feat: add single tailnet support to moons (#8587)

enterprise/tailnet/coordinator.go

@@ -56,7 +56,6 @@ func NewCoordinator(logger slog.Logger, ps pubsub.Pubsub) (agpl.Coordinator, err
 func (c *haCoordinator) ServeMultiAgent(id uuid.UUID) agpl.MultiAgentConn {
 	m := (&agpl.MultiAgent{
 		ID:                id,
-		Logger:            c.log,
 		AgentIsLegacyFunc: c.agentIsLegacy,
 		OnSubscribe:       c.clientSubscribeToAgent,
 		OnNodeUpdate:      c.clientNodeUpdate,

enterprise/tailnet/workspaceproxy.go

@@ -0,0 +1,95 @@
+package tailnet
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"net"
+	"time"
+
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/enterprise/wsproxy/wsproxysdk"
+	agpl "github.com/coder/coder/tailnet"
+)
+
+func ServeWorkspaceProxy(ctx context.Context, conn net.Conn, ma agpl.MultiAgentConn) error {
+	go func() {
+		err := forwardNodesToWorkspaceProxy(ctx, conn, ma)
+		if err != nil {
+			_ = conn.Close()
+		}
+	}()
+
+	decoder := json.NewDecoder(conn)
+	for {
+		var msg wsproxysdk.CoordinateMessage
+		err := decoder.Decode(&msg)
+		if err != nil {
+			return xerrors.Errorf("read json: %w", err)
+		}
+
+		switch msg.Type {
+		case wsproxysdk.CoordinateMessageTypeSubscribe:
+			err := ma.SubscribeAgent(msg.AgentID)
+			if err != nil {
+				return xerrors.Errorf("subscribe agent: %w", err)
+			}
+		case wsproxysdk.CoordinateMessageTypeUnsubscribe:
+			err := ma.UnsubscribeAgent(msg.AgentID)
+			if err != nil {
+				return xerrors.Errorf("unsubscribe agent: %w", err)
+			}
+		case wsproxysdk.CoordinateMessageTypeNodeUpdate:
+			err := ma.UpdateSelf(msg.Node)
+			if err != nil {
+				return xerrors.Errorf("update self: %w", err)
+			}
+
+		default:
+			return xerrors.Errorf("unknown message type %q", msg.Type)
+		}
+	}
+}
+
+func forwardNodesToWorkspaceProxy(ctx context.Context, conn net.Conn, ma agpl.MultiAgentConn) error {
+	var lastData []byte
+	for {
+		nodes, ok := ma.NextUpdate(ctx)
+		if !ok {
+			return xerrors.New("multiagent is closed")
+		}
+
+		data, err := json.Marshal(wsproxysdk.CoordinateNodes{Nodes: nodes})
+		if err != nil {
+			return err
+		}
+		if bytes.Equal(lastData, data) {
+			continue
+		}
+
+		// Set a deadline so that hung connections don't put back pressure on the system.
+		// Node updates are tiny, so even the dinkiest connection can handle them if it's not hung.
+		err = conn.SetWriteDeadline(time.Now().Add(agpl.WriteTimeout))
+		if err != nil {
+			// often, this is just because the connection is closed/broken, so only log at debug.
+			return err
+		}
+		_, err = conn.Write(data)
+		if err != nil {
+			// often, this is just because the connection is closed/broken, so only log at debug.
+			return err
+		}
+
+		// nhooyr.io/websocket has a bugged implementation of deadlines on a websocket net.Conn.  What they are
+		// *supposed* to do is set a deadline for any subsequent writes to complete, otherwise the call to Write()
+		// fails.  What nhooyr.io/websocket does is set a timer, after which it expires the websocket write context.
+		// If this timer fires, then the next write will fail *even if we set a new write deadline*.  So, after
+		// our successful write, it is important that we reset the deadline before it fires.
+		err = conn.SetWriteDeadline(time.Time{})
+		if err != nil {
+			return err
+		}
+		lastData = data
+	}
+}