feat: add explicit SUBSCRIBE message to initiate subscriptions

runner/pkg/ibp/client.go

@@ -9,20 +9,23 @@ import (
 	"github.com/aspect-build/aspect-gazelle/runner/pkg/socket"
 )
 
-type IncrementalClient interface {
+type WatchClient interface {
 	Connect() error
 	Disconnect() error
-	AwaitCycle() iter.Seq2[*CycleSourcesMessage, error]
+	Subscribe(options WatchOptions) iter.Seq2[*CycleSourcesMessage, error]
 }
 
 type incClient struct {
 	socketPath string
 	socket     socket.Socket[interface{}, map[string]interface{}]
+
+	// The negotiated protocol version
+	version ProtocolVersion
 }
 
-var _ IncrementalClient = (*incClient)(nil)
+var _ WatchClient = (*incClient)(nil)
 
-func NewClient(host string) IncrementalClient {
+func NewClient(host string) WatchClient {
 	return &incClient{
 		socketPath: host,
 	}
@@ -56,22 +59,39 @@ func (c *incClient) negotiate() error {
 	if negReq["versions"] == nil {
 		return fmt.Errorf("Received NEGOTIATE without versions: %v", negReq)
 	}
-	if !slices.Contains(negReq["versions"].([]interface{}), (interface{})(float64(PROTOCOL_VERSION))) {
-		return fmt.Errorf("Received NEGOTIATE with unsupported versions %v, expected %d", negReq["versions"], PROTOCOL_VERSION)
+	rawVersions, isArray := negReq["versions"].([]interface{})
+	if !isArray {
+		return fmt.Errorf("Invalid versions, expected []int, received type: %T", negReq["versions"])
+	}
+
+	negotiatedVersion, err := negotiateVersion(rawVersions)
+	if err != nil {
+		return err
 	}
 
 	err = c.socket.Send(negotiateResponseMessage{
 		Message: Message{
 			Kind: "NEGOTIATE_RESPONSE",
 		},
-		Version: PROTOCOL_VERSION,
+		Version: negotiatedVersion,
 	})
 	if err != nil {
 		return fmt.Errorf("failed to negotiate protocol version: %w", err)
 	}
+
+	c.version = negotiatedVersion
 	return nil
 }
 
+func negotiateVersion(acceptedVersions []interface{}) (ProtocolVersion, error) {
+	for _, v := range slices.Backward(acceptedVersions) {
+		if slices.Contains(abazelSupportedProtocolVersions, ProtocolVersion(v.(float64))) {
+			return ProtocolVersion(v.(float64)), nil
+		}
+	}
+	return -1, fmt.Errorf("unsupported versions %v, expected one of %v", acceptedVersions, abazelSupportedProtocolVersions)
+}
+
 func (c *incClient) Disconnect() error {
 	if c.socket == nil {
 		return fmt.Errorf("client not connected")
@@ -85,8 +105,33 @@ func (c *incClient) Disconnect() error {
 	return err
 }
 
-func (c *incClient) AwaitCycle() iter.Seq2[*CycleSourcesMessage, error] {
+func (c *incClient) Subscribe(options WatchOptions) iter.Seq2[*CycleSourcesMessage, error] {
 	return func(yield func(*CycleSourcesMessage, error) bool) {
+		// Version 1+ require the initial SUBSCRIBE to start the subscription
+		if c.version >= VERSION_1 {
+			err := c.socket.Send(SubscribeMessage{
+				Message: Message{
+					Kind: "SUBSCRIBE",
+				},
+				WatchType: options.Type,
+			})
+			if err != nil {
+				yield(nil, err)
+				return
+			}
+
+			msg, err := c.socket.Recv()
+			if err != nil {
+				yield(nil, err)
+				return
+			}
+
+			if msg["kind"] != "SUBSCRIBE_RESPONSE" {
+				yield(nil, fmt.Errorf("expected SUBSCRIBE_RESPONSE, got %v", msg))
+				return
+			}
+		}
+
 		for {
 			msg, err := c.socket.Recv()
 			if err != nil {

runner/pkg/ibp/protocol.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"slices"
 	"sync/atomic"
 
 	"github.com/aspect-build/aspect-gazelle/runner/pkg/socket"
@@ -14,9 +15,15 @@ import (
 type ProtocolVersion int
 
 const (
-	PROTOCOL_VERSION ProtocolVersion = 0
+	LEGACY_VERSION_0 ProtocolVersion = 0
+	VERSION_1                        = 1
+	LATEST_VERSION                   = VERSION_1
 )
 
+func (v ProtocolVersion) HasExplicitSubscribe() bool {
+	return v >= 1
+}
+
 const PROTOCOL_SOCKET_ENV = "ABAZEL_WATCH_SOCKET_FILE"
 
 type IncrementalBazel interface {
@@ -57,6 +64,22 @@ type capMessage struct {
 	Caps map[string]bool `json:"caps"`
 }
 
+type WatchType string
+
+const (
+	WatchTypeRunfiles WatchType = "runfiles"
+	WatchTypeSources  WatchType = "sources"
+)
+
+type WatchOptions struct {
+	Type WatchType
+}
+
+type SubscribeMessage struct {
+	Message
+	WatchType WatchType `json:"watch_type"`
+}
+
 type exitMessage struct {
 	Message
 	Description string `json:"description"`
@@ -81,7 +104,10 @@ type CycleSourcesMessage struct {
 }
 
 // The versions supported by this host implementation of the protocol.
-var abazelSupportedProtocolVersions = []ProtocolVersion{PROTOCOL_VERSION}
+var abazelSupportedProtocolVersions = []ProtocolVersion{
+	LEGACY_VERSION_0,
+	VERSION_1,
+}
 
 type aspectBazelSocket = socket.Server[interface{}, map[string]any]
 
@@ -176,8 +202,8 @@ func (p *aspectBazelProtocol) acceptNegotiation() error {
 	if negResp["version"] == nil {
 		return fmt.Errorf("Received NEGOTIATE_RESPONSE without version: %v", negResp)
 	}
-	if ProtocolVersion(negResp["version"].(float64)) != PROTOCOL_VERSION {
-		return fmt.Errorf("Received NEGOTIATE_RESPONSE with unsupported version %v, expected %v", negResp["version"], PROTOCOL_VERSION)
+	if !slices.Contains(abazelSupportedProtocolVersions, ProtocolVersion(negResp["version"].(float64))) {
+		return fmt.Errorf("Received NEGOTIATE_RESPONSE with unsupported version %v, expected one of %v", negResp["version"], abazelSupportedProtocolVersions)
 	}
 
 	p.connectedCh <- ProtocolVersion(negResp["version"].(float64))

runner/runner.go

@@ -238,8 +238,8 @@ func (p *GazelleRunner) Watch(watchAddress string, cmd GazelleCommand, mode Gaze
 	))
 	defer t.End()
 
-	// Subscribe to further changes
-	for cs, err := range watch.AwaitCycle() {
+	// Subscribe to further changes to all sources
+	for cs, err := range watch.Subscribe(ibp.WatchOptions{Type: ibp.WatchTypeSources}) {
 		if err != nil {
 			fmt.Printf("ERROR: watch cycle error: %v\n", err)
 			return err