ua_network_tcp.c

/* This work is licensed under a Creative Commons CCZero 1.0 Universal License.
 * See http://creativecommons.org/publicdomain/zero/1.0/ for more information. */

#if defined(__MINGW32__) && (!defined(WINVER) || WINVER < 0x501)
/* Assume the target is newer than Windows XP */
# undef WINVER
# undef _WIN32_WINDOWS
# undef _WIN32_WINNT
# define WINVER 0x0501
# define _WIN32_WINDOWS 0x0501
# define _WIN32_WINNT 0x0501
#endif

#include "ua_network_tcp.h"

#include <stdlib.h> // malloc, free
#include <stdio.h> // snprintf
#include <string.h> // memset
#include <errno.h>
#ifdef _WIN32
# ifndef __clang__
#  include <malloc.h>
# endif
/* Fix redefinition of SLIST_ENTRY on mingw winnt.h */
# ifdef SLIST_ENTRY
#  undef SLIST_ENTRY
# endif
/* inet_ntoa is deprecated on MSVC but used for compatibility */
# define _WINSOCK_DEPRECATED_NO_WARNINGS
# include <winsock2.h>
# include <ws2tcpip.h>
# define CLOSESOCKET(S) closesocket((SOCKET)S)
# define ssize_t int
# define WIN32_INT (int)
#else
# define CLOSESOCKET(S) close(S)
# define SOCKET int
# define WIN32_INT
# include <arpa/inet.h>
# include <netinet/in.h>
# include <sys/select.h>
# include <sys/ioctl.h>
# include <fcntl.h>
# include <unistd.h> // read, write, close
# include <netdb.h>
# ifdef __QNX__
#  include <sys/socket.h>
# endif
#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
# include <sys/param.h>
# if defined(BSD)
#  include<sys/socket.h>
# endif
#endif
# ifndef __CYGWIN__
#  include <netinet/tcp.h>
# endif
#endif

/* unsigned int for windows and workaround to a glibc bug */
/* Additionally if GNU_LIBRARY is not defined, it may be using musl libc (e.g. Docker Alpine) */
#if defined(_WIN32) || defined(__OpenBSD__) || \
    (defined(__GNU_LIBRARY__) && (__GNU_LIBRARY__ <= 6) && \
     (__GLIBC__ <= 2) && (__GLIBC_MINOR__ < 16) || \
    !defined(__GNU_LIBRARY__))
# define UA_fd_set(fd, fds) FD_SET((unsigned int)fd, fds)
# define UA_fd_isset(fd, fds) FD_ISSET((unsigned int)fd, fds)
#else
# define UA_fd_set(fd, fds) FD_SET(fd, fds)
# define UA_fd_isset(fd, fds) FD_ISSET(fd, fds)
#endif

#ifdef UA_ENABLE_MULTITHREADING
# include <urcu/uatomic.h>
#endif

#ifdef _WIN32
#define errno__ WSAGetLastError()
# define INTERRUPTED WSAEINTR
# define WOULDBLOCK WSAEWOULDBLOCK
# define AGAIN WSAEWOULDBLOCK
#else
# define errno__ errno
# define INTERRUPTED EINTR
# define WOULDBLOCK EWOULDBLOCK
# define AGAIN EAGAIN
#endif

/****************************/
/* Generic Socket Functions */
/****************************/

static void
socket_close(UA_Connection *connection) {
    connection->state = UA_CONNECTION_CLOSED;
    shutdown((SOCKET)connection->sockfd,2);
    CLOSESOCKET(connection->sockfd);
}

