[esp8266] Eliminate up to 16ms socket latency (#12397)

esphome/components/socket/lwip_raw_tcp_impl.cpp

@@ -14,13 +14,36 @@
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 
+#ifdef USE_ESP8266
+#include <coredecls.h>  // For esp_schedule()
+#endif
+
 namespace esphome {
 namespace socket {
 
+#ifdef USE_ESP8266
+// Flag to signal socket activity - checked by socket_delay() to exit early
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+static volatile bool s_socket_woke = false;
+
+void socket_delay(uint32_t ms) {
+  // Use esp_delay with a callback that checks if socket data arrived.
+  // This allows the delay to exit early when socket_wake() is called by
+  // lwip recv_fn/accept_fn callbacks, reducing socket latency.
+  s_socket_woke = false;
+  esp_delay(ms, []() { return !s_socket_woke; });
+}
+
+void socket_wake() {
+  s_socket_woke = true;
+  esp_schedule();
+}
+#endif
+
 static const char *const TAG = "socket.lwip";
 
 // set to 1 to enable verbose lwip logging
-#if 0
+#if 0  // NOLINT(readability-avoid-unconditional-preprocessor-if)
 #define LWIP_LOG(msg, ...) ESP_LOGVV(TAG, "socket %p: " msg, this, ##__VA_ARGS__)
 #else
 #define LWIP_LOG(msg, ...)
@@ -323,9 +346,10 @@ class LWIPRawImpl : public Socket {
     for (int i = 0; i < iovcnt; i++) {
       ssize_t err = read(reinterpret_cast<uint8_t *>(iov[i].iov_base), iov[i].iov_len);
       if (err == -1) {
-        if (ret != 0)
+        if (ret != 0) {
           // if we already read some don't return an error
           break;
+        }
         return err;
       }
       ret += err;
@@ -393,9 +417,10 @@ class LWIPRawImpl : public Socket {
     ssize_t written = internal_write(buf, len);
     if (written == -1)
       return -1;
-    if (written == 0)
+    if (written == 0) {
       // no need to output if nothing written
       return 0;
+    }
     if (nodelay_) {
       int err = internal_output();
       if (err == -1)
@@ -408,18 +433,20 @@ class LWIPRawImpl : public Socket {
     for (int i = 0; i < iovcnt; i++) {
       ssize_t err = internal_write(reinterpret_cast<uint8_t *>(iov[i].iov_base), iov[i].iov_len);
       if (err == -1) {
-        if (written != 0)
+        if (written != 0) {
           // if we already read some don't return an error
           break;
+        }
         return err;
       }
       written += err;
       if ((size_t) err != iov[i].iov_len)
         break;
     }
-    if (written == 0)
+    if (written == 0) {
       // no need to output if nothing written
       return 0;
+    }
     if (nodelay_) {
       int err = internal_output();
       if (err == -1)
@@ -473,6 +500,10 @@ class LWIPRawImpl : public Socket {
     } else {
       pbuf_cat(rx_buf_, pb);
     }
+#ifdef USE_ESP8266
+    // Wake the main loop immediately so it can process the received data.
+    socket_wake();
+#endif
     return ERR_OK;
   }
 
@@ -612,7 +643,7 @@ class LWIPRawListenImpl : public LWIPRawImpl {
   }
 
  private:
-  err_t accept_fn(struct tcp_pcb *newpcb, err_t err) {
+  err_t accept_fn_(struct tcp_pcb *newpcb, err_t err) {
     LWIP_LOG("accept(newpcb=%p err=%d)", newpcb, err);
     if (err != ERR_OK || newpcb == nullptr) {
       // "An error code if there has been an error accepting. Only return ERR_ABRT if you have
@@ -633,12 +664,16 @@ class LWIPRawListenImpl : public LWIPRawImpl {
     sock->init();
     accepted_sockets_[accepted_socket_count_++] = std::move(sock);
     LWIP_LOG("Accepted connection, queue size: %d", accepted_socket_count_);
+#ifdef USE_ESP8266
+    // Wake the main loop immediately so it can accept the new connection.
+    socket_wake();
+#endif
     return ERR_OK;
   }
 
   static err_t s_accept_fn(void *arg, struct tcp_pcb *newpcb, err_t err) {
     LWIPRawListenImpl *arg_this = reinterpret_cast<LWIPRawListenImpl *>(arg);
-    return arg_this->accept_fn(newpcb, err);
+    return arg_this->accept_fn_(newpcb, err);
   }
 
   // Accept queue - holds incoming connections briefly until the event loop calls accept()

esphome/components/socket/socket.h

@@ -82,6 +82,15 @@ socklen_t set_sockaddr(struct sockaddr *addr, socklen_t addrlen, const std::stri
 /// Set a sockaddr to the any address and specified port for the IP version used by socket_ip().
 socklen_t set_sockaddr_any(struct sockaddr *addr, socklen_t addrlen, uint16_t port);
 
+#if defined(USE_ESP8266) && defined(USE_SOCKET_IMPL_LWIP_TCP)
+/// Delay that can be woken early by socket activity.
+/// On ESP8266, lwip callbacks set a flag and call esp_schedule() to wake the delay.
+void socket_delay(uint32_t ms);
+
+/// Called by lwip callbacks to signal socket activity and wake delay.
+void socket_wake();
+#endif
+
 }  // namespace socket
 }  // namespace esphome
 #endif

esphome/core/application.cpp

@@ -12,6 +12,10 @@
 #include "esphome/components/status_led/status_led.h"
 #endif
 
+#if defined(USE_ESP8266) && defined(USE_SOCKET_IMPL_LWIP_TCP)
+#include "esphome/components/socket/socket.h"
+#endif
+
 #ifdef USE_SOCKET_SELECT_SUPPORT
 #include <cerrno>
 
@@ -627,6 +631,9 @@ void Application::yield_with_select_(uint32_t delay_ms) {
     // No sockets registered, use regular delay
     delay(delay_ms);
   }
+#elif defined(USE_ESP8266) && defined(USE_SOCKET_IMPL_LWIP_TCP)
+  // No select support but can wake on socket activity via esp_schedule()
+  socket::socket_delay(delay_ms);
 #else
   // No select support, use regular delay
   delay(delay_ms);