Expvar

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Overview

• Go runtime metrics
• Memory usage monitoring
• Custom variable export

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Installation

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

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Quick Start

app := mizu.New()

// Expose expvar endpoint
app.Get("/debug/vars", expvar.Handler())

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Examples

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Basic Setup

app.Get("/debug/vars", expvar.Handler())

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Custom Variables

import "expvar"

// Publish custom variable
var requests = expvar.NewInt("requests")

app.Use(func(next mizu.Handler) mizu.Handler {
    return func(c *mizu.Ctx) error {
        requests.Add(1)
        return next(c)
    }
})

app.Get("/debug/vars", expvar.Handler())

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With Auth Protection

debug := app.Group("/debug")
debug.Use(basicauth.New(adminCredentials))
debug.Get("/vars", expvar.Handler())

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Default Variables

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API Reference

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Functions

// Handler returns expvar HTTP handler
func Handler() mizu.Handler

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Response Format

{
    "cmdline": ["./myapp"],
    "memstats": {
        "Alloc": 1234567,
        "TotalAlloc": 9876543,
        "Sys": 12345678,
        ...
    },
    "requests": 42
}

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Technical Details

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Standard Library Integration

• Uses expvar.Handler() to serve the variables endpoint
• Exports all published variables as JSON
• Includes built-in cmdline and memstats variables

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Path Matching

• Only intercepts requests to the configured path (default: /debug/vars)
• All other requests pass through to the next handler
• Efficient path comparison using string equality

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Helper Functions

• NewInt(name): Creates and publishes an expvar.Int
• NewFloat(name): Creates and publishes an expvar.Float
• NewString(name): Creates and publishes an expvar.String
• NewMap(name): Creates and publishes an expvar.Map

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Thread Safety

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Best Practices

• Protect endpoint in production
• Use for debugging and monitoring
• Combine with custom metrics
• Don’t expose sensitive data

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Testing

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Related Middlewares

• prometheus - Prometheus metrics
• pprof - Profiling
• healthcheck - Health checks