Function PeekLength

pkg/util/encoding/encoding.go:1973–2095

PeekLength returns the length of the encoded value at the start of b. Note: if this function succeeds, it's not a guarantee that decoding the value will succeed. PeekLength is meant to be used on key encoded data only.

(b []byte)

// if this function succeeds, it's not a guarantee that decoding the value will
// succeed. PeekLength is meant to be used on key encoded data only.
func PeekLength(b []byte) (int, error) {
	if len(b) == 0 {
		return 0, errors.Errorf("empty slice")
	}
	m := b[0]
	switch m {
	case encodedNull, encodedNullDesc, encodedNotNull, encodedNotNullDesc,
		floatNaN, floatNaNDesc, floatZero, decimalZero, byte(True), byte(False),
		emptyArray, voidMarker, jsonNullKeyMarker, jsonNullKeyDescendingMarker,
		jsonFalseKeyMarker, jsonFalseKeyDescendingMarker, jsonTrueKeyMarker,
		jsonTrueKeyDescendingMarker:
		// ascendingNullWithinArrayKey and descendingNullWithinArrayKey also
		// contain the same byte values as encodedNotNull and encodedNotNullDesc
		// respectively, but they cannot be included explicitly in the case
		// statement.
		return 1, nil
	case bitArrayMarker, bitArrayDescMarker:
		terminator := byte(bitArrayDataTerminator)
		if m == bitArrayDescMarker {
			terminator = bitArrayDataDescTerminator
		}
		_, n, err := getBitArrayWordsLen(b[1:], terminator)
		if err != nil {
			return 1 + n, err
		}
		m, err := getVarintLen(b[n+2:])
		if err != nil {
			return 1 + n + m + 1, err
		}
		return 1 + n + m + 1, nil
	case jsonStringKeyMarker, jsonStringKeyDescendingMarker,
		jsonNumberKeyMarker, jsonNumberKeyDescendingMarker:
		dir := Ascending
		if (m == jsonStringKeyDescendingMarker) ||
			(m == jsonNumberKeyDescendingMarker) {
			dir = Descending
		}
		length, err := getArrayOrJSONLength(b[1:], dir, IsJSONKeyDone)
		return 1 + length, err
	case jsonArrayKeyMarker, jsonArrayKeyDescendingMarker,
		jsonObjectKeyMarker, jsonObjectKeyDescendingMarker,
		jsonEmptyArrayKeyMarker, jsonEmptyArrayKeyDescendingMarker:
		dir := Ascending
		if (m == jsonArrayKeyDescendingMarker) ||
			(m == jsonObjectKeyDescendingMarker) ||
			(m == jsonEmptyArrayKeyDescendingMarker) {
			dir = Descending
		}
		// removing the starter tag
		b = b[1:]

		// Getting the number of elements present
		// in the container.
		numberElems, err := getVarintLen(b)
		if err != nil {
			return -1, errors.AssertionFailedf("failed to get the number of elements" +
				"in the container")
		}