1 /* Copyright (c) 2012-2021. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
10 #include "s4u-peer.hpp"
11 #include "s4u-tracker.hpp"
13 XBT_LOG_NEW_DEFAULT_CATEGORY(s4u_bt_peer, "Messages specific for the peers");
16 * User parameters for transferred file data. For the test, the default values are :
17 * File size: 10 pieces * 5 blocks/piece * 16384 bytes/block = 819200 bytes
19 constexpr unsigned long FILE_PIECES = 10UL;
20 constexpr unsigned long PIECES_BLOCKS = 5UL;
21 constexpr int BLOCK_SIZE = 16384;
23 /** Number of blocks asked by each request */
24 constexpr unsigned long BLOCKS_REQUESTED = 2UL;
26 constexpr double SLEEP_DURATION = 1.0;
27 #define BITS_TO_BYTES(x) (((x) / 8 + (x) % 8) ? 1 : 0)
30 * Sizes based on report by A. Legout et al, Understanding BitTorrent: An Experimental Perspective
31 * http://hal.inria.fr/inria-00000156/en
33 constexpr unsigned message_size(MessageType type)
35 constexpr std::array<unsigned, 10> sizes{{/* HANDSHAKE */ 68,
39 /* NOTINTERESTED */ 5,
45 return sizes[static_cast<int>(type)];
48 constexpr const char* message_name(MessageType type)
50 constexpr std::array<const char*, 10> names{{"HANDSHAKE", "CHOKE", "UNCHOKE", "INTERESTED", "NOTINTERESTED", "HAVE",
51 "BITFIELD", "REQUEST", "PIECE", "CANCEL"}};
52 return names[static_cast<int>(type)];
55 Peer::Peer(std::vector<std::string> args)
58 xbt_assert(args.size() == 3 || args.size() == 4, "Wrong number of arguments");
60 id = std::stoi(args[1]);
61 mailbox_ = simgrid::s4u::Mailbox::by_name(std::to_string(id));
62 } catch (const std::invalid_argument&) {
63 throw std::invalid_argument("Invalid ID:" + args[1]);
68 deadline = std::stod(args[2]);
69 } catch (const std::invalid_argument&) {
70 throw std::invalid_argument("Invalid deadline:" + args[2]);
72 xbt_assert(deadline > 0, "Wrong deadline supplied");
74 if (args.size() == 4 && args[3] == "1") {
75 bitfield_ = (1U << FILE_PIECES) - 1U;
76 bitfield_blocks = (1ULL << (FILE_PIECES * PIECES_BLOCKS)) - 1ULL;
78 pieces_count.resize(FILE_PIECES);
80 XBT_INFO("Hi, I'm joining the network with id %d", id);
83 /** Peer main function */
84 void Peer::operator()()
86 // Getting peer data from the tracker.
87 if (getPeersFromTracker()) {
88 XBT_DEBUG("Got %zu peers from the tracker. Current status is: %s", connected_peers.size(), getStatus().c_str());
89 begin_receive_time = simgrid::s4u::Engine::get_clock();
90 mailbox_->set_receiver(simgrid::s4u::Actor::self());
92 sendHandshakeToAllPeers();
98 XBT_INFO("Couldn't contact the tracker.");
101 XBT_INFO("Here is my current status: %s", getStatus().c_str());
104 bool Peer::getPeersFromTracker()
106 simgrid::s4u::Mailbox* tracker_mailbox = simgrid::s4u::Mailbox::by_name(TRACKER_MAILBOX);
107 // Build the task to send to the tracker
108 auto* peer_request = new TrackerQuery(id, mailbox_);
110 XBT_DEBUG("Sending a peer request to the tracker.");
111 tracker_mailbox->put(peer_request, TRACKER_COMM_SIZE, GET_PEERS_TIMEOUT);
112 } catch (const simgrid::TimeoutException&) {
113 XBT_DEBUG("Timeout expired when requesting peers to tracker");
119 auto answer = mailbox_->get_unique<TrackerAnswer>(GET_PEERS_TIMEOUT);
120 // Add the peers the tracker gave us to our peer list.
