/
b2f.go
633 lines (545 loc) · 15.7 KB
/
b2f.go
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// Copyright 2015 Martin Hebnes Pedersen (LA5NTA). All rights reserved.
// Use of this source code is governed by the MIT-license that can be
// found in the LICENSE file.
package fbb
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"log"
"mime"
"strconv"
"strings"
"time"
"github.com/la5nta/wl2k-go/transport"
)
var ErrOffsetLimitExceeded error = errors.New("Protocol does not support offset larger than 6 digits")
const (
ProtocolOffsetSizeLimit = 999999
MaxBlockSize = 5
// Paclink-unix uses 250, protocol maximum is 255, but we use 125 to allow use of AX.25 links with a paclen of 128.
// TODO: Consider setting this dynamically.
MaxMsgLength = 125
)
const (
cmdPrefix = 'F'
cmdPrompt = '>'
cmdNoMoreMessages = 'F'
cmdQuit = 'Q'
cmdPropAnswer = 'S'
cmdPropA = 'A'
cmdPropB = 'B'
cmdPropC = 'C' // Wl2k extended B2 message
cmdPropD = 'D' // Gzip compressed B2 message (GZIP_EXPERIMENT)
)
const (
_CHRNUL byte = 0
_CHRSOH = 1
_CHRSTX = 2
_CHREOT = 4
)
func (s *Session) handleOutbound(rw io.ReadWriter) (quitSent bool, err error) {
var sent map[string]bool
// Send outbound messages
if len(s.outbound()) > 0 {
sent, err = s.sendOutbound(rw)
if err != nil {
return
}
}
// Report rejected now, they can safely be omitted even if an error occures
for mid, rej := range sent {
if rej {
s.h.SetSent(mid, rej)
delete(sent, mid)
}
}
// If all messages was deferred/rejected, we should propose new messages
if len(sent) == 0 && len(s.outbound()) > 0 {
return s.handleOutbound(rw)
}
// Handle session turnover
switch {
case len(sent) > 0:
// Turnover is implied
case s.remoteNoMsgs && len(sent) == 0:
s.pLog.Print(">FQ")
fmt.Fprint(rw, "FQ\r")
quitSent = true
return // No need to check for remote error since we did not send any messages
default:
s.pLog.Print(">FF")
fmt.Fprint(rw, "FF\r")
}
// Error reporting from remote is not defined by the protocol,
// but usually indicated by sending a line prefixed with '***'.
// The only valid bytes (according to protocol) after a session
// turnover is 'F' or ';', so we use those to confirm the block
// was successfully received.
var p []byte
if p, err = s.rd.Peek(1); err != nil {
return
} else if p[0] != 'F' && p[0] != ';' {
var line string
line, err = s.nextLine()
if err != nil {
return
}
err = fmt.Errorf("Unexpected response: '%s'", line)
return
}
// Report successfully sent messages
for mid, rej := range sent {
s.h.SetSent(mid, rej)
if !rej {
s.trafficStats.Sent = append(s.trafficStats.Sent, mid)
}
}
return
}
func (s *Session) sendOutbound(rw io.ReadWriter) (sent map[string]bool, err error) {
sent = make(map[string]bool) // Use this to keep track of sent (rejected or not) mids.
var checksum int64
outbound := s.outbound()
if len(outbound) > MaxBlockSize {
outbound = outbound[0:MaxBlockSize]
}
for _, prop := range outbound {
sp := fmt.Sprintf("F%c %s %s %d %d %d",
prop.code, // Proposal code
prop.msgType, // Message type (1 or 2 alphanumeric)
prop.mid, // Max 12 characters
prop.size, // Uncompressed size of message
prop.compressedSize, // Compressed size of message
0) // ?
