I was wondering how to read and write from a Socket in the most performant way. According to the library documentation from GHC, 'hGetBuf' and 'hPutBuf' are the way to go. But my problem with these functions is that they expect to read exactly the number of bytes I gave them!
The IO computation
hGetBuf sock ptr 1024
wants to read 1024 bytes, no less. This doesn't work for me, because I need to drive an interactive line-based protocol session. I need the read operation to consume as much data as is available and then to return immediately, so that I can process the command right away.
As an alternative, I looked at 'hGetLine', but this doesn't work for me either, at least not very well, because in my protocol, lines are terminated by "\r\n" -- not just "\n", like hGetLine expects it.
hGetLine should work fine, indeed that's what I used in the Haskell Web Server. Each line will have an extra '\r' at the end, but you just need to allow for that. We really should have non-blocking versions of hGetBuf and hPutBuf, and in fact I have the code sitting in my tree. I'll take a look and see if it can be committed. Cheers, Simon