static UA_StatusCode
socket_write(UA_Connection *connection, UA_ByteString *buf) {
    size_t nWritten = 0;
    do {
        ssize_t n = 0;
        do {
        /* If the OS throws EMSGSIZE, force a smaller packet size:
         * size_t bytes_to_send = buf->length - nWritten >  1024 ? 1024 : buf->length - nWritten; */
            size_t bytes_to_send = buf->length - nWritten;
            n = send((SOCKET)connection->sockfd, (const char*)buf->data + nWritten,
                     WIN32_INT bytes_to_send, 0);
            if(n < 0 && errno__ != INTERRUPTED && errno__ != AGAIN) {
                connection->close(connection);
                socket_close(connection);
                UA_ByteString_deleteMembers(buf);
                return UA_STATUSCODE_BADCONNECTIONCLOSED;
            }
        } while(n < 0);
        nWritten += (size_t)n;
    } while(nWritten < buf->length);
    UA_ByteString_deleteMembers(buf);
    return UA_STATUSCODE_GOOD;
}

static UA_StatusCode
socket_recv(UA_Connection *connection, UA_ByteString *response, UA_UInt32 timeout) {
    response->data = malloc(connection->localConf.recvBufferSize);
    if(!response->data) {
        response->length = 0;
        return UA_STATUSCODE_BADOUTOFMEMORY; /* not enough memory retry */
    }

    if(timeout > 0) {
        /* currently, only the client uses timeouts */
#ifndef _WIN32
        UA_UInt32 timeout_usec = timeout * 1000;
# ifdef __APPLE__
        struct timeval tmptv = {(long int)(timeout_usec / 1000000), timeout_usec % 1000000};
# else
        struct timeval tmptv = {(long int)(timeout_usec / 1000000), (long int)(timeout_usec % 1000000)};
# endif
        int ret = setsockopt(connection->sockfd, SOL_SOCKET, SO_RCVTIMEO,
                             (const char *)&tmptv, sizeof(struct timeval));
#else
        DWORD timeout_dw = timeout;
        int ret = setsockopt(connection->sockfd, SOL_SOCKET, SO_RCVTIMEO,
                             (const char*)&timeout_dw, sizeof(DWORD));
#endif
        if(0 != ret) {
            UA_ByteString_deleteMembers(response);
            socket_close(connection);
            return UA_STATUSCODE_BADCONNECTIONCLOSED;
        }
    }

#ifdef __CYGWIN__
    /* Workaround for https://cygwin.com/ml/cygwin/2013-07/msg00107.html */
    ssize_t ret;
    if(timeout > 0) {
        fd_set fdset;
        FD_ZERO(&fdset);
        UA_fd_set(connection->sockfd, &fdset);
        UA_UInt32 timeout_usec = timeout * 1000;
        struct timeval tmptv = {(long int)(timeout_usec / 1000000),
                                (long int)(timeout_usec % 1000000)};
        int retval = select(connection->sockfd+1, &fdset, NULL, NULL, &tmptv);
        if(retval && UA_fd_isset(connection->sockfd, &fdset)) {
            ret = recv(connection->sockfd, (char*)response->data,
                       connection->localConf.recvBufferSize, 0);
        } else {
            ret = 0;
        }
    } else {
        ret = recv(connection->sockfd, (char*)response->data,
                   connection->localConf.recvBufferSize, 0);
    }
#else
    ssize_t ret = recv(connection->sockfd, (char*)response->data,
                       connection->localConf.recvBufferSize, 0);
#endif

    /* server has closed the connection */
    if(ret == 0) {
        UA_ByteString_deleteMembers(response);
        socket_close(connection);
        return UA_STATUSCODE_BADCONNECTIONCLOSED;
    }

    /* error case */
    if(ret < 0) {
        UA_ByteString_deleteMembers(response);
        if(errno__ == INTERRUPTED || (timeout > 0) ?
           false : (errno__ == EAGAIN || errno__ == WOULDBLOCK))
            return UA_STATUSCODE_GOOD; /* statuscode_good but no data -> retry */
        socket_close(connection);
        return UA_STATUSCODE_BADCONNECTIONCLOSED;
    }
    
