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RoutingBasic Routing

Basic Routing

Steel provides a fast and flexible routing system built on a radix tree for optimal performance. Learn the fundamentals of URL routing, parameter extraction, and route organization.

Creating a Router

import router "github.com/xraph/steel"
 
func main() {
    r := router.NewRouter()
 
    // Your routes here...
 
    log.Fatal(http.ListenAndServe(":8080", r))
}

HTTP Methods

Steel supports all standard HTTP methods:

r := router.NewRouter()
 
r.GET("/users", getUsersHandler)
r.POST("/users", createUserHandler)
r.PUT("/users/:id", updateUserHandler)
r.DELETE("/users/:id", deleteUserHandler)
r.PATCH("/users/:id", patchUserHandler)
r.HEAD("/users/:id", headUserHandler)
r.OPTIONS("/users", optionsHandler)

Generic Handler Registration

You can also use the generic Handle method:

r.Handle("GET", "/users", getUsersHandler)
r.Handle("POST", "/users", createUserHandler)
 
// Or with http.HandlerFunc
r.HandleFunc("GET", "/health", func(w http.ResponseWriter, r *http.Request) {
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("OK"))
})

Path Parameters

Extract dynamic values from URLs using path parameters:

Basic Parameters

// Single parameter
r.GET("/users/:id", func(w http.ResponseWriter, r *http.Request) {
    userID := router.URLParam(r, "id")
    fmt.Fprintf(w, "User ID: %s", userID)
})
 
// Multiple parameters
r.GET("/users/:userId/posts/:postId", func(w http.ResponseWriter, r *http.Request) {
    userID := router.URLParam(r, "userId")
    postID := router.URLParam(r, "postId")
    fmt.Fprintf(w, "User: %s, Post: %s", userID, postID)
})

URL Examples

// Route: /users/:id
"/users/123"           // id = "123"
"/users/abc"           // id = "abc"
"/users/user-456"      // id = "user-456"
 
// Route: /users/:userId/posts/:postId
"/users/123/posts/456" // userId = "123", postId = "456"
"/users/john/posts/my-first-post" // userId = "john", postId = "my-first-post"

Parameter Constraints

While Steel doesn’t have built-in parameter constraints, you can validate them in your handlers:

r.GET("/users/:id", func(w http.ResponseWriter, r *http.Request) {
    idStr := router.URLParam(r, "id")
 
    // Validate numeric ID
    id, err := strconv.Atoi(idStr)
    if err != nil {
        http.Error(w, "Invalid user ID", http.StatusBadRequest)
        return
    }
 
    if id <= 0 {
        http.Error(w, "User ID must be positive", http.StatusBadRequest)
        return
    }
 
    // Continue with valid ID...
    fmt.Fprintf(w, "Valid user ID: %d", id)
})

Wildcard Routes

Use wildcards to match any path under a prefix:

// Catch-all wildcard
r.GET("/static/*", func(w http.ResponseWriter, r *http.Request) {
    // Serves any file under /static/
    filePath := r.URL.Path[len("/static/"):]
    fmt.Fprintf(w, "Serving file: %s", filePath)
})
 
// File server example
r.GET("/assets/*", func(w http.ResponseWriter, r *http.Request) {
    fs := http.FileServer(http.Dir("./assets/"))
    http.StripPrefix("/assets/", fs).ServeHTTP(w, r)
})

Wildcard Examples

// Route: /static/*
"/static/css/style.css"     // Matches
"/static/js/app.js"         // Matches
"/static/images/logo.png"   // Matches
"/static/fonts/arial.woff"  // Matches
 
// Route: /api/v1/*
"/api/v1/users"             // Matches
"/api/v1/users/123"         // Matches
"/api/v1/posts/456/comments" // Matches

Route Priority

Steel matches routes in this order:

  1. Static routes (exact matches)
  2. Parameter routes (:param)
  3. Wildcard routes (*)
r.GET("/users/admin", staticHandler)     // Highest priority
r.GET("/users/:id", paramHandler)       // Medium priority
r.GET("/users/*", wildcardHandler)      // Lowest priority
 
// URL: /users/admin -> staticHandler
// URL: /users/123   -> paramHandler
// URL: /users/admin/settings -> wildcardHandler

Specific vs Generic Routes

When defining routes, place more specific routes before generic ones:

// âś… Good: Specific routes first
r.GET("/api/health", healthHandler)
r.GET("/api/version", versionHandler)
r.GET("/api/:resource", genericHandler)
 
// ❌ Avoid: Generic route would catch everything
r.GET("/api/:resource", genericHandler)
r.GET("/api/health", healthHandler)      // Never reached!

