Share the lwIP error mapping and address conversion, keep poll_connect in one place, and pin the socket layout

esphome/components/async_tcp/async_tcp_socket.cpp

@@ -6,7 +6,6 @@
 #include "esphome/components/network/util.h"
 #include "esphome/core/log.h"
 #include <cerrno>
-#include <sys/select.h>
 
 namespace esphome::async_tcp {
 
@@ -42,7 +41,16 @@ bool AsyncClient::connect(const char *host, uint16_t port) {
     return false;
   }
 
-  socket_->setblocking(false);
+  if (socket_->setblocking(false) != 0) {
+    // Capture before the log and reset() below can clobber errno; a blocking
+    // connect()/read() would otherwise stall the whole loop
+    const int saved_errno = errno;
+    ESP_LOGE(TAG, "Failed to set nonblocking: errno %d", saved_errno);
+    close();
+    if (error_cb_)
+      error_cb_(error_arg_, this, saved_errno);
+    return false;
+  }
 
   int err = socket_->connect((struct sockaddr *) &addr, addrlen);
   if (err == 0) {
@@ -97,45 +105,22 @@ void AsyncClient::loop() {
     return;
 
   if (connecting_) {
-    // For connecting, we need to check writability, not readability
-    // The Application's select() only monitors read FDs, so we do our own check here
-    // For ESP platforms lwip_select() might be faster, but this code isn't used
-    // on those platforms anyway. If it was, we'd fix the Application select()
-    // to report writability instead of doing it this way.
-    int fd = socket_->get_fd();
-    if (fd < 0) {
-      ESP_LOGW(TAG, "Invalid socket fd");
-      close();
-      return;
-    }
-
-    fd_set writefds;
-    FD_ZERO(&writefds);
-    FD_SET(fd, &writefds);
-
-    struct timeval tv = {0, 0};
-    int ret = select(fd + 1, nullptr, &writefds, nullptr, &tv);
-
-    if (ret > 0 && FD_ISSET(fd, &writefds)) {
-      int error = 0;
-      socklen_t len = sizeof(error);
-      if (socket_->getsockopt(SOL_SOCKET, SO_ERROR, &error, &len) == 0 && error == 0) {
+    int err = 0;
+    switch (socket::poll_connect(*socket_, err)) {
+      case socket::ConnectPollResult::CONNECT_POLL_PENDING:
+        break;
+      case socket::ConnectPollResult::CONNECT_POLL_CONNECTED:
         connecting_ = false;
         connected_ = true;
         if (connect_cb_)
           connect_cb_(connect_arg_, this);
-      } else {
-        ESP_LOGW(TAG, "Connection failed: %d", error);
+        break;
+      case socket::ConnectPollResult::CONNECT_POLL_ERROR:
+        ESP_LOGW(TAG, "Connection failed: %d", err);
         close();
         if (error_cb_)
-          error_cb_(error_arg_, this, error);
-      }
-    } else if (ret < 0) {
-      const int err = errno;
-      ESP_LOGE(TAG, "Select error: %d", err);
-      close();
-      if (error_cb_)
-        error_cb_(error_arg_, this, err);
+          error_cb_(error_arg_, this, err);
+        break;
     }
   } else if (connected_) {
     // For connected sockets, use the Application's select() results

esphome/components/esphome/ota/ota_esphome.cpp

@@ -407,7 +407,10 @@ void ESPHomeOTAComponent::handle_data_() {
   tv.tv_usec = 0;
   this->client_->setsockopt(SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
   this->client_->setsockopt(SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
-  this->client_->setblocking(true);
+  if (this->client_->setblocking(true) != 0) {
+    this->log_socket_error_(LOG_STR("blocking"));
+    goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
+  }
 
   // Acknowledge auth OK - 1 byte
   this->data_write_byte_(ota::OTA_RESPONSE_AUTH_OK);

esphome/components/socket/bsd_sockets_impl.cpp

@@ -59,13 +59,15 @@ int BSDSocketImpl::close() {
 
 int BSDSocketImpl::setblocking(bool blocking) {
   int fl = ::fcntl(this->fd_, F_GETFL, 0);
+  if (fl < 0) {
+    return fl;
+  }
   if (blocking) {
     fl &= ~O_NONBLOCK;
   } else {
     fl |= O_NONBLOCK;
   }
-  ::fcntl(this->fd_, F_SETFL, fl);
-  return 0;
+  return ::fcntl(this->fd_, F_SETFL, fl);
 }
 
 size_t BSDSocketImpl::getpeername_to(std::span<char, SOCKADDR_STR_LEN> buf) {

esphome/components/socket/headers.h

@@ -205,6 +205,13 @@ static constexpr size_t SOCKADDR_STR_LEN = 46;  // INET6_ADDRSTRLEN
 static constexpr size_t SOCKADDR_STR_LEN = 16;  // INET_ADDRSTRLEN
 #endif
 
