tcpserver.cc

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/* Copyright 1999,2000,2001 BrightStation PLC
 * Copyright 2002 Ananova Ltd
 * Copyright 2002,2003,2004,2005,2006,2007,2008,2009,2010,2011,2012,2015,2017,2018 Olly Betts
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
 * USA
 */

#include <config.h>

#include "tcpserver.h"

#include <xapian/error.h>

#include "safefcntl.h"
#include "safenetdb.h"
#include "safesysexits.h"
#include "safesyssocket.h"

#include "noreturn.h"
#include "remoteconnection.h"
#include "resolver.h"
#include "str.h"

#ifdef __WIN32__
# include <process.h>    /* _beginthreadex, _endthreadex */
#else
# include <netinet/in_systm.h>
# include <netinet/in.h>
# include <netinet/ip.h>
# include <netinet/tcp.h>
# include <arpa/inet.h>
# include <signal.h>
# include <sys/wait.h>
#endif

#include <iostream>

#include <cerrno>
#include <cstring>
#include <cstdlib>
#include <sys/types.h>

using namespace std;

// Handle older systems.
#if !defined SIGCHLD && defined SIGCLD
# define SIGCHLD SIGCLD
#endif

#ifdef __WIN32__
// We must call closesocket() (instead of just close()) under __WIN32__ or
// else the socket remains in the CLOSE_WAIT state.
# define CLOSESOCKET(S) closesocket(S)
#else
# define CLOSESOCKET(S) close(S)
#endif

TcpServer::TcpServer(const std::string & host, int port, bool tcp_nodelay,
                     bool verbose_)
    : listen_socket(get_listening_socket(host, port, tcp_nodelay
#if defined __CYGWIN__ || defined __WIN32__
                                         , mutex
#endif
                                         )),
      verbose(verbose_)
{
}

int
TcpServer::get_listening_socket(const std::string & host, int port,
                                bool tcp_nodelay
#if defined __CYGWIN__ || defined __WIN32__
                                , HANDLE &mutex
#endif
                                )
{
    int socketfd = -1;
    int bind_errno = 0;
    for (auto&& r : Resolver(host, port, AI_PASSIVE)) {
        int socktype = r.ai_socktype | SOCK_CLOEXEC;
        int fd = socket(r.ai_family, socktype, r.ai_protocol);
        if (fd == -1)
            continue;

#if !defined __WIN32__ && defined F_SETFD && defined FD_CLOEXEC
        // We can't use a preprocessor check on the *value* of SOCK_CLOEXEC as on
        // Linux SOCK_CLOEXEC is an enum, with '#define SOCK_CLOEXEC SOCK_CLOEXEC'
        // to allow '#ifdef SOCK_CLOEXEC' to work.
        if (SOCK_CLOEXEC == 0)
            (void)fcntl(fd, F_SETFD, FD_CLOEXEC);
#endif

        int retval = 0;

        if (tcp_nodelay) {
            int optval = 1;
            // 4th argument might need to be void* or char* - cast it to char*
            // since C++ allows implicit conversion to void* but not from
            // void*.
            retval = setsockopt(fd, IPPROTO_TCP, TCP_NODELAY,
                                reinterpret_cast<char *>(&optval),
                                sizeof(optval));
        }

        int optval = 1;
#if defined __CYGWIN__ || defined __WIN32__
        // Windows has screwy semantics for SO_REUSEADDR - it allows the user
        // to bind to a port which is already bound and listening!  That's
        // just not suitable as we don't want multiple processes listening on
        // the same port, so we guard against that by using a named win32 mutex
        // object (and we create it in the 'Global namespace' so that this
        // still works in a Terminal Services environment).
        string name = "Global\\xapian-tcpserver-listening-" + str(port);
        if ((mutex = CreateMutex(NULL, TRUE, name.c_str())) == NULL) {
            // We failed to create the mutex, probably the error is
            // ERROR_ACCESS_DENIED, which simply means that TcpServer is
            // already running on this port but as a different user.
        } else if (GetLastError() == ERROR_ALREADY_EXISTS) {
            // The mutex already existed, so TcpServer is already running
            // on this port.
            CloseHandle(mutex);
            mutex = NULL;
        }
        if (mutex == NULL) {
            cerr << "Server is already running on port " << port << endl;
            // 69 is EX_UNAVAILABLE.  Scripts can use this to detect if the
            // server failed to bind to the requested port.
            exit(69); // FIXME: calling exit() here isn't ideal...
        }
#endif
        if (retval >= 0) {
            retval = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
                                reinterpret_cast<char *>(&optval),
                                sizeof(optval));
        }

        if (retval < 0) {
            int saved_errno = socket_errno(); // note down in case close hits an error
            CLOSESOCKET(fd);
            throw Xapian::NetworkError("setsockopt failed", saved_errno);
        }

        if (::bind(fd, r.ai_addr, r.ai_addrlen) == 0) {
            socketfd = fd;
            break;
        }

