Refactor logging middleware

This commit is contained in:
William Easton 2025-08-26 23:54:34 -05:00
commit 27401a3d5f
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2 changed files with 286 additions and 121 deletions

View file

@ -3,13 +3,19 @@
import json
import logging
from collections.abc import Callable
from logging import Logger
from typing import Any
from fastmcp.tools.tool import default_serializer
import pydantic_core
from .middleware import CallNext, Middleware, MiddlewareContext
def default_serializer(data: Any) -> str:
"""The default serializer for Payloads in the logging middleware."""
return pydantic_core.to_json(data, fallback=str).decode()
class LoggingMiddleware(Middleware):
"""Middleware that provides comprehensive request and response logging.
@ -36,6 +42,7 @@ class LoggingMiddleware(Middleware):
include_payloads: bool = False,
max_payload_length: int = 1000,
methods: list[str] | None = None,
payload_serializer: Callable[[Any], str] | None = None,
):
"""Initialize logging middleware.
@ -46,13 +53,14 @@ class LoggingMiddleware(Middleware):
max_payload_length: Maximum length of payload to log (prevents huge logs)
methods: List of methods to log. If None, logs all methods.
"""
self.logger = logger or logging.getLogger("fastmcp.requests")
self.log_level = log_level
self.include_payloads = include_payloads
self.max_payload_length = max_payload_length
self.methods = methods
self.logger: Logger = logger or logging.getLogger("fastmcp.requests")
self.log_level: int = log_level
self.include_payloads: bool = include_payloads
self.max_payload_length: int = max_payload_length
self.methods: list[str] | None = methods
self.payload_serializer: Callable[[Any], str] | None = payload_serializer
def _format_message(self, context: MiddlewareContext) -> str:
def _format_message(self, context: MiddlewareContext[Any]) -> str:
"""Format a message for logging."""
parts = [
f"source={context.source}",
@ -60,18 +68,29 @@ class LoggingMiddleware(Middleware):
f"method={context.method or 'unknown'}",
]
if self.include_payloads and hasattr(context.message, "__dict__"):
try:
payload = json.dumps(context.message.__dict__, default=str)
if len(payload) > self.max_payload_length:
payload = payload[: self.max_payload_length] + "..."
parts.append(f"payload={payload}")
except (TypeError, ValueError):
parts.append("payload=<non-serializable>")
if self.include_payloads:
payload: str
if not self.payload_serializer:
payload = default_serializer(context.message)
else:
try:
payload = self.payload_serializer(context.message)
except Exception as e:
self.logger.warning(
f"Failed {str(e)} to serialize payload: {context.type} {context.method} {context.source}."
)
payload = default_serializer(context.message)
if len(payload) > self.max_payload_length:
payload = payload[: self.max_payload_length] + "..."
parts.append(f"payload={payload}")
return " ".join(parts)
async def on_message(self, context: MiddlewareContext, call_next: CallNext) -> Any:
async def on_message(
self, context: MiddlewareContext[Any], call_next: CallNext[Any, Any]
) -> Any:
"""Log all messages."""
message_info = self._format_message(context)
if self.methods and context.method not in self.methods:
@ -114,7 +133,7 @@ class StructuredLoggingMiddleware(Middleware):
log_level: int = logging.INFO,
include_payloads: bool = False,
methods: list[str] | None = None,
serializer: Callable[[Any], str] | None = None,
payload_serializer: Callable[[Any], str] | None = None,
):
"""Initialize structured logging middleware.
@ -126,15 +145,15 @@ class StructuredLoggingMiddleware(Middleware):
serializer: Callable that converts objects to a JSON string for the
payload. If not provided, uses FastMCP's default tool serializer.
"""
self.logger = logger or logging.getLogger("fastmcp.structured")
self.log_level = log_level
self.include_payloads = include_payloads
self.methods = methods
self.serializer = serializer or default_serializer
self.logger: Logger = logger or logging.getLogger("fastmcp.structured")
self.log_level: int = log_level
self.include_payloads: bool = include_payloads
self.methods: list[str] | None = methods
self.payload_serializer: Callable[[Any], str] | None = payload_serializer
def _create_log_entry(
self, context: MiddlewareContext, event: str, **extra_fields
) -> dict:
self, context: MiddlewareContext[Any], event: str, **extra_fields: Any
) -> dict[str, Any]:
"""Create a structured log entry."""
entry = {
"event": event,
@ -146,22 +165,26 @@ class StructuredLoggingMiddleware(Middleware):
}
if self.include_payloads:
payload_obj = (
context.message.__dict__
if hasattr(context.message, "__dict__")
else context.message
)
payload: str
try:
payload_str = self.serializer(payload_obj)
except Exception:
payload_str = default_serializer(payload_obj)
if not self.payload_serializer:
payload = default_serializer(context.message)
else:
try:
payload = self.payload_serializer(context.message)
except Exception as e:
self.logger.warning(
f"Failed {str(e)} to serialize payload: {context.type} {context.method} {context.source}."