+/// Outcome of polling a non-blocking connect(); see socket::poll_connect().
+enum class ConnectPollResult : uint8_t {
+  CONNECT_POLL_PENDING,
+  CONNECT_POLL_CONNECTED,
+  CONNECT_POLL_ERROR,
+};
+
 }  // namespace esphome::socket
 
 #endif

esphome/components/socket/lwip_raw_tcp_impl.cpp

@@ -48,8 +48,33 @@ static const char *const TAG = "socket";
 #ifdef USE_ESP8266
 // optimistic_yield() rate limit in microseconds of CONT time; cheap when hot.
 static constexpr uint32_t ESP8266_YIELD_INTERVAL_US = 1000;
+// Let SYS run so queued WiFi traffic reaches lwip; CONT and SYS are cooperative
+static inline void yield_to_sys() { optimistic_yield(ESP8266_YIELD_INTERVAL_US); }
+#else
+static inline void yield_to_sys() {}
 #endif
 
+// errno for a failed tcp_* call
+static int lwip_err_to_errno(err_t err) {
+  switch (err) {
+    case ERR_MEM:
+      return ENOMEM;
+    case ERR_BUF:
+      return EAGAIN;  // no free local port
+    case ERR_RTE:
+      return EHOSTUNREACH;  // no route or no address yet
+    case ERR_VAL:
+    case ERR_ARG:
+      return EINVAL;
+    case ERR_USE:
+      return EADDRINUSE;
+    case ERR_ISCONN:
+      return EISCONN;
+    default:
+      return EIO;
+  }
+}
+
 // set to 1 to enable verbose lwip logging
 #if 0  // NOLINT(readability-avoid-unconditional-preprocessor-if)
 #define LWIP_LOG(msg, ...) ESP_LOGVV(TAG, "socket %p: " msg, this, ##__VA_ARGS__)
@@ -63,7 +88,8 @@ static constexpr uint32_t ESP8266_YIELD_INTERVAL_US = 1000;
 // tcp_abort() triggers the err callback synchronously, which would
 // otherwise call back into a partially-destroyed object.
 // tcp_sent/tcp_poll are not cleared because this implementation
-// never registers them.
+// never registers them, and the tcp_connect callback only fires on
+// SYN_SENT -> ESTABLISHED, which cannot follow an abort or close.
 static void pcb_detach_abort(struct tcp_pcb *pcb) {
   tcp_arg(pcb, nullptr);
   tcp_recv(pcb, nullptr);
@@ -76,8 +102,8 @@ static void pcb_detach_abort(struct tcp_pcb *pcb) {
 // After tcp_close(), the PCB remains alive during the TCP close handshake
 // (FIN_WAIT, TIME_WAIT states). Without clearing callbacks first, LWIP
 // would call recv/err on a destroyed socket object, corrupting the heap.
-// tcp_sent/tcp_poll are not cleared because this implementation
-// never registers them.
+// tcp_sent/tcp_poll and the tcp_connect callback are not cleared for the
+// same reasons as in pcb_detach_abort().
 // Returns ERR_OK on success; on failure the PCB is aborted instead.
 static err_t pcb_detach_close(struct tcp_pcb *pcb) {
   tcp_arg(pcb, nullptr);
@@ -101,67 +127,51 @@ LWIPRawCommon::~LWIPRawCommon() {
   }
 }
 
