feat(go): Add cancelAction and early trace ID to headers in go reflection server

go/core/action.go

@@ -260,7 +260,7 @@ func (a *ActionDef[In, Out, Stream]) RunJSON(ctx context.Context, input json.Raw
 	return r.Result, nil
 }
 
-// RunJSON runs the action with a JSON input, and returns a JSON result along with telemetry info.
+// RunJSONWithTelemetry runs the action with a JSON input, and returns a JSON result along with telemetry info.
 func (a *ActionDef[In, Out, Stream]) RunJSONWithTelemetry(ctx context.Context, input json.RawMessage, cb StreamCallback[json.RawMessage]) (*api.ActionRunResult[json.RawMessage], error) {
 	i, err := base.UnmarshalAndNormalize[In](input, a.desc.InputSchema)
 	if err != nil {

go/core/flow.go

@@ -112,7 +112,7 @@ func (f *Flow[In, Out, Stream]) RunJSON(ctx context.Context, input json.RawMessa
 	return (*ActionDef[In, Out, Stream])(f).RunJSON(ctx, input, cb)
 }
 
-// RunJSON runs the flow with JSON input and streaming callback and returns the output as JSON.
+// RunJSONWithTelemetry runs the flow with JSON input and streaming callback and returns the output as JSON along with telemetry info.
 func (f *Flow[In, Out, Stream]) RunJSONWithTelemetry(ctx context.Context, input json.RawMessage, cb StreamCallback[json.RawMessage]) (*api.ActionRunResult[json.RawMessage], error) {
 	return (*ActionDef[In, Out, Stream])(f).RunJSONWithTelemetry(ctx, input, cb)
 }

go/core/schemas.config

@@ -26,6 +26,10 @@ SpanStatus omit
 TimeEvent omit
 TimeEventAnnotation omit
 TraceData omit
+SpanStartEvent omit
+SpanEndEvent omit
+SpanEventBase omit
+TraceEvent omit
 
 GenerationCommonConfig.maxOutputTokens type int
 GenerationCommonConfig.topK type int

go/core/tracing/tracing.go

@@ -173,6 +173,8 @@ type SpanMetadata struct {
 
 // RunInNewSpan runs f on input in a new span with the provided metadata.
 // The metadata contains all span configuration including name, type, labels, etc.
+// If a telemetry callback was set on the context via WithTelemetryCallback,
+// it will be called with the trace ID and span ID as soon as the span is created.
 func RunInNewSpan[I, O any](
 	ctx context.Context,
 	metadata *SpanMetadata,
@@ -239,6 +241,12 @@ func RunInNewSpan[I, O any](
 		TraceID: span.SpanContext().TraceID().String(),
 		SpanID:  span.SpanContext().SpanID().String(),
 	}
+
+	// Fire telemetry callback immediately if one was set on the context
+	if cb := telemetryCallback(ctx); cb != nil {
+		cb(sm.TraceInfo.TraceID, sm.TraceInfo.SpanID)
+	}
+
 	defer span.End()
 	defer func() { span.SetAttributes(sm.attributes()...) }()
 	ctx = spanMetaKey.NewContext(ctx, sm)
@@ -371,6 +379,20 @@ func (sm *spanMetadata) attributes() []attribute.KeyValue {
 // spanMetaKey is for storing spanMetadatas in a context.
 var spanMetaKey = base.NewContextKey[*spanMetadata]()
 
+// telemetryCbKey is the context key for telemetry callbacks.
+var telemetryCbKey = base.NewContextKey[func(traceID, spanID string)]()
+
+// WithTelemetryCallback returns a context with the telemetry callback attached.
+// Used by the reflection server to pass callbacks to actions.
+func WithTelemetryCallback(ctx context.Context, cb func(traceID, spanID string)) context.Context {
+	return telemetryCbKey.NewContext(ctx, cb)
+}
+
+// telemetryCallback retrieves the telemetry callback from context, or nil if not set.
+func telemetryCallback(ctx context.Context) func(traceID, spanID string) {
+	return telemetryCbKey.FromContext(ctx)
+}
+
 // SpanPath returns the path as recorded in the current span metadata.
 func SpanPath(ctx context.Context) string {
 	return spanMetaKey.FromContext(ctx).Path

go/genkit/reflection.go

@@ -19,6 +19,7 @@ package genkit
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log/slog"
 	"net"
@@ -28,6 +29,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/firebase/genkit/go/core"
@@ -52,7 +54,46 @@ type runtimeFileData struct {
 // reflectionServer encapsulates everything needed to serve the Reflection API.
 type reflectionServer struct {
 	*http.Server
-	RuntimeFilePath string // Path to the runtime file that was written at startup.
+	RuntimeFilePath string            // Path to the runtime file that was written at startup.
+	activeActions   *activeActionsMap // Tracks active actions for cancellation support.
+}
+
+// activeAction represents an in-flight action that can be cancelled.
+type activeAction struct {
+	cancel    context.CancelFunc
+	startTime time.Time
+	traceID   string
+}
+
+// activeActionsMap safely manages active actions.
+type activeActionsMap struct {
+	mu      sync.RWMutex
+	actions map[string]*activeAction
+}
+
+func newActiveActionsMap() *activeActionsMap {
+	return &activeActionsMap{
+		actions: make(map[string]*activeAction),
+	}
+}
+
+func (m *activeActionsMap) Set(traceID string, action *activeAction) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.actions[traceID] = action
+}
+
+func (m *activeActionsMap) Get(traceID string) (*activeAction, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	action, ok := m.actions[traceID]
+	return action, ok
+}
+
+func (m *activeActionsMap) Delete(traceID string) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	delete(m.actions, traceID)
 }
 
