jackc/pgx · error

invalid length for UUID

Error message

invalid length for UUID: %v

What it means

UnmarshalJSON requires exactly 38 bytes: a 36-character hyphenated UUID enclosed in two JSON quote characters. Any other length — unquoted input, a bare 32-char UUID, missing quotes, or trailing data — trips this length guard before parseUUID is ever invoked.

Solutions

1. Feed valid JSON: a quoted 36-character hyphenated UUID
2. Unquote the payload yourself and use pgtype.UUID.Scan if input may lack quotes
3. Validate the JSON string length before unmarshaling

When it happens

Trigger: Thrown at pgtype/uuid.go:128 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of jackc/pgx@ec1a0befd2 (2026-08-04). Data as JSON: /api/errors/1946ff17c767a5e4. Report an issue: GitHub.

Appendix: source

Thrown at pgtype/uuid.go:128

	if !src.Valid {
		return []byte("null"), nil
	}

	var buff bytes.Buffer
	buff.WriteByte('"')
	buff.WriteString(encodeUUID(src.Bytes))
	buff.WriteByte('"')
	return buff.Bytes(), nil
}

// UnmarshalJSON implements the [encoding/json.Unmarshaler] interface.
func (dst *UUID) UnmarshalJSON(src []byte) error {
	if bytes.Equal(src, []byte("null")) {
		*dst = UUID{}
		return nil
	}
	if len(src) != 38 {
		return fmt.Errorf("invalid length for UUID: %v", len(src))
	}
	buf, err := parseUUID(string(src[1 : len(src)-1]))
	if err != nil {
		return err
	}
	*dst = UUID{Bytes: buf, Valid: true}
	return nil
}

type UUIDCodec struct{}

func (UUIDCodec) FormatSupported(format int16) bool {
	return format == TextFormatCode || format == BinaryFormatCode
}

func (UUIDCodec) PreferredFormat() int16 {
	return BinaryFormatCode
}

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