIO.withBuffer with size 0 doesn't make sense"
+withBuffer n = bracket cons dest
+ where
+ cons = mallocArray (fromIntegral n) >>= \p -> return (Buf n p 0)
+ dest = \(Buf _ p _) -> free p
+
+-- |Drop the first @n <= size@ octets from the buffer.
+
+flush :: ByteCount -> Buffer -> IO Buffer
+flush 0 buf = return buf
+flush n (Buf cap ptr len) = assert (n <= len) $ do
+ let ptr' = ptr `plusPtr` (fromIntegral n)
+ len' = (fromIntegral len) - (fromIntegral n)
+ when (len' > 0) (copyArray ptr ptr' len')
+ return (Buf cap ptr (fromIntegral len'))
+
+-- |Timeouts are represented in microseconds.
+
+type Timeout = Int
+
+-- |If there is space, read and append more octets; then
+-- return the modified buffer. In case of 'hIsEOF',
+-- 'Nothing' is returned. If the buffer is full already,
+-- 'throwDyn' a 'BufferOverflow' exception. When the timeout
+-- exceeds, 'ReadTimeout' is thrown.
+
+slurp :: Timeout -> ReadHandle -> Buffer -> IO (Maybe Buffer)
+slurp to h b@(Buf cap ptr len) = do
+ when (cap <= len) (throwDyn (BufferOverflow h b))
+ timeout to (handleEOF wrap) >>=
+ maybe (throwDyn (ReadTimeout to h b)) return
+ where
+ wrap = do let ptr' = ptr `plusPtr` (fromIntegral len)
+ n = cap - len
+ rc <- hGetBufNonBlocking h ptr' (fromIntegral n)
+ if rc > 0
+ then return (Buf cap ptr (len + (fromIntegral rc)))
+ else hWaitForInput h (-1) >> wrap
+
+-- * BlockHandler and I\/O Driver
+
+-- |A callback function suitable for use with 'runLoop'
+-- takes a buffer and a state, then returns a modified
+-- buffer and a modified state. Usually the callback will
+-- use 'slurp' to remove data it has processed already.
+
+type BlockHandler st = Buffer -> st -> IO (Buffer, st)
+
+-- |Our main I\/O driver.
+
+runLoopNB
+ :: (st -> Timeout) -- ^ user state provides timeout
+ -> (Exception -> st -> IO st) -- ^ user provides I\/O error handler
+ -> ReadHandle -- ^ the input source
+ -> Capacity -- ^ I\/O buffer size
+ -> BlockHandler st -- ^ callback
+ -> st -- ^ initial callback state
+ -> IO st -- ^ return final callback state
+runLoopNB mkTO errH hIn cap f initST = withBuffer cap (flip ioloop $ initST)
+ where
+ ioloop buf st = buf `seq` st `seq`
+ handle (\e -> errH e st) $ do
+ rc <- slurp (mkTO st) hIn buf
+ case rc of
+ Nothing -> return st
+ Just buf' -> f buf' st >>= uncurry ioloop
+
+-- |A variant which won't time out and will just 'throw' all
+-- exceptions.
+
+runLoop :: ReadHandle -> Capacity -> BlockHandler st -> st -> IO st
+runLoop = runLoopNB (const (-1)) (\e _ -> throw e)
+
+-- * Handler Combinators
+
+-- |Signal how many bytes have been consumed from the
+-- /front/ of the list; these octets will be dropped.
+
+type StreamHandler st = [Word8] -> st -> IO (ByteCount, st)
+
+handleStream :: StreamHandler st -> BlockHandler st
+handleStream f buf@(Buf _ ptr len) st = do
+ (i, st') <- peekArray (fromIntegral len) ptr >>= (flip f) st
+ buf' <- flush i buf
+ return (buf', st')
+
+-- * I\/O Exceptions
+
+-- |Thrown by 'slurp'.
+
+data BufferOverflow = BufferOverflow ReadHandle Buffer
+ deriving (Show, Typeable)
+
+-- |Thrown by 'slurp'.
+
+data ReadTimeout = ReadTimeout Timeout ReadHandle Buffer
+ deriving (Show, Typeable)
+
+
+-- * Internal Helper Functions
+
+-- |Return 'Nothing' if the given computation throws an
+-- 'isEOFError' exception. Used by 'slurp'.
+
+handleEOF :: IO a -> IO (Maybe a)
+handleEOF f =
+ catchJust ioErrors
+ (fmap Just f)
+ (\e -> if isEOFError e then return Nothing else ioError e)
+
+-- |Our version of C's @strstr(3)@.
+
+strstr :: [Word8] -> [Word8] -> Maybe Int
+strstr tok = strstr' 0
+ where
+ strstr' _ [] = Nothing
+ strstr' pos ls@(_:xs)
+ | tok `isPrefixOf` ls = Just (pos + length tok)
+ | otherwise = strstr' (pos + 1) xs
+
+-- |Split a list by some delimiter. Will soon be provided by
+-- "Data.List".
+
+splitList :: Eq a => [a] -> [a] -> [[a]]
+splitList d' l' =
+ unfoldr (\x -> if (null x) then Nothing else Just $ nextToken d' [] (snd $ splitAt (length d') x)) (d'++l')
+ where nextToken _ r [] = (r, [])
+ nextToken d r l@(h:t) | (d `isPrefixOf` l) = (r, l)
+ | otherwise = nextToken d (r++[h]) t
+
+-- * Socket Handlers
+
+type SocketHandler = (Socket,SockAddr) -> IO ()
+
+-- |Creates a listening socket for the given port, then
+-- calls 'acceptor' to start the given computation for every
+-- incoming connection.
