Content Type

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Overview

• JSON-only API endpoints
• Form submission validation
• Content-Type enforcement
• Default response types

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Installation

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

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Quick Start

app := mizu.New()

// Require JSON for all POST/PUT/PATCH requests
app.Use(contenttype.RequireJSON())

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Functions

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Request Validation

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Response Headers

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Examples

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Require JSON

// Only accept JSON requests
app.Use(contenttype.RequireJSON())

app.Post("/api/users", func(c *mizu.Ctx) error {
    // Guaranteed to receive JSON
    var user User
    if err := c.BindJSON(&user); err != nil {
        return err
    }
    return c.JSON(201, user)
})

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Require Form Data

// Only accept form submissions
app.Post("/contact", contactHandler, contenttype.RequireForm())

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Multiple Content Types

// Accept either JSON or XML
app.Use(contenttype.Require("application/json", "application/xml"))

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Set Default Content-Type

// Set default for requests without Content-Type
app.Use(contenttype.Default("application/json"))

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Set Response Content-Type

// All responses are JSON
app.Use(contenttype.SetResponse("application/json; charset=utf-8"))

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Per-Route Configuration

// API routes: JSON only
api := app.Group("/api")
api.Use(contenttype.RequireJSON())

// Form routes: Form data only
forms := app.Group("/forms")
forms.Use(contenttype.RequireForm())

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Combined Request/Response

// Require JSON input, set JSON output
app.Use(contenttype.RequireJSON())
app.Use(contenttype.SetResponse("application/json; charset=utf-8"))

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API Reference

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Functions

// Require specific content types
func Require(types ...string) mizu.Middleware

// RequireJSON requires application/json
func RequireJSON() mizu.Middleware

// RequireForm requires form content types
func RequireForm() mizu.Middleware

// Default sets default Content-Type if not present
func Default(contentType string) mizu.Middleware

// SetResponse sets response Content-Type
func SetResponse(contentType string) mizu.Middleware

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Behavior

• Only validates POST, PUT, PATCH requests (methods with bodies)
• Compares media type only, ignores parameters (charset, boundary)
• Returns 415 Unsupported Media Type on validation failure

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Common Content Types

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Technical Details

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Implementation Overview

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Request Validation (Require, RequireJSON, RequireForm)

1. Method Filtering: Only validates requests with body content (POST, PUT, PATCH). GET, DELETE, and other methods bypass validation.
2. Header Extraction: Retrieves the Content-Type header from the incoming request.
3. Media Type Parsing: Extracts the base media type by:
   • Finding the semicolon separator (if present)
   • Stripping parameters (charset, boundary, etc.)
   • Trimming whitespace from the result
4. Case-Insensitive Matching: Compares the extracted media type against allowed types using case-insensitive comparison.
5. Error Response: Returns HTTP 415 (Unsupported Media Type) if:
   • Content-Type header is missing (for methods that require it)
   • The media type doesn’t match any allowed types

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Default Content-Type (Default)

• Checks if the Content-Type header exists
• Sets the header to the specified default value if missing
• Preserves existing headers without modification

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Response Content-Type (SetResponse)

• Unconditionally sets the response Content-Type header
• Executes before the handler processes the request
• Can be combined with request validation middleware

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Key Design Decisions

• Parameter Stripping: Media type parameters are ignored during validation, allowing application/json; charset=utf-8 to match application/json
• Method-Specific: Only methods with request bodies are validated
• Fail-Fast: Validation happens before the handler executes
• Composable: Multiple middleware can be chained for complex scenarios

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Best Practices

• Use RequireJSON() for REST APIs
• Use RequireForm() for traditional forms
• Set response Content-Type for consistency
• Combine Default() with Require() to provide fallback behavior
• Apply validation at the router group level for route-specific rules

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Testing

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Test Cases

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Related Middlewares

• bodylimit - Body size limits
• validator - Request validation