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[fix](trx-server): comply with APRS-IS IGate spec

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- Append mandatory q-construct (,qAR,<callsign>) to all forwarded
  TNC2 packets via updated format_tnc2(pkt, igate_call)
- Add TCPIP/TCPXX loop-prevention check before forwarding
- Drain server-sent data in select! loop to prevent TCP backpressure
- Enable TCP_NODELAY for low-latency packet forwarding
- Guard against history replays: skip packets older than 2 minutes
- Use "trx-rs" in login string and keepalive comment

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>
This commit is contained in:
Stan Grams
2026-03-14 09:24:03 +01:00
parent 1dec2c2663
commit ecb058a9d2
1 changed files with 49 additions and 14 deletions
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src/trx-server/src/aprsfi.rs
+49 -14
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@@ -46,14 +46,19 @@ pub fn compute_passcode(callsign: &str) -> u16 {
hash & 0x7fff
}
/// Format an [`AprsPacket`] as a TNC2 line (CRLF-terminated) for APRS-IS.
fn format_tnc2(pkt: &AprsPacket) -> String {
/// Format an [`AprsPacket`] as a TNC2 line (CRLF-terminated) for APRS-IS,
/// appending the mandatory `,qAR,<igate_call>` q-construct that identifies
/// the RF entry point per the APRS-IS IGate specification.
fn format_tnc2(pkt: &AprsPacket, igate_call: &str) -> String {
if pkt.path.is_empty() {
format!("{}>{}:{}\r\n", pkt.src_call, pkt.dest_call, pkt.info)
format!(
"{}>{},qAR,{}:{}\r\n",
pkt.src_call, pkt.dest_call, igate_call, pkt.info
)
} else {
format!(
"{}>{},{}:{}\r\n",
pkt.src_call, pkt.dest_call, pkt.path, pkt.info
"{}>{},{},qAR,{}:{}\r\n",
pkt.src_call, pkt.dest_call, pkt.path, igate_call, pkt.info
)
}
}
@@ -99,6 +104,11 @@ pub async fn run_aprsfi_uplink(
}
};
// Disable Nagle algorithm for low-latency packet forwarding.
if let Err(e) = stream.set_nodelay(true) {
warn!("APRS-IS IGate: set_nodelay failed: {}", e);
}
let (read_half, mut write_half) = stream.into_split();
let mut reader = BufReader::new(read_half);
@@ -106,7 +116,7 @@ pub async fn run_aprsfi_uplink(
// Login
// ----------------------------------------------------------------
let login = format!(
"user {} pass {} vers trx-server {}\r\n",
"user {} pass {} vers trx-rs {}\r\n",
callsign,
passcode,
env!("CARGO_PKG_VERSION")
@@ -184,11 +194,13 @@ pub async fn run_aprsfi_uplink(
let first_at = time::Instant::now() + period;
let mut keepalive_tick = time::interval_at(first_at, period);
let mut stats_tick = time::interval_at(first_at, period);
// Reuse a single allocation for draining server-sent lines.
let mut server_line = String::new();
'forward: loop {
tokio::select! {
_ = keepalive_tick.tick() => {
if let Err(e) = write_half.write_all(b"# trx-server keepalive\r\n").await {
if let Err(e) = write_half.write_all(b"# trx-rs keepalive\r\n").await {
warn!("APRS-IS IGate: keepalive write failed: {}", e);
stats_write_errors += 1;
break 'forward;
@@ -203,6 +215,20 @@ pub async fn run_aprsfi_uplink(
);
}
// Drain the server feed. The server sends a full APRS stream;
// if we never read it the TCP receive buffer fills and stalls
// the connection via flow control. EOF triggers reconnect.
result = reader.read_line(&mut server_line) => {
server_line.clear();
match result {
Ok(0) | Err(_) => {
warn!("APRS-IS IGate: server closed connection");
break 'forward;
}
Ok(_) => {} // discard — we do not gate IS→RF
}
}
recv = decode_rx.recv() => {
match recv {
Ok(DecodedMessage::Aprs(pkt)) | Ok(DecodedMessage::HfAprs(pkt)) => {
@@ -225,7 +251,13 @@ pub async fn run_aprsfi_uplink(
continue 'forward;
}
}
let tnc2 = format_tnc2(&pkt);
// Loop prevention: do not re-gate packets that already
// passed through APRS-IS (TCPIP or TCPXX in path).
if pkt.path.contains("TCPIP") || pkt.path.contains("TCPXX") {
stats_skipped += 1;
continue 'forward;
}
let tnc2 = format_tnc2(&pkt, &callsign);
debug!("APRS-IS: forwarded {}>{},...", pkt.src_call, pkt.dest_call);
if let Err(e) = write_half.write_all(tnc2.as_bytes()).await {
warn!("APRS-IS IGate: packet write failed: {}", e);
@@ -248,7 +280,7 @@ pub async fn run_aprsfi_uplink(
}
}
// Forward loop exited due to a write error — reconnect with backoff
// Forward loop exited due to a write error or server EOF — reconnect with backoff
stats_reconnects += 1;
warn!(
"APRS-IS IGate: disconnected from {}:{}, reconnecting in {}s",
@@ -311,7 +343,7 @@ mod tests {
}
#[test]
fn tnc2_with_path() {
fn tnc2_with_path_adds_qar() {
let pkt = make_pkt(
"N0CALL-9",
"APRS",
@@ -320,14 +352,17 @@ mod tests {
true,
);
assert_eq!(
format_tnc2(&pkt),
"N0CALL-9>APRS,WIDE1-1,WIDE2-1:!1234.56N/01234.56E-Test\r\n"
format_tnc2(&pkt, "SP2SJG"),
"N0CALL-9>APRS,WIDE1-1,WIDE2-1,qAR,SP2SJG:!1234.56N/01234.56E-Test\r\n"
);
}
#[test]
fn tnc2_without_path() {
fn tnc2_without_path_adds_qar() {
let pkt = make_pkt("W1AW", "BEACON", "", ">Test status", true);
assert_eq!(format_tnc2(&pkt), "W1AW>BEACON:>Test status\r\n");
assert_eq!(
format_tnc2(&pkt, "SP2SJG"),
"W1AW>BEACON,qAR,SP2SJG:>Test status\r\n"
);
}
}