    /* default case */
    response->length = (size_t)ret;
    return UA_STATUSCODE_GOOD;
}

static UA_StatusCode socket_set_nonblocking(SOCKET sockfd) {
#ifdef _WIN32
    u_long iMode = 1;
    if(ioctlsocket(sockfd, FIONBIO, &iMode) != NO_ERROR)
        return UA_STATUSCODE_BADINTERNALERROR;
#else
    int opts = fcntl(sockfd, F_GETFL);
    if(opts < 0 || fcntl(sockfd, F_SETFL, opts|O_NONBLOCK) < 0)
        return UA_STATUSCODE_BADINTERNALERROR;
#endif
    return UA_STATUSCODE_GOOD;
}

static void FreeConnectionCallback(UA_Server *server, void *ptr) {
    UA_Connection_deleteMembers((UA_Connection*)ptr);
    free(ptr);
 }

/***************************/
/* Server NetworkLayer TCP */
/***************************/

/**
 * For the multithreaded mode, assume a single thread that periodically "gets
 * work" from the network layer. In addition, several worker threads are
 * asynchronously calling into the callbacks of the UA_Connection that holds a
 * single connection.
 *
 * Creating a connection: When "GetJobs" encounters a new connection, it creates
 * a UA_Connection with the socket information. This is added to the mappings
 * array that links sockets to UA_Connection structs.
 *
 * Reading data: In "GetJobs", we listen on the sockets in the mappings array.
 * If data arrives (or the connection closes), a WorkItem is created that
 * carries the work and a pointer to the connection.
 *
 * Closing a connection: Closing can happen in two ways. Either it is triggered
 * by the server in an asynchronous callback. Or the connection is close by the
 * client and this is detected in "GetJobs". The server needs to do some
 * internal cleanups (close attached securechannels, etc.). So even when a
 * closed connection is detected in "GetJobs", we trigger the server to close
 * the connection (with a WorkItem) and continue from the callback.
 *
 * - Server calls close-callback: We close the socket, set the connection-state
 *   to closed and add the connection to a linked list from which it is deleted
 *   later. The connection cannot be freed right away since other threads might
 *   still be using it.
 *
 * - GetJobs: We remove the connection from the mappings array. In the
 *   non-multithreaded case, the connection is freed. For multithreading, we
 *   return a workitem that is delayed, i.e. that is called only after all
 *   workitems created before are finished in all threads. This workitems
 *   contains a callback that goes through the linked list of connections to be
 *   freed. */

#define MAXBACKLOG 100

typedef struct {
    UA_ConnectionConfig conf;
    UA_UInt16 port;
    UA_Logger logger; // Set during start

    /* open sockets and connections */
    UA_Int32 serversockfd;
    size_t mappingsSize;
    struct ConnectionMapping {
        UA_Connection *connection;
        UA_Int32 sockfd;
    } *mappings;
} ServerNetworkLayerTCP;

static UA_StatusCode
ServerNetworkLayerGetSendBuffer(UA_Connection *connection, size_t length, UA_ByteString *buf) {
    if(length > connection->remoteConf.recvBufferSize)
        return UA_STATUSCODE_BADCOMMUNICATIONERROR;
    return UA_ByteString_allocBuffer(buf, length);
}

static void
ServerNetworkLayerReleaseSendBuffer(UA_Connection *connection, UA_ByteString *buf) {
    UA_ByteString_deleteMembers(buf);
}

static void
ServerNetworkLayerReleaseRecvBuffer(UA_Connection *connection, UA_ByteString *buf) {
    UA_ByteString_deleteMembers(buf);
}

/* after every select, we need to reset the sockets we want to listen on */
static UA_Int32
setFDSet(ServerNetworkLayerTCP *layer, fd_set *fdset) {
    FD_ZERO(fdset);
    UA_fd_set(layer->serversockfd, fdset);
    UA_Int32 highestfd = layer->serversockfd;
    for(size_t i = 0; i < layer->mappingsSize; ++i) {
        UA_fd_set(layer->mappings[i].sockfd, fdset);
        if(layer->mappings[i].sockfd > highestfd)
            highestfd = layer->mappings[i].sockfd;
    }
    return highestfd;
}

