fix: harden tcp bridge reconnect handling

App/tcp_client.c

@@ -7,6 +7,8 @@
 
 #include "main.h"
 
+#include "SEGGER_RTT.h"
+
 #include "lwip/ip_addr.h"
 #include "lwip/pbuf.h"
 #include "lwip/tcp.h"
@@ -85,11 +87,15 @@ static err_t tcp_client_on_sent(void *arg, struct tcp_pcb *pcb, u16_t len)
 static void tcp_client_on_err(void *arg, err_t err)
 {
     tcp_client_ctx_t *ctx = (tcp_client_ctx_t *)arg;
-    (void)err;
+    if (ctx == NULL) {
+        return;
+    }
+
     ctx->pcb = NULL;
     ctx->status.state = TCP_CLIENT_STATE_DISCONNECTED;
     ctx->status.errors++;
     ctx->next_retry_ms = HAL_GetTick() + ctx->config.reconnect_interval_ms;
+    SEGGER_RTT_printf(0, "TCP client error=%d, reconnect scheduled\r\n", (int)err);
 }
 
 static err_t tcp_client_on_connected(void *arg, struct tcp_pcb *pcb, err_t err)
@@ -101,11 +107,17 @@ static err_t tcp_client_on_connected(void *arg, struct tcp_pcb *pcb, err_t err)
         ctx->status.state = TCP_CLIENT_STATE_DISCONNECTED;
         ctx->status.errors++;
         ctx->next_retry_ms = HAL_GetTick() + ctx->config.reconnect_interval_ms;
+        SEGGER_RTT_printf(0, "TCP client connect callback failed err=%d\r\n", (int)err);
         return err;
     }
 
     ctx->pcb = pcb;
     ctx->status.state = TCP_CLIENT_STATE_CONNECTED;
+    SEGGER_RTT_printf(0,
+                      "TCP client connected to %u.%u.%u.%u:%u\r\n",
+                      ctx->config.server_ip[0], ctx->config.server_ip[1],
+                      ctx->config.server_ip[2], ctx->config.server_ip[3],
+                      ctx->config.server_port);
     tcp_nagle_disable(pcb);
     tcp_arg(pcb, ctx);
     tcp_recv(pcb, tcp_client_on_recv);
@@ -147,6 +159,8 @@ int tcp_client_connect(void)
     pcb = tcp_new_ip_type(IPADDR_TYPE_V4);
     if (pcb == NULL) {
         g_client.status.errors++;
+        g_client.status.state = TCP_CLIENT_STATE_ERROR;
+        SEGGER_RTT_WriteString(0, "TCP client connect failed: no PCB\r\n");
         return -1;
     }
 
@@ -157,6 +171,7 @@ int tcp_client_connect(void)
             g_client.status.state = TCP_CLIENT_STATE_DISCONNECTED;
             g_client.status.errors++;
             g_client.next_retry_ms = HAL_GetTick() + g_client.config.reconnect_interval_ms;
+            SEGGER_RTT_printf(0, "TCP client bind failed err=%d\r\n", (int)err);
             return -1;
         }
     }
@@ -169,16 +184,24 @@ int tcp_client_connect(void)
 
     g_client.status.state = TCP_CLIENT_STATE_CONNECTING;
     tcp_arg(pcb, &g_client);
+    tcp_err(pcb, tcp_client_on_err);
     err = tcp_connect(pcb, &remote_addr, g_client.config.server_port, tcp_client_on_connected);
     if (err != ERR_OK) {
+        tcp_err(pcb, NULL);
         tcp_abort(pcb);
         g_client.status.state = TCP_CLIENT_STATE_DISCONNECTED;
         g_client.status.errors++;
         g_client.next_retry_ms = HAL_GetTick() + g_client.config.reconnect_interval_ms;
+        SEGGER_RTT_printf(0, "TCP client connect start failed err=%d\r\n", (int)err);
         return -1;
     }
 
     g_client.pcb = pcb;
+    SEGGER_RTT_printf(0,
+                      "TCP client connecting to %u.%u.%u.%u:%u\r\n",
+                      g_client.config.server_ip[0], g_client.config.server_ip[1],
+                      g_client.config.server_ip[2], g_client.config.server_ip[3],
+                      g_client.config.server_port);
     return 0;
 }
 
@@ -194,6 +217,7 @@ int tcp_client_disconnect(void)
     }
 
     g_client.status.state = TCP_CLIENT_STATE_DISCONNECTED;
+    SEGGER_RTT_WriteString(0, "TCP client disconnected\r\n");
     return 0;
 }
 
@@ -288,7 +312,11 @@ void tcp_client_poll(void)
 {
     uint32_t now;
 
-    if (!g_client.config.auto_reconnect || g_client.pcb != NULL) {
+    if (!g_client.config.auto_reconnect || tcp_client_is_connected()) {
+        return;
+    }
+
+    if ((g_client.pcb != NULL) && (g_client.status.state == TCP_CLIENT_STATE_CONNECTING)) {
         return;
     }
 
