开箱即用的Haskell插件系统

问题描述

我已经阅读了Haskell的插件，但是我无法达到我的目的（最好是在生产环境中使用）。

我的插件系统目标是：

1. 生产环境必须开箱即用（全部预编译）。
   
2. 加载插件已启用重置应用程序/服务，但理想情况下，它可以即时加载和更新插件。
   

be：

链接库（编译每个插件{Nth} 作为共享库）可以工作（如FFI），但

1. link library (compiling each Plugin{Nth} as shared library) could works (as FFI) but
   1. How enumerate and load each shared library at runtime? (get every getPlugin function point)
   2. Exists some better way? (Eg. some "magic" process before run application/service)

   Thank you!

   UPDATE

   Full running example

   Following the great @xnyhps answer, a full running example using ghc 7.10

   SharedTypes.hs

   module SharedTypes (
     PluginInterface (..)
   ) where
   
   data PluginInterface =
        PluginInterface { pluginName :: String
                        , runPlugin  :: Int -> Int
                        }
   

   Plugin1.hs

   module Plugin1 (
     getPlugin
   ) where
   
   import SharedTypes
   
   getPlugin :: PluginInterface
   getPlugin = PluginInterface "Plugin1" $ \x -> 1 * x
   

   Plugin2.hs

   module Plugin2 (
     getPlugin
   ) where
   
   import SharedTypes
   
   getPlugin :: PluginInterface
   getPlugin = PluginInterface "Plugin2" $ \x -> 2 * x
   

   app.hs

   import SharedTypes
   import System.Plugins.DynamicLoader
   import System.Directory
   import Data.Maybe
   import Control.Applicative
   import Data.List
   import System.FilePath
   import Control.Monad
   
   loadPlugins :: FilePath -> IO [PluginInterface]
   loadPlugins path = getDirectoryContents path >>= mapM loadPlugin . filter (".plugin" `isSuffixOf`)
     where loadPlugin file = do
             m <- loadModuleFromPath (combine path file)  -- absolute path
                                     (Just path)          -- base of qualified name (or you'll get not found)
             resolveFunctions
             getPlugin <- loadFunction m "getPlugin"
             return getPlugin
   
   main = do
   
     -- and others used by plugins
     addDLL "/usr/lib/ghc-7.10.1/base_I5BErHzyOm07EBNpKBEeUv/libHSbase-4.8.0.0-I5BErHzyOm07EBNpKBEeUv-ghc7.10.1.so"
     loadModuleFromPath "/srv/despierto/home/josejuan/Projects/Solveet/PluginSystem/SharedTypes.o" Nothing
   
     plugins <- loadPlugins "/srv/despierto/home/josejuan/Projects/Solveet/PluginSystem/plugins"
   
     forM_ plugins $ \plugin -> do
       putStrLn $ "Plugin name: " ++ pluginName plugin
       putStrLn $ "     Run := " ++ show (runPlugin plugin 34)
   

   Compilation and execution

   [josejuan@centella PluginSystem]$ ghc --make -dynamic -fPIC -O3 Plugin1.hs
   [1 of 2] Compiling SharedTypes      ( SharedTypes.hs, SharedTypes.o )
   [2 of 2] Compiling Plugin1          ( Plugin1.hs, Plugin1.o )
   [josejuan@centella PluginSystem]$ ghc --make -dynamic -fPIC -O3 Plugin2.hs
   [2 of 2] Compiling Plugin2          ( Plugin2.hs, Plugin2.o )
   [josejuan@centella PluginSystem]$ mv Plugin1.o plugins/Plugin1.plugin
   [josejuan@centella PluginSystem]$ mv Plugin2.o plugins/Plugin2.plugin
   [josejuan@centella PluginSystem]$ ghc --make -dynamic -fPIC -O3 app.hs
   [2 of 2] Compiling Main             ( app.hs, app.o )
   Linking app ...
   [josejuan@centella PluginSystem]$ ./app
   Plugin name: Plugin1
        Run := 34
   Plugin name: Plugin2
        Run := 68
   

   解决方案

   There is the dynamic-loader package, which allows you to load extra object files or shared libraries into your process. (The version on Hackage doesn't work with 7.10, but the current version on GitHub does.)

   With this, you could do:

   import System.Plugins.DynamicLoader
   import System.Directory
   
   loadPlugins :: FilePath -> IO [PluginInterface]
   loadPlugins path = do
       files <- getDirectoryContents path
       mapM (\plugin_path -> do
           m <- loadModuleFromPath (path ++ "/" ++ plugin_path) (Just path)
           resolveFunctions
           plugin <- loadFunction m "getPlugin"
           return plugin) files
   

   However, you have to keep in mind that the entire process is very unsafe: if you change your PluginInterface data type and try to load a plugin compiled with the old version, your application will crash. You have to hope that the getPlugin function has type PluginInterface, there's no check for that. Lastly, if the plugin comes from an untrusted source, it could execute anything, even though the function you try to call should be pure in Haskel.

   这篇关于开箱即用的Haskell插件系统的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！