From 815511a2757f1399c5cb408d4b09847e78d8553c Mon Sep 17 00:00:00 2001
From: "Sergio R. Caprile" <scaprile@cesanta.com>
Date: Tue, 31 Oct 2023 18:51:30 -0300
Subject: [PATCH] improve randomness in non-random environments

---
 mongoose.c       | 760 ++++++++++++++++++++++++-----------------------
 test/unit_test.c |  13 +-
 2 files changed, 391 insertions(+), 382 deletions(-)

diff --git a/mongoose.c b/mongoose.c
index b768dbadadd..310f5cca6d4 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4070,273 +4070,6 @@ struct mg_connection *mg_mqtt_listen(struct mg_mgr *mgr, const char *url,
   return c;
 }
 
-#ifdef MG_ENABLE_LINES
-#line 1 "src/net.c"
-#endif
-
-
-
-
-
-
-
-
-size_t mg_vprintf(struct mg_connection *c, const char *fmt, va_list *ap) {
-  size_t old = c->send.len;
-  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, ap);
-  return c->send.len - old;
-}
-
-size_t mg_printf(struct mg_connection *c, const char *fmt, ...) {
-  size_t len = 0;
-  va_list ap;
-  va_start(ap, fmt);
-  len = mg_vprintf(c, fmt, &ap);
-  va_end(ap);
-  return len;
-}
-
-static bool mg_atonl(struct mg_str str, struct mg_addr *addr) {
-  uint32_t localhost = mg_htonl(0x7f000001);
-  if (mg_vcasecmp(&str, "localhost") != 0) return false;
-  memcpy(addr->ip, &localhost, sizeof(uint32_t));
-  addr->is_ip6 = false;
-  return true;
-}
-
-static bool mg_atone(struct mg_str str, struct mg_addr *addr) {
-  if (str.len > 0) return false;
-  memset(addr->ip, 0, sizeof(addr->ip));
-  addr->is_ip6 = false;
-  return true;
-}
-
-static bool mg_aton4(struct mg_str str, struct mg_addr *addr) {
-  uint8_t data[4] = {0, 0, 0, 0};
-  size_t i, num_dots = 0;
-  for (i = 0; i < str.len; i++) {
-    if (str.ptr[i] >= '0' && str.ptr[i] <= '9') {
-      int octet = data[num_dots] * 10 + (str.ptr[i] - '0');
-      if (octet > 255) return false;
-      data[num_dots] = (uint8_t) octet;
-    } else if (str.ptr[i] == '.') {
-      if (num_dots >= 3 || i == 0 || str.ptr[i - 1] == '.') return false;
-      num_dots++;
-    } else {
-      return false;
-    }
-  }
-  if (num_dots != 3 || str.ptr[i - 1] == '.') return false;
-  memcpy(&addr->ip, data, sizeof(data));
-  addr->is_ip6 = false;
-  return true;
-}
-
-static bool mg_v4mapped(struct mg_str str, struct mg_addr *addr) {
-  int i;
-  uint32_t ipv4;
-  if (str.len < 14) return false;
-  if (str.ptr[0] != ':' || str.ptr[1] != ':' || str.ptr[6] != ':') return false;
-  for (i = 2; i < 6; i++) {
-    if (str.ptr[i] != 'f' && str.ptr[i] != 'F') return false;
-  }
-  // struct mg_str s = mg_str_n(&str.ptr[7], str.len - 7);
-  if (!mg_aton4(mg_str_n(&str.ptr[7], str.len - 7), addr)) return false;
-  memcpy(&ipv4, addr->ip, sizeof(ipv4));
-  memset(addr->ip, 0, sizeof(addr->ip));
-  addr->ip[10] = addr->ip[11] = 255;
-  memcpy(&addr->ip[12], &ipv4, 4);
-  addr->is_ip6 = true;
-  return true;
-}
-
-static bool mg_aton6(struct mg_str str, struct mg_addr *addr) {
-  size_t i, j = 0, n = 0, dc = 42;
-  addr->scope_id = 0;
-  if (str.len > 2 && str.ptr[0] == '[') str.ptr++, str.len -= 2;
-  if (mg_v4mapped(str, addr)) return true;
-  for (i = 0; i < str.len; i++) {
-    if ((str.ptr[i] >= '0' && str.ptr[i] <= '9') ||
-        (str.ptr[i] >= 'a' && str.ptr[i] <= 'f') ||
-        (str.ptr[i] >= 'A' && str.ptr[i] <= 'F')) {
-      unsigned long val;
-      if (i > j + 3) return false;
-      // MG_DEBUG(("%lu %lu [%.*s]", i, j, (int) (i - j + 1), &str.ptr[j]));
-      val = mg_unhexn(&str.ptr[j], i - j + 1);
-      addr->ip[n] = (uint8_t) ((val >> 8) & 255);
-      addr->ip[n + 1] = (uint8_t) (val & 255);
-    } else if (str.ptr[i] == ':') {
-      j = i + 1;
-      if (i > 0 && str.ptr[i - 1] == ':') {
-        dc = n;  // Double colon
-        if (i > 1 && str.ptr[i - 2] == ':') return false;
-      } else if (i > 0) {
-        n += 2;
-      }
-      if (n > 14) return false;
-      addr->ip[n] = addr->ip[n + 1] = 0;  // For trailing ::
-    } else if (str.ptr[i] == '%') {       // Scope ID
-      for (i = i + 1; i < str.len; i++) {
-        if (str.ptr[i] < '0' || str.ptr[i] > '9') return false;
-        addr->scope_id *= 10, addr->scope_id += (uint8_t) (str.ptr[i] - '0');
-      }
-    } else {
-      return false;
-    }
-  }
-  if (n < 14 && dc == 42) return false;
-  if (n < 14) {
-    memmove(&addr->ip[dc + (14 - n)], &addr->ip[dc], n - dc + 2);
-    memset(&addr->ip[dc], 0, 14 - n);
-  }
-
-  addr->is_ip6 = true;
-  return true;
-}
-
-bool mg_aton(struct mg_str str, struct mg_addr *addr) {
-  // MG_INFO(("[%.*s]", (int) str.len, str.ptr));
-  return mg_atone(str, addr) || mg_atonl(str, addr) || mg_aton4(str, addr) ||
