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# peerwireclient.cpp Example File
network/torrent/peerwireclient.cpp

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     #include "peerwireclient.h"

     #include <QHostAddress>
     #include <QTimerEvent>

     static const int PendingRequestTimeout = 60 * 1000;
     static const int ClientTimeout = 120 * 1000;
     static const int ConnectTimeout = 60 * 1000;
     static const int KeepAliveInterval = 30 * 1000;
     static const int RateControlTimerDelay = 2000;
     static const int MinimalHeaderSize = 48;
     static const int FullHeaderSize = 68;
     static const char ProtocolId[] = "BitTorrent protocol";
     static const char ProtocolIdSize = 19;

     // Reads a 32bit unsigned int from data in network order.
     static inline quint32 fromNetworkData(const char *data)
     {
         const unsigned char *udata = (const unsigned char *)data;
         return (quint32(udata[0]) << 24)
             | (quint32(udata[1]) << 16)
             | (quint32(udata[2]) << 8)
             | (quint32(udata[3]));
     }

     // Writes a 32bit unsigned int from num to data in network order.
     static inline void toNetworkData(quint32 num, char *data)
     {
         unsigned char *udata = (unsigned char *)data;
         udata[3] = (num & 0xff);
         udata[2] = (num & 0xff00) >> 8;
         udata[1] = (num & 0xff0000) >> 16;
         udata[0] = (num & 0xff000000) >> 24;
     }

     // Constructs an unconnected PeerWire client and starts the connect timer.
     PeerWireClient::PeerWireClient(const QByteArray &peerId, QObject *parent)
         : QTcpSocket(parent), pendingBlockSizes(0),
           pwState(ChokingPeer | ChokedByPeer), receivedHandShake(false), gotPeerId(false),
           sentHandShake(false), nextPacketLength(-1), pendingRequestTimer(0), invalidateTimeout(false),
           keepAliveTimer(0), torrentPeer(0)
     {
         memset(uploadSpeedData, 0, sizeof(uploadSpeedData));
         memset(downloadSpeedData, 0, sizeof(downloadSpeedData));

         transferSpeedTimer = startTimer(RateControlTimerDelay);
         timeoutTimer = startTimer(ConnectTimeout);
         peerIdString = peerId;

         connect(this, SIGNAL(readyRead()), this, SIGNAL(readyToTransfer()));
         connect(this, SIGNAL(connected()), this, SIGNAL(readyToTransfer()));

         connect(&socket, SIGNAL(connected()),
                 this, SIGNAL(connected()));
         connect(&socket, SIGNAL(readyRead()),
                 this, SIGNAL(readyRead()));
         connect(&socket, SIGNAL(disconnected()),
                 this, SIGNAL(disconnected()));
         connect(&socket, SIGNAL(error(QAbstractSocket::SocketError)),
                 this, SIGNAL(error(QAbstractSocket::SocketError)));
         connect(&socket, SIGNAL(bytesWritten(qint64)),
                 this, SIGNAL(bytesWritten(qint64)));
         connect(&socket, SIGNAL(stateChanged(QAbstractSocket::SocketState)),
                 this, SLOT(socketStateChanged(QAbstractSocket::SocketState)));

     }

     // Registers the peer ID and SHA1 sum of the torrent, and initiates
     // the handshake.
     void PeerWireClient::initialize(const QByteArray &infoHash, int pieceCount)
     {
         this->infoHash = infoHash;
         peerPieces.resize(pieceCount);
         if (!sentHandShake)
             sendHandShake();
     }

     void PeerWireClient::setPeer(TorrentPeer *peer)
     {
         torrentPeer = peer;
     }

     TorrentPeer *PeerWireClient::peer() const
     {
         return torrentPeer;
     }

     QBitArray PeerWireClient::availablePieces() const
     {
         return peerPieces;
     }

     QList<TorrentBlock> PeerWireClient::incomingBlocks() const
     {
         return incoming;
     }

     // Sends a "choke" message, asking the peer to stop requesting blocks.
     void PeerWireClient::chokePeer()
     {
         const char message[] = {0, 0, 0, 1, 0};
         write(message, sizeof(message));
         pwState |= ChokingPeer;