+bool LWIPRawCommon::sockaddr2ip_(const struct sockaddr *name, socklen_t addrlen, ip_addr_t *ip, uint16_t *port) const {
+  if (name == nullptr) {
+    errno = EINVAL;
+    return false;
+  }
+#if LWIP_IPV6
+  if (this->family_ == AF_INET6) {
+    if (addrlen < sizeof(sockaddr_in6)) {
+      errno = EINVAL;
+      return false;
+    }
+    auto *addr6 = reinterpret_cast<const sockaddr_in6 *>(name);
+    *port = ntohs(addr6->sin6_port);
+    inet6_addr_to_ip6addr(ip_2_ip6(ip), &addr6->sin6_addr);
+    // ANY lets bind() accept both families; connect() picks the concrete type
+    IP_SET_TYPE_VAL(*ip, IPADDR_TYPE_ANY);
+    return true;
+  }
+#endif
+  if (this->family_ != AF_INET || addrlen < sizeof(sockaddr_in)) {
+    errno = EINVAL;
+    return false;
+  }
+  auto *addr4 = reinterpret_cast<const sockaddr_in *>(name);
+  *port = ntohs(addr4->sin_port);
+  ip_addr_set_ip4_u32(ip, addr4->sin_addr.s_addr);
+  return true;
+}
+
 int LWIPRawCommon::bind(const struct sockaddr *name, socklen_t addrlen) {
   LWIP_LOCK();
   if (this->pcb_ == nullptr) {
     errno = EBADF;
     return -1;
   }
-  if (name == nullptr) {
-    errno = EINVAL;
-    return -1;
-  }
   ip_addr_t ip;
-  in_port_t port;
-#if LWIP_IPV6
-  if (this->family_ == AF_INET) {
-    if (addrlen < sizeof(sockaddr_in)) {
-      errno = EINVAL;
-      return -1;
-    }
-    auto *addr4 = reinterpret_cast<const sockaddr_in *>(name);
-    port = ntohs(addr4->sin_port);
-    ip.type = IPADDR_TYPE_V4;
-    ip.u_addr.ip4.addr = addr4->sin_addr.s_addr;
-    LWIP_LOG("tcp_bind(%p ip=%s port=%u)", this->pcb_, ip4addr_ntoa(&ip.u_addr.ip4), port);
-  } else if (this->family_ == AF_INET6) {
-    if (addrlen < sizeof(sockaddr_in6)) {
-      errno = EINVAL;
-      return -1;
-    }
-    auto *addr6 = reinterpret_cast<const sockaddr_in6 *>(name);
-    port = ntohs(addr6->sin6_port);
-    ip.type = IPADDR_TYPE_ANY;
-    memcpy(&ip.u_addr.ip6.addr, &addr6->sin6_addr.un.u8_addr, 16);
-    LWIP_LOG("tcp_bind(%p ip=%s port=%u)", this->pcb_, ip6addr_ntoa(&ip.u_addr.ip6), port);
-  } else {
-    errno = EINVAL;
+  uint16_t port;
+  if (!this->sockaddr2ip_(name, addrlen, &ip, &port)) {
     return -1;
   }
-#else
-  if (this->family_ != AF_INET) {
-    errno = EINVAL;
-    return -1;
-  }
-  auto *addr4 = reinterpret_cast<const sockaddr_in *>(name);
-  port = ntohs(addr4->sin_port);
-  ip.addr = addr4->sin_addr.s_addr;
-  LWIP_LOG("tcp_bind(%p ip=%u port=%u)", this->pcb_, ip.addr, port);
-#endif
+  LWIP_LOG("tcp_bind(%p ip=%s port=%u)", this->pcb_, ipaddr_ntoa(&ip), port);
   err_t err = tcp_bind(this->pcb_, &ip, port);
-  if (err == ERR_USE) {
-    LWIP_LOG("  -> err ERR_USE");
-    errno = EADDRINUSE;
-    return -1;
-  }
-  if (err == ERR_VAL) {
-    LWIP_LOG("  -> err ERR_VAL");
-    errno = EINVAL;
-    return -1;
-  }
   if (err != ERR_OK) {
     LWIP_LOG("  -> err %d", err);
-    errno = EIO;
+    errno = lwip_err_to_errno(err);
     return -1;
   }
   return 0;
@@ -178,7 +188,7 @@ int LWIPRawCommon::close() {
   this->pcb_ = nullptr;
   if (err != ERR_OK) {
     LWIP_LOG("  -> err %d", err);
-    errno = err == ERR_MEM ? ENOMEM : EIO;
+    errno = lwip_err_to_errno(err);
