go-fmp/fmp/fmp_chunk.go

package fmp

func (ctx *FmpFile) readChunk(payload []byte) (*FmpChunk, error) {

	// https://github.com/evanmiller/fmptools/blob/02eb770e59e0866dab213d80e5f7d88e17648031/HACKING
	// https://github.com/Rasmus20B/fmplib/blob/66245e5269275724bacfe1437fb1f73bc587a2f3/src/fmp_format/chunk.rs#L57-L60

	chunk := &FmpChunk{}

	if (payload[0] & 0xC0) == 0xC0 {
		payload[0] &= 0x3F
		chunk.Delayed = true
	}

	switch payload[0] {
	case 0x00:
		chunk.Type = FMP_CHUNK_SIMPLE_DATA
		chunk.Value = payload[1 : 1+1]
		chunk.Length = 2

	case 0x01:
		chunk.Type = FMP_CHUNK_SIMPLE_KEY_VALUE
		chunk.Key = uint64(payload[1])
		chunk.Value = payload[2 : 2+1]
		chunk.Length = 3

	case 0x02, 0x03, 0x04, 0x05:
		valueLength := uint64(2 * (payload[0] - 1))
		chunk.Type = FMP_CHUNK_SIMPLE_KEY_VALUE
		chunk.Key = uint64(payload[1])
		chunk.Value = payload[2 : 2+valueLength]
		chunk.Length = 2 + uint64(valueLength)

	case 0x06:
		valueLength := uint64(payload[2])
		chunk.Type = FMP_CHUNK_SIMPLE_KEY_VALUE
		chunk.Key = uint64(payload[1])
		chunk.Value = payload[3 : 3+valueLength]
		chunk.Length = 3 + uint64(valueLength)

	case 0x07:
		valueLength := parseVarUint64(payload[2 : 2+2])
		payloadLimit := min(4+valueLength, uint64(len(payload)))
		chunk.Type = FMP_CHUNK_SEGMENTED_DATA
		chunk.Index = uint64(payload[1])
		chunk.Value = payload[4:payloadLimit]
		chunk.Length = 4 + uint64(valueLength)

	case 0x08:
		chunk.Type = FMP_CHUNK_SIMPLE_DATA
		chunk.Value = payload[1 : 1+2]
		chunk.Length = 3

	case 0x09:
		chunk.Type = FMP_CHUNK_SIMPLE_KEY_VALUE
		chunk.Key = parseVarUint64(payload[1 : 1+2])
		chunk.Value = payload[3 : 3+1]
		chunk.Length = 4

	case 0x0A, 0x0B, 0x0C, 0x0D:
		valueLength := uint64(2 * (payload[0] - 0x09))
		chunk.Type = FMP_CHUNK_SIMPLE_KEY_VALUE
		chunk.Key = parseVarUint64(payload[1 : 1+2])
		chunk.Value = payload[3 : 3+valueLength]
		chunk.Length = 3 + uint64(valueLength)

	case 0x0E:
		if payload[1] == 0xFE {
			chunk.Type = FMP_CHUNK_PATH_PUSH
			chunk.Value = payload[1 : 1+8]
			chunk.Length = 10
			break
		}

		if payload[1] == 0xFF {
			chunk.Type = FMP_CHUNK_SIMPLE_DATA
			chunk.Value = payload[2 : 2+5]
			chunk.Length = 7
			break
		}

		valueLength := uint64(payload[2])
		chunk.Type = FMP_CHUNK_SIMPLE_KEY_VALUE
		chunk.Key = parseVarUint64(payload[1 : 1+2])
		chunk.Value = payload[4 : 4+valueLength]
		chunk.Length = 4 + uint64(valueLength)

	case 0x0F:
		valueLength := parseVarUint64(payload[3 : 3+2])
		payloadLimit := min(5+valueLength, uint64(len(payload)))
		chunk.Type = FMP_CHUNK_SEGMENTED_DATA
		chunk.Index = parseVarUint64(payload[1 : 1+2])
		chunk.Value = payload[5:payloadLimit]
		chunk.Length = 5 + valueLength