+
+listener :: PortID -> SocketHandler -> IO ()
+listener p h = bracket (listenOn p) (sClose) (acceptor h)
+
+-- |Given a listening socket, this function will loop
+-- forever 'accept'ing incoming connections. For each
+-- connection a 'SocketHandler' thread is forked.
+
+acceptor :: SocketHandler -> Socket -> IO ()
+acceptor h ls = do
+ Postmaster.Base.bracketOnError
+ (accept ls)
+ (sClose . fst)
+ (\peer@(s,_) -> fork $ h peer `finally` sClose s)
+ acceptor h ls
+ where
+ fork f = forkIO f >> return ()
+
+type LazyHandler = (Handle, Maybe SockAddr) -> IO ()
+
+handleLazy :: IOMode -> LazyHandler -> SocketHandler
+handleLazy m f (s,sa) =
+ bracket (socketToHandle s m) (hClose) (\h -> f (h, Just sa))
+
+
+-- * Non-blocking I\/O
+
+-- |The exception we throw when writes time out.
+-- 'ReadTimeout' is throw by "System.IO.Driver".
+
+data WriteTimeout = WriteTimeout Timeout
+ deriving (Typeable, Show)
+
+setReadTimeout :: Timeout -> Smtpd ()
+setReadTimeout = local . setVar (mkVar "ReadTimeout")
+
+getReadTimeout :: Smtpd Timeout
+getReadTimeout = local $ getVarDef (mkVar "ReadTimeout") (90 * 1000000)
+
+setWriteTimeout :: Timeout -> Smtpd ()
+setWriteTimeout = local . setVar (mkVar "WriteTimeout")
+
+getWriteTimeout :: Smtpd Timeout
+getWriteTimeout = local $ getVarDef (mkVar "WriteTimeout") (90 * 1000000)
+
+safeWrite :: IO a -> Smtpd a
+safeWrite f = do
+ to <- getWriteTimeout
+ liftIO $ timeout to f >>= maybe (throwDyn (WriteTimeout to)) return
+
+safeReply :: WriteHandle -> SmtpReply -> Smtpd ()
+safeReply hOut r = safeWrite (hPutStr hOut (show r))
+
+safeFlush :: WriteHandle -> Smtpd ()
+safeFlush hOut = safeWrite (hFlush hOut)
diff --git a/Postmaster/Main.hs b/Postmaster/Main.hs
new file mode 100644
--- /dev/null
+++ b/Postmaster/Main.hs
@@ -0,0 +1,187 @@
+{- |
+ Module : Postmaster.Main
+ Copyright : (c) 2004-2008 by Peter Simons
+ License : GPL2
+
+ Maintainer : simons@cryp.to
+ Stability : provisional
+ Portability : Haskell 2-pre
+
+ Postmaster's IO driver and general initialization functions.
+-}
+
+module Postmaster.Main where
+
+import Prelude hiding ( catch )
+import Data.Maybe
+import Control.Concurrent.MVar
+import Control.Monad.RWS hiding ( local )
+import Control.Monad.State
+import System.IO
+import System.Posix.Signals
+import Network ( PortID(..) )
+import Network.Socket
+import Network.BSD ( getHostName )
+import ADNS
+import Foreign
+import Postmaster.Base
+import Postmaster.FSM
+import Postmaster.FSM.DNSResolver ( setDNSResolver )
+import Postmaster.FSM.EventHandler ( setEventHandler )
+import Postmaster.FSM.PeerAddr ( setPeerAddr )
+import Postmaster.FSM.SessionState ( setSessionState )
+import Postmaster.IO
+import Text.ParserCombinators.Parsec.Rfc2821
+import System.Posix.Syslog
+
+-- * Speaking ESMTP
+
+-- |This function ties it all together to build a
+-- 'BlockHandler' for "System.IO.Driver".
+
+smtpdHandler :: WriteHandle -> GlobalEnv -> BlockHandler SmtpdState
+smtpdHandler hOut theEnv buf = runSmtpd (smtpd buf >>= handler) theEnv
+ where
+ handler :: ([SmtpReply], Buffer) -> Smtpd Buffer
+ handler (rs, buf') = do
+ safeWrite (hPutStr hOut (concatMap show rs) >> hFlush hOut)
+ when (any isShutdown rs) (fail "shutdown")
+ return buf'
+
+-- |The unified interface to dialog and data section. This
+-- function relies on the fact that pipelining ends with
+-- @DATA@ commands: dialog and payload must /not/ come in a
+-- single buffer. See
+-- section 3.1.
