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| 1 | +// Command mcpfixture is a deterministic MCP upstream fixture for the release |
| 2 | +// QA gate (Spec 081, FR-006/FR-007). One binary serves the same two tools over |
| 3 | +// three transports so gate matrix cells never depend on third-party services: |
| 4 | +// |
| 5 | +// mcpfixture --transport stdio # newline-delimited JSON-RPC on stdin/stdout |
| 6 | +// mcpfixture --transport http --port 18080 # streamable-http at http://127.0.0.1:18080/mcp |
| 7 | +// mcpfixture --transport sse --port 18081 # legacy SSE at http://127.0.0.1:18081/sse (+ POST /message) |
| 8 | +// |
| 9 | +// Transports are served by mark3labs/mcp-go's server package — the same |
| 10 | +// library whose CLIENT side mcpproxy pins (internal/upstream/core uses |
| 11 | +// transport.CreateSSEClient / NewStreamableHTTP / NewStdio), so the wire |
| 12 | +// contract is protocol-correct by construction instead of hand-rolled: |
| 13 | +// - sse: GET /sse opens the event stream and announces the message endpoint |
| 14 | +// ("endpoint" event, relative URL resolved against the client's base URL); |
| 15 | +// requests are POSTed to /message?sessionId=… and responses stream back as |
| 16 | +// SSE "message" events. |
| 17 | +// - http: POST /mcp single-shot JSON responses (StreamableHTTPServer). |
| 18 | +// - stdio: newline-delimited JSON-RPC frames (StdioServer). |
| 19 | +// |
| 20 | +// Tools (deterministic, FR-007c): |
| 21 | +// - echo — returns the call arguments back as JSON text: |
| 22 | +// {"echo": {...arguments...}} |
| 23 | +// - ping — returns {"message":"pong","counter":N,"instance_id":"…"}; the |
| 24 | +// counter increases monotonically per process and the instance_id is |
| 25 | +// random per process start, so kill/restart tests (FR-007d) can prove the |
| 26 | +// reconnected upstream is a NEW instance (counter reset, new id). |
| 27 | +// |
| 28 | +// SIGTERM/SIGINT exits cleanly with code 0 on every transport (docker stop |
| 29 | +// sends SIGTERM to PID 1, and the gate kills fixtures between matrix steps). |
| 30 | +// |
| 31 | +// Docker cell (FR-009) argv composition, verified against |
| 32 | +// internal/upstream/core/isolation.go + connection_docker.go: |
| 33 | +// |
| 34 | +// server config: command="/mcpfixture", args=["--transport","stdio"], |
| 35 | +// isolation.image="mcpfixture:gate" |
| 36 | +// DetectRuntimeType(filepath.Base("/mcpfixture")) → "binary" (default case) |
| 37 | +// TransformCommandForContainer(binary) → command+args passed through unchanged |
| 38 | +// GetDockerImage → buildFullImageName("mcpfixture:gate") → "docker.io/library/mcpfixture:gate" |
| 39 | +// (no slash ⇒ registry+library prefix; Docker normalizes local short tags |
| 40 | +// the same way, so a locally built `mcpfixture:gate` resolves without a pull) |
| 41 | +// final argv: docker run --rm -i --name mcpproxy-<server>-<rand> <labels> |
| 42 | +// [--log-opt …] [--network <mode>] [limits] [-e K=V …] |
| 43 | +// docker.io/library/mcpfixture:gate /mcpfixture --transport stdio |
| 44 | +// |
| 45 | +// Because the container command is always appended explicitly after the image, |
| 46 | +// the image must NOT set an ENTRYPOINT (it would prefix the argv and break |
| 47 | +// `/mcpfixture --transport stdio`); it ships CMD ["/mcpfixture","--transport","stdio"] |
| 48 | +// as a default for bare `docker run` instead. See cmd/mcpfixture/Dockerfile and |
| 49 | +// scripts/gate/build-fixture-image.sh. |
| 50 | +package main |
| 51 | + |
| 52 | +import ( |
| 53 | + "context" |
| 54 | + "crypto/rand" |
| 55 | + "encoding/hex" |
| 56 | + "encoding/json" |
| 57 | + "errors" |
| 58 | + "flag" |
| 59 | + "fmt" |
| 60 | + "net/http" |
| 61 | + "os" |
| 62 | + "os/signal" |
| 63 | + "sync/atomic" |
| 64 | + "syscall" |
| 65 | + "time" |
| 66 | + |
| 67 | + "github.com/mark3labs/mcp-go/mcp" |
| 68 | + "github.com/mark3labs/mcp-go/server" |
| 69 | +) |
| 70 | + |
| 71 | +const ( |
| 72 | + fixtureName = "mcpfixture" |
| 73 | + fixtureVersion = "0.1.0" |
| 74 | + |
| 75 | + transportStdio = "stdio" |
| 76 | + transportHTTP = "http" |