-         mg_aton6(str, addr);
-}
-
-struct mg_connection *mg_alloc_conn(struct mg_mgr *mgr) {
-  struct mg_connection *c =
-      (struct mg_connection *) calloc(1, sizeof(*c) + mgr->extraconnsize);
-  if (c != NULL) {
-    c->mgr = mgr;
-    c->send.align = c->recv.align = MG_IO_SIZE;
-    c->id = ++mgr->nextid;
-  }
-  return c;
-}
-
-void mg_close_conn(struct mg_connection *c) {
-  mg_resolve_cancel(c);  // Close any pending DNS query
-  LIST_DELETE(struct mg_connection, &c->mgr->conns, c);
-  if (c == c->mgr->dns4.c) c->mgr->dns4.c = NULL;
-  if (c == c->mgr->dns6.c) c->mgr->dns6.c = NULL;
-  // Order of operations is important. `MG_EV_CLOSE` event must be fired
-  // before we deallocate received data, see #1331
-  mg_call(c, MG_EV_CLOSE, NULL);
-  MG_DEBUG(("%lu %ld closed", c->id, c->fd));
-
-  mg_tls_free(c);
-  mg_iobuf_free(&c->recv);
-  mg_iobuf_free(&c->send);
-  mg_bzero((unsigned char *) c, sizeof(*c));
-  free(c);
-}
-
-struct mg_connection *mg_connect(struct mg_mgr *mgr, const char *url,
-                                 mg_event_handler_t fn, void *fn_data) {
-  struct mg_connection *c = NULL;
-  if (url == NULL || url[0] == '\0') {
-    MG_ERROR(("null url"));
-  } else if ((c = mg_alloc_conn(mgr)) == NULL) {
-    MG_ERROR(("OOM"));
-  } else {
-    LIST_ADD_HEAD(struct mg_connection, &mgr->conns, c);
-    c->is_udp = (strncmp(url, "udp:", 4) == 0);
-    c->fd = (void *) (size_t) MG_INVALID_SOCKET;
-    c->fn = fn;
-    c->is_client = true;
-    c->fn_data = fn_data;
-    MG_DEBUG(("%lu %ld %s", c->id, c->fd, url));
-    mg_call(c, MG_EV_OPEN, (void *) url);
-    mg_resolve(c, url);
-  }
-  return c;
-}
-
-struct mg_connection *mg_listen(struct mg_mgr *mgr, const char *url,
-                                mg_event_handler_t fn, void *fn_data) {
-  struct mg_connection *c = NULL;
-  if ((c = mg_alloc_conn(mgr)) == NULL) {
-    MG_ERROR(("OOM %s", url));
-  } else if (!mg_open_listener(c, url)) {
-    MG_ERROR(("Failed: %s, errno %d", url, errno));
-    free(c);
-    c = NULL;
-  } else {
-    c->is_listening = 1;
-    c->is_udp = strncmp(url, "udp:", 4) == 0;
-    LIST_ADD_HEAD(struct mg_connection, &mgr->conns, c);
-    c->fn = fn;
-    c->fn_data = fn_data;
-    mg_call(c, MG_EV_OPEN, NULL);
-    if (mg_url_is_ssl(url)) c->is_tls = 1;  // Accepted connection must
-    MG_DEBUG(("%lu %ld %s", c->id, c->fd, url));
-  }
-  return c;
-}
-
-struct mg_connection *mg_wrapfd(struct mg_mgr *mgr, int fd,
-                                mg_event_handler_t fn, void *fn_data) {
-  struct mg_connection *c = mg_alloc_conn(mgr);
-  if (c != NULL) {
-    c->fd = (void *) (size_t) fd;
-    c->fn = fn;
-    c->fn_data = fn_data;
-    MG_EPOLL_ADD(c);
-    mg_call(c, MG_EV_OPEN, NULL);
-    LIST_ADD_HEAD(struct mg_connection, &mgr->conns, c);
-  }
-  return c;
-}
-
-struct mg_timer *mg_timer_add(struct mg_mgr *mgr, uint64_t milliseconds,
-                              unsigned flags, void (*fn)(void *), void *arg) {
-  struct mg_timer *t = (struct mg_timer *) calloc(1, sizeof(*t));
-  if (t != NULL) {
-    mg_timer_init(&mgr->timers, t, milliseconds, flags, fn, arg);
-    t->id = mgr->timerid++;
-  }
-  return t;
-}
-
-void mg_mgr_free(struct mg_mgr *mgr) {
-  struct mg_connection *c;
-  struct mg_timer *tmp, *t = mgr->timers;
-  while (t != NULL) tmp = t->next, free(t), t = tmp;
-  mgr->timers = NULL;  // Important. Next call to poll won't touch timers
-  for (c = mgr->conns; c != NULL; c = c->next) c->is_closing = 1;
-  mg_mgr_poll(mgr, 0);
-#if MG_ENABLE_FREERTOS_TCP
-  FreeRTOS_DeleteSocketSet(mgr->ss);
-#endif
-  MG_DEBUG(("All connections closed"));
-#if MG_ENABLE_EPOLL
-  if (mgr->epoll_fd >= 0) close(mgr->epoll_fd), mgr->epoll_fd = -1;
-#endif
-  mg_tls_ctx_free(mgr);
-}
-
-void mg_mgr_init(struct mg_mgr *mgr) {
-  memset(mgr, 0, sizeof(*mgr));
-#if MG_ENABLE_EPOLL
-  if ((mgr->epoll_fd = epoll_create1(EPOLL_CLOEXEC)) < 0)
-    MG_ERROR(("epoll_create1 errno %d", errno));
-#else
-  mgr->epoll_fd = -1;
-#endif
-#if MG_ARCH == MG_ARCH_WIN32 && MG_ENABLE_WINSOCK
-  // clang-format off
-  { WSADATA data; WSAStartup(MAKEWORD(2, 2), &data); }
-  // clang-format on
-#elif MG_ENABLE_FREERTOS_TCP
-  mgr->ss = FreeRTOS_CreateSocketSet();
-#elif defined(__unix) || defined(__unix__) || defined(__APPLE__)
-  // Ignore SIGPIPE signal, so if client cancels the request, it
-  // won't kill the whole process.
-  signal(SIGPIPE, SIG_IGN);
-#endif
-  mgr->dnstimeout = 3000;
-  mgr->dns4.url = "udp://8.8.8.8:53";
-  mgr->dns6.url = "udp://[2001:4860:4860::8888]:53";
-  mg_tls_ctx_init(mgr);
-}
-
