added ContainsOnly validator

Author: tomi77

README.md

@@ -55,6 +55,14 @@ Count occurrences of a chars and compares it with required value.
 passwordValidator := validator.New(validator.ContainsAtLeast(5, "abcdefghijklmnopqrstuvwxyz", nil))
 ~~~
 
+### ContainsOnly
+
+Check if password contains only selected chars.
+
+~~~go
+passwordValidator := validator.New(validator.ContainsOnly("abcdefghijklmnopqrstuvwxyz", nil))
+~~~
+
 ### MaxLength
 
 Check if password length is not greater that defined length.

TODO.md

@@ -1,3 +1,2 @@
 * Unique
 * NotSequential
-* NotContains or ContainsOnly

contains_only.go

@@ -0,0 +1,25 @@
+package validator
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+)
+
+// ContainsOnly returns a ValidateFunc that check if password contains only selected chars
+func ContainsOnly(chars string, customError error) ValidateFunc {
+	return ValidateFunc(func(password string) error {
+		bChars := []byte(chars)
+		for _, char := range strings.Split(password, "") {
+			bChar := []byte(char)[0]
+			idx := bytes.IndexByte(bChars, bChar)
+			if idx == -1 {
+				if customError != nil {
+					return customError
+				}
+				return fmt.Errorf("the password must contains only %s", chars)
+			}
+		}
+		return nil
+	})
+}

contains_only_test.go

@@ -0,0 +1,29 @@
+package validator
+
+import (
+	"errors"
+	"fmt"
+)
+
+func ExampleContainsOnly() {
+	passwordValidator := ContainsOnly("abcdefghijklmnopqrstuvwxyz", nil)
+	fmt.Println(passwordValidator("password"))
+	fmt.Println(passwordValidator("password0"))
+	fmt.Println(passwordValidator("passWORD"))
+	// Output:
+	// <nil>
+	// the password must contains only abcdefghijklmnopqrstuvwxyz
+	// the password must contains only abcdefghijklmnopqrstuvwxyz
+}
+
+func ExampleContainsOnly_customError() {
+	err := errors.New("custom error message")
+	passwordValidator := ContainsOnly("abcdefghijklmnopqrstuvwxyz", err)
+	fmt.Println(passwordValidator("password"))
+	fmt.Println(passwordValidator("password0"))
+	fmt.Println(passwordValidator("passWORD"))
+	// Output:
+	// <nil>
+	// custom error message
+	// custom error message
+}