s.pLog.Printf(">%s", sp)
fmt.Fprintf(rw, "%s\r", sp)
for _, c := range sp {
checksum += int64(c)
}
checksum += int64('\r')
}
checksum = (-checksum) & 0xff
s.log.Printf(`Sending checksum %02X`, checksum)
fmt.Fprintf(rw, "F> %02X\r", checksum)
var reply string
for reply == "" {
line, err := s.nextLine()
switch {
case err != nil:
return sent, err
case strings.HasPrefix(line, "FS "):
reply = line // The expected proposal answer
case strings.HasPrefix(line, ";"):
continue // Ignore comment
default:
return sent, fmt.Errorf("Expected proposal answer from remote. Got: '%s'", reply)
}
}
if err = parseProposalAnswer(reply, outbound, s.log); err != nil {
return sent, fmt.Errorf("Unable to parse proposal answer: %w", err)
}
if len(outbound) == 0 {
return
}
if r, ok := rw.(transport.Robust); ok && s.robustMode == RobustAuto {
r.SetRobust(false)
defer r.SetRobust(true)
}
for _, prop := range outbound {
switch prop.answer {
case Defer:
s.h.SetDeferred(prop.mid)
case Reject:
sent[prop.mid] = true
case Accept:
if err = s.writeCompressed(rw, prop); err != nil {
return
}
sent[prop.mid] = false
}
}
return
}
func (s *Session) handleInbound(rw io.ReadWriter) (quitReceived bool, err error) {
var ourChecksum int64
proposals := make([]*Proposal, 0)
var nAccepted int
Loop:
for {
var line string
line, err = s.nextLine()
if err != nil {
return
}
// Ignore comments and empty lines
if line == "" || line[0] == ';' {
continue
}
// The line should be prefixed F? (? is the command character)
if len(line) < 2 || line[0] != 'F' {
return false, fmt.Errorf("Got unexpected protocol line: '%s'", line)
}
switch line[:2] {
case "FA", "FB", "FC", "FD": // Proposals
for _, c := range line {
ourChecksum += int64(c)
}
ourChecksum += int64('\r')
prop := new(Proposal)
if err = parseProposal(line, prop); err != nil {
err = fmt.Errorf("Unable to parse proposal: %w", err)
return
}
proposals = append(proposals, prop)
case "FF": // No more messages
break Loop
case "FQ": // Quit
quitReceived = true
break Loop
case "F>": // Prompt (end of proposal block)
// Verify checksum
ourChecksum = (-ourChecksum) & 0xff
their, _ := strconv.ParseInt(line[3:], 16, 64)
if their != ourChecksum {
err = errors.New(fmt.Sprintf(`Checksum error (%d-%d)`, ourChecksum, their))
return
}
// If we didn't get any proposals, return
if len(proposals) == 0 {
return
}
// Answer proposal
s.log.Printf(`%d proposal(s) received`, len(proposals))
nAccepted, err = s.writeProposalsAnswer(rw, proposals)
if err != nil {
return quitReceived, err
}
if nAccepted > 0 {
break Loop // Session turn over is implied after receiving the messages
}
// Continue receiving proposals if all where rejected/deferred
return s.handleInbound(rw)
default: //TODO: Ignore?
return false, fmt.Errorf("Unknown protocol command %c", line[1])
}
}
if quitReceived && nAccepted > 0 {
return true, errors.New("Got quit command when inbound proposals were pending")
}
// Fetch and decompress accepted
s.remoteNoMsgs = true
for _, prop := range proposals {
if prop.answer != Accept {
continue
}
s.remoteNoMsgs = false
var msg *Message
if err = s.readCompressed(rw, prop); err != nil {
return
} else if msg, err = prop.Message(); err != nil {
return
}
if err = s.h.ProcessInbound(msg); err != nil {
return
}
s.trafficStats.Received = append(s.trafficStats.Received, prop.MID())
}
return
}
// The B2F protocol does not support offsets larger than 6 digits, the author of the protocol
// seems to have thrown away the idea of supporting transfer of fragmented messages.
//
// If we ever want to support requests of message with offset, we must guard against asking for
// offsets > 999999. RMS Express does not do this (in Winmor P2P anyway), we must avoid that pitfall.
func (s *Session) writeProposalsAnswer(rw io.ReadWriter, proposals []*Proposal) (nAccepted int, err error) {
answers := make([]byte, len(proposals))
seen := make(map[string]bool)
for i, prop := range proposals {
if seen[prop.MID()] {
// Radio Only gateways will sometimes send multiple proposals for the same MID in the same batch.
