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
}
// 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)
}
// 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
}
// 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
}
// 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
}