1 /* Copyright (c) 2012-2022. 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");
14 namespace sg4 = simgrid::s4u;
17 * User parameters for transferred file data. For the test, the default values are :
18 * File size: 10 pieces * 5 blocks/piece * 16384 bytes/block = 819200 bytes
20 constexpr unsigned long FILE_PIECES = 10UL;
21 constexpr unsigned long PIECES_BLOCKS = 5UL;
22 constexpr int BLOCK_SIZE = 16384;
24 /** Number of blocks asked by each request */
25 constexpr unsigned long BLOCKS_REQUESTED = 2UL;
27 constexpr double SLEEP_DURATION = 1.0;
28 #define BITS_TO_BYTES(x) (((x) / 8 + (x) % 8) ? 1 : 0)
31 * Sizes based on report by A. Legout et al, Understanding BitTorrent: An Experimental Perspective
32 * http://hal.inria.fr/inria-00000156/en
34 constexpr unsigned message_size(MessageType type)
36 constexpr std::array<unsigned, 10> sizes{{/* HANDSHAKE */ 68,
40 /* NOTINTERESTED */ 5,
46 return sizes[static_cast<int>(type)];
49 constexpr const char* message_name(MessageType type)
51 constexpr std::array<const char*, 10> names{{"HANDSHAKE", "CHOKE", "UNCHOKE", "INTERESTED", "NOTINTERESTED", "HAVE",
52 "BITFIELD", "REQUEST", "PIECE", "CANCEL"}};
53 return names[static_cast<int>(type)];
56 Peer::Peer(std::vector<std::string> args)
59 xbt_assert(args.size() == 3 || args.size() == 4, "Wrong number of arguments");
61 id = std::stoi(args[1]);
62 mailbox_ = sg4::Mailbox::by_name(std::to_string(id));
63 } catch (const std::invalid_argument&) {
64 throw std::invalid_argument("Invalid ID:" + args[1]);
69 deadline = std::stod(args[2]);
70 } catch (const std::invalid_argument&) {
71 throw std::invalid_argument("Invalid deadline:" + args[2]);
73 xbt_assert(deadline > 0, "Wrong deadline supplied");
75 if (args.size() == 4 && args[3] == "1") {
76 bitfield_ = (1U << FILE_PIECES) - 1U;
77 bitfield_blocks = (1ULL << (FILE_PIECES * PIECES_BLOCKS)) - 1ULL;
79 pieces_count.resize(FILE_PIECES);
81 XBT_INFO("Hi, I'm joining the network with id %d", id);
84 /** Peer main function */
85 void Peer::operator()()
87 // Getting peer data from the tracker.
88 if (getPeersFromTracker()) {
89 XBT_DEBUG("Got %zu peers from the tracker. Current status is: %s", connected_peers.size(), getStatus().c_str());
90 begin_receive_time = sg4::Engine::get_clock();
91 mailbox_->set_receiver(sg4::Actor::self());
93 sendHandshakeToAllPeers();
99 XBT_INFO("Couldn't contact the tracker.");
102 XBT_INFO("Here is my current status: %s", getStatus().c_str());
105 bool Peer::getPeersFromTracker()
107 sg4::Mailbox* tracker_mailbox = sg4::Mailbox::by_name(TRACKER_MAILBOX);
108 // Build the task to send to the tracker
109 auto* peer_request = new TrackerQuery(id, mailbox_);
111 XBT_DEBUG("Sending a peer request to the tracker.");
112 tracker_mailbox->put(peer_request, TRACKER_COMM_SIZE, GET_PEERS_TIMEOUT);
113 } catch (const simgrid::TimeoutException&) {
114 XBT_DEBUG("Timeout expired when requesting peers to tracker");
120 auto answer = mailbox_->get_unique<TrackerAnswer>(GET_PEERS_TIMEOUT);
121 // Add the peers the tracker gave us to our peer list.
