Return the error of a failed listen from usockets to Bun.serve and Bun.listen

packages/bun-usockets/src/bsd.c

@@ -1173,6 +1173,7 @@ inline __attribute__((always_inline)) LIBUS_SOCKET_DESCRIPTOR bsd_bind_listen_fd
 ) {
 
     if (bsd_set_reuse(listenFd, options) != 0) {
+        *error = LIBUS_ERR;
         return LIBUS_SOCKET_ERROR;
     }
 
@@ -1189,6 +1190,7 @@ inline __attribute__((always_inline)) LIBUS_SOCKET_DESCRIPTOR bsd_bind_listen_fd
     if (listenAddr->ai_family == AF_INET6) {
         int enabled = (options & LIBUS_SOCKET_IPV6_ONLY) != 0;
         if (setsockopt(listenFd, IPPROTO_IPV6, IPV6_V6ONLY, &enabled, sizeof(enabled)) != 0) {
+            *error = LIBUS_ERR;
             return LIBUS_SOCKET_ERROR;
         }
     }
@@ -1357,7 +1359,7 @@ LIBUS_SOCKET_DESCRIPTOR bsd_create_bound_socket(const char *host, int port, int
     return fd;
 }
 
-LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket(const char *host, int port, int options, int* error) {
+LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket(const char *host, int port, int options, int* error, int* dns_error) {
     bsd_winsock_ensure();
     struct addrinfo hints, *result;
     memset(&hints, 0, sizeof(struct addrinfo));
@@ -1369,15 +1371,36 @@ LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket(const char *host, int port, int
     char port_string[16];
     snprintf(port_string, 16, "%d", port);
 
-    if (getaddrinfo(host, port_string, &hints, &result)) {
+#ifndef _WIN32
+    errno = 0;
+#endif
+    int gai = getaddrinfo(host, port_string, &hints, &result);
+    if (gai != 0) {
+#ifndef _WIN32
+        /* At the descriptor limit glibc answers EAI_NONAME or EAI_SYSTEM, with the cause in errno. */
+        if (errno != 0 && (gai == EAI_SYSTEM || errno == EMFILE || errno == ENFILE)) {
+            *error = errno;
+            return LIBUS_SOCKET_ERROR;
+        }
+#endif
+        if (host && strchr(host, ':')) {
+            /* An IPv6 literal needs no lookup. It fails when its %zone names no interface. */
+#ifdef _WIN32
+            *error = WSAEINVAL;
+#else
+            *error = EINVAL;
+#endif
+            return LIBUS_SOCKET_ERROR;
+        }
+        *dns_error = gai;
         return LIBUS_SOCKET_ERROR;
     }
 
     LIBUS_SOCKET_DESCRIPTOR listenFd = LIBUS_SOCKET_ERROR;
     struct addrinfo *listenAddr;
     for (struct addrinfo *a = result; a != NULL; a = a->ai_next) {
         if (a->ai_family == AF_INET6) {
-            listenFd = bsd_create_socket(a->ai_family, a->ai_socktype, a->ai_protocol, NULL);
+            listenFd = bsd_create_socket(a->ai_family, a->ai_socktype, a->ai_protocol, error);
             if (listenFd == LIBUS_SOCKET_ERROR) {
                 continue;
             }
@@ -1394,7 +1417,7 @@ LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket(const char *host, int port, int
 
     for (struct addrinfo *a = result; a != NULL; a = a->ai_next) {
         if (a->ai_family == AF_INET) {
-            listenFd = bsd_create_socket(a->ai_family, a->ai_socktype, a->ai_protocol, NULL);
+            listenFd = bsd_create_socket(a->ai_family, a->ai_socktype, a->ai_protocol, error);
             if (listenFd == LIBUS_SOCKET_ERROR) {
                 continue;
             }
@@ -1554,20 +1577,18 @@ static LIBUS_SOCKET_DESCRIPTOR bsd_create_unix_socket_address(const char *path,
 static LIBUS_SOCKET_DESCRIPTOR internal_bsd_create_listen_socket_unix(const char* path, int options, struct sockaddr_un* server_address, size_t addrlen, int* error) {
     LIBUS_SOCKET_DESCRIPTOR listenFd = LIBUS_SOCKET_ERROR;
 