)
payload = default_serializer(context.message)
entry["payload"] = payload_str
entry["payload"] = payload
return entry
async def on_message(self, context: MiddlewareContext, call_next: CallNext) -> Any:
async def on_message(
self, context: MiddlewareContext[Any], call_next: CallNext[Any, Any]
) -> Any:
"""Log structured message information."""
start_entry = self._create_log_entry(context, "request_start")
if self.methods and context.method not in self.methods:

View file

@ -1,31 +1,58 @@
"""Tests for logging middleware."""
import datetime
import json
import logging
from typing import Any
from typing import Any, Literal, TypeVar
from unittest.mock import AsyncMock, MagicMock
import mcp
import pytest
from inline_snapshot import snapshot
from pydantic import AnyUrl
from fastmcp.resources.template import ResourceTemplate
from fastmcp.server.middleware.logging import (
LoggingMiddleware,
StructuredLoggingMiddleware,
)
from fastmcp.server.middleware.middleware import MiddlewareContext
from fastmcp.server.middleware.middleware import CallNext, MiddlewareContext
from fastmcp.server.server import FastMCP
FIXED_DATE = datetime.datetime(2023, 1, 1, tzinfo=datetime.timezone.utc)
T = TypeVar("T")
def new_mock_context(
message: T,
method: str | None = None,
source: Literal["server", "client"] | None = None,
type: Literal["request", "notification"] | None = None,
) -> MiddlewareContext[T]:
"""Create a new mock middleware context."""
context = MagicMock(spec=MiddlewareContext[T])
context.method = method or "test_method"
context.source = source or "client"
context.type = type or "request"
context.message = message
context.timestamp = FIXED_DATE
return context
@pytest.fixture
def mock_context():
"""Create a mock middleware context."""
context = MagicMock(spec=MiddlewareContext)
context.method = "test_method"
context.source = "client"
context.type = "request"
context.message = MagicMock()
context.message.__dict__ = {"param": "value"}
context.timestamp = MagicMock()
context.timestamp.isoformat.return_value = "2023-01-01T00:00:00Z"
return context
return new_mock_context(
message=mcp.types.CallToolRequest(
method="tools/call",
params=mcp.types.CallToolRequestParams(
name="test_method",
arguments={"param": "value"},
),
)
)
@pytest.fixture
@ -59,7 +86,9 @@ class TestLoggingMiddleware:
assert middleware.include_payloads is True
assert middleware.max_payload_length == 500
def test_format_message_without_payloads(self, mock_context):
def test_format_message_without_payloads(
self, mock_context: MiddlewareContext[Any]
):
"""Test message formatting without payloads."""
middleware = LoggingMiddleware()
formatted = middleware._format_message(mock_context)
@ -69,17 +98,16 @@ class TestLoggingMiddleware:
assert "method=test_method" in formatted
assert "payload=" not in formatted
def test_format_message_with_payloads(self, mock_context):
def test_format_message_with_payloads(self, mock_context: MiddlewareContext[Any]):
"""Test message formatting with payloads."""
middleware = LoggingMiddleware(include_payloads=True)
formatted = middleware._format_message(mock_context)
assert "source=client" in formatted
assert "type=request" in formatted
assert "method=test_method" in formatted
assert 'payload={"param": "value"}' in formatted
assert formatted == snapshot(
'source=client type=request method=test_method payload={"method":"tools/call","params":{"_meta":null,"name":"test_method","arguments":{"param":"value"}}}'
)
def test_format_message_long_payload(self, mock_context):
def test_format_message_long_payload(self, mock_context: MiddlewareContext[Any]):
"""Test message formatting with long payload truncation."""
middleware = LoggingMiddleware(include_payloads=True, max_payload_length=10)
formatted = middleware._format_message(mock_context)
@ -87,7 +115,12 @@ class TestLoggingMiddleware:
assert "payload=" in formatted
assert "..." in formatted
async def test_on_message_success(self, mock_context, mock_call_next, caplog):
async def test_on_message_success(
self,
mock_context: MiddlewareContext[Any],
mock_call_next: CallNext[Any, Any],
caplog: pytest.LogCaptureFixture,
):
"""Test logging successful messages."""
