buffering go-msgio breaks the protocol

[whyrusleeping]

I was playing around with improving performance over the network and decided to reduce the number of write syscalls we made, so i did the following patch:

diff --git a/Godeps/_workspace/src/github.com/jbenet/go-msgio/msgio.go b/Godeps/_workspace/src/github.com/jbenet/go-msgio/msgio.go
index 6547e68..09a9de0 100644
--- a/Godeps/_workspace/src/github.com/jbenet/go-msgio/msgio.go
+++ b/Godeps/_workspace/src/github.com/jbenet/go-msgio/msgio.go
@@ -1,6 +1,7 @@
 package msgio

 import (
+       "bytes"
        "encoding/binary"
        "errors"
        "io"
@@ -102,11 +103,14 @@ func (s *writer) WriteMsg(msg []byte) (err error) {
        s.lock.Lock()
        defer s.lock.Unlock()

+       buf := new(bytes.Buffer)
        length := uint32(len(msg))
-       if err := binary.Write(s.W, NBO, &length); err != nil {
+       if err := binary.Write(buf, NBO, &length); err != nil {
                return err
        }
-       _, err = s.W.Write(msg)
+       buf.Write(msg)
+
+       _, err = buf.WriteTo(s.W)
        return err
 }

It writes the data to a buffer, then dumps that buffer to the intended writer. (i know i could have used a bufio.Writer but when have i ever done things the easy way). After this patch, i cannot connect to any other node.

[whyrusleeping]

@jbenet @cryptix @wking if anyone can point out what i'm doing wrong, that would be great.

[wking]

On Fri, May 29, 2015 at 02:43:33PM -0700, Jeromy Johnson wrote:

•   _, err = s.W.Write(msg)
  

•   buf.Write(msg)
  

It's not likely to be the cause of your problem, but you're not
checking for errors here.

Other than that, this looks innocuous to me. Not sure why it's
breaking shrug

[jbenet]

@whyrusleeping what is being output by the node? run two of them (one new, one old) and then nc | hexdump -C on both of them.

[whyrusleeping]

This has been fixed in 0.4.0