     return -1;
   }
   return 0;
@@ -205,7 +215,7 @@ int LWIPRawCommon::shutdown(int how) {
   err_t err = tcp_shutdown(this->pcb_, shut_rx, shut_tx);
   if (err != ERR_OK) {
     LWIP_LOG("  -> err %d", err);
-    errno = err == ERR_MEM ? ENOMEM : EIO;
+    errno = lwip_err_to_errno(err);
     return -1;
   }
   return 0;
@@ -425,7 +435,79 @@ void LWIPRawImpl::s_err_fn(void *arg, err_t err) {
   // ERR_ABRT: aborted through tcp_abort or TCP timer
   auto *arg_this = reinterpret_cast<LWIPRawImpl *>(arg);
   ESP_LOGVV(TAG, "socket %p: err(err=%d)", arg_this, err);
+  if (arg_this->connect_err_ == EINPROGRESS) {
+    // A connect that never established: RST is a refusal, anything else is
+    // the SYN retransmits giving up. Written before pcb_ so poll_connect()
+    // never sees a dead pcb without its reason.
+    arg_this->connect_err_ = err == ERR_RST ? ECONNREFUSED : ETIMEDOUT;
+  }
   arg_this->pcb_ = nullptr;
+  esphome::wake_loop_any_context();
+}
+
+err_t LWIPRawImpl::s_connected_fn(void *arg, struct tcp_pcb *pcb, err_t err) {
+  // LWIP CALLBACK — same constraints as s_err_fn. err is always ERR_OK; a
+  // failed connect arrives through s_err_fn instead.
+  auto *arg_this = reinterpret_cast<LWIPRawImpl *>(arg);
+  arg_this->connect_err_ = 0;
+  esphome::wake_loop_any_context();
+  return ERR_OK;
+}
+
+int LWIPRawImpl::connect(const struct sockaddr *addr, socklen_t addrlen) {
+  LWIP_LOCK();
+  if (this->pcb_ == nullptr) {
+    errno = EBADF;
+    return -1;
+  }
+  if (this->connect_err_ != 0) {
+    errno = EALREADY;
+    return -1;
+  }
+  ip_addr_t ip;
+  uint16_t port;
+  if (!this->sockaddr2ip_(addr, addrlen, &ip, &port)) {
+    return -1;
+  }
+#if LWIP_IPV6
+  // tcp_connect needs a concrete address type. A remembered IPv4 peer on an
+  // IPv6 build arrives as a v4-mapped address and must be dialed as IPv4.
+  if (IP_IS_ANY_TYPE_VAL(ip)) {
+    if (ip6_addr_isipv4mappedipv6(ip_2_ip6(&ip))) {
+      unmap_ipv4_mapped_ipv6(ip_2_ip4(&ip), ip_2_ip6(&ip));
+      IP_SET_TYPE_VAL(ip, IPADDR_TYPE_V4);
+    } else {
+      IP_SET_TYPE_VAL(ip, IPADDR_TYPE_V6);
+    }
+  }
+#endif
+  LWIP_LOG("tcp_connect(%p ip=%s port=%u)", this->pcb_, ipaddr_ntoa(&ip), port);
+  err_t err = tcp_connect(this->pcb_, &ip, port, LWIPRawImpl::s_connected_fn);
+  if (err != ERR_OK) {
+    LWIP_LOG("  -> err %d", err);
+    errno = lwip_err_to_errno(err);
+    return -1;
+  }
+  this->connect_err_ = EINPROGRESS;
+  errno = EINPROGRESS;
+  return -1;
+}
+
+ConnectPollResult LWIPRawImpl::poll_connect(int &err_out) const {
+  // pcb_ first; see the ordering note on the declaration
+  if (this->pcb_ == nullptr) {
+    err_out = this->connect_err_ == 0 || this->connect_err_ == EINPROGRESS ? ECONNRESET : this->connect_err_;
+    return ConnectPollResult::CONNECT_POLL_ERROR;
+  }
+  if (this->connect_err_ == EINPROGRESS) {
+    yield_to_sys();  // so the SYN-ACK is processed between polls
+    return ConnectPollResult::CONNECT_POLL_PENDING;
+  }
+  if (this->connect_err_ != 0) {
+    err_out = this->connect_err_;
+    return ConnectPollResult::CONNECT_POLL_ERROR;
+  }
+  return ConnectPollResult::CONNECT_POLL_CONNECTED;
 }
 