/* callback triggered from the server */
static void
ServerNetworkLayerTCP_closeConnection(UA_Connection *connection) {
#ifdef UA_ENABLE_MULTITHREADING
    if(uatomic_xchg(&connection->state, UA_CONNECTION_CLOSED) == UA_CONNECTION_CLOSED)
        return;
#else
    if(connection->state == UA_CONNECTION_CLOSED)
        return;
    connection->state = UA_CONNECTION_CLOSED;
#endif
#if UA_LOGLEVEL <= 300
   //cppcheck-suppress unreadVariable
    ServerNetworkLayerTCP *layer = connection->handle;
    UA_LOG_INFO(layer->logger, UA_LOGCATEGORY_NETWORK,
                "Connection %i | Force closing the connection",
                connection->sockfd);
#endif
    /* only "shutdown" here. this triggers the select, where the socket is
       "closed" in the mainloop */
    shutdown(connection->sockfd, 2);
}

/* call only from the single networking thread */
static UA_StatusCode
ServerNetworkLayerTCP_add(ServerNetworkLayerTCP *layer, UA_Int32 newsockfd) {
    UA_Connection *c = malloc(sizeof(UA_Connection));
    if(!c)
        return UA_STATUSCODE_BADINTERNALERROR;

    struct sockaddr_in addr;
    socklen_t addrlen = sizeof(struct sockaddr_in);
    int res = getpeername(newsockfd, (struct sockaddr*)&addr, &addrlen);
    
    if(res == 0) {
        UA_LOG_INFO(layer->logger, UA_LOGCATEGORY_NETWORK,
                    "Connection %i | New connection over TCP from %s:%d",
                    newsockfd, inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
    } else {
        UA_LOG_WARNING(layer->logger, UA_LOGCATEGORY_NETWORK,
                       "Connection %i | New connection over TCP, "
                       "getpeername failed with errno %i", newsockfd, errno);
    }

    memset(c, 0, sizeof(UA_Connection));
    c->sockfd = newsockfd;
    c->handle = layer;
    c->localConf = layer->conf;
    c->remoteConf = layer->conf;
    c->send = socket_write;
    c->close = ServerNetworkLayerTCP_closeConnection;
    c->getSendBuffer = ServerNetworkLayerGetSendBuffer;
    c->releaseSendBuffer = ServerNetworkLayerReleaseSendBuffer;
    c->releaseRecvBuffer = ServerNetworkLayerReleaseRecvBuffer;
    c->state = UA_CONNECTION_OPENING;
    struct ConnectionMapping *nm;
    nm = realloc(layer->mappings,
                 sizeof(struct ConnectionMapping)*(layer->mappingsSize+1));
    if(!nm) {
        UA_LOG_ERROR(layer->logger, UA_LOGCATEGORY_NETWORK,
                     "No memory for a new Connection");
        free(c);
        return UA_STATUSCODE_BADINTERNALERROR;
    }
    layer->mappings = nm;
    layer->mappings[layer->mappingsSize].connection = c;
    layer->mappings[layer->mappingsSize].sockfd = newsockfd;
    ++layer->mappingsSize;
    return UA_STATUSCODE_GOOD;
}

static UA_StatusCode
ServerNetworkLayerTCP_start(UA_ServerNetworkLayer *nl, UA_Logger logger) {
    ServerNetworkLayerTCP *layer = nl->handle;
    layer->logger = logger;