-    listenFd = bsd_create_socket(AF_UNIX, SOCK_STREAM, 0, NULL);
+    listenFd = bsd_create_socket(AF_UNIX, SOCK_STREAM, 0, error);
 
     if (listenFd == LIBUS_SOCKET_ERROR) {
         return LIBUS_SOCKET_ERROR;
     }
 
     if (us_internal_bind_and_listen(listenFd, (struct sockaddr *) server_address, (socklen_t) addrlen, 512, error)) {
-        #if defined(_WIN32)
-          int shouldSimulateENOENT = WSAGetLastError() == WSAENETDOWN;
-        #endif
         bsd_close_socket(listenFd);
         #if defined(_WIN32)
-            if (shouldSimulateENOENT) {
-                SetLastError(ERROR_PATH_NOT_FOUND);
+            /* bind() answers WSAENETDOWN when the directory of the path does not exist. */
+            if (*error == WSAENETDOWN) {
+                *error = ERROR_PATH_NOT_FOUND;
             }
         #endif
         return LIBUS_SOCKET_ERROR;
@@ -1582,17 +1603,21 @@ LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket_unix(const char *path, size_t l
     size_t addrlen = 0;
     if (bsd_create_unix_socket_address(path, len, &dirfd_workaround_for_unix_path_len, &server_address, &addrlen)) {
         /* The path could not be expressed as a sockaddr_un (the basename
-         * exceeds sun_path even with the dirfd workaround); surface the errno
-         * so the caller can report something better than a codeless failure. */
-        if (error && errno) *error = errno;
+         * exceeds sun_path even with the dirfd workaround). That helper
+         * reports through SetLastError on Windows and errno elsewhere. */
+#if defined(_WIN32)
+        *error = (int) GetLastError();
+#else
+        *error = errno;
+#endif
         return LIBUS_SOCKET_ERROR;
     }
 
 #if defined(__APPLE__)
     if (dirfd_workaround_for_unix_path_len != -1) {
         if (__pthread_fchdir(dirfd_workaround_for_unix_path_len) != 0) {
             close(dirfd_workaround_for_unix_path_len);
-            errno = ENAMETOOLONG;
+            *error = ENAMETOOLONG;
             return LIBUS_SOCKET_ERROR;
         }
     }
@@ -1602,10 +1627,8 @@ LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket_unix(const char *path, size_t l
 
 #if defined(__APPLE__)
     if (dirfd_workaround_for_unix_path_len != -1) {
-        int saved_errno = errno;
         __pthread_fchdir(-1);
         close(dirfd_workaround_for_unix_path_len);
-        errno = saved_errno;
     }
 #elif defined(__linux__)
     if (dirfd_workaround_for_unix_path_len != -1) {

packages/bun-usockets/src/context.c

@@ -373,23 +373,19 @@ static void us_internal_init_listen_socket(struct us_listen_socket_t *ls,
 
 struct us_listen_socket_t *us_socket_group_listen(struct us_socket_group_t *group,
         unsigned char kind, struct ssl_ctx_st *ssl_ctx,
-        const char *host, int port, int options, int socket_ext_size, int *error) {
-    LIBUS_SOCKET_DESCRIPTOR listen_socket_fd = bsd_create_listen_socket(host, port, options, error);
+        const char *host, int port, int options, int socket_ext_size, int *error, int *dns_error) {
+    LIBUS_SOCKET_DESCRIPTOR listen_socket_fd = bsd_create_listen_socket(host, port, options, error, dns_error);
     if (listen_socket_fd == LIBUS_SOCKET_ERROR) {
         return 0;
     }
 
     struct us_poll_t *p = us_create_poll(group->loop, 0, sizeof(struct us_listen_socket_t));
     us_poll_init(p, listen_socket_fd, POLL_TYPE_SEMI_SOCKET);
     if (us_poll_start_rc(p, group->loop, LIBUS_SOCKET_READABLE) != 0) {
-        /* EPOLL_CTL_ADD failed (e.g. ENOSPC at fs.epoll.max_user_watches).
-         * Report via both the out-param and thread-local errno: Bun.listen
-         * reads *error, Bun.serve reads errno. */
-        int saved_errno = errno;
+        /* EPOLL_CTL_ADD failed (e.g. ENOSPC at fs.epoll.max_user_watches). */
+        *error = errno;
         bsd_close_socket(listen_socket_fd);
         us_poll_free(p, group->loop);
-        *error = saved_errno;
-        errno = saved_errno;
         return 0;
     }
 
