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fix(mcp): stop reporting a dropped backend response as success (#3562)

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Co-authored-by: nova28 <17953305+nova28@users.noreply.github.com>
Co-authored-by: Carlos Florencio <carlosmflorencio@gmail.com>
This commit is contained in:
Henry
2026-09-10 19:09:30 +08:00
committed by GitHub
parent f367c9b125
commit b1b28d72a3
7 changed files with 378 additions and 8 deletions
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apps/backend/internal/mcp/server/backend_client.go
+17 -4
View File
@@ -3,6 +3,7 @@ package mcp
import (
"context"
"encoding/json"
"errors"
"fmt"
"sync"
"time"
@@ -13,6 +14,9 @@ import (
"go.uber.org/zap"
)
// ErrEmptyBackendPayload identifies a response with no payload bytes when a result sink was provided.
var ErrEmptyBackendPayload = errors.New("mcp backend response payload was empty")
// MCPRequest represents an MCP request to be sent to the backend.
type MCPRequest struct {
ID string `json:"id"`
@@ -236,10 +240,19 @@ func (c *ChannelBackendClient) RequestPayload(ctx context.Context, action string
}
return fmt.Errorf("backend error: %s", string(resp.Payload))
}
if result != nil && len(resp.Payload) > 0 {
if err := json.Unmarshal(resp.Payload, result); err != nil {
return fmt.Errorf("failed to unmarshal response: %w", err)
}
if result == nil {
return nil
}
if len(resp.Payload) == 0 {
c.logger.Warn(ErrEmptyBackendPayload.Error(),
zap.String("request_id", id),
zap.String("action", action),
zap.String("session_id", response.sessionID),
zap.Duration("duration", time.Since(start)))
return fmt.Errorf("empty response payload for action %q: %w", action, ErrEmptyBackendPayload)
}
if err := json.Unmarshal(resp.Payload, result); err != nil {
return fmt.Errorf("failed to unmarshal response: %w", err)
}
return nil
case <-ctx.Done():
apps/backend/internal/mcp/server/backend_client_test.go
+150
View File
@@ -2,6 +2,7 @@ package mcp
import (
"context"
"encoding/json"
"errors"
"testing"
"time"
@@ -10,6 +11,7 @@ import (
ws "github.com/kandev/kandev/pkg/websocket"
"github.com/stretchr/testify/require"
"go.uber.org/zap"
"go.uber.org/zap/zapcore"
"go.uber.org/zap/zaptest/observer"
)
@@ -126,6 +128,154 @@ func TestChannelBackendClientTerminalFailureLogIncludesConfiguredSession(t *test
require.Equal(t, "session-log", entries[0].ContextMap()["session_id"])
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.1
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.2
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.9
func TestChannelBackendClientEmptyPayloadWithResultSinkErrors(t *testing.T) {
core, observed := observer.New(zap.WarnLevel)
log, err := logger.NewFromZap(zap.New(core))
require.NoError(t, err)
client := NewChannelBackendClient(log)
t.Cleanup(client.Close)
var result map[string]interface{}
errCh := make(chan error, 1)
go func() {
errCh <- client.RequestPayload(context.Background(), "test.action", map[string]any{"secret": "canary-leak-9f3a"}, &result)
}()
request := <-client.GetRequestChannel()
response, err := ws.NewResponse(request.ID, request.Action, nil)
require.NoError(t, err)
response.Payload = nil
client.HandleResponse(response)
respErr := <-errCh
require.Error(t, respErr)
require.ErrorIs(t, respErr, ErrEmptyBackendPayload)
require.Contains(t, respErr.Error(), "test.action")
require.NotContains(t, respErr.Error(), "secret")
entries := observed.FilterMessage(ErrEmptyBackendPayload.Error()).All()
require.Len(t, entries, 1)
require.Equal(t, zapcore.WarnLevel, entries[0].Level)
fields := entries[0].ContextMap()
require.Equal(t, request.ID, fields["request_id"])
require.Equal(t, "test.action", fields["action"])
require.Contains(t, fields, "session_id")
require.Contains(t, fields, "duration")
logJSON, err := json.Marshal(fields)
require.NoError(t, err)
require.NotContains(t, string(logJSON), "secret")
require.NotContains(t, string(logJSON), "canary-leak-9f3a")
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.3
func TestChannelBackendClientEmptyPayloadWithNilResultSucceeds(t *testing.T) {
client := NewChannelBackendClient(nil)
t.Cleanup(client.Close)
errCh := make(chan error, 1)
go func() {
errCh <- client.RequestPayload(context.Background(), "test.action", nil, nil)
}()
request := <-client.GetRequestChannel()
response, err := ws.NewResponse(request.ID, request.Action, nil)