 #ifdef MG_ENABLE_LINES
 #line 1 "src/net_builtin.c"
 #endif
@@ -5316,141 +5049,408 @@ void mg_tcpip_init(struct mg_mgr *mgr, struct mg_tcpip_if *ifp) {
                                            // MG_EPHEMERAL_PORT_BASE to 65535
     if (ifp->tx.ptr == NULL || ifp->recv_queue.buf == NULL) MG_ERROR(("OOM"));
   }
-}
+}
+
+void mg_tcpip_free(struct mg_tcpip_if *ifp) {
+  free(ifp->recv_queue.buf);
+  free((char *) ifp->tx.ptr);
+}
+
+static void send_syn(struct mg_connection *c) {
+  struct connstate *s = (struct connstate *) (c + 1);
+  uint32_t isn = mg_htonl((uint32_t) mg_ntohs(c->loc.port));
+  struct mg_tcpip_if *ifp = (struct mg_tcpip_if *) c->mgr->priv;
+  uint32_t rem_ip;
+  memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
+  tx_tcp(ifp, s->mac, rem_ip, TH_SYN, c->loc.port, c->rem.port, isn, 0, NULL,
+         0);
+}
+
+void mg_connect_resolved(struct mg_connection *c) {
+  struct mg_tcpip_if *ifp = (struct mg_tcpip_if *) c->mgr->priv;
+  uint32_t rem_ip;
+  memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
+  c->is_resolving = 0;
+  if (ifp->eport < MG_EPHEMERAL_PORT_BASE) ifp->eport = MG_EPHEMERAL_PORT_BASE;
+  memcpy(c->loc.ip, &ifp->ip, sizeof(uint32_t));
+  c->loc.port = mg_htons(ifp->eport++);
+  MG_DEBUG(("%lu %M -> %M", c->id, mg_print_ip_port, &c->loc, mg_print_ip_port,
+            &c->rem));
+  mg_call(c, MG_EV_RESOLVE, NULL);
+  if (c->is_udp && (rem_ip == 0xffffffff || rem_ip == (ifp->ip | ~ifp->mask))) {
+    struct connstate *s = (struct connstate *) (c + 1);
+    memset(s->mac, 0xFF, sizeof(s->mac));  // global or local broadcast
+  } else if (((rem_ip & ifp->mask) == (ifp->ip & ifp->mask))) {
+    // If we're in the same LAN, fire an ARP lookup.
+    MG_DEBUG(("%lu ARP lookup...", c->id));
+    arp_ask(ifp, rem_ip);
+    settmout(c, MIP_TTYPE_ARP);
+    c->is_arplooking = 1;
+    c->is_connecting = 1;
+  } else if ((*((uint8_t *) &rem_ip) & 0xE0) == 0xE0) {
+    struct connstate *s = (struct connstate *) (c + 1);  // 224 to 239, E0 to EF
+    uint8_t mcastp[3] = {0x01, 0x00, 0x5E};              // multicast group
+    memcpy(s->mac, mcastp, 3);
+    memcpy(s->mac + 3, ((uint8_t *) &rem_ip) + 1, 3);  // 23 LSb
+    s->mac[3] &= 0x7F;
+  } else {
+    struct connstate *s = (struct connstate *) (c + 1);
+    memcpy(s->mac, ifp->gwmac, sizeof(ifp->gwmac));
+    if (c->is_udp) {
+      mg_call(c, MG_EV_CONNECT, NULL);
+    } else {
+      send_syn(c);
+      settmout(c, MIP_TTYPE_SYN);
+      c->is_connecting = 1;
+    }
+  }
+}
+
+bool mg_open_listener(struct mg_connection *c, const char *url) {
+  c->loc.port = mg_htons(mg_url_port(url));
+  return true;
+}
+
+static void write_conn(struct mg_connection *c) {
+  long len = c->is_tls ? mg_tls_send(c, c->send.buf, c->send.len)
+                       : mg_io_send(c, c->send.buf, c->send.len);
+  if (len > 0) {
+    mg_iobuf_del(&c->send, 0, (size_t) len);
+    mg_call(c, MG_EV_WRITE, &len);
+  }
+}
+
+static void init_closure(struct mg_connection *c) {
+  struct connstate *s = (struct connstate *) (c + 1);
+  if (c->is_udp == false && c->is_listening == false &&
+      c->is_connecting == false) {  // For TCP conns,
+    struct mg_tcpip_if *ifp =
+        (struct mg_tcpip_if *) c->mgr->priv;  // send TCP FIN
+    uint32_t rem_ip;
+    memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
+    tx_tcp(ifp, s->mac, rem_ip, TH_FIN | TH_ACK, c->loc.port, c->rem.port,
+           mg_htonl(s->seq), mg_htonl(s->ack), NULL, 0);
+    settmout(c, MIP_TTYPE_FIN);
+  }
+}
+
+static void close_conn(struct mg_connection *c) {
+  struct connstate *s = (struct connstate *) (c + 1);
+  mg_iobuf_free(&s->raw);  // For TLS connections, release raw data
+  mg_close_conn(c);
+}
+
+static bool can_write(struct mg_connection *c) {
+  return c->is_connecting == 0 && c->is_resolving == 0 && c->send.len > 0 &&
+         c->is_tls_hs == 0 && c->is_arplooking == 0;
+}
+
+void mg_mgr_poll(struct mg_mgr *mgr, int ms) {
+  struct mg_connection *c, *tmp;
+  uint64_t now = mg_millis();
+  mg_tcpip_poll((struct mg_tcpip_if *) mgr->priv, now);
+  mg_timer_poll(&mgr->timers, now);
+  for (c = mgr->conns; c != NULL; c = tmp) {
+    tmp = c->next;
+    struct connstate *s = (struct connstate *) (c + 1);
+    mg_call(c, MG_EV_POLL, &now);
+    MG_VERBOSE(("%lu .. %c%c%c%c%c", c->id, c->is_tls ? 'T' : 't',
+                c->is_connecting ? 'C' : 'c', c->is_tls_hs ? 'H' : 'h',
+                c->is_resolving ? 'R' : 'r', c->is_closing ? 'C' : 'c'));
+    if (c->is_tls_hs) mg_tls_handshake(c);
+    if (can_write(c)) write_conn(c);