Route Groups

Organize related routes using route groups:

Basic Grouping

r.Route("/api", func(api router.Router) {
    api.GET("/users", getUsersHandler)
    api.POST("/users", createUserHandler)
    api.GET("/posts", getPostsHandler)
})
 
// Creates routes:
// GET  /api/users
// POST /api/users
// GET  /api/posts

Nested Groups

r.Route("/api", func(api router.Router) {
    api.Route("/v1", func(v1 router.Router) {
        v1.Route("/users", func(users router.Router) {
            users.GET("/", listUsersHandler)
            users.POST("/", createUserHandler)
            users.GET("/:id", getUserHandler)
            users.PUT("/:id", updateUserHandler)
            users.DELETE("/:id", deleteUserHandler)
        })
    })
})
 
// Creates routes:
// GET    /api/v1/users/
// POST   /api/v1/users/
// GET    /api/v1/users/:id
// PUT    /api/v1/users/:id
// DELETE /api/v1/users/:id

Practical Example

func setupRoutes() *router.SteelRouter {
    r := router.NewRouter()
 
    // Public routes
    r.GET("/", homeHandler)
    r.GET("/health", healthHandler)
 
    // API v1
    r.Route("/api/v1", func(v1 router.Router) {
        // Public API endpoints
        v1.GET("/products", getProductsHandler)
        v1.GET("/products/:id", getProductHandler)
 
        // User management
        v1.Route("/users", func(users router.Router) {
            users.POST("/register", registerHandler)
            users.POST("/login", loginHandler)
 
            // Protected user routes would go here with middleware
        })
 
        // Admin endpoints
        v1.Route("/admin", func(admin router.Router) {
            // Admin routes would include auth middleware
            admin.GET("/stats", getStatsHandler)
            admin.GET("/users", getAllUsersHandler)
        })
    })
 
    return r
}

Mounting Sub-Routers

Mount existing HTTP handlers or sub-applications:

Basic Mounting

// Mount a file server
fileServer := http.FileServer(http.Dir("./uploads/"))
r.Mount("/uploads", fileServer)
 
// Mount another HTTP handler
adminMux := http.NewServeMux()
adminMux.HandleFunc("/dashboard", dashboardHandler)
adminMux.HandleFunc("/settings", settingsHandler)
r.Mount("/admin", adminMux)

Mounting with Middleware

// Create a sub-router with its own middleware
apiV2 := router.NewRouter()
apiV2.Use(v2AuthMiddleware)
apiV2.Use(v2RateLimitMiddleware)
apiV2.GET("/users", v2GetUsersHandler)
apiV2.POST("/users", v2CreateUserHandler)
 
// Mount the sub-router
r.Mount("/api/v2", apiV2)

Real-world Example

func main() {
    r := router.NewRouter()
 
    // Mount Prometheus metrics
    r.Mount("/metrics", promhttp.Handler())
 
    // Mount pprof for debugging (development only)
    if os.Getenv("ENV") == "development" {
        r.Mount("/debug", http.DefaultServeMux)
    }
 
    // Mount static file servers
    r.Mount("/static", http.FileServer(http.Dir("./static/")))
    r.Mount("/uploads", http.FileServer(http.Dir("./uploads/")))
 
    // Mount API documentation
    docsHandler := http.FileServer(http.Dir("./docs/"))
    r.Mount("/docs", http.StripPrefix("/docs", docsHandler))
 
    // Your API routes
    r.Route("/api", func(api router.Router) {
        // API routes here...
    })
 
    log.Fatal(http.ListenAndServe(":8080", r))
}

Query Parameters

Access query parameters using the standard library or Context:

Standard Way

r.GET("/search", func(w http.ResponseWriter, r *http.Request) {
    query := r.URL.Query().Get("q")
    page := r.URL.Query().Get("page")
    limit := r.URL.Query().Get("limit")
 
    fmt.Fprintf(w, "Query: %s, Page: %s, Limit: %s", query, page, limit)
})

