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transmission/libtransmission/handshake.cc

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// This file Copyright © 2017-2023 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#include <algorithm>
#include <array>
#include <cerrno>
#include <chrono>
#include <string_view>
#include <utility>
#include <fmt/core.h>
#include "libtransmission/transmission.h"
#include "libtransmission/bitfield.h"
#include "libtransmission/clients.h"
#include "libtransmission/crypto-utils.h"
#include "libtransmission/handshake.h"
#include "libtransmission/log.h"
#include "libtransmission/peer-io.h"
#include "libtransmission/timer.h"
#include "libtransmission/tr-assert.h"
#include "libtransmission/tr-buffer.h"
#include "libtransmission/utils.h"
#define tr_logAddTraceHand(handshake, msg) tr_logAddTrace(msg, (handshake)->peer_io_->display_name())
using namespace std::literals;
using DH = tr_message_stream_encryption::DH;
bool tr_handshake::build_handshake_message(tr_peerIo* io, uint8_t* buf) const
{
auto const& info_hash = io->torrent_hash();
TR_ASSERT_MSG(info_hash != tr_sha1_digest_t{}, "build_handshake_message requires an info_hash");
auto const info = mediator_->torrent(info_hash);
if (!info)
{
return false;
}
auto flags = tr_bitfield{ HandshakeFlagsBits };
flags.set(LtepFlag);
flags.set(FextFlag);
if (mediator_->allows_dht())
{
flags.set(DhtFlag);
}
auto const flag_bytes = flags.raw();
[[maybe_unused]] auto* walk = buf;
walk = std::copy_n(reinterpret_cast<uint8_t const*>(std::data(HandshakeName)), std::size(HandshakeName), walk);
walk = std::copy(std::begin(flag_bytes), std::end(flag_bytes), walk);
walk = std::copy_n(reinterpret_cast<char const*>(std::data(info_hash)), std::size(info_hash), walk);
walk = std::copy(std::begin(info->client_peer_id), std::end(info->client_peer_id), walk);
TR_ASSERT(walk - buf == HandshakeSize);
return true;
}
tr_handshake::ParseResult tr_handshake::parse_handshake(tr_peerIo* peer_io)
{
tr_logAddTraceHand(this, fmt::format("payload: need {}, got {}", HandshakeSize, peer_io->read_buffer_size()));
if (peer_io->read_buffer_size() < HandshakeSize)
{
return ParseResult::EncryptionWrong;
}
/* confirm the protocol */
auto name = decltype(HandshakeName){};
peer_io->read_bytes(std::data(name), std::size(name));
if (name != HandshakeName)
{
return ParseResult::EncryptionWrong;
}
/* read the reserved bytes */
auto flags = tr_bitfield{ HandshakeFlagsBits };
auto reserved = std::array<uint8_t, HandshakeFlagsBytes>{};
peer_io->read_bytes(std::data(reserved), std::size(reserved));
flags.set_raw(std::data(reserved), std::size(reserved));
peer_io->set_supports_dht(flags.test(DhtFlag));
peer_io->set_supports_ltep(flags.test(LtepFlag));
peer_io->set_supports_fext(flags.test(FextFlag));
// torrent hash
auto info_hash = tr_sha1_digest_t{};
peer_io->read_bytes(std::data(info_hash), std::size(info_hash));
if (info_hash == tr_sha1_digest_t{} || info_hash != peer_io->torrent_hash())
{
tr_logAddTraceHand(this, "peer returned the wrong hash. wtf?");
return ParseResult::BadTorrent;
}
// peer_id
auto peer_id = tr_peer_id_t{};
peer_io->read_bytes(std::data(peer_id), std::size(peer_id));
set_peer_id(peer_id);
/* peer id */
auto const peer_id_sv = std::string_view{ std::data(peer_id), std::size(peer_id) };
tr_logAddTraceHand(this, fmt::format("peer-id is '{}'", peer_id_sv));
if (auto const info = mediator_->torrent(info_hash); info && info->client_peer_id == peer_id)
{
