thirdparty-AsyncTCPSock/src/AsyncTCP.cpp

/*
  Reimplementation of an asynchronous TCP library for Espressif MCUs, using
  BSD sockets.

  Copyright (c) 2020 Alex Villacís Lasso.

  Original AsyncTCP API Copyright (c) 2016 Hristo Gochkov. All rights reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include "Arduino.h"

#include "AsyncTCP.h"
#include "esp_task_wdt.h"

#include <lwip/sockets.h>
#include <lwip/netdb.h>
#include <errno.h>

#include <lwip/dns.h>

#include <list>

#undef close
#undef connect
#undef write
#undef read

static TaskHandle_t _asyncsock_service_task_handle = NULL;
static SemaphoreHandle_t _asyncsock_mutex = NULL;

typedef std::list<AsyncSocketBase *>::iterator sockIterator;

void _asynctcpsock_task(void *);

#define MAX_PAYLOAD_SIZE    1360

// Since the only task reading from these sockets is the asyncTcpPSock task
// and all socket clients are serviced sequentially, only one read buffer
// is needed, and it can therefore be statically allocated
static uint8_t _readBuffer[MAX_PAYLOAD_SIZE];

// Start async socket task
static bool _start_asyncsock_task(void)
{
    if (!_asyncsock_service_task_handle) {
        xTaskCreateUniversal(
            _asynctcpsock_task,
            "asyncTcpSock",
            8192 * 2,
            NULL,
            3,                              // <-- TODO: make priority a compile-time parameter
            &_asyncsock_service_task_handle,
            CONFIG_ASYNC_TCP_RUNNING_CORE);
        if (!_asyncsock_service_task_handle) return false;
    }
    return true;
}

// Actual asynchronous socket task
void _asynctcpsock_task(void *)
{
    auto & _socketBaseList = AsyncSocketBase::_getSocketBaseList();

    while (true) {
        sockIterator it;
        fd_set sockSet_r;
        fd_set sockSet_w;
        int max_sock = 0;

        std::list<AsyncSocketBase *> dnsSockList;

        // Collect all of the active sockets into socket set
        FD_ZERO(&sockSet_r); FD_ZERO(&sockSet_w);
        xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
        for (it = _socketBaseList.begin(); it != _socketBaseList.end(); it++) {
            if ((*it)->_socket != -1) {
                FD_SET((*it)->_socket, &sockSet_r);
                FD_SET((*it)->_socket, &sockSet_w);
                (*it)->_selected = true;
                if (max_sock <= (*it)->_socket) max_sock = (*it)->_socket + 1;
            }

            // Collect socket that has finished resolving DNS (with or without error)
            if ((*it)->_isdnsfinished) {
                dnsSockList.push_back(*it);
            }
        }
        xSemaphoreGive(_asyncsock_mutex);

        // Wait for activity on all monitored sockets
        struct timeval tv;
        tv.tv_sec = 0;
        tv.tv_usec = 0;
        uint32_t t1 = millis();
        int r = select(max_sock, &sockSet_r, &sockSet_w, NULL, &tv);

        // Check all sockets to see which ones are active
        std::list<AsyncSocketBase *> wrSockList;
        std::list<AsyncSocketBase *> rdSockList;

        uint32_t nActive = 0;
        if (r > 0) {
            // Collect all writable and readable sockets
            xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
            for (it = _socketBaseList.begin(); it != _socketBaseList.end(); it++) {
                if ((*it)->_selected && FD_ISSET((*it)->_socket, &sockSet_w)) {
                    wrSockList.push_back(*it);
                }
                if ((*it)->_selected && FD_ISSET((*it)->_socket, &sockSet_r)) {
                    rdSockList.push_back(*it);
                }
            }
            xSemaphoreGive(_asyncsock_mutex);

            // Notify all collected writable sockets
            for (it = wrSockList.begin(); it != wrSockList.end(); it++) {
#if CONFIG_ASYNC_TCP_USE_WDT
                if(esp_task_wdt_add(NULL) != ESP_OK){
                    log_e("Failed to add async task to WDT");
                }
#endif
                if ((*it)->_sockIsWriteable()) {
                    (*it)->_sock_lastactivity = millis();
                    nActive++;
                }
#if CONFIG_ASYNC_TCP_USE_WDT
                if(esp_task_wdt_delete(NULL) != ESP_OK){
                    log_e("Failed to remove loop task from WDT");
                }
#endif
            }
            wrSockList.clear();

