Tutorial - 💧 Mizu

In this tutorial, you’ll build a todo list API with full CRUD operations. CRUD stands for Create, Read, Update, Delete - the four basic operations for managing data. This is the foundation of almost every web application, and you’ll learn the patterns used in production Mizu APIs.

What We’re Building

A REST API with these endpoints:

Method	Path	Description
GET	/api/todos	List all todos
POST	/api/todos	Create a todo
GET	/api/todos/:id	Get a todo by ID
PUT	/api/todos/:id	Update a todo
DELETE	/api/todos/:id	Delete a todo

Step 1: Create the Project

mizu new todoapi --template api
cd todoapi
go mod tidy

Verify it works:

mizu dev
# In another terminal:
curl http://localhost:8080/health

You should see {"status":"ok"}.

Step 2: Create the Todo Feature

Create the feature directory:

mkdir -p feature/todos

Create feature/todos/http.go:

package todos

import (
    "sync"
    "github.com/go-mizu/mizu"
)

// Todo represents a todo item.
type Todo struct {
    ID        string `json:"id"`
    Title     string `json:"title"`
    Completed bool   `json:"completed"`
}

// Store is an in-memory todo store.
type Store struct {
    mu     sync.RWMutex
    todos  map[string]*Todo
    nextID int
}

// NewStore creates a new todo store.
func NewStore() *Store {
    return &Store{
        todos: make(map[string]*Todo),
    }
}

This sets up our data types and a simple in-memory store.

Step 3: Implement List Handler

Add to feature/todos/http.go:

// List returns a handler that lists all todos.
func List(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        store.mu.RLock()
        defer store.mu.RUnlock()

        todos := make([]*Todo, 0, len(store.todos))
        for _, t := range store.todos {
            todos = append(todos, t)
        }

        return c.JSON(200, todos)
    }
}

Step 4: Implement Create Handler

Add to feature/todos/http.go:

import (
    "fmt"
    // ... other imports
)

// CreateInput is the input for creating a todo.
type CreateInput struct {
    Title string `json:"title"`
}

// Create returns a handler that creates a todo.
func Create(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        var input CreateInput
        if err := c.Bind(&input); err != nil {
            return err
        }

        if input.Title == "" {
            return c.JSON(400, map[string]string{
                "error": "title is required",
            })
        }

        store.mu.Lock()
        defer store.mu.Unlock()

        store.nextID++
        todo := &Todo{
            ID:        fmt.Sprintf("%d", store.nextID),
            Title:     input.Title,
            Completed: false,
        }
        store.todos[todo.ID] = todo

        return c.JSON(201, todo)
    }
}

Step 5: Implement Get Handler

Add to feature/todos/http.go:

// Get returns a handler that gets a todo by ID.
func Get(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        id := c.Param("id")

        store.mu.RLock()
        defer store.mu.RUnlock()

        todo, ok := store.todos[id]
        if !ok {
            return c.JSON(404, map[string]string{
                "error": "todo not found",
            })
        }

        return c.JSON(200, todo)
    }
}

Step 6: Implement Update Handler

Add to feature/todos/http.go:

// UpdateInput is the input for updating a todo.
type UpdateInput struct {
    Title     *string `json:"title"`
    Completed *bool   `json:"completed"`
}

// Update returns a handler that updates a todo.
func Update(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        id := c.Param("id")

        var input UpdateInput
        if err := c.Bind(&input); err != nil {
            return err
        }

        store.mu.Lock()
        defer store.mu.Unlock()

        todo, ok := store.todos[id]
        if !ok {
            return c.JSON(404, map[string]string{
                "error": "todo not found",
            })
        }

        if input.Title != nil {
            todo.Title = *input.Title
        }
        if input.Completed != nil {
            todo.Completed = *input.Completed
        }

        return c.JSON(200, todo)
    }
}

Step 7: Implement Delete Handler

Add to feature/todos/http.go:

// Delete returns a handler that deletes a todo.
func Delete(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        id := c.Param("id")

        store.mu.Lock()
        defer store.mu.Unlock()

        if _, ok := store.todos[id]; !ok {
            return c.JSON(404, map[string]string{
                "error": "todo not found",
            })
        }

        delete(store.todos, id)

        return c.JSON(200, map[string]string{
            "message": "deleted",
        })
    }
}

Step 8: Register Routes

Update app/api/app.go to include the store:

package api

import (
    "github.com/go-mizu/mizu"
    "example.com/todoapi/feature/todos"
)

type App struct {
    cfg        Config
    app        *mizu.App
    todoStore  *todos.Store
}

func New(cfg Config) *App {
    a := &App{
        cfg:       cfg,
        todoStore: todos.NewStore(),
    }
    a.app = mizu.New()
    a.routes()
    return a
}

func (a *App) Listen(addr string) error {
    return a.app.Listen(addr)
}

Update app/api/routes.go:

package api

import (
    "example.com/todoapi/feature/health"
    "example.com/todoapi/feature/todos"
)

func (a *App) routes() {
    // Health check
    a.app.Get("/health", health.Handler())

