panel — open-source game server manager (public release)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

agent/internal/rcon/stdio.go

@@ -0,0 +1,110 @@
+package rcon
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"sync"
+	"time"
+)
+
+// StdioDialer "RCON"s a game by attaching to the container's stdin and writing
+// the admin console command, trusting the game to execute it. It's the correct
+// choice for games whose admin surface is stdin-only — Valheim, Terraria,
+// Barotrauma, Enshrouded, Sons Of The Forest — where no TCP RCON exists.
+//
+// v1 is write-only: Exec returns empty string. Command output arrives via the
+// panel's log pipeline (docker logs → agent → bus → SSE) because the game's
+// replies appear on the same stdout the log stream is tailing. A future
+// revision could correlate a response window with each write if we ever need
+// structured replies for state polling.
+//
+// Requires the container to have been created with OpenStdin=true; the module
+// resolver auto-enables that whenever manifest.Rcon.Adapter == "stdio".
+type StdioDialer struct{}
+
+// Name identifies this adapter in the module manifest.
+func (StdioDialer) Name() string { return "stdio" }
+
+// Dial attaches to the container's stdio stream. A background goroutine drains
+// the multiplexed stdout/stderr so the stream never blocks from our side; the
+// docker logs pipeline is the canonical consumer of that output.
+func (StdioDialer) Dial(ctx context.Context, opts DialOptions) (Client, error) {
+	if opts.Stdio == nil {
+		return nil, errors.New("stdio dial: Stdio backend required (agent must provide one)")
+	}
+	if opts.ContainerID == "" {
+		return nil, errors.New("stdio dial: ContainerID required")
+	}
+	session, err := opts.Stdio.AttachStdio(ctx, opts.ContainerID)
+	if err != nil {
+		return nil, fmt.Errorf("stdio attach %q: %w", opts.ContainerID, err)
+	}
+	c := &stdioClient{session: session}
+	go func() {
+		// Drain the attached stream so Docker doesn't buffer indefinitely.
+		// We deliberately discard: the log pipeline already surfaces this
+		// output to the panel via a separate docker logs call.
+		_, _ = io.Copy(io.Discard, session)
+	}()
+	return c, nil
+}
+
+type stdioClient struct {
+	session io.ReadWriteCloser
+	mu      sync.Mutex
+	closed  bool
+}
+
+// Exec writes cmd + "\n" to the container's stdin. Returns empty string; the
+// game's response (if any) lands in the log stream and is surfaced in the
+// Console tab.
+//
+// The write is bounded by ctx (and a hard 10s fallback). A raw Write to a
+// hijacked stdin pipe can block FOREVER if the container's stdin read side
+// stalls (game paused, buffer full, or the process not draining stdin). Because
+// the agent dispatches RCON inline on its single recv loop, an unbounded write
+// here freezes the WHOLE agent — no stop/start/anything — until restart. That's
+// the Valheim+stdio "stop never lands" hang. We run the write in a goroutine and
+// abandon it on timeout so the dispatcher stays responsive.
+func (c *stdioClient) Exec(ctx context.Context, cmd string) (string, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.closed {
+		return "", errors.New("stdio: session closed")
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	wctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	done := make(chan error, 1)
+	go func() {
+		_, err := c.session.Write([]byte(cmd + "\n"))
+		done <- err
+	}()
+	select {
+	case err := <-done:
+		if err != nil {
+			return "", fmt.Errorf("stdio write: %w", err)
+		}
+		return "", nil
+	case <-wctx.Done():
+		// The write is wedged — leave the goroutine parked (it'll unblock if the
+		// pipe ever drains, or die when the session closes) but DON'T let it hold
+		// up the caller / the agent's recv loop.
+		return "", fmt.Errorf("stdio write timed out after 10s (container stdin not draining): %w", wctx.Err())
+	}
+}
+
+// Close shuts down the hijacked attach connection.
+func (c *stdioClient) Close() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.closed {
+		return nil
+	}
+	c.closed = true
+	return c.session.Close()
+}