Last Modified

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Overview

• Date-based caching
• Conditional GET requests
• Bandwidth optimization

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Installation

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

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Quick Start

app := mizu.New()

app.Use(lastmodified.New())

app.Get("/resource", func(c *mizu.Ctx) error {
    lastmodified.Set(c, resource.UpdatedAt)
    return c.JSON(200, resource)
})

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Examples

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Set Last-Modified

app.Get("/article/:id", func(c *mizu.Ctx) error {
    article := getArticle(c.Param("id"))
    lastmodified.Set(c, article.UpdatedAt)
    return c.JSON(200, article)
})

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Auto Last-Modified

app.Use(lastmodified.Auto(func(c *mizu.Ctx) time.Time {
    // Return modification time based on request
    return getModTime(c.Request().URL.Path)
}))

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Static Files

// Last-Modified is automatic for static files
app.Use(static.New("./public"))

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How It Works

1. Handler sets Last-Modified
2. Client receives Last-Modified header
3. Next request includes If-Modified-Since
4. If not modified, returns 304 Not Modified
5. If modified, returns full response

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API Reference

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Functions

// New creates Last-Modified middleware
func New() mizu.Middleware

// Set sets Last-Modified for response
func Set(c *mizu.Ctx, t time.Time)

// Auto creates auto Last-Modified middleware
func Auto(getModTime func(*mizu.Ctx) time.Time) mizu.Middleware

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Technical Details

• Time Format: Uses HTTP-date format (RFC 5322) for Last-Modified headers
• Time Comparison: Truncates to seconds precision for accurate comparison
• Method Filtering: Only processes GET and HEAD requests
• Header Parsing: Uses http.ParseTime which supports multiple date formats
• 304 Response: Returns Not Modified when If-Modified-Since >= Last-Modified

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Implementation Features

• Options Configuration: Options struct allows customization with TimeFunc and SkipPaths
• Path Skipping: Can skip specific paths using the SkipPaths option
• Zero Time Handling: Skips middleware processing when time function returns zero time
• UTC Normalization: Automatically converts times to UTC before setting headers

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Helper Functions

• Static(t time.Time): Creates middleware with a fixed modification time
• Now(): Uses current time for each request (useful for development/testing)
• StartupTime(): Uses application startup time (useful for versioned assets)
• FromHeader(header string): Reads modification time from a custom request header

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Best Practices

• Use with ETag for robust caching
• Set accurate modification times
• Use for static and semi-static content
• Combine with Cache-Control

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Testing

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Related Middlewares

• etag - ETag generation
• cache - Cache-Control headers
• static - Static files