@@ -296,6 +324,9 @@ void tcp_client_poll(void)
     if (now >= g_client.next_retry_ms) {
         g_client.status.reconnect_count++;
         g_client.next_retry_ms = now + g_client.config.reconnect_interval_ms;
+        SEGGER_RTT_printf(0,
+                          "TCP client reconnect attempt %lu\r\n",
+                          g_client.status.reconnect_count);
         (void)tcp_client_connect();
     }
 }

App/tcp_server.c

@@ -8,6 +8,8 @@
 #include "lwip/pbuf.h"
 #include "lwip/tcp.h"
 
+#include "SEGGER_RTT.h"
+
 #include <string.h>
 
 typedef struct {
@@ -49,6 +51,7 @@ static err_t tcp_server_on_recv(void *arg, struct tcp_pcb *pcb, struct pbuf *p,
         }
         ctx->client_pcb = NULL;
         ctx->status.state = TCP_SERVER_STATE_LISTENING;
+        SEGGER_RTT_WriteString(0, "TCP server peer disconnected\r\n");
         return ERR_OK;
     }
 
@@ -85,6 +88,7 @@ static void tcp_server_on_err(void *arg, err_t err)
     ctx->client_pcb = NULL;
     ctx->status.state = TCP_SERVER_STATE_LISTENING;
     ctx->status.errors++;
+    SEGGER_RTT_printf(0, "TCP server connection error=%d\r\n", (int)err);
 }
 
 static err_t tcp_server_on_accept(void *arg, struct tcp_pcb *newpcb, err_t err)
@@ -103,6 +107,7 @@ static err_t tcp_server_on_accept(void *arg, struct tcp_pcb *newpcb, err_t err)
     ctx->client_pcb = newpcb;
     ctx->status.state = TCP_SERVER_STATE_CONNECTED;
     ctx->status.connections++;
+    SEGGER_RTT_WriteString(0, "TCP server client connected\r\n");
 
     tcp_nagle_disable(newpcb);
 
@@ -158,6 +163,7 @@ int tcp_server_start(void)
     tcp_arg(g_server.listen_pcb, &g_server);
     tcp_accept(g_server.listen_pcb, tcp_server_on_accept);
     g_server.status.state = TCP_SERVER_STATE_LISTENING;
+    SEGGER_RTT_printf(0, "TCP server listening on %u\r\n", g_server.config.port);
     return 0;
 }
 

Core/Src/main.c

@@ -68,19 +68,44 @@ static volatile uint16_t g_led_blink_ticks = 0;
 static uint8_t g_clock_fallback_to_hsi = 0u;
 volatile uint8_t g_uart1_rx_probe_byte = 0u;
 
+typedef struct {
+    uint8_t data[256];
+    uint16_t len;
+} tcp_bridge_buffer_t;
+
+static tcp_bridge_buffer_t g_server_to_client;
+static tcp_bridge_buffer_t g_client_to_server;
+
 static void App_ForwardTcpPair(void)
 {
-    uint8_t buffer[256];
+    int rc;
-    int len;
 
-    len = tcp_server_recv(buffer, sizeof(buffer), 0u);
+    if ((g_server_to_client.len == 0u) && tcp_server_is_connected()) {
-    if (len > 0) {
+        rc = tcp_server_recv(g_server_to_client.data, sizeof(g_server_to_client.data), 0u);
-        (void)tcp_client_send(buffer, (uint16_t)len);
+        if (rc > 0) {
+            g_server_to_client.len = (uint16_t)rc;
+        }
     }
 
-    len = tcp_client_recv(buffer, sizeof(buffer), 0u);
+    if ((g_server_to_client.len != 0u) && tcp_client_is_connected()) {
-    if (len > 0) {
+        rc = tcp_client_send(g_server_to_client.data, g_server_to_client.len);
-        (void)tcp_server_send(buffer, (uint16_t)len);
+        if (rc == (int)g_server_to_client.len) {
+            g_server_to_client.len = 0u;
+        }
+    }
+
+    if ((g_client_to_server.len == 0u) && tcp_client_is_connected()) {
+        rc = tcp_client_recv(g_client_to_server.data, sizeof(g_client_to_server.data), 0u);
+        if (rc > 0) {
+            g_client_to_server.len = (uint16_t)rc;
+        }
+    }
+
+    if ((g_client_to_server.len != 0u) && tcp_server_is_connected()) {
+        rc = tcp_server_send(g_client_to_server.data, g_client_to_server.len);
+        if (rc == (int)g_client_to_server.len) {
+            g_client_to_server.len = 0u;
+        }
     }
 }
 

