feat: the browser terminal on a WebSocket too, long polls when it does not connect or drops

internal/server/handlers_panel_term.go

@@ -1,9 +1,14 @@
 package server
 
 import (
+	"context"
 	"encoding/json"
 	"log"
 	"net/http"
+	"time"
+
+	"github.com/coder/websocket"
+	"github.com/coder/websocket/wsjson"
 
 	"github.com/x-grk/longpolling-remote-access/internal/proto"
 )
@@ -66,8 +71,14 @@ func (s *Server) handlePanelIn(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "bad request", http.StatusBadRequest)
 		return
 	}
+	takePanelIn(sess, m)
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// takePanelIn passes the browser's keystrokes or resize on to the agent; a
+// repeat of one already taken is dropped.
+func takePanelIn(sess *Session, m panelInMsg) {
 	if m.Seq > 0 && !sess.TakeSeq(m.Seq) {
-		w.WriteHeader(http.StatusNoContent) // a repeat of one already taken
 		return
 	}
 	switch m.T {
@@ -76,7 +87,70 @@ func (s *Server) handlePanelIn(w http.ResponseWriter, r *http.Request) {
 	case "r":
 		sess.PushIn(proto.InFrame{Type: proto.FrameResize, Cols: m.Cols, Rows: m.Rows})
 	}
-	w.WriteHeader(http.StatusNoContent)
+}
+
+// GET /api/panel/term/{sid}/ws - the browser's terminal on a WebSocket: what
+// the "in" requests send comes as messages, and output goes out as soon as
+// it is there, in the "out" answers' shape. The page falls back to those
+// requests when this does not connect.
+func (s *Server) handlePanelTermWS(w http.ResponseWriter, r *http.Request) {
+	sess := s.hub.Session(r.PathValue("sid"))
+	if sess == nil {
+		http.Error(w, "closed", http.StatusGone)
+		return
+	}
+	conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{CompressionMode: websocket.CompressionDisabled})
+	if err != nil {
+		return
+	}
+	conn.SetReadLimit(1 << 20)
+	defer conn.CloseNow()
+	ctx, cancel := context.WithCancel(r.Context())
+	defer cancel()
+	go func() {
+		defer cancel()
+		for ctx.Err() == nil {
+			msgs, alive := sess.PollOutUntil(ctx.Done(), pollHold)
+			if ctx.Err() != nil {
+				return
+			}
+			out := map[string]any{"frames": msgs}
+			if !alive {
+				out = map[string]any{"closed": true}
+			}
+			wctx, wcancel := context.WithTimeout(ctx, 30*time.Second)
+			err := wsjson.Write(wctx, conn, out)
+			wcancel()
+			if err != nil || !alive {
+				return
+			}
+		}
+	}()
+	go func() {
+		t := time.NewTicker(wsPing)
+		defer t.Stop()
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-t.C:
+				pctx, pcancel := context.WithTimeout(ctx, 15*time.Second)
+				err := conn.Ping(pctx)
+				pcancel()
+				if err != nil {
+					cancel()
+					return
+				}
+			}
+		}
+	}()
+	for {
+		var m panelInMsg
+		if err := wsjson.Read(ctx, conn, &m); err != nil {
+			return
+		}
+		takePanelIn(sess, m)
+	}
 }
 
 // POST /api/panel/term/{sid}/close - tear the session down.