121 for (auto const& peer_id : answer->getPeers())
123 connected_peers.emplace(peer_id, Connection(peer_id));
124 } catch (const simgrid::TimeoutException&) {
125 XBT_DEBUG("Timeout expired when requesting peers to tracker");
131 void Peer::sendHandshakeToAllPeers()
133 for (auto const& kv : connected_peers) {
134 const Connection& remote_peer = kv.second;
135 auto* handshake = new Message(MessageType::HANDSHAKE, id, mailbox_);
136 remote_peer.mailbox_->put_init(handshake, message_size(MessageType::HANDSHAKE))->detach();
137 XBT_DEBUG("Sending a HANDSHAKE to %d", remote_peer.id);
141 void Peer::sendMessage(simgrid::s4u::Mailbox* mailbox, MessageType type, uint64_t size)
143 XBT_DEBUG("Sending %s to %s", message_name(type), mailbox->get_cname());
144 mailbox->put_init(new Message(type, id, bitfield_, mailbox_), size)->detach();
147 void Peer::sendBitfield(simgrid::s4u::Mailbox* mailbox)
149 XBT_DEBUG("Sending a BITFIELD to %s", mailbox->get_cname());
151 ->put_init(new Message(MessageType::BITFIELD, id, bitfield_, mailbox_),
152 message_size(MessageType::BITFIELD) + BITS_TO_BYTES(FILE_PIECES))
156 void Peer::sendPiece(simgrid::s4u::Mailbox* mailbox, unsigned int piece, int block_index, int block_length)
158 xbt_assert(not hasNotPiece(piece), "Tried to send a unavailable piece.");
159 XBT_DEBUG("Sending the PIECE %u (%d,%d) to %s", piece, block_index, block_length, mailbox->get_cname());
160 mailbox->put_init(new Message(MessageType::PIECE, id, mailbox_, piece, block_index, block_length), BLOCK_SIZE)
164 void Peer::sendHaveToAllPeers(unsigned int piece)
166 XBT_DEBUG("Sending HAVE message to all my peers");
167 for (auto const& kv : connected_peers) {
168 const Connection& remote_peer = kv.second;
169 remote_peer.mailbox_->put_init(new Message(MessageType::HAVE, id, mailbox_, piece), message_size(MessageType::HAVE))
174 void Peer::sendRequestTo(Connection* remote_peer, unsigned int piece)
176 remote_peer->current_piece = piece;
177 xbt_assert(remote_peer->hasPiece(piece));
178 int block_index = getFirstMissingBlockFrom(piece);
179 if (block_index != -1) {
180 int block_length = static_cast<int>(std::min(BLOCKS_REQUESTED, PIECES_BLOCKS - block_index));
181 XBT_DEBUG("Sending a REQUEST to %s for piece %u (%d,%d)", remote_peer->mailbox_->get_cname(), piece, block_index,
183 remote_peer->mailbox_
184 ->put_init(new Message(MessageType::REQUEST, id, mailbox_, piece, block_index, block_length),
185 message_size(MessageType::REQUEST))
190 std::string Peer::getStatus() const
193 for (unsigned i = 0; i < FILE_PIECES; i++)
194 res += (bitfield_ & (1U << i)) ? '1' : '0';
198 bool Peer::hasFinished() const
200 return bitfield_ == (1U << FILE_PIECES) - 1U;
203 /** Indicates if the remote peer has a piece not stored by the local peer */
204 bool Peer::isInterestedBy(const Connection* remote_peer) const
206 return remote_peer->bitfield & (bitfield_ ^ ((1 << FILE_PIECES) - 1));
209 bool Peer::isInterestedByFree(const Connection* remote_peer) const
211 for (unsigned int i = 0; i < FILE_PIECES; i++)
212 if (hasNotPiece(i) && remote_peer->hasPiece(i) && isNotDownloadingPiece(i))
217 void Peer::updatePiecesCountFromBitfield(unsigned int bitfield)
219 for (unsigned int i = 0; i < FILE_PIECES; i++)
220 if (bitfield & (1U << i))
224 unsigned int Peer::countPieces(unsigned int bitfield) const
226 unsigned int count = 0U;
227 unsigned int n = bitfield;
235 int Peer::nbInterestedPeers() const