tr_logAddTraceHand(this, "streuth! we've connected to ourselves.");
return ParseResult::PeerIsSelf;
}
return ParseResult::Ok;
}
// --- Outgoing Connections
// 1 A->B: our public key (Ya) and some padding (PadA)
void tr_handshake::send_ya(tr_peerIo* io)
{
send_public_key_and_pad<PadaMaxlen>(io);
set_state(tr_handshake::State::AwaitingYb);
}
[[nodiscard]] uint32_t tr_handshake::get_crypto_select(tr_encryption_mode encryption_mode, uint32_t crypto_provide) noexcept
{
auto choices = std::array<uint32_t, 2>{};
int n_choices = 0;
switch (encryption_mode)
{
case TR_ENCRYPTION_REQUIRED:
choices[n_choices++] = CryptoProvideCrypto;
break;
case TR_ENCRYPTION_PREFERRED:
choices[n_choices++] = CryptoProvideCrypto;
choices[n_choices++] = CryptoProvidePlaintext;
break;
case TR_CLEAR_PREFERRED:
choices[n_choices++] = CryptoProvidePlaintext;
choices[n_choices++] = CryptoProvideCrypto;
break;
}
for (auto const& choice : choices)
{
if ((crypto_provide & choice) != 0)
{
return choice;
}
}
return 0;
}
ReadState tr_handshake::read_yb(tr_peerIo* peer_io)
{
if (peer_io->read_buffer_size() < std::size(HandshakeName))
{
return READ_LATER;
}
bool const is_encrypted = !peer_io->read_buffer_starts_with(HandshakeName);
auto peer_public_key = DH::key_bigend_t{};
if (is_encrypted && (peer_io->read_buffer_size() < std::size(peer_public_key)))
{
return READ_LATER;
}
tr_logAddTraceHand(this, is_encrypted ? "got an encrypted handshake" : "got a plain handshake");
if (!is_encrypted)
{
set_state(tr_handshake::State::AwaitingHandshake);
return READ_NOW;
}
set_have_read_anything_from_peer(true);
// get the peer's public key
peer_io->read_bytes(std::data(peer_public_key), std::size(peer_public_key));
dh_.setPeerPublicKey(peer_public_key);
/* now send these: HASH('req1', S), HASH('req2', SKEY) xor HASH('req3', S),
* ENCRYPT(VC, crypto_provide, len(PadC), PadC, len(IA)), ENCRYPT(IA) */
auto outbuf = libtransmission::Buffer{};
/* HASH('req1', S) */
outbuf.add(tr_sha1::digest("req1"sv, dh_.secret()));
auto const& info_hash = peer_io->torrent_hash();
TR_ASSERT_MSG(info_hash != tr_sha1_digest_t{}, "readYb requires an info_hash");
/* HASH('req2', SKEY) xor HASH('req3', S) */
{
auto const req2 = tr_sha1::digest("req2"sv, info_hash);
auto const req3 = tr_sha1::digest("req3"sv, dh_.secret());
auto x_or = tr_sha1_digest_t{};
for (size_t i = 0, n = std::size(x_or); i < n; ++i)
{
x_or[i] = req2[i] ^ req3[i];
}
outbuf.add(x_or);
}
/* ENCRYPT(VC, crypto_provide, len(PadC), PadC
* PadC is reserved for future extensions to the handshake...
* standard practice at this time is for it to be zero-length */
peer_io->write(outbuf, false);
peer_io->encrypt_init(peer_io->is_incoming(), dh_, info_hash);
outbuf.add(VC);
outbuf.add_uint32(crypto_provide());
outbuf.add_uint16(0);
/* ENCRYPT len(IA)), ENCRYPT(IA) */
if (auto msg = std::array<uint8_t, HandshakeSize>{}; build_handshake_message(peer_io, std::data(msg)))
{
outbuf.add_uint16(std::size(msg));
outbuf.add(msg);
have_sent_bittorrent_handshake_ = true;
}
else
{
return done(false);
}
/* send it */
set_state(State::AwaitingVc);
peer_io->write(outbuf, false);
return READ_NOW;
}
// MSE spec: "Since the length of [PadB is] unknown,
// A will be able to resynchronize on ENCRYPT(VC)"
ReadState tr_handshake::read_vc(tr_peerIo* peer_io)
{
auto const info_hash = peer_io->torrent_hash();
TR_ASSERT_MSG(info_hash != tr_sha1_digest_t{}, "readVC requires an info_hash");
// We need to find the end of PadB by looking for `ENCRYPT(VC)`,
// so calculate and cache the value of `ENCRYPT(VC)`.
