Function MaxEncodedLen

encode.go:78–108

MaxEncodedLen returns the maximum length of a snappy block, given its uncompressed length. It will return a negative value if srcLen is too large to encode.

(srcLen int)

//
// It will return a negative value if srcLen is too large to encode.
func MaxEncodedLen(srcLen int) int {
	n := uint64(srcLen)
	if n > 0xffffffff {
		return -1
	}
	// Compressed data can be defined as:
	//    compressed := item* literal*
	//    item       := literal* copy
	//
	// The trailing literal sequence has a space blowup of at most 62/60
	// since a literal of length 60 needs one tag byte + one extra byte
	// for length information.
	//
	// Item blowup is trickier to measure. Suppose the "copy" op copies
	// 4 bytes of data. Because of a special check in the encoding code,
	// we produce a 4-byte copy only if the offset is < 65536. Therefore
	// the copy op takes 3 bytes to encode, and this type of item leads
	// to at most the 62/60 blowup for representing literals.
	//
	// Suppose the "copy" op copies 5 bytes of data. If the offset is big
	// enough, it will take 5 bytes to encode the copy op. Therefore the
	// worst case here is a one-byte literal followed by a five-byte copy.
	// That is, 6 bytes of input turn into 7 bytes of "compressed" data.
	//
	// This last factor dominates the blowup, so the final estimate is:
	n = 32 + n + n/6
	if n > 0xffffffff {
		return -1
	}
	return int(n)
}

var errClosed = errors.New("snappy: Writer is closed")