+
+smtpd :: Buffer -> Smtpd ([SmtpReply], Buffer)
+smtpd buf@(Buf _ _ 0) = return ([], buf)
+smtpd buf@(Buf _ ptr n) = do
+ sst <- getSessionState
+ if (sst == HaveData)
+ then do (r, buf') <- feed buf
+ return (maybeToList r, buf')
+ else do xs <- liftIO (peekArray (fromIntegral n) ptr)
+ let xs' = map (toEnum . fromEnum) xs
+ ls' = splitList "\r\n" xs'
+ ls = reverse . tail $ reverse ls'
+ rest = head $ reverse ls'
+ i = length xs - length rest
+ rs <- mapM handleDialog ls
+ buf' <- liftIO $ flush (fromIntegral i) buf
+ return (rs, buf')
+
+handleDialog :: String -> Smtpd SmtpReply
+handleDialog line = do
+ sst <- getSessionState
+ let (e, sst') = runState (smtpdFSM (fixCRLF line)) sst
+ r <- trigger e
+ case (e, isSuccess r) of
+ (_, True) -> setSessionState sst'
+ (StartData, False) -> trigger ResetState >> setSessionState HaveHelo
+ _ -> return ()
+ return r
+
+
+-- * Running 'Smtpd' Computations
+
+-- |Run the given 'Smtpd' computation and write the logging
+-- output via the given 'Logger'. Use 'withGlobalEnv' to
+-- create the global environment and 'emptyEnv' to
+-- initialize the 'SmtpdState'.
+
+runSmtpd' :: Logger -> Smtpd a -> GlobalEnv -> SmtpdState
+ -> IO (a, SmtpdState)
+runSmtpd' logger f = runStateT . withLogger logger f
+
+-- |Convenience wrapper for 'runSmtpd'' with 'Logger'
+-- hard-coded to 'syslogger'.
+
+runSmtpd :: Smtpd a -> GlobalEnv -> SmtpdState
+ -> IO (a, SmtpdState)
+runSmtpd = runSmtpd' syslogger
+
+-- |Run the given computation with an initialized global
+-- environment for 'Smtpd'. The environment is destroyed
+-- when this function returns.
+
+withGlobalEnv :: HostName -- ^ 'myHeloName'
+ -> Resolver
+ -> EventT
+ -> (GlobalEnv -> IO a)
+ -> IO a
+withGlobalEnv myHelo dns eventT f = do
+ let eventH = eventT (mkEvent myHelo "/tmp/test-spool")
+ initEnv = do setDNSResolver dns
+ setEventHandler eventH
+ newMVar (execState initEnv emptyEnv) >>= f
+
+
+-- * ESMTP Network Daemon
+
+smtpdServer :: Capacity -> GlobalEnv -> SocketHandler
+smtpdServer cap theEnv =
+ handleLazy ReadWriteMode $ \(h, Just sa) -> do
+ hSetBuffering h (BlockBuffering (Just (fromIntegral cap)))
+ let st = execState (setPeerAddr sa) emptyEnv
+ smtpdMain cap theEnv h h st >> return ()
+
+smtpdMain :: Capacity
+ -> GlobalEnv
+ -> ReadHandle
+ -> WriteHandle
+ -> SmtpdState
+ -> IO SmtpdState
+smtpdMain cap theEnv hIn hOut initST = do
+ let greet = do r <- trigger Greeting
+ safeReply hOut r >> safeFlush hOut
+ to <- getReadTimeout
+ sid <- mySessionID
+ return (r, to, sid)
+ ((r, to, sid), st) <- runSmtpd greet theEnv initST
+ st' <- case r of
+ Reply (Code Success _ _) _ -> do
+ let getTO = evalState (getVarDef (mkVar "ReadTimeout") to)
+ yellIO = syslogger . LogMsg sid st
+ hMain = smtpdHandler hOut theEnv
+ errH e st' = yellIO (CaughtException e) >> return st'
+ runLoopNB getTO errH hIn cap hMain st
+ _ -> return st
+ let bye = do sst <- getSessionState
+ when (sst /= HaveQuit)
+ (trigger Shutdown >> return ())
+ fmap snd (runSmtpd bye theEnv st')
+
+main' :: Capacity -> PortID -> EventT -> IO ()
+main' cap port eventT = do
+ installHandler sigPIPE Ignore Nothing
+ installHandler sigCHLD (Catch (return ())) Nothing
+ whoami <- getHostName
+ withSocketsDo $
+ withSyslog "postmaster" [PID, PERROR] MAIL $
+ initResolver [NoErrPrint,NoServerWarn] $ \dns ->
+ withGlobalEnv whoami dns eventT $
+ listener port . smtpdServer cap
+
+main :: IO ()
+main = main' 1024 (PortNumber 2525) id
+
+-- ** Logging
+
+type Logger = LogMsg -> IO ()
+
+-- |Bind the logging back-end to demote 'Smtpd' to an
+-- ordinary 'StateT' computation.
+
+withLogger :: Logger -> Smtpd a -> GlobalEnv -> StateT SmtpdState IO a
+withLogger logger f theEnv = do
+ (a, st, w) <- get >>= liftIO . runRWST f theEnv
+ liftIO $ mapM_ logger w
+ put st
+ return a
+
+-- |Our default logging back-end.
+
+syslogger :: Logger
+syslogger (LogMsg sid _ e) = syslog Info $
+ showString "SID " . shows sid . (':':) . (' ':) $ show e
diff --git a/README b/README
new file mode 100644
--- /dev/null
+++ b/README
@@ -0,0 +1,205 @@
+Postmaster ESMTP Server
+=======================
+
+:Latest Release: postmaster-0.1.tar.gz_
+:Darcs: darcs_ get http://postmaster.cryp.to/ postmaster
+
+.. contents::
+
+The Sales Pitch
+---------------
+
+ Postmaster is the mail transport agent of choice for the
+ discriminating hacker. Or, to be more accurate: for the
+ discriminating Haskell_ hacker, because if you don't know
+ any Haskell, you have about zero chance of running this
+ software right now. I plan on turning Postmaster into
+ something an end-user can run, but that's a long road.
