Context

The Ctx interface (Context) provides methods for handling HTTP requests and responses. It’s the most important parameter passed to route handlers and middleware.

What is Ctx?

The Ctx object encapsulates the HTTP request and response, providing methods to:

Read request data (headers, body, parameters)
Send responses (JSON, HTML, files)
Set response headers and status codes
Access request metadata

app.Get("/user/:id", func(c fiber.Ctx) error {
    // c is the context
    id := c.Params("id")
    return c.JSON(fiber.Map{
        "id": id,
    })
})

Request Methods

Reading Parameters

Access URL parameters defined in routes:

app.Get("/user/:id", func(c fiber.Ctx) error {
    id := c.Params("id")
    return c.SendString("User ID: " + id)
})

// With default value
app.Get("/user/:id?", func(c fiber.Ctx) error {
    id := c.Params("id", "guest")
    return c.SendString("User ID: " + id)
})

// Type-safe parameters
import "strconv"

app.Get("/user/:id<int>", func(c fiber.Ctx) error {
    idStr := c.Params("id")
    id, _ := strconv.Atoi(idStr)
    return c.SendString(fmt.Sprintf("User ID: %d", id))
})

Query Strings

Retrieve query parameters from the URL:

// GET /search?q=fiber&limit=10
app.Get("/search", func(c fiber.Ctx) error {
    query := c.Query("q")
    limit := c.Query("limit", "20") // default value
    
    return c.JSON(fiber.Map{
        "query": query,
        "limit": limit,
    })
})

Request Headers

Read request headers:

app.Get("/", func(c fiber.Ctx) error {
    userAgent := c.Get("User-Agent")
    contentType := c.Get("Content-Type")
    
    // Get all headers
    headers := c.GetReqHeaders()
    
    return c.JSON(fiber.Map{
        "userAgent":   userAgent,
        "contentType": contentType,
        "allHeaders":  headers,
    })
})

Request Body

Parse request body in various formats:

type User struct {
    Name  string `json:"name"`
    Email string `json:"email"`
}

app.Post("/user", func(c fiber.Ctx) error {
    user := new(User)
    
    // Parse JSON body
    if err := c.Bind().JSON(user); err != nil {
        return err
    }
    
    return c.JSON(user)
})

// Parse form data
app.Post("/form", func(c fiber.Ctx) error {
    name := c.FormValue("name")
    email := c.FormValue("email")
    
    return c.JSON(fiber.Map{
        "name":  name,
        "email": email,
    })
})

Cookies

Read and write cookies:

app.Get("/cookie", func(c fiber.Ctx) error {
    // Read cookie
    value := c.Cookies("session_id")
    
    return c.SendString("Cookie value: " + value)
})

app.Post("/login", func(c fiber.Ctx) error {
    // Set cookie
    c.Cookie(&fiber.Cookie{
        Name:     "session_id",
        Value:    "abc123",
        MaxAge:   3600,
        HTTPOnly: true,
        Secure:   true,
    })
    
    return c.SendString("Cookie set")
})

Response Methods

Sending Text

app.Get("/", func(c fiber.Ctx) error {
    return c.SendString("Hello, World!")
})

Sending JSON

app.Get("/user", func(c fiber.Ctx) error {
    return c.JSON(fiber.Map{
        "name":  "John",
        "email": "[email protected]",
    })
})

// With struct
type User struct {
    Name  string `json:"name"`
    Email string `json:"email"`
}

app.Get("/user", func(c fiber.Ctx) error {
    user := User{
        Name:  "John",
        Email: "[email protected]",
    }
    return c.JSON(user)
})

Setting Status Codes

app.Post("/user", func(c fiber.Ctx) error {
    // Set status and send response
    return c.Status(fiber.StatusCreated).JSON(fiber.Map{
        "message": "User created",
    })
})

// Send status only
app.Delete("/user/:id", func(c fiber.Ctx) error {
    // Delete user...
    return c.SendStatus(fiber.StatusNoContent)
})