237 return static_cast<int>(std::count_if(connected_peers.begin(), connected_peers.end(),
238 [](const auto& kv) { return kv.second.interested; }));
243 double next_choked_update = simgrid::s4u::Engine::get_clock() + UPDATE_CHOKED_INTERVAL;
244 XBT_DEBUG("Start downloading.");
246 /* Send a "handshake" message to all the peers it got (since it couldn't have gotten more than 50 peers) */
247 sendHandshakeToAllPeers();
248 XBT_DEBUG("Starting main leech loop listening on mailbox: %s", mailbox_->get_cname());
250 while (simgrid::s4u::Engine::get_clock() < deadline && countPieces(bitfield_) < FILE_PIECES) {
251 if (comm_received == nullptr) {
252 comm_received = mailbox_->get_async<Message>(&message);
254 if (comm_received->test()) {
257 comm_received = nullptr;
259 // We don't execute the choke algorithm if we don't already have a piece
260 if (simgrid::s4u::Engine::get_clock() >= next_choked_update && countPieces(bitfield_) > 0) {
262 next_choked_update += UPDATE_CHOKED_INTERVAL;
264 simgrid::s4u::this_actor::sleep_for(SLEEP_DURATION);
269 XBT_DEBUG("%d becomes a seeder", id);
274 double next_choked_update = simgrid::s4u::Engine::get_clock() + UPDATE_CHOKED_INTERVAL;
275 XBT_DEBUG("Start seeding.");
276 // start the main seed loop
277 while (simgrid::s4u::Engine::get_clock() < deadline) {
278 if (comm_received == nullptr) {
279 comm_received = mailbox_->get_async<Message>(&message);
281 if (comm_received->test()) {
284 comm_received = nullptr;
286 if (simgrid::s4u::Engine::get_clock() >= next_choked_update) {
288 // TODO: Change the choked peer algorithm when seeding.
289 next_choked_update += UPDATE_CHOKED_INTERVAL;
291 simgrid::s4u::this_actor::sleep_for(SLEEP_DURATION);
297 void Peer::updateActivePeersSet(Connection* remote_peer)
299 if (remote_peer->interested && not remote_peer->choked_upload)
300 active_peers.insert(remote_peer);
302 active_peers.erase(remote_peer);
305 void Peer::handleMessage()
307 XBT_DEBUG("Received a %s message from %s", message_name(message->type), message->return_mailbox->get_cname());
309 auto known_peer = connected_peers.find(message->peer_id);
310 Connection* remote_peer = (known_peer == connected_peers.end()) ? nullptr : &known_peer->second;
311 xbt_assert(remote_peer != nullptr || message->type == MessageType::HANDSHAKE,
312 "The impossible did happened: A not-in-our-list peer sent us a message.");
314 switch (message->type) {
315 case MessageType::HANDSHAKE:
316 // Check if the peer is in our connection list.
317 if (remote_peer == nullptr) {
318 XBT_DEBUG("This peer %d was unknown, answer to its handshake", message->peer_id);
319 connected_peers.emplace(message->peer_id, Connection(message->peer_id));
320 sendMessage(message->return_mailbox, MessageType::HANDSHAKE, message_size(MessageType::HANDSHAKE));
322 // Send our bitfield to the peer
323 sendBitfield(message->return_mailbox);
325 case MessageType::BITFIELD:
326 // Update the pieces list
327 updatePiecesCountFromBitfield(message->bitfield);
328 // Store the bitfield
329 remote_peer->bitfield = message->bitfield;
330 xbt_assert(not remote_peer->am_interested, "Should not be interested at first");
331 if (isInterestedBy(remote_peer)) {
332 remote_peer->am_interested = true;
333 sendMessage(message->return_mailbox, MessageType::INTERESTED, message_size(MessageType::INTERESTED));
336 case MessageType::INTERESTED:
337 // Update the interested state of the peer.