            // Notify all collected readable sockets
            for (it = rdSockList.begin(); it != rdSockList.end(); it++) {
#if CONFIG_ASYNC_TCP_USE_WDT
                if(esp_task_wdt_add(NULL) != ESP_OK){
                    log_e("Failed to add async task to WDT");
                }
#endif
                (*it)->_sock_lastactivity = millis();
                (*it)->_sockIsReadable();
                nActive++;
#if CONFIG_ASYNC_TCP_USE_WDT
                if(esp_task_wdt_delete(NULL) != ESP_OK){
                    log_e("Failed to remove loop task from WDT");
                }
#endif
            }
            rdSockList.clear();
        }

        // Notify all sockets waiting for DNS completion
        for (it = dnsSockList.begin(); it != dnsSockList.end(); it++) {
#if CONFIG_ASYNC_TCP_USE_WDT
            if(esp_task_wdt_add(NULL) != ESP_OK){
                log_e("Failed to add async task to WDT");
            }
#endif
            (*it)->_isdnsfinished = false;
            (*it)->_sockDelayedConnect();
#if CONFIG_ASYNC_TCP_USE_WDT
            if(esp_task_wdt_delete(NULL) != ESP_OK){
                log_e("Failed to remove loop task from WDT");
            }
#endif
        }

        uint32_t t2 = millis();

        // Ugly hack to work around the apparent situation of select() call NOT
        // yielding to other tasks if using a nonzero wait period.
        uint32_t d = (nActive == 0 && t2 - t1 < 125) ? 125 - (t2 - t1) : 1;
        delay(d);

        // Collect all pollable sockets
        std::list<AsyncSocketBase *> pollSockList;
        xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
        for (it = _socketBaseList.begin(); it != _socketBaseList.end(); it++) {
            (*it)->_selected = false;
            if (millis() - (*it)->_sock_lastactivity >= 125) {
                (*it)->_sock_lastactivity = millis();
                pollSockList.push_back(*it);
            }
        }
        xSemaphoreGive(_asyncsock_mutex);

        // Run activity poll on all pollable sockets
        for (it = pollSockList.begin(); it != pollSockList.end(); it++) {
#if CONFIG_ASYNC_TCP_USE_WDT
            if(esp_task_wdt_add(NULL) != ESP_OK){
                log_e("Failed to add async task to WDT");
            }
#endif
            (*it)->_sockPoll();
#if CONFIG_ASYNC_TCP_USE_WDT
            if(esp_task_wdt_delete(NULL) != ESP_OK){
                log_e("Failed to remove loop task from WDT");
            }
#endif
        }
        pollSockList.clear();
    }

    vTaskDelete(NULL);
    _asyncsock_service_task_handle = NULL;
}

AsyncSocketBase::AsyncSocketBase()
{
    if (_asyncsock_mutex == NULL) _asyncsock_mutex = xSemaphoreCreateMutex();

    _sock_lastactivity = millis();
    _selected = false;

    // Add this base socket to the monitored list
    auto & _socketBaseList = AsyncSocketBase::_getSocketBaseList();
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    _socketBaseList.push_back(this);
    xSemaphoreGive(_asyncsock_mutex);
}

std::list<AsyncSocketBase *> & AsyncSocketBase::_getSocketBaseList(void)
{
    // List of monitored socket objects
    static std::list<AsyncSocketBase *> _socketBaseList;
    return _socketBaseList;
}

AsyncSocketBase::~AsyncSocketBase()
{
    // Remove this base socket from the monitored list
    auto & _socketBaseList = AsyncSocketBase::_getSocketBaseList();
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    _socketBaseList.remove(this);
    xSemaphoreGive(_asyncsock_mutex);
}