122 for (auto const& peer_id : answer->getPeers())
124 connected_peers.try_emplace(peer_id, peer_id);
125 } catch (const simgrid::TimeoutException&) {
126 XBT_DEBUG("Timeout expired when requesting peers to tracker");
132 void Peer::sendHandshakeToAllPeers()
134 for (auto const& kv : connected_peers) {
135 const Connection& remote_peer = kv.second;
136 auto* handshake = new Message(MessageType::HANDSHAKE, id, mailbox_);
137 remote_peer.mailbox_->put_init(handshake, message_size(MessageType::HANDSHAKE))->detach();
138 XBT_DEBUG("Sending a HANDSHAKE to %d", remote_peer.id);
142 void Peer::sendMessage(sg4::Mailbox* mailbox, MessageType type, uint64_t size)
144 XBT_DEBUG("Sending %s to %s", message_name(type), mailbox->get_cname());
145 mailbox->put_init(new Message(type, id, bitfield_, mailbox_), size)->detach();
148 void Peer::sendBitfield(sg4::Mailbox* mailbox)
150 XBT_DEBUG("Sending a BITFIELD to %s", mailbox->get_cname());
152 ->put_init(new Message(MessageType::BITFIELD, id, bitfield_, mailbox_),
153 message_size(MessageType::BITFIELD) + BITS_TO_BYTES(FILE_PIECES))
157 void Peer::sendPiece(sg4::Mailbox* mailbox, unsigned int piece, int block_index, int block_length)
159 xbt_assert(not hasNotPiece(piece), "Tried to send a unavailable piece.");
160 XBT_DEBUG("Sending the PIECE %u (%d,%d) to %s", piece, block_index, block_length, mailbox->get_cname());
161 mailbox->put_init(new Message(MessageType::PIECE, id, mailbox_, piece, block_index, block_length), BLOCK_SIZE)
165 void Peer::sendHaveToAllPeers(unsigned int piece)
167 XBT_DEBUG("Sending HAVE message to all my peers");
168 for (auto const& kv : connected_peers) {
169 const Connection& remote_peer = kv.second;
170 remote_peer.mailbox_->put_init(new Message(MessageType::HAVE, id, mailbox_, piece), message_size(MessageType::HAVE))
175 void Peer::sendRequestTo(Connection* remote_peer, unsigned int piece)
177 remote_peer->current_piece = piece;
178 xbt_assert(remote_peer->hasPiece(piece));
179 int block_index = getFirstMissingBlockFrom(piece);
180 if (block_index != -1) {
181 int block_length = static_cast<int>(std::min(BLOCKS_REQUESTED, PIECES_BLOCKS - block_index));
182 XBT_DEBUG("Sending a REQUEST to %s for piece %u (%d,%d)", remote_peer->mailbox_->get_cname(), piece, block_index,
184 remote_peer->mailbox_
185 ->put_init(new Message(MessageType::REQUEST, id, mailbox_, piece, block_index, block_length),
186 message_size(MessageType::REQUEST))
191 std::string Peer::getStatus() const
194 for (unsigned i = 0; i < FILE_PIECES; i++)
195 res += (bitfield_ & (1U << i)) ? '1' : '0';
199 bool Peer::hasFinished() const
201 return bitfield_ == (1U << FILE_PIECES) - 1U;
204 /** Indicates if the remote peer has a piece not stored by the local peer */
205 bool Peer::isInterestedBy(const Connection* remote_peer) const
207 return remote_peer->bitfield & (bitfield_ ^ ((1 << FILE_PIECES) - 1));
210 bool Peer::isInterestedByFree(const Connection* remote_peer) const
212 for (unsigned int i = 0; i < FILE_PIECES; i++)
213 if (hasNotPiece(i) && remote_peer->hasPiece(i) && isNotDownloadingPiece(i))
218 void Peer::updatePiecesCountFromBitfield(unsigned int bitfield)
220 for (unsigned int i = 0; i < FILE_PIECES; i++)
221 if (bitfield & (1U << i))
225 unsigned int Peer::countPieces(unsigned int bitfield) const
227 unsigned int count = 0U;
228 unsigned int n = bitfield;
236 int Peer::nbInterestedPeers() const
238 return static_cast<int>(std::count_if(connected_peers.begin(), connected_peers.end(),
239 [](const auto& kv) { return kv.second.interested; }));
244 double next_choked_update = sg4::Engine::get_clock() + UPDATE_CHOKED_INTERVAL;
245 XBT_DEBUG("Start downloading.");
247 /* Send a "handshake" message to all the peers it got (since it couldn't have gotten more than 50 peers) */
248 sendHandshakeToAllPeers();
249 XBT_DEBUG("Starting main leech loop listening on mailbox: %s", mailbox_->get_cname());