    /* get the discovery url from the hostname */
    UA_String du = UA_STRING_NULL;
    char hostname[256];
    if(gethostname(hostname, 255) == 0) {
        char discoveryUrl[256];
#ifndef _MSC_VER
        du.length = (size_t)snprintf(discoveryUrl, 255, "opc.tcp://%s:%d",
                                     hostname, layer->port);
#else
        du.length = (size_t)_snprintf_s(discoveryUrl, 255, _TRUNCATE,
                                        "opc.tcp://%s:%d", hostname, layer->port);
#endif
        du.data = (UA_Byte*)discoveryUrl;
    }
    UA_String_copy(&du, &nl->discoveryUrl);

    /* Create the server socket */
    SOCKET newsock = socket(PF_INET, SOCK_STREAM, 0);
#ifdef _WIN32
    if(newsock == INVALID_SOCKET)
#else
    if(newsock < 0)
#endif
    {
        UA_LOG_WARNING(layer->logger, UA_LOGCATEGORY_NETWORK,
                       "Error opening the server socket");
        return UA_STATUSCODE_BADINTERNALERROR;
    }

    /* Set socket options */
    int optval = 1;
    if(setsockopt(newsock, SOL_SOCKET, SO_REUSEADDR,
                  (const char *)&optval, sizeof(optval)) == -1 ||
       socket_set_nonblocking(newsock) != UA_STATUSCODE_GOOD) {
        UA_LOG_WARNING(layer->logger, UA_LOGCATEGORY_NETWORK,
                       "Error during setting of server socket options");
        CLOSESOCKET(newsock);
        return UA_STATUSCODE_BADINTERNALERROR;
    }

    /* Bind socket to address */
    const struct sockaddr_in serv_addr = {
        .sin_family = AF_INET, .sin_addr.s_addr = INADDR_ANY,
        .sin_port = htons(layer->port), .sin_zero = {0}};
    if(bind(newsock, (const struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        UA_LOG_WARNING(layer->logger, UA_LOGCATEGORY_NETWORK,
                       "Error during binding of the server socket");
        CLOSESOCKET(newsock);
        return UA_STATUSCODE_BADINTERNALERROR;
    }

    /* Start listening */
    if(listen(newsock, MAXBACKLOG) < 0) {
        UA_LOG_WARNING(layer->logger, UA_LOGCATEGORY_NETWORK,
                       "Error listening on server socket");
        CLOSESOCKET(newsock);
        return UA_STATUSCODE_BADINTERNALERROR;
    }

    layer->serversockfd = (UA_Int32)newsock; /* cast on win32 */
    UA_LOG_INFO(layer->logger, UA_LOGCATEGORY_NETWORK,
                "TCP network layer listening on %.*s",
                nl->discoveryUrl.length, nl->discoveryUrl.data);
    return UA_STATUSCODE_GOOD;
}

static size_t
removeClosedConnections(ServerNetworkLayerTCP *layer, UA_Job *js) {
    size_t c = 0;
    for(size_t i = 0; i < layer->mappingsSize; ++i) {
        if(layer->mappings[i].connection &&
           layer->mappings[i].connection->state != UA_CONNECTION_CLOSED)
            continue;
        /* the socket was closed from remote */
        UA_Connection *conn = layer->mappings[i].connection;
        js[c].type = UA_JOBTYPE_DETACHCONNECTION;
        js[c].job.closeConnection = conn;
        layer->mappings[i] = layer->mappings[layer->mappingsSize-1];
        --layer->mappingsSize;
        ++c;
        js[c].type = UA_JOBTYPE_METHODCALL_DELAYED;
        js[c].job.methodCall.method = FreeConnectionCallback;
        js[c].job.methodCall.data = conn;
        ++c;
    }
    return c;
}

static size_t
ServerNetworkLayerTCP_getJobs(UA_ServerNetworkLayer *nl, UA_Job **jobs,
                              UA_UInt16 timeout) {
    /* Every open socket can generate two jobs */
    ServerNetworkLayerTCP *layer = nl->handle;
    UA_Job *js = malloc(sizeof(UA_Job) * (size_t)((layer->mappingsSize * 2)));
    if(!js)
        return UA_STATUSCODE_BADOUTOFMEMORY;

