feat: Validate UUID without creating new UUID (google#141)

* feat: Validate UUID without creating new UUID

* fix: update comment

uuid.go

@@ -186,6 +186,59 @@ func Must(uuid UUID, err error) UUID {
 	return uuid
 }
 
+// Validate returns an error if s is not a properly formatted UUID in one of the following formats:
+//   xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
+//   urn:uuid:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
+//   xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+//   {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}
+// It returns an error if the format is invalid, otherwise nil.
+func Validate(s string) error {
+	switch len(s) {
+	// Standard UUID format
+	case 36:
+
+	// UUID with "urn:uuid:" prefix
+	case 36 + 9:
+		if !strings.EqualFold(s[:9], "urn:uuid:") {
+			return fmt.Errorf("invalid urn prefix: %q", s[:9])
+		}
+		s = s[9:]
+
+	// UUID enclosed in braces
+	case 36 + 2:
+		if s[0] != '{' || s[len(s)-1] != '}' {
+			return fmt.Errorf("invalid bracketed UUID format")
+		}
+		s = s[1 : len(s)-1]
+
+	// UUID without hyphens
+	case 32:
+		for i := 0; i < len(s); i += 2 {
+			_, ok := xtob(s[i], s[i+1])
+			if !ok {
+				return errors.New("invalid UUID format")
+			}
+		}
+
+	default:
+		return invalidLengthError{len(s)}
+	}
+
+	// Check for standard UUID format
+	if len(s) == 36 {
+		if s[8] != '-' || s[13] != '-' || s[18] != '-' || s[23] != '-' {
+			return errors.New("invalid UUID format")
+		}
+		for _, x := range []int{0, 2, 4, 6, 9, 11, 14, 16, 19, 21, 24, 26, 28, 30, 32, 34} {
+			if _, ok := xtob(s[x], s[x+1]); !ok {
+				return errors.New("invalid UUID format")
+			}
+		}
+	}
+
+	return nil
+}
+
 // String returns the string form of uuid, xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
 // , or "" if uuid is invalid.
 func (uuid UUID) String() string {

uuid_test.go

@@ -6,6 +6,7 @@ package uuid
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"os"
 	"runtime"
@@ -605,6 +606,34 @@ func FuzzFromBytes(f *testing.F) {
 	})
 }
 
+// TestValidate checks various scenarios for the Validate function
+func TestValidate(t *testing.T) {
+	testCases := []struct {
+		name   string
+		input  string
+		expect error
+	}{
+		{"Valid UUID", "123e4567-e89b-12d3-a456-426655440000", nil},
+		{"Valid UUID with URN", "urn:uuid:123e4567-e89b-12d3-a456-426655440000", nil},
+		{"Valid UUID with Braces", "{123e4567-e89b-12d3-a456-426655440000}", nil},
+		{"Valid UUID No Hyphens", "123e4567e89b12d3a456426655440000", nil},
+		{"Invalid UUID", "invalid-uuid", errors.New("invalid UUID length: 12")},
+		{"Invalid Length", "123", fmt.Errorf("invalid UUID length: %d", len("123"))},
+		{"Invalid URN Prefix", "urn:test:123e4567-e89b-12d3-a456-426655440000", fmt.Errorf("invalid urn prefix: %q", "urn:test:")},
+		{"Invalid Brackets", "[123e4567-e89b-12d3-a456-426655440000]", fmt.Errorf("invalid bracketed UUID format")},
+		{"Invalid UUID Format", "12345678gabc1234abcd1234abcd1234", fmt.Errorf("invalid UUID format")},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := Validate(tc.input)
+			if (err != nil) != (tc.expect != nil) || (err != nil && err.Error() != tc.expect.Error()) {
+				t.Errorf("Validate(%q) = %v, want %v", tc.input, err, tc.expect)
+			}
+		})
+	}
+}
+
 var asString = "f47ac10b-58cc-0372-8567-0e02b2c3d479"
 var asBytes = []byte(asString)