         // After receiving a choke message, the peer will assume all
         // pending requests are lost.
         pendingBlocks.clear();
         pendingBlockSizes = 0;
     }

     // Sends an "unchoke" message, allowing the peer to start/resume
     // requesting blocks.
     void PeerWireClient::unchokePeer()
     {
         const char message[] = {0, 0, 0, 1, 1};
         write(message, sizeof(message));
         pwState &= ~ChokingPeer;

         if (pendingRequestTimer)
             killTimer(pendingRequestTimer);
     }

     // Sends a "keep-alive" message to prevent the peer from closing
     // the connection when there's no activity
     void PeerWireClient::sendKeepAlive()
     {
         const char message[] = {0, 0, 0, 0};
         write(message, sizeof(message));
     }

     // Sends an "interested" message, informing the peer that it has got
     // pieces that we'd like to download.
     void PeerWireClient::sendInterested()
     {
         const char message[] = {0, 0, 0, 1, 2};
         write(message, sizeof(message));
         pwState |= InterestedInPeer;

         // After telling the peer that we're interested, we expect to get
         // unchoked within a certain timeframe; otherwise we'll drop the
         // connection.
         if (pendingRequestTimer)
             killTimer(pendingRequestTimer);
         pendingRequestTimer = startTimer(PendingRequestTimeout);
     }

     // Sends a "not interested" message, informing the peer that it does
     // not have any pieces that we'd like to download.
     void PeerWireClient::sendNotInterested()
     {
         const char message[] = {0, 0, 0, 1, 3};
         write(message, sizeof(message));
         pwState &= ~InterestedInPeer;
     }

     // Sends a piece notification / a "have" message, informing the peer
     // that we have just downloaded a new piece.
     void PeerWireClient::sendPieceNotification(int piece)
     {
         if (!sentHandShake)
             sendHandShake();

         char message[] = {0, 0, 0, 5, 4, 0, 0, 0, 0};
         toNetworkData(piece, &message[5]);
         write(message, sizeof(message));
     }

     // Sends the complete list of pieces that we have downloaded.
     void PeerWireClient::sendPieceList(const QBitArray &bitField)
     {
         // The bitfield message may only be sent immediately after the
         // handshaking sequence is completed, and before any other
         // messages are sent.
         if (!sentHandShake)
             sendHandShake();

         // Don't send the bitfield if it's all zeros.
         if (bitField.count(true) == 0)
             return;

         int bitFieldSize = bitField.size();
         int size = (bitFieldSize + 7) / 8;
         QByteArray bits(size, '\0');
         for (int i = 0; i < bitFieldSize; ++i) {
             if (bitField.testBit(i)) {
                 quint32 byte = quint32(i) / 8;
                 quint32 bit = quint32(i) % 8;
                 bits[byte] = uchar(bits.at(byte)) | (1 << (7 - bit));
             }
         }

         char message[] = {0, 0, 0, 1, 5};
         toNetworkData(bits.size() + 1, &message[0]);
         write(message, sizeof(message));
         write(bits);
     }

     // Sends a request for a block.
     void PeerWireClient::requestBlock(int piece, int offset, int length)
     {
         char message[] = {0, 0, 0, 1, 6};
         toNetworkData(13, &message[0]);
         write(message, sizeof(message));

         char numbers[4 * 3];
         toNetworkData(piece, &numbers[0]);
         toNetworkData(offset, &numbers[4]);
         toNetworkData(length, &numbers[8]);
         write(numbers, sizeof(numbers));

         incoming << TorrentBlock(piece, offset, length);

         // After requesting a block, we expect the block to be sent by the
         // other peer within a certain number of seconds. Otherwise, we
         // drop the connection.
         if (pendingRequestTimer)
             killTimer(pendingRequestTimer);
         pendingRequestTimer = startTimer(PendingRequestTimeout);
     }

