Fix nil pointer panic on PUT /users/:id for a non-existent user

cookbook/crud/server.go

@@ -56,8 +56,12 @@ func updateUser(c *echo.Context) error {
 		return err
 	}
 	id, _ := strconv.Atoi(c.Param("id"))
-	users[id].Name = u.Name
-	return c.JSON(http.StatusOK, users[id])
+	existingUser, ok := users[id]
+	if !ok {
+		return echo.NewHTTPError(http.StatusNotFound, "user not found")
+	}
+	existingUser.Name = u.Name
+	return c.JSON(http.StatusOK, existingUser)
 }
 
 func deleteUser(c *echo.Context) error {

cookbook/crud/server_test.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/labstack/echo/v5"
+	"github.com/labstack/echo/v5/middleware"
+)
+
+func newTestServer() *echo.Echo {
+	lock.Lock()
+	users = map[int]*user{}
+	seq = 1
+	lock.Unlock()
+
+	e := echo.New()
+	e.Use(middleware.RequestLogger())
+	e.Use(middleware.Recover())
+	e.GET("/users", getAllUsers)
+	e.POST("/users", createUser)
+	e.GET("/users/:id", getUser)
+	e.PUT("/users/:id", updateUser)
+	e.DELETE("/users/:id", deleteUser)
+	return e
+}
+
+func TestUpdateUserNotFound(t *testing.T) {
+	e := newTestServer()
+	req := httptest.NewRequest(http.MethodPut, "/users/9999", strings.NewReader(`{"name":"x"}`))
+	req.Header.Set(echo.HeaderContentType, echo.MIMEApplicationJSON)
+	rec := httptest.NewRecorder()
+
+	e.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("expected status %d, got %d: %s", http.StatusNotFound, rec.Code, rec.Body.String())
+	}
+}
+
+func TestUpdateUser(t *testing.T) {
+	e := newTestServer()
+	createReq := httptest.NewRequest(http.MethodPost, "/users", strings.NewReader(`{"name":"before"}`))
+	createReq.Header.Set(echo.HeaderContentType, echo.MIMEApplicationJSON)
+	createRec := httptest.NewRecorder()
+	e.ServeHTTP(createRec, createReq)
+	if createRec.Code != http.StatusCreated {
+		t.Fatalf("expected create status %d, got %d: %s", http.StatusCreated, createRec.Code, createRec.Body.String())
+	}
+
+	updateReq := httptest.NewRequest(http.MethodPut, "/users/1", strings.NewReader(`{"name":"after"}`))
+	updateReq.Header.Set(echo.HeaderContentType, echo.MIMEApplicationJSON)
+	updateRec := httptest.NewRecorder()
+	e.ServeHTTP(updateRec, updateReq)
+	if updateRec.Code != http.StatusOK {
+		t.Fatalf("expected update status %d, got %d: %s", http.StatusOK, updateRec.Code, updateRec.Body.String())
+	}
+
+	var updated user
+	if err := json.Unmarshal(updateRec.Body.Bytes(), &updated); err != nil {
+		t.Fatalf("decode updated user: %v", err)
+	}
+	if updated.Name != "after" {
+		t.Fatalf("expected updated name %q, got %q", "after", updated.Name)
+	}
+}