AsyncClient::AsyncClient(int sockfd)
: _connect_cb(0)
, _connect_cb_arg(0)
, _discard_cb(0)
, _discard_cb_arg(0)
, _sent_cb(0)
, _sent_cb_arg(0)
, _error_cb(0)
, _error_cb_arg(0)
, _recv_cb(0)
, _recv_cb_arg(0)
, _timeout_cb(0)
, _timeout_cb_arg(0)
, _rx_last_packet(0)
, _rx_since_timeout(0)
, _ack_timeout(ASYNC_MAX_ACK_TIME)
, _connect_port(0)
, _writeSpaceRemaining(TCP_SND_BUF)
, _conn_state(0)
{
    if (sockfd != -1) {
        int r = fcntl( sockfd, F_SETFL, fcntl( sockfd, F_GETFL, 0 ) | O_NONBLOCK );

        // Updating state visible to asyncTcpSock task
        xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
        _conn_state = 4;
        _socket = sockfd;
        xSemaphoreGive(_asyncsock_mutex);
    }
}

AsyncClient::~AsyncClient()
{
    if (_socket != -1) _close();
}

void AsyncClient::setRxTimeout(uint32_t timeout){
    _rx_since_timeout = timeout;
}

uint32_t AsyncClient::getRxTimeout(){
    return _rx_since_timeout;
}

uint32_t AsyncClient::getAckTimeout(){
    return _ack_timeout;
}

void AsyncClient::setAckTimeout(uint32_t timeout){
    _ack_timeout = timeout;
}

void AsyncClient::setNoDelay(bool nodelay){
    if (_socket == -1) return;

    int flag = nodelay;
    int res = setsockopt(_socket, IPPROTO_TCP, TCP_NODELAY, (char *) &flag, sizeof(int));
    if(res < 0) {
        log_e("fail on fd %d, errno: %d, \"%s\"", _socket, errno, strerror(errno));
    }
}

bool AsyncClient::getNoDelay(){
    if (_socket == -1) return false;

    int flag = 0;
    size_t size = sizeof(int);
    int res = getsockopt(_socket, IPPROTO_TCP, TCP_NODELAY, (char *)&flag, &size);
    if(res < 0) {
        log_e("fail on fd %d, errno: %d, \"%s\"", _socket, errno, strerror(errno));
    }
    return flag;
}

/*
 * Callback Setters
 * */

void AsyncClient::onConnect(AcConnectHandler cb, void* arg){
    _connect_cb = cb;
    _connect_cb_arg = arg;
}

void AsyncClient::onDisconnect(AcConnectHandler cb, void* arg){
    _discard_cb = cb;
    _discard_cb_arg = arg;
}

void AsyncClient::onAck(AcAckHandler cb, void* arg){
    _sent_cb = cb;
    _sent_cb_arg = arg;
}

void AsyncClient::onError(AcErrorHandler cb, void* arg){
    _error_cb = cb;
    _error_cb_arg = arg;
}

void AsyncClient::onData(AcDataHandler cb, void* arg){
    _recv_cb = cb;
    _recv_cb_arg = arg;
}

void AsyncClient::onTimeout(AcTimeoutHandler cb, void* arg){
    _timeout_cb = cb;
    _timeout_cb_arg = arg;
}

void AsyncClient::onPoll(AcConnectHandler cb, void* arg){
    _poll_cb = cb;
    _poll_cb_arg = arg;
}

bool AsyncClient::connected(){
    if (_socket == -1) {
        return false;
    }
    return _conn_state == 4;
}

bool AsyncClient::freeable(){
    if (_socket == -1) {
        return true;
    }
    return _conn_state == 0 || _conn_state > 4;
}

uint32_t AsyncClient::getRemoteAddress() {
    if(_socket == -1) {
        return 0;
    }

    struct sockaddr_storage addr;
    socklen_t len = sizeof addr;
    getpeername(_socket, (struct sockaddr*)&addr, &len);
    struct sockaddr_in *s = (struct sockaddr_in *)&addr;

    return s->sin_addr.s_addr;
}

uint16_t AsyncClient::getRemotePort() {
    if(_socket == -1) {
        return 0;
    }

    struct sockaddr_storage addr;
    socklen_t len = sizeof addr;
    getpeername(_socket, (struct sockaddr*)&addr, &len);
    struct sockaddr_in *s = (struct sockaddr_in *)&addr;