+    if (c->is_draining && c->send.len == 0 && s->ttype != MIP_TTYPE_FIN)
+      init_closure(c);
+    if (c->is_closing) close_conn(c);
+  }
+  (void) ms;
+}
+
+bool mg_send(struct mg_connection *c, const void *buf, size_t len) {
+  struct mg_tcpip_if *ifp = (struct mg_tcpip_if *) c->mgr->priv;
+  bool res = false;
+  uint32_t rem_ip;
+  memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
+  if (ifp->ip == 0 || ifp->state != MG_TCPIP_STATE_READY) {
+    mg_error(c, "net down");
+  } else if (c->is_udp) {
+    struct connstate *s = (struct connstate *) (c + 1);
+    len = trim_len(c, len);   // Trimming length if necessary
+    tx_udp(ifp, s->mac, ifp->ip, c->loc.port, rem_ip, c->rem.port, buf, len);
+    res = true;
+  } else {
+    res = mg_iobuf_add(&c->send, c->send.len, buf, len);
+  }
+  return res;
+}
+#endif  // MG_ENABLE_TCPIP
+
+#ifdef MG_ENABLE_LINES
+#line 1 "src/net.c"
+#endif
+
+
+
+
+
+
+
+
+size_t mg_vprintf(struct mg_connection *c, const char *fmt, va_list *ap) {
+  size_t old = c->send.len;
+  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, ap);
+  return c->send.len - old;
+}
+
+size_t mg_printf(struct mg_connection *c, const char *fmt, ...) {
+  size_t len = 0;
+  va_list ap;
+  va_start(ap, fmt);
+  len = mg_vprintf(c, fmt, &ap);
+  va_end(ap);
+  return len;
+}
+
+static bool mg_atonl(struct mg_str str, struct mg_addr *addr) {
+  uint32_t localhost = mg_htonl(0x7f000001);
+  if (mg_vcasecmp(&str, "localhost") != 0) return false;
+  memcpy(addr->ip, &localhost, sizeof(uint32_t));
+  addr->is_ip6 = false;
+  return true;
+}
+
+static bool mg_atone(struct mg_str str, struct mg_addr *addr) {
+  if (str.len > 0) return false;
+  memset(addr->ip, 0, sizeof(addr->ip));
+  addr->is_ip6 = false;
+  return true;
+}
+
+static bool mg_aton4(struct mg_str str, struct mg_addr *addr) {
+  uint8_t data[4] = {0, 0, 0, 0};
+  size_t i, num_dots = 0;
+  for (i = 0; i < str.len; i++) {
+    if (str.ptr[i] >= '0' && str.ptr[i] <= '9') {
+      int octet = data[num_dots] * 10 + (str.ptr[i] - '0');
+      if (octet > 255) return false;
+      data[num_dots] = (uint8_t) octet;
+    } else if (str.ptr[i] == '.') {
+      if (num_dots >= 3 || i == 0 || str.ptr[i - 1] == '.') return false;
+      num_dots++;
+    } else {
+      return false;
+    }
+  }
+  if (num_dots != 3 || str.ptr[i - 1] == '.') return false;
+  memcpy(&addr->ip, data, sizeof(data));
+  addr->is_ip6 = false;
+  return true;
+}
+
+static bool mg_v4mapped(struct mg_str str, struct mg_addr *addr) {
+  int i;
+  uint32_t ipv4;
+  if (str.len < 14) return false;
+  if (str.ptr[0] != ':' || str.ptr[1] != ':' || str.ptr[6] != ':') return false;
+  for (i = 2; i < 6; i++) {
+    if (str.ptr[i] != 'f' && str.ptr[i] != 'F') return false;
+  }
+  // struct mg_str s = mg_str_n(&str.ptr[7], str.len - 7);
+  if (!mg_aton4(mg_str_n(&str.ptr[7], str.len - 7), addr)) return false;
+  memcpy(&ipv4, addr->ip, sizeof(ipv4));
+  memset(addr->ip, 0, sizeof(addr->ip));
+  addr->ip[10] = addr->ip[11] = 255;
+  memcpy(&addr->ip[12], &ipv4, 4);
+  addr->is_ip6 = true;
+  return true;
+}
+
+static bool mg_aton6(struct mg_str str, struct mg_addr *addr) {
+  size_t i, j = 0, n = 0, dc = 42;
+  addr->scope_id = 0;
+  if (str.len > 2 && str.ptr[0] == '[') str.ptr++, str.len -= 2;
+  if (mg_v4mapped(str, addr)) return true;
+  for (i = 0; i < str.len; i++) {
+    if ((str.ptr[i] >= '0' && str.ptr[i] <= '9') ||
+        (str.ptr[i] >= 'a' && str.ptr[i] <= 'f') ||
+        (str.ptr[i] >= 'A' && str.ptr[i] <= 'F')) {
+      unsigned long val;
+      if (i > j + 3) return false;
+      // MG_DEBUG(("%lu %lu [%.*s]", i, j, (int) (i - j + 1), &str.ptr[j]));
+      val = mg_unhexn(&str.ptr[j], i - j + 1);
+      addr->ip[n] = (uint8_t) ((val >> 8) & 255);
+      addr->ip[n + 1] = (uint8_t) (val & 255);
+    } else if (str.ptr[i] == ':') {
+      j = i + 1;
+      if (i > 0 && str.ptr[i - 1] == ':') {
+        dc = n;  // Double colon
+        if (i > 1 && str.ptr[i - 2] == ':') return false;
+      } else if (i > 0) {
+        n += 2;
+      }
+      if (n > 14) return false;
+      addr->ip[n] = addr->ip[n + 1] = 0;  // For trailing ::
+    } else if (str.ptr[i] == '%') {       // Scope ID
+      for (i = i + 1; i < str.len; i++) {
+        if (str.ptr[i] < '0' || str.ptr[i] > '9') return false;
+        addr->scope_id *= 10, addr->scope_id += (uint8_t) (str.ptr[i] - '0');
+      }
+    } else {
+      return false;
+    }
+  }
+  if (n < 14 && dc == 42) return false;
+  if (n < 14) {
+    memmove(&addr->ip[dc + (14 - n)], &addr->ip[dc], n - dc + 2);
+    memset(&addr->ip[dc], 0, 14 - n);
+  }
 
