UDT: Fix critical bug in udtSocket.Write use after return. CC #43

udt/readme.md

@@ -19,6 +19,16 @@ while the messaging semantics can be regarded as a subset of SCTP
 [RFC4960]. 
 ```
 
+From `udtSocket.Read`:
+
+```
+// for datagram sockets, block until we have a message to return and then return it
+// if the buffer isn't big enough, return a truncated message (discarding the rest) and return an error
+
+// for streaming sockets, block until we have at least something to return, then
+// fill up the passed buffer as far as we can without blocking again
+```
+
 ## Deviations
 
 MTU negotiation is disabled. Peernet uses a hardcoded max packet size (see protocol package). Packets may be routed through any network adapter, therefore pinning a MTU specific to a network adapter would not make much sense.

udt/udtsocket.go

@@ -198,7 +198,7 @@ func (s *udtSocket) Read(p []byte) (n int, err error) {
 		}
 		n = copy(p, msg)
 		if n < len(msg) {
-			err = errors.New("Message truncated")
+			err = errors.New("Message truncated") // <- evil buggy
 		}
 	} else {
 		// for streaming sockets, block until we have at least something to return, then
@@ -260,7 +260,10 @@ func (s *udtSocket) Write(p []byte) (n int, err error) {
 		return
 	}
 
+	// previous bug: io.Writer documentation says "Implementations must not retain p.", but it was passed on in s.messageOut
 	n = len(p)
+	data := make([]byte, n)
+	copy(data, p)
 
 	for {
 		if s.writeDeadlinePassed {
@@ -272,7 +275,7 @@ func (s *udtSocket) Write(p []byte) (n int, err error) {
 			deadline = s.writeDeadline.C
 		}
 		select {
-		case s.messageOut <- sendMessage{content: p, tim: time.Now()}:
+		case s.messageOut <- sendMessage{content: data, tim: time.Now()}:
 			// send successful
 			return
 		case _, ok := <-deadline: