Creating helpers.go file : allowing us to extract readIDParam method for further use. Updating showMovieHandler with the new method.

cmd/api/helpers.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"errors"
+	"github.com/julienschmidt/httprouter"
+	"net/http"
+	"strconv"
+)
+
+/*
+Note: The readIDParam() method doesn't use any dependencies from our
+application struct so it could just be a regular function, rather than a method on
+application. But in general, I suggest setting up all your application-specific handlers
+and helpers so that they are methods on application. It helps maintain consistency in
+your code structure, and also future-proofs your code for when those handlers and
+helpers change later and they do need access to dependency.
+
+Retrieve the "id" URL parameter from the current request context, then convert it to
+an integer and return it. If the operation isn't successful, return 0 and an error.
+*/
+func (app *application) readIDParam(r *http.Request) (int64, error) {
+	/*
+		When httprouter is parsing a request, any interpolated URL parameters will be
+		stored in the request context. We can use the ParamsFromContext() function to
+		retrieve a slice containing these parameter names and values.
+	*/
+	params := httprouter.ParamsFromContext(r.Context())
+
+	/*
+		We can then use the ByName() method to get the value of the "id" parameter from
+		the slice. In our project all movies will have a unique positive integer ID, but
+		the value returned by ByName() is always a string. So we try to convert it to a
+		base 10 integer (with a bit size of 64). If the parameter couldn't be converted,
+		or is less than 1, we know the ID is invalid so we use the http.NotFound()
+		func to return a 404 Not Found Response.
+	*/
+	id, err := strconv.ParseInt(params.ByName("id"), 10, 64)
+	if err != nil || id < 1 {
+		return 0, errors.New("invalid id parameter")
+	}
+
+	return id, nil
+}

cmd/api/movies.go

@@ -2,9 +2,7 @@ package main
 
 import (
 	"fmt"
-	"github.com/julienschmidt/httprouter"
 	"net/http"
-	"strconv"
 )
 
 // "POST /v1/movies" endpoint.
@@ -14,22 +12,8 @@ func (app *application) createMovieHandler(w http.ResponseWriter, r *http.Reques
 
 // "GET /v1/movies/:id"
 func (app *application) showMovieHandler(w http.ResponseWriter, r *http.Request) {
-	/*
-		When httprouter is parsing a request, any interpolated URL parameters will be
-		stored in the request context. We can use the ParamsFromContext() function to
-		retrieve a slice containing these parameter names and values.
-	*/
-	params := httprouter.ParamsFromContext(r.Context())
+	id, err := app.readIDParam(r)
 
-	/*
-		We can then use the ByName() method to get the value of the "id" parameter from
-		the slice. In our project all movies will have a unique positive integer ID, but
-		the value returned by ByName() is always a string. So we try to convert it to a
-		base 10 integer (with a bit size of 64). If the parameter couldn't be converted,
-		or is less than 1, we know the ID is invalid so we use the http.NotFound()
-		func to return a 404 Not Found Response.
-	*/
-	id, err := strconv.ParseInt(params.ByName("id"), 10, 64)
 	if err != nil || id < 1 {
 		http.NotFound(w, r)
 		return