Go HTTP Server Routes (Go 1.22+)

Enhanced routing patterns for net/http.ServeMux introduced in Go 1.22.

Reference URLs

• https://go.dev/blog/routing-enhancements - Official announcement
• https://pkg.go.dev/net/http#ServeMux - ServeMux documentation

Method Matching

Specify HTTP methods directly in patterns:

mux := http.NewServeMux()

mux.HandleFunc("GET /posts/{id}", getPost)
mux.HandleFunc("POST /posts", createPost)
mux.HandleFunc("PUT /posts/{id}", updatePost)
mux.HandleFunc("DELETE /posts/{id}", deletePost)

• GET also matches HEAD requests
• All other methods match exactly
• Unmatched methods return 405 Method Not Allowed with Allow header

Wildcards

Single Segment: {name}

Matches exactly one path segment:

mux.HandleFunc("GET /users/{id}", func(w http.ResponseWriter, r *http.Request) {
    id := r.PathValue("id")
    fmt.Fprintf(w, "User ID: %s", id)
})

Remaining Segments: {name...}

Matches all remaining path segments:

mux.HandleFunc("GET /files/{pathname...}", func(w http.ResponseWriter, r *http.Request) {
    pathname := r.PathValue("pathname")
    // /files/docs/readme.txt -> pathname = "docs/readme.txt"
})

Exact Trailing Slash: {$}

Matches only the path with trailing slash:

mux.HandleFunc("GET /posts/{$}", listPosts)   // matches /posts/ only
mux.HandleFunc("GET /posts/{id}", getPost)    // matches /posts/123

PathValue API

Extract wildcard values from requests:

func getPost(w http.ResponseWriter, r *http.Request) {
    id := r.PathValue("id")
    // use id...
}

For third-party routers to integrate:

r.SetPathValue("id", "123")

Precedence Rules

The most specific pattern wins. A pattern is more specific if it matches a strict subset of requests.

Examples

Conflicts

Two patterns conflict if neither is more specific than the other. Registering conflicting patterns causes a panic.

// CONFLICT - will panic
mux.HandleFunc("/posts/{id}", handler1)
mux.HandleFunc("/{resource}/latest", handler2)
// Both match /posts/latest, neither is more specific

Host Precedence

Patterns with hosts take precedence over patterns without:

mux.HandleFunc("example.com/", hostHandler)  // wins for example.com
mux.HandleFunc("/", defaultHandler)          // wins for other hosts

Complete Example

package main

import (
    "encoding/json"
    "net/http"
)

func main() {
    mux := http.NewServeMux()

    mux.HandleFunc("GET /api/posts", listPosts)
    mux.HandleFunc("GET /api/posts/{id}", getPost)
    mux.HandleFunc("POST /api/posts", createPost)
    mux.HandleFunc("PUT /api/posts/{id}", updatePost)
    mux.HandleFunc("DELETE /api/posts/{id}", deletePost)

    mux.HandleFunc("GET /static/{filepath...}", serveStatic)

    http.ListenAndServe(":8080", mux)
}

func getPost(w http.ResponseWriter, r *http.Request) {
    id := r.PathValue("id")

    post, err := findPost(id)
    if err != nil {
        http.Error(w, "not found", http.StatusNotFound)
        return
    }

    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(post)
}

func serveStatic(w http.ResponseWriter, r *http.Request) {
    filepath := r.PathValue("filepath")
    http.ServeFile(w, r, "static/"+filepath)
}

Common Patterns

Resource CRUD

mux.HandleFunc("GET /api/{resource}", listHandler)
mux.HandleFunc("GET /api/{resource}/{id}", getHandler)
mux.HandleFunc("POST /api/{resource}", createHandler)
mux.HandleFunc("PUT /api/{resource}/{id}", updateHandler)
mux.HandleFunc("DELETE /api/{resource}/{id}", deleteHandler)

Nested Resources

mux.HandleFunc("GET /users/{userID}/posts", listUserPosts)
mux.HandleFunc("GET /users/{userID}/posts/{postID}", getUserPost)

Special Routes Before Wildcards

mux.HandleFunc("GET /posts/latest", getLatestPost)  // more specific
mux.HandleFunc("GET /posts/{id}", getPost)          // less specific

Compatibility

For code that relied on pre-1.22 behavior (literal braces in patterns):

GODEBUG=httpmuxgo121=1 ./myapp

Common Mistakes

• Forgetting method prefix - /posts/{id} matches all methods
• Conflicting patterns - causes panic at registration, not runtime
• Missing {$} - /posts/ matches /posts/anything, use /posts/{$} for exact match
• Wildcard naming - {id} and {identifier} are different wildcards, name doesn't affect precedence