     // Cancels a request for a block.
     void PeerWireClient::cancelRequest(int piece, int offset, int length)
     {
         char message[] = {0, 0, 0, 1, 8};
         toNetworkData(13, &message[0]);
         write(message, sizeof(message));

         char numbers[4 * 3];
         toNetworkData(piece, &numbers[0]);
         toNetworkData(offset, &numbers[4]);
         toNetworkData(length, &numbers[8]);
         write(numbers, sizeof(numbers));

         incoming.removeAll(TorrentBlock(piece, offset, length));
     }

     // Sends a block to the peer.
     void PeerWireClient::sendBlock(int piece, int offset, const QByteArray &data)
     {
         QByteArray block;

         char message[] = {0, 0, 0, 1, 7};
         toNetworkData(9 + data.size(), &message[0]);
         block += QByteArray(message, sizeof(message));

         char numbers[4 * 2];
         toNetworkData(piece, &numbers[0]);
         toNetworkData(offset, &numbers[4]);
         block += QByteArray(numbers, sizeof(numbers));
         block += data;

         BlockInfo blockInfo;
         blockInfo.pieceIndex = piece;
         blockInfo.offset = offset;
         blockInfo.length = data.size();
         blockInfo.block = block;

         pendingBlocks << blockInfo;
         pendingBlockSizes += block.size();

         if (pendingBlockSizes > 32 * 16384) {
             chokePeer();
             unchokePeer();
             return;
         }
         emit readyToTransfer();
     }

     // Attempts to write 'bytes' bytes to the socket from the buffer.
     // This is used by RateController, which precisely controls how much
     // each client can write.
     qint64 PeerWireClient::writeToSocket(qint64 bytes)
     {
         qint64 totalWritten = 0;
         do {
             if (outgoingBuffer.isEmpty() && !pendingBlocks.isEmpty()) {
                 BlockInfo block = pendingBlocks.takeFirst();
                 pendingBlockSizes -= block.length;
                 outgoingBuffer += block.block;
             }
             qint64 written = socket.write(outgoingBuffer.constData(),
                                           qMin<qint64>(bytes - totalWritten, outgoingBuffer.size()));
             if (written <= 0)
                 return totalWritten ? totalWritten : written;

             totalWritten += written;
             uploadSpeedData[0] += written;
             outgoingBuffer.remove(0, written);
         } while (totalWritten < bytes && (!outgoingBuffer.isEmpty() || !pendingBlocks.isEmpty()));

         return totalWritten;
     }

     // Attempts to read at most 'bytes' bytes from the socket.
     qint64 PeerWireClient::readFromSocket(qint64 bytes)
     {
         char buffer[1024];
         qint64 totalRead = 0;
         do {
             qint64 bytesRead = socket.read(buffer, qMin<qint64>(sizeof(buffer), bytes - totalRead));
             if (bytesRead <= 0)
                 break;
             qint64 oldSize = incomingBuffer.size();
             incomingBuffer.resize(oldSize + bytesRead);
             memcpy(incomingBuffer.data() + oldSize, buffer, bytesRead);

             totalRead += bytesRead;
         } while (totalRead < bytes);

         if (totalRead > 0) {
             downloadSpeedData[0] += totalRead;
             emit bytesReceived(totalRead);
             processIncomingData();
         }
         return totalRead;
     }

     // Returns the average number of bytes per second this client is
     // downloading.
     qint64 PeerWireClient::downloadSpeed() const
     {
         qint64 sum = 0;
         for (unsigned int i = 0; i < sizeof(downloadSpeedData) / sizeof(qint64); ++i)
             sum += downloadSpeedData[i];
         return sum / (8 * 2);
     }

     // Returns the average number of bytes per second this client is
     // uploading.
     qint64 PeerWireClient::uploadSpeed() const
     {
         qint64 sum = 0;
         for (unsigned int i = 0; i < sizeof(uploadSpeedData) / sizeof(qint64); ++i)
             sum += uploadSpeedData[i];
         return sum / (8 * 2);
     }

     void PeerWireClient::setReadBufferSize(int size)
     {
         socket.setReadBufferSize(size);
     }

     bool PeerWireClient::canTransferMore() const
     {
         return bytesAvailable() > 0 || socket.bytesAvailable() > 0
             || !outgoingBuffer.isEmpty() || !pendingBlocks.isEmpty();
     }

     void PeerWireClient::connectToHostImplementation(const QString &hostName,
                                                      quint16 port, OpenMode openMode)