 err_t LWIPRawImpl::s_recv_fn(void *arg, struct tcp_pcb *pcb, struct pbuf *pb, err_t err) {
@@ -540,14 +622,12 @@ ssize_t LWIPRawImpl::read_locked_(void *buf, size_t len) {
 }
 
 ssize_t LWIPRawImpl::read(void *buf, size_t len) {
-#ifdef USE_ESP8266
-  // Would block: yield to SYS so queued WiFi RX reaches lwip and this read
-  // may succeed. Without this, inbound segments can sit unprocessed for
-  // seconds while the main loop polls (CONT/SYS are cooperative on ESP8266).
+  // Would block: let queued WiFi RX reach lwip first so this read may
+  // succeed; otherwise inbound segments can sit unprocessed for seconds
+  // while the main loop polls
   if (this->waiting_for_data_()) {
-    optimistic_yield(ESP8266_YIELD_INTERVAL_US);
+    yield_to_sys();
   }
-#endif
   // See waiting_for_data_() for safety of unlocked reads.
   if (this->recv_timeout_cs_ > 0 && this->waiting_for_data_()) {
     this->wait_for_data_();
@@ -636,12 +716,10 @@ int LWIPRawImpl::internal_output_() {
       return -1;
     }
   }
-#ifdef USE_ESP8266
   // Flushed: yield to SYS so the queued segments reach the WiFi driver
   // instead of waiting seconds for an unrelated SYS slot. Callers only get
   // here after a successful tcp_write, so idle paths never yield.
-  optimistic_yield(ESP8266_YIELD_INTERVAL_US);
-#endif
+  yield_to_sys();
   return 0;
 }
 

esphome/components/socket/lwip_raw_tcp_impl.h

@@ -50,6 +50,9 @@ class LWIPRawCommon {
 
  protected:
   int ip2sockaddr_(ip_addr_t *ip, uint16_t port, struct sockaddr *name, socklen_t *addrlen);
+  /// Convert a sockaddr of this socket's family to an lwip address and port.
+  /// Returns false with errno set on a family or length mismatch.
+  bool sockaddr2ip_(const struct sockaddr *name, socklen_t addrlen, ip_addr_t *ip, uint16_t *port) const;
 
   // Member ordering optimized to minimize padding on 32-bit systems
   struct tcp_pcb *pcb_;
@@ -58,7 +61,16 @@ class LWIPRawCommon {
   bool nodelay_ = false;
   sa_family_t family_ = 0;
   uint8_t recv_timeout_cs_ = 0;  // SO_RCVTIMEO in centiseconds (0 = no timeout, max 2.55s)
+  // State of a connect() started on this socket: 0 when none is pending (or
+  // it completed), EINPROGRESS while the SYN is out, otherwise the errno the
+  // lwip callbacks recorded for its failure. Fits the padding byte here.
+  uint8_t connect_err_ = 0;
+  static_assert(EINPROGRESS < 256 && ECONNREFUSED < 256 && ECONNRESET < 256 && ETIMEDOUT < 256,
+                "connect_err_ stores errno values in a byte");
 };
+// The connect state must stay inside the padding: no socket, listening or
+// accepted, pays RAM for it
+static_assert(sizeof(LWIPRawCommon) == sizeof(struct tcp_pcb *) + 4, "LWIPRawCommon grew past one word of flags");
 
 /// Connected socket implementation for LWIP raw TCP.
 /// No virtual methods — callers always use the concrete type.
@@ -83,6 +95,13 @@ class LWIPRawImpl : public LWIPRawCommon {
     errno = EOPNOTSUPP;
     return -1;
   }
+  /// Start a non-blocking connect. Always returns -1 with errno EINPROGRESS
+  /// when the SYN was queued; completion is reported by poll_connect().
+  int connect(const struct sockaddr *addr, socklen_t addrlen);
+  // Intentionally unlocked like ready(): reads one pointer and one byte that
+  // the callbacks write in the order the checks depend on (error byte first,
+  // then pcb_), so a torn read only costs one extra poll.
+  ConnectPollResult poll_connect(int &err_out) const;
   ssize_t read(void *buf, size_t len);
   ssize_t readv(const struct iovec *iov, int iovcnt);
   ssize_t recvfrom(void *, size_t, sockaddr *, socklen_t *) {
@@ -120,6 +139,7 @@ class LWIPRawImpl : public LWIPRawCommon {
 
   static void s_err_fn(void *arg, err_t err);
   static err_t s_recv_fn(void *arg, struct tcp_pcb *pcb, struct pbuf *pb, err_t err);
+  static err_t s_connected_fn(void *arg, struct tcp_pcb *pcb, err_t err);
 
  protected:
   // True when the socket could receive data but none has arrived yet.
@@ -137,6 +157,8 @@ class LWIPRawImpl : public LWIPRawCommon {
   size_t rx_buf_offset_ = 0;
   bool rx_closed_ = false;
 };
+static_assert(sizeof(LWIPRawImpl) == sizeof(LWIPRawCommon) + sizeof(pbuf *) + sizeof(size_t) + sizeof(void *),
+              "LWIPRawImpl layout changed");
 