+
+ So why yet *another* MTA? Aren't Sendmail, Qmail, Postfix,
+ and Exim enough already?
+
+ No, unfortunately they are not, because none of those
+ programs comes even close to the degree of configurability
+ I need. Postmaster allows you to configure *anything*. I
+ really mean it. You'd like to configure your MTA to do
+ mail relaying for the site ``example.org`` only on
+ Saturdays in a leap year? No problem at all. You'd like to
+ put your entire mail configuration into a DNS zone and
+ distribute it through the domain name system to your mail
+ exchangers? Be my guest. You'd like to rewrite the word
+ "no" to "yes" in any e-mail you receive which has
+ "Michelle" in the ``From:`` header and was sent between
+ 8am and 10am CET? Sure thing.
+
+ Postmaster is not really an MTA, it is a framework in
+ which you can easily write your own, custom-built MTA!
+ This means that Postmaster contains everything *except
+ for* the routine ``main``. That's what you have to write.
+
+What can it do?
+'''''''''''''''
+
+ Postmaster implements an ESMTP server. Given a
+ configuration, it starts up and listens for incoming SMTP
+ connections, handles them, and pipes the accepted e-mail
+ messages into an arbitrary local mailer of your choice. A
+ good local mailer is Procmail_.
+
+ Beyond that, you can configure and modify every little
+ step of the SMTP transaction. All the real work is done
+ through a call-back function. Postmaster triggers an
+ "event" every time a state change is required, and hopes
+ that the call-back does whatever is necessary. Among the
+ known events, this one is popular::
+
+ AddRcptTo Mailbox
+
+ So by writing a handler function for this event, you can
+ configure what user addresses the server will accept. For
+ example::
+
+ joe, jane :: Mailbox
+ joe = Mailbox [] "joe" "example.net"
+ jane = Mailbox [] "jane" "example.net"
+
+ admin :: Mailbox
+ admin = Mailbox [] "janes.husband" "example.com"
+
+ event :: Event -> Smtpd SmtpReply
+ event (AddRcptTo mbox)
+ | mbox == joe = procmail mbox "joe" []
+ | mbox == jane = do
+ from <- gets mailFrom
+ when (from == joe)
+ (relay [admin] >> return ())
+ procmail mbox "jane" []
+ | otherwise = say 5 5 3 "unknown recipient"
+
+ You could also read that configuration from a file, query
+ the DNS for that recipient, or accept / refuse addresses
+ randomly. It's entirely up to you.
+
+ Postmaster provides a wealth of SMTP-related functions you
+ can use. You can (asynchronously) resolve ``A``, ``PTR``,
+ or ``MX`` records. There is a generic, type-safe Unix-like
+ environment for each session and a global one for the
+ entire daemon in which you can store any data your event
+ handler needs. Postmaster provides a framework for logging
+ messages through ``syslog(3)``. And, last but not least,
+ there is a rapidly growing collection of re-usable event
+ handlers which you can plug together to configure complex
+ setups in a few lines of code.
+
+What can it *not* do?
+'''''''''''''''''''''
+
+ At the moment, Postmaster has no mail queue. Until that is
+ implemented, there is no way to deliver outbound messages
+ via SMTP. If you have to relay e-mail for others, you will
+ need another MTA installed to do that. Sendmail_ is
+ particularly well suited for the task. Just modify your
+ ``sendmail.mc`` file to contain the lines ::
+
+ FEATURE(no_default_msa)
+ dnl DAEMON_OPTIONS(`Port=25, Name=MTA')
+ DAEMON_OPTIONS(`Port=587, Name=MSA, M=E')
+
+ and your ``submit.mc`` file to contain::
+
+ FEATURE(`msp', `', `MSA')
+
+ This configures Sendmail to act as a "mail submission
+ agent". Meaning that it will not listen on port 25 but on
+ port 587 instead. Correspondingly, your local mail system
+ will not inject messages via ``localhost:25`` but
+ ``localhost:587``. You'll effectively use Postmaster as
+ your MTA to the outside world, and Sendmail as your MTA on
+ the inside. It's not beautiful, but it will work very
+ reliably until Postmaster's own delivery agent is ready.
+
+Documentation
+-------------
+
+ `Postmaster Tutorial`_
+ A walk through "Config.hs" -- this is work in progress.
+
+ `Reference Documentation`_
+ Haddock-generated reference of all exported functions.
+
+Building Postmaster
+-------------------
+
+ To compile the software, you need GHC_ version 6.6 or
+ later (only tested with GHC 6.8.x). Furthermore, you'll
+ need the `GNU adns`_ and OpenSSL_ C libraries installed.
+
+ You can install through your distro, if it provides postmaster,
+ or from source. The source can be gotten from the Darcs repo or
+ Hackage.
+
+ Once you've fetched the sources, do the following:
+
+ 1) Build and install through Cabal as for other Haskell packages:
+
+ runhaskell Setup configure --user --prefix=$HOME
+ runhaskell Setup build
+ runhaskell Setup install --user
+
+ (You may want to remove the --user flag when installing as root.)
+
+ You can also install via the GNU Autotools.
+
+ 1) Edit ``GNUmakefile`` to fit your system. You'll have to
+ adapt the variable ``HDI_PATH`` to point to the base
+ directory where the Haddock interface files for your
+ compiler are installed or the documentation won't
+ (re-)build.
