TUN-5724: Fix SSE streaming by guaranteeing we write everything we read

origin/proxy.go

@@ -271,11 +271,20 @@ func (wr *bidirectionalStream) Write(p []byte) (n int, err error) {
 func (p *Proxy) writeEventStream(w connection.ResponseWriter, respBody io.ReadCloser) {
 	reader := bufio.NewReader(respBody)
 	for {
-		line, err := reader.ReadBytes('\n')
-		if err != nil {
-			break
+		line, readErr := reader.ReadBytes('\n')
+
+		// We first try to write whatever we read even if an error occurred
+		// The reason for doing it is to guarantee we really push everything to the eyeball side
+		// before returning
+		if len(line) > 0 {
+			if _, writeErr := w.Write(line); writeErr != nil {
+				return
+			}
+		}
+
+		if readErr != nil {
+			return
 		}
-		_, _ = w.Write(line)
 	}
 }
 

origin/proxy_test.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -138,6 +139,7 @@ func TestProxySingleOrigin(t *testing.T) {
 	t.Run("testProxyHTTP", testProxyHTTP(proxy))
 	t.Run("testProxyWebsocket", testProxyWebsocket(proxy))
 	t.Run("testProxySSE", testProxySSE(proxy))
+	t.Run("testProxySSEAllData", testProxySSEAllData(proxy))
 	cancel()
 	wg.Wait()
 }
@@ -256,6 +258,21 @@ func testProxySSE(proxy connection.OriginProxy) func(t *testing.T) {
 	}
 }
 
+// Regression test to guarantee that we always write the contents downstream even if EOF is reached without
+// hitting the delimiter
+func testProxySSEAllData(proxy *Proxy) func(t *testing.T) {
+	return func(t *testing.T) {
+		eyeballReader := io.NopCloser(strings.NewReader("data\r\r"))
+		responseWriter := newMockSSERespWriter()
+
+		// responseWriter uses an unbuffered channel, so we call in a different go-routine
+		go proxy.writeEventStream(responseWriter, eyeballReader)
+
+		result := string(<-responseWriter.writeNotification)
+		require.Equal(t, "data\r\r", result)
+	}
+}
+
 func TestProxyMultipleOrigins(t *testing.T) {
 	api := httptest.NewServer(mockAPI{})
 	defer api.Close()