251 while (sg4::Engine::get_clock() < deadline && countPieces(bitfield_) < FILE_PIECES) {
252 if (comm_received == nullptr) {
253 comm_received = mailbox_->get_async<Message>(&message);
255 if (comm_received->test()) {
258 comm_received = nullptr;
260 // We don't execute the choke algorithm if we don't already have a piece
261 if (sg4::Engine::get_clock() >= next_choked_update && countPieces(bitfield_) > 0) {
263 next_choked_update += UPDATE_CHOKED_INTERVAL;
265 sg4::this_actor::sleep_for(SLEEP_DURATION);
270 XBT_DEBUG("%d becomes a seeder", id);
275 double next_choked_update = sg4::Engine::get_clock() + UPDATE_CHOKED_INTERVAL;
276 XBT_DEBUG("Start seeding.");
277 // start the main seed loop
278 while (sg4::Engine::get_clock() < deadline) {
279 if (comm_received == nullptr) {
280 comm_received = mailbox_->get_async<Message>(&message);
282 if (comm_received->test()) {
285 comm_received = nullptr;
287 if (sg4::Engine::get_clock() >= next_choked_update) {
289 // TODO: Change the choked peer algorithm when seeding.
290 next_choked_update += UPDATE_CHOKED_INTERVAL;
292 sg4::this_actor::sleep_for(SLEEP_DURATION);
298 void Peer::updateActivePeersSet(Connection* remote_peer)
300 if (remote_peer->interested && not remote_peer->choked_upload)
301 active_peers.insert(remote_peer);
303 active_peers.erase(remote_peer);
306 void Peer::handleMessage()
308 XBT_DEBUG("Received a %s message from %s", message_name(message->type), message->return_mailbox->get_cname());
310 auto known_peer = connected_peers.find(message->peer_id);
311 Connection* remote_peer = (known_peer == connected_peers.end()) ? nullptr : &known_peer->second;
312 xbt_assert(remote_peer != nullptr || message->type == MessageType::HANDSHAKE,
313 "The impossible did happened: A not-in-our-list peer sent us a message.");
315 switch (message->type) {
316 case MessageType::HANDSHAKE:
317 // Check if the peer is in our connection list.
318 if (remote_peer == nullptr) {
319 XBT_DEBUG("This peer %d was unknown, answer to its handshake", message->peer_id);
320 connected_peers.try_emplace(message->peer_id, message->peer_id);
321 sendMessage(message->return_mailbox, MessageType::HANDSHAKE, message_size(MessageType::HANDSHAKE));
323 // Send our bitfield to the peer
324 sendBitfield(message->return_mailbox);
326 case MessageType::BITFIELD:
327 // Update the pieces list
328 updatePiecesCountFromBitfield(message->bitfield);
329 // Store the bitfield
330 remote_peer->bitfield = message->bitfield;
331 xbt_assert(not remote_peer->am_interested, "Should not be interested at first");
332 if (isInterestedBy(remote_peer)) {
333 remote_peer->am_interested = true;
334 sendMessage(message->return_mailbox, MessageType::INTERESTED, message_size(MessageType::INTERESTED));
337 case MessageType::INTERESTED:
338 // Update the interested state of the peer.
339 remote_peer->interested = true;
340 updateActivePeersSet(remote_peer);
342 case MessageType::NOTINTERESTED:
343 remote_peer->interested = false;
344 updateActivePeersSet(remote_peer);
346 case MessageType::UNCHOKE:
347 xbt_assert(remote_peer->choked_download);
348 remote_peer->choked_download = false;
349 // Send requests to the peer, since it has unchoked us
350 if (remote_peer->am_interested)
351 requestNewPieceTo(remote_peer);
353 case MessageType::CHOKE:
354 xbt_assert(not remote_peer->choked_download);
355 remote_peer->choked_download = true;
356 if (remote_peer->current_piece != -1)
357 removeCurrentPiece(remote_peer, remote_peer->current_piece);
359 case MessageType::HAVE:
360 XBT_DEBUG("\t for piece %d", message->piece);
361 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
362 "Wrong HAVE message received");
363 remote_peer->bitfield = remote_peer->bitfield | (1U << static_cast<unsigned int>(message->piece));
364 pieces_count[message->piece]++;
365 // If the piece is in our pieces, we tell the peer that we are interested.
