[socket] Add BSD socket support for nRF52 (#16699)

Co-authored-by: tomaszduda23 <tomaszduda23@gmail.com>
Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>
Co-authored-by: Jonathan Swoboda <154711427+swoboda1337@users.noreply.github.com>

esphome/components/socket/__init__.py

@@ -149,6 +149,7 @@ CONFIG_SCHEMA = cv.Schema(
             ln882x=IMPLEMENTATION_LWIP_SOCKETS,
             rtl87xx=IMPLEMENTATION_LWIP_SOCKETS,
             host=IMPLEMENTATION_BSD_SOCKETS,
+            nrf52=IMPLEMENTATION_BSD_SOCKETS,
         ): cv.one_of(
             IMPLEMENTATION_LWIP_TCP,
             IMPLEMENTATION_LWIP_SOCKETS,
@@ -168,6 +169,11 @@ async def to_code(config):
         cg.add_define("USE_SOCKET_IMPL_LWIP_SOCKETS")
     elif impl == IMPLEMENTATION_BSD_SOCKETS:
         cg.add_define("USE_SOCKET_IMPL_BSD_SOCKETS")
+        if CORE.using_zephyr:
+            from esphome.components.zephyr import zephyr_add_prj_conf
+
+            zephyr_add_prj_conf("NET_SOCKETS", True)
+            zephyr_add_prj_conf("POSIX_API", True)
     # ESP32 and LibreTiny both have LwIP >= 2.1.3 with lwip_socket_dbg_get_socket()
     # and FreeRTOS task notifications — enable fast select to bypass lwip_select().
     # Only when not using lwip_tcp, which does not provide select() support.

esphome/components/socket/bsd_sockets_impl.cpp

@@ -22,11 +22,13 @@ BSDSocketImpl::BSDSocketImpl(int fd, bool monitor_loop) {
   if (flags >= 0)
     ::fcntl(this->fd_, F_SETFD, flags | FD_CLOEXEC);
 #endif
+  // Guard structure matches socket_ready_fd(): non-HOST platforms (nRF52/OpenThread)
+  // do not register fds with the esphome select loop, so monitor_loop is a no-op there.
   if (!monitor_loop)
     return;
 #ifdef USE_LWIP_FAST_SELECT
   this->cached_sock_ = hook_fd_for_fast_select(this->fd_);
-#else
+#elif defined(USE_HOST)
   this->loop_monitored_ = wake_register_fd(this->fd_);
 #endif
 }
@@ -45,7 +47,7 @@ int BSDSocketImpl::close() {
   // touch an unrelated socket's pcb. No per-socket callback unhook is needed —
   // all LwIP sockets share the same static event_callback.
   this->cached_sock_ = nullptr;
-#else
+#elif defined(USE_HOST)
   if (this->loop_monitored_) {
     wake_unregister_fd(this->fd_);
   }

esphome/components/socket/bsd_sockets_impl.h

@@ -76,7 +76,7 @@ class BSDSocketImpl {
 #endif
   }
   ssize_t recvfrom(void *buf, size_t len, sockaddr *addr, socklen_t *addr_len) {
-#if defined(USE_ESP32) || defined(USE_HOST)
+#if defined(USE_ESP32) || defined(USE_HOST) || defined(USE_ZEPHYR)
     return ::recvfrom(this->fd_, buf, len, 0, addr, addr_len);
 #else
     return ::lwip_recvfrom(this->fd_, buf, len, 0, addr, addr_len);
@@ -85,6 +85,19 @@ class BSDSocketImpl {
   ssize_t readv(const struct iovec *iov, int iovcnt) {
 #if defined(USE_ESP32)
     return ::lwip_readv(this->fd_, iov, iovcnt);
+#elif defined(USE_ZEPHYR)
+    // Zephyr does not provide readv(); emulate with a read() loop. Stream sockets only:
+    // on a datagram socket each read() would consume a separate datagram, not scatter one.
+    ssize_t total = 0;
+    for (int i = 0; i < iovcnt; i++) {
+      ssize_t n = ::read(this->fd_, iov[i].iov_base, iov[i].iov_len);
+      if (n < 0)
+        return total > 0 ? total : n;
+      total += n;
+      if (static_cast<size_t>(n) < iov[i].iov_len)
+        break;
+    }
+    return total;
 #else
     return ::readv(this->fd_, iov, iovcnt);
 #endif
@@ -100,6 +113,19 @@ class BSDSocketImpl {
   ssize_t writev(const struct iovec *iov, int iovcnt) {
 #if defined(USE_ESP32)
     return ::lwip_writev(this->fd_, iov, iovcnt);
+#elif defined(USE_ZEPHYR)
+    // Zephyr does not provide writev(); emulate with a write() loop. Stream sockets only:
+    // on a datagram socket each write() would emit a separate datagram, not gather one.
+    ssize_t total = 0;
+    for (int i = 0; i < iovcnt; i++) {
+      ssize_t n = ::write(this->fd_, iov[i].iov_base, iov[i].iov_len);
+      if (n < 0)
+        return total > 0 ? total : n;
+      total += n;
+      if (static_cast<size_t>(n) < iov[i].iov_len)
+        break;  // partial write: stop so caller resumes from the correct stream offset
+    }
+    return total;
 #else
     return ::writev(this->fd_, iov, iovcnt);
 #endif

