Пример #1
0
func DecodeLiteral(buf *swrap.SWrap) (value string) {
	// 最初のバイトを取り出す
	first := (*buf)[0]

	// 最初の 1bit をみて huffman かどうか取得
	huffmanEncoded := (first&0x80 == 0x80)

	Trace("huffman = %t", huffmanEncoded)
	if huffmanEncoded {
		// 最初のバイトから 1 bit 目を消す
		(*buf)[0] = first & 127

		// ここで prefixed Integer 7 で読む。
		b := DecodePrefixedInteger(buf, 7)
		Trace("Literal Length = %v, buf size=%v", b, buf.Len())

		// その長さの分だけバイト値を取り出す
		code := make([]byte, 0)
		for ; b > 0; b-- {
			code = append(code, buf.Shift())
		}

		// ハフマンデコード
		value = string(huffman.Decode(code))
		Trace("decoded = %v", value)
	} else {
		valueLength := DecodePrefixedInteger(buf, 7)
		value = DecodeString(buf, valueLength)
	}
	return value
}
Пример #2
0
// read n byte from buffer as string
func DecodeString(buf *swrap.SWrap, n uint32) string {
	valueBytes := make([]byte, 0, n)
	for i := n; i > 0; i-- {
		valueBytes = append(valueBytes, buf.Shift())
	}
	return string(valueBytes)
}
Пример #3
0
// Decode N bit prefixed Representation
// to Integer
//
// Read N bit from first 1 byte as I
// If I < 2^N-1
//     decode I
// Else
//     i = 0
//     read next 1 byte as b
//     While b > 128
//         I += (b - 128) * 128^(i-1)
//         i++
func Decode(buf swrap.SWrap, N uint8) uint32 {
	boundary := uint32(1<<N - 1) // 2^N-1
	I := uint32(buf.Shift())     // Read N bit from first 1 byte as I
	if I < boundary {            // less than 2^N-1
		return I // as is
	}
	for i := 0; ; i++ { // continue while follow bites are bigger than 128
		b := buf.Shift()
		shift := uint8(7 * i)
		if b >= 128 { // if first bit is 1
			// to 0 at first bit (- 128) and shift 7*i bit
			// and add
			I += uint32(b-128) << shift
		} else { // if first bit is 0
			// shit 7*i shift
			// and add
			I += uint32(b) << shift
			break
		}
	}
	return I
}
Пример #4
0
// read prefixed N bytes from buffer
// if N bit of first byte is 2^N-1 (ex 1111 in N=4)
// read follow byte until it's smaller than 128
func ReadPrefixedInteger(buf *swrap.SWrap, N uint8) swrap.SWrap {
	boundary := byte(1<<N - 1) // 2^N-1
	first := buf.Shift()

	first = first & boundary // mask N bit
	prefix := swrap.New([]byte{first})

	// if first byte is smaller than boundary
	// it's end of the prefixed bytes
	if first < boundary {
		return prefix
	}

	// read bytes while bytes smaller than 128
	for {
		tmp := buf.Shift()
		prefix.Add(tmp)
		if tmp < 128 {
			break
		}
	}

	return prefix
}
Пример #5
0
// Decode single Frame from buffer and return it
func DecodeHeader(buf *swrap.SWrap) Frame {
	// check first byte
	types := (*buf)[0]
	Trace("types = %v", types)
	if types >= 0x80 { // 1xxx xxxx
		Debug("Indexed Header Representation")

		index := DecodePrefixedInteger(buf, 7)
		Trace("Indexed = %v", index)
		frame := NewIndexedHeader(index)

		if index == 0 {
			// TODO: Decoding Error
			// log.Fatal("Decoding Error: The index value of 0 is not used.")
		}
		return frame
	}
	if types == 0 { // 0000 0000
		Debug("StringLiteral (indexing = WITHOUT)")

		// remove first byte defines type
		buf.Shift()

		indexing := WITHOUT
		name := DecodeLiteral(buf)
		Trace("StringLiteral name = %v", name)
		value := DecodeLiteral(buf)
		Trace("StringLiteral value = %v", value)
		frame := NewStringLiteral(indexing, name, value)
		return frame
	}
	if types == 0x10 { // 0001 0000
		Debug("StringLiteral (indexing = NEVER)")

		// remove first byte defines type
		buf.Shift()

		indexing := NEVER
		name := DecodeLiteral(buf)
		Trace("StringLiteral name = %v", name)
		value := DecodeLiteral(buf)
		Trace("StringLiteral value = %v", value)
		frame := NewStringLiteral(indexing, name, value)
		return frame
	}
	if types == 0x40 { // 0100 0000
		Debug("StringLiteral (indexing = WITH)")

		// remove first byte defines type
		buf.Shift()

		indexing := WITH
		name := DecodeLiteral(buf)
		Trace("StringLiteral name = %v", name)
		value := DecodeLiteral(buf)
		Trace("StringLiteral value = %v", value)
		frame := NewStringLiteral(indexing, name, value)
		return frame
	}
	if types&0xc0 == 0x40 { // 01xx xxxx & 1100 0000 == 0100 0000
		Debug("IndexedLiteral (indexing = WITH)")

		indexing := WITH
		index := DecodePrefixedInteger(buf, 6)
		Trace("IndexedLiteral index = %v", index)
		value := DecodeLiteral(buf)
		Trace("IndexedLiteral value = %v", value)
		frame := NewIndexedLiteral(indexing, index, value)
		return frame
	}
	if types&0xf0 == 0 { // 0000 xxxx & 1111 0000 == 0000 0000
		Debug("IndexedLiteral (indexing = WITHOUT)")

		indexing := WITHOUT
		index := DecodePrefixedInteger(buf, 4)
		Trace("IndexedLiteral index = %v", index)
		value := DecodeLiteral(buf)
		Trace("IndexedLiteral value = %v", value)
		frame := NewIndexedLiteral(indexing, index, value)
		return frame
	}
	if types&0xf0 == 0x10 { // 0000 xxxx & 1111 0000 == 0001 0000
		Debug("IndexedLiteral (indexing = NEVER)")

		indexing := NEVER
		index := DecodePrefixedInteger(buf, 4)
		Trace("IndexedLiteral index = %v", index)
		value := DecodeLiteral(buf)
		Trace("IndexedLiteral value = %v", value)
		frame := NewIndexedLiteral(indexing, index, value)
		return frame
	}
	if types&0xe0 == 0x20 { // 001x xxxx & 1110 0000 == 0010 0000
		Debug("Header Table Size Update")

		maxSize := DecodePrefixedInteger(buf, 5)
		frame := NewDynamicTableSizeUpdate(maxSize)
		return frame
	}
	return nil
}