     {
         setOpenMode(openMode);
         socket.connectToHost(hostName, port, openMode);
     }

     void PeerWireClient::diconnectFromHostImplementation()
     {
         socket.disconnectFromHost();
     }

     void PeerWireClient::timerEvent(QTimerEvent *event)
     {
         if (event->timerId() == transferSpeedTimer) {
             // Rotate the upload / download records.
             for (int i = 6; i >= 0; --i) {
                 uploadSpeedData[i + 1] = uploadSpeedData[i];
                 downloadSpeedData[i + 1] = downloadSpeedData[i];
             }
             uploadSpeedData[0] = 0;
             downloadSpeedData[0] = 0;
         } else if (event->timerId() == timeoutTimer) {
             // Disconnect if we timed out; otherwise the timeout is
             // restarted.
             if (invalidateTimeout) {
                 invalidateTimeout = false;
             } else {
                 abort();
                 emit infoHashReceived(QByteArray());
             }
         } else if (event->timerId() == pendingRequestTimer) {
             abort();
         } else if (event->timerId() == keepAliveTimer) {
             sendKeepAlive();
         }
         QTcpSocket::timerEvent(event);
     }

     // Sends the handshake to the peer.
     void PeerWireClient::sendHandShake()
     {
         sentHandShake = true;

         // Restart the timeout
         if (timeoutTimer)
             killTimer(timeoutTimer);
         timeoutTimer = startTimer(ClientTimeout);

         // Write the 68 byte PeerWire handshake.
         write(&ProtocolIdSize, 1);
         write(ProtocolId, ProtocolIdSize);
         write(QByteArray(8, '\0'));
         write(infoHash);
         write(peerIdString);
     }

     void PeerWireClient::processIncomingData()
     {
         invalidateTimeout = true;
         if (!receivedHandShake) {
             // Check that we received enough data
             if (bytesAvailable() < MinimalHeaderSize)
                 return;

             // Sanity check the protocol ID
             QByteArray id = read(ProtocolIdSize + 1);
             if (id.at(0) != ProtocolIdSize || !id.mid(1).startsWith(ProtocolId)) {
                 abort();
                 return;
             }

             // Discard 8 reserved bytes, then read the info hash and peer ID
             (void) read(8);

             // Read infoHash
             QByteArray peerInfoHash = read(20);
             if (!infoHash.isEmpty() && peerInfoHash != infoHash) {
                 abort();
                 return;
             }

             emit infoHashReceived(peerInfoHash);
             if (infoHash.isEmpty()) {
                 abort();
                 return;
             }

             // Send handshake
             if (!sentHandShake)
                 sendHandShake();
             receivedHandShake = true;
         }

         // Handle delayed peer id arrival
         if (!gotPeerId) {
             if (bytesAvailable() < 20)
                 return;
             gotPeerId = true;
             if (read(20) == peerIdString) {
                 // We connected to ourself
                 abort();
                 return;
             }
         }

         // Initialize keep-alive timer
         if (!keepAliveTimer)
             keepAliveTimer = startTimer(KeepAliveInterval);

         do {
             // Find the packet length
             if (nextPacketLength == -1) {
                 if (bytesAvailable() < 4)
                     return;

                 char tmp[4];
                 read(tmp, sizeof(tmp));
                 nextPacketLength = fromNetworkData(tmp);

                 if (nextPacketLength < 0 || nextPacketLength > 200000) {
                     // Prevent DoS
                     abort();
                     return;
                 }
             }

             // KeepAlive
             if (nextPacketLength == 0) {
                 nextPacketLength = -1;
                 continue;
             }

             // Wait with parsing until the whole packet has been received
             if (bytesAvailable() < nextPacketLength)
                 return;

