Adding ValidateFilters method in filters.go and use it in our listMoviesHandler

cmd/api/movies.go

@@ -227,6 +227,14 @@ func (app *application) listMoviesHandler(w http.ResponseWriter, r *http.Request
 
 	// Extract the sort query string value, falling back to "id" if it is not provided by the client (which will imply an ascending sort on movie ID)
 	input.Filters.Sort = app.readString(qs, "sort", "id")
+	// Add the supported sort values for this endpoint to the sort safelist
+	input.Filters.SortSafelist = []string{"id", "title", "year", "runtime", "-id", "-title", "-year", "-runtime"}
+
+	// Execute the validation checks on Filters struct and send a response
+	if data.ValidateFilters(v, input.Filters); !v.Valid() {
+		app.failedValidationResponse(w, r, v.Errors)
+		return
+	}
 
 	// Check the Validator instance for any errors and use the failedValidationResponse() helper to send the client a response if necessary
 	if !v.Valid() {

internal/data/filters.go

@@ -1,7 +1,21 @@
 package data
 
+import "greenlight.craftr.fr/internal/validator"
+
 type Filters struct {
-	Page     int
-	PageSize int
-	Sort     string
+	Page         int
+	PageSize     int
+	Sort         string
+	SortSafelist []string
+}
+
+func ValidateFilters(v *validator.Validator, f Filters) {
+	// Check that the page and page_size parameters contain sensible values
+	v.Check(f.Page > 0, "page", "must be greater than 0")
+	v.Check(f.Page <= 10_000_000, "page", "must be a maximum of 10 million")
+	v.Check(f.PageSize > 0, "page_size", "must be greater than 0")
+	v.Check(f.PageSize <= 100, "page_size", "must be a maximum of 100")
+
+	// Check that the sort parameter matches a value in the safelist
+	v.Check(validator.PermittedValue(f.Sort, f.SortSafelist...), "sort", "invalid sort value")
 }