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|
package sideband64k
import (
"fmt"
"io"
"codeberg.org/lindenii/furgit/format/pktline"
)
// ReadOptions controls sideband decoding behavior.
type ReadOptions struct {
// ChompLF removes one trailing '\n' from FrameData payloads only.
ChompLF bool
}
// Decoder reads side-band-64k frames from an io.Reader.
//
// It preserves frame boundaries and supports one-frame lookahead via
// PeekFrame.
type Decoder struct {
dec *pktline.Decoder
maxData int
opts ReadOptions
peeked bool
peek Frame
peekErr error
}
// NewDecoder creates a decoder over r.
func NewDecoder(r io.Reader, opts ReadOptions) *Decoder {
d := &Decoder{
dec: pktline.NewDecoder(r, pktline.ReadOptions{}),
maxData: DataMax,
opts: opts,
}
d.dec.SetMaxData(pktline.LargePacketDataMax)
return d
}
// SetMaxData sets maximum payload size accepted for one sideband data packet.
//
// Non-positive n resets to DataMax.
func (d *Decoder) SetMaxData(n int) {
if n <= 0 {
d.maxData = DataMax
return
}
d.maxData = n
}
// ReadFrame reads one frame.
func (d *Decoder) ReadFrame() (Frame, error) {
if d.peeked {
d.peeked = false
return cloneFrame(d.peek), d.peekErr
}
return d.readFrame()
}
// PeekFrame returns the next frame without consuming it.
func (d *Decoder) PeekFrame() (Frame, error) {
if !d.peeked {
d.peek, d.peekErr = d.readFrame()
d.peeked = true
}
return cloneFrame(d.peek), d.peekErr
}
func (d *Decoder) readFrame() (Frame, error) {
f, err := d.dec.ReadFrame()
if err != nil {
return Frame{}, err
}
switch f.Type {
case pktline.PacketFlush:
return Frame{Type: FrameFlush}, nil
case pktline.PacketDelim:
return Frame{Type: FrameDelim}, nil
case pktline.PacketResponseEnd:
return Frame{Type: FrameResponseEnd}, nil
case pktline.PacketData:
if len(f.Payload) == 0 {
return Frame{}, &ProtocolError{Reason: "missing sideband designator"}
}
payload := f.Payload[1:]
if len(payload) > d.effectiveMaxData() {
return Frame{}, fmt.Errorf("%w: %d > %d", ErrTooLarge, len(payload), d.effectiveMaxData())
}
band := Band(f.Payload[0])
if !validBand(band) {
return Frame{}, &ProtocolError{Reason: fmt.Sprintf("%v: %d", ErrInvalidBand, band)}
}
payload = append([]byte(nil), payload...)
if d.opts.ChompLF && band == BandData && len(payload) > 0 && payload[len(payload)-1] == '\n' {
payload = payload[:len(payload)-1]
}
return Frame{
Type: frameTypeForBand(band),
Payload: payload,
}, nil
default:
return Frame{}, &ProtocolError{Reason: "unknown pkt-line frame type"}
}
}
func (d *Decoder) effectiveMaxData() int {
return effectiveMaxData(d.maxData)
}
func cloneFrame(f Frame) Frame {
if f.Type == FrameFlush || f.Type == FrameDelim || f.Type == FrameResponseEnd {
return Frame{Type: f.Type}
}
out := Frame{Type: f.Type}
if f.Payload != nil {
out.Payload = append([]byte(nil), f.Payload...)
}
return out
}
func validBand(band Band) bool {
return band == BandData || band == BandProgress || band == BandError
}
func frameTypeForBand(band Band) FrameType {
switch band {
case BandData:
return FrameData
case BandProgress:
return FrameProgress
case BandError:
return FrameError
default:
panic("invalid sideband64k band")
}
}
func effectiveMaxData(n int) int {
if n <= 0 || n > DataMax {
return DataMax
}
return n
}
|
