tls_socket.h

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// Copyright (C) 2021 Internet Systems Consortium, Inc. ("ISC")
//
// 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/.

#ifndef TLS_SOCKET_H
#define TLS_SOCKET_H

#ifndef BOOST_ASIO_HPP
#error "asio.hpp must be included before including this, see asiolink.h as to why"
#endif

#include <asiolink/crypto_tls.h>
#include <asiolink/tcp_socket.h>

#include <boost/noncopyable.hpp>

namespace isc {
namespace asiolink {

template <typename C>
class TLSSocket : public IOAsioSocket<C>, private boost::noncopyable {
public:

    TLSSocket(TlsStream<C>& stream);

    TLSSocket(IOService& service, TlsContextPtr context);

    virtual ~TLSSocket() { }

    virtual int getNative() const {
#if BOOST_VERSION < 106600
        return (socket_.native());
#else
        return (socket_.native_handle());
#endif
    }

    virtual int getProtocol() const {
        return (IPPROTO_TCP);
    }

    virtual bool isOpenSynchronous() const {
        return (false);
    }

    bool isUsable() const {
        // If the socket is open it doesn't mean that it is still
        // usable. The connection could have been closed on the other
        // end. We have to check if we can still use this socket.
        if (socket_.is_open()) {
            // Remember the current non blocking setting.
            const bool non_blocking_orig = socket_.non_blocking();

            // Set the socket to non blocking mode. We're going to
            // test if the socket returns would_block status on the
            // attempt to read from it.
            socket_.non_blocking(true);

            // Use receive with message peek flag to avoid removing
            // the data awaiting to be read.
            char data[2];
            int err = 0;
            int cc = recv(getNative(), data, sizeof(data), MSG_PEEK);
            if (cc < 0) {
                // Error case.
                err = errno;
            } else if (cc == 0) {
                // End of file.
                err = -1;
            }

            // Revert the original non_blocking flag on the socket.
            socket_.non_blocking(non_blocking_orig);

            // If the connection is alive we'd typically get
            // would_block status code.  If there are any data that
            // haven't been read we may also get success status. We're
            // guessing that try_again may also be returned by some
            // implementations in some situations. Any other error
            // code indicates a problem with the connection so we
            // assume that the connection has been closed.
            return ((err == 0) || (err == EAGAIN) || (err == EWOULDBLOCK));
        }

        return (false);
    }

    virtual void open(const IOEndpoint* endpoint, C& callback);

    virtual void handshake(C& callback);

    virtual void asyncSend(const void* data, size_t length,
                           const IOEndpoint* endpoint, C& callback);

    void asyncSend(const void* data, size_t length, C& callback);

    virtual void asyncReceive(void* data, size_t length, size_t offset,
                              IOEndpoint* endpoint, C& callback);

    virtual bool processReceivedData(const void* staging, size_t length,
                                     size_t& cumulative, size_t& offset,
                                     size_t& expected,
                                     isc::util::OutputBufferPtr& outbuff);

    virtual void cancel();

    virtual void close();

    virtual void shutdown(C& callback);

    virtual typename TlsStream<C>::lowest_layer_type& getASIOSocket() const {
        return (socket_);
    }

    virtual TlsStream<C>& getTlsStream() const {
        return (stream_);
    }

private:

    std::unique_ptr<TlsStream<C>> stream_ptr_;

    TlsStream<C>& stream_;

    typename TlsStream<C>::lowest_layer_type& socket_;


    isc::util::OutputBufferPtr send_buffer_;
};

// Constructor - caller manages socket.

template <typename C>
TLSSocket<C>::TLSSocket(TlsStream<C>& stream) :
    stream_ptr_(), stream_(stream),
    socket_(stream_.lowest_layer()), send_buffer_() {
}

// Constructor - create socket on the fly.

template <typename C>
TLSSocket<C>::TLSSocket(IOService& service, TlsContextPtr context) :
    stream_ptr_(new TlsStream<C>(service, context)),
    stream_(*stream_ptr_), socket_(stream_.lowest_layer()), send_buffer_()
{
}