+
+ 2) Say ``make``. You need GNU make to build Postmaster, so
+ if you're running a BSD Unix, ``gmake`` should be used
+ instead.
+
+ 3) If you get this compiler error::
+
+ .objs/Digest.o(.text+0x357): In function `spyU_info':
+ : undefined reference to `EVP_mdc2'
+
+ then your OpenSSL version doesn't contain the MDC2 hash
+ algorithm yet. That's no problem ... just comment out
+ the (three or so) references to it in
+ ``hopenssl/Digest.hs`` -- or upgrade to OpenSSL 0.9.7e
+ or later.
+
+
+Copyleft
+--------
+
+ Copyright (c) 2008 Peter Simons . All
+ rights reserved. This software is released under the terms
+ of the `GNU General Public License
+ `_.
+
+-----------------------------------------------------------------
+
+`[Homepage] `_
+
+.. _Haskell: http://haskell.org/
+
+.. _darcs: http://darcs.net/
+
+.. _Reference Documentation: docs/index.html
+
+.. _Procmail: http://www.procmail.org/
+
+.. _Sendmail: http://sendmail.org/
+
+.. _postmaster-0.1.tar.gz: http://postmaster.cryp.to/postmaster-0.1.tar.gz
+
+.. _GHC: http://haskell.org/ghc/
+
+.. _GNU adns: http://www.gnu.org/software/adns/
+
+.. _OpenSSL: http://www.openssl.org/
+
+.. _Postmaster Tutorial: docs/tutorial.html
diff --git a/Setup.lhs b/Setup.lhs
new file mode 100644
--- /dev/null
+++ b/Setup.lhs
@@ -0,0 +1,8 @@
+#!/usr/bin/env runhaskell
+
+> module Main (main) where
+>
+> import Distribution.Simple
+>
+> main :: IO ()
+> main = defaultMain
diff --git a/postmaster.cabal b/postmaster.cabal
new file mode 100644
--- /dev/null
+++ b/postmaster.cabal
@@ -0,0 +1,26 @@
+Name: postmaster
+Version: 0.1
+Synopsis: Postmaster ESMTP Server
+Description: Postmaster implements an ESMTP server. Given a configuration,
+ it starts up and listens for incoming SMTP connections, handles
+ them, and pipes the accepted e-mail messages into an arbitrary
+ local mailer of your choice. A good local mailer is Procmail.
+ Beyond that, you can configure and modify every little step
+ of the SMTP transaction. All the real work is done through
+ call-back functions.
+Homepage: http://postmaster.cryp.to/
+Category: Network
+License: GPL
+License-File: COPYING
+Author: Peter Simons
+Maintainer: Peter Simons
+Data-Files: README
+Build-Type: Simple
+
+Executable: postmaster
+Main-Is: tutorial.lhs
+GHC-Options: -Wall -threaded
+Extra-Libraries: adns crypto
+Build-Depends: base, haskell98, directory, mtl, network, unix, parsec,
+ containers, bytestring, old-time, hsyslog, hsdns, hsemail,
+ hopenssl
diff --git a/tutorial.lhs b/tutorial.lhs
new file mode 100644
--- /dev/null
+++ b/tutorial.lhs
@@ -0,0 +1,545 @@
+> {-# LANGUAGE DeriveDataTypeable, PatternGuards #-}
+
+A Walk Through "Config.hs"
+==========================
+
+:Author: Peter Simons
+:Date: 2008-02-20
+:Note: This text is *nowhere* near being complete.
+
+.. contents::
+
+Welcome To The Real World
+-------------------------
+
+The purpose of this document is to provide a hands-on
+introduction to the Postmaster ESMTP server. Naturally, it
+is written as a literate Haskell `source code`_, so you can
+load it into ``ghci`` and run any of the examples in the
+interactive development environment while reading the text.
+Note that Postmaster must be linked to the system libraries
+``-ladns -lcrypto``, so you'll have to start the interpreter
+with those flags given on the command-line. (If you run
+``ghci`` from Emacs this should be configured
+automatically.)
+
+I have decided against explaining the internals of the
+daemon. I'll write this text treating the functions
+Postmaster provides just like any other Haskell library. I
+think it is better to do it this way because you, as the
+user, probably don't care how Postmaster works. You only
+care how to configure a real bad-ass MTA. So I'll do just
+that and refer you to the `reference documentation`_ for
+the details.
+
+::
+
+> module Main where
+>
+> import System.IO
+> import System.Time
+> import System.Posix.User
+> import Network.Socket ( SockAddr(..) )
+> import Data.Char
+> import Data.List
+> import Postmaster hiding ( main )
+
+> ioBufferSize :: Capacity
+> ioBufferSize = 1024
+
+> port :: PortID
+> port = PortNumber 2525
+
+> run :: EventT -> IO ()
+> run f = main' ioBufferSize port f
+
+You have a working SMTP daemon now. Just start it with ``run
+id`` and ``telnet`` to the server::
+
+ $ telnet localhost 2525
+ Trying 127.0.0.1...
+ Connected to localhost.
+ Escape character is '^]'.
+ 220 peti.cryp.to Postmaster ESMTP Server
+ NOOP
+ 250 Massive system failure. Just kidding ... OK.
+ QUIT
+ 221 peti.cryp.to closing connection
+ Connection closed by foreign host.
+
+The default configuration will ...