middleware = LoggingMiddleware()
@ -99,7 +132,9 @@ class TestLoggingMiddleware:
assert "Processing message:" in caplog.text
assert "Completed message: test_method" in caplog.text
async def test_on_message_failure(self, mock_context, caplog):
async def test_on_message_failure(
self, mock_context: MiddlewareContext[Any], caplog: pytest.LogCaptureFixture
):
"""Test logging failed messages."""
middleware = LoggingMiddleware()
mock_call_next = AsyncMock(side_effect=ValueError("test error"))
@ -122,26 +157,40 @@ class TestStructuredLoggingMiddleware:
assert middleware.log_level == logging.INFO
assert middleware.include_payloads is False
def test_create_log_entry_basic(self, mock_context):
def test_create_log_entry_basic(self, mock_context: MiddlewareContext[Any]):
"""Test creating basic log entry."""
middleware = StructuredLoggingMiddleware()
entry = middleware._create_log_entry(mock_context, "test_event")
assert entry["event"] == "test_event"
assert entry["timestamp"] == "2023-01-01T00:00:00Z"
assert entry["source"] == "client"
assert entry["type"] == "request"
assert entry["method"] == "test_method"
assert "payload" not in entry
assert entry == snapshot(
{
"event": "test_event",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
}
)
def test_create_log_entry_with_payload(self, mock_context):
def test_create_log_entry_with_payload(self, mock_context: MiddlewareContext[Any]):
"""Test creating log entry with payload."""
middleware = StructuredLoggingMiddleware(include_payloads=True)
entry = middleware._create_log_entry(mock_context, "test_event")
assert isinstance(entry["payload"], str)
assert json.loads(entry["payload"]) == {"param": "value"}
def test_create_log_entry_with_extra_fields(self, mock_context):
assert entry == snapshot(
{
"event": "test_event",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"payload": '{"method":"tools/call","params":{"_meta":null,"name":"test_method","arguments":{"param":"value"}}}',
}
)
def test_create_log_entry_with_extra_fields(
self, mock_context: MiddlewareContext[Any]
):
"""Test creating log entry with extra fields."""
middleware = StructuredLoggingMiddleware()
entry = middleware._create_log_entry(
@ -150,7 +199,12 @@ class TestStructuredLoggingMiddleware:
assert entry["extra_field"] == "extra_value"
async def test_on_message_success(self, mock_context, mock_call_next, caplog):
async def test_on_message_success(
self,
mock_context: MiddlewareContext[Any],
mock_call_next: CallNext[Any, Any],
caplog: pytest.LogCaptureFixture,
):
"""Test structured logging of successful messages."""
middleware = StructuredLoggingMiddleware()
@ -161,17 +215,33 @@ class TestStructuredLoggingMiddleware:
# Check that we have structured JSON logs
log_lines = [record.message for record in caplog.records]
assert len(log_lines) == 2 # start and success entries
start_entry = json.loads(log_lines[0])
assert start_entry["event"] == "request_start"
assert start_entry["method"] == "test_method"
assert json.loads(log_lines[0]) == snapshot(
{
"event": "request_start",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
}
)
success_entry = json.loads(log_lines[1])
assert success_entry["event"] == "request_success"
assert success_entry["result_type"] == "str"
assert json.loads(log_lines[1]) == snapshot(
{
"event": "request_success",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"result_type": "str",
}
)
async def test_on_message_failure(self, mock_context, caplog):
async def test_on_message_failure(
self, mock_context: MiddlewareContext[Any], caplog: pytest.LogCaptureFixture
):
"""Test structured logging of failed messages."""
middleware = StructuredLoggingMiddleware()
mock_call_next = AsyncMock(side_effect=ValueError("test error"))
@ -187,47 +257,80 @@ class TestStructuredLoggingMiddleware:
start_entry = json.loads(log_lines[0])
assert start_entry["event"] == "request_start"
error_entry = json.loads(log_lines[1])
assert error_entry["event"] == "request_error"
assert error_entry["error_type"] == "ValueError"
assert error_entry["error_message"] == "test error"
async def test_on_message_with_pydantic_types_in_payload(
self, mock_context, mock_call_next, caplog
):
"""Ensure Pydantic AnyUrl in payload serializes correctly when include_payloads=True."""
