libreoffice-online/net/socket.hpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

#include "config.h"

#include <poll.h>
#include <unistd.h>

#include <atomic>
#include <cerrno>
#include <cstdlib>
#include <cstring>
#include <sstream>

#include <Poco/Net/SocketAddress.h>

#include "ssl.hpp"

/// A non-blocking, streaming socket.
class Socket
{
public:
    Socket() :
        _fd(socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK, 0))
    {
        setNoDelay();
    }

    virtual ~Socket()
    {
        //TODO: Should we shutdown here or up to the client?

        // Doesn't block on sockets; no error handling needed.
        close(_fd);
    }

    // Returns the OS native socket fd.
    int getFD() const { return _fd; }

    /// Return a mask of events we should be polling for
    virtual int getPollEvents() = 0;

    /// Handle results of events returned from poll
    enum class HandleResult { CONTINUE, SOCKET_CLOSED };
    virtual HandleResult handlePoll( int events ) = 0;

    /// manage latency issues around packet aggregation
    void setNoDelay(bool noDelay = true)
    {
        int val = noDelay ? 1 : 0;
        setsockopt (_fd, IPPROTO_TCP, TCP_NODELAY,
                    (char *) &val, sizeof(val));
    }

    /// Sets the send buffer in size bytes.
    /// Must be called before accept or connect.
    /// Note: TCP will allocate twice this size for admin purposes,
    /// so a subsequent call to getSendBufferSize will return
    /// the larger (actual) buffer size, if this succeeds.
    /// Note: the upper limit is set via /proc/sys/net/core/wmem_max,
    /// and there is an unconfigurable lower limit as well.
    /// Returns true on success only.
    bool setSendBufferSize(const int size)
    {
        constexpr unsigned int len = sizeof(size);
        const int rc = ::setsockopt(_fd, SOL_SOCKET, SO_SNDBUF, &size, len);
        return (rc == 0);
    }

    /// Gets the actual send buffer size in bytes, -1 for failure.
    int getSendBufferSize() const
    {
        int size;
        unsigned int len = sizeof(size);
        const int rc = ::getsockopt(_fd, SOL_SOCKET, SO_SNDBUF, &size, &len);
        return (rc == 0 ? size : -1);
    }

    /// Sets the receive buffer size in bytes.
    /// Must be called before accept or connect.
    /// Note: TCP will allocate twice this size for admin purposes,
    /// so a subsequent call to getSendBufferSize will return
    /// the larger (actual) buffer size, if this succeeds.
    /// Note: the upper limit is set via /proc/sys/net/core/rmem_max,
    /// and there is an unconfigurable lower limit as well.
    /// Returns true on success only.
    bool setReceiveBufferSize(const int size)
    {
        constexpr unsigned int len = sizeof(size);
        const int rc = ::setsockopt(_fd, SOL_SOCKET, SO_RCVBUF, &size, len);
        return (rc == 0);
    }

    /// Gets the actual receive buffer size in bytes, -1 on error.
    int getReceiveBufferSize() const
    {
        int size;
        unsigned int len = sizeof(size);
        const int rc = ::getsockopt(_fd, SOL_SOCKET, SO_RCVBUF, &size, &len);
        return (rc == 0 ? size : -1);
    }

    /// Gets the error code.
    /// Sets errno on success and returns it.
    /// Returns -1 on failure to get the error code.
    int getError() const
    {
        int error;
        unsigned int len = sizeof(error);
        const int rc = ::getsockopt(_fd, SOL_SOCKET, SO_ERROR, &error, &len);
        if (rc == 0)
        {
            // Set errno so client can use strerror etc.
            errno = error;
            return error;
        }

        return rc;
    }

protected:

    /// Construct based on an existing socket fd.
    /// Used by accept() only.
    Socket(const int fd) :
        _fd(fd)
    {
        setNoDelay();
    }

private:
    const int _fd;
};


