From 98dc1334978683bb0bec263fe809a70e3ec00e91 Mon Sep 17 00:00:00 2001
From: Fedor Lapshin <fe.lap.prog@gmail.com>
Date: Sat, 5 Jul 2025 17:13:50 +0300
Subject: [PATCH] feat(Session): resume gateway url (#1307)

---
 event.go   |  3 +++
 events.go  | 15 ++++++++-------
 structs.go |  3 +++
 wsapi.go   | 45 +++++++++++++++++++++++++++++++--------------
 4 files changed, 45 insertions(+), 21 deletions(-)

diff --git a/event.go b/event.go
index 84dbdc7..6e6c500 100644
--- a/event.go
+++ b/event.go
@@ -244,4 +244,7 @@ func (s *Session) onReady(r *Ready) {
 
 	// Store the SessionID within the Session struct.
 	s.sessionID = r.SessionID
+
+	// Store the ResumeGatewayURL within the Session struct.
+	s.resumeGatewayURL = r.ResumeGatewayURL
 }
diff --git a/events.go b/events.go
index ccc7346..0ff2cb4 100644
--- a/events.go
+++ b/events.go
@@ -36,13 +36,14 @@ type Event struct {
 
 // A Ready stores all data for the websocket READY event.
 type Ready struct {
-	Version         int          `json:"v"`
-	SessionID       string       `json:"session_id"`
-	User            *User        `json:"user"`
-	Shard           *[2]int      `json:"shard"`
-	Application     *Application `json:"application"`
-	Guilds          []*Guild     `json:"guilds"`
-	PrivateChannels []*Channel   `json:"private_channels"`
+	Version          int          `json:"v"`
+	SessionID        string       `json:"session_id"`
+	User             *User        `json:"user"`
+	Shard            *[2]int      `json:"shard"`
+	ResumeGatewayURL string       `json:"resume_gateway_url"`
+	Application      *Application `json:"application"`
+	Guilds           []*Guild     `json:"guilds"`
+	PrivateChannels  []*Channel   `json:"private_channels"`
 }
 
 // ChannelCreate is the data for a ChannelCreate event.
diff --git a/structs.go b/structs.go
index 24c10c2..920581a 100644
--- a/structs.go
+++ b/structs.go
@@ -126,6 +126,9 @@ type Session struct {
 	// sequence tracks the current gateway api websocket sequence number
 	sequence *int64
 
+	// stores sessions current Discord Resume Gateway
+	resumeGatewayURL string
+
 	// stores sessions current Discord Gateway
 	gateway string
 
diff --git a/wsapi.go b/wsapi.go
index d101c54..5b94cb6 100644
--- a/wsapi.go
+++ b/wsapi.go
@@ -62,22 +62,32 @@ func (s *Session) Open() error {
 		return ErrWSAlreadyOpen
 	}
 
+	sequence := atomic.LoadInt64(s.sequence)
+
+	var gateway string
 	// Get the gateway to use for the Websocket connection
-	if s.gateway == "" {
-		s.gateway, err = s.Gateway()
-		if err != nil {
-			return err
+	if sequence != 0 && s.sessionID != "" && s.resumeGatewayURL != "" {
+		s.log(LogDebug, "using resume gateway %s", s.resumeGatewayURL)
+		gateway = s.resumeGatewayURL
+	} else {
+		if s.gateway == "" {
+			s.gateway, err = s.Gateway()
+			if err != nil {
+				return err
+			}
 		}
 
-		// Add the version and encoding to the URL
-		s.gateway = s.gateway + "?v=" + APIVersion + "&encoding=json"
+		gateway = s.gateway
 	}
 
+	// Add the version and encoding to the URL
+	gateway += "?v=" + APIVersion + "&encoding=json"
+
 	// Connect to the Gateway
-	s.log(LogInformational, "connecting to gateway %s", s.gateway)
+	s.log(LogInformational, "connecting to gateway %s", gateway)
 	header := http.Header{}
 	header.Add("accept-encoding", "zlib")
-	s.wsConn, _, err = s.Dialer.Dial(s.gateway, header)
+	s.wsConn, _, err = s.Dialer.Dial(gateway, header)
 	if err != nil {
 		s.log(LogError, "error connecting to gateway %s, %s", s.gateway, err)
 		s.gateway = "" // clear cached gateway
@@ -123,7 +133,6 @@ func (s *Session) Open() error {
 
 	// Now we send either an Op 2 Identity if this is a brand new
 	// connection or Op 6 Resume if we are resuming an existing connection.
-	sequence := atomic.LoadInt64(s.sequence)
 	if s.sessionID == "" && sequence == 0 {
 
 		// Send Op 2 Identity Packet
@@ -616,15 +625,23 @@ func (s *Session) onEvent(messageType int, message []byte) (*Event, error) {
 	// Invalid Session
 	// Must respond with a Identify packet.
 	if e.Operation == 9 {
+		s.log(LogInformational, "Closing and reconnecting in response to Op9")
+		s.CloseWithCode(websocket.CloseServiceRestart)
 
-		s.log(LogInformational, "sending identify packet to gateway in response to Op9")
-
-		err = s.identify()
-		if err != nil {
-			s.log(LogWarning, "error sending gateway identify packet, %s, %s", s.gateway, err)
+		var resumable bool
+		if err := json.Unmarshal(e.RawData, &resumable); err != nil {
+			s.log(LogError, "error unmarshalling invalid session event, %s", err)
 			return e, err
 		}
 
+		if !resumable {
+			s.log(LogInformational, "Gateway session is not resumable, discarding its information")
+			s.resumeGatewayURL = ""
+			s.sessionID = ""
+			atomic.StoreInt64(s.sequence, 0)
+		}
+
+		s.reconnect()
 		return e, nil
 	}