URL checker is added. (#97)

# Describe Request

URL checker is added.

Fixes #96

# Change Type

Checker added.

README.md

@@ -91,6 +91,7 @@ This package currently provides the following checkers:
 - [regexp](doc/checkers/regexp.md) checks if the given string matches the regexp pattern.
 - [required](doc/checkers/required.md) checks if the required value is provided.
 - [same](doc/checkers/same.md) checks if the given value is equal to the value of the field with the given name.
+- [url](doc/checkers/url.md) checks if the given value is a valid URL.
 
 # Normalizers Provided
 

checker.go

@@ -50,6 +50,7 @@ var makers = map[string]MakeFunc{
 	CheckerRegexp:       makeRegexp,
 	CheckerRequired:     makeRequired,
 	CheckerSame:         makeSame,
+	CheckerURL:          makeURL,
 	NormalizerLower:     makeLower,
 	NormalizerUpper:     makeUpper,
 	NormalizerTitle:     makeTitle,

doc/checkers/url.md

@@ -0,0 +1,29 @@
+# URL Checker
+
+The ```url``` checker checks if the given value is a valid URL. If the given value is not a valid URL, the checker will return the ```NOT_URL``` result. The checker uses [ParseRequestURI](https://pkg.go.dev/net/url#ParseRequestURI) function to parse the URL, and then checks if the schema or the host are both set.
+
+Here is an example:
+
+```golang
+type Bookmark struct {
+  URL string `checkers:"url"`
+}
+
+bookmark := &Bookmark{
+  URL: "https://zdo.com",
+}
+
+_, valid := checker.Check(bookmark)
+if !valid {
+  // Send the mistakes back to the user
+}
+```
+
+In your custom checkers, you can call the ```url``` checker function ```IsURL``` to validate the user input. Here is an example:
+
+```golang
+result := checker.IsURL("https://zdo.com")
+if result != checker.ResultValid {
+  // Send the mistakes back to the user
+}
+```

url.go

@@ -0,0 +1,44 @@
+package checker
+
+import (
+	"net/url"
+	"reflect"
+)
+
+// CheckerURL is the name of the checker.
+const CheckerURL = "url"
+
+// ResultNotURL indicates that the given value is not a valid URL.
+const ResultNotURL = "NOT_URL"
+
+// IsURL checks if the given value is a valid URL.
+func IsURL(value string) Result {
+	url, err := url.ParseRequestURI(value)
+	if err != nil {
+		return ResultNotURL
+	}
+
+	if url.Scheme == "" {
+		return ResultNotURL
+	}
+
+	if url.Host == "" {
+		return ResultNotURL
+	}
+
+	return ResultValid
+}
+
+// makeURL makes a checker function for the URL checker.
+func makeURL(_ string) CheckFunc {
+	return checkURL
+}
+
+// checkURL checks if the given value is a valid URL.
+func checkURL(value, _ reflect.Value) Result {
+	if value.Kind() != reflect.String {
+		panic("string expected")
+	}
+
+	return IsURL(value.String())
+}

url_test.go

@@ -0,0 +1,93 @@
+package checker_test
+
+import (
+	"testing"
+
+	"github.com/cinar/checker"
+)
+
+func TestIsURLValid(t *testing.T) {
+	result := checker.IsURL("https://zdo.com")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsURLInvalid(t *testing.T) {
+	result := checker.IsURL("https:://index.html")
+	if result == checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestCheckURLNonString(t *testing.T) {
+	defer checker.FailIfNoPanic(t)
+
+	type Bookmark struct {
+		URL int `checkers:"url"`
+	}
+
+	bookmark := &Bookmark{}
+
+	checker.Check(bookmark)
+}
+
+func TestCheckURLValid(t *testing.T) {
+	type Bookmark struct {
+		URL string `checkers:"url"`
+	}
+
+	bookmark := &Bookmark{
+		URL: "https://zdo.com",
+	}
+
+	_, valid := checker.Check(bookmark)
+	if !valid {
+		t.Fail()
+	}
+}
+
+func TestCheckURLInvalid(t *testing.T) {
+	type Bookmark struct {
+		URL string `checkers:"url"`
+	}
+
+	bookmark := &Bookmark{
+		URL: "zdo.com/index.html",
+	}
+
+	_, valid := checker.Check(bookmark)
+	if valid {
+		t.Fail()
+	}
+}
+
+func TestCheckURLWithoutSchema(t *testing.T) {
+	type Bookmark struct {
+		URL string `checkers:"url"`
+	}
+
+	bookmark := &Bookmark{
+		URL: "//zdo.com/index.html",
+	}
+
+	_, valid := checker.Check(bookmark)
+	if valid {
+		t.Fail()
+	}
+}
+
+func TestCheckURLWithoutHost(t *testing.T) {
+	type Bookmark struct {
+		URL string `checkers:"url"`
+	}
+
+	bookmark := &Bookmark{
+		URL: "https:://index.html",
+	}
+
+	_, valid := checker.Check(bookmark)
+	if valid {
+		t.Fail()
+	}
+}