Adding general yaml validation

README.md

@@ -209,6 +209,7 @@ Baked-in Validations
 | semver | Semantic Versioning 2.0.0 |
 | ulid | Universally Unique Lexicographically Sortable Identifier ULID |
 | cve | Common Vulnerabilities and Exposures Identifier (CVE id) |
+| yaml | Yaml document |
 
 ### Comparisons:
 | Tag | Description |

baked_in.go

@@ -21,6 +21,7 @@ import (
 
 	"golang.org/x/crypto/sha3"
 	"golang.org/x/text/language"
+	"gopkg.in/yaml.v3"
 
 	"github.com/gabriel-vasile/mimetype"
 	"github.com/leodido/go-urn"
@@ -231,6 +232,7 @@ var (
 		"mongodb":                       isMongoDB,
 		"cron":                          isCron,
 		"spicedb":                       isSpiceDB,
+		"yaml":                          isYaml,
 	}
 )
 
@@ -2878,3 +2880,12 @@ func isCron(fl FieldLevel) bool {
 	cronString := fl.Field().String()
 	return cronRegex.MatchString(cronString)
 }
+
+// isYaml is the validation for validating if the the current fields value is a valid yaml document
+func isYaml(f1 FieldLevel) bool {
+	document := f1.Field().String()
+	var parsedDoc interface{}
+	err := yaml.Unmarshal([]byte(document), &parsedDoc)
+
+	return err == nil
+}

go.mod

@@ -15,4 +15,5 @@ require (
 require (
 	golang.org/x/net v0.8.0 // indirect
 	golang.org/x/sys v0.6.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

validator_test.go

@@ -13487,3 +13487,42 @@ func TestNestedStructValidation(t *testing.T) {
 		})
 	}
 }
+
+func TestIsYamlValidation(t *testing.T) {
+
+	rawLiteral := `
+- first_element: element name
+  a: true
+  b:
+    - inner_element: Only element of the inner list.
+      c:
+        d: "This string is on the deepest level"`
+
+	tests := []struct {
+		value    string `validate:"yaml"`
+		tag      string
+		expected bool
+	}{
+		{"singleline: one line", "yaml", true},
+		{"multiline: A\nb: B\n", "yaml", true},
+		{"mixedtype: 1\nb: True\nc: [ 1, 1, 2, 3, 5]", "yaml", true},
+		{rawLiteral, "yaml", true},
+		{"a: ?", "yaml", false},
+		{"...", "yaml", false},
+	}
+
+	validate := New()
+
+	for i, test := range tests {
+		errs := validate.Var(test.value, test.tag)
+		if test.expected {
+			if !IsEqual(errs, nil) {
+				t.Fatalf(`Index: %d yaml "%s" failed Error: %s`, i, test.value, errs)
+			}
+		} else {
+			if IsEqual(errs, nil) {
+				t.Fatalf(`Index: %d yaml "%s" should have errs`, i, test.value)
+			}
+		}
+	}
+}