| 77 | + transportSSE = "sse" |
| 78 | + |
| 79 | + shutdownTimeout = 5 * time.Second |
| 80 | +) |
| 81 | + |
| 82 | +// pingCounter increases monotonically per tools/call of `ping` within one |
| 83 | +// process. It intentionally resets on restart so reconnect tests can detect a |
| 84 | +// fresh instance. |
| 85 | +var pingCounter atomic.Int64 |
| 86 | + |
| 87 | +// instanceID is random per process start — the second discriminator (besides |
| 88 | +// the counter reset) that kill/restart tests use to distinguish instances. |
| 89 | +var instanceID = newInstanceID() |
| 90 | + |
| 91 | +func newInstanceID() string { |
| 92 | + buf := make([]byte, 8) |
| 93 | + if _, err := rand.Read(buf); err != nil { |
| 94 | + // Deterministic fallback still unique enough across restarts. |
| 95 | + return fmt.Sprintf("pid-%d-%d", os.Getpid(), time.Now().UnixNano()) |
| 96 | + } |
| 97 | + return hex.EncodeToString(buf) |
| 98 | +} |
| 99 | + |
| 100 | +// pingResult is the JSON payload returned by the ping tool. |
| 101 | +type pingResult struct { |
| 102 | + Message string `json:"message"` |
| 103 | + Counter int64 `json:"counter"` |
| 104 | + InstanceID string `json:"instance_id"` |
| 105 | +} |
| 106 | + |
| 107 | +func main() { |
| 108 | + transportFlag := flag.String("transport", transportStdio, "Transport to serve: stdio|http|sse") |
| 109 | + port := flag.Int("port", 0, "TCP port to bind (required for http/sse)") |
| 110 | + addr := flag.String("addr", "127.0.0.1", "Bind address (http/sse)") |
| 111 | + flag.Parse() |
| 112 | + |
| 113 | + mcpSrv := newFixtureServer() |
| 114 | + |
| 115 | + // A stdio parent (mcpproxy, or mcp-go's stdio client) may close our stderr |
| 116 | + // pipe before we write the final shutdown line; without this, Go's runtime |
| 117 | + // treats EPIPE on fd 1/2 as a fatal SIGPIPE and the fixture would die with |
| 118 | + // a non-zero "signal: broken pipe" status instead of exiting cleanly. |
| 119 | + signal.Ignore(syscall.SIGPIPE) |
| 120 | + |
| 121 | + // All operational logging goes to stderr: stdout is the protocol channel |
| 122 | + // for the stdio transport. |
| 123 | + fmt.Fprintf(os.Stderr, "[mcpfixture] transport=%s instance_id=%s pid=%d\n", *transportFlag, instanceID, os.Getpid()) |
| 124 | + |
| 125 | + switch *transportFlag { |
| 126 | + case transportStdio: |
| 127 | + // server.ServeStdio installs its own SIGTERM/SIGINT handler and |
| 128 | + // returns context.Canceled after a signal — treat that as clean. |
| 129 | + if err := server.ServeStdio(mcpSrv); err != nil && !errors.Is(err, context.Canceled) { |
| 130 | + fmt.Fprintf(os.Stderr, "[mcpfixture] stdio serve failed: %v\n", err) |
| 131 | + os.Exit(1) |
| 132 | + } |
| 133 | + case transportHTTP, transportSSE: |
| 134 | + if *port == 0 { |
| 135 | + fmt.Fprintln(os.Stderr, "[mcpfixture] --port is required for http/sse transports") |
| 136 | + os.Exit(2) |
| 137 | + } |
| 138 | + listenAddr := fmt.Sprintf("%s:%d", *addr, *port) |
| 139 | + if err := serveNetwork(*transportFlag, mcpSrv, listenAddr); err != nil { |
| 140 | + fmt.Fprintf(os.Stderr, "[mcpfixture] %s serve failed: %v\n", *transportFlag, err) |
| 141 | + os.Exit(1) |
| 142 | + } |
| 143 | + default: |
| 144 | + fmt.Fprintf(os.Stderr, "[mcpfixture] unknown --transport %q (want stdio|http|sse)\n", *transportFlag) |
| 145 | + os.Exit(2) |
| 146 | + } |
| 147 | + |
| 148 | + fmt.Fprintln(os.Stderr, "[mcpfixture] clean shutdown") |
| 149 | +} |
| 150 | + |
| 151 | +// newFixtureServer builds the MCP server with the two deterministic tools. |
| 152 | +func newFixtureServer() *server.MCPServer { |
| 153 | + s := server.NewMCPServer(fixtureName, fixtureVersion, server.WithToolCapabilities(false)) |
| 154 | + |
| 155 | + // Both tools are annotated read-only: without annotations the MCP spec |
| 156 | + // default is destructiveHint=true and mcpproxy's intent validation |
| 157 | + // (Spec 018) would reject them through call_tool_read. |
| 158 | + s.AddTool(mcp.NewTool("echo", |
| 159 | + mcp.WithDescription("Returns the provided arguments back as JSON text."), |
| 160 | + mcp.WithString("text", mcp.Description("Text to echo back.")), |