// Instead of rejecting them right away, let's defer the dups until we know we have sucessfully received at least one of the copies.
s.log.Printf("Defering duplicate message %s", prop.MID())
prop.answer = Defer
} else if prop.code != Wl2kProposal && prop.code != GzipProposal {
s.log.Printf("Defering %s (unsupported format)", prop.MID())
prop.answer = Defer
} else if s.h == nil {
s.log.Printf("Defering %s (missing handler)", prop.MID())
prop.answer = Defer
} else if prop.answer = s.h.GetInboundAnswer(*prop); prop.answer == Accept {
s.log.Printf("Accepting %s", prop.MID()) //TODO: Remove?
nAccepted++
}
seen[prop.MID()] = true
answers[i] = byte(prop.answer)
}
_, err = fmt.Fprintf(rw, "FS %s\r", answers)
return
}
// Parses the proposal answer (str) and updates the proposals given (in that order)
func parseProposalAnswer(str string, props []*Proposal, l *log.Logger) error {
str = strings.TrimPrefix(str, "FS ")
var c byte
for i := 0; len(str) > 0; i++ {
if i >= len(props) {
return errors.New("Got answer for more proposals than expected")
}
prop := props[i]
c, str = str[0], str[1:]
switch c {
case 'Y', 'y', '+':
if l != nil {
l.Printf("Remote accepted %s", prop.MID())
}
prop.answer = Accept
case 'N', 'n', 'R', 'r', '-':
if l != nil {
l.Printf("Remote already received %s", prop.MID())
}
prop.answer = Reject
case 'L', 'l', '=', 'H', 'h':
if l != nil {
l.Printf("Remote defered %s", prop.MID())
}
prop.answer = Defer
case 'A', 'a', '!':
idx := strings.LastIndexAny(str, "0123456789")
if idx < 0 {
return errors.New("Got offset request without offset index")
}
prop.answer = Accept // Offset is not implemented as a ProposalAnswer
prop.offset, _ = strconv.Atoi(str[:idx+1])
str = str[idx+1:]
if prop.offset > ProtocolOffsetSizeLimit { // RMS Express does this (in Winmor P2P for sure)
prop.offset = 0
if l != nil {
l.Printf(
"Remote requested %s at offset %d which exceeds the binary protocol offset limit. Ignoring offset.",
prop.MID(), prop.offset,
)
}
} else if l != nil {
l.Printf("Remote accepted %s at offset %d", prop.MID(), prop.offset)
}
default:
return fmt.Errorf("Invalid character (%c) in proposal answer line", c)
}
}
return nil
}
func (s *Session) writeCompressed(rw io.ReadWriter, p *Proposal) (err error) {
s.log.Printf("Transmitting [%s] [offset %d]", p.title, p.offset)
if p.code == GzipProposal {
s.log.Println("GZIP_EXPERIMENT:", "Transmitting gzip compressed message.")
}
writer := bufio.NewWriter(rw)
var (
title = mime.QEncoding.Encode("utf-8", p.title) // Word-encode the title since this field must be ASCII-only
offset = fmt.Sprintf("%d", p.offset)
length = len(title) + len(offset) + 2
checksum int64
)
writer.Write([]byte{_CHRSOH, byte(length)})
writer.WriteString(title) // Max 80 bytes, min 1 byte
writer.WriteByte(_CHRNUL)
writer.WriteString(offset) // Max 6 bytes, min 1 byte. Highest supported offset is 1MB-1B.
writer.WriteByte(_CHRNUL)
writer.Flush()
if p.compressedSize < 6 { // lzhuf's smallest valid length (empty)
return errors.New(`Invalid compressed data`)
}
buffer := bytes.NewBuffer(p.compressedData[p.offset:])
// Update Status of message transfer every 250ms
statusTicker := time.NewTicker(250 * time.Millisecond)
statusDone := make(chan struct{})
go func() {
for {
select {
case <-statusTicker.C:
if s.statusUpdater == nil || buffer == nil {
continue
}
// Take into account that the modem has an internal tx buffer (if possible).
var txBufLen int
if b, ok := rw.(transport.TxBuffer); ok {
txBufLen = b.TxBufferLen()
}
transferred := p.compressedSize - buffer.Len() - txBufLen
if transferred < 0 {
transferred = 0
}
if s.statusUpdater != nil {
s.statusUpdater.UpdateStatus(Status{
Sending: p,
BytesTransferred: transferred,
BytesTotal: p.compressedSize,
})
}
case <-statusDone:
if s.statusUpdater != nil {
s.statusUpdater.UpdateStatus(Status{
Sending: p,
BytesTransferred: p.compressedSize - buffer.Len(),
BytesTotal: p.compressedSize,
Done: true,
})
}
return
}
}
}()
defer func() { close(statusDone) }()
// Data (in chunks of max 250)
for buffer.Len() > 0 {
msgLen := MaxMsgLength
if buffer.Len() < MaxMsgLength {
msgLen = buffer.Len()
}
if _, err = writer.Write([]byte{_CHRSTX, byte(msgLen)}); err != nil {
return err
}
for i := 0; i < msgLen; i++ {
c, _ := buffer.ReadByte()
if err := writer.WriteByte(c); err != nil {
return err
}
checksum += int64(c)
}
if err = writer.Flush(); err != nil {
return err
}
}
// Checksum
checksum = -checksum & 0xff
_, err = writer.Write([]byte{_CHREOT, byte(checksum)})
err = writer.Flush()
// Flush connection buffers.