	case 0x10, 0x11:
		valueLength := 3 + (uint64(payload[0]) - 0x10)
		chunk.Type = FMP_CHUNK_SIMPLE_DATA
		chunk.Value = payload[1 : 1+valueLength]
		chunk.Length = 1 + uint64(valueLength)

	case 0x12, 0x13, 0x14, 0x15:
		valueLength := 1 + 2*(uint64(payload[0])-0x10)
		chunk.Type = FMP_CHUNK_SIMPLE_DATA
		chunk.Value = payload[1 : 1+valueLength]
		chunk.Length = 1 + uint64(valueLength)

	case 0x16:
		valueLength := uint64(payload[4])
		chunk.Type = FMP_CHUNK_LONG_KEY_VALUE
		chunk.Key = parseVarUint64(payload[1 : 1+3])
		chunk.Value = payload[5 : 5+valueLength]
		chunk.Length = 5 + uint64(valueLength)

	case 0x17:
		valueLength := parseVarUint64(payload[4 : 4+2])
		chunk.Type = FMP_CHUNK_LONG_KEY_VALUE
		chunk.Key = parseVarUint64(payload[1 : 1+3])
		chunk.Value = payload[6 : 6+valueLength]
		chunk.Length = 6 + uint64(valueLength)

	case 0x19:
		chunk.Type = FMP_CHUNK_SIMPLE_DATA
		chunk.Value = payload[1 : 1+1]
		chunk.Length = 2

	case 0x1A, 0x1B, 0x1C, 0x1D:
		valueLength := 2 * uint64(payload[0]-0x19)
		chunk.Type = FMP_CHUNK_SIMPLE_DATA
		chunk.Value = payload[1 : 1+valueLength]
		chunk.Length = 1 + valueLength

	case 0x1E:
		keyLength := uint64(payload[1])
		valueLength := uint64(payload[2+keyLength])
		chunk.Type = FMP_CHUNK_LONG_KEY_VALUE
		chunk.Key = parseVarUint64(payload[2 : 2+keyLength])
		chunk.Value = payload[2+keyLength+1 : 2+keyLength+1+valueLength]
		chunk.Length = 2 + uint64(keyLength) + 1 + uint64(valueLength)

	case 0x1F:
		keyLength := uint64(uint64(payload[1]))
		valueLength := parseVarUint64(payload[2+keyLength : 2+keyLength+2+1])
		chunk.Type = FMP_CHUNK_LONG_KEY_VALUE
		chunk.Key = parseVarUint64(payload[2 : 2+keyLength])
		chunk.Value = payload[2+keyLength+2 : 2+keyLength+2+valueLength]
		chunk.Length = 2 + uint64(keyLength) + 2 + uint64(valueLength)

	case 0x20:
		if payload[1] == 0xFE {
			chunk.Type = FMP_CHUNK_PATH_PUSH
			chunk.Value = payload[1 : 1+8]
			chunk.Length = 10
			break
		}

		chunk.Type = FMP_CHUNK_PATH_PUSH
		chunk.Value = payload[1 : 1+1]
		chunk.Length = 2

	case 0x23:
		chunk.Type = FMP_CHUNK_SIMPLE_DATA
		chunk.Value = payload[1 : 1+1]
		chunk.Length = 2

	case 0x28:
		chunk.Type = FMP_CHUNK_PATH_PUSH
		chunk.Value = payload[1 : 1+2]
		chunk.Length = 3

	case 0x30:
		chunk.Type = FMP_CHUNK_PATH_PUSH
		chunk.Value = payload[1 : 1+3]
		chunk.Length = 4

	case 0x38:
		valueLength := uint64(payload[1])
		chunk.Type = FMP_CHUNK_PATH_PUSH
		chunk.Value = payload[2 : 2+valueLength]
		chunk.Length = 2 + uint64(valueLength)

	case 0x3D, 0x40:
		chunk.Type = FMP_CHUNK_PATH_POP
		chunk.Length = 1

	case 0x80:
		chunk.Type = FMP_CHUNK_NOOP
		chunk.Length = 1

	default:
		return nil, ErrBadChunk
	}

	return chunk, nil
}