-void mg_tcpip_free(struct mg_tcpip_if *ifp) {
-  free(ifp->recv_queue.buf);
-  free((char *) ifp->tx.ptr);
+  addr->is_ip6 = true;
+  return true;
 }
 
-static void send_syn(struct mg_connection *c) {
-  struct connstate *s = (struct connstate *) (c + 1);
-  uint32_t isn = mg_htonl((uint32_t) mg_ntohs(c->loc.port));
-  struct mg_tcpip_if *ifp = (struct mg_tcpip_if *) c->mgr->priv;
-  uint32_t rem_ip;
-  memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
-  tx_tcp(ifp, s->mac, rem_ip, TH_SYN, c->loc.port, c->rem.port, isn, 0, NULL,
-         0);
+bool mg_aton(struct mg_str str, struct mg_addr *addr) {
+  // MG_INFO(("[%.*s]", (int) str.len, str.ptr));
+  return mg_atone(str, addr) || mg_atonl(str, addr) || mg_aton4(str, addr) ||
+         mg_aton6(str, addr);
 }
 
-void mg_connect_resolved(struct mg_connection *c) {
-  struct mg_tcpip_if *ifp = (struct mg_tcpip_if *) c->mgr->priv;
-  uint32_t rem_ip;
-  memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
-  c->is_resolving = 0;
-  if (ifp->eport < MG_EPHEMERAL_PORT_BASE) ifp->eport = MG_EPHEMERAL_PORT_BASE;
-  memcpy(c->loc.ip, &ifp->ip, sizeof(uint32_t));
-  c->loc.port = mg_htons(ifp->eport++);
-  MG_DEBUG(("%lu %M -> %M", c->id, mg_print_ip_port, &c->loc, mg_print_ip_port,
-            &c->rem));
-  mg_call(c, MG_EV_RESOLVE, NULL);
-  if (c->is_udp && (rem_ip == 0xffffffff || rem_ip == (ifp->ip | ~ifp->mask))) {
-    struct connstate *s = (struct connstate *) (c + 1);
-    memset(s->mac, 0xFF, sizeof(s->mac));  // global or local broadcast
-  } else if (((rem_ip & ifp->mask) == (ifp->ip & ifp->mask))) {
-    // If we're in the same LAN, fire an ARP lookup.
-    MG_DEBUG(("%lu ARP lookup...", c->id));
-    arp_ask(ifp, rem_ip);
-    settmout(c, MIP_TTYPE_ARP);
-    c->is_arplooking = 1;
-    c->is_connecting = 1;
-  } else if ((*((uint8_t *) &rem_ip) & 0xE0) == 0xE0) {
-    struct connstate *s = (struct connstate *) (c + 1);  // 224 to 239, E0 to EF
-    uint8_t mcastp[3] = {0x01, 0x00, 0x5E};              // multicast group
-    memcpy(s->mac, mcastp, 3);
-    memcpy(s->mac + 3, ((uint8_t *) &rem_ip) + 1, 3);  // 23 LSb
-    s->mac[3] &= 0x7F;
-  } else {
-    struct connstate *s = (struct connstate *) (c + 1);
-    memcpy(s->mac, ifp->gwmac, sizeof(ifp->gwmac));
-    if (c->is_udp) {
-      mg_call(c, MG_EV_CONNECT, NULL);
-    } else {
-      send_syn(c);
-      settmout(c, MIP_TTYPE_SYN);
-      c->is_connecting = 1;
-    }
+struct mg_connection *mg_alloc_conn(struct mg_mgr *mgr) {
+  struct mg_connection *c =
+      (struct mg_connection *) calloc(1, sizeof(*c) + mgr->extraconnsize);
+  if (c != NULL) {
+    c->mgr = mgr;
+    c->send.align = c->recv.align = MG_IO_SIZE;
+    c->id = ++mgr->nextid;
   }
+  return c;
 }
 
