Templ HTTP

Templ HTTP Integration

Overview

Connect templ components to Go's net/http server. Render components in HTTP handlers and serve dynamic HTML pages.

When to Use This Skill

Use when:

• Setting up HTTP server with templ
• Creating route handlers
• User mentions "serve templ", "HTTP server", "web server"
• Connecting components to routes
• Rendering templ in handlers

Basic Integration

Simple Handler

package main

import (
    "net/http"
    "myapp/components"
)

func homeHandler(w http.ResponseWriter, r *http.Request) {
    components.HomePage().Render(r.Context(), w)
}

func main() {
    http.HandleFunc("/", homeHandler)
    http.ListenAndServe(":8080", nil)
}

Handler with Data

func userHandler(w http.ResponseWriter, r *http.Request) {
    user := getUserFromDB(r.URL.Query().Get("id"))

    components.UserProfile(user).Render(r.Context(), w)
}

Rendering Patterns

Pattern 1: Direct Render

func handler(w http.ResponseWriter, r *http.Request) {
    component := components.Page("Title")
    component.Render(r.Context(), w)
}

Pattern 2: Error Handling

func handler(w http.ResponseWriter, r *http.Request) {
    err := components.Page("Title").Render(r.Context(), w)
    if err != nil {
        http.Error(w, "Render failed", http.StatusInternalServerError)
        log.Printf("Render error: %v", err)
    }
}

Pattern 3: With Layout

func pageHandler(w http.ResponseWriter, r *http.Request) {
    content := components.PageContent()

    components.Layout("Page Title", content).Render(r.Context(), w)
}

Routing

ServeMux

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

    // Static pages
    mux.HandleFunc("/", homeHandler)
    mux.HandleFunc("/about", aboutHandler)

    // Dynamic routes
    mux.HandleFunc("/user/", userHandler)
    mux.HandleFunc("/post/", postHandler)

    // Static files
    fs := http.FileServer(http.Dir("static"))
    mux.Handle("/static/", http.StripPrefix("/static/", fs))

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

RESTful Routes

func usersHandler(w http.ResponseWriter, r *http.Request) {
    switch r.Method {
    case "GET":
        users := getAllUsers()
        components.UserList(users).Render(r.Context(), w)

    case "POST":
        // Handle create
        user := createUser(r)
        components.UserCard(user).Render(r.Context(), w)

    default:
        http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
    }
}

Request Data

Query Parameters

func searchHandler(w http.ResponseWriter, r *http.Request) {
    query := r.URL.Query().Get("q")
    page := r.URL.Query().Get("page")

    results := search(query, page)

    components.SearchResults(query, results).Render(r.Context(), w)
}

Form Data

func loginHandler(w http.ResponseWriter, r *http.Request) {
    if r.Method == "GET" {
        components.LoginForm().Render(r.Context(), w)
        return
    }

    // POST
    r.ParseForm()
    email := r.FormValue("email")
    password := r.FormValue("password")

    if authenticate(email, password) {
        http.Redirect(w, r, "/dashboard", http.StatusSeeOther)
    } else {
        components.LoginForm("Invalid credentials").Render(r.Context(), w)
    }
}

Path Parameters

// /user/123
func userHandler(w http.ResponseWriter, r *http.Request) {
    // Extract ID from path
    path := strings.TrimPrefix(r.URL.Path, "/user/")
    userID := path

    user := getUserByID(userID)
    if user == nil {
        http.NotFound(w, r)
        return
    }

    components.UserProfile(user).Render(r.Context(), w)
}

Middleware

Logging Middleware

func loggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        log.Printf("%s %s", r.Method, r.URL.Path)
        next.ServeHTTP(w, r)
    })
}

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/", homeHandler)

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

Auth Middleware

func authMiddleware(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        session := getSession(r)
        if session == nil {
            http.Redirect(w, r, "/login", http.StatusSeeOther)
            return
        }

        next(w, r)
    }
}

// Usage
http.HandleFunc("/dashboard", authMiddleware(dashboardHandler))

