Adding a Package

The internal/app folder

Backend packages are located in the /internal/app folder.

root
|--internal
|  |--app
|     |--[package 1]
|     |--[package 2]
|     |--[...]

Each package should have its own folder which should contain an exposed API and all the code for the package's internal workings.

Example

Lets create a simple todo list app called mytodo which will keep track of todo lists. Todo list must have no more than 20 items.

Start by initializing a new project githib.com/myorg/mytodo.

Now lets create a folder for our package called list that will contain all the business logic for a todo list.

Create the list module folder

mytodo
|--internal
|  |--app
|     |--list

info

The app folder itself must be created for a newly initialized project.

Create the list api

Create a new file /internal/app/list/list.go with the List struct and function for adding items to the list.

mytodo
|--internal
|  |--app
|     |--list
|        |--list.go

package list

import "errors"

const MaxItems = 20

type List struct {
	Items []string
}

func (l *List) AddItem(item string) error {
	// Check if the list is full
	if len(l.Items) >= MaxItems {
		return errors.New("todo list is full")
	}

	l.Items = append(l.Items, item)
	return nil
}

func (l *List) IsValid() bool {
	return len(l.Items) <= MaxItems
}

Accessing lists

warning

In this example we will store todo lists in the server object for illustration purposes only. To store todo lists correctly in a database, see the next section.

Add a map of lists to the server /internal/server/server.go so they can be accessed by the frontend

type Server struct {
	r       *http.ServeMux
	srv     http.Server
	conf    config.Config
	db      db.DB
	closeFn []func(context.Context) error
	lm	map[string]list.List	// todo list map
}

Now lists can be accessed from frontend handlers by passing them as a parameter to routes /internal/server/routes.go.

func (s *Server) Routes() {
    ...
    http.Handle("/lists", page.All(s.lm))
    ...
}