/// Handles non-blocking socket event polling.
/// Only polls on N-Sockets and invokes callback and
/// doesn't manage buffers or client data.
/// Note: uses poll(2) since it has very good performance
/// compared to epoll up to a few hundred sockets and
/// doesn't suffer select(2)'s poor API. Since this will
/// be used per-document we don't expect to have several
/// hundred users on same document to suffer poll(2)'s
/// scalability limit. Meanwhile, epoll(2)'s high
/// overhead to adding/removing sockets is not helpful.
class SocketPoll
{
public:
    SocketPoll()
    {
        // Create the wakeup fd.
        if (::pipe2(_wakeup, O_CLOEXEC | O_NONBLOCK) == -1)
        {
            // FIXME: Can't have wakeup pipe, should we exit?
            // FIXME: running out of sockets should be a case we handle elegantly here - and also in our accept / ClientSocket creation I guess.
            _wakeup[0] = -1;
            _wakeup[1] = -1;
        }
    }

    ~SocketPoll()
    {
        ::close(_wakeup[0]);
        ::close(_wakeup[1]);
    }

    /// Poll the sockets for available data to read or buffer to write.
    void poll(const int timeoutMs)
    {
        const size_t size = _pollSockets.size();

        // The events to poll on change each spin of the loop.
        setupPollFds();

        int rc;
        do
        {
            rc = ::poll(&_pollFds[0], size + 1, timeoutMs);
        }
        while (rc < 0 && errno == EINTR);

        // Fire the callback and remove dead fds.
        for (int i = static_cast<int>(size) - 1; i >= 0; --i)
        {
            if (_pollFds[i].revents)
            {
                if (_pollSockets[i]->handlePoll(_pollFds[i].revents) ==
                    Socket::HandleResult::SOCKET_CLOSED)
                {
                    std::cout << "Removing client #" << _pollFds[i].fd << std::endl;
                    _pollSockets.erase(_pollSockets.begin() + i);
                    // Don't remove from pollFds; we'll recreate below.
                }
            }
        }

        // Process the wakeup pipe (always the last entry).
        if (_pollFds[size].revents)
        {
            // Add new sockets first.
            addNewSocketsToPoll();

            // Clear the data.
            int dump;
            while (::read(_wakeup[0], &dump, sizeof(dump)) == -1 && errno == EINTR)
            {
                // Nothing to do.
            }
        }
    }

    /// Insert a new socket to be polled.
    /// Sockets are removed only when the handler return false.
    void insertNewSocket(const std::shared_ptr<Socket>& newSocket)
    {
        std::lock_guard<std::mutex> lock(_mutex);

        _newSockets.emplace_back(newSocket);

        // wakeup the main-loop.
        int rc;
        do
        {
            // wakeup pipe is already full.
            rc = ::write(_wakeup[1], "w", 1);
        }
        while (rc == -1 && errno == EINTR);

        if (rc == -1)
        {
            assert(errno == EAGAIN || errno == EWOULDBLOCK);
        }
    }

private:

    /// Add the new sockets to list of those to poll.
    void addNewSocketsToPoll()
    {
        std::lock_guard<std::mutex> lock(_mutex);

        // Copy the new sockets over and clear.
        _pollSockets.insert(_pollSockets.end(), _newSockets.begin(), _newSockets.end());
        _newSockets.clear();
    }

    void removeSocketFromPoll(const std::shared_ptr<Socket>& socket)
    {
        auto it = std::find(_pollSockets.begin(), _pollSockets.end(), socket);
        assert (it != _pollSockets.end());
        _pollSockets.erase(it);
    }

    /// Initialize the poll fds array with the right events
    void setupPollFds()
    {
        const size_t size = _pollSockets.size();

        _pollFds.resize(size + 1); // + wakeup pipe

        for (size_t i = 0; i < size; ++i)
        {
            _pollFds[i].fd = _pollSockets[i]->getFD();
            _pollFds[i].events = _pollSockets[i]->getPollEvents();
            _pollFds[i].revents = 0;
        }

        // Add the read-end of the wake pipe.
        _pollFds[size].fd = _wakeup[0];
        _pollFds[size].events = POLLIN;
        _pollFds[size].revents = 0;
    }

private:
    /// main-loop wakeup pipe
    int _wakeup[2];
    /// The sockets we're controlling
    std::vector<std::shared_ptr<Socket>> _pollSockets;
    /// Protects _newSockets
    std::mutex _mutex;
    std::vector<std::shared_ptr<Socket>> _newSockets;
    /// The fds to poll.
    std::vector<pollfd> _pollFds;
};

/// Abstract buffering socket.
class BufferingSocket : public Socket
{
public:

