ClientContext (tcp) updates (#5089)

* +sync, get/set default nodelay, sync

* default nodelay=1

* update flush()

* fix return value

* ClientContext: put things together

* ClientContext: fix debugging messages

* WiFiClient: move static members out of the class, add comments

* remove circular dependency

* parameter and return value for Client::flush&stop, flush timeout raised to 300ms

* tcp flush: restart timer on ack receive

* OTA protocol needs setNoDelay(true)

* fix Ethernet with Client changes

* 1 line unredable -> 5 lines readable code

* doc

* Update client-class.rst

* Added details for getters

cores/esp8266/Client.h

@@ -34,8 +34,8 @@ class Client: public Stream {
         virtual int read() = 0;
         virtual int read(uint8_t *buf, size_t size) = 0;
         virtual int peek() = 0;
-        virtual void flush() = 0;
+        virtual bool flush(unsigned int maxWaitMs = 0) = 0;
-        virtual void stop() = 0;
+        virtual bool stop(unsigned int maxWaitMs = 0) = 0;
         virtual uint8_t connected() = 0;
         virtual operator bool() = 0;
     protected:

doc/esp8266wifi/client-class.rst

@@ -18,6 +18,17 @@ Methods documented for `Client <https://www.arduino.cc/en/Reference/WiFiClientCo
 
 Methods and properties described further down are specific to ESP8266. They are not covered in `Arduino WiFi library <https://www.arduino.cc/en/Reference/WiFi>`__ documentation. Before they are fully documented please refer to information below.
 
+flush and stop
+~~~~~~~~~~~~~~
+
+``flush(timeoutMs)`` and ``stop(timeoutMs)`` both have now an optional argument: ``timeout`` in millisecond, and both return a boolean.
+
+Default input value 0 means that effective value is left at the discretion of the implementer.
+
+``flush()`` returning ``true`` indicates that output data have effectively been sent, and ``false`` that a timeout has occurred.
+
+``stop()`` returns ``false`` in case of an issue when closing the client (for instance a timed-out ``flush``). Depending on implementation, its parameter can be passed to ``flush()``.
+
 setNoDelay
 ~~~~~~~~~~
 
@@ -35,6 +46,47 @@ This algorithm is intended to reduce TCP/IP traffic of small packets sent over t
 
     client.setNoDelay(true);
 
+getNoDelay
+~~~~~~~~~~
+
+Returns whether NoDelay is enabled or not for the current connection.
+
+setSync
+~~~~~~~
+
+This is an experimental API that will set the client in synchronized mode.
+In this mode, every ``write()`` is flushed.  It means that after a call to
+``write()``, data are ensured to be received where they went sent to (that is
+``flush`` semantic).
+
+When set to ``true`` in ``WiFiClient`` implementation,
+
+- It slows down transfers, and implicitely disable the Nagle algorithm.
+
+- It also allows to avoid a temporary copy of data that otherwise consumes
+  at most ``TCP_SND_BUF`` = (2 * ``MSS``) bytes per connection,
+
+getSync
+~~~~~~~
+
+Returns whether Sync is enabled or not for the current connection.
+
+setDefaultNoDelay and setDefaultSync
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These set the default value for both ``setSync`` and ``setNoDelay`` for
+every future instance of ``WiFiClient`` (including those coming from
+``WiFiServer.available()`` by default).
+
+Default values are false for both ``NoDelay`` and ``Sync``.
+
+This means that Nagle is enabled by default *for all new connections*.
+
+getDefaultNoDelay and getDefaultSync
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Return the values to be used as default for NoDelay and Sync for all future connections.
+
 Other Function Calls
 ~~~~~~~~~~~~~~~~~~~~
 
@@ -54,7 +106,6 @@ Other Function Calls
     uint16_t  remotePort () 
     IPAddress  localIP () 
     uint16_t  localPort () 
-    bool  getNoDelay () 
 
 Documentation for the above functions is not yet prepared.
 

doc/esp8266wifi/server-class.rst

@@ -32,6 +32,10 @@ This algorithm is intended to reduce TCP/IP traffic of small packets sent over t
     server.begin();
     server.setNoDelay(true);
 