from pydantic import AnyUrl
mock_context.message.__dict__["url"] = AnyUrl("test://example/1")
middleware = StructuredLoggingMiddleware(include_payloads=True)
with caplog.at_level(logging.INFO):
result = await middleware.on_message(mock_context, mock_call_next)
assert result == "test_result"
log_lines = [record.message for record in caplog.records]
assert len(log_lines) == 2
start_entry = json.loads(log_lines[0])
assert start_entry["event"] == "request_start"
payload = json.loads(start_entry["payload"])
assert payload["url"] == "test://example/1"
async def test_on_message_with_resource_template_in_payload(
self, mock_context, mock_call_next, caplog
):
"""Ensure ResourceTemplate in payload serializes via pydantic conversion without errors."""
from fastmcp.resources import ResourceTemplate
template = ResourceTemplate(
name="tmpl",
uri_template="tmpl://{id}",
parameters={"id": {"type": "string"}},
assert json.loads(log_lines[1]) == snapshot(
{
"event": "request_error",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"error_type": "ValueError",
"error_message": "test error",
}
)
mock_context.message.__dict__["template"] = template
async def test_on_message_with_pydantic_types_in_payload(
self,
mock_call_next: CallNext[Any, Any],
caplog: pytest.LogCaptureFixture,
):
"""Ensure Pydantic AnyUrl in payload serializes correctly when include_payloads=True."""
mock_context = new_mock_context(
message=mcp.types.ReadResourceRequest(
method="resources/read",
params=mcp.types.ReadResourceRequestParams(
uri=AnyUrl("test://example/1"),
),
)
)
middleware = StructuredLoggingMiddleware(include_payloads=True)
with caplog.at_level(logging.INFO):
result = await middleware.on_message(mock_context, mock_call_next)
assert result == "test_result"
log_lines = [record.message for record in caplog.records]
assert len(log_lines) == 2
assert json.loads(log_lines[0]) == snapshot(
{
"event": "request_start",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"payload": '{"method":"resources/read","params":{"_meta":null,"uri":"test://example/1"}}',
}
)
assert json.loads(log_lines[1]) == snapshot(
{
"event": "request_success",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"result_type": "str",
"payload": '{"method":"resources/read","params":{"_meta":null,"uri":"test://example/1"}}',
}
)
async def test_on_message_with_resource_template_in_payload(
self,
mock_call_next: CallNext[Any, Any],
caplog: pytest.LogCaptureFixture,
):
"""Ensure ResourceTemplate in payload serializes via pydantic conversion without errors."""
mock_context = new_mock_context(
message=ResourceTemplate(
name="tmpl",
uri_template="tmpl://{id}",
parameters={"id": {"type": "string"}},
)
)
middleware = StructuredLoggingMiddleware(include_payloads=True)
@ -238,15 +341,19 @@ class TestStructuredLoggingMiddleware:
log_lines = [record.message for record in caplog.records]
assert len(log_lines) == 2
start_entry = json.loads(log_lines[0])
assert start_entry["event"] == "request_start"
payload = json.loads(start_entry["payload"])
assert "template" in payload
assert isinstance(payload["template"], dict)
assert payload["template"]["uri_template"] == "tmpl://{id}"
assert json.loads(log_lines[0]) == snapshot(
{
"event": "request_start",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"payload": '{"name":"tmpl","title":null,"description":null,"tags":[],"meta":null,"enabled":true,"uri_template":"tmpl://{id}","mime_type":"text/plain","parameters":{"id":{"type":"string"}},"annotations":null}',
}
)
async def test_on_message_with_nonserializable_payload_falls_back_to_str(
self, mock_context, mock_call_next, caplog
self, mock_call_next: CallNext[Any, Any], caplog: pytest.LogCaptureFixture
):
"""Ensure non-JSONable objects fall back to string serialization in payload."""
@ -254,7 +361,15 @@ class TestStructuredLoggingMiddleware:
def __str__(self) -> str:
return "NON_SERIALIZABLE"
mock_context.message.__dict__["obj"] = NonSerializable()
mock_context = new_mock_context(
message=mcp.types.CallToolRequest(
method="tools/call",
params=mcp.types.CallToolRequestParams(
name="test_method",
arguments={"obj": NonSerializable()},
),
)
)
middleware = StructuredLoggingMiddleware(include_payloads=True)
@ -265,13 +380,19 @@ class TestStructuredLoggingMiddleware:
log_lines = [record.message for record in caplog.records]
assert len(log_lines) >= 2
start_entry = json.loads(log_lines[0])
assert start_entry["event"] == "request_start"
payload = json.loads(start_entry["payload"])
assert payload["obj"] == "NON_SERIALIZABLE"
assert json.loads(log_lines[0]) == snapshot(
{
"event": "request_start",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"payload": '{"method":"tools/call","params":{"_meta":null,"name":"test_method","arguments":{"obj":"NON_SERIALIZABLE"}}}',
}
)
async def test_on_message_with_custom_serializer_applied(
self, mock_context, mock_call_next, caplog
self, mock_call_next: CallNext[Any, Any], caplog: pytest.LogCaptureFixture
):
"""Ensure a custom serializer is used for non-JSONable payloads."""