    /// Called when a polling event is received.
    /// @events is the mask of events that triggered the wake.
    HandleResult handlePoll(const int events) override
    {
        // FIXME: need to close input, but not output (?)
        bool closeSocket = false;

        // Always try to read.
        closeSocket = !readIncomingData();

        // If we have data, allow the app to consume.
        size_t oldSize = 0;
        while (!_inBuffer.empty() && oldSize != _inBuffer.size())
        {
            oldSize = _inBuffer.size();
            handleIncomingMessage();
        }

        // SSL might want to do handshake,
        // even if we have no data to write.
        if ((events & POLLOUT) || !_outBuffer.empty())
        {
            writeOutgoingData();
        }

        if (events & (POLLHUP | POLLERR | POLLNVAL))
            closeSocket = true;

        return closeSocket ? HandleResult::SOCKET_CLOSED :
                             HandleResult::CONTINUE;
    }

    /// Reads data by invoking readData() and buffering.
    /// Return false iff the socket is closed.
    virtual bool readIncomingData()
    {
        // SSL decodes blocks of 16Kb, so for efficiency we use the same.
        char buf[16 * 1024];
        ssize_t len;
        do
        {
            // Drain the read buffer.
            // TODO: Cap the buffer size, lest we grow beyond control.
            do
            {
                len = readData(buf, sizeof(buf) - 1);
            }
            while (len < 0 && errno == EINTR);

            if (len > 0)
            {
                assert (len < ssize_t(sizeof(buf)));
                _inBuffer.insert(_inBuffer.end(), &buf[0], &buf[len]);
                continue;
            }
            // else poll will handle errors.
        }
        while (len == (sizeof(buf) - 1));

        return len != 0; // zero is eof / clean socket close.
    }

    /// Override to write data out to socket.
    virtual void writeOutgoingData()
    {
        while (!_outBuffer.empty())
        {
            ssize_t len;
            do
            {
                len = writeData(&_outBuffer[0], _outBuffer.size());
            }
            while (len < 0 && errno == EINTR);

            if (len > 0)
            {
                _outBuffer.erase(_outBuffer.begin(),
                                _outBuffer.begin() + len);
            }
            else
            {
                // Poll will handle errors.
                break;
            }
        }
    }

    /// Override to handle reading of socket data differently.
    virtual int readData(char* buf, int len)
    {
        return ::read(getFD(), buf, len);
    }

    /// Override to handle writing data to socket differently.
    virtual int writeData(const char* buf, const int len)
    {
        return ::write(getFD(), buf, len);
    }

    int getPollEvents() override
    {
        // Only poll for read if we have nothing to write.
        return (_outBuffer.empty() ? POLLIN : POLLIN | POLLOUT);
    }

protected:
    BufferingSocket(const int fd) :
        Socket(fd)
    {
    }

    std::vector< char > _inBuffer;
    std::vector< char > _outBuffer;

private:
    /// Override to handle read data.
    /// Called after successful socket reads.
    virtual void handleIncomingMessage() = 0;
};

/// A plain, non-blocking, data streaming socket.
class StreamSocket : public BufferingSocket
{
protected:
    StreamSocket(const int fd) :
        BufferingSocket(fd)
    {
    }

    // Will construct us upon accept.
    template<class T> friend class ServerSocket;
};

/// An SSL/TSL, non-blocking, data streaming socket.
class SslStreamSocket : public BufferingSocket
{
public:
    ~SslStreamSocket()
    {
        shutdown();
        SSL_free(_ssl);
    }

    /// Shutdown the TLS/SSL connection properly.
    void shutdown()
    {
        if (SSL_shutdown(_ssl) == 0)
        {
            // Complete the bidirectional shutdown.
            SSL_shutdown(_ssl);
        }
    }

    bool readIncomingData() override
    {
        const int rc = doHandshake();
        if (rc <= 0)
        {
            return (rc != 0);
        }

        // Default implementation.
        return BufferingSocket::readIncomingData();
    }

    void writeOutgoingData() override
    {
        const int rc = doHandshake();
        if (rc <= 0)
        {
            return;
        }