+By default, ``nodelay`` value will depends on global ``WiFiClient::getDefaultNoDelay()`` (currently false by default).
+
+However, a call to ``wiFiServer.setNoDelay()`` will override ``NoDelay`` for all new ``WiFiClient`` provided by the calling instance (``wiFiServer``).
+
 Other Function Calls
 ~~~~~~~~~~~~~~~~~~~~
 

libraries/ArduinoOTA/ArduinoOTA.cpp

@@ -290,6 +290,8 @@ void ArduinoOTAClass::_runUpdate() {
     }
     _state = OTA_IDLE;
   }
+  // OTA sends little packets
+  client.setNoDelay(true);
 
   uint32_t written, total = 0;
   while (!Update.isFinished() && client.connected()) {

libraries/ESP8266WiFi/src/WiFiClient.cpp

@@ -43,6 +43,34 @@ extern "C"
 
 uint16_t WiFiClient::_localPort = 0;
 
+static bool defaultNoDelay = false; // false == Nagle enabled by default
+static bool defaultSync = false;
+
+bool getDefaultPrivateGlobalSyncValue ()
+{
+    return defaultSync;
+}
+
+void WiFiClient::setDefaultNoDelay (bool noDelay)
+{
+    defaultNoDelay = noDelay;
+}
+
+void WiFiClient::setDefaultSync (bool sync)
+{
+    defaultSync = sync;
+}
+
+bool WiFiClient::getDefaultNoDelay ()
+{
+    return defaultNoDelay;
+}
+
+bool WiFiClient::getDefaultSync ()
+{
+    return defaultSync;
+}
+
 template<>
 WiFiClient* SList<WiFiClient>::_s_first = 0;
 
@@ -60,6 +88,9 @@ WiFiClient::WiFiClient(ClientContext* client)
     _timeout = 5000;
     _client->ref();
     WiFiClient::_add(this);
+
+    setSync(defaultSync);
+    setNoDelay(defaultNoDelay);
 }
 
 WiFiClient::~WiFiClient()
@@ -91,7 +122,6 @@ WiFiClient& WiFiClient::operator=(const WiFiClient& other)
     return *this;
 }
 
-
 int WiFiClient::connect(const char* host, uint16_t port)
 {
     IPAddress remote_addr;
@@ -147,6 +177,9 @@ int WiFiClient::connect(IPAddress ip, uint16_t port)
         return 0;
     }
 
+    setSync(defaultSync);
+    setNoDelay(defaultNoDelay);
+
     return 1;
 }
 
@@ -156,12 +189,26 @@ void WiFiClient::setNoDelay(bool nodelay) {
     _client->setNoDelay(nodelay);
 }
 
-bool WiFiClient::getNoDelay() {
+bool WiFiClient::getNoDelay() const {
     if (!_client)
         return false;
     return _client->getNoDelay();
 }
 
+void WiFiClient::setSync(bool sync)
+{
+    if (!_client)
+        return;
+    _client->setSync(sync);
+}
+
+bool WiFiClient::getSync() const
+{
+    if (!_client)
+        return false;
+    return _client->getSync();
+}
+
 size_t WiFiClient::availableForWrite ()
 {
     return _client? _client->availableForWrite(): 0;
@@ -264,19 +311,25 @@ size_t WiFiClient::peekBytes(uint8_t *buffer, size_t length) {
     return _client->peekBytes((char *)buffer, count);
 }
 
-void WiFiClient::flush()
+bool WiFiClient::flush(unsigned int maxWaitMs)
-{
-    if (_client)
-        _client->wait_until_sent();
-}
-
-void WiFiClient::stop()
 {
     if (!_client)
-        return;
+        return true;
 
-    flush();
+    if (maxWaitMs == 0)
-    _client->close();
+        maxWaitMs = WIFICLIENT_MAX_FLUSH_WAIT_MS;
+    return _client->wait_until_sent(maxWaitMs);
+}
+
+bool WiFiClient::stop(unsigned int maxWaitMs)
+{
+    if (!_client)
+        return true;
+
+    bool ret = flush(maxWaitMs); // virtual, may be ssl's
+    if (_client->close() != ERR_OK)
+        ret = false;
+    return ret;
 }
 
 uint8_t WiFiClient::connected()

libraries/ESP8266WiFi/src/WiFiClient.h

@@ -28,7 +28,12 @@
 #include "IPAddress.h"
 #include "include/slist.h"
 
-#define WIFICLIENT_MAX_PACKET_SIZE 1460
+#ifndef TCP_MSS
+#define TCP_MSS 1460 // lwip1.4
+#endif
+
+#define WIFICLIENT_MAX_PACKET_SIZE TCP_MSS
+#define WIFICLIENT_MAX_FLUSH_WAIT_MS 300
 
 #define TCP_DEFAULT_KEEPALIVE_IDLE_SEC          7200 // 2 hours
 #define TCP_DEFAULT_KEEPALIVE_INTERVAL_SEC      75   // 75 sec
@@ -67,8 +72,8 @@ public:
   size_t peekBytes(char *buffer, size_t length) {
     return peekBytes((uint8_t *) buffer, length);
   }