-bool mg_open_listener(struct mg_connection *c, const char *url) {
-  c->loc.port = mg_htons(mg_url_port(url));
-  return true;
+void mg_close_conn(struct mg_connection *c) {
+  mg_resolve_cancel(c);  // Close any pending DNS query
+  LIST_DELETE(struct mg_connection, &c->mgr->conns, c);
+  if (c == c->mgr->dns4.c) c->mgr->dns4.c = NULL;
+  if (c == c->mgr->dns6.c) c->mgr->dns6.c = NULL;
+  // Order of operations is important. `MG_EV_CLOSE` event must be fired
+  // before we deallocate received data, see #1331
+  mg_call(c, MG_EV_CLOSE, NULL);
+  MG_DEBUG(("%lu %ld closed", c->id, c->fd));
+
+  mg_tls_free(c);
+  mg_iobuf_free(&c->recv);
+  mg_iobuf_free(&c->send);
+  mg_bzero((unsigned char *) c, sizeof(*c));
+  free(c);
 }
 
-static void write_conn(struct mg_connection *c) {
-  long len = c->is_tls ? mg_tls_send(c, c->send.buf, c->send.len)
-                       : mg_io_send(c, c->send.buf, c->send.len);
-  if (len > 0) {
-    mg_iobuf_del(&c->send, 0, (size_t) len);
-    mg_call(c, MG_EV_WRITE, &len);
+struct mg_connection *mg_connect(struct mg_mgr *mgr, const char *url,
+                                 mg_event_handler_t fn, void *fn_data) {
+  struct mg_connection *c = NULL;
+  if (url == NULL || url[0] == '\0') {
+    MG_ERROR(("null url"));
+  } else if ((c = mg_alloc_conn(mgr)) == NULL) {
+    MG_ERROR(("OOM"));
+  } else {
+    LIST_ADD_HEAD(struct mg_connection, &mgr->conns, c);
+    c->is_udp = (strncmp(url, "udp:", 4) == 0);
+    c->fd = (void *) (size_t) MG_INVALID_SOCKET;
+    c->fn = fn;
+    c->is_client = true;
+    c->fn_data = fn_data;
+    MG_DEBUG(("%lu %ld %s", c->id, c->fd, url));
+    mg_call(c, MG_EV_OPEN, (void *) url);
+    mg_resolve(c, url);
   }
+  return c;
 }
 
