From 4fe5c94d9caf9d218d2b893b99d5799d37ce99c4 Mon Sep 17 00:00:00 2001
From: Elara Musayelyan <elara@elara.ws>
Date: Mon, 9 Jan 2023 12:54:06 -0800
Subject: [PATCH] Add WebSocket reconnects

---
 go.mod       |  1 +
 go.sum       |  2 ++
 websocket.go | 81 ++++++++++++++++++++++++++++++++++++++++++++++++----
 3 files changed, 78 insertions(+), 6 deletions(-)

diff --git a/go.mod b/go.mod
index 37807a5..7ba8bf1 100644
--- a/go.mod
+++ b/go.mod
@@ -5,6 +5,7 @@ go 1.19
 retract v0.0.0-20230105203020-27ef17a00e22
 
 require (
+	github.com/cenkalti/backoff/v4 v4.2.0
 	github.com/dave/jennifer v1.6.0
 	github.com/google/go-querystring v1.1.0
 	github.com/gorilla/websocket v1.4.2
diff --git a/go.sum b/go.sum
index bfce658..98632fd 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,5 @@
+github.com/cenkalti/backoff/v4 v4.2.0 h1:HN5dHm3WBOgndBH6E8V0q2jIYIR3s9yglV8k/+MN3u4=
+github.com/cenkalti/backoff/v4 v4.2.0/go.mod h1:Y3VNntkOUPxTVeUxJ/G5vcM//AlwfmyYozVcomhLiZE=
 github.com/dave/jennifer v1.6.0 h1:MQ/6emI2xM7wt0tJzJzyUik2Q3Tcn2eE0vtYgh4GPVI=
 github.com/dave/jennifer v1.6.0/go.mod h1:AxTG893FiZKqxy3FP1kL80VMshSMuz2G+EgvszgGRnk=
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
diff --git a/websocket.go b/websocket.go
index fa2bffa..24347ab 100644
--- a/websocket.go
+++ b/websocket.go
@@ -3,10 +3,15 @@ package lemmy
 import (
 	"context"
 	"encoding/json"
+	"fmt"
+	"net"
 	"net/http"
 	"net/url"
 	"reflect"
+	"strings"
+	"time"
 
+	"github.com/cenkalti/backoff/v4"
 	"github.com/gorilla/websocket"
 	"go.arsenm.dev/go-lemmy/types"
 )
@@ -17,11 +22,12 @@ type authData struct {
 
 // WSClient is a client for Lemmy's WebSocket API
 type WSClient struct {
-	conn    *websocket.Conn
-	baseURL *url.URL
-	respCh  chan types.LemmyWebSocketMsg
-	errCh   chan error
-	Token   string
+	conn       *websocket.Conn
+	baseURL    *url.URL
+	respCh     chan types.LemmyWebSocketMsg
+	errCh      chan error
+	recHandler func(c *WSClient)
+	Token      string
 }
 
 // NewWebSocket creates and returns a new WSClient, and
@@ -33,7 +39,7 @@ func NewWebSocket(baseURL string) (*WSClient, error) {
 	}
 	u = u.JoinPath("/api/v3")
 
-	conn, _, err := websocket.DefaultDialer.Dial(u.JoinPath("ws").String(), nil)
+	conn, _, err := keepaliveDialer().Dial(u.JoinPath("ws").String(), nil)
 	if err != nil {
 		return nil, err
 	}
@@ -51,6 +57,31 @@ func NewWebSocket(baseURL string) (*WSClient, error) {
 			err = conn.ReadJSON(&msg)
 			if err != nil {
 				out.errCh <- err
+
+				// gorilla/websocket eats the error type, so I have to check
+				// the string itself
+				if strings.HasSuffix(err.Error(), "connection timed out") {
+					err = backoff.RetryNotify(
+						func() error {
+							conn, _, err = keepaliveDialer().Dial(u.JoinPath("ws").String(), nil)
+							if err != nil {
+								out.errCh <- err
+								return err
+							}
+							out.conn = conn
+							out.recHandler(out)
+							return nil
+						},
+						backoff.NewExponentialBackOff(),
+						func(err error, d time.Duration) {
+							out.errCh <- fmt.Errorf("reconnect backoff (%s): %w", d, err)
+						},
+					)
+					if err != nil {
+						out.errCh <- err
+					}
+				}
+
 				continue
 			}
 			out.respCh <- msg
@@ -116,6 +147,10 @@ func (c *WSClient) Errors() <-chan error {
 	return c.errCh
 }
 
+func (c *WSClient) OnReconnect(rh func(c *WSClient)) {
+	c.recHandler = rh
+}
+
 // setAuth uses reflection to automatically
 // set struct fields called Auth of type
 // string or types.Optional[string] to the
@@ -147,3 +182,37 @@ func (c *WSClient) setAuth(data any) any {
 func DecodeResponse(data json.RawMessage, out any) error {
 	return json.Unmarshal(data, out)
 }
+
+func keepaliveDialer() *websocket.Dialer {
+	d := &websocket.Dialer{
+		NetDial: func(network, addr string) (net.Conn, error) {
+			tcpAddr, err := net.ResolveTCPAddr(network, addr)
+			if err != nil {
+				return nil, err
+			}
+
+			conn, err := net.DialTCP(network, nil, tcpAddr)
+			if err != nil {
+				return nil, err
+			}
+
+			err = conn.SetKeepAlive(true)
+			if err != nil {
+				return nil, err
+			}
+
+			err = conn.SetKeepAlivePeriod(time.Second)
+			if err != nil {
+				return nil, err
+			}
+
+			return conn, nil
+		},
+	}
+
+	d.NetDialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
+		return d.NetDial(network, addr)
+	}
+
+	return d
+}