 func (s *reflectionServer) runtimeID() string {
@@ -102,6 +143,7 @@ func startReflectionServer(ctx context.Context, g *Genkit, errCh chan<- error, s
 		Server: &http.Server{
 			Addr: addr,
 		},
+		activeActions: newActiveActionsMap(),
 	}
 	s.Handler = serveMux(g, s)
 
@@ -258,8 +300,9 @@ func serveMux(g *Genkit, s *reflectionServer) *http.ServeMux {
 		w.WriteHeader(http.StatusOK)
 	})
 	mux.HandleFunc("GET /api/actions", wrapReflectionHandler(handleListActions(g)))
-	mux.HandleFunc("POST /api/runAction", wrapReflectionHandler(handleRunAction(g)))
+	mux.HandleFunc("POST /api/runAction", wrapReflectionHandler(handleRunAction(g, s.activeActions)))
 	mux.HandleFunc("POST /api/notify", wrapReflectionHandler(handleNotify()))
+	mux.HandleFunc("POST /api/cancelAction", wrapReflectionHandler(handleCancelAction(s.activeActions)))
 	return mux
 }
 
@@ -290,7 +333,7 @@ func wrapReflectionHandler(h func(w http.ResponseWriter, r *http.Request) error)
 
 // handleRunAction looks up an action by name in the registry, runs it with the
 // provided JSON input, and writes back the JSON-marshaled request.
-func handleRunAction(g *Genkit) func(w http.ResponseWriter, r *http.Request) error {
+func handleRunAction(g *Genkit, activeActions *activeActionsMap) func(w http.ResponseWriter, r *http.Request) error {
 	return func(w http.ResponseWriter, r *http.Request) error {
 		ctx := r.Context()
 
@@ -312,11 +355,54 @@ func handleRunAction(g *Genkit) func(w http.ResponseWriter, r *http.Request) err
 
 		logger.FromContext(ctx).Debug("running action", "key", body.Key, "stream", stream)
 
+		// Create cancellable context for this action
+		actionCtx, cancel := context.WithCancel(ctx)
+		defer cancel()
+
+		// Track whether headers have been sent
+		headersSent := false
+		var callbackTraceID string // Trace ID captured from telemetry callback for early header sending
+		var mu sync.Mutex
+
+		// Set up telemetry callback to capture and send trace ID early
+		// This is used for BOTH streaming and non-streaming to match JS behavior
+		telemetryCb := func(tid string, sid string) {
+			mu.Lock()
+			defer mu.Unlock()
+
+			if !headersSent {
+				callbackTraceID = tid
+
+				// Track active action for cancellation
+				activeActions.Set(callbackTraceID, &activeAction{
+					cancel:    cancel,
+					startTime: time.Now(),
+					traceID:   callbackTraceID,
+				})
+
+				// Send headers immediately with trace ID
+				w.Header().Set("X-Genkit-Trace-Id", callbackTraceID)
+				w.Header().Set("X-Genkit-Span-Id", sid)
+				w.Header().Set("X-Genkit-Version", "go/"+internal.Version)
+
+				if stream {
+					w.Header().Set("Content-Type", "text/plain")
+					w.Header().Set("Transfer-Encoding", "chunked")
+				} else {
+					w.Header().Set("Content-Type", "application/json")
+				}
+
+				w.WriteHeader(http.StatusOK)
+				if f, ok := w.(http.Flusher); ok {
+					f.Flush()
+				}
+				headersSent = true
+			}
+		}
+
+		// Set up streaming callback if needed
 		var cb streamingCallback[json.RawMessage]
 		if stream {
-			w.Header().Set("Content-Type", "text/plain")
-			w.Header().Set("Transfer-Encoding", "chunked")
-			// Stream results are newline-separated JSON.
 			cb = func(ctx context.Context, msg json.RawMessage) error {
 				_, err := fmt.Fprintf(w, "%s\n", msg)
 				if err != nil {
@@ -334,35 +420,119 @@ func handleRunAction(g *Genkit) func(w http.ResponseWriter, r *http.Request) err
 			json.Unmarshal(body.Context, &contextMap)
 		}
 