338 remote_peer->interested = true;
339 updateActivePeersSet(remote_peer);
341 case MessageType::NOTINTERESTED:
342 remote_peer->interested = false;
343 updateActivePeersSet(remote_peer);
345 case MessageType::UNCHOKE:
346 xbt_assert(remote_peer->choked_download);
347 remote_peer->choked_download = false;
348 // Send requests to the peer, since it has unchoked us
349 if (remote_peer->am_interested)
350 requestNewPieceTo(remote_peer);
352 case MessageType::CHOKE:
353 xbt_assert(not remote_peer->choked_download);
354 remote_peer->choked_download = true;
355 if (remote_peer->current_piece != -1)
356 removeCurrentPiece(remote_peer, remote_peer->current_piece);
358 case MessageType::HAVE:
359 XBT_DEBUG("\t for piece %d", message->piece);
360 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
361 "Wrong HAVE message received");
362 remote_peer->bitfield = remote_peer->bitfield | (1U << static_cast<unsigned int>(message->piece));
363 pieces_count[message->piece]++;
364 // If the piece is in our pieces, we tell the peer that we are interested.
365 if (not remote_peer->am_interested && hasNotPiece(message->piece)) {
366 remote_peer->am_interested = true;
367 sendMessage(message->return_mailbox, MessageType::INTERESTED, message_size(MessageType::INTERESTED));
368 if (not remote_peer->choked_download)
369 requestNewPieceTo(remote_peer);
372 case MessageType::REQUEST:
373 xbt_assert(remote_peer->interested);
374 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
375 "Wrong HAVE message received");
376 if (not remote_peer->choked_upload) {
377 XBT_DEBUG("\t for piece %d (%d,%d)", message->piece, message->block_index,
378 message->block_index + message->block_length);
379 if (not hasNotPiece(message->piece)) {
380 sendPiece(message->return_mailbox, message->piece, message->block_index, message->block_length);
383 XBT_DEBUG("\t for piece %d but he is choked.", message->peer_id);
386 case MessageType::PIECE:
387 XBT_DEBUG(" \t for piece %d (%d,%d)", message->piece, message->block_index,
388 message->block_index + message->block_length);
389 xbt_assert(not remote_peer->choked_download);
390 xbt_assert(not remote_peer->choked_download, "Can't received a piece if I'm choked !");
391 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
392 "Wrong piece received");
393 // TODO: Execute a computation.
394 if (hasNotPiece(static_cast<unsigned int>(message->piece))) {
395 updateBitfieldBlocks(message->piece, message->block_index, message->block_length);
396 if (hasCompletedPiece(static_cast<unsigned int>(message->piece))) {
397 // Removing the piece from our piece list
398 removeCurrentPiece(remote_peer, message->piece);
399 // Setting the fact that we have the piece
400 bitfield_ = bitfield_ | (1U << static_cast<unsigned int>(message->piece));
401 XBT_DEBUG("My status is now %s", getStatus().c_str());
402 // Sending the information to all the peers we are connected to
403 sendHaveToAllPeers(message->piece);
404 // sending UNINTERESTED to peers that do not have what we want.
405 updateInterestedAfterReceive();
406 } else { // piece not completed
407 sendRequestTo(remote_peer, message->piece); // ask for the next block
410 XBT_DEBUG("However, we already have it");
411 requestNewPieceTo(remote_peer);
414 case MessageType::CANCEL:
419 // Update the peer speed.
421 remote_peer->addSpeedValue(1.0 / (simgrid::s4u::Engine::get_clock() - begin_receive_time));
423 begin_receive_time = simgrid::s4u::Engine::get_clock();
426 /** Selects the appropriate piece to download and requests it to the remote_peer */
427 void Peer::requestNewPieceTo(Connection* remote_peer)
429 int piece = selectPieceToDownload(remote_peer);
431 current_pieces |= (1U << (unsigned int)piece);
432 sendRequestTo(remote_peer, piece);
436 void Peer::removeCurrentPiece(Connection* remote_peer, unsigned int current_piece)
438 current_pieces &= ~(1U << current_piece);
439 remote_peer->current_piece = -1;
442 /** @brief Return the piece to be downloaded
443 * There are two cases (as described in "Bittorrent Architecture Protocol", Ryan Toole :
444 * If a piece is partially downloaded, this piece will be selected prioritarily
445 * If the peer has strictly less than 4 pieces, he chooses a piece at random.
446 * If the peer has more than pieces, he downloads the pieces that are the less replicated (rarest policy).
447 * If all pieces have been downloaded or requested, we select a random requested piece (endgame mode).
