#!/usr/bin/env stack
{- stack
runghc
--resolver lts-8.18
--install-ghc
--package turtle
--package language-dockerfile
--package containers
-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE NamedFieldPuns #-}
module Main where
import qualified Control.Foldl as Fold
import Control.Monad (guard, when)
import Data.Either (rights)
import qualified Data.Map.Strict as Map
import Data.Maybe (catMaybes, isJust, mapMaybe)
import qualified Data.Text as Text
import Data.Text (Text)
import Filesystem.Path (FilePath)
import Language.Dockerfile hiding (Tag)
import Prelude hiding (FilePath)
import Text.Read
import Text.ParserCombinators.ReadP hiding (choice)
import Turtle
{- Glossary:
- InstructionPos: in the AST for a docker file, each of the lines are described with the type InstructionPos
- Dockerfile: A list of InstructionPos
- stage: Each of the FROM instructions in a Dockerfile
- cache buster: Files inside a docker image that can be compared with files locally under the same path
-}
newtype App =
App Text
deriving (Show)
newtype Branch =
Branch Text
deriving (Show)
newtype Tag =
Tag Text
deriving (Show, Eq)
newtype SourcePath =
SourcePath FilePath
deriving (Show, Eq)
newtype TargetPath =
TargetPath FilePath
deriving (Show, Eq)
-- | A Stage is one of the FROM directives ina dockerfile
--
data Stage = Stage
{ stageName :: Text -- The image name
, stageTag :: Tag -- The image tag
, stagePos :: Linenumber -- Where in the docker file this line is found
, stageAlias :: Text -- The alias used for building
, directives :: Dockerfile -- Dockerfile is an alias for [InstructionPos]
, alreadyCached :: Bool -- Whether or not we have this stage built separately on the host
} deriving (Show, Eq)
data InspectedStage
= NotCached Stage -- When the image has not yet been built separetely
| Cached { stage :: Stage -- When the image was built and tagged as a separate image
, cacheBusters :: [(SourcePath, TargetPath)] -- List of files that are able to bust the cache
}
deriving (Show)
-- | This script has 2 modes. One for building the Dockerfile, and another for caching its stages
data Mode
= Build
| Cache
deriving (Show)
instance Read Mode where
readPrec =
Text.Read.choice $
strValMap
[ ("Build", Build) -- Accept both casings
, ("build", Build)
, ("Cache", Cache)
, ("cache", Cache)
]
where
strValMap = map (\(x, y) -> lift $ string x >> return y)
-- | Describes the arguments this script takes from the command line
parser :: Parser Mode
parser = argRead "mode" "Whether to build or to cache (options: build | cache)"
main = do
mode <- options "Builds a docker file and caches its stages" parser -- Parse the CLI arguments as a Mode
app <- App <$> needEnv "APP_NAME" -- Get the APP environment variable and then wrap it in App
branch <- Branch <$> needEnv "GIT_BRANCH"
maybeFile <-
do f <- need "DOCKERFILE" -- Get the dockerfile path if any
return (fmap fromText f) -- And transform it to a FilePath
--
-- if DOCKERFILE is not present, we assume is in the current directory
currentDirectory <- pwd
let Just file = maybeFile <|> Just (currentDirectory </> "Dockerfile")
--
-- Now we try to parse the dockefile
dockerFile <- parseFile (Text.unpack (format fp file)) -- Convert the dockerfile to an AST
case dockerFile of
Left message -> error ("There was an error parsing the docker file: " <> show message)
Right ast ->
case mode of
Cache -> sh (cacheBuild app branch ast)
Build -> do
tag <- Tag <$> needEnv "DOCKER_TAG"
sh (build app branch tag ast)
-- | Builds the provided Dockerfile. If it is a multi-stage build, check if those stages are already cached
-- and change the dockerfile to take advantage of that.
build :: App -> Branch -> Tag -> Dockerfile -> Shell ()
build app branch tag ast = do
changedStages <- getChangedStages app branch ast -- Inspect the dockerfile and return the stages that got their cache invalidated
echo "I'll start building now the main Dockerfile"
let bustedStages = replaceStages (filter alreadyCached changedStages) ast -- We replace the busted stages with cached primed ones
status <- buildDockerfile app tag bustedStages -- Build the main docker file with the maybe changed stages
case status of
ExitSuccess -> do
echo
"I built the main dockerfile without a problem. Now call this same script with the `Cache` mode"
ExitFailure _ -> do
die "Boo, I could not build the project"
-- | One a dockefile is built, we can extrac each of the stages separately and then tag them, so the cache
-- can be retreived at a later point.