@ -279,10 +400,18 @@ class TestStructuredLoggingMiddleware:
def custom_serializer(_: Any) -> str:
return "CUSTOM_PAYLOAD"
mock_context.message.__dict__["special"] = object()
mock_context = new_mock_context(
message=mcp.types.CallToolRequest(
method="tools/call",
params=mcp.types.CallToolRequestParams(
name="test_method",
arguments={"obj": "OBJECT"},
),
)
)
middleware = StructuredLoggingMiddleware(
include_payloads=True, serializer=custom_serializer
include_payloads=True, payload_serializer=custom_serializer
)
with caplog.at_level(logging.INFO):
@ -292,9 +421,16 @@ class TestStructuredLoggingMiddleware:
log_lines = [record.message for record in caplog.records]
assert len(log_lines) >= 2
start_entry = json.loads(log_lines[0])
assert start_entry["event"] == "request_start"
assert start_entry["payload"] == "CUSTOM_PAYLOAD"
assert json.loads(log_lines[0]) == snapshot(
{
"event": "request_start",
"timestamp": "2023-01-01T00:00:00+00:00",
"source": "client",
"type": "request",
"method": "test_method",
"payload": "CUSTOM_PAYLOAD",
}
)
@pytest.fixture
@ -338,7 +474,7 @@ class TestLoggingMiddlewareIntegration:
"""Integration tests for logging middleware with real FastMCP server."""
async def test_logging_middleware_logs_successful_operations(
self, logging_server, caplog
self, logging_server: FastMCP, caplog: pytest.LogCaptureFixture
):
"""Test that logging middleware captures successful operations."""
from fastmcp.client import Client
@ -364,7 +500,9 @@ class TestLoggingMiddlewareIntegration:
assert processing_count == 2
assert completion_count == 2
async def test_logging_middleware_logs_failures(self, logging_server, caplog):
async def test_logging_middleware_logs_failures(
self, logging_server: FastMCP, caplog: pytest.LogCaptureFixture
):
"""Test that logging middleware captures failed operations."""
from fastmcp.client import Client
@ -384,7 +522,9 @@ class TestLoggingMiddlewareIntegration:
assert "Processing message:" in log_text
assert "Failed message: tools/call" in log_text
async def test_logging_middleware_with_payloads(self, logging_server, caplog):
async def test_logging_middleware_with_payloads(
self, logging_server: FastMCP, caplog: pytest.LogCaptureFixture
):
"""Test logging middleware when configured to include payloads."""
from fastmcp.client import Client
@ -405,7 +545,7 @@ class TestLoggingMiddlewareIntegration:
assert "payload=" in log_text
async def test_structured_logging_middleware_produces_json(
self, logging_server, caplog
self, logging_server: FastMCP, caplog: pytest.LogCaptureFixture
):
"""Test that structured logging middleware produces parseable JSON logs."""
import json
@ -439,7 +579,7 @@ class TestLoggingMiddlewareIntegration:
assert "method" in log_entry
async def test_structured_logging_middleware_handles_errors(
self, logging_server, caplog
self, logging_server: FastMCP, caplog: pytest.LogCaptureFixture
):
"""Test structured logging of errors with JSON format."""
import json
@ -480,7 +620,7 @@ class TestLoggingMiddlewareIntegration:
assert "error_message" in error_entry
async def test_logging_middleware_with_different_operations(
self, logging_server, caplog
self, logging_server: FastMCP, caplog: pytest.LogCaptureFixture
):
"""Test logging middleware with various MCP operations."""
from fastmcp.client import Client
@ -515,7 +655,9 @@ class TestLoggingMiddlewareIntegration:
assert processing_count == 4
assert completion_count == 4
async def test_logging_middleware_custom_configuration(self, logging_server):
async def test_logging_middleware_custom_configuration(
self, logging_server: FastMCP
):
"""Test logging middleware with custom logger configuration."""
import io
import logging