With Context

r.GET("/search", func(w http.ResponseWriter, r *http.Request) {
    ctx := &router.Context{
        Request:  r,
        Response: w,
    }
 
    query := ctx.Query("q")
    page := ctx.Query("page")
    limit := ctx.Query("limit")
 
    fmt.Fprintf(w, "Query: %s, Page: %s, Limit: %s", query, page, limit)
})

Query Parameter Examples

// URL: /search?q=golang&page=2&limit=10&sort=date&order=desc
r.URL.Query().Get("q")     // "golang"
r.URL.Query().Get("page")  // "2"
r.URL.Query().Get("limit") // "10"
r.URL.Query().Get("sort")  // "date"
r.URL.Query().Get("order") // "desc"
r.URL.Query().Get("missing") // "" (empty string)
 
// Multiple values
// URL: /filter?tags=go&tags=web&tags=api
r.URL.Query()["tags"] // []string{"go", "web", "api"}

Headers

Access request headers:

r.GET("/api/data", func(w http.ResponseWriter, r *http.Request) {
    // Get specific headers
    contentType := r.Header.Get("Content-Type")
    userAgent := r.Header.Get("User-Agent")
    authorization := r.Header.Get("Authorization")
 
    // Custom headers
    requestID := r.Header.Get("X-Request-ID")
    apiKey := r.Header.Get("X-API-Key")
 
    // Check if header exists
    if auth := r.Header.Get("Authorization"); auth == "" {
        http.Error(w, "Authorization header required", http.StatusUnauthorized)
        return
    }
 
    // Set response headers
    w.Header().Set("Content-Type", "application/json")
    w.Header().Set("X-Response-ID", generateResponseID())
 
    // Response...
})

Request Body

Handle request bodies for POST, PUT, and PATCH requests:

JSON Body

type CreateUserRequest struct {
    Name  string `json:"name"`
    Email string `json:"email"`
    Age   int    `json:"age"`
}
 
r.POST("/users", func(w http.ResponseWriter, r *http.Request) {
    var req CreateUserRequest
 
    if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
        http.Error(w, "Invalid JSON", http.StatusBadRequest)
        return
    }
 
    // Validate request
    if req.Name == "" {
        http.Error(w, "Name is required", http.StatusBadRequest)
        return
    }
 
    // Process request...
    user := createUser(req.Name, req.Email, req.Age)
 
    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(user)
})

Form Data

r.POST("/contact", func(w http.ResponseWriter, r *http.Request) {
    if err := r.ParseForm(); err != nil {
        http.Error(w, "Invalid form data", http.StatusBadRequest)
        return
    }
 
    name := r.FormValue("name")
    email := r.FormValue("email")
    message := r.FormValue("message")
 
    // Process form...
    processContactForm(name, email, message)
 
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("Message sent"))
})

Raw Body

r.POST("/webhook", func(w http.ResponseWriter, r *http.Request) {
    body, err := io.ReadAll(r.Body)
    if err != nil {
        http.Error(w, "Failed to read body", http.StatusBadRequest)
        return
    }
 
    // Verify webhook signature
    signature := r.Header.Get("X-Signature")
    if !verifySignature(body, signature) {
        http.Error(w, "Invalid signature", http.StatusUnauthorized)
        return
    }
 
    // Process webhook...
    processWebhook(body)
 
    w.WriteHeader(http.StatusOK)
})

Router Configuration

Customize router behavior:

r := router.NewRouter()
 
// Configure trailing slash behavior
r.SetTrailingSlashRedirect(true)  // Redirect /users/ to /users
r.SetFixedPathRedirect(true)      // Handle case-insensitive redirects
 
// Custom 404 handler
r.SetNotFoundHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(http.StatusNotFound)
    json.NewEncoder(w).Encode(map[string]string{
        "error":   "Not Found",
        "message": "The requested resource was not found",
        "path":    r.URL.Path,
    })
}))
 
// Custom method not allowed handler
r.SetMethodNotAllowedHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(http.StatusMethodNotAllowed)
    json.NewEncoder(w).Encode(map[string]string{
        "error":   "Method Not Allowed",
        "message": fmt.Sprintf("Method %s is not allowed for this resource", r.Method),
        "path":    r.URL.Path,
    })
}))

Route Debugging

Debug your routes during development:

r := router.NewRouter()
 