-		resp, err := runAction(ctx, g, body.Key, body.Input, body.TelemetryLabels, cb, contextMap)
+		// Attach telemetry callback to context so action can invoke it when span is created
+		actionCtx = tracing.WithTelemetryCallback(actionCtx, telemetryCb)
+		resp, err := runAction(actionCtx, g, body.Key, body.Input, body.TelemetryLabels, cb, contextMap)
+
+		// Clean up active action using the trace ID from response
+		if resp != nil && resp.Telemetry.TraceID != "" {
+			activeActions.Delete(resp.Telemetry.TraceID)
+		}
+
 		if err != nil {
-			if stream {
-				refErr := core.ToReflectionError(err)
-				refErr.Details.TraceID = &resp.Telemetry.TraceID
-				reflectErr, err := json.Marshal(refErr)
-				if err != nil {
-					return err
+			// Check if context was cancelled
+			if errors.Is(err, context.Canceled) {
+				// Use gRPC CANCELLED code (1) in JSON body to match TypeScript behavior
+				var traceIDPtr *string
+				if resp != nil && resp.Telemetry.TraceID != "" {
+					traceIDPtr = &resp.Telemetry.TraceID
+				}
+				errResp := errorResponse{
+					Error: core.ReflectionError{
+						Code:    core.CodeCancelled, // gRPC CANCELLED = 1
+						Message: "Action was cancelled",
+						Details: &core.ReflectionErrorDetails{
+							TraceID: traceIDPtr,
+						},
+					},
 				}
 
-				_, err = fmt.Fprintf(w, "{\"error\": %s }", reflectErr)
-				if err != nil {
-					return err
+				if stream {
+					// For streaming, write error as final chunk
+					json.NewEncoder(w).Encode(errResp)
+				} else {
+					// For non-streaming, return error response
+					if !headersSent {
+						w.WriteHeader(http.StatusOK) // Match TS: response.status(200).json(...)
+					}
+					json.NewEncoder(w).Encode(errResp)
 				}
+				return nil
+			}
 
-				if f, ok := w.(http.Flusher); ok {
-					f.Flush()
+			// Handle other errors
+			if stream {
+				refErr := core.ToReflectionError(err)
+				if resp != nil && resp.Telemetry.TraceID != "" {
+					refErr.Details.TraceID = &resp.Telemetry.TraceID
 				}
+
+				json.NewEncoder(w).Encode(errorResponse{Error: refErr})
 				return nil
 			}
+
+			// Non-streaming error
 			errorResponse := core.ToReflectionError(err)
-			if resp != nil {
+			if resp != nil && resp.Telemetry.TraceID != "" {
 				errorResponse.Details.TraceID = &resp.Telemetry.TraceID
 			}
-			w.WriteHeader(errorResponse.Code)
+
+			if !headersSent {
+				w.WriteHeader(errorResponse.Code)
+			}
 			return writeJSON(ctx, w, errorResponse)
 		}
 
-		return writeJSON(ctx, w, resp)
+		// Success case
+		if stream {
+			// For streaming, write the final chunk with result and telemetry
+			// This matches JS: response.write(JSON.stringify({result, telemetry}))
+			finalResponse := runActionResponse{
+				Result:    resp.Result,
+				Telemetry: telemetry{TraceID: resp.Telemetry.TraceID},
+			}
+			json.NewEncoder(w).Encode(finalResponse)
+		} else {
+			// For non-streaming, headers were already sent via telemetry callback
+			// Response already includes telemetry.traceId in body
+			return writeJSON(ctx, w, resp)
+		}
+
+		return nil
+	}
+}
+
+// handleCancelAction cancels an in-flight action by trace ID.
+func handleCancelAction(activeActions *activeActionsMap) func(w http.ResponseWriter, r *http.Request) error {
+	return func(w http.ResponseWriter, r *http.Request) error {
+		var body struct {
+			TraceID string `json:"traceId"`
+		}
+
+		defer r.Body.Close()
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			return core.NewError(core.INVALID_ARGUMENT, err.Error())
+		}
+
+		if body.TraceID == "" {
+			return core.NewError(core.INVALID_ARGUMENT, "traceId is required")
+		}
+
+		action, exists := activeActions.Get(body.TraceID)
+		if !exists {
+			w.WriteHeader(http.StatusNotFound)
+			return writeJSON(r.Context(), w, map[string]string{
+				"error": "Action not found or already completed",
+			})
+		}
+
+		// Cancel the action's context
+		action.cancel()
+		activeActions.Delete(body.TraceID)
+
+		return writeJSON(r.Context(), w, map[string]string{
+			"message": "Action cancelled",
+		})
 	}
 }
 
@@ -462,6 +632,10 @@ type telemetry struct {
 	TraceID string `json:"traceId"`
 }
 
+type errorResponse struct {
+	Error core.ReflectionError `json:"error"`
+}
+
 func runAction(ctx context.Context, g *Genkit, key string, input json.RawMessage, telemetryLabels json.RawMessage, cb streamingCallback[json.RawMessage], runtimeContext map[string]any) (*runActionResponse, error) {
 	action := g.reg.ResolveAction(key)
 	if action == nil {