| 161 | + mcp.WithReadOnlyHintAnnotation(true), |
| 162 | + mcp.WithDestructiveHintAnnotation(false), |
| 163 | + mcp.WithOpenWorldHintAnnotation(false), |
| 164 | + ), handleEcho) |
| 165 | + |
| 166 | + s.AddTool(mcp.NewTool("ping", |
| 167 | + mcp.WithDescription("Returns pong with a per-process monotonically increasing counter and a per-process instance id."), |
| 168 | + mcp.WithReadOnlyHintAnnotation(true), |
| 169 | + mcp.WithDestructiveHintAnnotation(false), |
| 170 | + mcp.WithOpenWorldHintAnnotation(false), |
| 171 | + ), handlePing) |
| 172 | + |
| 173 | + return s |
| 174 | +} |
| 175 | + |
| 176 | +func handleEcho(_ context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) { |
| 177 | + args := req.GetArguments() |
| 178 | + if args == nil { |
| 179 | + args = map[string]any{} |
| 180 | + } |
| 181 | + payload, err := json.Marshal(map[string]any{"echo": args}) |
| 182 | + if err != nil { |
| 183 | + return mcp.NewToolResultError(fmt.Sprintf("marshal echo payload: %v", err)), nil |
| 184 | + } |
| 185 | + return mcp.NewToolResultText(string(payload)), nil |
| 186 | +} |
| 187 | + |
| 188 | +func handlePing(_ context.Context, _ mcp.CallToolRequest) (*mcp.CallToolResult, error) { |
| 189 | + payload, err := json.Marshal(pingResult{ |
| 190 | + Message: "pong", |
| 191 | + Counter: pingCounter.Add(1), |
| 192 | + InstanceID: instanceID, |
| 193 | + }) |
| 194 | + if err != nil { |
| 195 | + return mcp.NewToolResultError(fmt.Sprintf("marshal ping payload: %v", err)), nil |
| 196 | + } |
| 197 | + return mcp.NewToolResultText(string(payload)), nil |
| 198 | +} |
| 199 | + |
| 200 | +// networkServer is the common surface of mcp-go's StreamableHTTPServer and |
| 201 | +// SSEServer that serveNetwork needs. |
| 202 | +type networkServer interface { |
| 203 | + Start(addr string) error |
| 204 | + Shutdown(ctx context.Context) error |
| 205 | +} |
| 206 | + |
| 207 | +// serveNetwork runs the given transport until SIGTERM/SIGINT, then shuts it |
| 208 | +// down gracefully (5s deadline). A listen failure surfaces as the returned |
| 209 | +// error. |
| 210 | +func serveNetwork(transportName string, mcpSrv *server.MCPServer, listenAddr string) error { |
| 211 | + var srv networkServer |
| 212 | + switch transportName { |
| 213 | + case transportHTTP: |
| 214 | + srv = server.NewStreamableHTTPServer(mcpSrv) |
| 215 | + case transportSSE: |
| 216 | + // No WithBaseURL: the endpoint event advertises a relative |
| 217 | + // /message?sessionId=… URL, which mcp-go's SSE client (the one |
| 218 | + // mcpproxy pins) resolves against its base URL. |
| 219 | + srv = server.NewSSEServer(mcpSrv) |
| 220 | + default: |
| 221 | + return fmt.Errorf("unknown network transport %q", transportName) |
| 222 | + } |
| 223 | + |
| 224 | + errCh := make(chan error, 1) |
| 225 | + go func() { |
| 226 | + err := srv.Start(listenAddr) |
| 227 | + if err != nil && !errors.Is(err, http.ErrServerClosed) { |
| 228 | + errCh <- err |
| 229 | + } |
| 230 | + close(errCh) |
| 231 | + }() |
| 232 | + |
| 233 | + fmt.Fprintf(os.Stderr, "[mcpfixture] listening on %s\n", listenAddr) |
| 234 | + |
| 235 | + sigCh := make(chan os.Signal, 1) |
| 236 | + signal.Notify(sigCh, syscall.SIGTERM, syscall.SIGINT) |
| 237 | + defer signal.Stop(sigCh) |
| 238 | + |
| 239 | + select { |
| 240 | + case sig := <-sigCh: |
| 241 | + fmt.Fprintf(os.Stderr, "[mcpfixture] received %v, shutting down\n", sig) |
| 242 | + ctx, cancel := context.WithTimeout(context.Background(), shutdownTimeout) |
| 243 | + defer cancel() |
| 244 | + if err := srv.Shutdown(ctx); err != nil && !errors.Is(err, http.ErrServerClosed) && !errors.Is(err, context.Canceled) { |
| 245 | + return fmt.Errorf("shutdown: %w", err) |
| 246 | + } |
| 247 | + // Drain the Start goroutine so a late listen error is not lost. |
| 248 | + if err, ok := <-errCh; ok && err != nil { |
| 249 | + return err |
| 250 | + } |
| 251 | + return nil |
| 252 | + case err, ok := <-errCh: |
| 253 | + if ok && err != nil { |
| 254 | + return err |
| 255 | + } |
| 256 | + return nil |
| 257 | + } |
| 258 | +} |
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