+
+- accept every HELO and EHLO command,
+- accept every MAIL command,
+- refuse every RCPT command;
+- thus, refuse DATA commands for lack of recipients.
+
+Writing Event Handlers
+''''''''''''''''''''''
+
+::
+
+> debugEH :: String -> EventT
+> debugEH name f e = do
+> yell (StartEventHandler name e)
+> r@(Reply rc _) <- f e
+> yell (EventHandlerResult name e rc)
+> return r
+
+The constructors ``StartEventHandler`` etc. are defined by
+Postmaster; it's one of many ``LogEvents`` you may trigger
+whenever you think it's appropriate. By wrapping any event
+handler with this combinator, we can trace its input and
+output values. With two little helper functions, we can try
+it out right away::
+
+> mainDebug :: IO ()
+> mainDebug = run (debugEH "default")
+
+If you speak with Postmaster now, you should notice the new
+log messages that show up on your ``ghci`` terminal (and in
+the system log file you've configured for ``syslog(3)``)::
+
+ SID 1: StartEventHandler "default" Greeting
+ SID 1: EventHandlerResult "default" Greeting 220
+
+
+Standard Unix Configuration
+'''''''''''''''''''''''''''
+
+Let's configure a real MTA that actually does something. As
+a simple example, let us reimplement the way MTAs have
+worked traditionally under Unix: (1) The MTA has a list of
+"local hostnames". Any recipient which is not in one of
+these domains is refused. (2) Recipients *in* the local
+domains are delivered to the Unix user with the same name as
+the local part. (3) All system users are valid e-mail
+recipients. (4) Everything else needs an manual entry a.k.a.
+"alias".
+
+One straightforward way to implement this scheme is by
+splitting these requirements into the three functions: The
+first one checks whether the address of the ``AddRcptTo``
+event is a local hostname; the second checks the system
+users database, and the third one unconditionally delivers
+to the local-part. By wrapping these functions around each
+other in the right order, we get exactly the behavior
+described above.
+
+The implementation is trivial::
+
+> localHosts :: [HostName] -> EventT
+> localHosts lhosts _ (AddRcptTo (Mailbox _ _ host)) = do
+> if (map toLower host) `elem` lhosts
+> then say 2 5 0 "TODO: We accept everything right now"
+> else say 5 5 3 "unknown recipient"
+> localHosts _ f e = f e
+
+For it to work, the list you give the function must contain
+the local hostnames in all lower-case, obviously. Note that
+this combinator works differently than the earlier ones: It
+doesn't use ``f`` as a fallback but *guards* access to ``f``!
+
+Our database lookup isn't complicated either: [5]_ ::
+
+> exposePasswd :: EventT
+> exposePasswd f e@(AddRcptTo (Mailbox _ lpart _)) = do
+> pwdentry <- liftIO (getUserEntryForName lpart)
+> if userName pwdentry == lpart -- kludge for ghc
+> then f e
+> else say 5 5 3 "unknown recipient"
+> exposePasswd f e = f e
+
+Another function that guards access to ``f`` on the
+``AddRcptTo`` event. And our local mailer is::
+
+ TODO: broken with spooler
+
+ | localProcmail :: EventT
+ | localProcmail _ (AddRcptTo mbox@(Mailbox _ lpart _)) =
+ | procmail [mbox] lpart []
+ | localProcmail f e = f e
+
+Done. ::
+
+> stdConfig :: EventT
+> stdConfig =
+> localHosts myHostNames . exposePasswd -- TODO: . localProcmail
+
+The code is point-free, so it must be good. Now edit the
+list of local hostnames to suit your system's setup ... ::
+
+> myHostNames :: [HostName]
+> myHostNames = [ "localhost"
+> , "change-me.example.org"
+> ]
+
+and run your MTA::
+
+> stdMTA :: IO ()
+> stdMTA = run stdConfig
+
+ | runStdMTA :: [String] -> IO ()
+ | runStdMTA = runTest stdConfig
+
+A good test session should be::
+
+> stdTest :: [String]
+> stdTest =
+> [ "EHLO [127.0.0.1]"
+> , "MAIL FROM:<\"foo\\\".bar\"@example.net>"
+> , "RCPT TO:"
+> , "RCPT TO:"
+> , "RCPT TO:"
+> , "DATA"
+> , "From: simons@cryp.to (Peter Simons)"
+> , "Subject: Testing Postmaster"
+> , ""
+> , "Won't work anyway."
+> , "."
+> ]
+
+If you run ``testStdMTA stdTest``, you'll most likely find
+the e-mail in the file ``/var/mail/root`` now. Procmail,
+which we used for local delivery, doesn't care about any
+``/etc/mail/aliases`` you might have. Which is good, because
+we want to determine the aliases in Postmaster, not
+somewhere else.
+
+Aliases and Exploders
+'''''''''''''''''''''
+
+Aliases ... phew. That ought to be difficult? ::
+
+> alias :: [(Mailbox, Mailbox)] -> EventT
+> alias theDB f e
+> | AddRcptTo mbox <- e
+> , Just mbox' <- lookup mbox theDB
+> = trigger (AddRcptTo mbox')
+> | otherwise = f e
+
+Why do we need ``trigger``? Instead of that definition, we
+could equally well have used::
+
+ alias theDB f e
+ | ...