// Add some routes
r.GET("/", homeHandler)
r.GET("/users/:id", getUserHandler)
r.POST("/users", createUserHandler)
r.GET("/static/*", staticHandler)
 
// Print route tree (development only)
if os.Getenv("ENV") == "development" {
    r.DebugRoutes()
}

Output example:

=== Steel Debug Info ===
Method: GET
  Path: "", HasHandler: true, IsParam: false, ParamName: "", Wildcard: false
  Path: "users", HasHandler: false, IsParam: false, ParamName: "", Wildcard: false
    Path: "", HasHandler: false, IsParam: true, ParamName: "id", Wildcard: false
  Path: "static", HasHandler: false, IsParam: false, ParamName: "", Wildcard: false
    Path: "", HasHandler: true, IsParam: false, ParamName: "", Wildcard: true

Method: POST
  Path: "users", HasHandler: true, IsParam: false, ParamName: "", Wildcard: false

Performance Considerations

Performance: Steel uses a radix tree for O(log n) route lookup and pools parameter objects to minimize allocations.

Route Organization

// âś… Good: Organize routes logically
r.Route("/api/v1", func(v1 router.Router) {
    v1.Route("/users", func(users router.Router) {
        users.GET("/", listUsers)
        users.POST("/", createUser)
        users.GET("/:id", getUser)
        users.PUT("/:id", updateUser)
        users.DELETE("/:id", deleteUser)
    })
})
 
// âś… Good: Group related functionality
r.Route("/admin", func(admin router.Router) {
    admin.Use(adminAuthMiddleware)
    // All admin routes here
})

Efficient Parameter Extraction

// âś… Efficient: Extract parameters once
r.GET("/users/:userId/posts/:postId", func(w http.ResponseWriter, r *http.Request) {
    params := router.ParamsFromContext(r.Context())
    userID := params.Get("userId")
    postID := params.Get("postId")
 
    // Use userID and postID...
})
 
// ❌ Less efficient: Multiple extractions
r.GET("/users/:userId/posts/:postId", func(w http.ResponseWriter, r *http.Request) {
    userID := router.URLParam(r, "userId")    // Extracts from context
    postID := router.URLParam(r, "postId")    // Extracts from context again
 
    // This works but is less efficient
})

Common Patterns

RESTful Resource Routes

func setupUserRoutes(r router.Router) {
    r.Route("/users", func(users router.Router) {
        users.GET("/", listUsers)           // GET /users
        users.POST("/", createUser)         // POST /users
        users.GET("/:id", getUser)          // GET /users/:id
        users.PUT("/:id", updateUser)       // PUT /users/:id
        users.PATCH("/:id", patchUser)      // PATCH /users/:id
        users.DELETE("/:id", deleteUser)    // DELETE /users/:id
 
        // Nested resources
        users.Route("/:id/posts", func(posts router.Router) {
            posts.GET("/", getUserPosts)    // GET /users/:id/posts
            posts.POST("/", createUserPost) // POST /users/:id/posts
        })
    })
}

API Versioning

func setupVersionedAPI(r *router.SteelRouter) {
    // Version 1
    r.Route("/api/v1", func(v1 router.Router) {
        v1.GET("/users", v1GetUsers)
        v1.POST("/users", v1CreateUser)
    })
 
    // Version 2 with breaking changes
    r.Route("/api/v2", func(v2 router.Router) {
        v2.Use(v2Middleware)
        v2.GET("/users", v2GetUsers)
        v2.POST("/users", v2CreateUser)
    })
 
    // Latest version alias
    r.Route("/api/latest", func(latest router.Router) {
        latest.GET("/users", v2GetUsers)
        latest.POST("/users", v2CreateUser)
    })
}

Content Negotiation

r.GET("/api/data", func(w http.ResponseWriter, r *http.Request) {
    data := getData()
 
    switch r.Header.Get("Accept") {
    case "application/xml":
        w.Header().Set("Content-Type", "application/xml")
        xml.NewEncoder(w).Encode(data)
    case "text/csv":
        w.Header().Set("Content-Type", "text/csv")
        writeCSV(w, data)
    default: // JSON
        w.Header().Set("Content-Type", "application/json")
        json.NewEncoder(w).Encode(data)
    }
})

Basic routing in Steel provides a solid foundation for building scalable web applications with clean, maintainable URL structures.

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