Gzip compression support (negotiated)

consumer.go

@@ -1,18 +1,44 @@
 package eventsource
 
 import (
+	"compress/gzip"
+	"io"
 	"net"
 	"net/http"
+	"strings"
 	"time"
 )
 
 type consumer struct {
-	conn   net.Conn
+	conn   io.WriteCloser
 	es     *eventSource
 	in     chan []byte
 	staled bool
 }
 
+type gzipConn struct {
+	net.Conn
+	*gzip.Writer
+}
+
+func (gc gzipConn) Write(b []byte) (int, error) {
+	n, err := gc.Writer.Write(b)
+	if err != nil {
+		return n, err
+	}
+
+	return n, gc.Writer.Flush()
+}
+
+func (gc gzipConn) Close() error {
+	err := gc.Writer.Close()
+	if err != nil {
+		return err
+	}
+
+	return gc.Conn.Close()
+}
+
 func newConsumer(resp http.ResponseWriter, req *http.Request, es *eventSource) (*consumer, error) {
 	conn, _, err := resp.(http.Hijacker).Hijack()
 	if err != nil {
@@ -32,6 +58,22 @@ func newConsumer(resp http.ResponseWriter, req *http.Request, es *eventSource) (
 		return nil, err
 	}
 
+	_, err = conn.Write([]byte("Vary: Accept-Encoding\r\n"))
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	if es.gzip && (req == nil || strings.Contains(req.Header.Get("Accept-Encoding"), "gzip")) {
+		_, err = conn.Write([]byte("Content-Encoding: gzip\r\n"))
+		if err != nil {
+			conn.Close()
+			return nil, err
+		}
+
+		consumer.conn = gzipConn{conn, gzip.NewWriter(conn)}
+	}
+
 	if es.customHeadersFunc != nil {
 		for _, header := range es.customHeadersFunc(req) {
 			_, err = conn.Write(header)
@@ -64,7 +106,7 @@ func newConsumer(resp http.ResponseWriter, req *http.Request, es *eventSource) (
 					return
 				}
 				conn.SetWriteDeadline(time.Now().Add(consumer.es.timeout))
-				_, err := conn.Write(message)
+				_, err := consumer.conn.Write(message)
 				if err != nil {
 					netErr, ok := err.(net.Error)
 					if !ok || !netErr.Timeout() || consumer.es.closeOnTimeout {

eventsource.go

@@ -32,6 +32,7 @@ type eventSource struct {
 	retry          time.Duration
 	timeout        time.Duration
 	closeOnTimeout bool
+	gzip           bool
 
 	consumersLock sync.RWMutex
 	consumers     *list.List
@@ -55,13 +56,20 @@ type Settings struct {
 
 	// Sets the timeout for an idle connection. The default is 30 minutes.
 	IdleTimeout time.Duration
+
+	// Gzip sets whether to use gzip Content-Encoding for clients which
+	// support it.
+	//
+	// The default is true.
+	Gzip bool
 }
 
 func DefaultSettings() *Settings {
 	return &Settings{
 		Timeout:        2 * time.Second,
 		CloseOnTimeout: true,
 		IdleTimeout:    30 * time.Minute,
+		Gzip:           true,
 	}
 }
 
@@ -196,6 +204,7 @@ func New(settings *Settings, customHeadersFunc func(*http.Request) [][]byte) Eve
 	es.timeout = settings.Timeout
 	es.idleTimeout = settings.IdleTimeout
 	es.closeOnTimeout = settings.CloseOnTimeout
+	es.gzip = settings.Gzip
 	go controlProcess(es)
 	return es
 }