-static void init_closure(struct mg_connection *c) {
-  struct connstate *s = (struct connstate *) (c + 1);
-  if (c->is_udp == false && c->is_listening == false &&
-      c->is_connecting == false) {  // For TCP conns,
-    struct mg_tcpip_if *ifp =
-        (struct mg_tcpip_if *) c->mgr->priv;  // send TCP FIN
-    uint32_t rem_ip;
-    memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
-    tx_tcp(ifp, s->mac, rem_ip, TH_FIN | TH_ACK, c->loc.port, c->rem.port,
-           mg_htonl(s->seq), mg_htonl(s->ack), NULL, 0);
-    settmout(c, MIP_TTYPE_FIN);
+struct mg_connection *mg_listen(struct mg_mgr *mgr, const char *url,
+                                mg_event_handler_t fn, void *fn_data) {
+  struct mg_connection *c = NULL;
+  if ((c = mg_alloc_conn(mgr)) == NULL) {
+    MG_ERROR(("OOM %s", url));
+  } else if (!mg_open_listener(c, url)) {
+    MG_ERROR(("Failed: %s, errno %d", url, errno));
+    free(c);
+    c = NULL;
+  } else {
+    c->is_listening = 1;
+    c->is_udp = strncmp(url, "udp:", 4) == 0;
+    LIST_ADD_HEAD(struct mg_connection, &mgr->conns, c);
+    c->fn = fn;
+    c->fn_data = fn_data;
+    mg_call(c, MG_EV_OPEN, NULL);
+    if (mg_url_is_ssl(url)) c->is_tls = 1;  // Accepted connection must
+    MG_DEBUG(("%lu %ld %s", c->id, c->fd, url));
   }
+  return c;
 }
 
-static void close_conn(struct mg_connection *c) {
-  struct connstate *s = (struct connstate *) (c + 1);
-  mg_iobuf_free(&s->raw);  // For TLS connections, release raw data
-  mg_close_conn(c);
+struct mg_connection *mg_wrapfd(struct mg_mgr *mgr, int fd,
+                                mg_event_handler_t fn, void *fn_data) {
+  struct mg_connection *c = mg_alloc_conn(mgr);
+  if (c != NULL) {
+    c->fd = (void *) (size_t) fd;
+    c->fn = fn;
+    c->fn_data = fn_data;
+    MG_EPOLL_ADD(c);
+    mg_call(c, MG_EV_OPEN, NULL);
+    LIST_ADD_HEAD(struct mg_connection, &mgr->conns, c);
+  }
+  return c;
 }
 
-static bool can_write(struct mg_connection *c) {
-  return c->is_connecting == 0 && c->is_resolving == 0 && c->send.len > 0 &&
-         c->is_tls_hs == 0 && c->is_arplooking == 0;
+struct mg_timer *mg_timer_add(struct mg_mgr *mgr, uint64_t milliseconds,
+                              unsigned flags, void (*fn)(void *), void *arg) {
+  struct mg_timer *t = (struct mg_timer *) calloc(1, sizeof(*t));
+  if (t != NULL) {
+    mg_timer_init(&mgr->timers, t, milliseconds, flags, fn, arg);
+    t->id = mgr->timerid++;
+  }
+  return t;
 }
 
-void mg_mgr_poll(struct mg_mgr *mgr, int ms) {
-  struct mg_connection *c, *tmp;
-  uint64_t now = mg_millis();
-  mg_tcpip_poll((struct mg_tcpip_if *) mgr->priv, now);
-  mg_timer_poll(&mgr->timers, now);
-  for (c = mgr->conns; c != NULL; c = tmp) {
-    tmp = c->next;
-    struct connstate *s = (struct connstate *) (c + 1);
-    mg_call(c, MG_EV_POLL, &now);
-    MG_VERBOSE(("%lu .. %c%c%c%c%c", c->id, c->is_tls ? 'T' : 't',
-                c->is_connecting ? 'C' : 'c', c->is_tls_hs ? 'H' : 'h',
-                c->is_resolving ? 'R' : 'r', c->is_closing ? 'C' : 'c'));
-    if (c->is_tls_hs) mg_tls_handshake(c);
-    if (can_write(c)) write_conn(c);
-    if (c->is_draining && c->send.len == 0 && s->ttype != MIP_TTYPE_FIN)
-      init_closure(c);
-    if (c->is_closing) close_conn(c);
-  }
-  (void) ms;
+void mg_mgr_free(struct mg_mgr *mgr) {
+  struct mg_connection *c;
+  struct mg_timer *tmp, *t = mgr->timers;
+  while (t != NULL) tmp = t->next, free(t), t = tmp;
+  mgr->timers = NULL;  // Important. Next call to poll won't touch timers
+  for (c = mgr->conns; c != NULL; c = c->next) c->is_closing = 1;
+  mg_mgr_poll(mgr, 0);
+#if MG_ENABLE_FREERTOS_TCP
+  FreeRTOS_DeleteSocketSet(mgr->ss);
+#endif
+  MG_DEBUG(("All connections closed"));
+#if MG_ENABLE_EPOLL
+  if (mgr->epoll_fd >= 0) close(mgr->epoll_fd), mgr->epoll_fd = -1;
+#endif
+  mg_tls_ctx_free(mgr);
 }
 
