Gin

r := gin.New()

Custom middleware:

r := gin.New()
r.Use(gin.Logger())
r.Use(gin.Recovery())
r.Use(customMiddleware())

Routing

HTTP Methods

r.GET("/get", getHandler)
r.POST("/post", postHandler)
r.PUT("/put", putHandler)
r.DELETE("/delete", deleteHandler)
r.PATCH("/patch", patchHandler)
r.HEAD("/head", headHandler)
r.OPTIONS("/options", optionsHandler)

Path Parameters

// Match /user/john
r.GET("/user/:name", func(c *gin.Context) {
    name := c.Param("name")
    c.String(http.StatusOK, "Hello %s", name)
})

// Match /user/john/books
r.GET("/user/:name/:action", func(c *gin.Context) {
    name := c.Param("name")
    action := c.Param("action")
    c.String(http.StatusOK, "%s is %s", name, action)
})

Wildcard Routes

// Match /static/css/style.css or /static/js/app.js
r.GET("/static/*filepath", func(c *gin.Context) {
    filepath := c.Param("filepath")
    c.String(http.StatusOK, filepath)
})

Route Groups

v1 := r.Group("/v1")
{
    v1.GET("/users", listUsers)
    v1.POST("/users", createUser)
    v1.GET("/users/:id", getUser)
}

v2 := r.Group("/v2")
{
    v2.GET("/users", listUsersV2)
    v2.POST("/users", createUserV2)
}

Request Handling

Query Parameters

r.GET("/search", func(c *gin.Context) {
    // Default value if not provided
    query := c.DefaultQuery("q", "default")
    
    // Get query parameter (empty string if not exists)
    page := c.Query("page")
    
    // Get query parameter with existence check
    if name, ok := c.GetQuery("name"); ok {
        // name exists
    }
})

Form Data

r.POST("/form", func(c *gin.Context) {
    // Get form value
    username := c.PostForm("username")
    
    // Get with default value
    password := c.DefaultPostForm("password", "guest")
    
    // Get with existence check
    if email, ok := c.GetPostForm("email"); ok {
        // email exists
    }
})

JSON Binding

type Login struct {
    User     string `json:"user" binding:"required"`
    Password string `json:"password" binding:"required"`
}

r.POST("/login", func(c *gin.Context) {
    var json Login
    
    // Bind JSON - Returns 400 if validation fails
    if err := c.ShouldBindJSON(&json); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    
    c.JSON(http.StatusOK, gin.H{"user": json.User})
})

Query Binding

type Query struct {
    Name string `form:"name" binding:"required"`
    Age  int    `form:"age" binding:"gte=0"`
}

r.GET("/query", func(c *gin.Context) {
    var query Query
    if err := c.ShouldBindQuery(&query); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    c.JSON(http.StatusOK, query)
})

URI Binding

type User struct {
    ID int `uri:"id" binding:"required"`
}

r.GET("/users/:id", func(c *gin.Context) {
    var user User
    if err := c.ShouldBindUri(&user); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    c.JSON(http.StatusOK, gin.H{"id": user.ID})
})

File Upload

Single file:

r.POST("/upload", func(c *gin.Context) {
    file, err := c.FormFile("file")
    if err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    
    // Save file
    c.SaveUploadedFile(file, "uploads/" + file.Filename)
    c.JSON(http.StatusOK, gin.H{"filename": file.Filename})
})

Multiple files:

r.POST("/upload-multiple", func(c *gin.Context) {
    form, _ := c.MultipartForm()
    files := form.File["files"]
    
    for _, file := range files {
        c.SaveUploadedFile(file, "uploads/" + file.Filename)
    }
    c.JSON(http.StatusOK, gin.H{"count": len(files)})
})

Response Rendering

JSON Response

// gin.H is shortcut for map[string]interface{}
c.JSON(http.StatusOK, gin.H{
    "message": "success",
    "data": data,
})

// Or use struct
c.JSON(http.StatusOK, User{Name: "John", Age: 30})

// Pretty JSON with indentation
c.IndentedJSON(http.StatusOK, data)

// Secure JSON (prevents JSON hijacking)
c.SecureJSON(http.StatusOK, data)

// ASCII-only JSON
c.AsciiJSON(http.StatusOK, data)

// Pure JSON (don't replace special chars)
c.PureJSON(http.StatusOK, data)

XML Response

c.XML(http.StatusOK, gin.H{"message": "success"})

YAML Response

c.YAML(http.StatusOK, gin.H{"message": "success"})

TOML Response

c.TOML(http.StatusOK, gin.H{"message": "success"})

String Response

c.String(http.StatusOK, "Hello %s", name)

HTML Response

r.LoadHTMLGlob("templates/*")

r.GET("/index", func(c *gin.Context) {
    c.HTML(http.StatusOK, "index.html", gin.H{
        "title": "Main Page",
    })
})

File Response

// Serve file
c.File("/path/to/file.pdf")