cacheBuild :: App -> Branch -> Dockerfile -> Shell ()
cacheBuild app branch ast = do
changedStages <- getChangedStages app branch ast
when (changedStages /= []) $ do
echo "--> Let's make the cache great again"
mapM_ (buildAssetStage app) changedStages -- Build each of the stages so they can be reused later
-- | Returns a list of stages which needs to either be built separately or that did not have their cached busted
-- by the introduction of new code.
getChangedStages :: App -> Branch -> Dockerfile -> Shell [Stage]
getChangedStages app branch ast = do
let mainFile = last (getStages ast) -- Parse all the FROM instructions in the dockerfile
assetStages = takeWhile (/= mainFile) (getStages ast) -- Filter out the main FROM at the end
stages = mapMaybe (toStage app branch) assetStages -- Convert to Stage records, filter out errors
when (length assetStages > length stages) showAliasesWarning
-- Time to get all the stages having changed cache files
bustCacheStages <- fold (getAlreadyCached stages >>= inspectCache >>= shouldBustCache) Fold.list
return (catMaybes bustCacheStages) -- Remove the stages that did not actually change
where
showAliasesWarning = do
echo "::::::WARNING::::::"
echo "I found some FROM directives in the dockerfile that did not have an `as` alias"
echo "I'm not smart enough to build multi-stage docker files without aliases."
echo "While this is safe to do, you will get no cache benefits"
echo ""
echo "Please always write your FROM directives as `FROM image:tag as myalias`"
-- | Check whehther or not the tag exists for each of the passed stages
-- and return only those that already exist.
getAlreadyCached :: [Stage] -> Shell Stage
getAlreadyCached stages = do
echo "--> I'm checking whether or not the stage exists as a docker image already"
stage@(Stage {stageTag}) <- select stages -- foreach stages as stage
printLn ("----> Looking for image " %s) (taggedBuild stageTag)
existent <-
fold
(inproc "docker" ["image", "ls", taggedBuild stageTag, "--format", "{{.Repository}}"] empty)
Fold.list -- Get the output of the command as a list of lines
if existent == mempty
then do
echo "------> It does not exist, so I will need to build it myself later"
return (stage {alreadyCached = False})
else do
echo "------> It already exists, so I will then check if the cache files changed"
return (stage {alreadyCached = True})
-- | This will inspect how an image was build and extrack the ONBUILD directives. If any of those
-- instructions are copying or adding files to the build, they are considered "cache busters".
inspectCache :: Stage -> Shell InspectedStage
inspectCache stage@(Stage {..}) = do
case alreadyCached of
False -> return (NotCached stage)
True -> do
history <- imageHistory (Tag (taggedBuild stageTag))
let onBuildLines = extractOnBuild history
workdir = extractWorkdir history
parsedDirectivesWithErrors = fmap (parseString . Text.unpack) onBuildLines -- Parse each of the lines
parsedDirectives = (getFirst . rights) parsedDirectivesWithErrors -- We only keep the good lines
cacheBusters = extractCachePaths workdir parsedDirectives
return (Cached {..})
where
extractCachePaths workdir dir =
let filePairs = concat (mapMaybe doExtract dir) -- Get the (source, target) pairs of files copied
in fmap (prependWorkdir workdir) filePairs -- Some target paths need to have the WORKDIR prepended
--
-- | Prepend a given target dir to the target path
prependWorkdir workdir (source, TargetPath target) =
if relative target -- If the target path is relative, we need to prepend the workdir
then (source, TargetPath (collapse (workdir </> target))) -- Remove the ./ prefix and prepend workdir
else (source, TargetPath target)
--
-- | COPY allows multiple paths in the same line, we need to convert each to a separate path
doExtract (InstructionPos (Copy fr t) _ _) =
let target:allSources = (reverse . Text.words . Text.pack) t -- Make sure we get all the files in COPY
sourcePaths = fmap toSource allSources
in Just (zip sourcePaths (repeat (toTarget target)))
--
-- | This case is simpler, we only need to convert the source and target from ADD
doExtract (InstructionPos (Add fr t) _ _) =
Just [((toSource . Text.pack) fr, (toTarget . Text.pack) t)]
doExtract _ = Nothing
getFirst (first:_) = first
getFirst [] = []
-- | Here check each of the cache buster from the image and compare them with those we have locally,
-- if the files do not match, then we return the stage back as a result, otherwise return Nothing.