             // Read the packet
             QByteArray packet = read(nextPacketLength);
             if (packet.size() != nextPacketLength) {
                 abort();
                 return;
             }

             switch (packet.at(0)) {
             case ChokePacket:
                 // We have been choked.
                 pwState |= ChokedByPeer;
                 incoming.clear();
                 if (pendingRequestTimer)
                     killTimer(pendingRequestTimer);
                 emit choked();
                 break;
             case UnchokePacket:
                 // We have been unchoked.
                 pwState &= ~ChokedByPeer;
                 emit unchoked();
                 break;
             case InterestedPacket:
                 // The peer is interested in downloading.
                 pwState |= PeerIsInterested;
                 emit interested();
                 break;
             case NotInterestedPacket:
                 // The peer is not interested in downloading.
                 pwState &= ~PeerIsInterested;
                 emit notInterested();
                 break;
             case HavePacket: {
                 // The peer has a new piece available.
                 quint32 index = fromNetworkData(&packet.data()[1]);
                 if (index < quint32(peerPieces.size())) {
                     // Only accept indexes within the valid range.
                     peerPieces.setBit(int(index));
                 }
                 emit piecesAvailable(availablePieces());
                 break;
             }
             case BitFieldPacket:
                 // The peer has the following pieces available.
                 for (int i = 1; i < packet.size(); ++i) {
                     for (int bit = 0; bit < 8; ++bit) {
                         if (packet.at(i) & (1 << (7 - bit))) {
                             int bitIndex = int(((i - 1) * 8) + bit);
                             if (bitIndex >= 0 && bitIndex < peerPieces.size()) {
                                 // Occasionally, broken clients claim to have
                                 // pieces whose index is outside the valid range.
                                 // The most common mistake is the index == size
                                 // case.
                                 peerPieces.setBit(bitIndex);
                             }
                         }
                     }
                 }
                 emit piecesAvailable(availablePieces());
                 break;
             case RequestPacket: {
                 // The peer requests a block.
                 quint32 index = fromNetworkData(&packet.data()[1]);
                 quint32 begin = fromNetworkData(&packet.data()[5]);
                 quint32 length = fromNetworkData(&packet.data()[9]);
                 emit blockRequested(int(index), int(begin), int(length));
                 break;
             }
             case PiecePacket: {
                 int index = int(fromNetworkData(&packet.data()[1]));
                 int begin = int(fromNetworkData(&packet.data()[5]));

                 incoming.removeAll(TorrentBlock(index, begin, packet.size() - 9));

                 // The peer sends a block.
                 emit blockReceived(index, begin, packet.mid(9));

                 // Kill the pending block timer.
                 if (pendingRequestTimer) {
                     killTimer(pendingRequestTimer);
                     pendingRequestTimer = 0;
                 }
                 break;
             }
             case CancelPacket: {
                 // The peer cancels a block request.
                 quint32 index = fromNetworkData(&packet.data()[1]);
                 quint32 begin = fromNetworkData(&packet.data()[5]);
                 quint32 length = fromNetworkData(&packet.data()[9]);
                 for (int i = 0; i < pendingBlocks.size(); ++i) {
                     const BlockInfo &blockInfo = pendingBlocks.at(i);
                     if (blockInfo.pieceIndex == int(index)
                         && blockInfo.offset == int(begin)
                         && blockInfo.length == int(length)) {
                         pendingBlocks.removeAt(i);
                         break;
                     }
                 }
                 break;
             }
             default:
                 // Unsupported packet type; just ignore it.
                 break;
             }
             nextPacketLength = -1;
         } while (bytesAvailable() > 0);
     }

     void PeerWireClient::socketStateChanged(QAbstractSocket::SocketState state)
     {
         setLocalAddress(socket.localAddress());
         setLocalPort(socket.localPort());
         setPeerName(socket.peerName());
         setPeerAddress(socket.peerAddress());
         setPeerPort(socket.peerPort());
         setSocketState(state);
     }

     qint64 PeerWireClient::readData(char *data, qint64 size)
     {
         int n = qMin<int>(size, incomingBuffer.size());
         memcpy(data, incomingBuffer.constData(), n);
         incomingBuffer.remove(0, n);
         return n;
     }

     qint64 PeerWireClient::readLineData(char *data, qint64 maxlen)
     {
         return QIODevice::readLineData(data, maxlen);
     }

     qint64 PeerWireClient::writeData(const char *data, qint64 size)
     {
         int oldSize = outgoingBuffer.size();
         outgoingBuffer.resize(oldSize + size);
         memcpy(outgoingBuffer.data() + oldSize, data, size);
         emit readyToTransfer();
         return size;
     }