    return ntohs(s->sin_port);
}

uint32_t AsyncClient::getLocalAddress() {
    if(_socket == -1) {
        return 0;
    }

    struct sockaddr_storage addr;
    socklen_t len = sizeof addr;
    getsockname(_socket, (struct sockaddr*)&addr, &len);
    struct sockaddr_in *s = (struct sockaddr_in *)&addr;

    return s->sin_addr.s_addr;
}

uint16_t AsyncClient::getLocalPort() {
    if(_socket == -1) {
        return 0;
    }

    struct sockaddr_storage addr;
    socklen_t len = sizeof addr;
    getsockname(_socket, (struct sockaddr*)&addr, &len);
    struct sockaddr_in *s = (struct sockaddr_in *)&addr;

    ntohs(s->sin_port);
}

IPAddress AsyncClient::remoteIP() {
    return IPAddress(getRemoteAddress());
}

uint16_t AsyncClient::remotePort() {
    return getRemotePort();
}

IPAddress AsyncClient::localIP() {
    return IPAddress(getLocalAddress());
}

uint16_t AsyncClient::localPort() {
    return getLocalPort();
}


bool AsyncClient::connect(IPAddress ip, uint16_t port)
{
    if (_socket != -1) {
        log_w("already connected, state %d", _conn_state);
        return false;
    }

    if(!_start_asyncsock_task()){
        log_e("failed to start task");
        return false;
    }

    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        log_e("socket: %d", errno);
        return false;
    }
    int r = fcntl( sockfd, F_SETFL, fcntl( sockfd, F_GETFL, 0 ) | O_NONBLOCK );

    uint32_t ip_addr = ip;
    struct sockaddr_in serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    memcpy(&(serveraddr.sin_addr.s_addr), &ip_addr, 4);
    serveraddr.sin_port = htons(port);

#ifdef EINPROGRESS
    #if EINPROGRESS != 119
    #error EINPROGRESS invalid
    #endif
#endif

    //Serial.printf("DEBUG: connect to %08x port %d using IP... ", ip_addr, port);
    errno = 0; r = lwip_connect_r(sockfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr));
    //Serial.printf("r=%d errno=%d\r\n", r, errno);
    if (r < 0 && errno != EINPROGRESS) {
        //Serial.println("\t(connect failed)");
        log_e("connect on fd %d, errno: %d, \"%s\"", sockfd, errno, strerror(errno));
        close(sockfd);
        return false;
    }

    // Updating state visible to asyncTcpSock task
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    _conn_state = 2;
    _socket = sockfd;
    xSemaphoreGive(_asyncsock_mutex);

    // Socket is now connecting. Should become writable in asyncTcpSock task
    //Serial.printf("\twaiting for connect finished on socket: %d\r\n", _socket);
    return true;
}

void _tcpsock_dns_found(const char * name, struct ip_addr * ipaddr, void * arg);
bool AsyncClient::connect(const char* host, uint16_t port){
    ip_addr_t addr;
    
    if(!_start_asyncsock_task()){
      log_e("failed to start task");
      return false;
    }

    //Serial.printf("DEBUG: connect to %s port %d using DNS...\r\n", host, port);
    err_t err = dns_gethostbyname(host, &addr, (dns_found_callback)&_tcpsock_dns_found, this);
    if(err == ERR_OK) {
        //Serial.printf("\taddr resolved as %08x, connecting...\r\n", addr.u_addr.ip4.addr);
        return connect(IPAddress(addr.u_addr.ip4.addr), port);
    } else if(err == ERR_INPROGRESS) {
        //Serial.println("\twaiting for DNS resolution");
        _connect_port = port;
        return true;
    }
    log_e("error: %d", err);
    return false;
}

// This function runs in the LWIP thread
void _tcpsock_dns_found(const char * name, struct ip_addr * ipaddr, void * arg)
{
    AsyncClient * c = (AsyncClient *)arg;
    if (ipaddr) {
        memcpy(&(c->_connect_addr), ipaddr, sizeof(struct ip_addr));
    } else {
        memset(&(c->_connect_addr), 0, sizeof(struct ip_addr));
    }

    // Updating state visible to asyncTcpSock task
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    c->_isdnsfinished = true;
    xSemaphoreGive(_asyncsock_mutex);