require.NoError(t, err)
response.Payload = nil
client.HandleResponse(response)
require.NoError(t, <-errCh)
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.4
func TestChannelBackendClientErrorTypeWithEmptyPayloadKeepsBackendErrorBehavior(t *testing.T) {
client := NewChannelBackendClient(nil)
t.Cleanup(client.Close)
var result map[string]interface{}
errCh := make(chan error, 1)
go func() {
errCh <- client.RequestPayload(context.Background(), "test.action", nil, &result)
}()
request := <-client.GetRequestChannel()
response := &ws.Message{ID: request.ID, Action: request.Action, Type: ws.MessageTypeError, Payload: nil}
client.HandleResponse(response)
respErr := <-errCh
require.Error(t, respErr)
require.NotErrorIs(t, respErr, ErrEmptyBackendPayload)
require.Contains(t, respErr.Error(), "backend error")
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.5
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.8
func TestChannelBackendClientEmptyObjectPayloadDecodesToNonNilEmptyMap(t *testing.T) {
client := NewChannelBackendClient(nil)
t.Cleanup(client.Close)
var result map[string]interface{}
errCh := make(chan error, 1)
go func() {
errCh <- client.RequestPayload(context.Background(), "test.action", nil, &result)
}()
request := <-client.GetRequestChannel()
response, err := ws.NewResponse(request.ID, request.Action, map[string]interface{}{})
require.NoError(t, err)
client.HandleResponse(response)
require.NoError(t, <-errCh)
require.NotNil(t, result)
require.Empty(t, result)
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.6
func TestChannelBackendClientNullPayloadStillDecodesWithoutError(t *testing.T) {
client := NewChannelBackendClient(nil)
t.Cleanup(client.Close)
result := map[string]interface{}{"stale": "value"}
errCh := make(chan error, 1)
go func() {
errCh <- client.RequestPayload(context.Background(), "test.action", nil, &result)
}()
request := <-client.GetRequestChannel()
response, err := ws.NewResponse(request.ID, request.Action, nil)
require.NoError(t, err)
client.HandleResponse(response)
require.NoError(t, <-errCh)
require.Nil(t, result)
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.7
func TestChannelBackendClientInvalidJSONPayloadKeepsUnmarshalError(t *testing.T) {
client := NewChannelBackendClient(nil)
t.Cleanup(client.Close)
var result map[string]interface{}
errCh := make(chan error, 1)
go func() {
errCh <- client.RequestPayload(context.Background(), "test.action", nil, &result)
}()
request := <-client.GetRequestChannel()
response, err := ws.NewResponse(request.ID, request.Action, nil)
require.NoError(t, err)
response.Payload = []byte("not json")
client.HandleResponse(response)
respErr := <-errCh
require.Error(t, respErr)
require.Contains(t, respErr.Error(), "failed to unmarshal")
require.NotErrorIs(t, respErr, ErrEmptyBackendPayload)
}
func TestChannelBackendClientRedactsPluginInvocationPayload(t *testing.T) {
core, observed := observer.New(zap.DebugLevel)
log, err := logger.NewFromZap(zap.New(core))
apps/backend/internal/mcp/server/dispatcher_backend_client.go
+11 -4
View File
@@ -75,10 +75,17 @@ func (c *DispatcherBackendClient) RequestPayload(ctx context.Context, action str
}
return fmt.Errorf("backend error: %s", string(resp.Payload))
}
if result != nil && len(resp.Payload) > 0 {
if err := json.Unmarshal(resp.Payload, result); err != nil {
return fmt.Errorf("failed to unmarshal response for %s: %w", action, err)
}
if result == nil {
return nil
}
if len(resp.Payload) == 0 {
c.logger.Warn(ErrEmptyBackendPayload.Error(),
zap.String("request_id", id),
zap.String("action", action))
return fmt.Errorf("empty response payload for action %q: %w", action, ErrEmptyBackendPayload)
}
if err := json.Unmarshal(resp.Payload, result); err != nil {
return fmt.Errorf("failed to unmarshal response for %s: %w", action, err)
}
return nil
}
apps/backend/internal/mcp/server/dispatcher_backend_client_test.go
+116
View File
@@ -6,10 +6,14 @@ import (
"errors"
"testing"
"github.com/kandev/kandev/internal/common/logger"
mcporigin "github.com/kandev/kandev/internal/mcp/origin"
ws "github.com/kandev/kandev/pkg/websocket"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
"go.uber.org/zap"
"go.uber.org/zap/zapcore"
"go.uber.org/zap/zaptest/observer"
)
// fakeDispatcher is a minimal Dispatcher used to drive DispatcherBackendClient tests.
