Add basic error handling framework and 404 handling

controller/users/users.go

@@ -28,23 +28,28 @@ func HandleList(w http.ResponseWriter, r *http.Request) {
 	controller.EncodeJSONResponse(w, userviews.ListFrom(users))
 }
 
-func HandleRead(w http.ResponseWriter, r *http.Request) {
+func HandleRead(w http.ResponseWriter, r *http.Request) error {
 	userIDStr := chi.URLParam(r, "userID")
 	userID, err := strconv.Atoi(userIDStr)
 	if err != nil {
 		http.Error(w, "Invalid userID", http.StatusBadRequest)
-		return
+		return err
 	}
 
 	// Get DB instance
 	db, err := database.GetDBFrom(r)
 	if err != nil {
 		logrus.Error(err)
-		panic(err)
+		return err
 	}
 
-	user := model.GetUserByID(db, userID)
+	user, err := model.GetUserByID(db, userID)
+	if err != nil {
+		logrus.Error(err)
+		return err
+	}
 	controller.EncodeJSONResponse(w, userviews.SingleFrom(user))
+	return nil
 }
 
 func HandleCreate(w http.ResponseWriter, r *http.Request) {

internal/database/errors.go

@@ -0,0 +1,19 @@
+package database
+
+import (
+	"errors"
+	"fmt"
+
+	apierrors "github.com/source-academy/stories-backend/internal/errors"
+	"gorm.io/gorm"
+)
+
+func HandleDBError(err error, fromModel string) error {
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return apierrors.ClientNotFoundError{
+			Message: fmt.Sprintf("Cannot find requested %s.", fromModel),
+		}
+	}
+	// TODO: Handle more types of errors
+	return err
+}

internal/errors/404.go

@@ -0,0 +1,17 @@
+package apierrors
+
+import (
+	"net/http"
+)
+
+type ClientNotFoundError struct {
+	Message string
+}
+
+func (e ClientNotFoundError) Error() string {
+	return e.Message
+}
+
+func (e ClientNotFoundError) HTTPStatusCode() int {
+	return http.StatusNotFound
+}

internal/errors/errors.go

@@ -0,0 +1,8 @@
+package apierrors
+
+// ClientError is an interface for errors that should be returned to the client.
+// They generally start with a 4xx HTTP status code.
+type ClientError interface {
+	error
+	HTTPStatusCode() int
+}

internal/router/errors.go

@@ -0,0 +1,28 @@
+package router
+
+import (
+	"errors"
+	"net/http"
+
+	apierrors "github.com/source-academy/stories-backend/internal/errors"
+)
+
+func handleAPIError(handler func(w http.ResponseWriter, r *http.Request) error) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		err := handler(w, r)
+		if err == nil {
+			// No error, response already written
+			return
+		}
+
+		var clientError apierrors.ClientError
+		if errors.As(err, &clientError) {
+			// Client error (status 4xx), write error message and status code
+			http.Error(w, clientError.Error(), clientError.HTTPStatusCode())
+			return
+		}
+
+		// 500 Internal Server Error as a catch-all
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	}
+}

internal/router/router.go

@@ -41,7 +41,7 @@ func Setup(config *config.Config, injectMiddleWares []func(http.Handler) http.Ha
 
 	r.Route("/users", func(r chi.Router) {
 		r.Get("/", users.HandleList)
-		r.Get("/{userID}", users.HandleRead)
+		r.Get("/{userID}", handleAPIError(users.HandleRead))
 		r.Post("/", users.HandleCreate)
 	})
 

model/users.go

@@ -1,6 +1,7 @@
 package model
 
 import (
+	"github.com/source-academy/stories-backend/internal/database"
 	"gorm.io/gorm"
 )
 
@@ -16,10 +17,13 @@ func GetAllUsers(db *gorm.DB) []User {
 	return users
 }
 
-func GetUserByID(db *gorm.DB, id int) User {
+func GetUserByID(db *gorm.DB, id int) (User, error) {
 	var user User
-	db.First(&user, id)
-	return user
+	err := db.First(&user, id).Error
+	if err != nil {
+		return user, database.HandleDBError(err, "user")
+	}
+	return user, err
 }
 
 func CreateUser(db *gorm.DB, user *User) {