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v1.0.12: Fix link MTU clamping, echo-back prevention, oversized frame detection

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MTU Clamping (Bug 8a): Clamp link MTU signalling in LINKREQUEST packets
when forwarding through transport node, matching Python reference impl.
Without this, TCP endpoints negotiate 8192-byte segments that exceed the
V3's 1064-byte HDLC buffer, causing silent truncation and permanent
resource transfer stalls at ~70%.

Fixed MTU declaration (Bug 8b): Set FIXED_MTU=true on TcpInterface so
Transport uses HW_MTU for clamping decisions.

Oversized frame detection (Bug 8c): Track truncated HDLC frames and
drop them with a diagnostic log instead of silently delivering corrupt
data to Transport.

Echo-back prevention (v1.0.10): Track which TCP client originated each
inbound frame and skip that client in send_outgoing() to prevent
flooding TCP buffers.

Register local client interface: Enable Transport forwarding of
announces, link packets, and proofs to TCP clients.

Document all discovered microReticulum bugs in MICRORETICULUM_BUGS.md.
This commit is contained in:
James L
2026-02-28 12:49:30 -05:00
parent 4e5d4ee8ad
commit 1122e9a0ee
5 changed files with 259 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

46
TcpInterface.h
View File

@@ -57,6 +57,7 @@ struct TcpClient {
// HDLC deframe state
bool in_frame;
bool escape;
bool truncated;
uint8_t rxbuf[TCP_IF_HW_MTU];
uint16_t rxlen;
};
@@ -84,6 +85,9 @@ public:
_IN = true;
_OUT = true;
_HW_MTU = TCP_IF_HW_MTU;
// v1.0.12: Tell Transport this interface has a known fixed MTU,
// enabling link MTU clamping when forwarding LINKREQUEST packets.
_FIXED_MTU = true;
// TCP links are effectively 10 Mbps+. Setting a realistic
// bitrate lets Transport prefer TCP paths over LoRa when
// both exist for the same destination.
@@ -100,6 +104,7 @@ public:
_clients[i].active = false;
_clients[i].in_frame = false;
_clients[i].escape = false;
_clients[i].truncated = false;
_clients[i].rxlen = 0;
_clients[i].last_activity = 0;
}
@@ -189,6 +194,7 @@ public:
}
}
}
}
// Process incoming data from all active clients
@@ -245,8 +251,14 @@ protected:
}
frame_buf[flen++] = HDLC_FLAG;
// Send to all connected clients (non-blocking: no flush)
// Send to all connected clients EXCEPT the one that sent this packet.
// v1.0.10: Echo prevention — if this send_outgoing was triggered by
// Transport forwarding a packet received from client N, skip client N
// to prevent echo-back that floods TCP buffers and stalls resource transfers.
for (int i = 0; i < TCP_IF_MAX_CLIENTS; i++) {
if (i == _last_rx_client_idx) {
continue; // Don't echo back to sender
}
if (_clients[i].active && _clients[i].client.connected()) {
size_t written = _clients[i].client.write(frame_buf, flen);
if (written == 0) {
@@ -292,6 +304,7 @@ private:
c.active = false;
c.in_frame = false;
c.escape = false;
c.truncated = false;
c.rxlen = 0;
_num_clients--;
@@ -307,13 +320,29 @@ private:
if (byte == HDLC_FLAG) {
if (c.in_frame && c.rxlen > 0) {
// End of frame — deliver to RNS
RNS::Bytes data(c.rxbuf, c.rxlen);
handle_incoming(data);
c.rxlen = 0;
// v1.0.12: If the frame exceeded the buffer, drop it entirely
// instead of delivering a truncated/corrupt packet to Transport.
if (c.truncated) {
Serial.printf("[TcpIF] DROPPED oversized frame from client %d (>%d bytes, buffered %u)\r\n",
idx, TCP_IF_HW_MTU, c.rxlen);
c.truncated = false;
c.rxlen = 0;
} else {
// End of frame — deliver to RNS
// v1.0.10: Set _last_rx_client_idx so send_outgoing() can
// skip echoing this packet back to the client that sent it.
// The entire call chain (handle_incoming → Transport::inbound
// → transmit → send_outgoing) is synchronous, so this is safe.
RNS::Bytes data(c.rxbuf, c.rxlen);
_last_rx_client_idx = idx;
handle_incoming(data);
_last_rx_client_idx = -1;
c.rxlen = 0;
}
}
c.in_frame = true;
c.escape = false;
c.truncated = false;
c.rxlen = 0;
} else if (c.in_frame) {
if (c.escape) {
@@ -321,12 +350,16 @@ private:
c.escape = false;
if (c.rxlen < TCP_IF_HW_MTU) {
c.rxbuf[c.rxlen++] = byte;
} else {
c.truncated = true;
}
} else if (byte == HDLC_ESC) {
c.escape = true;
} else {
if (c.rxlen < TCP_IF_HW_MTU) {
c.rxbuf[c.rxlen++] = byte;
} else {
c.truncated = true;
}
}
}
@@ -355,6 +388,7 @@ private:
_clients[i].active = true;
_clients[i].in_frame = false;
_clients[i].escape = false;
_clients[i].truncated = false;
_clients[i].rxlen = 0;
_clients[i].last_activity = millis();
_num_clients++;
@@ -410,6 +444,7 @@ private:
_clients[0].active = true;
_clients[0].in_frame = false;
_clients[0].escape = false;
_clients[0].truncated = false;
_clients[0].rxlen = 0;
_clients[0].last_activity = millis();
_num_clients = 1;
@@ -446,6 +481,7 @@ private:
IPAddress _resolved_ip;
uint16_t _consecutive_failures;
bool _started;
int _last_rx_client_idx = -1; // v1.0.10: echo prevention — tracks which client is currently delivering an inbound frame
};
#endif // BOUNDARY_MODE