Setting Headers

app.Get("/download", func(c fiber.Ctx) error {
    // Set single header
    c.Set("Content-Type", "application/pdf")
    c.Set("Content-Disposition", "attachment; filename=file.pdf")
    
    return c.SendFile("./file.pdf")
})

// Set multiple headers
app.Get("/api", func(c fiber.Ctx) error {
    c.Set("X-Custom-Header", "value")
    c.Append("Vary", "Accept-Encoding")
    
    return c.JSON(fiber.Map{"status": "ok"})
})

Sending Files

app.Get("/download", func(c fiber.Ctx) error {
    // Send file
    return c.SendFile("./file.pdf")
})

app.Get("/download", func(c fiber.Ctx) error {
    // Send file with custom name
    return c.Download("./report.pdf", "monthly-report.pdf")
})

Redirects

app.Get("/old", func(c fiber.Ctx) error {
    return c.Redirect("/new")
})

// Redirect to external URL
app.Get("/external", func(c fiber.Ctx) error {
    return c.Redirect("https://example.com")
})

// Redirect with custom status
app.Get("/moved", func(c fiber.Ctx) error {
    return c.Redirect().Status(301).To("/new-location")
})

Context Metadata

Request Information

app.Get("/info", func(c fiber.Ctx) error {
    return c.JSON(fiber.Map{
        "method":   c.Method(),           // GET
        "path":     c.Path(),             // /info
        "url":      c.OriginalURL(),      // /info?query=value
        "protocol": c.Protocol(),         // http or https
        "ip":       c.IP(),               // Client IP
        "hostname": c.Hostname(),         // example.com
    })
})

Request Context

Access the standard context.Context:

app.Get("/", func(c fiber.Ctx) error {
    ctx := c.Context()
    
    // Use with database calls
    user, err := db.GetUserContext(ctx, id)
    if err != nil {
        return err
    }
    
    return c.JSON(user)
})

Locals Storage

Store request-scoped data:

app.Use(func(c fiber.Ctx) error {
    // Set data
    c.Locals("user", User{
        Name: "John",
        ID:   123,
    })
    return c.Next()
})

app.Get("/profile", func(c fiber.Ctx) error {
    // Get data
    user := c.Locals("user").(User)
    return c.JSON(user)
})

Zero-Allocation Patterns

Fiber is designed for performance with zero-allocation in mind:

Immutable vs Mutable

By default, values are mutable (zero-allocation) and only valid within the handler:

app.Get("/", func(c fiber.Ctx) error {
    // Mutable - fast but only valid in handler
    path := c.Path()
    
    // DON'T do this - value becomes invalid
    go func() {
        time.Sleep(time.Second)
        fmt.Println(path) // UNSAFE - may be corrupted
    }()
    
    return c.SendString("Hello")
})

Enable Immutable mode for safe concurrent access:

app := fiber.New(fiber.Config{
    Immutable: true,
})

app.Get("/", func(c fiber.Ctx) error {
    // Immutable - safe for concurrent use
    path := c.Path()
    
    go func() {
        time.Sleep(time.Second)
        fmt.Println(path) // SAFE - value is copied
    }()
    
    return c.SendString("Hello")
})

Making Copies

Manually copy values when needed:

app.Get("/", func(c fiber.Ctx) error {
    // Make a copy for async use
    path := c.Path()
    pathCopy := string([]byte(path))
    
    go func() {
        fmt.Println(pathCopy) // Safe
    }()
    
    return c.SendString("Hello")
})

Advanced Features

Request Binding

Bind request data to structs:

type CreateUserRequest struct {
    Name  string `json:"name" form:"name"`
    Email string `json:"email" form:"email"`
}

app.Post("/user", func(c fiber.Ctx) error {
    req := new(CreateUserRequest)
    
    // Bind from JSON or form data
    if err := c.Bind().Body(req); err != nil {
        return err
    }
    
    return c.JSON(req)
})