    /* Remove closed sockets */
    size_t totalJobs = removeClosedConnections(layer, js);

    /* Listen on open sockets (including the server) */
    fd_set fdset, errset;
    UA_Int32 highestfd = setFDSet(layer, &fdset);
    setFDSet(layer, &errset);
    struct timeval tmptv = {0, timeout * 1000};
    UA_Int32 resultsize = select(highestfd+1, &fdset, NULL, &errset, &tmptv);
    if(totalJobs == 0 && resultsize <= 0) {
        free(js);
        *jobs = NULL;
        return 0;
    }

    /* Accept new connection via the server socket (can only be a single one) */
    if(UA_fd_isset(layer->serversockfd, &fdset)) {
        --resultsize;
        SOCKET newsockfd = accept((SOCKET)layer->serversockfd, NULL, NULL);
#ifdef _WIN32
        if(newsockfd != INVALID_SOCKET)
#else
        if(newsockfd >= 0)
#endif
        {
            socket_set_nonblocking(newsockfd);
            /* Do not merge packets on the socket (disable Nagle's algorithm) */
            int i = 1;
            setsockopt(newsockfd, IPPROTO_TCP, TCP_NODELAY, (void *)&i, sizeof(i));
            ServerNetworkLayerTCP_add(layer, (UA_Int32)newsockfd);
        }
    }

    /* Read from established sockets */
    UA_ByteString buf = UA_BYTESTRING_NULL;
    size_t j = 0;
    for(size_t i = 0; i < layer->mappingsSize && j < (size_t)resultsize; ++i) {
        if(!UA_fd_isset(layer->mappings[i].sockfd, &errset) &&
           !UA_fd_isset(layer->mappings[i].sockfd, &fdset))
          continue;

        UA_StatusCode retval = socket_recv(layer->mappings[i].connection, &buf, 0);
        if(retval == UA_STATUSCODE_GOOD) {
            js[totalJobs + j].job.binaryMessage.connection = layer->mappings[i].connection;
            js[totalJobs + j].job.binaryMessage.message = buf;
            js[totalJobs + j].type = UA_JOBTYPE_BINARYMESSAGE_NETWORKLAYER;
            ++j;
        } else if (retval == UA_STATUSCODE_BADCONNECTIONCLOSED) {
            UA_Connection *c = layer->mappings[i].connection;
            UA_LOG_INFO(layer->logger, UA_LOGCATEGORY_NETWORK,
                        "Connection %i | Connection closed from remote", c->sockfd);
            /* the socket was closed from remote */
            js[totalJobs + j].type = UA_JOBTYPE_DETACHCONNECTION;
            js[totalJobs + j].job.closeConnection = c;
            layer->mappings[i] = layer->mappings[layer->mappingsSize-1];
            --layer->mappingsSize;
            ++totalJobs; /* increase j only once */
            js[totalJobs + j].type = UA_JOBTYPE_METHODCALL_DELAYED;
            js[totalJobs + j].job.methodCall.method = FreeConnectionCallback;
            js[totalJobs + j].job.methodCall.data = c;
            ++j;
        }
    }
    totalJobs += j;

    if(totalJobs == 0) {
        free(js);
        js = NULL;
    }
    *jobs = js;
    return totalJobs;
}

static size_t
ServerNetworkLayerTCP_stop(UA_ServerNetworkLayer *nl, UA_Job **jobs) {
    ServerNetworkLayerTCP *layer = nl->handle;
    UA_LOG_INFO(layer->logger, UA_LOGCATEGORY_NETWORK,
                "Shutting down the TCP network layer with %d open connection(s)",
                layer->mappingsSize);
    shutdown((SOCKET)layer->serversockfd,2);
    CLOSESOCKET(layer->serversockfd);
    UA_Job *items = malloc(sizeof(UA_Job) * layer->mappingsSize * 2);
    if(!items)
        return 0;
    for(size_t i = 0; i < layer->mappingsSize; ++i) {
        socket_close(layer->mappings[i].connection);
        items[i*2].type = UA_JOBTYPE_DETACHCONNECTION;
        items[i*2].job.closeConnection = layer->mappings[i].connection;
        items[(i*2)+1].type = UA_JOBTYPE_METHODCALL_DELAYED;
        items[(i*2)+1].job.methodCall.method = FreeConnectionCallback;
        items[(i*2)+1].job.methodCall.data = layer->mappings[i].connection;
    }
#ifdef _WIN32
    WSACleanup();
#endif
    *jobs = items;
    return layer->mappingsSize*2;
}

