adds custom errors and validation on input

cmd/api/errors.go

@@ -35,3 +35,7 @@ func (app *application) methodNotAllowedResponse(w http.ResponseWriter, r *http.
 	message := fmt.Sprintf("the %s method is not supported for this resource", r.Method)
 	app.errorResponse(w, r, http.StatusMethodNotAllowed, message)
 }
+
+func (app *application) badRequestResponse(w http.ResponseWriter, r *http.Request, err error) {
+	app.errorResponse(w, r, http.StatusBadRequest, err.Error())
+}

cmd/api/healthcheck.go

@@ -16,8 +16,7 @@ func (app *application) healthCheckHandler(w http.ResponseWriter, r *http.Reques
 
 	err := app.writeJSON(w, http.StatusOK, envelopedHealth, nil)
 	if err != nil {
-		app.logger.Print(err)
+		app.serverErrorResponse(w, r, err)
-		http.Error(w, "the server encountered an error and could process your request", http.StatusInternalServerError)
 	}
 
 }

cmd/api/helpers.go

@@ -3,14 +3,70 @@ package main
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
+	"io"
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/julienschmidt/httprouter"
 )
 
 type envelope map[string]any
 
+func (app *application) readJSON(w http.ResponseWriter, r *http.Request, dest any) error {
+	maxBytes := 1_048_576
+	r.Body = http.MaxBytesReader(w, r.Body, int64(maxBytes))
+
+	decoder := json.NewDecoder(r.Body)
+	decoder.DisallowUnknownFields()
+
+	err := decoder.Decode(dest)
+
+	if err != nil {
+		var syntaxError *json.SyntaxError
+		var unmarshallError *json.UnmarshalTypeError
+		var invalidUnmarshall *json.InvalidUnmarshalError
+		var maxBytesError *http.MaxBytesError
+
+		switch {
+		case errors.As(err, &syntaxError):
+			return fmt.Errorf("body contains badly-formed JSON (at character %d)", syntaxError.Offset)
+
+		case errors.Is(err, io.ErrUnexpectedEOF):
+			return errors.New("body contains badly-formed JSON")
+
+		case errors.As(err, &unmarshallError):
+			if unmarshallError.Field != "" {
+				return fmt.Errorf("the body contains incorrect json type for field %q", unmarshallError.Field)
+			}
+			return fmt.Errorf("body contains incorrect JSON type (at character %d)", unmarshallError.Offset)
+
+		case errors.Is(err, io.EOF):
+			return errors.New("body must not be empty")
+
+		case strings.HasPrefix(err.Error(), "json: unknown field "):
+			fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
+			return fmt.Errorf("body contains uknown key %s", fieldName)
+
+		case errors.As(err, &maxBytesError):
+			return fmt.Errorf("body must not be larger than %d bytes", maxBytesError.Limit)
+
+		case errors.As(err, &invalidUnmarshall):
+			panic(err)
+
+		default:
+			return err
+		}
+	}
+	err = decoder.Decode(&struct{}{})
+	if err != io.EOF {
+		return errors.New("body must only contain a single JSON value")
+	}
+
+	return nil // no errors
+}
+
 func (app *application) readIDParam(r *http.Request) (int64, error) {
 	params := httprouter.ParamsFromContext(r.Context())
 

cmd/api/movies.go

@@ -9,13 +9,26 @@ import (
 )
 
 func (app *application) createMovieHandler(w http.ResponseWriter, r *http.Request) {
-	fmt.Fprintln(w, "create a new movie")
+	var input struct {
+		Title   string   `json:"title"`
+		Year    int32    `json:"year"`
+		Runtime int32    `json:"runtime"`
+		Genres  []string `json:"genres"`
+	}
+
+	err := app.readJSON(w, r, &input)
+	if err != nil {
+		app.badRequestResponse(w, r, err)
+		return
+	}
+
+	fmt.Fprintf(w, "%v+\n", input)
 }
 
 func (app *application) showMovieHandler(w http.ResponseWriter, r *http.Request) {
 	id, err := app.readIDParam(r)
 	if err != nil {
-		http.NotFound(w, r)
+		app.notFoundResponse(w, r)
 		return
 	}
 
@@ -31,8 +44,7 @@ func (app *application) showMovieHandler(w http.ResponseWriter, r *http.Request)
 	envelopedMovie := envelope{"movie": movie}
 	err = app.writeJSON(w, http.StatusOK, envelopedMovie, nil)
 	if err != nil {
-		app.logger.Print(err)
+		app.serverErrorResponse(w, r, err)
-		http.Error(w, "the server encountered an error and could process your request", http.StatusInternalServerError)
 	}
 
 }

cmd/api/routes.go

@@ -8,6 +8,8 @@ import (
 
 func (app *application) routes() *httprouter.Router {
 	router := httprouter.New()
+	router.NotFound = http.HandlerFunc(app.notFoundResponse)
+	router.MethodNotAllowed = http.HandlerFunc(app.methodNotAllowedResponse)
 
 	router.HandlerFunc(http.MethodGet, "/v1/healthcheck", app.healthCheckHandler)
 	router.HandlerFunc(http.MethodPost, "/v1/movies", app.createMovieHandler)