@@ -448,11 +444,9 @@ struct us_listen_socket_t *us_socket_group_listen_unix(struct us_socket_group_t
     struct us_poll_t *p = us_create_poll(group->loop, 0, sizeof(struct us_listen_socket_t));
     us_poll_init(p, listen_socket_fd, POLL_TYPE_SEMI_SOCKET);
     if (us_poll_start_rc(p, group->loop, LIBUS_SOCKET_READABLE) != 0) {
-        int saved_errno = errno;
+        *error = errno;
         bsd_close_socket(listen_socket_fd);
         us_poll_free(p, group->loop);
-        *error = saved_errno;
-        errno = saved_errno;
         return 0;
     }
 

packages/bun-usockets/src/internal/networking/bsd.h

@@ -231,7 +231,7 @@ int bsd_send_is_transient_error();
 
 // return LIBUS_SOCKET_ERROR or the fd that represents listen socket
 // listen both on ipv6 and ipv4
-LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket(const char *host, int port, int options, int* error);
+LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket(const char *host, int port, int options, int* error, int* dns_error);
 
 LIBUS_SOCKET_DESCRIPTOR bsd_create_listen_socket_unix(const char *path, size_t pathlen, int options, int* error);
 

packages/bun-usockets/src/libusockets.h

@@ -395,11 +395,16 @@ void us_socket_set_first_flight_before_fin(us_socket_r s) nonnull_fn_decl;
 /* ── Listen ───────────────────────────────────────────────────────────────
  * The listener owns: an embedded group for accepted sockets, the SSL_CTX
  * (borrowed ref, optional), the SNI tree (optional), and the kind to stamp on
- * accepted sockets. */
+ * accepted sockets.
+ *
+ * On NULL, *error is the code of the call that failed: errno, or a WSA /
+ * Win32 code on Windows. When the lookup of `host` failed instead, *error is
+ * as the caller set it and *dns_error is what getaddrinfo() returned. The two
+ * number spaces overlap, so callers zero both first. */
 struct us_listen_socket_t *us_socket_group_listen(us_socket_group_r group,
     unsigned char kind, struct ssl_ctx_st *ssl_ctx,
-    const char *host, int port, int options, int socket_ext_size, int *error)
-    __attribute__((nonnull(1, 8)));  /* ssl_ctx, host nullable */
+    const char *host, int port, int options, int socket_ext_size, int *error, int *dns_error)
+    __attribute__((nonnull(1, 8, 9)));  /* ssl_ctx, host nullable */
 struct us_listen_socket_t *us_socket_group_listen_unix(us_socket_group_r group,
     unsigned char kind, struct ssl_ctx_st *ssl_ctx,
     const char *path, size_t pathlen, int options, int socket_ext_size, int *error)

packages/bun-uws/src/App.h

@@ -727,31 +727,13 @@ struct TemplatedApp {
     struct ssl_ctx_st *sslCtxOrNull() { return SSL ? sslCtx : nullptr; }
 
 public:
-    /* Host, port, options, callback */
-    TemplatedApp &&listen(const std::string &host, int port, int options, MoveOnlyFunction<void(us_listen_socket_t *)> &&handler) {
-        if (host.empty()) {
-            return listen(port, options, std::move(handler));
-        }
-        handler(httpContext ? trackListenSocket(httpContext->listen(sslCtxOrNull(), host.c_str(), port, options)) : nullptr);
-        return std::move(*this);
-    }
-
-    /* Port, callback */
-    TemplatedApp &&listen(int port, MoveOnlyFunction<void(us_listen_socket_t *)> &&handler) {
-        handler(httpContext ? trackListenSocket(httpContext->listen(sslCtxOrNull(), nullptr, port, 0)) : nullptr);
-        return std::move(*this);
+    /* host is nullptr for every address. The out-params are those of us_socket_group_listen. */
+    us_listen_socket_t *listen(const char *host, int port, int options, int *error, int *dnsError) {
+        return httpContext ? trackListenSocket(httpContext->listen(sslCtxOrNull(), host, port, options, error, dnsError)) : nullptr;
     }
 