+ = alias theDB f (AddRcptTo mbox')
+
+The semantics differ insofar as that this variant will
+properly recurse, but it will bypass the access checks that
+might have run *before* ``alias`` was even called. We don't
+know how deeply nested we are in the event transformer
+chain! The function ``triggers`` allows us to call the
+entire chain from the beginning.
+
+By-passing the checks might be what you want in some cases,
+actually. But I'd rather define an explicit handler for
+addresses like that. ``alias`` rewrites addresses; nothing
+more, nothing less. Here is a short demo function::
+
+ | runAliasTest :: IO ()
+ | runAliasTest = runTest (myalias . stdConfig) stdTest
+ | where
+ | lhs = read "non.existent@localhost"
+ | rhs = read "root@localhost"
+ | myalias = alias [(lhs,rhs)]
+
+You will have noticed that the mechanism doesn't look like
+the usual aliases file. It maps addresses one-to-one, not
+one-to-many. In fact, it is more similar to Sendmail's
+``virtusertable``. because our left handside of the rewrite
+is a full e-mail address, not just a local part. If we want
+to have one-to-many mappings, this a simple way to do it::
+
+> explode :: Mailbox -> Smtpd SmtpReply -> EventT
+> explode lhs mkRhs f e
+> | AddRcptTo mbox <- e, lhs == mbox
+> = mkRhs
+> | otherwise = f e
+
+ | runExploderTest :: IO ()
+ | runExploderTest = runTest (expl . stdConfig) stdTest
+ | where
+ | expl = explode (read "non.existent@localhost")
+ | (do shell [] "cat >/dev/null"
+ | shell [] "cat >/dev/null"
+ | -- add more
+ | say 2 5 0 "great")
+
+Cooler Event Handlers
+---------------------
+
+The Generic Environment
+'''''''''''''''''''''''
+
+Which brings us to the question of how we write a stateful
+handler then? What if we want to keep transient information
+for a session -- or beyond the life-time of a session?
+
+For that purpose Postmaster features two finite-map
+environments: a global one, and a per-TCP-session one. These
+environments work almost exactly the like Shell variables
+under Unix do. ::
+
+ local :: EnvT a -> Smtpd a
+ global :: EnvT a -> Smtpd a
+
+Disallow Routing Addresses
+''''''''''''''''''''''''''
+
+::
+
+> noRouteAddr :: EventT
+> noRouteAddr _ (SetMailFrom (Mailbox (_:_) _ _))
+> = say 5 0 4 "You are kidding, right?"
+> noRouteAddr _ (AddRcptTo (Mailbox (_:_) _ _))
+> = say 5 0 4 "no source routing"
+> noRouteAddr f e = f e
+
+Dynamic Blacklisting
+''''''''''''''''''''
+
+::
+
+> data (Typeable a) => TimeStamped a = TS ClockTime a
+> deriving (Typeable, Show)
+>
+> type Blacklist = [TimeStamped HostAddress]
+>
+> blacklist :: TimeDiff -> EventT
+> blacklist ttl f e = do
+> r <- f e
+> if e /= Greeting || isFailure r then return r else do
+> peer <- getPeerAddr
+> case peer of
+> Nothing -> return r
+> Just (SockAddrUnix _) -> return r
+> Just sa@(SockAddrInet _ addr) -> do
+> now <- liftIO getClockTime
+> let delta = addToClockTime ttl
+> stale = \(TS ts _) -> delta ts < now
+> clean = reverse . dropWhile stale . reverse
+> expire = (\bl -> (bl,bl)) . maybe [] clean
+> blackl <- global (modifyVar (mkVar "blacklist") expire)
+> if all (\(TS _ a) -> a /= addr) blackl
+> then return r
+> else do yell (Msg (msg sa))
+> say 5 5 4 "no SMTP service here"
+> Just (SockAddrInet6 _ _ _ _) -> return r
+> where
+> msg = showString "blacklist: refuse peer " . show
+
+Now we need a function to add a peer to the blacklist
+whenever we feel like it::
+
+> ban :: Smtpd ()
+> ban = do
+> peer <- getPeerAddr
+> case peer of
+> Nothing -> return ()
+> Just (SockAddrUnix _) -> return ()
+> Just (SockAddrInet6 _ _ _ _) -> return ()
+> Just sa@(SockAddrInet _ a) -> do
+> yell (Msg (msg sa))
+> now <- liftIO getClockTime
+> let a' = TS now a
+> append = maybe [a'] (\as -> a' : as)
+> global (modifyVar_ (mkVar "blacklist") append)
+> return ()
+> where
+> msg = showString "black-listing peer: " . show
+
+An SMTP reply code of 221 or 421 from the event handler
+causes Postmaster to drop the connection after the reply::
+
+> bye :: Smtpd SmtpReply
+> bye = do
+> whoami <- myHeloName
+> say 4 2 1 (showString whoami " Hasta la vista, baby.")
+
+::
+
+> impatient :: Int -> EventT
+> impatient permFailBound f e = do
+> r@(Reply (Code rc _ _) _) <- f e
+> case rc of
+> PermanentFailure -> do
+> c <- local (tick (mkVar "permFailures"))
+> if c >= permFailBound
+> then ban >> bye
+> else return r
+> _ -> return r
+
+> badass :: EventT
+> badass = blacklist ttl . impatient maxPF . noRouteAddr
+> where
+> ttl = noTimeDiff { tdMin = 30 }
+> maxPF = 3
+
+The Rules Of RFC2821
+--------------------
+
+In all of the text I assume you are familiar with
+[RFC2821]_. So I'll just explain a few minor details
+concerning `how the RFC is implemented `_ in
+Postmaster.