esphome/components/socket/headers.h

@@ -158,7 +158,9 @@ using socklen_t = uint32_t;
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <sys/types.h>
+#ifndef USE_ZEPHYR
 #include <sys/uio.h>
+#endif
 #include <unistd.h>
 
 #ifdef USE_HOST
@@ -167,6 +169,10 @@ using socklen_t = uint32_t;
 #include <netinet/ip.h>
 #include <netinet/tcp.h>
 #endif  // USE_HOST
+#ifdef USE_ZEPHYR
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#endif  // USE_ZEPHYR
 
 #ifdef USE_ARDUINO
 // arduino-esp32 declares a global var called INADDR_NONE which is replaced

esphome/components/socket/socket.cpp

@@ -12,9 +12,19 @@
 namespace esphome::socket {
 
 #ifdef USE_HOST
-// Shared ready() implementation for fd-based socket implementations (BSD and LWIP sockets).
-// Checks if the host wake select() loop has marked this fd as ready.
+// Host: ready when the wake select() loop has flagged this fd (or it isn't monitored).
 bool socket_ready_fd(int fd, bool loop_monitored) { return !loop_monitored || wake_fd_ready(fd); }
+#elif defined(USE_ZEPHYR)
+// Zephyr (nRF52): fd monitoring isn't wired into the esphome select loop
+// (wake_register_fd is USE_HOST-only), so loop_monitored is always false. Always
+// return true — the caller handles EAGAIN/EWOULDBLOCK on read.
+//
+// Cost (known trade-off, not an oversight): loop-monitored sockets (API, web_server)
+// are read every loop() iteration and bail on EAGAIN; there is no event-driven wake,
+// so the main loop busy-polls at loop frequency and cannot idle between packets.
+// TODO: wire Zephyr fds into an event-driven wake source (e.g. zsock_poll/k_poll) so
+// the loop can sleep between packets on battery/OpenThread targets.
+bool socket_ready_fd(int /*fd*/, bool /*loop_monitored*/) { return true; }
 #endif
 