        // Note down the error code for the first address we try, which seems
        // likely to be more helpful than the last in the case where they
        // differ.
        if (bind_errno == 0)
            bind_errno = socket_errno();

        CLOSESOCKET(fd);
    }

    if (socketfd == -1) {
        if (bind_errno == EADDRINUSE) {
            cerr << host << ':' << port << " already in use" << endl;
            // EX_UNAVAILABLE is 69.  Scripts can use this to detect that the
            // requested port was already in use.
            exit(EX_UNAVAILABLE);
        }
        if (bind_errno == EACCES) {
            cerr << "Can't bind to privileged port " << port << endl;
            // EX_NOPERM is 77.  Scripts can use this to detect if
            // xapian-tcpsrv failed to bind to the requested port.
            exit(EX_NOPERM);
        }
        throw Xapian::NetworkError("bind failed", bind_errno);
    }

    if (listen(socketfd, 5) < 0) {
        int saved_errno = socket_errno(); // note down in case close hits an error
        CLOSESOCKET(socketfd);
        throw Xapian::NetworkError("listen failed", saved_errno);
    }
    return socketfd;
}

int
TcpServer::accept_connection()
{
    struct sockaddr_in remote_address;
    SOCKLEN_T remote_address_size = sizeof(remote_address);
    // accept connections
    int con_socket = accept(listen_socket,
                            reinterpret_cast<sockaddr *>(&remote_address),
                            &remote_address_size);

    if (con_socket < 0) {
#ifdef __WIN32__
        if (WSAGetLastError() == WSAEINTR) {
            // Our CtrlHandler function closed the socket.
            if (mutex) CloseHandle(mutex);
            mutex = NULL;
            return -1;
        }
#endif
        throw Xapian::NetworkError("accept failed", socket_errno());
    }

    if (remote_address_size != sizeof(remote_address)) {
        throw Xapian::NetworkError("accept: unexpected remote address size");
    }

    if (verbose) {
        char buf[INET_ADDRSTRLEN];
#ifndef __WIN32__
        // Under __WIN32__, inet_ntop()'s second parameter isn't const for some
        // reason.  We don't currently use inet_ntop() there, but allow for a
        // non-const second parameter in case it's more widespread.
        void * src = &remote_address.sin_addr;
        const char * r = inet_ntop(AF_INET, src, buf, sizeof(buf));
        if (!r)
            throw Xapian::NetworkError("inet_ntop failed", errno);
#else
        // inet_ntop() isn't always available, at least with mingw.
        // WSAAddressToString() supports both IPv4 and IPv6, so just use that.
        DWORD size = sizeof(buf);
        if (WSAAddressToString(reinterpret_cast<sockaddr*>(&remote_address),
                               sizeof(remote_address), NULL, buf, &size) != 0) {
            throw Xapian::NetworkError("WSAAddressToString failed",
                                       WSAGetLastError());
        }
        const char * r = buf;
#endif
        int port = remote_address.sin_port;
        cout << "Connection from " << r << ", port " << port << endl;
    }

    return con_socket;
}

TcpServer::~TcpServer()
{
    CLOSESOCKET(listen_socket);
#if defined __CYGWIN__ || defined __WIN32__
    if (mutex) CloseHandle(mutex);
#endif
}

#ifdef HAVE_FORK
// A fork() based implementation.

extern "C" {

XAPIAN_NORETURN(static void on_SIGTERM(int /*sig*/));

static void
on_SIGTERM(int /*sig*/)
{
    signal(SIGTERM, SIG_DFL);
    /* terminate all processes in my process group */
#ifdef HAVE_KILLPG
    killpg(0, SIGTERM);
#else
    kill(0, SIGTERM);
#endif
    exit(0);
}

#ifdef HAVE_WAITPID
static void
on_SIGCHLD(int /*sig*/)
{
    int status;
    while (waitpid(-1, &status, WNOHANG) > 0);
}
#endif

}

void
TcpServer::run()
{
    // Handle connections until shutdown.

    // Set up signal handlers.
#ifdef HAVE_WAITPID
    signal(SIGCHLD, on_SIGCHLD);
#else
    signal(SIGCHLD, SIG_IGN);
#endif
    signal(SIGTERM, on_SIGTERM);

    while (true) {
        try {
            int connected_socket = accept_connection();
            pid_t pid = fork();
            if (pid == 0) {
                // Child process.
                close(listen_socket);

                handle_one_connection(connected_socket);
                close(connected_socket);

                if (verbose) cout << "Connection closed." << endl;
                _exit(0);
            }

            // Parent process.

            if (pid < 0) {
                // fork() failed.