Format Negotiation

Send different responses based on Accept header:

app.Get("/user", func(c fiber.Ctx) error {
    return c.Format(fiber.Map{
        "name":  "John",
        "email": "[email protected]",
    })
})

// Accepts:
// - application/json → JSON response
// - text/html → HTML response
// - text/plain → Plain text response

MultipartForm

Handle file uploads:

app.Post("/upload", func(c fiber.Ctx) error {
    // Get file from form
    file, err := c.FormFile("document")
    if err != nil {
        return err
    }
    
    // Save file
    if err := c.SaveFile(file, "./uploads/" + file.Filename); err != nil {
        return err
    }
    
    return c.SendString("File uploaded: " + file.Filename)
})

Context Lifecycle

The Ctx object is pooled and reused for performance:

app.Get("/", func(c fiber.Ctx) error {
    // Context is valid here
    
    // DON'T store the context itself
    // storedCtx = c  // WRONG!
    
    // DO copy the values you need
    path := string(c.Path())
    
    return c.SendString("Hello")
})
// After handler returns, context is returned to pool

Best Practices

Don't store Ctx references

Never store the Ctx object itself - it’s pooled and reused.

// WRONG
var globalCtx fiber.Ctx
app.Get("/", func(c fiber.Ctx) error {
    globalCtx = c  // Don't do this!
    return nil
})

// RIGHT
app.Get("/", func(c fiber.Ctx) error {
    path := c.Path()  // Copy the value
    return nil
})

Use Locals for request-scoped data

Store data that should be shared between middleware and handlers using Locals.

app.Use(func(c fiber.Ctx) error {
    c.Locals("requestID", generateID())
    return c.Next()
})

Enable Immutable for goroutines

If you need to use Ctx values in goroutines, enable Immutable mode.

app := fiber.New(fiber.Config{
    Immutable: true,
})

Check errors from Bind methods

Always validate the error returned from binding methods.

if err := c.Bind().JSON(&data); err != nil {
    return c.Status(400).JSON(fiber.Map{
        "error": err.Error(),
    })
}

Routing

Define routes and access parameters

Middleware

Process requests with middleware

Error Handling

Handle errors in handlers

Request Binding

Bind request data to structs

Get Started

Core Concepts

Guides

Client

Add-ons

Extra

What is Ctx?

Request Methods

Reading Parameters

Query Strings

Request Headers

Request Body

Cookies

Response Methods

Sending Text

Sending JSON

Setting Status Codes

Setting Headers

Sending Files

Redirects

Context Metadata

Request Information

Request Context

Locals Storage

Zero-Allocation Patterns

Immutable vs Mutable

Making Copies

Advanced Features

Request Binding

Format Negotiation

MultipartForm

Context Lifecycle

Best Practices

See Also

Routing

Middleware

Error Handling

Request Binding

Build docs developers (and LLMs) love

Get Started

Core Concepts

Guides

Client

Add-ons

Extra

​What is Ctx?

​Request Methods

​Reading Parameters

​Query Strings

​Request Headers

​Request Body

​Cookies

​Response Methods

​Sending Text

​Sending JSON

​Setting Status Codes

​Setting Headers

​Sending Files

​Redirects

​Context Metadata

​Request Information

​Request Context

​Locals Storage

​Zero-Allocation Patterns

​Immutable vs Mutable

​Making Copies

​Advanced Features

​Request Binding

​Format Negotiation

​MultipartForm

​Context Lifecycle

​Best Practices

​See Also

Routing

Middleware

Error Handling

Request Binding

Build docs developers (and LLMs) love

What is Ctx?

Request Methods

Reading Parameters

Query Strings

Request Headers

Request Body

Cookies

Response Methods

Sending Text

Sending JSON

Setting Status Codes

Setting Headers

Sending Files

Redirects

Context Metadata

Request Information

Request Context

Locals Storage

Zero-Allocation Patterns

Immutable vs Mutable

Making Copies

Advanced Features

Request Binding

Format Negotiation

MultipartForm

Context Lifecycle

Best Practices

See Also