366 if (not remote_peer->am_interested && hasNotPiece(message->piece)) {
367 remote_peer->am_interested = true;
368 sendMessage(message->return_mailbox, MessageType::INTERESTED, message_size(MessageType::INTERESTED));
369 if (not remote_peer->choked_download)
370 requestNewPieceTo(remote_peer);
373 case MessageType::REQUEST:
374 xbt_assert(remote_peer->interested);
375 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
376 "Wrong HAVE message received");
377 if (not remote_peer->choked_upload) {
378 XBT_DEBUG("\t for piece %d (%d,%d)", message->piece, message->block_index,
379 message->block_index + message->block_length);
380 if (not hasNotPiece(message->piece)) {
381 sendPiece(message->return_mailbox, message->piece, message->block_index, message->block_length);
384 XBT_DEBUG("\t for piece %d but he is choked.", message->peer_id);
387 case MessageType::PIECE:
388 XBT_DEBUG(" \t for piece %d (%d,%d)", message->piece, message->block_index,
389 message->block_index + message->block_length);
390 xbt_assert(not remote_peer->choked_download);
391 xbt_assert(not remote_peer->choked_download, "Can't received a piece if I'm choked !");
392 xbt_assert((message->piece >= 0 && static_cast<unsigned int>(message->piece) < FILE_PIECES),
393 "Wrong piece received");
394 // TODO: Execute a computation.
395 if (hasNotPiece(static_cast<unsigned int>(message->piece))) {
396 updateBitfieldBlocks(message->piece, message->block_index, message->block_length);
397 if (hasCompletedPiece(static_cast<unsigned int>(message->piece))) {
398 // Removing the piece from our piece list
399 removeCurrentPiece(remote_peer, message->piece);
400 // Setting the fact that we have the piece
401 bitfield_ = bitfield_ | (1U << static_cast<unsigned int>(message->piece));
402 XBT_DEBUG("My status is now %s", getStatus().c_str());
403 // Sending the information to all the peers we are connected to
404 sendHaveToAllPeers(message->piece);
405 // sending UNINTERESTED to peers that do not have what we want.
406 updateInterestedAfterReceive();
407 } else { // piece not completed
408 sendRequestTo(remote_peer, message->piece); // ask for the next block
411 XBT_DEBUG("However, we already have it");
412 requestNewPieceTo(remote_peer);
415 case MessageType::CANCEL:
420 // Update the peer speed.
422 remote_peer->addSpeedValue(1.0 / (sg4::Engine::get_clock() - begin_receive_time));
424 begin_receive_time = sg4::Engine::get_clock();
427 /** Selects the appropriate piece to download and requests it to the remote_peer */
428 void Peer::requestNewPieceTo(Connection* remote_peer)
430 int piece = selectPieceToDownload(remote_peer);
432 current_pieces |= (1U << (unsigned int)piece);
433 sendRequestTo(remote_peer, piece);
437 void Peer::removeCurrentPiece(Connection* remote_peer, unsigned int current_piece)
439 current_pieces &= ~(1U << current_piece);
440 remote_peer->current_piece = -1;
443 /** @brief Return the piece to be downloaded
444 * There are two cases (as described in "Bittorrent Architecture Protocol", Ryan Toole :
445 * If a piece is partially downloaded, this piece will be selected prioritarily
446 * If the peer has strictly less than 4 pieces, he chooses a piece at random.
447 * If the peer has more than pieces, he downloads the pieces that are the less replicated (rarest policy).
448 * If all pieces have been downloaded or requested, we select a random requested piece (endgame mode).