// Serve file as attachment (download)
c.FileAttachment("/path/to/file.pdf", "download.pdf")

// Serve from filesystem
c.FileFromFS("index.html", http.Dir("./public"))

Redirect

// HTTP redirect
c.Redirect(http.StatusMovedPermanently, "https://google.com")

// Router redirect
c.Request.URL.Path = "/new-path"
r.HandleContext(c)

Middleware

Custom Middleware

func AuthRequired() gin.HandlerFunc {
    return func(c *gin.Context) {
        token := c.GetHeader("Authorization")
        if token == "" {
            c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{
                "error": "authorization required",
            })
            return
        }
        
        // Continue to next handler
        c.Next()
    }
}

// Apply globally
r.Use(AuthRequired())

// Apply to route group
authorized := r.Group("/api")
authorized.Use(AuthRequired())
{
    authorized.GET("/users", listUsers)
}

// Apply to specific route
r.GET("/protected", AuthRequired(), protectedHandler)

Middleware Execution Flow

func MyMiddleware() gin.HandlerFunc {
    return func(c *gin.Context) {
        // Before request
        
        c.Next() // Execute remaining handlers
        
        // After request
    }
}

func AbortMiddleware() gin.HandlerFunc {
    return func(c *gin.Context) {
        if !authorized {
            c.AbortWithStatus(http.StatusUnauthorized)
            return
        }
        c.Next()
    }
}

Built-in Middleware

Basic Auth:

authorized := r.Group("/admin", gin.BasicAuth(gin.Accounts{
    "admin": "secret",
    "user":  "password",
}))

CORS (requires github.com/gin-contrib/cors):

import "github.com/gin-contrib/cors"

r.Use(cors.Default())
// Or custom config
r.Use(cors.New(cors.Config{
    AllowOrigins:     []string{"https://example.com"},
    AllowMethods:     []string{"GET", "POST"},
    AllowHeaders:     []string{"Origin"},
    ExposeHeaders:    []string{"Content-Length"},
    AllowCredentials: true,
    MaxAge: 12 * time.Hour,
}))

Context Methods

Set/Get Values

// Store value in context
c.Set("user", user)

// Retrieve value
if val, exists := c.Get("user"); exists {
    user := val.(User)
}

// MustGet (panics if not exists)
user := c.MustGet("user").(User)

Client Information

// Client IP
ip := c.ClientIP()

// Content type
contentType := c.ContentType()

// Request header
userAgent := c.GetHeader("User-Agent")

// Check if WebSocket
isWebsocket := c.IsWebsocket()

Cookies

// Set cookie
c.SetCookie(
    "session",      // name
    "value",        // value
    3600,           // max age (seconds)
    "/",            // path
    "localhost",    // domain
    false,          // secure
    true,           // httpOnly
)

// Get cookie
value, err := c.Cookie("session")

Request Body

// Read body bytes (can only be read once)
bodyBytes, _ := c.GetRawData()

// To allow multiple reads, bind to GetRawData and bind again
c.Set(gin.BodyBytesKey, bodyBytes)

Error Handling

Custom Error Responses

r.GET("/error", func(c *gin.Context) {
    // Attach error to context
    c.Error(errors.New("something went wrong"))
    
    // Abort with error
    c.AbortWithError(http.StatusInternalServerError, errors.New("error"))
    
    // Abort with JSON
    c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{
        "error": "invalid input",
    })
})

Error Middleware

r.Use(func(c *gin.Context) {
    c.Next()
    
    // Check for errors after handlers executed
    if len(c.Errors) > 0 {
        c.JSON(http.StatusInternalServerError, gin.H{
            "errors": c.Errors,
        })
    }
})

HTML Templates

Load Templates

// Load all templates
r.LoadHTMLGlob("templates/**/*")

// Load specific files
r.LoadHTMLFiles("templates/index.html", "templates/about.html")

Custom Delimiters

r.Delims("{[{", "}]}")

Custom Functions

import "html/template"

r.SetFuncMap(template.FuncMap{
    "formatDate": func(t time.Time) string {
        return t.Format("2006-01-02")
    },
})

Render Template

r.GET("/", func(c *gin.Context) {
    c.HTML(http.StatusOK, "index.html", gin.H{
        "title": "Home",
        "user": user,
    })
})

Static Files

// Serve single file
r.StaticFile("/favicon.ico", "./resources/favicon.ico")

// Serve directory
r.Static("/assets", "./assets")

// Serve from embedded FS (Go 1.16+)
r.StaticFS("/public", http.FS(embeddedFS))

Testing

import (
    "net/http"
    "net/http/httptest"
    "testing"
    "github.com/gin-gonic/gin"
    "github.com/stretchr/testify/assert"
)

func TestPingRoute(t *testing.T) {
    gin.SetMode(gin.TestMode)
    
    r := setupRouter()
    
    w := httptest.NewRecorder()
    req, _ := http.NewRequest("GET", "/ping", nil)
    r.ServeHTTP(w, req)
    
    assert.Equal(t, http.StatusOK, w.Code)
    assert.Equal(t, "pong", w.Body.String())
}