    // Todo routes
    a.app.Get("/api/todos", todos.List(a.todoStore))
    a.app.Post("/api/todos", todos.Create(a.todoStore))
    a.app.Get("/api/todos/:id", todos.Get(a.todoStore))
    a.app.Put("/api/todos/:id", todos.Update(a.todoStore))
    a.app.Delete("/api/todos/:id", todos.Delete(a.todoStore))
}

Step 9: Test the API

Start the server:

mizu dev

In another terminal, test each endpoint:

List (empty)

curl http://localhost:8080/api/todos

Output: []

Create

curl -X POST http://localhost:8080/api/todos \
  -H "Content-Type: application/json" \
  -d '{"title":"Buy groceries"}'

Output:

{"id":"1","title":"Buy groceries","completed":false}

Create Another

curl -X POST http://localhost:8080/api/todos \
  -H "Content-Type: application/json" \
  -d '{"title":"Walk the dog"}'

List All

curl http://localhost:8080/api/todos

Output:

[{"id":"1","title":"Buy groceries","completed":false},{"id":"2","title":"Walk the dog","completed":false}]

Get One

curl http://localhost:8080/api/todos/1

Update

curl -X PUT http://localhost:8080/api/todos/1 \
  -H "Content-Type: application/json" \
  -d '{"completed":true}'

Output:

{"id":"1","title":"Buy groceries","completed":true}

Delete

curl -X DELETE http://localhost:8080/api/todos/2

Output:

{"message":"deleted"}

Complete Code

Here’s the complete feature/todos/http.go:

package todos

import (
    "fmt"
    "sync"

    "github.com/go-mizu/mizu"
)

// Todo represents a todo item.
type Todo struct {
    ID        string `json:"id"`
    Title     string `json:"title"`
    Completed bool   `json:"completed"`
}

// Store is an in-memory todo store.
type Store struct {
    mu     sync.RWMutex
    todos  map[string]*Todo
    nextID int
}

// NewStore creates a new todo store.
func NewStore() *Store {
    return &Store{
        todos: make(map[string]*Todo),
    }
}

// CreateInput is the input for creating a todo.
type CreateInput struct {
    Title string `json:"title"`
}

// UpdateInput is the input for updating a todo.
type UpdateInput struct {
    Title     *string `json:"title"`
    Completed *bool   `json:"completed"`
}

// List returns a handler that lists all todos.
func List(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        store.mu.RLock()
        defer store.mu.RUnlock()

        todos := make([]*Todo, 0, len(store.todos))
        for _, t := range store.todos {
            todos = append(todos, t)
        }
        return c.JSON(200, todos)
    }
}

// Create returns a handler that creates a todo.
func Create(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        var input CreateInput
        if err := c.Bind(&input); err != nil {
            return err
        }
        if input.Title == "" {
            return c.JSON(400, map[string]string{"error": "title is required"})
        }

        store.mu.Lock()
        defer store.mu.Unlock()

        store.nextID++
        todo := &Todo{
            ID:        fmt.Sprintf("%d", store.nextID),
            Title:     input.Title,
            Completed: false,
        }
        store.todos[todo.ID] = todo
        return c.JSON(201, todo)
    }
}

// Get returns a handler that gets a todo by ID.
func Get(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        id := c.Param("id")

        store.mu.RLock()
        defer store.mu.RUnlock()

        todo, ok := store.todos[id]
        if !ok {
            return c.JSON(404, map[string]string{"error": "todo not found"})
        }
        return c.JSON(200, todo)
    }
}

// Update returns a handler that updates a todo.
func Update(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        id := c.Param("id")

        var input UpdateInput
        if err := c.Bind(&input); err != nil {
            return err
        }

        store.mu.Lock()
        defer store.mu.Unlock()

        todo, ok := store.todos[id]
        if !ok {
            return c.JSON(404, map[string]string{"error": "todo not found"})
        }

        if input.Title != nil {
            todo.Title = *input.Title
        }
        if input.Completed != nil {
            todo.Completed = *input.Completed
        }
        return c.JSON(200, todo)
    }
}

// Delete returns a handler that deletes a todo.
func Delete(store *Store) mizu.Handler {
    return func(c *mizu.Ctx) error {
        id := c.Param("id")

        store.mu.Lock()
        defer store.mu.Unlock()

        if _, ok := store.todos[id]; !ok {
            return c.JSON(404, map[string]string{"error": "todo not found"})
        }
        delete(store.todos, id)
        return c.JSON(200, map[string]string{"message": "deleted"})
    }
}

What You Learned

Feature organization - Grouping related code together
Handler factories - Functions that return handlers
Dependency injection - Passing the store to handlers
CRUD operations - Create, Read, Update, Delete patterns
Input validation - Checking required fields
Error responses - Returning appropriate status codes

Next Steps

Add a Database

Replace in-memory store with a real database

Contract Template

Learn about multi-protocol APIs

Add Middleware

Add logging, auth, and more

Error Handling

Improve error responses