                // Note down errno from fork() in case close() hits an error.
                int saved_errno = socket_errno();
                close(connected_socket);
                throw Xapian::NetworkError("fork failed", saved_errno);
            }

            close(connected_socket);
        } catch (const Xapian::Error &e) {
            // FIXME: better error handling.
            cerr << "Caught " << e.get_description() << endl;
        } catch (...) {
            // FIXME: better error handling.
            cerr << "Caught exception." << endl;
        }
    }
}

#elif defined __WIN32__

// A threaded, Windows specific, implementation.

static const int *pShutdownSocket = NULL;

static BOOL
CtrlHandler(DWORD fdwCtrlType)
{
    switch (fdwCtrlType) {
        case CTRL_C_EVENT:
        case CTRL_CLOSE_EVENT:
            //  Console is about to die.
            // CTRL_CLOSE_EVENT gives us 5 seconds before displaying a
            // confirmation dialog asking if we really are sure.
        case CTRL_LOGOFF_EVENT:
        case CTRL_SHUTDOWN_EVENT:
            // These 2 will probably need to change when we get service
            // support - the service will prevent these being seen, so only
            // apply interactively.
            cout << "Shutting down..." << endl;
            break; // default behaviour
        case CTRL_BREAK_EVENT:
            // This (probably) means the developer is struggling to get
            // things to behave, and really wants to shutdown so let the OS
            // handle Ctrl+Break in the default way.
            cout << "Ctrl+Break: aborting process" << endl;
            return FALSE;
        default:
            cerr << "unexpected CtrlHandler: " << fdwCtrlType << endl;
            return FALSE;
    }

    // Note: close() does not cause a blocking accept() call to terminate.
    // However, it appears closesocket() does.  This is much easier than trying
    // to setup a non-blocking accept().
    if (!pShutdownSocket || closesocket(*pShutdownSocket) == SOCKET_ERROR) {
        // We failed to close the socket, so just let the OS handle the
        // event in the default way.
        return FALSE;
    }

    pShutdownSocket = NULL;
    return TRUE; // Tell the OS that we've handled the event.
}

struct thread_param
{
    thread_param(TcpServer *s, int c) : server(s), connected_socket(c) {}
    TcpServer *server;
    int connected_socket;
};

static unsigned __stdcall
run_thread(void * param_)
{
    thread_param * param(reinterpret_cast<thread_param *>(param_));
    int socket = param->connected_socket;

    param->server->handle_one_connection(socket);
    closesocket(socket);

    delete param;

    _endthreadex(0);
    return 0;
}

void
TcpServer::run()
{
    // Handle connections until shutdown.

    // Set up the shutdown handler - this is a bit hacky, and sadly involves
    // a global variable.
    pShutdownSocket = &listen_socket;
    if (!::SetConsoleCtrlHandler((PHANDLER_ROUTINE) CtrlHandler, TRUE))
        throw Xapian::NetworkError("Failed to install shutdown handler");

    while (true) {
        try {
            int connected_socket = accept_connection();
            if (connected_socket == -1)
               return; // Shutdown has happened

            // Spawn a new thread to handle the connection.
            // (This seems like lots of hoops just to end up calling
            // this->handle_one_connection() on a new thread. There might be a
            // better way...)
            thread_param *param = new thread_param(this, connected_socket);
            HANDLE hthread = (HANDLE)_beginthreadex(NULL, 0, ::run_thread, param, 0, NULL);
            if (hthread == 0) {
                // errno holds the error code from _beginthreadex, and
                // closesocket() doesn't set errno.
                closesocket(connected_socket);
                throw Xapian::NetworkError("_beginthreadex failed", errno);
            }

            // FIXME: keep track of open thread handles so we can gracefully
            // close each thread down.  OTOH, when we want to kill them all its
            // likely to mean the process is on its way down, so it doesn't
            // really matter...
            CloseHandle(hthread);
        } catch (const Xapian::Error &e) {
            // FIXME: better error handling.
            cerr << "Caught " << e.get_description() << endl;
        } catch (...) {
            // FIXME: better error handling.
            cerr << "Caught exception." << endl;
        }
    }
}

#else
# error Neither HAVE_FORK nor __WIN32__ are defined.
#endif

void
TcpServer::run_once()
{
    // Run a single request in the current process/thread.
    int fd = accept_connection();
    handle_one_connection(fd);
    CLOSESOCKET(fd);
}