Updating createMovieHandler accepting data.Runtime for the Runtime field. Updating internal/data/runtime.go with the json.Unmarshaler interface to transform our client's runtime string field '%d mins' into a Runtime type format.

cmd/api/movies.go

@@ -13,7 +13,7 @@ func (app *application) createMovieHandler(w http.ResponseWriter, r *http.Reques
 	var input struct {
 		Title   string       `json:"title"`
 		Year    int32        `json:"year"`
-		Runtime int32    `json:"runtime"`
+		Runtime data.Runtime `json:"runtime"`
 		Genres  []string     `json:"genres"`
 	}
 

internal/data/runtime.go

@@ -1,10 +1,15 @@
 package data
 
 import (
+	"errors"
 	"fmt"
 	"strconv"
+	"strings"
 )
 
+// ErrInvalidRuntimeFormat : Define an error that our UnmarshalJSON() method can return if we're unable to parse or convert the JSON string successfully
+var ErrInvalidRuntimeFormat = errors.New("invalid runtime format")
+
 // Runtime
 /*
 Declare a custom Runtime type, which has the underlying type int32
@@ -28,3 +33,32 @@ func (r Runtime) MarshalJSON() ([]byte, error) {
 	// Convert the quoted string value to a byte slice and return it.
 	return []byte(quotedJSONValue), nil
 }
+
+// UnmarshalJSON
+// Implement a UnmarshalJSON() method on the Runtime type so that it satisfies the json.Unmarshaler interface. IMPORTANT: Because UnmarshalJSON() needs to modify the receiver (our Runtime type), we must use a pointer receiver for this to work correctly. Otherwise, we will only be modifying a copy (which is then discarded when this method returns).
+func (r *Runtime) UnmarshalJSON(jsonValue []byte) error {
+	// We expect that the incoming JSON value will be a string in the format "<runtimes> mins", and the first thing we need to do is remove the surrounding double-quotes from this string. If we can't unquote it, then we return the ErrInvalidRuntimeFormat error.
+	unquotedJSONValue, err := strconv.Unquote(string(jsonValue))
+	if err != nil {
+		return ErrInvalidRuntimeFormat
+	}
+
+	// Split the string to isolate the part containing the number.
+	parts := strings.Split(unquotedJSONValue, " ")
+
+	// Sanity check the parts of the string to make sure it was in the expected format. If it isn't, we return the ErrInvalidRuntimeFormat error again.
+	if len(parts) != 2 || parts[1] != "mins" {
+		return ErrInvalidRuntimeFormat
+	}
+
+	// Otherwise, parse the string containing the number into an int32. Again, if this fails, return the ErrInvalidRuntimeFormat error.
+	i, err := strconv.ParseInt(parts[0], 10, 32)
+	if err != nil {
+		return ErrInvalidRuntimeFormat
+	}
+
+	// Convert the int32 to a Runtime type and assign this to the receiver. Note that we use the * operator to deference the receiver (which is a pointer to a Runtime type) in order to set the underlying value of the pointer.
+	*r = Runtime(i)
+
+	return nil
+}