Add JoinMessages

Fixes #441.

Issue #441 specified a message separator. This PR has a message terminator. A message terminator can be read immediately following a message. A message separator cannot be read until the start of the next message. The message terminator is more useful when the reader is scanning to the terminator before performing some action.

join.go

@@ -0,0 +1,42 @@
+// Copyright 2019 The Gorilla WebSocket Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package websocket
+
+import (
+	"io"
+	"strings"
+)
+
+// JoinMessages concatenates received messages to create a single io.Reader.
+// The string term is appended to each message. The returned reader does not
+// support concurrent calls to the Read method.
+func JoinMessages(c *Conn, term string) io.Reader {
+	return &joinReader{c: c, term: term}
+}
+
+type joinReader struct {
+	c    *Conn
+	term string
+	r    io.Reader
+}
+
+func (r *joinReader) Read(p []byte) (int, error) {
+	if r.r == nil {
+		var err error
+		_, r.r, err = r.c.NextReader()
+		if err != nil {
+			return 0, err
+		}
+		if r.term != "" {
+			r.r = io.MultiReader(r.r, strings.NewReader(r.term))
+		}
+	}
+	n, err := r.r.Read(p)
+	if err == io.EOF {
+		err = nil
+		r.r = nil
+	}
+	return n, err
+}

join_test.go

@@ -0,0 +1,36 @@
+// Copyright 2019 The Gorilla WebSocket Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package websocket
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestJoinMessages(t *testing.T) {
+	messages := []string{"a", "bc", "def", "ghij", "klmno", "0", "12", "345", "6789"}
+	for _, readChunk := range []int{1, 2, 3, 4, 5, 6, 7} {
+		for _, term := range []string{"", ","} {
+			var connBuf bytes.Buffer
+			wc := newTestConn(nil, &connBuf, true)
+			rc := newTestConn(&connBuf, nil, false)
+			for _, m := range messages {
+				wc.WriteMessage(BinaryMessage, []byte(m))
+			}
+
+			var result bytes.Buffer
+			_, err := io.CopyBuffer(&result, JoinMessages(rc, term), make([]byte, readChunk))
+			if IsUnexpectedCloseError(err, CloseAbnormalClosure) {
+				t.Errorf("readChunk=%d, term=%q: unexpected error %v", readChunk, term, err)
+			}
+			want := strings.Join(messages, term) + term
+			if result.String() != want {
+				t.Errorf("readChunk=%d, term=%q, got %q, want %q", readChunk, term, result.String(), want)
+			}
+		}
+	}
+}