Conditional

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Overview

• Skip middleware for certain routes
• Apply middleware conditionally
• Dynamic middleware chains

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Installation

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

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Quick Start

app := mizu.New()

// Only apply auth for /api routes
app.Use(conditional.If(
    func(c *mizu.Ctx) bool {
        return strings.HasPrefix(c.Request().URL.Path, "/api")
    },
    authMiddleware,
))

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Examples

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Path-Based

// Skip for health checks
app.Use(conditional.Unless(
    func(c *mizu.Ctx) bool {
        return c.Request().URL.Path == "/health"
    },
    rateLimitMiddleware,
))

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Method-Based

// Only for mutations
app.Use(conditional.If(
    func(c *mizu.Ctx) bool {
        m := c.Request().Method
        return m == "POST" || m == "PUT" || m == "DELETE"
    },
    csrfMiddleware,
))

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Header-Based

// Only for API requests
app.Use(conditional.If(
    func(c *mizu.Ctx) bool {
        return c.Request().Header.Get("Accept") == "application/json"
    },
    apiMiddleware,
))

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Combine Conditions

app.Use(conditional.If(
    conditional.And(
        conditional.PathPrefix("/api"),
        conditional.Not(conditional.Path("/api/public")),
    ),
    authMiddleware,
))

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API Reference

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Functions

// If applies middleware when condition is true
func If(cond func(*mizu.Ctx) bool, m mizu.Middleware) mizu.Middleware

// Unless applies middleware when condition is false
func Unless(cond func(*mizu.Ctx) bool, m mizu.Middleware) mizu.Middleware

// Condition helpers
func Path(path string) func(*mizu.Ctx) bool
func PathPrefix(prefix string) func(*mizu.Ctx) bool
func Method(methods ...string) func(*mizu.Ctx) bool
func Header(key, value string) func(*mizu.Ctx) bool
func And(conditions ...func(*mizu.Ctx) bool) func(*mizu.Ctx) bool
func Or(conditions ...func(*mizu.Ctx) bool) func(*mizu.Ctx) bool
func Not(cond func(*mizu.Ctx) bool) func(*mizu.Ctx) bool

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Technical Details

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HTTP Conditional Request Processing

1. Response Capture: The middleware intercepts the response using a custom responseCapture writer that buffers both the status code and body content before sending it to the client.
2. ETag Generation: By default, ETags are generated using MD5 hashing of the response body. The middleware supports both strong and weak ETags:
   • Strong ETag: "hash-value"
   • Weak ETag: W/"hash-value"
3. Last-Modified Handling: When a ModTimeFunc is provided, the middleware sets the Last-Modified header and processes If-Modified-Since conditional requests.

1. Check if request method is GET or HEAD (only these methods support conditional requests)
2. Capture the response body and status code
3. Generate ETag from response body (if enabled)
4. Set Last-Modified header (if configured)
5. Check If-None-Match header against ETag
6. Check If-Modified-Since header against modification time
7. Return 304 Not Modified if conditions match, or send full response

• The middleware buffers the entire response body for ETag generation
• MD5 hashing is used for ETag (not for security, just content fingerprinting)
• Only processes 2xx status codes to avoid caching errors
• Skips processing for non-GET/HEAD methods

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Security Considerations

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Best Practices

• Use clear condition names
• Keep conditions simple
• Document conditional behavior
• Test edge cases
• Consider response size when buffering for ETag generation
• Use weak ETags for frequently changing content
• Combine ETag and Last-Modified for optimal caching
• Provide custom ETagFunc for better performance with large responses

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Testing

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Related Middlewares

• filter - Request filtering
• feature - Feature flags