        // Default implementation.
        BufferingSocket::writeOutgoingData();
    }

    virtual int readData(char* buf, int len)
    {
        return handleSslState(SSL_read(_ssl, buf, len));
    }

    virtual int writeData(const char* buf, const int len)
    {
        assert (len > 0); // Never write 0 bytes.
        return handleSslState(SSL_write(_ssl, buf, len));
    }

    int getPollEvents() override
    {
        if (_sslWantsTo == SslWantsTo::Read)
        {
            // Must read next before attempting to write.
            return POLLIN;
        }
        else if (_sslWantsTo == SslWantsTo::Write)
        {
            // Must write next before attempting to read.
            return POLLOUT;
        }

        // Do the default.
        return BufferingSocket::getPollEvents();
    }

protected:
    SslStreamSocket(const int fd) :
        BufferingSocket(fd),
        _ssl(nullptr),
        _sslWantsTo(SslWantsTo::ReadOrWrite),
        _doHandshake(true)
    {
        BIO* bio = BIO_new(BIO_s_socket());
        if (bio == nullptr)
        {
            throw std::runtime_error("Failed to create SSL BIO.");
        }

        BIO_set_fd(bio, fd, BIO_NOCLOSE);

        _ssl = SslContext::newSsl();
        if (!_ssl)
        {
            BIO_free(bio);
            throw std::runtime_error("Failed to create SSL.");
        }

        SSL_set_bio(_ssl, bio, bio);

        // We are a server-side socket.
        SSL_set_accept_state(_ssl);
    }

    // Will construct us upon accept.
    template<class T> friend class ServerSocket;

private:

    /// The possible next I/O operation that SSL want to do.
    enum class SslWantsTo
    {
        ReadOrWrite,
        Read,
        Write
    };

    int doHandshake()
    {
        if (_doHandshake)
        {
            int rc;
            do
            {
                rc = SSL_do_handshake(_ssl);
            }
            while (rc < 0 && errno == EINTR);

            if (rc <= 0)
            {
                rc = handleSslState(rc);
                if (rc <= 0)
                {
                    return (rc != 0);
                }
            }

            _doHandshake = false;
        }

        // Handshake complete.
        return 1;
    }

    /// Handles the state of SSL after read or write.
    int handleSslState(const int rc)
    {
        if (rc > 0)
        {
            // Success: Reset so we can do either.
            _sslWantsTo = SslWantsTo::ReadOrWrite;
            return rc;
        }

        // Last operation failed. Find out if SSL was trying
        // to do something different that failed, or not.
        const int sslError = SSL_get_error(_ssl, rc);
        switch (sslError)
        {
        case SSL_ERROR_ZERO_RETURN:
            // Shutdown complete, we're disconnected.
            return 0;

        case SSL_ERROR_WANT_READ:
            _sslWantsTo = SslWantsTo::Read;
            return rc;

        case SSL_ERROR_WANT_WRITE:
            _sslWantsTo = SslWantsTo::Write;
            return rc;

        case SSL_ERROR_WANT_CONNECT:
        case SSL_ERROR_WANT_ACCEPT:
        case SSL_ERROR_WANT_X509_LOOKUP:
            // Unexpected.
            return rc;

        case SSL_ERROR_SYSCALL:
            if (errno != 0)
            {
                // Posix API error, let the caller handle.
                return rc;
            }

            // Fallthrough...
        default:
            {
                // The error is comming from BIO. Find out what happened.
                const long bioError = ERR_get_error();
                if (bioError == 0)
                {
                    if (rc == 0)
                    {
                        // Socket closed.
                        return 0;
                    }
                    else if (rc == -1)
                    {
                        throw std::runtime_error("SSL Socket closed unexpectedly.");
                    }
                    else
                    {
                        throw std::runtime_error("SSL BIO reported error [" + std::to_string(rc) + "].");
                    }
                }
                else
                {
                    char buf[512];
                    ERR_error_string_n(bioError, buf, sizeof(buf));
                    throw std::runtime_error(buf);
                }
            }
            break;
        }

        return rc;
    }

private:
    SSL* _ssl;
    /// During handshake SSL might want to read
    /// on write, or write on read.
    SslWantsTo _sslWantsTo;
    /// We must do the handshake during the first
    /// read or write in non-blocking.
    bool _doHandshake;
};

/* vim:set shiftwidth=4 softtabstop=4 expandtab: */