linux - 为读取系统调用编写 Haskell FFI

Question

read 函数定义如下:

#include <unistd.h>

ssize_t read(int fd, void *buf, size_t len)

我想为此编写一个 Haskell FFI。这是我的尝试(无法编译):

foreign import ccall unsafe "read" c_read :: CInt -> Ptr () -> CSize -> IO CSsize

read :: Int -- ^ file descriptor
     -> Int64 -- ^ Bytes to allocate
     -> Word64 -- ^ Read upto this many bytes
     -> IO (String, Int64)
read fd bytes len = do
  allocaBytes (fromIntegral bytes) (\ptr -> do
                       size <- c_read (fromIntegral fd) ptr (fromIntegral len)
                       dat <- peekByteOff (castPtr ptr) (fromIntegral size) :: IO String
                       return (dat, (fromIntegral size))
                    )

它无法编译，因为没有用于 Storable 的 String 实例。关于如何为此编写 FFI 的任何提示？

Answer 1

Foreign.C.String是这里的传统解决方案。