if (!encrypted_vc_)
{
auto needle = VC;
auto filter = tr_message_stream_encryption::Filter{};
filter.encryptInit(true, dh_, info_hash);
filter.encrypt(std::size(needle), std::data(needle));
encrypted_vc_ = needle;
}
for (size_t i = 0; i < PadbMaxlen; ++i)
{
if (peer_io->read_buffer_size() < std::size(*encrypted_vc_))
{
tr_logAddTraceHand(this, "not enough bytes... returning read_more");
return READ_LATER;
}
if (peer_io->read_buffer_starts_with(*encrypted_vc_))
{
tr_logAddTraceHand(this, "got it!");
// We already know it's a match; now we just need to
// consume it from the read buffer.
peer_io->decrypt_init(peer_io->is_incoming(), dh_, info_hash);
peer_io->read_bytes(std::data(*encrypted_vc_), std::size(*encrypted_vc_));
set_state(tr_handshake::State::AwaitingCryptoSelect);
return READ_NOW;
}
peer_io->read_buffer_drain(1);
}
tr_logAddTraceHand(this, "couldn't find ENCRYPT(VC)");
return done(false);
}
ReadState tr_handshake::read_crypto_select(tr_peerIo* peer_io)
{
if (static size_t constexpr NeedLen = sizeof(uint32_t) + sizeof(uint16_t); peer_io->read_buffer_size() < NeedLen)
{
return READ_LATER;
}
auto crypto_select = uint32_t{};
peer_io->read_uint32(&crypto_select);
crypto_select_ = crypto_select;
tr_logAddTraceHand(this, fmt::format("crypto select is {}", crypto_select));
if ((crypto_select & crypto_provide()) == 0)
{
tr_logAddTraceHand(this, "peer selected an encryption option we didn't offer");
return done(false);
}
uint16_t pad_d_len = 0;
peer_io->read_uint16(&pad_d_len);
tr_logAddTraceHand(this, fmt::format("pad_d_len is {}", pad_d_len));
if (pad_d_len > 512)
{
tr_logAddTraceHand(this, "encryption handshake: pad_d_len is too long");
return done(false);
}
pad_d_len_ = pad_d_len;
set_state(tr_handshake::State::AwaitingPadD);
return READ_NOW;
}
ReadState tr_handshake::read_pad_d(tr_peerIo* peer_io)
{
size_t const needlen = pad_d_len_;
tr_logAddTraceHand(this, fmt::format("pad d: need {}, got {}", needlen, peer_io->read_buffer_size()));
if (peer_io->read_buffer_size() < needlen)
{
return READ_LATER;
}
peer_io->read_buffer_drain(needlen);
set_state(tr_handshake::State::AwaitingHandshake);
return READ_NOW;
}
// --- Incoming Connections
ReadState tr_handshake::read_handshake(tr_peerIo* peer_io)
{
static auto constexpr Needlen = IncomingHandshakeLen;
tr_logAddTraceHand(this, fmt::format("payload: need {}, got {}", Needlen, peer_io->read_buffer_size()));
if (peer_io->read_buffer_size() < Needlen)
{
return READ_LATER;
}
set_have_read_anything_from_peer(true);
if (peer_io->read_buffer_starts_with(HandshakeName)) // unencrypted
{
if (encryption_mode_ == TR_ENCRYPTION_REQUIRED)
{
tr_logAddTraceHand(this, "peer is unencrypted, and we're disallowing that");
return done(false);
}
}
else // either encrypted or corrupt
{
if (is_incoming())
{
tr_logAddTraceHand(this, "I think peer is sending us an encrypted handshake...");
set_state(tr_handshake::State::AwaitingYa);
return READ_NOW;
}
}
auto name = decltype(HandshakeName){};
peer_io->read_bytes(std::data(name), std::size(name));
if (name != HandshakeName)
{
return done(false);
}
// reserved bytes / flags
auto reserved = std::array<uint8_t, HandshakeFlagsBytes>{};
auto flags = tr_bitfield{ HandshakeFlagsBits };
peer_io->read_bytes(std::data(reserved), std::size(reserved));
flags.set_raw(std::data(reserved), std::size(reserved));
peer_io->set_supports_dht(flags.test(DhtFlag));
peer_io->set_supports_ltep(flags.test(LtepFlag));
peer_io->set_supports_fext(flags.test(FextFlag));
/* torrent hash */