-  virtual void flush();
+  virtual bool flush(unsigned int maxWaitMs = 0);
-  virtual void stop();
+  virtual bool stop(unsigned int maxWaitMs = 0);
   virtual uint8_t connected();
   virtual operator bool();
 
@@ -76,8 +81,7 @@ public:
   uint16_t  remotePort();
   IPAddress localIP();
   uint16_t  localPort();
-  bool getNoDelay();
+
-  void setNoDelay(bool nodelay);
   static void setLocalPortStart(uint16_t port) { _localPort = port; }
 
   size_t availableForWrite();
@@ -96,6 +100,24 @@ public:
   uint8_t  getKeepAliveCount () const;
   void     disableKeepAlive () { keepAlive(0, 0, 0); }
 
+  // default NoDelay=False (Nagle=True=!NoDelay)
+  // Nagle is for shortly delaying outgoing data, to send less/bigger packets
+  // Nagle should be disabled for telnet-like/interactive streams
+  // Nagle is meaningless/ignored when Sync=true
+  static void setDefaultNoDelay (bool noDelay);
+  static bool getDefaultNoDelay ();
+  bool getNoDelay() const;
+  void setNoDelay(bool nodelay);
+
+  // default Sync=false
+  // When sync is true, all writes are automatically flushed.
+  // This is slower but also does not allocate
+  // temporary memory for sending data
+  static void setDefaultSync (bool sync);
+  static bool getDefaultSync ();
+  bool getSync() const;
+  void setSync(bool sync);
+
 protected:
 
   static int8_t _s_connected(void* arg, void* tpcb, int8_t err);

libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.cpp

@@ -271,12 +271,12 @@ uint8_t WiFiClientSecure::connected()
     return false;
 }
 
-void WiFiClientSecure::stop()
+bool WiFiClientSecure::stop(unsigned int maxWaitMs)
 {
     if (_ssl) {
         _ssl->stop();
     }
-    WiFiClient::stop();
+    return WiFiClient::stop(maxWaitMs);
 }
 
 static bool parseHexNibble(char pb, uint8_t* res)

libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.h

@@ -51,7 +51,7 @@ public:
   int read() override;
   int peek() override;
   size_t peekBytes(uint8_t *buffer, size_t length) override;
-  void stop() override;
+  bool stop(unsigned int maxWaitMs = 0) override;
 
   bool setCACert(const uint8_t* pk, size_t size);
   bool setCertificate(const uint8_t* pk, size_t size);

libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp

@@ -175,23 +175,19 @@ void WiFiClientSecure::setBufferSizes(int recv, int xmit) {
   _iobuf_out_size = xmit;
 }
 
-void WiFiClientSecure::stop() {
+bool WiFiClientSecure::stop(unsigned int maxWaitMs) {
-  flush();
+  bool ret = WiFiClient::stop(maxWaitMs); // calls our virtual flush()
-  if (_client) {
-    _client->wait_until_sent();
-    _client->abort();
-  }
-  WiFiClient::stop();
   // Only if we've already connected, clear the connection options
   if (_handshake_done) {
     _clearAuthenticationSettings();
   }
   _freeSSL();
+  return ret;
 }
 
-void WiFiClientSecure::flush() {
+bool WiFiClientSecure::flush(unsigned int maxWaitMs) {
   (void) _run_until(BR_SSL_SENDAPP);
-  WiFiClient::flush();
+  return WiFiClient::flush(maxWaitMs);
 }
 
 int WiFiClientSecure::connect(IPAddress ip, uint16_t port) {

libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.h

@@ -55,8 +55,8 @@ class WiFiClientSecure : public WiFiClient {
     int read() override;
     int peek() override;
     size_t peekBytes(uint8_t *buffer, size_t length) override;
-    void stop() override;
+    bool flush(unsigned int maxWaitMs = 0) override;
-    void flush() override;
+    bool stop(unsigned int maxWaitMs = 0) override;
 
     // Don't validate the chain, just accept whatever is given.  VERY INSECURE!
     void setInsecure() {

libraries/ESP8266WiFi/src/WiFiServer.cpp

@@ -88,11 +88,16 @@ void WiFiServer::begin(uint16_t port) {
 }
 
 void WiFiServer::setNoDelay(bool nodelay) {
-    _noDelay = nodelay;
+    _noDelay = nodelay? _ndTrue: _ndFalse;
 }
 
 bool WiFiServer::getNoDelay() {