// This enables us to block until the whole message has been transmitted over the air.
if f, ok := rw.(transport.Flusher); ok {
err = f.Flush()
}
statusTicker.Stop()
return err
}
func (s *Session) readCompressed(rw io.ReadWriter, p *Proposal) (err error) {
var (
ourChecksum int
buf bytes.Buffer
)
var c byte
if c, err = s.rd.ReadByte(); err != nil {
return
}
switch c {
case _CHRSOH:
// what we expected...
case '*':
line, _ := s.nextLine()
return errors.New(fmt.Sprintf(`Got error from CMS: %s`, line))
default:
return errors.New(fmt.Sprintf(`First byte not as expected, got %d`, int(c)))
}
if c, err = s.rd.ReadByte(); err != nil {
return
}
headerLength := int(c)
// Read proposal title.
title, err := s.rd.ReadString(_CHRNUL)
if err != nil {
return fmt.Errorf("Unable to parse title: %w", err)
}
title = title[:len(title)-1] // Remove _CHRNUL
// The proposal title should be ASCII-only according to the protocol specification. Since RMS Express and CMS puts
// the raw subject header here, we need to handle this by decoding it the same way as the subject header.
p.title, _ = new(WordDecoder).DecodeHeader(title)
// Read offset part
var offsetStr string
if offsetStr, err = s.rd.ReadString(_CHRNUL); err != nil {
return fmt.Errorf("Unable to parse offset: %w", err)
} else {
offsetStr = offsetStr[:len(offsetStr)-1]
}
// Check overall length of header
actualHeaderLength := (len(title) + len(offsetStr)) + 2
if headerLength != actualHeaderLength {
return errors.New(fmt.Sprintf(`Header length mismatch: expected %d, got %d`, headerLength, actualHeaderLength))
}
// Parse offset as integer (and do some sanity checks)
offset, err := strconv.Atoi(offsetStr)
switch {
case err != nil:
return fmt.Errorf("Offset header not parseable as integer: %w", err)
case offset != p.offset:
return fmt.Errorf(`Expected offset %d, got %d`, p.offset, offset)
}
s.log.Printf("Receiving [%s] [offset %d]", p.title, p.offset)
if p.code == GzipProposal {
s.log.Println("GZIP_EXPERIMENT:", "Receiving gzip compressed message.")
}
statusUpdate := make(chan struct{})
go func() {
for {
_, ok := <-statusUpdate
if s.statusUpdater != nil {
s.statusUpdater.UpdateStatus(Status{
Receiving: p,
BytesTransferred: buf.Len(),
BytesTotal: p.compressedSize,
Done: !ok,
})
}
if !ok {
return
}
}
}()
defer func() { close(statusUpdate) }()
updateStatus := func() {
select {
case statusUpdate <- struct{}{}:
default:
}
}
for {
updateStatus()
c, err = s.rd.ReadByte()
if err != nil {
return err
}
switch c {
case _CHRSTX:
c, _ := s.rd.ReadByte()
length := int(c)
if length == 0 {
length = 256
}
for i := 0; i < length; i++ {
c, err = s.rd.ReadByte()
if err != nil {
return
}
buf.WriteByte(c)
ourChecksum = (ourChecksum + int(c)) % 256
if i%10 == 0 {
updateStatus()
}
}
case _CHREOT:
c, _ = s.rd.ReadByte()
ourChecksum = (ourChecksum + int(c)) % 256
if ourChecksum != 0 {
return errors.New(`Bad checksum`)
} else if p.compressedSize != buf.Len() {
return errors.New(`Length mismatch after EOT`)
} else {
p.compressedData = buf.Bytes()
}
return
default:
return errors.New(`Unexpected byte in compressed stream: ` + string(c))
}
}
}