-bool mg_send(struct mg_connection *c, const void *buf, size_t len) {
-  struct mg_tcpip_if *ifp = (struct mg_tcpip_if *) c->mgr->priv;
-  bool res = false;
-  uint32_t rem_ip;
-  memcpy(&rem_ip, c->rem.ip, sizeof(uint32_t));
-  if (ifp->ip == 0 || ifp->state != MG_TCPIP_STATE_READY) {
-    mg_error(c, "net down");
-  } else if (c->is_udp) {
-    struct connstate *s = (struct connstate *) (c + 1);
-    len = trim_len(c, len);   // Trimming length if necessary
-    tx_udp(ifp, s->mac, ifp->ip, c->loc.port, rem_ip, c->rem.port, buf, len);
-    res = true;
-  } else {
-    res = mg_iobuf_add(&c->send, c->send.len, buf, len);
-  }
-  return res;
+void mg_mgr_init(struct mg_mgr *mgr) {
+  memset(mgr, 0, sizeof(*mgr));
+#if MG_ENABLE_EPOLL
+  if ((mgr->epoll_fd = epoll_create1(EPOLL_CLOEXEC)) < 0)
+    MG_ERROR(("epoll_create1 errno %d", errno));
+#else
+  mgr->epoll_fd = -1;
+#endif
+#if MG_ARCH == MG_ARCH_WIN32 && MG_ENABLE_WINSOCK
+  // clang-format off
+  { WSADATA data; WSAStartup(MAKEWORD(2, 2), &data); }
+  // clang-format on
+#elif MG_ENABLE_FREERTOS_TCP
+  mgr->ss = FreeRTOS_CreateSocketSet();
+#elif defined(__unix) || defined(__unix__) || defined(__APPLE__)
+  // Ignore SIGPIPE signal, so if client cancels the request, it
+  // won't kill the whole process.
+  signal(SIGPIPE, SIG_IGN);
+#endif
+  mgr->dnstimeout = 3000;
+  mgr->dns4.url = "udp://8.8.8.8:53";
+  mgr->dns6.url = "udp://[2001:4860:4860::8888]:53";
+  mg_tls_ctx_init(mgr);
 }
-#endif  // MG_ENABLE_TCPIP
 
 #ifdef MG_ENABLE_LINES
 #line 1 "src/ota_dummy.c"
@@ -9297,6 +9297,7 @@ static size_t mg_tcpip_driver_stm32h_tx(const void *buf, size_t len,
     MG_ERROR(("Frame too big, %ld", (long) len));
     len = 0;  // Frame is too big
   } else if ((s_txdesc[s_txno][3] & BIT(31))) {
+    ifp->nerr++;
     MG_ERROR(("No free descriptors: %u %08X %08X %08X", s_txno,
               s_txdesc[s_txno][3], ETH->DMACSR, ETH->DMACTCR));
     for (int i = 0; i < ETH_DESC_CNT; i++) MG_ERROR(("%08X", s_txdesc[i][3]));
@@ -9551,6 +9552,7 @@ static size_t mg_tcpip_driver_tm4c_tx(const void *buf, size_t len,
     MG_ERROR(("Frame too big, %ld", (long) len));
     len = 0;  // fail
   } else if ((s_txdesc[s_txno][0] & BIT(31))) {
+    ifp->nerr++;
     MG_ERROR(("No descriptors available"));
     // printf("D0 %lx SR %lx\n", (long) s_txdesc[0][0], (long)
     // EMAC->EMACDMARIS);
diff --git a/test/unit_test.c b/test/unit_test.c
index b53297f2138..de04c3d39e3 100644
--- a/test/unit_test.c
+++ b/test/unit_test.c
@@ -521,6 +521,13 @@ static void check_mqtt_message(struct mg_mqtt_opts *opts,
   }
 }
 
+// generate a random string ending in three digits taken from current time
+static struct mg_str gentopic(char *t, unsigned int sz) {
+  mg_random_str(t, sz - 3);
+  snprintf(t + sz - 4, 4, "%03u", (unsigned int) mg_millis() % 1000);
+  return mg_str(t);
+}
+
 static void test_mqtt_basic(void) {
   char tbuf[16], mbuf[50] = {0}, topic[16];
   struct mqtt_data test_data = {tbuf, mbuf, 16, 50, 0};
@@ -539,7 +546,7 @@ static void test_mqtt_basic(void) {
   ASSERT(test_data.flags == 0);
 
   // Subscribe with QoS1
-  opts.topic = mg_str(mg_random_str(topic, sizeof(topic)));
+  opts.topic = gentopic(topic, sizeof(topic));
   opts.qos = 1;
   mg_mqtt_sub(c, &opts);
   for (i = 0; i < 500 && test_data.flags == 0; i++) mg_mgr_poll(&mgr, 10);
@@ -596,7 +603,7 @@ static void test_mqtt_ver(uint8_t mqtt_version) {
 
   opts.clean = true, opts.qos = 1, opts.retain = false, opts.keepalive = 20;
   opts.version = mqtt_version;
-  opts.topic = mg_str(mg_random_str(topic, sizeof(topic)));
+  opts.topic = gentopic(topic, sizeof(topic));
   opts.message = mg_str("mg_will_messsage");
   opts.client_id = mg_str(mg_random_str(client_id, sizeof(client_id)));
   c = mg_mqtt_connect(&mgr, url, &opts, mqtt_cb, &test_data);
@@ -606,7 +613,7 @@ static void test_mqtt_ver(uint8_t mqtt_version) {
   ASSERT(test_data.flags == 0);
 
   // Subscribe with QoS2 (reception downgrades to published QoS)
-  opts.topic = mg_str(mg_random_str(topic, sizeof(topic)));
+  opts.topic = gentopic(topic, sizeof(topic));
   opts.qos = 2;
   mg_mqtt_sub(c, &opts);
   for (i = 0; i < 500 && test_data.flags == 0; i++) mg_mgr_poll(&mgr, 10);