449 * @param remote_peer: information about the connection
450 * @return the piece to download if possible. -1 otherwise
452 int Peer::selectPieceToDownload(const Connection* remote_peer)
454 int piece = partiallyDownloadedPiece(remote_peer);
455 // strict priority policy
460 if (countPieces(current_pieces) >= (FILE_PIECES - countPieces(bitfield_)) && isInterestedBy(remote_peer)) {
461 int nb_interesting_pieces = 0;
462 // compute the number of interesting pieces
463 for (unsigned int i = 0; i < FILE_PIECES; i++)
464 if (remotePeerHasMissingPiece(remote_peer, i))
465 nb_interesting_pieces++;
467 xbt_assert(nb_interesting_pieces != 0);
468 // get a random interesting piece
469 int random_piece_index = random.uniform_int(0, nb_interesting_pieces - 1);
470 int current_index = 0;
471 for (unsigned int i = 0; i < FILE_PIECES; i++) {
472 if (remotePeerHasMissingPiece(remote_peer, i)) {
473 if (random_piece_index == current_index) {
480 xbt_assert(piece != -1);
483 // Random first policy
484 if (countPieces(bitfield_) < 4 && isInterestedByFree(remote_peer)) {
485 int nb_interesting_pieces = 0;
486 // compute the number of interesting pieces
487 for (unsigned int i = 0; i < FILE_PIECES; i++)
488 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
489 nb_interesting_pieces++;
490 xbt_assert(nb_interesting_pieces != 0);
491 // get a random interesting piece
492 int random_piece_index = random.uniform_int(0, nb_interesting_pieces - 1);
493 int current_index = 0;
494 for (unsigned int i = 0; i < FILE_PIECES; i++) {
495 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i)) {
496 if (random_piece_index == current_index) {
503 xbt_assert(piece != -1);
505 } else { // Rarest first policy
506 short min = SHRT_MAX;
507 int nb_min_pieces = 0;
508 int current_index = 0;
509 // compute the smallest number of copies of available pieces
510 for (unsigned int i = 0; i < FILE_PIECES; i++) {
511 if (pieces_count[i] < min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
512 min = pieces_count[i];
515 xbt_assert(min != SHRT_MAX || not isInterestedByFree(remote_peer));
516 // compute the number of rarest pieces
517 for (unsigned int i = 0; i < FILE_PIECES; i++)
518 if (pieces_count[i] == min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i))
521 xbt_assert(nb_min_pieces != 0 || not isInterestedByFree(remote_peer));
522 // get a random rarest piece
523 int random_rarest_index = 0;
524 if (nb_min_pieces > 0) {
525 random_rarest_index = random.uniform_int(0, nb_min_pieces - 1);
527 for (unsigned int i = 0; i < FILE_PIECES; i++)
528 if (pieces_count[i] == min && remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i)) {
529 if (random_rarest_index == current_index) {
536 xbt_assert(piece != -1 || not isInterestedByFree(remote_peer));
541 void Peer::updateChokedPeers()
543 if (nbInterestedPeers() == 0)
545 XBT_DEBUG("(%d) update_choked peers %zu active peers", id, active_peers.size());
546 // update the current round
547 round_ = (round_ + 1) % 3;
548 Connection* chosen_peer = nullptr;
549 // select first active peer and remove it from the set
550 Connection* choked_peer;
551 if (active_peers.empty()) {
552 choked_peer = nullptr;
554 choked_peer = *active_peers.begin();
555 active_peers.erase(choked_peer);
558 /**If we are currently seeding, we unchoke the peer which has been unchoked the last time.*/
560 double unchoke_time = sg4::Engine::get_clock() + 1;
561 for (auto& kv : connected_peers) {
562 Connection& remote_peer = kv.second;
563 if (remote_peer.last_unchoke < unchoke_time && remote_peer.interested && remote_peer.choked_upload) {
564 unchoke_time = remote_peer.last_unchoke;
565 chosen_peer = &remote_peer;
569 // Random optimistic unchoking
573 // We choose a random peer to unchoke.
574 auto chosen_peer_it = connected_peers.begin();
575 std::advance(chosen_peer_it, random.uniform_int(0, static_cast<int>(connected_peers.size() - 1)));
576 chosen_peer = &chosen_peer_it->second;
577 if (not chosen_peer->interested || not chosen_peer->choked_upload)
578 chosen_peer = nullptr;
580 XBT_DEBUG("Nothing to do, keep going");
582 } while (chosen_peer == nullptr && j < MAXIMUM_PEERS);
584 // Use the "fastest download" policy.
585 double fastest_speed = 0.0;
586 for (auto& kv : connected_peers) {
587 Connection& remote_peer = kv.second;
588 if (remote_peer.peer_speed > fastest_speed && remote_peer.choked_upload && remote_peer.interested) {
589 fastest_speed = remote_peer.peer_speed;
590 chosen_peer = &remote_peer;
596 if (chosen_peer != nullptr)
597 XBT_DEBUG("(%d) update_choked peers unchoked (%d) ; int (%d) ; choked (%d) ", id, chosen_peer->id,
598 chosen_peer->interested, chosen_peer->choked_upload);
600 if (choked_peer != chosen_peer) {
601 if (choked_peer != nullptr) {
602 xbt_assert(not choked_peer->choked_upload, "Tries to choked a choked peer");
603 choked_peer->choked_upload = true;
604 updateActivePeersSet(choked_peer);
605 XBT_DEBUG("(%d) Sending a CHOKE to %d", id, choked_peer->id);
606 sendMessage(choked_peer->mailbox_, MessageType::CHOKE, message_size(MessageType::CHOKE));
608 if (chosen_peer != nullptr) {
609 xbt_assert((chosen_peer->choked_upload), "Tries to unchoked an unchoked peer");
610 chosen_peer->choked_upload = false;
611 active_peers.insert(chosen_peer);
612 chosen_peer->last_unchoke = sg4::Engine::get_clock();
613 XBT_DEBUG("(%d) Sending a UNCHOKE to %d", id, chosen_peer->id);
614 updateActivePeersSet(chosen_peer);
615 sendMessage(chosen_peer->mailbox_, MessageType::UNCHOKE, message_size(MessageType::UNCHOKE));
620 /** @brief Update "interested" state of peers: send "not interested" to peers that don't have any more pieces we want.*/
621 void Peer::updateInterestedAfterReceive()
623 for (auto& kv : connected_peers) {
624 Connection& remote_peer = kv.second;
625 if (remote_peer.am_interested) {
626 bool interested = false;
627 // Check if the peer still has a piece we want.
628 for (unsigned int i = 0; i < FILE_PIECES; i++)
629 if (remotePeerHasMissingPiece(&remote_peer, i)) {
634 if (not interested) { // no more piece to download from connection
635 remote_peer.am_interested = false;
636 sendMessage(remote_peer.mailbox_, MessageType::NOTINTERESTED, message_size(MessageType::NOTINTERESTED));
642 void Peer::updateBitfieldBlocks(int piece, int block_index, int block_length)
644 xbt_assert((piece >= 0 && static_cast<unsigned int>(piece) <= FILE_PIECES), "Wrong piece.");
645 xbt_assert((block_index >= 0 && static_cast<unsigned int>(block_index) <= PIECES_BLOCKS), "Wrong block : %d.",
647 for (int i = block_index; i < (block_index + block_length); i++)
648 bitfield_blocks |= (1ULL << static_cast<unsigned int>(piece * PIECES_BLOCKS + i));
651 bool Peer::hasCompletedPiece(unsigned int piece) const
653 for (unsigned int i = 0; i < PIECES_BLOCKS; i++)
654 if (not(bitfield_blocks & 1ULL << (piece * PIECES_BLOCKS + i)))
659 int Peer::getFirstMissingBlockFrom(int piece) const
661 for (unsigned int i = 0; i < PIECES_BLOCKS; i++)
662 if (not(bitfield_blocks & 1ULL << (piece * PIECES_BLOCKS + i)))
667 /** Returns a piece that is partially downloaded and stored by the remote peer if any -1 otherwise. */
668 int Peer::partiallyDownloadedPiece(const Connection* remote_peer) const
670 for (unsigned int i = 0; i < FILE_PIECES; i++)
671 if (remotePeerHasMissingPiece(remote_peer, i) && isNotDownloadingPiece(i) && getFirstMissingBlockFrom(i) > 0)