Advanced Features

Graceful Shutdown

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

func main() {
    r := gin.Default()
    
    srv := &http.Server{
        Addr:    ":8080",
        Handler: r,
    }
    
    go func() {
        if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
            log.Fatalf("listen: %s\n", err)
        }
    }()
    
    // Wait for interrupt signal
    quit := make(chan os.Signal, 1)
    signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
    <-quit
    
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel()
    
    if err := srv.Shutdown(ctx); err != nil {
        log.Fatal("Server forced to shutdown:", err)
    }
}

Custom Validators

import "github.com/go-playground/validator/v10"

type Booking struct {
    CheckIn  time.Time `binding:"required,bookabledate"`
    CheckOut time.Time `binding:"required,gtfield=CheckIn"`
}

var bookableDate validator.Func = func(fl validator.FieldLevel) bool {
    date, ok := fl.Field().Interface().(time.Time)
    if ok {
        return date.After(time.Now())
    }
    return false
}

// Register custom validator
if v, ok := binding.Validator.Engine().(*validator.Validate); ok {
    v.RegisterValidation("bookabledate", bookableDate)
}

Run Multiple Services

func main() {
    r1 := gin.Default()
    r2 := gin.Default()
    
    s1 := &http.Server{Addr: ":8080", Handler: r1}
    s2 := &http.Server{Addr: ":8081", Handler: r2}
    
    g := new(errgroup.Group)
    g.Go(func() error { return s1.ListenAndServe() })
    g.Go(func() error { return s2.ListenAndServe() })
    
    if err := g.Wait(); err != nil {
        log.Fatal(err)
    }
}

Auto TLS (HTTPS)

import "github.com/gin-gonic/autotls"

func main() {
    r := gin.Default()
    
    // Automatically obtain TLS certificates from Let's Encrypt
    log.Fatal(autotls.Run(r, "example1.com", "example2.com"))
}

Common Patterns

API Versioning

func main() {
    r := gin.Default()
    
    v1 := r.Group("/api/v1")
    {
        v1.GET("/users", v1GetUsers)
        v1.POST("/users", v1CreateUser)
    }
    
    v2 := r.Group("/api/v2")
    {
        v2.GET("/users", v2GetUsers)
        v2.POST("/users", v2CreateUser)
    }
    
    r.Run()
}

Structured Responses

type Response struct {
    Code    int         `json:"code"`
    Message string      `json:"message"`
    Data    interface{} `json:"data,omitempty"`
}

func Success(c *gin.Context, data interface{}) {
    c.JSON(http.StatusOK, Response{
        Code:    0,
        Message: "success",
        Data:    data,
    })
}

func Error(c *gin.Context, code int, message string) {
    c.JSON(code, Response{
        Code:    code,
        Message: message,
    })
}

Pagination

type PaginationQuery struct {
    Page     int `form:"page" binding:"min=1"`
    PageSize int `form:"page_size" binding:"min=1,max=100"`
}

r.GET("/users", func(c *gin.Context) {
    var query PaginationQuery
    query.Page = 1
    query.PageSize = 10
    
    if err := c.ShouldBindQuery(&query); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    
    offset := (query.Page - 1) * query.PageSize
    users := getUsersFromDB(query.PageSize, offset)
    
    c.JSON(http.StatusOK, gin.H{
        "page":      query.Page,
        "page_size": query.PageSize,
        "data":      users,
    })
})

Configuration

Gin Mode

// Set mode programmatically
gin.SetMode(gin.ReleaseMode)  // Production
gin.SetMode(gin.DebugMode)    // Development
gin.SetMode(gin.TestMode)     // Testing

// Or via environment variable
// export GIN_MODE=release

Disable Console Color

gin.DisableConsoleColor()

Custom Logger

import (
    "io"
    "os"
)

// Write logs to file
f, _ := os.Create("gin.log")
gin.DefaultWriter = io.MultiWriter(f, os.Stdout)

// Disable logs
gin.DefaultWriter = io.Discard

Trusted Proxies

r := gin.Default()
r.SetTrustedProxies([]string{"192.168.1.0/24"})

Performance Tips

1. Use gin.New() instead of gin.Default() if you don't need logger/recovery middleware
2. Disable console colors in production: gin.DisableConsoleColor()
3. Set release mode: gin.SetMode(gin.ReleaseMode)
4. Use c.ShouldBind* instead of c.Bind* for better error handling control
5. Reuse gin.Context carefully - Use c.Copy() for goroutines
6. Limit request body size with middleware or nginx

Examples Reference

See the references/examples.md file for additional working examples covering:

• WebSocket integration
• Server-Sent Events (SSE)
• gRPC integration
• Real-time chat
• OIDC authentication
• Rate limiting
• Reverse proxy
• And more

For complete API reference, see references/api.md.