diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,20 @@ +Copyright (c) 2015 Justin Leitgeb + +Permission is hereby granted, free of charge, to any person obtaining +a copy of this software and associated documentation files (the +"Software"), to deal in the Software without restriction, including +without limitation the rights to use, copy, modify, merge, publish, +distribute, sublicense, and/or sell copies of the Software, and to +permit persons to whom the Software is furnished to do so, subject to +the following conditions: + +The above copyright notice and this permission notice shall be included +in all copies or substantial portions of the Software. + +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, +EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF +MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. +IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY +CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, +TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE +SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,2 @@ +import Distribution.Simple +main = defaultMain diff --git a/atomic-write.cabal b/atomic-write.cabal new file mode 100644 --- /dev/null +++ b/atomic-write.cabal @@ -0,0 +1,75 @@ +name: atomic-write +version: 0.1.0.0 +synopsis: Atomically write to a file + +description: + . + Atomically write to a file on POSIX-compliant systems while preserving + permissions. + . + On most Unix systems, `mv` is an atomic operation. This makes it simple to write + to a file atomically just by using the mv operation. However, this will + destroy the permissions on the original file. This library does the following + to preserve permissions while atomically writing to a file: + . + * If an original file exists, take those permissions and apply them to the + temp file before `mv`ing the file into place. + * If the original file does not exist, create a following with default + permissions (based on the currently-active umask). + . + This way, when the file is `mv`'ed into place, the permissions will be the ones + held by the original file. + . + This library is based on similar implementations found in common libraries in + Ruby and Python: + . + * + * + * + . + Note that at this time Windows is not supported, however we would appreciate + contributions to the . +license: MIT +license-file: LICENSE +author: Justin Leitgeb +maintainer: justin@stackbuilders.com +copyright: 2015 Stack Builders Inc. +category: System +build-type: Simple +-- extra-source-files: +cabal-version: >=1.10 + +library + exposed-modules: System.AtomicWrite + -- other-modules: + -- other-extensions: + build-depends: base >=4.5 && <4.8 + , temporary + , unix + , directory + , filepath + + hs-source-dirs: src + default-language: Haskell2010 + ghc-options: -Wall + +test-suite atomic-write-test + type: exitcode-stdio-1.0 + hs-source-dirs: spec, src + main-is: Spec.hs + + build-depends: base >=4.5 && <4.8 + , temporary + , unix + , directory + , filepath + + , hspec + + default-language: Haskell2010 + ghc-options: -Wall + + +source-repository head + type: git + location: https://github.com/stackbuilders/atomic-file diff --git a/spec/Spec.hs b/spec/Spec.hs new file mode 100644 --- /dev/null +++ b/spec/Spec.hs @@ -0,0 +1,1 @@ +{-# OPTIONS_GHC -F -pgmF hspec-discover #-} diff --git a/src/System/AtomicWrite.hs b/src/System/AtomicWrite.hs new file mode 100644 --- /dev/null +++ b/src/System/AtomicWrite.hs @@ -0,0 +1,63 @@ +-- | +-- Module : System.AtomicWrite +-- Copyright : (c) 2015 Stack Builders Inc. +-- +-- License : MIT +-- Maintainer : justin@stackbuilders.com +-- Stability : experimental +-- Portability : GHC +-- +-- A library for atomically modifying files while preserving permissions +-- + +module System.AtomicWrite (atomicWriteFile) where + +import System.Directory (renameFile, doesFileExist) +import System.FilePath.Posix (takeDirectory) +import System.IO + (Handle, openTempFile, openTempFileWithDefaultPermissions, hPutStr, hClose) + +import System.Posix.Files (setFileMode, getFileStatus, fileMode) + + +-- | Creates a file atomically on POSIX-compliant systems while preserving +-- permissions. +atomicWriteFile :: + FilePath -- ^ The path where the file will be updated or created + -> String -- ^ The content to write to the file + -> IO () +atomicWriteFile f txt = do + (temppath, h) <- tempFileFor f + + hPutStr h txt + hClose h + + renameFile temppath f + + +-- | Returns a temporary file with permissions correctly set. chooses +-- either previously-set permissions if the file that we're writing +-- to existed, or permissions following the current umask. +tempFileFor :: FilePath -> IO (FilePath, Handle) +tempFileFor originalFilePath = do + let targetDirectory = takeDirectory originalFilePath + + doesFileExist originalFilePath >>= + tmpFile originalFilePath targetDirectory "atomic.write" + + where + + tmpFile :: FilePath -> FilePath -> String -> Bool -> IO (FilePath, Handle) + tmpFile originalPath workingDirectory template previousExisted = + + if previousExisted then do + (temppath, handle) <- openTempFile workingDirectory template + + oldStat <- getFileStatus originalPath + + setFileMode temppath $ fileMode oldStat + + return (temppath, handle) + + else + openTempFileWithDefaultPermissions workingDirectory template