Error Handling

Custom Error Pages

func errorHandler(w http.ResponseWriter, r *http.Request, status int, message string) {
    w.WriteHeader(status)
    components.ErrorPage(status, message).Render(r.Context(), w)
}

func userHandler(w http.ResponseWriter, r *http.Request) {
    user, err := getUserByID(r.URL.Query().Get("id"))
    if err != nil {
        errorHandler(w, r, 500, "Failed to load user")
        return
    }
    if user == nil {
        errorHandler(w, r, 404, "User not found")
        return
    }

    components.UserProfile(user).Render(r.Context(), w)
}

Error Component

// components/error.templ
package components

templ ErrorPage(code int, message string) {
    @Layout("Error") {
        <div class="error-page">
            <h1>{ strconv.Itoa(code) }</h1>
            <p>{ message }</p>
            <a href="/">Go Home</a>
        </div>
    }
}

Static Files

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

    // Serve static files
    fs := http.FileServer(http.Dir("static"))
    mux.Handle("/static/", http.StripPrefix("/static/", fs))

    // Routes
    mux.HandleFunc("/", homeHandler)

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

Context Usage

Passing Data via Context

func contextMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        ctx := context.WithValue(r.Context(), "userID", "123")
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

func handler(w http.ResponseWriter, r *http.Request) {
    userID := r.Context().Value("userID").(string)

    components.Page(userID).Render(r.Context(), w)
}

Full Example

package main

import (
    "log"
    "net/http"
    "myapp/components"
)

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

    // Static files
    fs := http.FileServer(http.Dir("static"))
    mux.Handle("/static/", http.StripPrefix("/static/", fs))

    // Routes
    mux.HandleFunc("/", homeHandler)
    mux.HandleFunc("/about", aboutHandler)
    mux.HandleFunc("/contact", contactHandler)

    // Start server
    addr := ":8080"
    log.Printf("Server starting on %s", addr)
    if err := http.ListenAndServe(addr, mux); err != nil {
        log.Fatal(err)
    }
}

func homeHandler(w http.ResponseWriter, r *http.Request) {
    components.HomePage().Render(r.Context(), w)
}

func aboutHandler(w http.ResponseWriter, r *http.Request) {
    components.AboutPage().Render(r.Context(), w)
}

func contactHandler(w http.ResponseWriter, r *http.Request) {
    if r.Method == "GET" {
        components.ContactForm().Render(r.Context(), w)
        return
    }

    // POST
    r.ParseForm()
    name := r.FormValue("name")
    email := r.FormValue("email")
    message := r.FormValue("message")

    // Send email...

    components.ContactSuccess(name).Render(r.Context(), w)
}

Best Practices

1. Always use r.Context() when rendering
2. Handle errors from Render()
3. Set appropriate status codes before rendering
4. Use middleware for common functionality
5. Separate routes from handler logic
6. Return early on errors

Common Patterns

Pattern: Redirect After Post

func formHandler(w http.ResponseWriter, r *http.Request) {
    if r.Method == "GET" {
        components.Form().Render(r.Context(), w)
        return
    }

    // POST - process form
    processForm(r)

    // Redirect
    http.Redirect(w, r, "/success", http.StatusSeeOther)
}

Pattern: JSON API + HTML

func usersHandler(w http.ResponseWriter, r *http.Request) {
    users := getUsers()

    // Check Accept header
    if r.Header.Get("Accept") == "application/json" {
        w.Header().Set("Content-Type", "application/json")
        json.NewEncoder(w).Encode(users)
        return
    }

    // Default: HTML
    components.UserList(users).Render(r.Context(), w)
}

Next Steps

• Add interactivity → Use templ-htmx skill
• Style components → Use templ-css skill
• Deploy → Use templ-deployment skill