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examples/wasm/vendor/github.com/quic-go/qpack/encoder.go 633735d797cc5f5d48cb2e22e8fd7cd743930daf (633735d7) Text, 2.63 KB
package qpack
import (
"io"
"golang.org/x/net/http2/hpack"
)
// An Encoder performs QPACK encoding.
type Encoder struct {
wrotePrefix bool
w io.Writer
buf []byte
}
// NewEncoder returns a new Encoder which performs QPACK encoding. An
// encoded data is written to w.
func NewEncoder(w io.Writer) *Encoder {
return &Encoder{w: w}
}
// WriteField encodes f into a single Write to e's underlying Writer.
// This function may also produce bytes for the Header Block Prefix
// if necessary. If produced, it is done before encoding f.
func (e *Encoder) WriteField(f HeaderField) error {
// write the Header Block Prefix
if !e.wrotePrefix {
e.buf = appendVarInt(e.buf, 8, 0)
e.buf = appendVarInt(e.buf, 7, 0)
e.wrotePrefix = true
}
idxAndVals, nameFound := encoderMap[f.Name]
if nameFound {
if idxAndVals.values == nil {
if len(f.Value) == 0 {
e.writeIndexedField(idxAndVals.idx)
} else {
e.writeLiteralFieldWithNameReference(&f, idxAndVals.idx)
}
} else {
valIdx, valueFound := idxAndVals.values[f.Value]
if valueFound {
e.writeIndexedField(valIdx)
} else {
e.writeLiteralFieldWithNameReference(&f, idxAndVals.idx)
}
}
} else {
e.writeLiteralFieldWithoutNameReference(f)
}
_, err := e.w.Write(e.buf)
e.buf = e.buf[:0]
return err
}
// Close declares that the encoding is complete and resets the Encoder
// to be reused again for a new header block.
func (e *Encoder) Close() error {
e.wrotePrefix = false
return nil
}
func (e *Encoder) writeLiteralFieldWithoutNameReference(f HeaderField) {
offset := len(e.buf)
e.buf = appendVarInt(e.buf, 3, hpack.HuffmanEncodeLength(f.Name))
e.buf[offset] ^= 0x20 ^ 0x8
e.buf = hpack.AppendHuffmanString(e.buf, f.Name)
offset = len(e.buf)
e.buf = appendVarInt(e.buf, 7, hpack.HuffmanEncodeLength(f.Value))
e.buf[offset] ^= 0x80
e.buf = hpack.AppendHuffmanString(e.buf, f.Value)
}
// Encodes a header field whose name is present in one of the tables.
func (e *Encoder) writeLiteralFieldWithNameReference(f *HeaderField, id uint8) {
offset := len(e.buf)
e.buf = appendVarInt(e.buf, 4, uint64(id))
// Set the 01NTxxxx pattern, forcing N to 0 and T to 1
e.buf[offset] ^= 0x50
offset = len(e.buf)
e.buf = appendVarInt(e.buf, 7, hpack.HuffmanEncodeLength(f.Value))
e.buf[offset] ^= 0x80
e.buf = hpack.AppendHuffmanString(e.buf, f.Value)
}
// Encodes an indexed field, meaning it's entirely defined in one of the tables.
func (e *Encoder) writeIndexedField(id uint8) {
offset := len(e.buf)
e.buf = appendVarInt(e.buf, 6, uint64(id))
// Set the 1Txxxxxx pattern, forcing T to 1
e.buf[offset] ^= 0xc0
}
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