auto hash = tr_sha1_digest_t{};
peer_io->read_bytes(std::data(hash), std::size(hash));
if (is_incoming())
{
if (!mediator_->torrent(hash))
{
tr_logAddTraceHand(this, "peer is trying to connect to us for a torrent we don't have.");
return done(false);
}
peer_io->set_torrent_hash(hash);
}
else // outgoing
{
if (peer_io->torrent_hash() != hash)
{
tr_logAddTraceHand(this, "peer returned the wrong hash. wtf?");
return done(false);
}
}
// If it's an incoming message, we need to send a response handshake
if (!have_sent_bittorrent_handshake_)
{
auto msg = std::array<uint8_t, HandshakeSize>{};
if (!build_handshake_message(peer_io, std::data(msg)))
{
return done(false);
}
peer_io->write_bytes(std::data(msg), std::size(msg), false);
have_sent_bittorrent_handshake_ = true;
}
set_state(State::AwaitingPeerId);
return READ_NOW;
}
ReadState tr_handshake::read_peer_id(tr_peerIo* peer_io)
{
// read the peer_id
auto peer_id = tr_peer_id_t{};
if (peer_io->read_buffer_size() < std::size(peer_id))
{
return READ_LATER;
}
peer_io->read_bytes(std::data(peer_id), std::size(peer_id));
set_peer_id(peer_id);
auto client = std::array<char, 128>{};
tr_clientForId(std::data(client), std::size(client), peer_id);
tr_logAddTraceHand(this, fmt::format("peer-id is '{}' ... isIncoming is {}", std::data(client), is_incoming()));
// if we've somehow connected to ourselves, don't keep the connection
auto const info_hash = peer_io_->torrent_hash();
auto const info = mediator_->torrent(info_hash);
auto const connected_to_self = info && info->client_peer_id == peer_id;
return done(!connected_to_self);
}
ReadState tr_handshake::read_ya(tr_peerIo* peer_io)
{
auto peer_public_key = DH::key_bigend_t{};
tr_logAddTraceHand(
this,
fmt::format("in readYa... need {}, have {}", std::size(peer_public_key), peer_io->read_buffer_size()));
if (peer_io->read_buffer_size() < std::size(peer_public_key))
{
return READ_LATER;
}
/* read the incoming peer's public key */
peer_io->read_bytes(std::data(peer_public_key), std::size(peer_public_key));
dh_.setPeerPublicKey(peer_public_key);
// send our public key to the peer
tr_logAddTraceHand(this, "sending B->A: Diffie Hellman Yb, PadB");
send_public_key_and_pad<PadbMaxlen>(peer_io);
set_state(State::AwaitingPadA);
return READ_NOW;
}
ReadState tr_handshake::read_pad_a(tr_peerIo* peer_io)
{
// find the end of PadA by looking for HASH('req1', S)
auto const needle = tr_sha1::digest("req1"sv, dh_.secret());
for (size_t i = 0; i < PadaMaxlen; ++i)
{
if (peer_io->read_buffer_size() < std::size(needle))
{
tr_logAddTraceHand(this, "not enough bytes... returning read_more");
return READ_LATER;
}
if (peer_io->read_buffer_starts_with(needle))
{
tr_logAddTraceHand(this, "found it... looking setting to awaiting_crypto_provide");
peer_io->read_buffer_drain(std::size(needle));
set_state(State::AwaitingCryptoProvide);
return READ_NOW;
}
peer_io->read_buffer_drain(1U);
}
tr_logAddTraceHand(this, "couldn't find HASH('req', S)");
return done(false);
}
ReadState tr_handshake::read_crypto_provide(tr_peerIo* peer_io)
{
/* HASH('req2', SKEY) xor HASH('req3', S), ENCRYPT(VC, crypto_provide, len(PadC)) */
uint16_t padc_len = 0;
uint32_t crypto_provide = 0;
auto obfuscated_hash = tr_sha1_digest_t{};
size_t const needlen = sizeof(obfuscated_hash) + /* HASH('req2', SKEY) xor HASH('req3', S) */
std::size(VC) + sizeof(crypto_provide) + sizeof(padc_len);
if (peer_io->read_buffer_size() < needlen)
{
return READ_LATER;
}
/* This next piece is HASH('req2', SKEY) xor HASH('req3', S) ...