 /// Listening socket implementation for LWIP raw TCP.
 /// Separate from LWIPRawImpl — no virtual dispatch needed.

esphome/components/socket/lwip_sockets_impl.cpp

@@ -49,13 +49,15 @@ int LwIPSocketImpl::close() {
 
 int LwIPSocketImpl::setblocking(bool blocking) {
   int fl = lwip_fcntl(this->fd_, F_GETFL, 0);
+  if (fl < 0) {
+    return fl;
+  }
   if (blocking) {
     fl &= ~O_NONBLOCK;
   } else {
     fl |= O_NONBLOCK;
   }
-  lwip_fcntl(this->fd_, F_SETFL, fl);
-  return 0;
+  return lwip_fcntl(this->fd_, F_SETFL, fl);
 }
 
 size_t LwIPSocketImpl::getpeername_to(std::span<char, SOCKADDR_STR_LEN> buf) {

esphome/components/socket/socket.cpp

@@ -2,6 +2,9 @@
 #if defined(USE_SOCKET_IMPL_LWIP_TCP) || defined(USE_SOCKET_IMPL_LWIP_SOCKETS) || defined(USE_SOCKET_IMPL_BSD_SOCKETS)
 #include <cerrno>
 #include <cstring>
+#ifdef USE_SOCKET_IMPL_BSD_SOCKETS
+#include <sys/select.h>
+#endif
 #include <string>
 #include "esphome/core/log.h"
 #include "esphome/core/application.h"
@@ -165,7 +168,10 @@ socklen_t set_sockaddr(struct sockaddr *addr, socklen_t addrlen, const char *ip_
 #else
     // Use LWIP-specific functions
     ip6_addr_t ip6;
-    inet6_aton(ip_address, &ip6);
+    if (inet6_aton(ip_address, &ip6) == 0) {
+      errno = EINVAL;
+      return 0;
+    }
     memcpy(server->sin6_addr.un.u32_addr, ip6.addr, sizeof(ip6.addr));
 #endif
     return sizeof(sockaddr_in6);
@@ -185,12 +191,58 @@ socklen_t set_sockaddr(struct sockaddr *addr, socklen_t addrlen, const char *ip_
     return 0;
   }
 #else
-  server->sin_addr.s_addr = inet_addr(ip_address);
+  // Unlike inet_addr(), inet_aton() can signal failure while still
+  // accepting the broadcast address 255.255.255.255
+  if (inet_aton(ip_address, &server->sin_addr) == 0) {
+    errno = EINVAL;
+    return 0;
+  }
 #endif
   server->sin_port = htons(port);
   return sizeof(sockaddr_in);
 }
 
+#if defined(USE_SOCKET_IMPL_BSD_SOCKETS) || defined(USE_SOCKET_IMPL_LWIP_SOCKETS)
+ConnectPollResult poll_connect(Socket &sock, int &err_out) {
+  int fd = sock.get_fd();
+  if (fd < 0 || fd >= FD_SETSIZE) {
+    // FD_SET on either is undefined behavior
+    err_out = EBADF;
+    return ConnectPollResult::CONNECT_POLL_ERROR;
+  }
+  // Connect completion is a write event; the main loop only selects on reads
+  fd_set writefds;
+  FD_ZERO(&writefds);
+  FD_SET(fd, &writefds);
+  struct timeval tv = {0, 0};
+#ifdef USE_SOCKET_IMPL_LWIP_SOCKETS
+  // LWIP_COMPAT_SOCKETS may be off (LibreTiny), so use the lwip symbol directly
+  int ret = lwip_select(fd + 1, nullptr, &writefds, nullptr, &tv);
+#else
+  // Global-scope select: the entity namespace esphome::select shadows it here
+  int ret = ::select(fd + 1, nullptr, &writefds, nullptr, &tv);
+#endif
+  if (ret < 0) {
+    err_out = errno;
+    return ConnectPollResult::CONNECT_POLL_ERROR;
+  }
+  if (ret == 0) {
+    return ConnectPollResult::CONNECT_POLL_PENDING;
+  }
+  int error = 0;
+  socklen_t len = sizeof(error);
+  if (sock.getsockopt(SOL_SOCKET, SO_ERROR, &error, &len) != 0) {
+    err_out = errno;
+    return ConnectPollResult::CONNECT_POLL_ERROR;
+  }
+  if (error != 0) {
+    err_out = error;
+    return ConnectPollResult::CONNECT_POLL_ERROR;
+  }
+  return ConnectPollResult::CONNECT_POLL_CONNECTED;
+}
+#endif
+
 socklen_t set_sockaddr_any(struct sockaddr *addr, socklen_t addrlen, uint16_t port) {
 #if USE_NETWORK_IPV6
   if (addrlen < sizeof(sockaddr_in6)) {

