fix: make mcp span names informative (envoyproxy#1288)

**Description**

Before everything was vaguely "mcp.request" which is not untrue, but not
helpful. There are plenty of low-cardinality choices for span or metric
names and the `req.Method` is the most intuitive. This uses the same
naming conventions as mcp-go

---------

Signed-off-by: Adrian Cole <[email protected]>
Signed-off-by: Hrushikesh Patil <[email protected]>

Author: codefromthecrypt

internal/mcpproxy/handlers.go

@@ -234,6 +234,7 @@ func (m *MCPProxy) servePOST(w http.ResponseWriter, r *http.Request) {
 			}
 			err = m.handleSetLoggingLevel(ctx, s, w, msg, p, span)
 		case "ping":
+			// Ping is intentionally not traced as it's a lightweight health check.
 			err = m.handlePing(ctx, w, msg)
 		case "prompts/list":
 			p := &mcp.ListPromptsParams{}

internal/tracing/mcp.go

@@ -86,7 +86,9 @@ func (m mcpTracer) StartSpanAndInjectMeta(ctx context.Context, req *jsonrpc.Requ
 	parentCtx := m.propagator.Extract(ctx, mc)
 
 	// Start the span with options appropriate for the semantic convention.
-	newCtx, span := m.tracer.Start(parentCtx, "mcp.request", trace.WithSpanKind(trace.SpanKindClient))
+	// Convert method name to span name following mcp-go SDK patterns
+	spanName := getSpanName(req.Method)
+	newCtx, span := m.tracer.Start(parentCtx, spanName, trace.WithSpanKind(trace.SpanKindClient))
 
 	// Always inject trace context into the header mutation if provided.
 	// This ensures trace propagation works even for unsampled spans.
@@ -174,3 +176,37 @@ func (c metaMapCarrier) Keys() []string {
 
 	return keys
 }
+
+// getSpanName converts MCP method names to span names following mcp-go SDK patterns.
+func getSpanName(method string) string {
+	switch method {
+	case "initialize":
+		return "Initialize"
+	case "tools/list":
+		return "ListTools"
+	case "tools/call":
+		return "CallTool"
+	case "prompts/list":
+		return "ListPrompts"
+	case "prompts/get":
+		return "GetPrompt"
+	case "resources/list":
+		return "ListResources"
+	case "resources/read":
+		return "ReadResource"
+	case "resources/subscribe":
+		return "Subscribe"
+	case "resources/unsubscribe":
+		return "Unsubscribe"
+	case "resources/templates/list":
+		return "ListResourceTemplates"
+	case "logging/setLevel":
+		return "SetLoggingLevel"
+	case "completion/complete":
+		return "Complete"
+	case "ping":
+		return "Ping"
+	default:
+		return method
+	}
+}

internal/tracing/mcp_test.go

@@ -6,6 +6,7 @@
 package tracing
 
 import (
+	"context"
 	"testing"
 
 	"github.com/modelcontextprotocol/go-sdk/jsonrpc"
@@ -15,6 +16,7 @@ import (
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/sdk/trace"
 	"go.opentelemetry.io/otel/sdk/trace/tracetest"
+	oteltrace "go.opentelemetry.io/otel/trace"
 )
 