// Open the socket.

template <typename C> void
TLSSocket<C>::open(const IOEndpoint* endpoint, C& callback) {
    // Ignore opens on already-open socket.  Don't throw a failure because
    // of uncertainties as to what precedes when using asynchronous I/O.
    // Also allows us a treat a passed-in socket as a self-managed socket.
    if (!socket_.is_open()) {
        if (endpoint->getFamily() == AF_INET) {
            socket_.open(boost::asio::ip::tcp::v4());
        } else {
            socket_.open(boost::asio::ip::tcp::v6());
        }

        // Set options on the socket:

        // Reuse address - allow the socket to bind to a port even if the port
        // is in the TIMED_WAIT state.
        socket_.set_option(boost::asio::socket_base::reuse_address(true));
    }

    // Upconvert to a TCPEndpoint.  We need to do this because although
    // IOEndpoint is the base class of UDPEndpoint and TCPEndpoint, it does not
    // contain a method for getting at the underlying endpoint type - that is in
    isc_throw_assert(endpoint->getProtocol() == IPPROTO_TCP);
    const TCPEndpoint* tcp_endpoint =
        static_cast<const TCPEndpoint*>(endpoint);

    // Connect to the remote endpoint.  On success, the handler will be
    // called (with one argument - the length argument will default to
    // zero).
    socket_.async_connect(tcp_endpoint->getASIOEndpoint(), callback);
}

// Perform the handshake.

template <typename C> void
TLSSocket<C>::handshake(C& callback) {
    if (!socket_.is_open()) {
        isc_throw(SocketNotOpen, "attempt to perform handshake on "
                  "a TLS socket that is not open");
    }
    stream_.handshake(callback);
}

// Send a message.  Should never do this if the socket is not open, so throw
// an exception if this is the case.

template <typename C> void
TLSSocket<C>::asyncSend(const void* data, size_t length, C& callback)
{
    if (!socket_.is_open()) {
        isc_throw(SocketNotOpen,
                  "attempt to send on a TLS socket that is not open");
    }

    try {
        send_buffer_.reset(new isc::util::OutputBuffer(length));
        send_buffer_->writeData(data, length);

        // Send the data.
        boost::asio::async_write(stream_,
                                 boost::asio::buffer(send_buffer_->getData(),
                                                     send_buffer_->getLength()),
                                 callback);
    } catch (const boost::numeric::bad_numeric_cast&) {
        isc_throw(BufferTooLarge,
                  "attempt to send buffer larger than 64kB");
    }
}

template <typename C> void
TLSSocket<C>::asyncSend(const void* data, size_t length,
                        const IOEndpoint*, C& callback)
{
    if (!socket_.is_open()) {
        isc_throw(SocketNotOpen,
                  "attempt to send on a TLS socket that is not open");
    }

    try {
        // Ensure it fits into 16 bits
        uint16_t count = boost::numeric_cast<uint16_t>(length);

        // Copy data into a buffer preceded by the count field.
        send_buffer_.reset(new isc::util::OutputBuffer(length + 2));
        send_buffer_->writeUint16(count);
        send_buffer_->writeData(data, length);

        // ... and send it
        boost::asio::async_write(stream_,
                                 boost::asio::buffer(send_buffer_->getData(),
                                                     send_buffer_->getLength()),
                                 callback);
    } catch (const boost::numeric::bad_numeric_cast&) {
        isc_throw(BufferTooLarge,
                  "attempt to send buffer larger than 64kB");
    }
}

// Receive a message. Note that the "offset" argument is used as an index
// into the buffer in order to decide where to put the data.  It is up to the
// caller to initialize the data to zero
template <typename C> void
TLSSocket<C>::asyncReceive(void* data, size_t length, size_t offset,
                           IOEndpoint* endpoint, C& callback)
{
    if (!socket_.is_open()) {
        isc_throw(SocketNotOpen,
                  "attempt to receive from a TLS socket that is not open");
    }