* we can get the first half of that (the obfuscatedTorrentHash)
* by building the latter and xor'ing it with what the peer sent us */
tr_logAddTraceHand(this, "reading obfuscated torrent hash...");
auto req2 = tr_sha1_digest_t{};
peer_io->read_bytes(std::data(req2), std::size(req2));
auto const req3 = tr_sha1::digest("req3"sv, dh_.secret());
for (size_t i = 0; i < std::size(obfuscated_hash); ++i)
{
obfuscated_hash[i] = req2[i] ^ req3[i];
}
if (auto const info = mediator_->torrent_from_obfuscated(obfuscated_hash); info)
{
bool const client_is_seed = info->is_done;
bool const peer_is_seed = mediator_->is_peer_known_seed(info->id, peer_io->address());
tr_logAddTraceHand(this, fmt::format("got INCOMING connection's encrypted handshake for torrent [{}]", info->id));
peer_io->set_torrent_hash(info->info_hash);
if (client_is_seed && peer_is_seed)
{
tr_logAddTraceHand(this, "another seed tried to reconnect to us!");
return done(false);
}
}
else
{
tr_logAddTraceHand(this, "can't find that torrent...");
return done(false);
}
/* next part: ENCRYPT(VC, crypto_provide, len(PadC), */
auto const& info_hash = peer_io->torrent_hash();
TR_ASSERT_MSG(info_hash != tr_sha1_digest_t{}, "readCryptoProvide requires an info_hash");
peer_io->decrypt_init(peer_io->is_incoming(), dh_, info_hash);
auto vc_in = vc_t{};
peer_io->read_bytes(std::data(vc_in), std::size(vc_in));
peer_io->read_uint32(&crypto_provide);
crypto_provide_ = crypto_provide;
tr_logAddTraceHand(this, fmt::format("crypto_provide is {}", crypto_provide));
peer_io->read_uint16(&padc_len);
tr_logAddTraceHand(this, fmt::format("padc is {}", padc_len));
if (padc_len > PadcMaxlen)
{
tr_logAddTraceHand(this, "peer's PadC is too big");
return done(false);
}
pad_c_len_ = padc_len;
set_state(State::AwaitingPadC);
return READ_NOW;
}
ReadState tr_handshake::read_pad_c(tr_peerIo* peer_io)
{
if (auto const needlen = pad_c_len_ + sizeof(uint16_t); peer_io->read_buffer_size() < needlen)
{
return READ_LATER;
}
// read the throwaway padc
auto pad_c = std::array<char, PadcMaxlen>{};
peer_io->read_bytes(std::data(pad_c), pad_c_len_);
/* read ia_len */
uint16_t ia_len = 0;
peer_io->read_uint16(&ia_len);
tr_logAddTraceHand(this, fmt::format("ia_len is {}", ia_len));
ia_len_ = ia_len;
set_state(State::AwaitingIa);
return READ_NOW;
}
ReadState tr_handshake::read_ia(tr_peerIo* peer_io)
{
size_t const needlen = ia_len_;
tr_logAddTraceHand(this, fmt::format("reading IA... have {}, need {}", peer_io->read_buffer_size(), needlen));
if (peer_io->read_buffer_size() < needlen)
{
return READ_LATER;
}
// B->A: ENCRYPT(VC, crypto_select, len(padD), padD), ENCRYPT2(Payload Stream)
auto const& info_hash = peer_io->torrent_hash();
TR_ASSERT_MSG(info_hash != tr_sha1_digest_t{}, "readIA requires an info_hash");
peer_io->encrypt_init(peer_io->is_incoming(), dh_, info_hash);
auto outbuf = libtransmission::Buffer{};
// send VC
tr_logAddTraceHand(this, "sending vc");
outbuf.add(VC);
/* send crypto_select */
uint32_t const crypto_select = get_crypto_select(encryption_mode_, crypto_provide_);
if (crypto_select != 0)
{
tr_logAddTraceHand(this, fmt::format("selecting crypto mode '{}'", crypto_select));
outbuf.add_uint32(crypto_select);
}
else
{
tr_logAddTraceHand(this, "peer didn't offer an encryption mode we like.");
return done(false);
}
tr_logAddTraceHand(this, "sending pad d");
/* ENCRYPT(VC, crypto_provide, len(PadD), PadD
* PadD is reserved for future extensions to the handshake...
* standard practice at this time is for it to be zero-length */
outbuf.add_uint16(0);
/* maybe de-encrypt our connection */
if (crypto_select == CryptoProvidePlaintext)
{
peer_io->write(outbuf, false);
TR_ASSERT(std::empty(outbuf));
}
tr_logAddTraceHand(this, "sending handshake");
/* send our handshake */
if (auto msg = std::array<uint8_t, HandshakeSize>{}; build_handshake_message(peer_io, std::data(msg)))
{
outbuf.add(msg);
have_sent_bittorrent_handshake_ = true;
}
else
{
return done(false);
}
/* send it out */
peer_io->write(outbuf, false);
/* now await the handshake */
set_state(State::AwaitingPayloadStream);
return READ_NOW;
}
ReadState tr_handshake::read_payload_stream(tr_peerIo* peer_io)
{
static auto constexpr Needlen = HandshakeSize;
tr_logAddTraceHand(this, fmt::format("reading payload stream... have {}, need {}", peer_io->read_buffer_size(), Needlen));
if (peer_io->read_buffer_size() < Needlen)
{
return READ_LATER;
}
/* parse the handshake ... */
auto const i = parse_handshake(peer_io);
tr_logAddTraceHand(this, fmt::format("parseHandshake returned {}", static_cast<int>(i)));
if (i != ParseResult::Ok)
{
return done(false);
}
/* we've completed the BT handshake... pass the work on to peer-msgs */
return done(true);
}
// ---
ReadState tr_handshake::can_read(tr_peerIo* peer_io, void* vhandshake, size_t* piece)
{
auto* handshake = static_cast<tr_handshake*>(vhandshake);
bool ready_for_more = true;
/* no piece data in handshake */
*piece = 0;
tr_logAddTraceHand(handshake, fmt::format("handling canRead; state is [{}]", handshake->state_string()));
ReadState ret = READ_NOW;
while (ready_for_more)
{
switch (handshake->state())
{
case State::AwaitingHandshake:
ret = handshake->read_handshake(peer_io);
break;
case State::AwaitingPeerId:
ret = handshake->read_peer_id(peer_io);
break;
case State::AwaitingYa:
ret = handshake->read_ya(peer_io);
break;
case State::AwaitingPadA:
ret = handshake->read_pad_a(peer_io);
break;
case State::AwaitingCryptoProvide:
ret = handshake->read_crypto_provide(peer_io);
break;
case State::AwaitingPadC:
ret = handshake->read_pad_c(peer_io);
break;
case State::AwaitingIa:
ret = handshake->read_ia(peer_io);
break;
case State::AwaitingPayloadStream:
ret = handshake->read_payload_stream(peer_io);
break;
case State::AwaitingYb:
ret = handshake->read_yb(peer_io);
break;
case State::AwaitingVc:
ret = handshake->read_vc(peer_io);
break;
case State::AwaitingCryptoSelect:
ret = handshake->read_crypto_select(peer_io);
break;
case State::AwaitingPadD:
ret = handshake->read_pad_d(peer_io);
break;
default:
#ifdef TR_ENABLE_ASSERTS
TR_ASSERT_MSG(
false,
fmt::format(FMT_STRING("unhandled handshake state {:d}"), static_cast<int>(handshake->state())));
#else
ret = READ_ERR;
break;
#endif
}
if (ret != READ_NOW)
{
ready_for_more = false;
}
else if (handshake->is_state(State::AwaitingPadC))
{
ready_for_more = peer_io->read_buffer_size() >= handshake->pad_c_len_;
}
else if (handshake->is_state(State::AwaitingPadD))
{
ready_for_more = peer_io->read_buffer_size() >= handshake->pad_d_len_;
}
else if (handshake->is_state(State::AwaitingIa))
{
ready_for_more = peer_io->read_buffer_size() >= handshake->ia_len_;
}
}
return ret;
}
void tr_handshake::on_error(tr_peerIo* io, tr_error const& error, void* vhandshake)
{
auto* handshake = static_cast<tr_handshake*>(vhandshake);
if (io->is_utp() && !io->is_incoming() && handshake->is_state(State::AwaitingYb))
{
// the peer probably doesn't speak µTP.
auto const info_hash = io->torrent_hash();
auto const info = handshake->mediator_->torrent(info_hash);
/* Don't mark a peer as non-µTP unless it's really a connect failure. */
if ((error.code == ETIMEDOUT || error.code == ECONNREFUSED) && info)
{
handshake->mediator_->set_utp_failed(info_hash, io->address());
}
if (handshake->mediator_->allows_tcp() && io->reconnect())
{
auto msg = std::array<uint8_t, HandshakeSize>{};
handshake->build_handshake_message(io, std::data(msg));
handshake->have_sent_bittorrent_handshake_ = true;
handshake->set_state(State::AwaitingHandshake);
io->write_bytes(std::data(msg), std::size(msg), false);
return;
}
}
/* if the error happened while we were sending a public key, we might
* have encountered a peer that doesn't do encryption... reconnect and
* try a plaintext handshake */
if ((handshake->is_state(State::AwaitingYb) || handshake->is_state(State::AwaitingVc)) &&
handshake->encryption_mode_ != TR_ENCRYPTION_REQUIRED && handshake->mediator_->allows_tcp() && io->reconnect())
{
auto msg = std::array<uint8_t, HandshakeSize>{};
tr_logAddTraceHand(handshake, "handshake failed, trying plaintext...");
handshake->build_handshake_message(io, std::data(msg));
handshake->have_sent_bittorrent_handshake_ = true;
handshake->set_state(State::AwaitingHandshake);
io->write_bytes(std::data(msg), std::size(msg), false);
return;
}
tr_logAddTraceHand(handshake, fmt::format("handshake socket err: {:s} ({:d})", error.message, error.code));
handshake->done(false);
}
bool tr_handshake::fire_done(bool is_connected)
{
maybe_recycle_dh();
if (!on_done_)
{
return false;
}
// handshake could get destroyed inside on_done,
// so handle all our housekeeping *before* calling it
auto cb = DoneFunc{};
std::swap(cb, on_done_);
auto peer_io = std::shared_ptr<tr_peerIo>{};
std::swap(peer_io, peer_io_);
bool const success = (cb)(Result{ std::move(peer_io), peer_id_, have_read_anything_from_peer_, is_connected });
return success;
}
std::string_view tr_handshake::state_string(State state) noexcept
{
switch (state)
{
case State::AwaitingHandshake:
return "awaiting handshake";
case State::AwaitingPeerId:
return "awaiting peer id";
case State::AwaitingYa:
return "awaiting ya";
case State::AwaitingPadA:
return "awaiting pad a";
case State::AwaitingCryptoProvide:
return "awaiting crypto provide";
case State::AwaitingPadC:
return "awaiting pad c";
case State::AwaitingIa:
return "awaiting ia";
case State::AwaitingPayloadStream:
return "awaiting payload stream";
// outgoing
case State::AwaitingYb:
return "awaiting yb";
case State::AwaitingVc:
return "awaiting vc";
case State::AwaitingCryptoSelect:
return "awaiting crypto select";
case State::AwaitingPadD:
return "awaiting pad d";
}
return "unknown state";
}
uint32_t tr_handshake::crypto_provide() const noexcept
{
auto provide = uint32_t{};
switch (encryption_mode_)
{
case TR_ENCRYPTION_REQUIRED:
case TR_ENCRYPTION_PREFERRED:
provide |= CryptoProvideCrypto;
break;
case TR_CLEAR_PREFERRED:
provide |= CryptoProvideCrypto | CryptoProvidePlaintext;
break;
}
return provide;
}
// ---
tr_handshake::tr_handshake(Mediator* mediator, std::shared_ptr<tr_peerIo> peer_io, tr_encryption_mode mode, DoneFunc on_done)
: dh_{ tr_handshake::get_dh(mediator) }
, on_done_{ std::move(on_done) }
, peer_io_{ std::move(peer_io) }
, timeout_timer_{ mediator->timer_maker().create([this]() { fire_done(false); }) }
, mediator_{ mediator }
, encryption_mode_{ mode }
{
timeout_timer_->start_single_shot(HandshakeTimeoutSec);
peer_io_->set_callbacks(&tr_handshake::can_read, nullptr, &tr_handshake::on_error, this);
if (is_incoming())
{
set_state(State::AwaitingHandshake);
}
else if (encryption_mode_ != TR_CLEAR_PREFERRED)
{
send_ya(peer_io_.get());
}
else
{
auto msg = std::array<uint8_t, HandshakeSize>{};
build_handshake_message(peer_io_.get(), std::data(msg));
have_sent_bittorrent_handshake_ = true;
set_state(State::AwaitingHandshake);
peer_io_->write_bytes(std::data(msg), std::size(msg), false);
}
}
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