tools/start_tcp_debug_server.ps1

@@ -0,0 +1,32 @@
+param(
+    [string]$BindHost = "0.0.0.0",
+    [int]$Port = 8081,
+    [switch]$Echo,
+    [switch]$NoStdin
+)
+
+$listeners = Get-NetTCPConnection -LocalPort $Port -State Listen -ErrorAction SilentlyContinue
+if ($listeners) {
+    $pids = $listeners | Select-Object -ExpandProperty OwningProcess -Unique
+    Write-Host "Stopping existing listeners on TCP ${Port}: $($pids -join ', ')"
+    foreach ($procId in $pids) {
+        try {
+            Stop-Process -Id $procId -Force -ErrorAction Stop
+        }
+        catch {
+            Write-Warning "Failed to stop process $procId : $_"
+        }
+    }
+    Start-Sleep -Milliseconds 300
+}
+
+$args = @("tools/tcp_debug_server.py", "--host", $BindHost, "--port", "$Port")
+if ($Echo) {
+    $args += "--echo"
+}
+if ($NoStdin) {
+    $args += "--no-stdin"
+}
+
+Write-Host "Starting TCP debug server on ${BindHost}:${Port}"
+python @args

tools/tcp_debug_server.py

@@ -0,0 +1,143 @@
+#!/usr/bin/env python3
+"""Simple TCP debug server for validating raw payload forwarding.
+
+Usage examples:
+    python tools/tcp_debug_server.py --host 0.0.0.0 --port 8081
+    python tools/tcp_debug_server.py --port 8081 --echo
+
+Features:
+    - Listen as a plain TCP server
+    - Print connect/disconnect events
+    - Print received payload as text and hex
+    - Optional echo mode
+    - Optional stdin -> socket sender for manual testing
+"""
+
+from __future__ import annotations
+
+import argparse
+import select
+import socket
+import sys
+import threading
+from datetime import datetime
+
+
+def ts() -> str:
+    return datetime.now().strftime("%H:%M:%S.%f")[:-3]
+
+
+def hex_bytes(data: bytes) -> str:
+    return " ".join(f"{b:02X}" for b in data)
+
+
+def text_view(data: bytes) -> str:
+    return "".join(chr(b) if 32 <= b < 127 else "." for b in data)
+
+
+def sender_loop(conn: socket.socket, stop_event: threading.Event) -> None:
+    print(f"[{ts()}] stdin sender ready. Type text and press Enter to send.")
+    while not stop_event.is_set():
+        line = sys.stdin.readline()
+        if line == "":
+            stop_event.set()
+            break
+        payload = line.encode("utf-8", errors="replace")
+        try:
+            conn.sendall(payload)
+            print(
+                f"[{ts()}] TX {len(payload)} bytes | text={payload!r} | hex={hex_bytes(payload)}"
+            )
+        except OSError as exc:
+            print(f"[{ts()}] TX failed: {exc}")
+            stop_event.set()
+            break
+
+
+def serve(host: str, port: int, echo: bool, no_stdin: bool) -> int:
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as server:
+        server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        server.bind((host, port))
+        server.listen(1)
+        print(f"[{ts()}] Listening on {host}:{port}")
+
+        conn, addr = server.accept()
+        with conn:
+            print(f"[{ts()}] Client connected from {addr[0]}:{addr[1]}")
+            stop_event = threading.Event()
+            sender_thread = None
+
+            if not no_stdin:
+                sender_thread = threading.Thread(
+                    target=sender_loop, args=(conn, stop_event), daemon=True
+                )
+                sender_thread.start()
+
+            conn.setblocking(False)
+
+            while not stop_event.is_set():
+                ready, _, _ = select.select([conn], [], [], 0.2)
+                if not ready:
+                    continue
+
+                try:
+                    data = conn.recv(4096)
+                except BlockingIOError:
+                    continue
+                except OSError as exc:
+                    print(f"[{ts()}] RX failed: {exc}")
+                    break
+
+                if not data:
+                    print(f"[{ts()}] Client disconnected")
+                    break
+
+                print(
+                    f"[{ts()}] RX {len(data)} bytes | text={text_view(data)} | hex={hex_bytes(data)}"
+                )
+
+                if echo:
+                    try:
+                        conn.sendall(data)
+                        print(f"[{ts()}] ECHO {len(data)} bytes")
+                    except OSError as exc:
+                        print(f"[{ts()}] Echo failed: {exc}")
+                        break
+
+            stop_event.set()
+            if sender_thread is not None:
+                sender_thread.join(timeout=0.5)
+
+    return 0
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(description="Minimal raw TCP debug server")
+    parser.add_argument(
+        "--host", default="0.0.0.0", help="Listen host, default: 0.0.0.0"
+    )
+    parser.add_argument(
+        "--port", type=int, default=8081, help="Listen port, default: 8081"
+    )
+    parser.add_argument(
+        "--echo", action="store_true", help="Echo received payload back to client"
+    )
+    parser.add_argument(
+        "--no-stdin",
+        action="store_true",
+        help="Disable stdin sender thread (receive-only mode)",
+    )
+    return parser.parse_args()
+
+
+def main() -> int:
+    args = parse_args()
+    try:
+        return serve(args.host, args.port, args.echo, args.no_stdin)
+    except KeyboardInterrupt:
+        print(f"\n[{ts()}] Stopped by user")
+        return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())