Add connectionGet' that works like B.hGet

[AlainODea]

Here is an implementation I am using as part of in my changes to support TLS in the amqp package:

connectionGet' :: Conn.Connection -> Int -> IO BC.ByteString
connectionGet' conn x = do
  bs <- Conn.connectionGet conn x
  let diff = BS.length bs - x
  if BS.length bs == 0 || diff == 0
    then do
      return bs
    else do
      next <- connectionGet' conn diff
      return $ BC.append bs next

Relevant qualified imports:

import qualified Network.Connection as Conn
import qualified Data.ByteString as BS
import qualified Data.ByteString.Char8 as BC

[vincenthz]

I'ld rather see this as a pull request than as a comment. I'm OK in principle but got few comments:

• the name should be GetExact (other better name can be suggested). my assumption when I see Get' is that it is some strict variant of Get.

• no new imports needed in connection, specially Data.ByteString.Char8 is not needed (append exist in Data.ByteString)

• I'ld rather see the recursion as an inner loop than a toplevel loop, which would factor the conn:

  connectionGetExact conn = loop
  where loop x | x == 0 = return ..
  | otherwise = do
  ...
  loop

[AlainODea]

Thank you. I'll incorporate your recommendations and submit a Pull request in the next few days.

[dagit]

I just ran into a problem using connectionGet and found this issue. The proposed solution works perfectly for me. Are you still planning to add connectionGetExact to the library? As a temporary solution I added connectionGetExact to my project, but it seems like a nice function to have in the official API.

[vincenthz]

sorry about the crappy delay. This shoudn't have take that long, I just didn't see it.

[AlainODea]

@vincenthz this and the family of crypto libraries around it are essential. Creating and maintaining them is a huge service to me and to the rest of the Haskell community. Thank you 👍

[dagit]

I second that. Thanks!