+
+Mailboxes
+'''''''''
+
+The data type ``Mailbox`` is of a certain importance in this
+text. It is defined like this::
+
+ data Mailbox = Mailbox [String] String String
+
+The most general e-mail address defined in the RFC has the
+form ``<[@route,...:]user@domain>``, and ``Mailbox`` mirrors
+that exactly. You'll find that the first field, the optional
+routing information, is rather unpopular these days. But
+what can I do? It is part of an e-mail address.
+
+``Mailbox`` is an instance of ``Read`` and ``Shown``, so you
+can use the text-representation to create mailboxes in a
+comfortable way. Just use ``read "user@domain.tld"`` and
+that's it. In case of mailboxes, ``read . show = id`` holds,
+but ``show . read = id`` does *not*, because a mailbox
+returned by ``show`` will always be enclosed in angular
+brackets. Mailbox is also in class ``Eq``, and ``(mb ==
+mb')`` will treat the hostname as case-insensitive, as the
+RFC requires.
+
+There are two special mailboxes defined for the SMTP dialogue::
+
+ nullPath, postmaster :: Mailbox
+ nullPath = Mailbox [] [] []
+ postmaster = Mailbox [] "postmaster" []
+
+Don't forget to do something with those. ``MAIL FROM:<>``
+and ``RCPT TO:`` must always be valid commands.
+
+SMTP Reply Codes by Function Groups
+''''''''''''''''''''''''''''''''''''
+
+These reply codes are suggested in the RFC. You ultimately,
+you can do what you want because nobody cares for more than
+the first digit anyway.
+
+``500``
+ Syntax error, command unrecognized
+``501``
+ Syntax error in parameters or arguments
+``502``
+ Command not implemented
+``503``
+ Bad sequence of commands
+``504``
+ Command parameter not implemented
+``211``
+ System status, or system help reply
+``214``
+ Help message
+ (Information on how to use the receiver or the meaning of a
+ particular non-standard command; this reply is useful only
+ to the human user)
+``220``
+ Service ready
+``221``
+ Service closing transmission channel. See 421.
+``421``
+ Service not available. This may be a reply to any
+ command if the service knows it must shut down. When the
+ event handler returns this code (or 221), Postmaster will
+ drop the connection after handling it.
+``250``
+ Requested mail action okay, completed
+``251``
+ User not local; will forward to
+``252``
+ Cannot VRFY user, but will accept message and attempt
+ delivery
+``450``
+ Requested mail action not taken: mailbox unavailable
+``550``
+ Requested action not taken: mailbox unavailable
+``451``
+ Requested action aborted: error in processing
+``551``
+ User not local; please try
+``452``
+ Requested action not taken: insufficient system storage
+``552``
+ Requested mail action aborted: exceeded storage allocation
+``553``
+ Requested action not taken: mailbox name not allowed
+ (e.g., mailbox syntax incorrect)
+``554``
+ Transaction failed (Or, in the case of a connection-opening
+ response, "No SMTP service here")
+
+Notes
+-----
+
+.. [1] The port-number argument doesn't have enough
+ granularity. I'll soon change that API to expect a
+ socket, so that you can specify on which IP address
+ to listen, too.
+
+.. [2] I wonder whether I should change that to ``Doc``, to
+ allow pretty-printing. Opinions are welcome.
+
+
+.. [3] In fact, the ``relay`` target is implemented on top
+ of ``pipe`` at the moment. Postmaster doesn't have a
+ mail queue yet, so it can't relay itself. (That will
+ change.) ``relay`` uses the field ``sendmailPath``
+ from the configuration and just pipes the message
+ into Sendmail with appropriate arguments.
+
+.. [4] Yes, the call to ``sed`` in ``shell`` is not nice.
+ That will change. Postmaster does support re-writing
+ of the data section already, I just wanted to keep
+ the internal structure as simple as possible for the
+ time being.
+
+.. [5] GHC seems to have a bug in ``getUserEntryForName``
+ which causes it to return an incorrect entry when the
+ requested one doesn't exist. Until that's fixed, we
+ use the comparison for equality of the user names to
+ determine success, rather than catching the exception
+ we were supposed to get in case of failure.
+
+.. [6] Mostly because I'll replace it with
+ ``Data.Dynamic.Dynamic`` soon anyway.
+
+Change me::
+
+> main :: IO ()
+> main = run (badass . stdConfig)
+
+References
+----------
+
+.. [RFC2821] Simple Mail Transfer Protocol: http://www.faqs.org/rfcs/rfc2821.html
+
+.. [Postmaster] Homepage: http://postmaster.cryp.to/
+
+.. [Haskell] The Haskell Homepage: http://www.haskell.org/
+
+.. [GHC] The Glorious Haskell Compiler: http://www.haskell.org/ghc/
+
+.. [Sendmail] Sendmail Homepage: http://sendmail.org/
+
+.. [Procmail] Procmail Homepage: http://www.procmail.org/
+
+.. _source code: http://postmaster.cryp.to/tutorial.lhs
+
+.. _reference documentation: index.html
+
+.. _events: Rfc2821.html#t%3AEvent
+
+
+.. ----- Configure Emacs -----
+..
+.. Local Variables: ***
+.. haskell-program-name: "ghci -ladns -lcrypto" ***
+.. End: ***