-    return _noDelay;
+    switch (_noDelay)
+    {
+    case _ndFalse: return false;
+    case _ndTrue: return true;
+    default: return WiFiClient::getDefaultNoDelay();
+    }
 }
 
 bool WiFiServer::hasClient() {
@@ -106,7 +111,7 @@ WiFiClient WiFiServer::available(byte* status) {
     if (_unclaimed) {
         WiFiClient result(_unclaimed);
         _unclaimed = _unclaimed->next();
-        result.setNoDelay(_noDelay);
+        result.setNoDelay(getNoDelay());
         DEBUGV("WS:av\r\n");
         return result;
     }

libraries/ESP8266WiFi/src/WiFiServer.h

@@ -43,7 +43,7 @@ protected:
 
   ClientContext* _unclaimed;
   ClientContext* _discarded;
-  bool _noDelay = false;
+  enum { _ndDefault, _ndFalse, _ndTrue } _noDelay = _ndDefault;
 
 public:
   WiFiServer(IPAddress addr, uint16_t port);

libraries/ESP8266WiFi/src/include/ClientContext.h

@@ -31,11 +31,14 @@ extern "C" void esp_schedule();
 
 #include "DataSource.h"
 
+bool getDefaultPrivateGlobalSyncValue ();
+
 class ClientContext
 {
 public:
     ClientContext(tcp_pcb* pcb, discard_cb_t discard_cb, void* discard_cb_arg) :
-        _pcb(pcb), _rx_buf(0), _rx_buf_offset(0), _discard_cb(discard_cb), _discard_cb_arg(discard_cb_arg), _refcnt(0), _next(0)
+        _pcb(pcb), _rx_buf(0), _rx_buf_offset(0), _discard_cb(discard_cb), _discard_cb_arg(discard_cb_arg), _refcnt(0), _next(0),
+        _sync(::getDefaultPrivateGlobalSyncValue())
     {
         tcp_setprio(pcb, TCP_PRIO_MIN);
         tcp_arg(pcb, this);
@@ -44,7 +47,7 @@ public:
         tcp_err(pcb, &_s_error);
         tcp_poll(pcb, &_s_poll, 1);
 
-        // not enabled by default for 2.4.0
+        // keep-alive not enabled by default
         //keepAlive();
     }
 
@@ -159,7 +162,7 @@ public:
         }
     }
 
-    bool getNoDelay()
+    bool getNoDelay() const
     {
         if(!_pcb) {
             return false;
@@ -172,12 +175,12 @@ public:
         _timeout_ms = timeout_ms;
     }
 
-    int getTimeout()
+    int getTimeout() const
     {
         return _timeout_ms;
     }
 
-    uint32_t getRemoteAddress()
+    uint32_t getRemoteAddress() const
     {
         if(!_pcb) {
             return 0;
@@ -186,7 +189,7 @@ public:
         return _pcb->remote_ip.addr;
     }
 
-    uint16_t getRemotePort()
+    uint16_t getRemotePort() const
     {
         if(!_pcb) {
             return 0;
@@ -195,7 +198,7 @@ public:
         return _pcb->remote_port;
     }
 
-    uint32_t getLocalAddress()
+    uint32_t getLocalAddress() const
     {
         if(!_pcb) {
             return 0;
@@ -204,7 +207,7 @@ public:
         return _pcb->local_ip.addr;
     }
 
-    uint16_t getLocalPort()
+    uint16_t getLocalPort() const
     {
         if(!_pcb) {
             return 0;
@@ -257,7 +260,7 @@ public:
         return size_read;
     }
 
-    char peek()
+    char peek() const
     {
         if(!_rx_buf) {
             return 0;
@@ -266,7 +269,7 @@ public:
         return reinterpret_cast<char*>(_rx_buf->payload)[_rx_buf_offset];
     }
 
-    size_t peekBytes(char *dst, size_t size)
+    size_t peekBytes(char *dst, size_t size) const
     {
         if(!_rx_buf) {
             return 0;
@@ -296,20 +299,48 @@ public:
         _rx_buf_offset = 0;
     }
 
-    void wait_until_sent()
+    bool wait_until_sent(int max_wait_ms = WIFICLIENT_MAX_FLUSH_WAIT_MS)
     {
-        // fix option 1 in
         // https://github.com/esp8266/Arduino/pull/3967#pullrequestreview-83451496
-        // TODO: option 2
+        // option 1 done
+        // option 2 / _write_some() not necessary since _datasource is always nullptr here
 
-        #define WAIT_TRIES_MS 10	// at most 10ms
+        if (!_pcb)
+            return true;
 
-        int tries = 1+ WAIT_TRIES_MS;
+        int loop = -1;
+        int prevsndbuf = -1;
+        max_wait_ms++;
 