esphome/components/socket/socket.h

@@ -145,6 +145,16 @@ inline socklen_t set_sockaddr(struct sockaddr *addr, socklen_t addrlen, const st
 /// 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);
 
+/// Check a non-blocking connect() for completion without blocking. On
+/// CONNECT_POLL_ERROR, err_out holds the socket's SO_ERROR (or errno when the
+/// poll itself failed) on fd based implementations, and the failure recorded
+/// by the lwip callbacks on the raw lwip implementation.
+#ifdef USE_SOCKET_IMPL_LWIP_TCP
+inline ConnectPollResult poll_connect(Socket &sock, int &err_out) { return sock.poll_connect(err_out); }
+#else
+ConnectPollResult poll_connect(Socket &sock, int &err_out);
+#endif
+
 /// Format sockaddr into caller-provided buffer, returns length written (excluding null)
 size_t format_sockaddr_to(const struct sockaddr *addr_ptr, socklen_t len, std::span<char, SOCKADDR_STR_LEN> buf);
 

esphome/components/udp/udp_component.cpp

@@ -13,7 +13,12 @@ void UDPComponent::setup() {
 #if defined(USE_SOCKET_IMPL_BSD_SOCKETS) || defined(USE_SOCKET_IMPL_LWIP_SOCKETS)
   for (const auto &address : this->addresses_) {
     struct sockaddr saddr {};
-    socket::set_sockaddr(&saddr, sizeof(saddr), address, this->broadcast_port_);
+    if (socket::set_sockaddr(&saddr, sizeof(saddr), address, this->broadcast_port_) == 0) {
+      ESP_LOGW(TAG, "Invalid address %s", address);
+      // A dropped address silently receives nothing; surface the misconfiguration
+      this->status_set_warning(LOG_STR("invalid address"));
+      continue;
+    }
     this->sockaddrs_.push_back(saddr);
   }
   // set up broadcast socket
@@ -94,7 +99,11 @@ void UDPComponent::setup() {
   // 8266 and RP2040 `Duino
   for (const auto &address : this->addresses_) {
     auto ipaddr = IPAddress();
-    ipaddr.fromString(address);
+    if (!ipaddr.fromString(address)) {
+      ESP_LOGW(TAG, "Invalid address %s", address);
+      this->status_set_warning(LOG_STR("invalid address"));
+      continue;
+    }
     this->ipaddrs_.push_back(ipaddr);
   }
   if (this->should_listen_)

esphome/components/wake_on_lan/wake_on_lan.cpp

@@ -34,6 +34,10 @@ void WakeOnLanButton::press_action() {
   struct sockaddr_storage saddr {};
   auto addr_len =
       socket::set_sockaddr(reinterpret_cast<sockaddr *>(&saddr), sizeof(saddr), "255.255.255.255", this->port_);
+  if (addr_len == 0) {
+    ESP_LOGW(TAG, "Invalid broadcast address");
+    return;
+  }
   uint8_t buffer[6 + sizeof this->macaddr_ * 16];
   memcpy(buffer, PREFIX, sizeof(PREFIX));
   for (size_t i = 0; i != 16; i++) {

tests/components/socket/test-ipv6.rp2040-ard.yaml

@@ -0,0 +1,4 @@
+substitutions:
+  network_enable_ipv6: "true"
+
+<<: !include common.yaml