@@ -114,3 +118,115 @@ func TestDispatcherBackendClient_NilResultIsAllowed(t *testing.T) {
err = client.RequestPayload(context.Background(), "test.action", nil, nil)
require.NoError(t, err)
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.1
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.2
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.9
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.10
func TestDispatcherBackendClient_EmptyPayloadWithResultSinkErrors(t *testing.T) {
core, observed := observer.New(zap.WarnLevel)
log, err := logger.NewFromZap(zap.New(core))
require.NoError(t, err)
d := &fakeDispatcher{resp: &ws.Message{Type: ws.MessageTypeResponse, Payload: nil}}
client := NewDispatcherBackendClient(d, log)
var result map[string]interface{}
respErr := client.RequestPayload(context.Background(), "test.action", map[string]any{"secret": "canary-leak-9f3a"}, &result)
require.Error(t, respErr)
require.ErrorIs(t, respErr, ErrEmptyBackendPayload)
require.Contains(t, respErr.Error(), "test.action")
require.NotContains(t, respErr.Error(), "secret")
require.Len(t, d.calls, 1)
outboundID := d.calls[0].ID
require.NotEmpty(t, outboundID)
entries := observed.FilterMessage(ErrEmptyBackendPayload.Error()).All()
require.Len(t, entries, 1)
require.Equal(t, zapcore.WarnLevel, entries[0].Level)
fields := entries[0].ContextMap()
require.Equal(t, outboundID, fields["request_id"])
require.Equal(t, "test.action", fields["action"])
_, hasSessionID := fields["session_id"]
require.False(t, hasSessionID)
_, hasDuration := fields["duration"]
require.False(t, hasDuration)
logJSON, err := json.Marshal(fields)
require.NoError(t, err)
require.NotContains(t, string(logJSON), "secret")
require.NotContains(t, string(logJSON), "canary-leak-9f3a")
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.3
func TestDispatcherBackendClient_EmptyPayloadWithNilResultSucceeds(t *testing.T) {
log := newTestLogger(t)
d := &fakeDispatcher{resp: &ws.Message{Type: ws.MessageTypeResponse, Payload: nil}}
client := NewDispatcherBackendClient(d, log)
err := client.RequestPayload(context.Background(), "test.action", nil, nil)
require.NoError(t, err)
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.4
func TestDispatcherBackendClient_ErrorTypeWithEmptyPayloadKeepsBackendErrorBehavior(t *testing.T) {
log := newTestLogger(t)
d := &fakeDispatcher{resp: &ws.Message{Type: ws.MessageTypeError, Payload: nil}}
client := NewDispatcherBackendClient(d, log)
var result map[string]interface{}
err := client.RequestPayload(context.Background(), "test.action", nil, &result)
require.Error(t, err)
require.NotErrorIs(t, err, ErrEmptyBackendPayload)
require.Contains(t, err.Error(), "backend error")
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.5
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.8
func TestDispatcherBackendClient_EmptyObjectPayloadDecodesToNonNilEmptyMap(t *testing.T) {
log := newTestLogger(t)
respMsg, err := ws.NewResponse("ignored", "test.action", map[string]interface{}{})
require.NoError(t, err)
d := &fakeDispatcher{resp: respMsg}
client := NewDispatcherBackendClient(d, log)
var result map[string]interface{}
err = client.RequestPayload(context.Background(), "test.action", nil, &result)
require.NoError(t, err)
require.NotNil(t, result)
require.Empty(t, result)
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.6
func TestDispatcherBackendClient_NullPayloadStillDecodesWithoutError(t *testing.T) {
log := newTestLogger(t)
respMsg, err := ws.NewResponse("ignored", "test.action", nil)
require.NoError(t, err)
d := &fakeDispatcher{resp: respMsg}
client := NewDispatcherBackendClient(d, log)
result := map[string]interface{}{"stale": "value"}
err = client.RequestPayload(context.Background(), "test.action", nil, &result)
require.NoError(t, err)
require.Nil(t, result)
}
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.7
func TestDispatcherBackendClient_InvalidJSONPayloadKeepsUnmarshalError(t *testing.T) {
log := newTestLogger(t)
respMsg := &ws.Message{Type: ws.MessageTypeResponse, Payload: json.RawMessage("not json")}
d := &fakeDispatcher{resp: respMsg}
client := NewDispatcherBackendClient(d, log)
var result map[string]interface{}
err := client.RequestPayload(context.Background(), "test.action", nil, &result)
require.Error(t, err)
require.Contains(t, err.Error(), "failed to unmarshal")
require.NotErrorIs(t, err, ErrEmptyBackendPayload)
}
apps/backend/internal/mcp/server/task_plan_empty_payload_test.go
+22
View File
@@ -0,0 +1,22 @@
package mcp
import (
"testing"
"github.com/stretchr/testify/require"
)
// @covers AC-AGENTS-MCP-BRIDGE-RELIABILITY-002.5
// TestGetTaskPlan_EmptyObjectPayloadStillRendersNoPlan guards the transport
// change against the deliberately unchanged "no plan" convention: a `{}`
// backend response must keep decoding successfully so this rendering is
// unaffected by the new empty-payload rule.
func TestGetTaskPlan_EmptyObjectPayloadStillRendersNoPlan(t *testing.T) {
backend := &testBackend{response: map[string]interface{}{}}
s := newTaskModeServer(t, backend, "task-A")
result := callTool(t, s, "get_task_plan_kandev", map[string]interface{}{})
require.False(t, result.IsError)
require.Equal(t, "No plan exists for this task yet.", resultText(t, result))
}