From 49c66ff242fc6f260163ab3cccf025c7e5181065 Mon Sep 17 00:00:00 2001
From: Tamir Duberstein <tamird@gmail.com>
Date: Thu, 25 Feb 2016 20:57:46 -0500
Subject: [PATCH] (*MuxConn).Read: fix erroneous io.EOF return

This fixes a bug where (*MuxConn).Read would return io.EOF if the
buffer was exactly the right size to fill the passed-in slice.
---
 cmux.go      |  8 ++++----
 cmux_test.go | 29 +++++++++++++++++++++--------
 2 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/cmux.go b/cmux.go
index 3e899e7..e9a886d 100644
--- a/cmux.go
+++ b/cmux.go
@@ -199,12 +199,12 @@ func newMuxConn(c net.Conn) *MuxConn {
 //
 // This function implements the latter behaviour, returning the
 // (non-nil) error from the same call.
-func (m *MuxConn) Read(b []byte) (int, error) {
-	n1, err := m.buf.Read(b)
-	if n1 == len(b) || err != io.EOF {
+func (m *MuxConn) Read(p []byte) (int, error) {
+	n1, err := m.buf.Read(p)
+	if err != io.EOF {
 		return n1, err
 	}
-	n2, err := m.Conn.Read(b[n1:])
+	n2, err := m.Conn.Read(p[n1:])
 	return n1 + n2, err
 }
 
diff --git a/cmux_test.go b/cmux_test.go
index 24d6249..669b713 100644
--- a/cmux_test.go
+++ b/cmux_test.go
@@ -183,27 +183,40 @@ func TestRead(t *testing.T) {
 		if _, err := io.WriteString(writer, strings.Repeat(payload, mult)); err != nil {
 			t.Fatal(err)
 		}
+		if err := writer.Close(); err != nil {
+			t.Fatal(err)
+		}
 	}()
 
 	l := newChanListener()
 	defer close(l.connCh)
 	l.connCh <- reader
 	muxl := New(l)
-	// Register a bogus matcher to force reading from the conn.
-	muxl.Match(HTTP2())
+	// Register a bogus matcher to force buffering exactly the right amount.
+	// Before this fix, this would trigger a bug where `Read` would incorrectly
+	// report `io.EOF` when only the buffer had been consumed.
+	muxl.Match(func(r io.Reader) bool {
+		var b [len(payload)]byte
+		_, _ = r.Read(b[:])
+		return false
+	})
 	anyl := muxl.Match(Any())
 	go safeServe(errCh, muxl)
 	muxedConn, err := anyl.Accept()
 	if err != nil {
 		t.Fatal(err)
 	}
-	var b [mult * len(payload)]byte
-	n, err := muxedConn.Read(b[:])
-	if err != nil {
-		t.Fatal(err)
+	for i := 0; i < mult; i++ {
+		var b [len(payload)]byte
+		if n, err := muxedConn.Read(b[:]); err != nil {
+			t.Error(err)
+		} else if e := len(b); n != e {
+			t.Errorf("expected to read %d bytes, but read %d bytes", e, n)
+		}
 	}
-	if e := len(b); n != e {
-		t.Errorf("expected to read %d bytes, but read %d bytes", e, n)
+	var b [1]byte
+	if _, err := muxedConn.Read(b[:]); err != io.EOF {
+		t.Errorf("unexpected error %v, expected %v", err, io.EOF)
 	}
 }