/* run only when the server is stopped */
static void ServerNetworkLayerTCP_deleteMembers(UA_ServerNetworkLayer *nl) {
    ServerNetworkLayerTCP *layer = nl->handle;
    free(layer->mappings);
    free(layer);
    UA_String_deleteMembers(&nl->discoveryUrl);
}

UA_ServerNetworkLayer
UA_ServerNetworkLayerTCP(UA_ConnectionConfig conf, UA_UInt16 port) {
#ifdef _WIN32
    WORD wVersionRequested;
    WSADATA wsaData;
    wVersionRequested = MAKEWORD(2, 2);
    WSAStartup(wVersionRequested, &wsaData);
#endif

    UA_ServerNetworkLayer nl;
    memset(&nl, 0, sizeof(UA_ServerNetworkLayer));
    ServerNetworkLayerTCP *layer = calloc(1,sizeof(ServerNetworkLayerTCP));
    if(!layer)
        return nl;
    
    layer->conf = conf;
    layer->port = port;

    nl.handle = layer;
    nl.start = ServerNetworkLayerTCP_start;
    nl.getJobs = ServerNetworkLayerTCP_getJobs;
    nl.stop = ServerNetworkLayerTCP_stop;
    nl.deleteMembers = ServerNetworkLayerTCP_deleteMembers;
    return nl;
}

/***************************/
/* Client NetworkLayer TCP */
/***************************/

static UA_StatusCode
ClientNetworkLayerGetBuffer(UA_Connection *connection, size_t length,
                            UA_ByteString *buf) {
    if(length > connection->remoteConf.recvBufferSize)
        return UA_STATUSCODE_BADCOMMUNICATIONERROR;
    if(connection->state == UA_CONNECTION_CLOSED)
        return UA_STATUSCODE_BADCONNECTIONCLOSED;
    return UA_ByteString_allocBuffer(buf, connection->remoteConf.recvBufferSize);
}

static void
ClientNetworkLayerReleaseBuffer(UA_Connection *connection, UA_ByteString *buf) {
    UA_ByteString_deleteMembers(buf);
}

static void
ClientNetworkLayerClose(UA_Connection *connection) {
#ifdef UA_ENABLE_MULTITHREADING
    if(uatomic_xchg(&connection->state, UA_CONNECTION_CLOSED) == UA_CONNECTION_CLOSED)
        return;
#else
    if(connection->state == UA_CONNECTION_CLOSED)
        return;
    connection->state = UA_CONNECTION_CLOSED;
#endif
    socket_close(connection);
}

/* we have no networklayer. instead, attach the reusable buffer to the handle */
UA_Connection
UA_ClientConnectionTCP(UA_ConnectionConfig conf, const char *endpointUrl,
                       UA_Logger logger) {
#ifdef _WIN32
    WORD wVersionRequested;
    WSADATA wsaData;
    wVersionRequested = MAKEWORD(2, 2);
    WSAStartup(wVersionRequested, &wsaData);
#endif

