[bugfix] send back Sec-Websocket-Protocol header for streaming WebSocket (#3169)

* [bugfix] send back Sec-Websocket-Protocol header for streaming WebSocket

Chrome expects the selected Sec-Websocket-Protocol to be sent back
on the WebSocket upgrade request (RFC6455 1.9).

* fiddle a bit to avoid getting headers multiple times

* add some explanatory notes

---------

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

internal/api/client/streaming/stream.go

@@ -19,6 +19,7 @@
 
 import (
 	"context"
+	"net/http"
 	"slices"
 	"time"
 
@@ -151,15 +152,24 @@
 //			description: bad request
 func (m *Module) StreamGETHandler(c *gin.Context) {
 	var (
+		token         string
+		tokenInHeader bool
 		account       *gtsmodel.Account
 		errWithCode   gtserror.WithCode
 	)
 
-	// Try query param access token.
-	token := c.Query(AccessTokenQueryKey)
-	if token == "" {
-		// Try fallback HTTP header provided token.
-		token = c.GetHeader(AccessTokenHeader)
+	if t := c.Query(AccessTokenQueryKey); t != "" {
+		// Token was provided as
+		// query param, no problem.
+		token = t
+	} else if t := c.GetHeader(AccessTokenHeader); t != "" {
+		// Token was provided in "Sec-Websocket-Protocol" header.
+		//
+		// This is hacky and not technically correct but some
+		// clients do it since Mastodon allows it, so we must
+		// also allow it to avoid breaking expectations.
+		token = t
+		tokenInHeader = true
 	}
 
 	if token != "" {
@@ -230,7 +240,16 @@ func (m *Module) StreamGETHandler(c *gin.Context) {
 	//
 	// If the upgrade fails, then Upgrade replies to the client
 	// with an HTTP error response.
-	wsConn, err := m.wsUpgrade.Upgrade(c.Writer, c.Request, nil)
+	var responseHeader http.Header
+	if tokenInHeader {
+		// Return the token in the response,
+		// else Chrome fails to connect.
+		//
+		// https://developer.mozilla.org/en-US/docs/Web/HTTP/Protocol_upgrade_mechanism#sec-websocket-protocol
+		responseHeader = http.Header{AccessTokenHeader: {token}}
+	}
+
+	wsConn, err := m.wsUpgrade.Upgrade(c.Writer, c.Request, responseHeader)
 	if err != nil {
 		l.Errorf("error upgrading websocket connection: %v", err)
 		stream.Close()

internal/api/client/streaming/streaming_test.go

@@ -22,7 +22,7 @@
 	"encoding/base64"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -236,7 +236,7 @@ func (suite *StreamingTestSuite) TestSecurityHeader() {
 
 	result := recorder.Result()
 	defer result.Body.Close()
-	b, err := ioutil.ReadAll(result.Body)
+	b, err := io.ReadAll(result.Body)
 	suite.NoError(err)
 
 	// check response