    // TODO: actually use name
}

// DNS resolving has finished. Check for error or connect
void AsyncClient::_sockDelayedConnect(void)
{
    if (_connect_addr.u_addr.ip4.addr) {
        connect(IPAddress(_connect_addr.u_addr.ip4.addr), _connect_port);
    } else {
        if(_error_cb) {
            _error_cb(_error_cb_arg, this, -55);
        }
        if(_discard_cb) {
            _discard_cb(_discard_cb_arg, this);
        }
    }
}

bool AsyncClient::_sockIsWriteable(void)
{
    int res;
    int sockerr;
    socklen_t len;
    bool activity = false;
    bool hasErr = false;

    //Serial.print("AsyncClient::_sockIsWriteable: "); Serial.println(_socket);

    // Socket is now writeable. What should we do?
    switch (_conn_state) {
    case 2:
    case 3:
        //Serial.println("\tconnect end");
        // Socket has finished connecting. What happened?
        len = (socklen_t)sizeof(int);
        res = getsockopt(_socket, SOL_SOCKET, SO_ERROR, &sockerr, &len);
        if (res < 0) {
            //Serial.printf("\terrno=%d\r\n", errno);
            _error(errno);
        } else if (sockerr != 0) {
            //Serial.printf("\tsockerr=%d\r\n", errno);
            _error(sockerr);
        } else {
            // Socket is now fully connected
            //Serial.println("SUCCESS");
            _conn_state = 4;
            activity = true;
            _rx_last_packet = millis();
            _ack_timeout_signaled = false;

            if(_connect_cb) {
                _connect_cb(_connect_cb_arg, this);
            }
        }
        break;
    case 4:
    default:
        // Socket can accept some new data...
        //Serial.printf("\tbefore: remaining %d\r\n", _writeSpaceRemaining);
        if (_writeQueue.size() > 0) {
            //Serial.printf("\tbuffers remaining: %d\r\n", _writeQueue.size());
            if (_writeQueue.front().written < _writeQueue.front().length) {
                uint8_t * p = _writeQueue.front().data + _writeQueue.front().written;
                size_t n = _writeQueue.front().length - _writeQueue.front().written;
                //Serial.printf("\tlwip_write(%p, %d) ... ", p, n);
                errno = 0; ssize_t r = lwip_write(_socket, p, n);
                //Serial.printf("r=%d errno=%d\r\n", r, errno);

                if (r >= 0) {
                    // Written some data into the socket
                    _writeQueue.front().written += r;
                    _writeSpaceRemaining += r;
                    activity = true;
                    //Serial.printf("\tduring: remaining %d\r\n", _writeSpaceRemaining);
                } else if (errno == EAGAIN || errno == EWOULDBLOCK) {
                    // Socket is full again
                    //Serial.println("\tEAGAIN");
                    break;  // NOTE: breaks from switch()
                } else {
                    hasErr = true;
                    _error(errno);
                }
            }

            if (!hasErr && _writeQueue.front().written >= _writeQueue.front().length) {
                // Buffer has been fully written to the socket
                _rx_last_packet = millis();
                if (_writeQueue.front().owned) ::free(_writeQueue.front().data);
                if (_sent_cb) {
                    _sent_cb(_sent_cb_arg, this, _writeQueue.front().length, (millis() - _writeQueue.front().queued_at));
                }

                _writeQueue.pop_front();
            }
        }
        //Serial.printf("\tafter: remaining %d\r\n", _writeSpaceRemaining);

        break;
    }

    return activity;
}

void AsyncClient::_sockIsReadable(void)
{
    //Serial.print("AsyncClient::_sockIsReadable: "); Serial.println(_socket);

    _rx_last_packet = millis();
    //Serial.print("\tlwip_read ... ");
    errno = 0; ssize_t r = lwip_read(_socket, _readBuffer, MAX_PAYLOAD_SIZE);
    //Serial.printf("r=%d errno=%d\r\n", r, errno);
    if (r > 0) {
        if(_recv_cb) {
            _recv_cb(_recv_cb_arg, this, _readBuffer, r);
        }
    } else if (r == 0) {
        // A successful read of 0 bytes indicates remote side closed connection
        _close();
    } else if (r < 0) {
        if (errno == EAGAIN || errno == EWOULDBLOCK) {
            //Serial.println("\tEAGAIN");
        } else {
            _error(errno);
        }
    }
}

void AsyncClient::_sockPoll(void)
{
    if (_socket == -1) return;

    uint32_t now = millis();

