NgxExport.Distribution

Quick and dirty build of simple shared libraries and collecting dependencies. This was designed to build custom Haskell handlers for nginx-haskell-module.

Usage and examples

This module allows for building simple shared libraries with Cabal.

Below is a simple example.

File ngx_distribution_test.hs

{-# LANGUAGE TemplateHaskell #-}

module NgxDistributionTest where

import           NgxExport

import           Data.ByteString (ByteString)
import qualified Data.ByteString.Lazy.Char8 as C8L
import           Data.Aeson
import           Data.Maybe

incCnt :: ByteString -> C8L.ByteString
incCnt = C8L.pack . show . succ . fromMaybe (0 :: Int) . decodeStrict
ngxExportYY 'incCnt

File ngx-distribution-test.cabal

name:                       ngx-distribution-test
version:                    0.1.0.0
build-type:                 Custom
cabal-version:              1.24

custom-setup
  setup-depends:            base >= 4.8 && < 5
                          , ngx-export-distribution

library
  default-language:         Haskell2010
  build-depends:            base >= 4.8 && < 5
                          , ngx-export
                          , bytestring
                          , aeson

  ghc-options:             -Wall -O2 -no-keep-hi-files -no-keep-o-files

File Setup.hs

import NgxExport.Distribution
main = defaultMain

The configuration step requires that utilities patchelf and hslibdeps were found in the paths of environment variable $PATH.

Building is a bit cumbersome: it expects explicit option --prefix at the configuration step (which will be interpreted as the prefix part of the rpath by utility hslibdeps) and explicit ghc option -o at the build step which is as well used by hslibdeps as the name of the target library.

Let's build the example with commands cabal v1-configure and cabal v1-build (the v2-commands should probably work as well).

$ cabal v1-configure --prefix=/var/lib/nginx
Resolving dependencies...
[1 of 1] Compiling Main             ( dist/setup/setup.hs, dist/setup/Main.o )
Linking ./dist/setup/setup ...
Configuring ngx-distribution-test-0.1.0.0...

$ cabal v1-build --ghc-options="ngx_distribution_test.hs -o ngx_distribution_test.so"
[1 of 1] Compiling NgxDistributionTest ( ngx_distribution_test.hs, ngx_distribution_test.o )
Linking ngx_distribution_test.so ...
---> Collecting libraries
'/usr/lib64/libHSrts-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSrts-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSngx-export-1.7.5-JzTEmHewqdC9gGi6rzcAtt-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSngx-export-1.7.5-JzTEmHewqdC9gGi6rzcAtt-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSmonad-loops-0.4.3-8Lx5Hn3pTtO62yOPdPW77x-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSmonad-loops-0.4.3-8Lx5Hn3pTtO62yOPdPW77x-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSasync-2.2.4-ENjuIeC23kaKyMVDRYThP3-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSasync-2.2.4-ENjuIeC23kaKyMVDRYThP3-ghc8.10.5.so'
'/usr/lib64/libHSstm-2.5.0.1-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSstm-2.5.0.1-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSaeson-1.5.6.0-6XeGmWHoO3vJYEUW5PXPgC-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSaeson-1.5.6.0-6XeGmWHoO3vJYEUW5PXPgC-ghc8.10.5.so'

   ...

'/usr/lib64/libHSbase-4.14.2.0-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSbase-4.14.2.0-ghc8.10.5.so'
'/usr/lib64/libHSinteger-gmp-1.0.3.0-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSinteger-gmp-1.0.3.0-ghc8.10.5.so'
'/usr/lib64/libHSghc-prim-0.6.1-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSghc-prim-0.6.1-ghc8.10.5.so'

---> Patching ngx_distribution_test.so
/var/lib/nginx/x86_64-linux-ghc-8.10.5:/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5:/usr/lib64:/usr/lib64/ghc-8.10.5/rts

Now the current working directory contains new files ngx_distribution_test.so and ngx-distribution-test-0.1.0.0.tar.gz and a new directory x86_64-linux-ghc-8.10.5. The tar-file contains the patched shared library and the directory with dependent libraries: it is ready for installation in directory /var/lib/nginx at the target system.

With this building approach, the following list of drawbacks must be taken into account.

• Utility hslibdeps collects only libraries prefixed with libHS,
• command cabal v1-clean only deletes directory dist, it does not delete build artifacts in the current working directory,
• behavior of Cabal commands other than configure, build and clean is not well defined.

buildSharedLib

Arguments

:: Verbosity

Verbosity level

-> PackageDescription

Package description

-> LocalBuildInfo

Local build info

-> BuildFlags

Build flags

-> IO FilePath

Builds a shared library.

Runs ghc compiler with the following arguments.

• -dynamic, -shared, -fPIC, -flink-rts,
• all arguments listed in ghc-options in the Cabal file,
• all arguments passed in option --ghc-options from command-line,
• if arguments do not contain -o path so far, then $pkg.hs, -o $pkg.so.

Returns the path to the built shared library.

patchAndCollectDependentLibs

Arguments

:: Verbosity

Verbosity level

-> FilePath

Path to the library

-> PackageDescription

Package description

-> LocalBuildInfo

Local build info

-> IO ()

Patches the shared library and collects dependent Haskell libraries.

Performs the following steps.

• Adds the value of prefix to the list of rpath in the shared library,
• collects all dependent Haskell libraries in a directory whose name forms as arch-os-compiler,
• archives the shared library and the directory with the collected dependent libraries in a tar.gz file.

The initial 2 steps are performed by utility hslibdeps. It collects all libraries with prefix libHS from the list returned by command ldd applied to the shared library.

ngxExportHooks

Arguments

:: Verbosity

Verbosity level

-> UserHooks

Build hooks.

Based on simpleUserHooks. Overrides

• confHook by configuring programs hslibdeps and patchelf and then running the original confHook from simpleUserHooks,
• buildHook by running in sequence buildSharedLib and patchAndCollectDependentLibs.

Other hooks from simpleUserHooks get derived as is. Running them is neither tested nor recommended.

defaultMain :: IO ()

A simple implementation of main for a Cabal setup script.

Implemented as

defaultMain = defaultMainWithHooks $ ngxExportHooks normal