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|
package pktline
import (
"errors"
"fmt"
"io"
)
// ReadOptions controls decoding behavior.
type ReadOptions struct {
// ChompLF removes one trailing '\n' from PacketData payloads.
ChompLF bool
}
// Decoder reads pkt-line frames from an io.Reader.
//
// It is advisable to supply a buffered reader.
//
// It preserves frame boundaries and supports one-frame lookahead via PeekFrame.
type Decoder struct {
r io.Reader
maxData int
opts ReadOptions
peeked bool
peek Frame
peekErr error
}
// NewDecoder creates a decoder over r.
func NewDecoder(r io.Reader, opts ReadOptions) *Decoder {
return &Decoder{
r: r,
maxData: LargePacketDataMax,
opts: opts,
}
}
// SetMaxData sets maximum payload size accepted for one data packet.
//
// Non-positive n resets to LargePacketDataMax.
func (d *Decoder) SetMaxData(n int) {
if n <= 0 {
d.maxData = LargePacketDataMax
return
}
d.maxData = n
}
func cloneFrame(f Frame) Frame {
if f.Type != PacketData {
return Frame{Type: f.Type}
}
out := Frame{Type: f.Type}
if f.Payload != nil {
out.Payload = append([]byte(nil), f.Payload...)
}
return out
}
// ReadFrame reads one frame.
//
// 0000 is a PacketFlush
// 0001 is a PacketDelim
// 0002 is a PacketResponseEnd
// 0004 is a PacketData with empty payload
//
// 0003 and malformed headers return *ProtocolError.
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.
//
// A subsequent ReadFrame returns the same frame.
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) {
var hdr [4]byte
_, err := io.ReadFull(d.r, hdr[:])
if err != nil {
if errors.Is(err, io.EOF) {
return Frame{}, io.EOF
}
if errors.Is(err, io.ErrUnexpectedEOF) {
return Frame{}, io.ErrUnexpectedEOF
}
return Frame{}, err
}
n, err := ParseLengthHeader(hdr)
if err != nil {
return Frame{}, &ProtocolError{Header: hdr, Reason: err.Error()}
}
switch n {
case 0:
return Frame{Type: PacketFlush}, nil
case 1:
return Frame{Type: PacketDelim}, nil
case 2:
return Frame{Type: PacketResponseEnd}, nil
case 3:
return Frame{}, &ProtocolError{Header: hdr, Reason: "invalid pkt-line length 3"}
}
if n < 4 {
return Frame{}, &ProtocolError{Header: hdr, Reason: fmt.Sprintf("invalid pkt-line length %d", n)}
}
if n > LargePacketMax {
perr := &ProtocolError{Header: hdr, Reason: fmt.Sprintf("pkt-line length %d exceeds max %d", n, LargePacketMax)}
err := d.discardPayload(n - 4)
if err != nil {
return Frame{}, errors.Join(perr, err)
}
return Frame{}, perr
}
payloadLen := n - 4
if payloadLen > d.maxData {
serr := fmt.Errorf("%w: %d > %d", ErrTooLarge, payloadLen, d.maxData)
err := d.discardPayload(payloadLen)
if err != nil {
return Frame{}, errors.Join(serr, err)
}
return Frame{}, serr
}
payload := make([]byte, payloadLen)
_, err = io.ReadFull(d.r, payload)
if err != nil {
if errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF) {
return Frame{}, io.ErrUnexpectedEOF
}
return Frame{}, err
}
if d.opts.ChompLF && len(payload) > 0 && payload[len(payload)-1] == '\n' {
payload = payload[:len(payload)-1]
}
return Frame{Type: PacketData, Payload: payload}, nil
}
func (d *Decoder) discardPayload(n int) error {
if n <= 0 {
return nil
}
_, err := io.CopyN(io.Discard, d.r, int64(n))
if err == nil {
return nil
}
if errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF) {
return io.ErrUnexpectedEOF
}
return err
}
|