    //Serial.print("AsyncClient::_sockPoll: "); Serial.println(_socket);

    // ACK Timeout - simulated by write queue staleness
    if (_writeQueue.size() > 0 && !_ack_timeout_signaled && _ack_timeout && (now - _writeQueue.front().queued_at) >= _ack_timeout) {
        _ack_timeout_signaled = true;
        //log_w("ack timeout %d", pcb->state);
        //Serial.println("\tACK TIMEOUT");
        if(_timeout_cb)
            _timeout_cb(_timeout_cb_arg, this, (now - _writeQueue.front().queued_at));
        return;
    }

    // RX Timeout
    if (_rx_since_timeout && (now - _rx_last_packet) >= (_rx_since_timeout * 1000)) {
        //log_w("rx timeout %d", pcb->state);
        //Serial.println("\tRX TIMEOUT");
        _close();
        return;
    }
    // Everything is fine
    if(_poll_cb) {
        _poll_cb(_poll_cb_arg, this);
    }
}

void AsyncClient::_close(void)
{
    //Serial.print("AsyncClient::_close: "); Serial.println(_socket);
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    _conn_state = 0;
    lwip_close_r(_socket);
    _socket = -1;
    xSemaphoreGive(_asyncsock_mutex);

    if (_discard_cb) _discard_cb(_discard_cb_arg, this);
    _clearWriteQueue();
}

void AsyncClient::_error(int8_t err)
{
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    _conn_state = 0;
    lwip_close_r(_socket);
    _socket = -1;
    xSemaphoreGive(_asyncsock_mutex);

    if (_error_cb) _error_cb(_error_cb_arg, this, err);
    if (_discard_cb) _discard_cb(_discard_cb_arg, this);
    _clearWriteQueue();
}

size_t AsyncClient::space()
{
    if (!connected()) return 0;
    return _writeSpaceRemaining;
}

size_t AsyncClient::add(const char* data, size_t size, uint8_t apiflags)
{
    queued_writebuf n_entry;

    if (!connected() || data == NULL || size <= 0) return 0;

    size_t room = space();
    if (!room) return 0;

    size_t will_send = (room < size) ? room : size;
    if (apiflags & ASYNC_WRITE_FLAG_COPY) {
        n_entry.data = (uint8_t *)malloc(will_send);
        if (n_entry.data == NULL) {
            return 0;
        }
        memcpy(n_entry.data, data, will_send);
        n_entry.owned = true;
    } else {
        n_entry.data = (uint8_t *)data;
        n_entry.owned = false;
    }
    n_entry.length = will_send;
    n_entry.written = 0;
    n_entry.queued_at = millis();

    _writeQueue.push_back(n_entry);
    _writeSpaceRemaining -= will_send;
    _ack_timeout_signaled = false;
    return will_send;
}

bool AsyncClient::send()
{
    // TODO: data was already queued, what should be done here?
    return true;
}

// In normal operation this should be a no-op. Will only free something in case
// of errors before all data was written.
void AsyncClient::_clearWriteQueue(void)
{
    while (_writeQueue.size() > 0) {
        if (_writeQueue.front().owned) {
            ::free(_writeQueue.front().data);
        }
        _writeQueue.pop_front();
    }
}

bool AsyncClient::free(){
    if (_socket == -1) return true;
    return (_conn_state == 0 || _conn_state > 4);
}

size_t AsyncClient::write(const char* data) {
    if(data == NULL) {
        return 0;
    }
    return write(data, strlen(data));
}

size_t AsyncClient::write(const char* data, size_t size, uint8_t apiflags) {
    size_t will_send = add(data, size, apiflags);
    if(!will_send || !send()) {
        return 0;
    }
    return will_send;
}