448 * @param remote_peer: information about the connection
449 * @return the piece to download if possible. -1 otherwise
451 int Peer::selectPieceToDownload(const Connection* remote_peer)
453 int piece = partiallyDownloadedPiece(remote_peer);
454 // strict priority policy
459 if (countPieces(current_pieces) >= (FILE_PIECES - countPieces(bitfield_)) && isInterestedBy(remote_peer)) {
460 int nb_interesting_pieces = 0;
461 // compute the number of interesting pieces
462 for (unsigned int i = 0; i < FILE_PIECES; i++)
463 if (remotePeerHasMissingPiece(remote_peer, i))
464 nb_interesting_pieces++;
466 xbt_assert(nb_interesting_pieces != 0);
467 // get a random interesting piece
468 int random_piece_index = random.uniform_int(0, nb_interesting_pieces - 1);
469 int current_index = 0;
470 for (unsigned int i = 0; i < FILE_PIECES; i++) {
471 if (remotePeerHasMissingPiece(remote_peer, i)) {
472 if (random_piece_index == current_index) {
479 xbt_assert(piece != -1);
482 // Random first policy
483 if (countPieces(bitfield_) < 4 && isInterestedByFree(remote_peer)) {
484 int nb_interesting_pieces = 0;
485 // compute the number of interesting pieces
486 for (unsigned int i = 0; i < FILE_PIECES; i++)
487 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
488 nb_interesting_pieces++;
489 xbt_assert(nb_interesting_pieces != 0);
490 // get a random interesting piece
491 int random_piece_index = random.uniform_int(0, nb_interesting_pieces - 1);
492 int current_index = 0;
493 for (unsigned int i = 0; i < FILE_PIECES; i++) {
494 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i)) {
495 if (random_piece_index == current_index) {
502 xbt_assert(piece != -1);
504 } else { // Rarest first policy
505 short min = SHRT_MAX;
506 int nb_min_pieces = 0;
507 int current_index = 0;
508 // compute the smallest number of copies of available pieces
509 for (unsigned int i = 0; i < FILE_PIECES; i++) {
510 if (pieces_count[i] < min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
511 min = pieces_count[i];
514 xbt_assert(min != SHRT_MAX || not isInterestedByFree(remote_peer));
515 // compute the number of rarest pieces
516 for (unsigned int i = 0; i < FILE_PIECES; i++)
517 if (pieces_count[i] == min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
520 xbt_assert(nb_min_pieces != 0 || not isInterestedByFree(remote_peer));
521 // get a random rarest piece
522 int random_rarest_index = 0;
523 if (nb_min_pieces > 0) {
524 random_rarest_index = random.uniform_int(0, nb_min_pieces - 1);
526 for (unsigned int i = 0; i < FILE_PIECES; i++)
527 if (pieces_count[i] == min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i)) {
528 if (random_rarest_index == current_index) {
535 xbt_assert(piece != -1 || not isInterestedByFree(remote_peer));
540 void Peer::updateChokedPeers()
542 if (nbInterestedPeers() == 0)
544 XBT_DEBUG("(%d) update_choked peers %zu active peers", id, active_peers.size());
545 // update the current round
546 round_ = (round_ + 1) % 3;
547 Connection* chosen_peer = nullptr;
548 // select first active peer and remove it from the set
549 Connection* choked_peer;
550 if (active_peers.empty()) {
551 choked_peer = nullptr;
553 choked_peer = *active_peers.begin();
554 active_peers.erase(choked_peer);
557 /**If we are currently seeding, we unchoke the peer which has been unchoked the last time.*/
559 double unchoke_time = simgrid::s4u::Engine::get_clock() + 1;
560 for (auto& kv : connected_peers) {
561 Connection& remote_peer = kv.second;
562 if (remote_peer.last_unchoke < unchoke_time && remote_peer.interested && remote_peer.choked_upload) {
563 unchoke_time = remote_peer.last_unchoke;
564 chosen_peer = &remote_peer;
568 // Random optimistic unchoking
572 // We choose a random peer to unchoke.
