Add browser gateway

Former-commit-id: 67b81c1f40

browsergateway/ssh_native.go

@@ -0,0 +1,107 @@
+package browsergateway
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+
+	"github.com/coder/websocket"
+	"github.com/creack/pty"
+)
+
+// NativeSSHConfig holds configuration for the native PTY/shell mode.
+type NativeSSHConfig struct {
+	// Shell is the executable to spawn (e.g. /bin/bash). Defaults to /bin/sh.
+	Shell string
+}
+
+// serveNativeSSHSession handles a WebSocket SSH session by spawning a local
+// PTY+shell instead of proxying to an external SSH server. The auth token has
+// already been validated at the WebSocket upgrade level, so this function only
+// reads (and discards) the initial "auth" frame for protocol compatibility with
+// the browser client before starting the shell.
+func serveNativeSSHSession(ctx context.Context, ws *websocket.Conn, cfg NativeSSHConfig) error {
+	// Read and discard the auth frame (token already validated at HTTP layer).
+	_, authBytes, err := ws.Read(ctx)
+	if err != nil {
+		return fmt.Errorf("read auth message: %w", err)
+	}
+	var authMsg sshClientMsg
+	if err := json.Unmarshal(authBytes, &authMsg); err != nil || authMsg.Type != "auth" {
+		return fmt.Errorf("expected auth message, got: %s", authBytes)
+	}
+
+	shell := cfg.Shell
+	if shell == "" {
+		shell = "/bin/sh"
+	}
+
+	log.Printf("SSH native: spawning %s", shell)
+
+	cmd := exec.CommandContext(ctx, shell)
+	cmd.Env = append(os.Environ(), "TERM=xterm-256color")
+
+	// Start the command with a PTY attached.
+	ptmx, err := pty.Start(cmd)
+	if err != nil {
+		sendSSHError(ctx, ws, fmt.Sprintf("Failed to spawn shell: %v", err))
+		return fmt.Errorf("pty start: %w", err)
+	}
+	defer func() {
+		_ = ptmx.Close()
+		_ = cmd.Wait()
+	}()
+
+	// Cancel context to unblock the WebSocket read loop when the shell exits.
+	sessCtx, cancelSess := context.WithCancel(ctx)
+	defer cancelSess()
+
+	// Pump PTY output → WebSocket.
+	go func() {
+		defer cancelSess()
+		buf := make([]byte, 4096)
+		for {
+			n, readErr := ptmx.Read(buf)
+			if n > 0 {
+				msg := sshServerMsg{Type: "data", Data: string(buf[:n])}
+				b, _ := json.Marshal(msg)
+				if writeErr := ws.Write(sessCtx, websocket.MessageText, b); writeErr != nil {
+					return
+				}
+			}
+			if readErr != nil {
+				return
+			}
+		}
+	}()
+
+	// Pump WebSocket input → PTY stdin / resize.
+	for {
+		_, msgBytes, readErr := ws.Read(sessCtx)
+		if readErr != nil {
+			break
+		}
+		var msg sshClientMsg
+		if err := json.Unmarshal(msgBytes, &msg); err != nil {
+			continue
+		}
+		switch msg.Type {
+		case "data":
+			if _, writeErr := ptmx.Write([]byte(msg.Data)); writeErr != nil {
+				return fmt.Errorf("write pty: %w", writeErr)
+			}
+		case "resize":
+			if msg.Cols > 0 && msg.Rows > 0 {
+				_ = pty.Setsize(ptmx, &pty.Winsize{
+					Cols: uint16(msg.Cols),
+					Rows: uint16(msg.Rows),
+				})
+			}
+		}
+	}
+
+	return nil
+}