-    /* Port, options, callback */
-    TemplatedApp &&listen(int port, int options, MoveOnlyFunction<void(us_listen_socket_t *)> &&handler) {
-        handler(httpContext ? trackListenSocket(httpContext->listen(sslCtxOrNull(), nullptr, port, options)) : nullptr);
-        return std::move(*this);
-    }
-
-    /* options, callback, path to unix domain socket */
-    TemplatedApp &&listen(int options, MoveOnlyFunction<void(us_listen_socket_t *)> &&handler, std::string_view path) {
-        handler(httpContext ? trackListenSocket(httpContext->listen_unix(sslCtxOrNull(), path.data(), path.length(), options)) : nullptr);
-        return std::move(*this);
+    us_listen_socket_t *listen_unix(std::string_view path, int options, int *error) {
+        return httpContext ? trackListenSocket(httpContext->listen_unix(sslCtxOrNull(), path.data(), path.length(), options, error)) : nullptr;
     }
 
     void setOnSocketClosed(HttpContextData<SSL>::OnSocketClosedCallback onClose) {

packages/bun-uws/src/HttpContext.h

@@ -1283,15 +1283,13 @@ struct HttpContext {
     }
 
     /* Listen to port using this HttpContext. ssl_ctx may be nullptr for plain HTTP. */
-    us_listen_socket_t *listen(struct ssl_ctx_st *sslCtx, const char *host, int port, int options) {
-        int error = 0;
-        return unrefListenSocket(us_socket_group_listen(&group, socketKind(), sslCtx, host, port, tcpListenOptions(options), socketExtSize(), &error));
+    us_listen_socket_t *listen(struct ssl_ctx_st *sslCtx, const char *host, int port, int options, int *error, int *dnsError) {
+        return unrefListenSocket(us_socket_group_listen(&group, socketKind(), sslCtx, host, port, tcpListenOptions(options), socketExtSize(), error, dnsError));
     }
 
     /* Listen to unix domain socket using this HttpContext */
-    us_listen_socket_t *listen_unix(struct ssl_ctx_st *sslCtx, const char *path, size_t pathlen, int options) {
-        int error = 0;
-        return unrefListenSocket(us_socket_group_listen_unix(&group, socketKind(), sslCtx, path, pathlen, options, socketExtSize(), &error));
+    us_listen_socket_t *listen_unix(struct ssl_ctx_st *sslCtx, const char *path, size_t pathlen, int options, int *error) {
+        return unrefListenSocket(us_socket_group_listen_unix(&group, socketKind(), sslCtx, path, pathlen, options, socketExtSize(), error));
     }
 };
 

src/runtime/dns_jsc/cares_jsc.rs

@@ -845,6 +845,15 @@ pub(crate) fn error_to_js_with_syscall_and_hostname(
     Ok(instance)
 }
 
+/// The `getaddrinfo <CODE> <hostname>` error for `gai`, a non-zero return of getaddrinfo(3).
+pub(crate) fn getaddrinfo_error(gai: c_int, hostname: &[u8]) -> Option<SystemError> {
+    if gai == 0 {
+        return None;
+    }
+    c_ares::Error::init_eai(gai)
+        .map(|error| system_error_with_syscall_and_hostname(error, b"getaddrinfo", hostname))
+}
+
 /// Thrown before uSockets' synchronous `getaddrinfo` can block on a name that can never resolve.
 pub(crate) fn not_a_hostname_error(global_this: &JSGlobalObject, hostname: &[u8]) -> JSValue {
     system_error_with_syscall_and_hostname(c_ares::Error::ENOTFOUND, b"getaddrinfo", hostname)