573 auto chosen_peer_it = connected_peers.begin();
574 std::advance(chosen_peer_it, random.uniform_int(0, static_cast<int>(connected_peers.size() - 1)));
575 chosen_peer = &chosen_peer_it->second;
576 if (not chosen_peer->interested || not chosen_peer->choked_upload)
577 chosen_peer = nullptr;
579 XBT_DEBUG("Nothing to do, keep going");
581 } while (chosen_peer == nullptr && j < MAXIMUM_PEERS);
583 // Use the "fastest download" policy.
584 double fastest_speed = 0.0;
585 for (auto& kv : connected_peers) {
586 Connection& remote_peer = kv.second;
587 if (remote_peer.peer_speed > fastest_speed && remote_peer.choked_upload && remote_peer.interested) {
588 fastest_speed = remote_peer.peer_speed;
589 chosen_peer = &remote_peer;
595 if (chosen_peer != nullptr)
596 XBT_DEBUG("(%d) update_choked peers unchoked (%d) ; int (%d) ; choked (%d) ", id, chosen_peer->id,
597 chosen_peer->interested, chosen_peer->choked_upload);
599 if (choked_peer != chosen_peer) {
600 if (choked_peer != nullptr) {
601 xbt_assert(not choked_peer->choked_upload, "Tries to choked a choked peer");
602 choked_peer->choked_upload = true;
603 updateActivePeersSet(choked_peer);
604 XBT_DEBUG("(%d) Sending a CHOKE to %d", id, choked_peer->id);
605 sendMessage(choked_peer->mailbox_, MessageType::CHOKE, message_size(MessageType::CHOKE));
607 if (chosen_peer != nullptr) {
608 xbt_assert((chosen_peer->choked_upload), "Tries to unchoked an unchoked peer");
609 chosen_peer->choked_upload = false;
610 active_peers.insert(chosen_peer);
611 chosen_peer->last_unchoke = simgrid::s4u::Engine::get_clock();
612 XBT_DEBUG("(%d) Sending a UNCHOKE to %d", id, chosen_peer->id);
613 updateActivePeersSet(chosen_peer);
614 sendMessage(chosen_peer->mailbox_, MessageType::UNCHOKE, message_size(MessageType::UNCHOKE));
619 /** @brief Update "interested" state of peers: send "not interested" to peers that don't have any more pieces we want.*/
620 void Peer::updateInterestedAfterReceive()
622 for (auto& kv : connected_peers) {
623 Connection& remote_peer = kv.second;
624 if (remote_peer.am_interested) {
625 bool interested = false;
626 // Check if the peer still has a piece we want.
627 for (unsigned int i = 0; i < FILE_PIECES; i++)
628 if (remotePeerHasMissingPiece(&remote_peer, i)) {
633 if (not interested) { // no more piece to download from connection
634 remote_peer.am_interested = false;
635 sendMessage(remote_peer.mailbox_, MessageType::NOTINTERESTED, message_size(MessageType::NOTINTERESTED));
641 void Peer::updateBitfieldBlocks(int piece, int block_index, int block_length)
643 xbt_assert((piece >= 0 && static_cast<unsigned int>(piece) <= FILE_PIECES), "Wrong piece.");
644 xbt_assert((block_index >= 0 && static_cast<unsigned int>(block_index) <= PIECES_BLOCKS), "Wrong block : %d.",
646 for (int i = block_index; i < (block_index + block_length); i++)
647 bitfield_blocks |= (1ULL << static_cast<unsigned int>(piece * PIECES_BLOCKS + i));
650 bool Peer::hasCompletedPiece(unsigned int piece) const
652 for (unsigned int i = 0; i < PIECES_BLOCKS; i++)
653 if (not(bitfield_blocks & 1ULL << (piece * PIECES_BLOCKS + i)))
658 int Peer::getFirstMissingBlockFrom(int piece) const
660 for (unsigned int i = 0; i < PIECES_BLOCKS; i++)
661 if (not(bitfield_blocks & 1ULL << (piece * PIECES_BLOCKS + i)))
666 /** Returns a piece that is partially downloaded and stored by the remote peer if any -1 otherwise. */
667 int Peer::partiallyDownloadedPiece(const Connection* remote_peer) const
669 for (unsigned int i = 0; i < FILE_PIECES; i++)
670 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i) && getFirstMissingBlockFrom(i) > 0)