void AsyncClient::close(bool now)
{
    if (_socket != -1) _close();
}

const char * AsyncClient::errorToString(int8_t error){
    switch(error){
        case ERR_OK: return "OK";
        case ERR_MEM: return "Out of memory error";
        case ERR_BUF: return "Buffer error";
        case ERR_TIMEOUT: return "Timeout";
        case ERR_RTE: return "Routing problem";
        case ERR_INPROGRESS: return "Operation in progress";
        case ERR_VAL: return "Illegal value";
        case ERR_WOULDBLOCK: return "Operation would block";
        case ERR_USE: return "Address in use";
        case ERR_ALREADY: return "Already connected";
        case ERR_CONN: return "Not connected";
        case ERR_IF: return "Low-level netif error";
        case ERR_ABRT: return "Connection aborted";
        case ERR_RST: return "Connection reset";
        case ERR_CLSD: return "Connection closed";
        case ERR_ARG: return "Illegal argument";
        case -55: return "DNS failed";
        default: return "UNKNOWN";
    }
}
/*
const char * AsyncClient::stateToString(){
    switch(state()){
        case 0: return "Closed";
        case 1: return "Listen";
        case 2: return "SYN Sent";
        case 3: return "SYN Received";
        case 4: return "Established";
        case 5: return "FIN Wait 1";
        case 6: return "FIN Wait 2";
        case 7: return "Close Wait";
        case 8: return "Closing";
        case 9: return "Last ACK";
        case 10: return "Time Wait";
        default: return "UNKNOWN";
    }
}
*/



/*
  Async TCP Server
 */

AsyncServer::AsyncServer(IPAddress addr, uint16_t port)
: _port(port)
, _addr(addr)
, _noDelay(false)
, _connect_cb(0)
, _connect_cb_arg(0)
{}

AsyncServer::AsyncServer(uint16_t port)
: _port(port)
, _addr((uint32_t) IPADDR_ANY)
, _noDelay(false)
, _connect_cb(0)
, _connect_cb_arg(0)
{}

AsyncServer::~AsyncServer(){
    end();
}

void AsyncServer::onClient(AcConnectHandler cb, void* arg){
    _connect_cb = cb;
    _connect_cb_arg = arg;
}

void AsyncServer::begin()
{
    if (_socket != -1) return;

    if (!_start_asyncsock_task()) {
        log_e("failed to start task");
        return;
    }

    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) return;

    struct sockaddr_in server;
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = (uint32_t) _addr;
    server.sin_port = htons(_port);
    if (bind(sockfd, (struct sockaddr *)&server, sizeof(server)) < 0) {
        lwip_close_r(sockfd);
        log_e("bind error: %d - %s", errno, strerror(errno));
        return;
    }

    static uint8_t backlog = 5;
    if (listen(sockfd , backlog) < 0) {
        lwip_close_r(sockfd);
        log_e("listen error: %d - %s", errno, strerror(errno));
        return;
    }
    int r = fcntl(sockfd, F_SETFL, O_NONBLOCK);

    // Updating state visible to asyncTcpSock task
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    _socket = sockfd;
    xSemaphoreGive(_asyncsock_mutex);
}

void AsyncServer::end()
{
    if (_socket == -1) return;
    xSemaphoreTake(_asyncsock_mutex, (TickType_t)portMAX_DELAY);
    lwip_close_r(_socket);
    _socket = -1;
    xSemaphoreGive(_asyncsock_mutex);
}

void AsyncServer::_sockIsReadable(void)
{
    //Serial.print("AsyncServer::_sockIsReadable: "); Serial.println(_socket);

    if (_connect_cb) {
        struct sockaddr_in client;
        size_t cs = sizeof(struct sockaddr_in);
        errno = 0; int accepted_sockfd = lwip_accept_r(_socket, (struct sockaddr *)&client, (socklen_t*)&cs);
        //Serial.printf("\t new sockfd=%d errno=%d\r\n", accepted_sockfd, errno);
        if (accepted_sockfd < 0) {
            log_e("accept error: %d - %s", errno, strerror(errno));
            return;
        }

        AsyncClient * c = new AsyncClient(accepted_sockfd);
        if (c) {
            c->setNoDelay(_noDelay);
            _connect_cb(_connect_cb_arg, c);
        }
    }
}