# servemux

This rule guides Go projects using http.ServeMux, with patterns for organizing handlers and routes. It’s aimed at API work with Go 1.22+.

- rule · `type=rule` · Cursor · ★ 3580
- Author: sanjeed5
- License: CC0-1.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/servemux.mdc
- Updated: 2026-05-19
- HTML: https://affpapa.org/en/nevibecode/rules/servemux

## What it does

The rule targets `**/*.go` files. It recommends creating one `http.ServeMux` at the application entry point, keeping handlers in a separate package, and passing business logic through interfaces. Route examples use HTTP method patterns, path values, and `{$}` for exact matches.

The examples also cover JSON decoding and HTTP responses. They contrast this structure with a global `http.DefaultServeMux`, handler logic in `main`, and manual method checks. The routing patterns described rely on Go 1.22 or later.

## Install

### Cursor (native platform)

**Manually: put the files in place**
- File: `.cursor/rules/servemux.mdc` — Frontmatter: description, globs, alwaysApply

### Claude Code

**Manually: put the files in place**
- File: `.claude/rules/servemux.md` — The paths frontmatter field limits the files: move globs from the source into paths

### Codex

**AGENTS.md**
- Codex reads AGENTS.md: paste the rule text there

### GitHub Copilot

**Manually: put the files in place**
- File: `.github/instructions/servemux.instructions.md` — The applyTo field sets which files it applies to: move globs from the source into applyTo

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/rules/servemux.md`

### Cline

**Manually: put the files in place**
- File: `.clinerules/servemux.md`

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/servemux.mdc

## When to use it
- separate route setup from handler code
- match routes by HTTP method
- read URL parameters with `PathValue`
- require an exact path match with `{$}`
- decode JSON requests and write HTTP responses

## Example prompts
- Organize my Go `http.ServeMux` routes using the servemux rule.
- Review these API routes and apply the servemux guidance for methods and path parameters.
- Refactor these handlers to receive business logic through an interface.

## Source text · servemux.mdc · CC0-1.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 51d7a8fbec41bde2.

BEGIN THIRD-PARTY FILE 51d7a8fbec41bde2
````text
---
description: This rule file provides definitive guidelines for using Go's `http.ServeMux` effectively, leveraging Go 1.22+ features for robust, maintainable, and secure API development.
globs: **/*.go
---
# servemux Best Practices

Go's `http.ServeMux`, especially with the enhancements in Go 1.22+, is the definitive choice for building performant and maintainable HTTP services. This guide outlines the best practices for its use.

## 1. Code Organization and Structure

Organize your application for clarity, testability, and scalability.

### ✅ GOOD: Centralized Mux Assembly, Dedicated Handlers

Create a single `http.ServeMux` instance in your application's entry point (`cmd/server/main.go`) and register handlers from a dedicated `handlers` package. Inject business logic into handlers via interfaces.

```go
// cmd/server/main.go
package main

import (
	"context"
	"log"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"yourproject/internal/handlers"
	"yourproject/internal/service" // Business logic interface
)

func main() {
	logger := log.New(os.Stdout, "API: ", log.Ldate|log.Ltime|log.Lshortfile)

	// Initialize business logic (e.g., database connection)
	userService := service.NewUserService(logger) // Assume concrete implementation

	// Create and configure the mux
	mux := http.NewServeMux()
	handlers.RegisterRoutes(mux, logger, userService) // Pass dependencies

	server := &http.Server{
		Addr:         ":8080",
		Handler:      mux,
		ReadTimeout:  5 * time.Second,
		WriteTimeout: 10 * time.Second,
		IdleTimeout:  120 * time.Second,
		ErrorLog:     logger,
	}

	// Start server in a goroutine
	go func() {
		logger.Printf("Server starting on %s", server.Addr)
		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			logger.Fatalf("Could not listen on %s: %v\n", server.Addr, err)
		}
	}()

	// Graceful shutdown
	quit := make(chan os.Signal, 1)
	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
	<-quit
	logger.Println("Server shutting down...")

	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	if err := server.Shutdown(ctx); err != nil {
		logger.Fatalf("Server forced to shutdown: %v", err)
	}
	logger.Println("Server exited gracefully")
}

// internal/handlers/user.go
package handlers

import (
	"encoding/json"
	"log"
	"net/http"
	"strconv"
	"yourproject/internal/service" // Business logic interface
)

// UserService defines the interface for user-related business logic.
type UserService interface {
	GetUser(id int) (*service.User, error)
	CreateUser(user *service.User) error
	// ... other user methods
}

// UserHandlers holds dependencies for user-related HTTP handlers.
type UserHandlers struct {
	log *log.Logger
	svc UserService
}

// RegisterRoutes registers all user-related HTTP routes with the given mux.
func RegisterRoutes(mux *http.ServeMux, logger *log.Logger, userService UserService) {
	uh := &UserHandlers{
		log: logger,
		svc: userService,
	}

	mux.HandleFunc("GET /users/{id}", uh.GetUser)
	mux.HandleFunc("POST /users", uh.CreateUser)
	// ... other route registrations
}

// GetUser handles GET requests for /users/{id}
func (uh *UserHandlers) GetUser(w http.ResponseWriter, r *http.Request) {
	idStr := r.PathValue("id")
	id, err := strconv.Atoi(idStr)
	if err != nil {
		uh.respondWithError(w, http.StatusBadRequest, "Invalid user ID")
		return
	}

	user, err := uh.svc.GetUser(id)
	if err != nil {
		uh.respondWithError(w, http.StatusNotFound, "User not found")
		return
	}

	uh.respondWithJSON(w, http.StatusOK, user)
}

// CreateUser handles POST requests for /users
func (uh *UserHandlers) CreateUser(w http.ResponseWriter, r *http.Request) {
	var user service.User // Assuming service.User is the DTO
	if err := json.NewDecoder(r.Body).Decode(&user); err != nil {
		uh.respondWithError(w, http.StatusBadRequest, "Invalid request payload")
		return
	}

	if err := uh.svc.CreateUser(&user); err != nil {
		uh.respondWithError(w, http.StatusInternalServerError, "Failed to create user")
		return
	}

	uh.respondWithJSON(w, http.StatusCreated, user)
````
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