shouldBustCache :: InspectedStage -> Shell (Maybe Stage)
shouldBustCache (NotCached stage) = return (Just stage)
shouldBustCache Cached {..} = do
printLn ("----> Checking cache buster files for stage " %s) (stageName stage)
containerId <- inproc "docker" ["create", (taggedBuild (stageTag stage))] empty
-- Get the cache buster files that have changed since last time
hasChanged <- fold (mfilter isJust (checkFileChanged containerId cacheBusters)) Fold.head
if isJust hasChanged
then do
printLn ("----> The stage " %s % " changed") (stageName stage)
return (Just stage)
else do
printLn ("----> The stage " %s % " did not change") (stageName stage)
return Nothing
where
checkFileChanged containerId files = do
(SourcePath file, TargetPath targetDir) <- select files
printLn ("------> Checking file '" %fp % "' in directory " %fp) file targetDir
currentDirectory <- pwd
tempFile <- mktempfile currentDirectory "comp"
let targetFile = targetDir </> file
status <-
proc "docker" ["cp", format (l % ":" %fp) containerId targetFile, format fp tempFile] empty
guard (status == ExitSuccess)
local <- liftIO (readTextFile file)
remote <- liftIO (readTextFile tempFile)
if local == remote
then return Nothing
else return (Just file)
-- | The goal is to create a temporary dockefile in this same folder with the contents
-- if the stage variable, call docker build with the generated file and tag the image
-- so we can find it later.
buildAssetStage :: App -> Stage -> Shell ()
buildAssetStage app Stage {..} = do
printLn ("\n--> Building asset stage " %s % " at line " %d) stageName stagePos
let filteredDirectives = filter isFrom directives
status <- buildDockerfile app stageTag filteredDirectives -- Only build the FROM
guard (status == ExitSuccess) -- Break if previous command failed
history <- imageHistory stageTag -- Get the commands used to build the docker image
newDockerfile <- createDockerfile stageTag (extractOnBuild history) -- Append the ONBUILD lines to the new file
finalStatus <- buildDockerfile app (Tag (taggedBuild stageTag)) newDockerfile -- Now build it
guard (finalStatus == ExitSuccess) -- Stop here if previous command failed
echo ""
echo "--> I have tagged a cache container that I can use next time to speed builds!"
where
isFrom (InstructionPos (From _) _ _) = True
isFrom _ = False
-- | Simply call docker build for the passed arguments
buildDockerfile :: App -> Tag -> Dockerfile -> Shell ExitCode
buildDockerfile (App app) (Tag tag) directives = do
currentDirectory <- pwd
tmpFile <- mktempfile currentDirectory "Dockerfile."
liftIO (writeTextFile tmpFile (Text.pack (prettyPrint directives))) -- Put the Dockerfile contents in the tmp file
proc
"docker"
["build", "--build-arg", "APP_NAME=" <> app, "-f", format fp tmpFile, "-t", tag, "."]
empty -- Build the generated dockerfile
-- | Given a list of instructions, build a dockerfile where the tag is the FROM for the file and
-- the list of instructions are wrapped with ONBUILD
createDockerfile :: Tag -> [Text] -> Shell Dockerfile
createDockerfile (Tag tag) onBuildLines = do
let eitherDirectives = map (parseString . Text.unpack) onBuildLines
file =
toDockerfile $ do
from (tagged (Text.unpack tag) "latest")
mapM (onBuildRaw . toInstruction) (rights eitherDirectives) -- Append each of the ONBUILD instructions
return file
where
toInstruction [(InstructionPos inst _ _)] = inst
toInstruction _ = error "This is not possible"
-- | Extracts the list of instructions appearing in ONBUILD for a given docker history for a tag
extractOnBuild :: [Line] -> [Text]
extractOnBuild lines = doExtract lines
where
onBuildPrefix = "/bin/sh -c #(nop) ONBUILD "
--
-- | First get the ONBUILD lines then strip the common prefix out of each.
-- Arguments flow from right to left in the functions chain
doExtract = mapMaybe (Text.stripPrefix onBuildPrefix . lineToText) . findOnBuildLines
--
-- | First drop the lines not starting with ONBUILD, then take only those.