    // Upconvert to a TCPEndpoint.  We need to do this because although
    // IOEndpoint is the base class of UDPEndpoint and TCPEndpoint, it
    // does not contain a method for getting at the underlying endpoint
    // type - that is in the derived class and the two classes differ on
    // return type.
    isc_throw_assert(endpoint->getProtocol() == IPPROTO_TCP);
    TCPEndpoint* tcp_endpoint = static_cast<TCPEndpoint*>(endpoint);

    // Write the endpoint details from the communications link.  Ideally
    // we should make IOEndpoint assignable, but this runs in to all sorts
    // of problems concerning the management of the underlying Boost
    // endpoint (e.g. if it is not self-managed, is the copied one
    // self-managed?) The most pragmatic solution is to let Boost take care
    // of everything and copy details of the underlying endpoint.
    tcp_endpoint->getASIOEndpoint() = socket_.remote_endpoint();

    // Ensure we can write into the buffer and if so, set the pointer to
    // where the data will be written.
    if (offset >= length) {
        isc_throw(BufferOverflow, "attempt to read into area beyond end of "
                  "TCP receive buffer");
    }
    void* buffer_start =
        static_cast<void*>(static_cast<uint8_t*>(data) + offset);

    // ... and kick off the read.
    stream_.async_read_some(boost::asio::buffer(buffer_start, length - offset),
                            callback);
}

// Is the receive complete?

template <typename C> bool
TLSSocket<C>::processReceivedData(const void* staging, size_t length,
                                  size_t& cumulative, size_t& offset,
                                  size_t& expected,
                                  isc::util::OutputBufferPtr& outbuff)
{
    // Point to the data in the staging buffer and note how much there is.
    const uint8_t* data = static_cast<const uint8_t*>(staging);
    size_t data_length = length;

    // Is the number is "expected" valid?  It won't be unless we have received
    // at least two bytes of data in total for this set of receives.
    if (cumulative < 2) {

        // "expected" is not valid.  Did this read give us enough data to
        // work it out?
        cumulative += length;
        if (cumulative < 2) {

            // Nope, still not valid.  This must have been the first packet and
            // was only one byte long.  Tell the fetch code to read the next
            // packet into the staging buffer beyond the data that is already
            // there so that the next time we are called we have a complete
            // TCP count.
            offset = cumulative;
            return (false);
        }

        // Have enough data to interpret the packet count, so do so now.
        expected = isc::util::readUint16(data, cumulative);

        // We have two bytes less of data to process.  Point to the start of the
        // data and adjust the packet size.  Note that at this point,
        // "cumulative" is the true amount of data in the staging buffer, not
        // "length".
        data += 2;
        data_length = cumulative - 2;
    } else {

        // Update total amount of data received.
        cumulative += length;
    }

    // Regardless of anything else, the next read goes into the start of the
    // staging buffer.
    offset = 0;

    // Work out how much data we still have to put in the output buffer. (This
    // could be zero if we have just interpreted the TCP count and that was
    // set to zero.)
    if (expected >= outbuff->getLength()) {

        // Still need data in the output packet.  Copy what we can from the
        // staging buffer to the output buffer.
        size_t copy_amount = std::min(expected - outbuff->getLength(),
                                      data_length);
        outbuff->writeData(data, copy_amount);
    }

    // We can now say if we have all the data.
    return (expected == outbuff->getLength());
}

// Cancel I/O on the socket.  No-op if the socket is not open.

template <typename C> void
TLSSocket<C>::cancel() {
    if (socket_.is_open()) {
        socket_.cancel();
    }
}

// TLS shutdown.  Can be used for orderly close.

template <typename C> void
TLSSocket<C>::shutdown(C& callback) {
    if (!socket_.is_open()) {
        isc_throw(SocketNotOpen, "attempt to perform shutdown on "
                  "a TLS socket that is not open");
    }
    stream_.shutdown(callback);
}

// Close the socket down.  Can only do this if the socket is open and we are
// managing it ourself.

template <typename C> void
TLSSocket<C>::close() {
    if (socket_.is_open() && stream_ptr_) {
        socket_.close();
    }
}

} // namespace asiolink
} // namespace isc

#endif // TLS_SOCKET_H