-        while (state() == ESTABLISHED && tcp_sndbuf(_pcb) != TCP_SND_BUF && --tries) {
+        // wait for peer's acks to flush lwIP's output buffer
-            _write_some();
+
-            delay(1); // esp_ schedule+yield
+        while (1) {
+
+            // force lwIP to send what can be sent
+            tcp_output(_pcb);
+
+            int sndbuf = tcp_sndbuf(_pcb);
+            if (sndbuf != prevsndbuf) {
+                // send buffer has changed (or first iteration)
+                // we received an ack: restart the loop counter
+                prevsndbuf = sndbuf;
+                loop = max_wait_ms;
             }
+
+            if (state() != ESTABLISHED || sndbuf == TCP_SND_BUF || --loop <= 0)
+                break;
+
+            delay(1);
+        }
+
+        #ifdef DEBUGV
+        if (loop <= 0) {
+            // wait until sent: timeout
+            DEBUGV(":wustmo\n");
+        }
+        #endif
+
+        return max_wait_ms > 0;
     }
 
     uint8_t state() const
@@ -321,7 +352,6 @@ public:
         return _pcb->state;
     }
 
-
     size_t write(const uint8_t* data, size_t size)
     {
         if (!_pcb) {
@@ -379,6 +409,16 @@ public:
         return isKeepAliveEnabled()? _pcb->keep_cnt: 0;
     }
 
+    bool getSync () const
+    {
+        return _sync;
+    }
+
+    void setSync (bool sync)
+    {
+        _sync = sync;
+    }
+
 protected:
 
     bool _is_timeout()
@@ -418,6 +458,10 @@ protected:
             esp_yield();
         } while(true);
         _send_waiting = 0;
+
+        if (_sync)
+            wait_until_sent();
+
         return _written;
     }
 
@@ -427,40 +471,50 @@ protected:
             return false;
         }
 
-        size_t left = _datasource->available();
+        DEBUGV(":wr %d %d\r\n", _datasource->available(), _written);
-        size_t can_send = tcp_sndbuf(_pcb);
+
-        if (_pcb->snd_queuelen >= TCP_SND_QUEUELEN) {
+        bool has_written = false;
-            can_send = 0;
+
-        }
+        while (_datasource) {
-        size_t will_send = (can_send < left) ? can_send : left;
+            if (state() == CLOSED)
-        DEBUGV(":wr %d %d %d\r\n", will_send, left, _written);
+                return false;
-        bool need_output = false;
+            size_t next_chunk_size = std::min((size_t)tcp_sndbuf(_pcb), _datasource->available());
-        while( will_send && _datasource) {
+            if (!next_chunk_size)
-            size_t next_chunk =
-                will_send > _write_chunk_size ? _write_chunk_size : will_send;
-            const uint8_t* buf = _datasource->get_buffer(next_chunk);
-            if (state() == CLOSED) {
-                need_output = false;
                 break;
-            }
+            const uint8_t* buf = _datasource->get_buffer(next_chunk_size);
-            err_t err = tcp_write(_pcb, buf, next_chunk, TCP_WRITE_FLAG_COPY);
+            // use TCP_WRITE_FLAG_MORE to remove PUSH flag from packet (lwIP's doc),
-            DEBUGV(":wrc %d %d %d\r\n", next_chunk, will_send, (int) err);
+            // because PUSH code implicitely disables Nagle code (see lwIP's tcp_out.c)
+            // Notes:
+            //   PUSH is meant for peer, telling to give data to user app as soon as received
+            //   PUSH "may be set" when sender has finished sending a meaningful data block
+            //   PUSH is quite unclear in its application
+            //   Nagle is for shortly delaying outgoing data, to send less/bigger packets
+            uint8_t flags = TCP_WRITE_FLAG_MORE; // do not tcp-PuSH
+            if (!_sync)
+                // user data must be copied when data are sent but not yet acknowledged
+                // (with sync, we wait for acknowledgment before returning to user)
+                flags |= TCP_WRITE_FLAG_COPY;
+            err_t err = tcp_write(_pcb, buf, next_chunk_size, flags);