-- Arguments flow from right to left in the functions chain
findOnBuildLines = takeWhile isOnBuild . dropWhile (not . isOnBuild)
isOnBuild line = Text.isPrefixOf onBuildPrefix (lineToText line)
extractWorkdir :: [Line] -> FilePath
extractWorkdir lines =
case reverse (doExtract lines) of
[] -> fromText "/"
lastWorkdir:_ -> fromText lastWorkdir -- We are on;y intereted in the latest WORKDIR declared
where
onBuildPrefix = "/bin/sh -c #(nop) ONBUILD " -- Curiously, ONBUILD is lead by 2 spaces
workdirPrefix = "/bin/sh -c #(nop) WORKDIR " -- Whereas WORKDIR only by one space
--
-- | First find all relevant lines, then kepp the lines starting with the workdir prefix
doExtract = mapMaybe (Text.stripPrefix workdirPrefix . lineToText) . findRelevantLines
--
-- | Take lines until a ONBUILD is found
-- Arguments flow from right to left in the functions chain
findRelevantLines = takeWhile (not . isOnBuild)
isOnBuild line = Text.isPrefixOf onBuildPrefix (lineToText line)
-- | Calls docker history for the given image name and returns the output as a list
imageHistory :: Tag -> Shell [Line]
imageHistory (Tag tag) = do
printLn ("----> Checking the docker image history for " %s) tag
out <- fold fetchHistory Fold.list -- Buffer all the output of the imageHistory shell
return (reverse out) -- The history comes in reverse order, sort it naturally
where
fetchHistory =
inproc "docker" ["history", "--no-trunc", "--format", "{{.CreatedBy}}", tag] empty
--
-- | Returns a list of directives grouped by the appeareance of the FROM directive
-- This will return the group of all stages found in the Dockerfile
getStages :: Dockerfile -> [Dockerfile]
getStages ast = filter startsWithFROM (group ast [])
where
group [] acc = reverse acc -- End of recursion
group (directive@(InstructionPos (From _) _ _):rest) acc = group rest ([directive] : acc) -- Append a new group
group (directive:rest) [] = group rest [[directive]] -- Create a new group
group (directive:rest) (current:prev) = group rest ((current ++ [directive]) : prev) -- Continue the currently open group
--
-- | Returns true if the first element in the list is a FROM directive
startsWithFROM ((InstructionPos (From _) _ _):_) = True
startsWithFROM _ = False
-- | Converts a list of instructions into a Stage record
toStage :: App -> Branch -> Dockerfile -> Maybe Stage
toStage (App app) (Branch branch) directives = do
(stageName, stagePos, stageAlias) <- getStageInfo directives -- If getStageInfo returns Nothing, skip the rest
let sanitized = sanitize stageName
stageTag = Tag (app <> "__branch__" <> branch <> "__stage__" <> sanitized)
alreadyCached = False
return Stage {..}
where
getStageInfo :: [InstructionPos] -> Maybe (Text, Linenumber, Text)
getStageInfo ((InstructionPos (From (TaggedImage name tag)) _ pos):_) =
if Text.isInfixOf " as " (Text.pack tag) -- Make sure the FROM is aliased
then Just (Text.pack name, pos, parseAlias tag)
else Nothing
getStageInfo _ = Nothing
--
-- | Makes a string safe to use it as a file name
sanitize = Text.replace "/" "-" . Text.replace ":" "-"
-- | Extracts the stage alias out of the FROM directive
parseAlias :: String -> Text
parseAlias = Text.strip . Text.replace "as " "" . snd . Text.breakOn " as " . Text.pack
taggedBuild :: Tag -> Text
taggedBuild (Tag tag) = tag <> "-build"
-- | Given a list of stages and the AST for a Dockerfile, replace all the FROM instructions
-- with their corresponding images as described in the Stage record.
replaceStages :: [Stage] -> Dockerfile -> Dockerfile
replaceStages stages dockerLines = fmap replaceStage dockerLines
where
stagesMap = Map.fromList (map createStagePairs stages)
createStagePairs stage@(Stage {..}) = (stageAlias, stage)
--
-- | Find whehter or not we have extracted a stage with the same alias
-- If we did, then replace the FROM directive with our own version
replaceStage directive@(InstructionPos (From (TaggedImage _ tag)) file pos) =
case Map.lookup (parseAlias tag) stagesMap of
Nothing -> directive
Just Stage {stageTag, stageAlias} ->
InstructionPos
(From (TaggedImage (Text.unpack (taggedBuild stageTag)) (formatAlias stageAlias)))
file
pos
replaceStage directive = directive
formatAlias alias = "latest as " <> Text.unpack alias
printLn message = printf (message % "\n")
-- | Transforms a text to SourcePath
toSource = SourcePath . fromText
-- | Transforms a text to TargetPath
toTarget = TargetPath . fromText
needEnv varName = do
value <- need varName
case value of
Nothing -> error ("I was expecting the " <> show varName <> " env var to be present.")
Just val -> return val