Add validation for directories

baked_in.go

@@ -158,6 +158,7 @@ var (
 		"html":             isHTML,
 		"html_encoded":     isHTMLEncoded,
 		"url_encoded":      isURLEncoded,
+		"dir":              isDir,
 	}
 )
 
@@ -1845,3 +1846,19 @@ func isFQDN(fl FieldLevel) bool {
 	return strings.ContainsAny(val, ".") &&
 		hostnameRegexRFC952.MatchString(val)
 }
+
+// IsDir is the validation function for validating if the current field's value is a valid directory.
+func isDir(fl FieldLevel) bool {
+	field := fl.Field()
+
+	if field.Kind() == reflect.String {
+		fileInfo, err := os.Stat(field.String())
+		if err != nil {
+			return false
+		}
+
+		return fileInfo.IsDir()
+	}
+
+	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
+}

doc.go

@@ -947,6 +947,14 @@ to https://tools.ietf.org/html/rfc3986#section-2.1
 
 	Usage: url_encoded
 
+Directory
+
+This validates that a string value contains a valid directory and that
+it exists on the machine.
+This is done using os.Stat, which is a platform independent function.
+
+	Usage: dir
+
 Alias Validators and Tags
 
 NOTE: When returning an error, the tag returned in "FieldError" will be

validator_test.go

@@ -8508,3 +8508,38 @@ func TestStructLevelValidationsPointerPassing(t *testing.T) {
 	NotEqual(t, errs, nil)
 	AssertError(t, errs, "TestStruct.StringVal", "TestStruct.String", "StringVal", "String", "badvalueteststruct")
 }
+
+func TestDirValidation(t *testing.T) {
+	validate := New()
+
+	tests := []struct {
+		title    string
+		param    string
+		expected bool
+	}{
+		{"existing dir", "testdata", true},
+		{"existing self dir", ".", true},
+		{"existing parent dir", "..", true},
+		{"empty dir", "", false},
+		{"missing dir", "non_existing_testdata", false},
+		{"a file not a directory", filepath.Join("testdata", "a.go"), false},
+	}
+
+	for _, test := range tests {
+		errs := validate.Var(test.param, "dir")
+
+		if test.expected {
+			if !IsEqual(errs, nil) {
+				t.Fatalf("Test: '%s' failed Error: %s", test.title, errs)
+			}
+		} else {
+			if IsEqual(errs, nil) {
+				t.Fatalf("Test: '%s' failed Error: %s", test.title, errs)
+			}
+		}
+	}
+
+	PanicMatches(t, func() {
+		validate.Var(2, "dir")
+	}, "Bad field type int")
+}