96 lines
2.6 KiB
Go
96 lines
2.6 KiB
Go
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package qpack
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import (
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"io"
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"golang.org/x/net/http2/hpack"
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)
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// An Encoder performs QPACK encoding.
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type Encoder struct {
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wrotePrefix bool
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w io.Writer
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buf []byte
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}
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// NewEncoder returns a new Encoder which performs QPACK encoding. An
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// encoded data is written to w.
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func NewEncoder(w io.Writer) *Encoder {
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return &Encoder{w: w}
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}
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// WriteField encodes f into a single Write to e's underlying Writer.
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// This function may also produce bytes for the Header Block Prefix
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// if necessary. If produced, it is done before encoding f.
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func (e *Encoder) WriteField(f HeaderField) error {
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// write the Header Block Prefix
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if !e.wrotePrefix {
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e.buf = appendVarInt(e.buf, 8, 0)
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e.buf = appendVarInt(e.buf, 7, 0)
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e.wrotePrefix = true
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}
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idxAndVals, nameFound := encoderMap[f.Name]
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if nameFound {
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if idxAndVals.values == nil {
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if len(f.Value) == 0 {
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e.writeIndexedField(idxAndVals.idx)
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} else {
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e.writeLiteralFieldWithNameReference(&f, idxAndVals.idx)
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}
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} else {
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valIdx, valueFound := idxAndVals.values[f.Value]
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if valueFound {
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e.writeIndexedField(valIdx)
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} else {
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e.writeLiteralFieldWithNameReference(&f, idxAndVals.idx)
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}
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}
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} else {
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e.writeLiteralFieldWithoutNameReference(f)
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}
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_, err := e.w.Write(e.buf)
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e.buf = e.buf[:0]
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return err
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}
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// Close declares that the encoding is complete and resets the Encoder
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// to be reused again for a new header block.
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func (e *Encoder) Close() error {
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e.wrotePrefix = false
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return nil
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}
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func (e *Encoder) writeLiteralFieldWithoutNameReference(f HeaderField) {
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offset := len(e.buf)
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e.buf = appendVarInt(e.buf, 3, hpack.HuffmanEncodeLength(f.Name))
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e.buf[offset] ^= 0x20 ^ 0x8
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e.buf = hpack.AppendHuffmanString(e.buf, f.Name)
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offset = len(e.buf)
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e.buf = appendVarInt(e.buf, 7, hpack.HuffmanEncodeLength(f.Value))
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e.buf[offset] ^= 0x80
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e.buf = hpack.AppendHuffmanString(e.buf, f.Value)
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}
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// Encodes a header field whose name is present in one of the tables.
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func (e *Encoder) writeLiteralFieldWithNameReference(f *HeaderField, id uint8) {
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offset := len(e.buf)
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e.buf = appendVarInt(e.buf, 4, uint64(id))
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// Set the 01NTxxxx pattern, forcing N to 0 and T to 1
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e.buf[offset] ^= 0x50
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offset = len(e.buf)
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e.buf = appendVarInt(e.buf, 7, hpack.HuffmanEncodeLength(f.Value))
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e.buf[offset] ^= 0x80
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e.buf = hpack.AppendHuffmanString(e.buf, f.Value)
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}
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// Encodes an indexed field, meaning it's entirely defined in one of the tables.
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func (e *Encoder) writeIndexedField(id uint8) {
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offset := len(e.buf)
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e.buf = appendVarInt(e.buf, 6, uint64(id))
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// Set the 1Txxxxxx pattern, forcing T to 1
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e.buf[offset] ^= 0xc0
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}
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