List and get handlers

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Goal

Add GET /items and GET /items/{id} using Go 1.22 http.ServeMux pattern routing. After this page the server returns items from SQLite.

Prerequisites

• Store layer — the Store type with List and Get

Go 1.22 ServeMux patterns

Go 1.22 added method and wildcard support to http.ServeMux. You can now write:

mux.Handle("GET /items", handler)
mux.Handle("GET /items/{id}", handler)

The leading GET restricts the route to GET requests only. {id} is a wildcard — its value is available inside the handler via r.PathValue("id"). No third-party router is needed.

The handlers

Add a new file handlers.go to your items/ module:

package main

import (
	"database/sql"
	"encoding/json"
	"net/http"
	"strconv"
)

func handleList(s *Store) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		items, err := s.List()
		if err != nil {
			http.Error(w, "internal error", http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(items)
	}
}

func handleGet(s *Store) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
		if err != nil {
			http.Error(w, "bad id", http.StatusBadRequest)
			return
		}
		it, err := s.Get(id)
		if err == sql.ErrNoRows {
			http.Error(w, "not found", http.StatusNotFound)
			return
		} else if err != nil {
			http.Error(w, "internal error", http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(it)
	}
}

Each handler is a constructor function — it takes a *Store and returns an http.HandlerFunc. The store is captured in a closure, so the handler always uses the same store instance.

handleGet distinguishes two error cases: sql.ErrNoRows means the ID does not exist (404), any other error is a server fault (500).

Wiring

Update main.go to create the mux and register both routes (you will replace main.go with the full version on page 07 — for now this skeleton is enough to test):

package main

import (
	"log"
	"net/http"
)

func main() {
	db, err := openDB("items.db")
	if err != nil {
		log.Fatal(err)
	}
	store := &Store{db: db}

	mux := http.NewServeMux()
	mux.Handle("GET /items", handleList(store))
	mux.Handle("GET /items/{id}", handleGet(store))

	log.Println("listening on :8080")
	log.Fatal(http.ListenAndServe(":8080", mux))
}

Checkpoint

go run .

In a second terminal:

curl http://localhost:8080/items

Expected output (empty database, so an empty array):

null

Note: json.NewEncoder.Encode encodes a nil slice as null. If you want [] for an empty list, initialise items as []Item{} inside List. Either is valid JSON — the tests on page 08 use the nil form.

curl http://localhost:8080/items/1

Expected:

not found

Stop the server with Ctrl-C.

Next → 06 Create handler