+            DEBUGV(":wrc %d %d %d\r\n", next_chunk_size, _datasource->available(), (int)err);
             if (err == ERR_OK) {
-                _datasource->release_buffer(buf, next_chunk);
+                _datasource->release_buffer(buf, next_chunk_size);
-                _written += next_chunk;
+                _written += next_chunk_size;
-                need_output = true;
+                has_written = true;
             } else {
 		// ERR_MEM(-1) is a valid error meaning
 		// "come back later". It leaves state() opened
                 break;
             }
-            will_send -= next_chunk;
         }
-        if( need_output ) {
+
+        if (has_written && (_sync || tcp_nagle_disabled(_pcb)))
+        {
+            // handle no-Nagle manually because of TCP_WRITE_FLAG_MORE
+            // lwIP's tcp_output doc: "Find out what we can send and send it"
             tcp_output(_pcb);
-            return true;
         }
-        return false;
+
+        return has_written;
     }
 
     void _write_some_from_cb()
@@ -482,14 +536,13 @@ protected:
 
     void _consume(size_t size)
     {
+        if(_pcb)
+            tcp_recved(_pcb, size);
         ptrdiff_t left = _rx_buf->len - _rx_buf_offset - size;
         if(left > 0) {
             _rx_buf_offset += size;
         } else if(!_rx_buf->next) {
             DEBUGV(":c0 %d, %d\r\n", size, _rx_buf->tot_len);
-            if(_pcb) {
-                tcp_recved(_pcb, _rx_buf->len);
-            }
             pbuf_free(_rx_buf);
             _rx_buf = 0;
             _rx_buf_offset = 0;
@@ -499,9 +552,6 @@ protected:
             _rx_buf = _rx_buf->next;
             _rx_buf_offset = 0;
             pbuf_ref(_rx_buf);
-            if(_pcb) {
-                tcp_recved(_pcb, head->len);
-            }
             pbuf_free(head);
         }
     }
@@ -592,7 +642,6 @@ private:
 
     DataSource* _datasource = nullptr;
     size_t _written = 0;
-    size_t _write_chunk_size = 256;
     uint32_t _timeout_ms = 5000;
     uint32_t _op_start_time = 0;
     uint8_t _send_waiting = 0;
@@ -600,6 +649,8 @@ private:
 
     int8_t _refcnt;
     ClientContext* _next;
+
+    bool _sync;
 };
 
 #endif//CLIENTCONTEXT_H

libraries/Ethernet/src/EthernetClient.cpp

@@ -119,13 +119,15 @@ int EthernetClient::peek() {
   return b;
 }
 
-void EthernetClient::flush() {
+bool EthernetClient::flush(unsigned int maxWaitMs) {
+  (void)maxWaitMs;
   ::flush(_sock);
+  return true;
 }
 
-void EthernetClient::stop() {
+bool EthernetClient::stop(unsigned int maxWaitMs) {
   if (_sock == MAX_SOCK_NUM)
-    return;
+    return true;
 
   // attempt to close the connection gracefully (send a FIN to other side)
   disconnect(_sock);
@@ -133,19 +135,27 @@ void EthernetClient::stop() {
 
   // wait up to a second for the connection to close
   uint8_t s;
+  if (maxWaitMs == 0)
+    maxWaitMs = 1000;
   do {
     s = status();
     if (s == SnSR::CLOSED)
       break; // exit the loop
     delay(1);
-  } while (millis() - start < 1000);
+  } while (millis() - start < maxWaitMs);
+
+  bool ret = true;
 
   // if it hasn't closed, close it forcefully
-  if (s != SnSR::CLOSED)
+  if (s != SnSR::CLOSED) {
+    ret = false;
     close(_sock);
+  }
 
   EthernetClass::_server_port[_sock] = 0;
   _sock = MAX_SOCK_NUM;
+
+  return ret;
 }
 
 uint8_t EthernetClient::connected() {

libraries/Ethernet/src/EthernetClient.h

@@ -20,8 +20,8 @@ public:
   virtual int read();
   virtual int read(uint8_t *buf, size_t size);
   virtual int peek();
-  virtual void flush();
+  virtual bool flush(unsigned int maxWaitMs = 0);
-  virtual void stop();
+  virtual bool stop(unsigned int maxWaitMs = 0);
   virtual uint8_t connected();
   virtual operator bool();
   virtual bool operator==(const bool value) { return bool() == value; }