 // Platform-specific inet_ntop wrappers
@@ -40,6 +50,19 @@ static inline const char *esphome_inet_ntop6(const void *addr, char *buf, size_t
   return lwip_inet_ntop(AF_INET6, addr, buf, size);
 }
 #endif
+#elif defined(USE_ZEPHYR)
+// Zephyr BSD sockets — use Zephyr native address formatting via POSIX-subset wrappers.
+// <zephyr/net/socket.h> is already included transitively through <sys/socket.h>.
+static inline const char *esphome_inet_ntop4(const void *addr, char *buf, size_t size) {
+  return zsock_inet_ntop(AF_INET, addr, buf, size);
+}
+// IPv6 is always enabled on nRF52 (config validation enforces enable_ipv6=True),
+// but the guard is retained for consistency with other platform blocks.
+#if USE_NETWORK_IPV6
+static inline const char *esphome_inet_ntop6(const void *addr, char *buf, size_t size) {
+  return zsock_inet_ntop(AF_INET6, addr, buf, size);
+}
+#endif
 #else
 // BSD sockets (host, ESP32-IDF)
 static inline const char *esphome_inet_ntop4(const void *addr, char *buf, size_t size) {
@@ -68,6 +91,15 @@ size_t format_sockaddr_to(const struct sockaddr *addr_ptr, socklen_t len, std::s
         esphome_inet_ntop4(&addr->sin6_addr.s6_addr[12], buf.data(), buf.size()) != nullptr) {
       return strlen(buf.data());
     }
+#elif defined(USE_ZEPHYR)
+    // Format IPv4-mapped IPv6 addresses as regular IPv4. Zephyr uses the standard POSIX
+    // s6_addr layout (not the LWIP union) but provides no IN6_IS_ADDR_V4MAPPED macro, so
+    // detect the ::ffff:0:0/96 prefix directly on the address words.
+    if (addr->sin6_addr.s6_addr32[0] == 0 && addr->sin6_addr.s6_addr32[1] == 0 &&
+        addr->sin6_addr.s6_addr32[2] == htonl(0xFFFF) &&
+        esphome_inet_ntop4(&addr->sin6_addr.s6_addr32[3], buf.data(), buf.size()) != nullptr) {
+      return strlen(buf.data());
+    }
 #elif !defined(USE_SOCKET_IMPL_LWIP_TCP)
     // Format IPv4-mapped IPv6 addresses as regular IPv4 (LWIP layout)
     if (addr->sin6_addr.un.u32_addr[0] == 0 && addr->sin6_addr.un.u32_addr[1] == 0 &&
@@ -117,11 +149,19 @@ socklen_t set_sockaddr(struct sockaddr *addr, socklen_t addrlen, const char *ip_
     server->sin6_port = htons(port);
 
 #ifdef USE_SOCKET_IMPL_BSD_SOCKETS
+#if defined(USE_ZEPHYR)
+    // Zephyr BSD sockets: use native address conversion
+    if (zsock_inet_pton(AF_INET6, ip_address, &server->sin6_addr) != 1) {
+      errno = EINVAL;
+      return 0;
+    }
+#else
     // Use standard inet_pton for BSD sockets
     if (inet_pton(AF_INET6, ip_address, &server->sin6_addr) != 1) {
       errno = EINVAL;
       return 0;
     }
+#endif
 #else
     // Use LWIP-specific functions
     ip6_addr_t ip6;
@@ -138,7 +178,15 @@ socklen_t set_sockaddr(struct sockaddr *addr, socklen_t addrlen, const char *ip_
   auto *server = reinterpret_cast<sockaddr_in *>(addr);
   memset(server, 0, sizeof(sockaddr_in));
   server->sin_family = AF_INET;
+#if defined(USE_ZEPHYR)
+  // Zephyr BSD sockets: use native address conversion
+  if (zsock_inet_pton(AF_INET, ip_address, &server->sin_addr) != 1) {
+    errno = EINVAL;
+    return 0;
+  }
+#else
   server->sin_addr.s_addr = inet_addr(ip_address);
+#endif
   server->sin_port = htons(port);
   return sizeof(sockaddr_in);
 }

esphome/components/socket/socket.h

@@ -60,11 +60,11 @@ inline struct lwip_sock *hook_fd_for_fast_select(int fd) {
   }
   return sock;
 }
-#elif defined(USE_HOST)
+#elif defined(USE_HOST) || defined(USE_ZEPHYR)
 /// Shared ready() helper for fd-based socket implementations.
 /// Checks if the Application's select() loop has marked this fd as ready.
 bool socket_ready_fd(int fd, bool loop_monitored);
-#endif
+#endif  // USE_LWIP_FAST_SELECT
 
 // Inline ready() — defined here because it depends on socket_ready/socket_ready_fd
 // declared above, while the impl headers are included before those declarations.

tests/components/socket/test.nrf52-adafruit.yaml

@@ -0,0 +1 @@
+socket:

tests/components/socket/test.nrf52-mcumgr.yaml

@@ -0,0 +1 @@
+socket:

tests/components/socket/test.nrf52-xiao-ble.yaml

@@ -0,0 +1 @@
+socket: