Add basic OpenTelemetry tracing for client and server requests (#2381)

tests/shared/test_otel.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+import pytest
+from logfire.testing import CaptureLogfire
+
+from mcp import types
+from mcp.client.client import Client
+from mcp.server.mcpserver import MCPServer
+
+pytestmark = pytest.mark.anyio
+
+
+# Logfire warns about propagated trace context by default (distributed_tracing=None).
+# This is expected here since we're testing cross-boundary context propagation.
+@pytest.mark.filterwarnings("ignore::RuntimeWarning")
+async def test_client_and_server_spans(capfire: CaptureLogfire):
+    """Verify that calling a tool produces client and server spans with correct attributes."""
+    server = MCPServer("test")
+
+    @server.tool()
+    def greet(name: str) -> str:
+        """Greet someone."""
+        return f"Hello, {name}!"
+
+    async with Client(server) as client:
+        result = await client.call_tool("greet", {"name": "World"})
+
+    assert isinstance(result.content[0], types.TextContent)
+    assert result.content[0].text == "Hello, World!"
+
+    spans = capfire.exporter.exported_spans_as_dict()
+    span_names = {s["name"] for s in spans}
+
+    assert "MCP send tools/call greet" in span_names
+    assert "MCP handle tools/call greet" in span_names
+
+    client_span = next(s for s in spans if s["name"] == "MCP send tools/call greet")
+    server_span = next(s for s in spans if s["name"] == "MCP handle tools/call greet")
+
+    assert client_span["attributes"]["mcp.method.name"] == "tools/call"
+    assert server_span["attributes"]["mcp.method.name"] == "tools/call"
+
+    # Server span should be in the same trace as the client span (context propagation).
+    assert server_span["context"]["trace_id"] == client_span["context"]["trace_id"]