Logger

Documentation Index

Fetch the complete documentation index at: https://docs.go-mizu.dev/llms.txt

Use this file to discover all available pages before exploring further.

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Overview

• HTTP request logging
• Access logs for debugging
• Request timing metrics

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Installation

import "github.com/go-mizu/mizu/middlewares/logger"

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Quick Start

app := mizu.New()

// Default logger (stdout)
app.Use(logger.New())

app.Get("/", func(c *mizu.Ctx) error {
    return c.Text(200, "Hello!")
})
// Output: 2024/01/15 10:30:00 | 200 | 1.2ms | GET /

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Configuration

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Options

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Format Tags

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Examples

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Default Logger

app.Use(logger.New())

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Custom Format

app.Use(logger.WithOptions(logger.Options{
    Format: "[${method}] ${path} -> ${status}\n",
}))
// Output: [GET] /api/users -> 200

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JSON Format

app.Use(logger.WithOptions(logger.Options{
    Format: `{"method":"${method}","path":"${path}","status":${status},"latency":"${latency}"}` + "\n",
}))

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Write to File

file, _ := os.OpenFile("access.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)

app.Use(logger.WithOptions(logger.Options{
    Output: file,
}))

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Skip Health Checks

app.Use(logger.WithOptions(logger.Options{
    Skip: func(c *mizu.Ctx) bool {
        return c.Request().URL.Path == "/health"
    },
}))

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Include Request ID

app.Use(logger.WithOptions(logger.Options{
    Format: "${header:X-Request-ID} | ${method} ${path} | ${status}\n",
}))

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Full Access Log

app.Use(logger.WithOptions(logger.Options{
    Format: `${ip} - [${time}] "${method} ${path} ${protocol}" ${status} ${bytes_out} "${referer}" "${user_agent}"` + "\n",
}))

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API Reference

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Functions

// New creates logger middleware with defaults
func New() mizu.Middleware

// WithOptions creates logger middleware with configuration
func WithOptions(opts Options) mizu.Middleware

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Technical Details

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Implementation Architecture

1. Response Writer Wrapping: A custom responseWriter type wraps the standard http.ResponseWriter to capture:
   • HTTP status code (defaults to 200)
   • Response size in bytes
2. Timing Measurement: Uses time.Now() before request processing and time.Since() after to calculate latency with nanosecond precision.
3. Client IP Detection: Implements intelligent IP extraction with fallback chain:
   • Checks X-Forwarded-For header (uses first IP if comma-separated list)
   • Checks X-Real-IP header
   • Falls back to RemoteAddr from the request
4. Format String Processing: The formatLog function performs template tag replacement:
   • Basic tags use strings.ReplaceAll() for simple substitution
   • Dynamic tags (${header:name}, ${form:name}) use index-based parsing to extract custom values
   • Supports all standard HTTP request/response attributes
5. Skip Function: Optional predicate function allows conditional logging based on request context, executed before timing starts to avoid overhead.

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Performance Characteristics

• Minimal overhead: Single writer wrap and string replacement operations
• Zero allocations for skipped requests
• String concatenation deferred until after request completion
• No buffering of response body (streaming-friendly)

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Best Practices

• Skip logging for health check endpoints
• Use structured (JSON) format for log aggregation
• Include request IDs for tracing
• Log to stderr in containers for proper log handling

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Testing

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Related Middlewares

• requestid - Request ID generation
• requestlog - Detailed request logging
• audit - Audit logging
• timing - Server-Timing header