Adjust LWIP intf to avoid hangs/crashes under load (#1286)

It seems possible now for TCP connection _pcbs to disappear while being
processed, due to the new async context configuration.  This would cause
LWIP to panic when a NULL pcb was passed in.

Check for and avoid passing in null PCBs in the ClientContext.

Undo special-casing of sys_check_timeouts wrapper

AdvancedWebServer with heavy F5-refresh and #1274 test both pass.

Fixes #1274

Author: earlephilhower

cores/rp2040/lwip_wrap.cpp

@@ -256,14 +256,10 @@ extern "C" {
     }
 
     // sys_check_timeouts is special case because the async process will call it.  If we're already in a timeout check, just do a noop
-    auto_init_mutex(__sys_check_timeouts_mtx);
-    extern void __real_sys_check_timeouts(void);
+    extern void __real_sys_check_timeouts();
     void __wrap_sys_check_timeouts(void) {
-        uint32_t owner;
-        if (mutex_try_enter(&__sys_check_timeouts_mtx, &owner)) {
-            __real_sys_check_timeouts();
-            mutex_exit(&__sys_check_timeouts_mtx);
-        }
+        LWIPMutex m;
+        __real_sys_check_timeouts();
     }
 
     extern err_t __real_dns_gethostbyname(const char *hostname, ip_addr_t *addr, dns_found_callback found, void *callback_arg);

libraries/WiFi/src/include/ClientContext.h

@@ -328,7 +328,9 @@ class ClientContext {
                 return false;
             }
 
-
+            if (!_pcb) {
+                return false;
+            }
             // force lwIP to send what can be sent
             tcp_output(_pcb);
 
@@ -522,6 +524,9 @@ class ClientContext {
             const auto remaining = _datalen - _written;
             size_t next_chunk_size;
             {
+                if (!_pcb) {
+                    return false;
+                }
                 next_chunk_size = std::min((size_t)tcp_sndbuf(_pcb), remaining);
                 // Potentially reduce transmit size if we are tight on memory, but only if it doesn't return a 0 chunk size
                 if (next_chunk_size > (size_t)(1 << scale)) {
@@ -550,6 +555,9 @@ class ClientContext {
                 flags |= TCP_WRITE_FLAG_COPY;
             }
 
+            if (!_pcb) {
+                return false;
+            }
             err_t err = tcp_write(_pcb, buf, next_chunk_size, flags);
 
             DEBUGV(":wrc %d %d %d\r\n", next_chunk_size, remaining, (int)err);
@@ -571,7 +579,7 @@ class ClientContext {
             }
         }
 
-        if (has_written) {
+        if (has_written && _pcb) {
             // lwIP's tcp_output doc: "Find out what we can send and send it"
             // *with respect to Nagle*
             // more info: https://lists.gnu.org/archive/html/lwip-users/2017-11/msg00134.html

libraries/lwIP_CYW43/library.properties

@@ -3,7 +3,7 @@ version=1
 author=Earle F. Philhower, III
 maintainer=Earle F. Philhower, III <[email protected]>
 sentence=RP2040 Cyw43XX wifi driver
-paragraph=Driver for the raspberry Pi Pico W wireless chip, CYW43439, to integrate witrh arduino-pico
+paragraph=Driver for the Raspberry Pi Pico W wireless chip, CYW43439, to integrate with arduino-pico
 category=Communication
 url=https://github.com/earlephilhower/arduino-pico
 architectures=rp2040