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Logging Middleware¶

Cello provides built-in request logging implemented in Rust. The logging middleware records HTTP method, path, status code, and response time for every request.

Quick Start¶

from cello import App

app = App()

# Enable request logging
app.enable_logging()

When enabled, each request produces a log line:

[2025-01-15 10:23:45] GET /api/users → 200 (2.3ms)
[2025-01-15 10:23:46] POST /api/users → 201 (5.1ms)
[2025-01-15 10:23:47] GET /api/users/999 → 404 (0.8ms)

Automatic Logging in Development¶

When you run your application with app.run(), logging is enabled automatically in development mode:

app = App()

# Logging enabled automatically (env defaults to "development")
app.run()

# Explicit development mode
app.run(env="development")

# Disable auto-logging in development
app.run(logs=False)

# Production mode -- no auto-logging
app.run(env="production")
Environment Auto-Logging
development Enabled
production Disabled

You can always explicitly enable logging regardless of environment:

app.enable_logging()
app.run(env="production")  # Logging still active

Log Format¶

Each log entry contains:

Field Description Example
Timestamp ISO 8601 format 2025-01-15 10:23:45
Method HTTP method GET, POST, DELETE
Path Request path /api/users/123
Status Response status code 200, 404, 500
Duration Processing time 2.3ms

Example Output¶

[2025-01-15 10:23:45] GET    /                → 200 (0.1ms)
[2025-01-15 10:23:45] GET    /api/users       → 200 (3.2ms)
[2025-01-15 10:23:46] POST   /api/users       → 201 (5.7ms)
[2025-01-15 10:23:46] GET    /api/users/1     → 200 (1.1ms)
[2025-01-15 10:23:47] DELETE /api/users/1     → 204 (2.0ms)
[2025-01-15 10:23:48] GET    /api/users/999   → 404 (0.5ms)
[2025-01-15 10:23:49] POST   /api/login       → 401 (1.8ms)

Status Code Colors¶

In terminal output, status codes are color-coded for quick visual identification:

Status Range Color Meaning
2xx Green Success
3xx Cyan Redirect
4xx Yellow Client error
5xx Red Server error

Filtering¶

Exclude Paths¶

Common paths like health checks and metrics are often excluded from logs to reduce noise:

# These paths are typically excluded by the logging middleware:
# /health, /metrics, /favicon.ico

Reducing Log Noise

If your application has a health check endpoint that is polled frequently (e.g., by Kubernetes), the default logging middleware keeps logs clean by focusing on application routes.

Performance¶

The logging middleware is implemented in Rust with asynchronous I/O:

Operation Overhead
Log entry creation ~100ns
Async write to stdout ~200ns
Total per request ~300ns

The middleware uses buffered, non-blocking writes so logging does not slow down request processing.

Combining with Other Middleware¶

Place the logging middleware after authentication but before compression so that logs include authenticated user context:

app = App()

# Recommended order
app.enable_cors()
app.use(JwtAuth(jwt_config))   # Auth runs first
app.enable_logging()            # Log with auth context
app.enable_compression()        # Compress after logging

CLI Options¶

Control logging from the command line:

# Enable logging (default in development)
python app.py

# Disable logging
python app.py --no-logs

# Debug mode (always enables logging)
python app.py --debug

Next Steps¶