    UA_Connection connection;
    memset(&connection, 0, sizeof(UA_Connection));
    connection.state = UA_CONNECTION_OPENING;
    connection.localConf = conf;
    connection.remoteConf = conf;
    connection.send = socket_write;
    connection.recv = socket_recv;
    connection.close = ClientNetworkLayerClose;
    connection.getSendBuffer = ClientNetworkLayerGetBuffer;
    connection.releaseSendBuffer = ClientNetworkLayerReleaseBuffer;
    connection.releaseRecvBuffer = ClientNetworkLayerReleaseBuffer;

    char hostname[512];
    UA_UInt16 port = 0;
    const char *path = NULL;

    UA_StatusCode parse_retval = UA_EndpointUrl_split(endpointUrl, hostname, &port, &path);
    if(parse_retval != UA_STATUSCODE_GOOD) {
        if(parse_retval == UA_STATUSCODE_BADOUTOFRANGE)
            UA_LOG_WARNING(logger, UA_LOGCATEGORY_NETWORK,
                           "Server url is invalid: %s", endpointUrl);
        else if(parse_retval == UA_STATUSCODE_BADATTRIBUTEIDINVALID)
            UA_LOG_WARNING(logger, UA_LOGCATEGORY_NETWORK,
                           "Server url does not begin with 'opc.tcp://'  '%s'",
                           endpointUrl);
        return connection;
    }

    if(port == 0) {
        port = 4840;
        UA_LOG_INFO(logger, UA_LOGCATEGORY_NETWORK,
                    "No port defined, using standard port %d", port);
    }

    struct addrinfo hints, *server;
    memset(&hints, 0, sizeof(hints));
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_family = AF_INET;
    char portStr[6];
#ifndef _MSC_VER
    snprintf(portStr, 6, "%d", port);
#else
    _snprintf_s(portStr, 6, _TRUNCATE, "%d", port);
#endif
    int error = getaddrinfo(hostname, portStr, &hints, &server);
    if(error != 0 || !server) {
        UA_LOG_WARNING(logger, UA_LOGCATEGORY_NETWORK,
                       "DNS lookup of %s failed with error %s",
                       hostname, gai_strerror(error));
        return connection;
    }

    /* Get a socket */
    SOCKET clientsockfd = socket(server->ai_family, server->ai_socktype,
                                 server->ai_protocol);
#ifdef _WIN32
    if(clientsockfd == INVALID_SOCKET) {
#else
    if(clientsockfd < 0) {
#endif
        UA_LOG_WARNING(logger, UA_LOGCATEGORY_NETWORK,
                       "Could not create client socket");
        freeaddrinfo(server);
        return connection;
    }

    /* Connect to the server */
    connection.sockfd = (UA_Int32)clientsockfd; /* cast for win32 */
    error = connect(clientsockfd, server->ai_addr, WIN32_INT server->ai_addrlen);
    freeaddrinfo(server);
    if(error < 0) {
        ClientNetworkLayerClose(&connection);
#ifdef _WIN32
        wchar_t *s = NULL;
        FormatMessageW(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                       FORMAT_MESSAGE_FROM_SYSTEM |
                       FORMAT_MESSAGE_IGNORE_INSERTS,
                       NULL, WSAGetLastError(),
                       MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                       (LPWSTR)&s, 0, NULL);
        UA_LOG_WARNING(logger, UA_LOGCATEGORY_NETWORK,
                       "Connection to %s failed. Error: %d: %S",
                       endpointUrl, WSAGetLastError(), s);
        LocalFree(s);
#else
        UA_LOG_WARNING(logger, UA_LOGCATEGORY_NETWORK,
                       "Connection to %s failed. Error: %d: %s",
                       endpointUrl, errno, strerror(errno));
#endif
        return connection;
    }

#ifdef SO_NOSIGPIPE
    int val = 1;
    int sso_result = setsockopt(connection.sockfd,
                                SOL_SOCKET, SO_NOSIGPIPE,
                                (void*)&val, sizeof(val));
    if(sso_result < 0)
        UA_LOG_WARNING(logger, UA_LOGCATEGORY_NETWORK,
                       "Couldn't set SO_NOSIGPIPE");
#endif

    return connection;
}