 func TestTracer_StartSpanAndInjectMeta(t *testing.T) {
@@ -134,3 +136,106 @@ func Test_getMCPAttributes(t *testing.T) {
 		})
 	}
 }
+
+func Test_getSpanName(t *testing.T) {
+	tests := []struct {
+		method   string
+		expected string
+	}{
+		{method: "initialize", expected: "Initialize"},
+		{method: "tools/list", expected: "ListTools"},
+		{method: "tools/call", expected: "CallTool"},
+		{method: "prompts/list", expected: "ListPrompts"},
+		{method: "prompts/get", expected: "GetPrompt"},
+		{method: "resources/list", expected: "ListResources"},
+		{method: "resources/read", expected: "ReadResource"},
+		{method: "resources/subscribe", expected: "Subscribe"},
+		{method: "resources/unsubscribe", expected: "Unsubscribe"},
+		{method: "resources/templates/list", expected: "ListResourceTemplates"},
+		{method: "logging/setLevel", expected: "SetLoggingLevel"},
+		{method: "completion/complete", expected: "Complete"},
+		{method: "ping", expected: "Ping"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.method, func(t *testing.T) {
+			actual := getSpanName(tt.method)
+			require.Equal(t, tt.expected, actual)
+		})
+	}
+}
+
+func TestMCPTracer_SpanName(t *testing.T) {
+	tests := []struct {
+		name             string
+		method           string
+		params           mcp.Params
+		expectedSpanName string
+	}{
+		{
+			name:             "tools/list",
+			method:           "tools/list",
+			params:           &mcp.ListToolsParams{},
+			expectedSpanName: "ListTools",
+		},
+		{
+			name:             "tools/call",
+			method:           "tools/call",
+			params:           &mcp.CallToolParams{Name: "test-tool"},
+			expectedSpanName: "CallTool",
+		},
+		{
+			name:             "prompts/list",
+			method:           "prompts/list",
+			params:           &mcp.ListPromptsParams{},
+			expectedSpanName: "ListPrompts",
+		},
+		{
+			name:             "prompts/get",
+			method:           "prompts/get",
+			params:           &mcp.GetPromptParams{Name: "test-prompt"},
+			expectedSpanName: "GetPrompt",
+		},
+		{
+			name:             "resources/list",
+			method:           "resources/list",
+			params:           &mcp.ListResourcesParams{},
+			expectedSpanName: "ListResources",
+		},
+		{
+			name:             "resources/read",
+			method:           "resources/read",
+			params:           &mcp.ReadResourceParams{URI: "test://uri"},
+			expectedSpanName: "ReadResource",
+		},
+		{
+			name:             "initialize",
+			method:           "initialize",
+			params:           &mcp.InitializeParams{},
+			expectedSpanName: "Initialize",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			exporter := tracetest.NewInMemoryExporter()
+			tp := trace.NewTracerProvider(trace.WithSyncer(exporter))
+
+			tracer := newMCPTracer(tp.Tracer("test"), autoprop.NewTextMapPropagator())
+
+			reqID, _ := jsonrpc.MakeID("test-id")
+			req := &jsonrpc.Request{ID: reqID, Method: tt.method}
+
+			span := tracer.StartSpanAndInjectMeta(context.Background(), req, tt.params)
+			require.NotNil(t, span)
+			span.EndSpan()
+
+			spans := exporter.GetSpans()
+			require.Len(t, spans, 1)
+			actualSpan := spans[0]
+
+			require.Equal(t, tt.expectedSpanName, actualSpan.Name)
+			require.Equal(t, oteltrace.SpanKindClient, actualSpan.SpanKind)
+		})
+	}
+}

tests/extproc/mcp/env.go

@@ -17,7 +17,6 @@ import (
 
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 	"github.com/stretchr/testify/require"
-	v1 "go.opentelemetry.io/proto/otlp/trace/v1"
 
 	"github.com/envoyproxy/ai-gateway/internal/filterapi"
 	"github.com/envoyproxy/ai-gateway/internal/testing/testotel"
@@ -241,16 +240,18 @@ func (m *mcpEnv) newSession(t *testing.T) *mcpSession {
 	ret.session, err = m.client.Connect(t.Context(), &mcp.StreamableClientTransport{Endpoint: m.baseURL}, nil)
 	require.NoError(t, err)
 	span := m.collector.TakeSpan()
-	require.Equal(t, "mcp.request", span.Name)
-	require.Equal(t, v1.Span_SPAN_KIND_CLIENT, span.Kind)
-
 	t.Log("created new MCP session with ID ", ret.session.ID(), ", first span: ", span.String())
-	require.NotNil(t, span)
+	requireMCPSpan(t, span, "Initialize", map[string]string{
+		"mcp.method.name":    "initialize",
+		"mcp.client.name":    "demo-http-client",
+		"mcp.client.title":   "",
+		"mcp.client.version": "0.1.0",
+	})
 
 	// **NOTE*** Do not add any direct access to the in-memory server session. Otherwise, the tests will result in
 	// not being able to run in end-to-end tests. The test code must solely operate through the client side sessions.
 	t.Cleanup(func() {
-		require.NoError(t, ret.session.Close())
+		_ = ret.session.Close()
 		m.mux.Lock()
 		defer m.mux.Unlock()
 		delete(m.sessions, ret.session.ID())