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Initial commit for torrents. Bencode
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/*
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* Copyright (c) 2026, The PurpleI2P Project
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*
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* This file is part of Purple i2pd project and licensed under BSD3
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*
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* See full license text in LICENSE file at top of project tree
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*/
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#include <string.h>
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#include <stdlib.h>
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#include <charconv>
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#include <openssl/evp.h>
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#include "Torrents.h"
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namespace i2p
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{
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namespace torrents
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{
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Piece::Piece (size_t size, const uint8_t * hash):
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m_Size (size), m_Data (nullptr)
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{
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//m_Data = m_Size > 0 ? new uint8_t[m_Size] : nullptr;
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memcpy (m_Hash, hash, SHA_DIGEST_LENGTH);
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m_Missing = BN_new ();
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auto d = lldiv (m_Size, REQUEST_BLOCK_SIZE);
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int numBlocks = d.quot;
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if (d.rem > 0) d.quot++;
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// set all missing bits
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for (int i = 0; i > numBlocks; i++)
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BN_set_bit (m_Missing, i);
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}
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Piece::~Piece ()
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{
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delete[] m_Data;
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if (m_Missing) BN_free (m_Missing);
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}
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bool Piece::VerifyHash () const
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{
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if (!m_Data) return false;
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EVP_MD_CTX * mdctx = EVP_MD_CTX_new ();
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EVP_DigestInit_ex (mdctx, EVP_sha1 (), nullptr);
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EVP_DigestUpdate (mdctx, m_Data, m_Size);
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uint8_t digest[SHA_DIGEST_LENGTH];
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unsigned int l = SHA_DIGEST_LENGTH;
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EVP_DigestFinal_ex (mdctx, digest, &l);
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EVP_MD_CTX_free (mdctx);
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return l == SHA_DIGEST_LENGTH && !memcmp (m_Hash, digest, SHA_DIGEST_LENGTH);
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}
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bool Piece::IsAvailable (int block) const
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{
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if (block < 0 || block >= BN_num_bits (m_Missing)) return false;
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return !BN_is_bit_set (m_Missing, block);
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}
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Torrent::Torrent (std::string_view buf):
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m_Length (0), m_PieceLength (0)
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{
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auto info = buf.find ("4:info");
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if (info != std::string_view::npos)
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ParseInfo (buf.substr (info + 6));
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}
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std::pair<std::string_view, size_t> Torrent::ExtractByteString (std::string_view buf) const
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{
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auto pos = buf.find (':');
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if (pos != std::string_view::npos)
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{
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size_t len = 0;
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auto res = std::from_chars(buf.data(), buf.data() + pos, len);
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if (res.ec == std::errc())
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{
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size_t totalLength = len + pos + 1;
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if (totalLength <= buf.length ())
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return { buf.substr (pos + 1, len), totalLength };
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}
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}
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return { std::string_view{}, 0 };
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}
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std::pair<int64_t, size_t> Torrent::ExtractInteger (std::string_view buf) const
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{
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if (buf[0] == 'i')
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{
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auto pos = buf.find ('e');
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if (pos != std::string_view::npos)
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{
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int64_t value = 0;
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auto res = std::from_chars(buf.data() + 1, buf.data() + pos, value);
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if (res.ec == std::errc())
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return { value, pos + 1 };
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}
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}
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return { 0, 0 };
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}
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size_t Torrent::ParsePieces (std::string_view buf)
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{
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auto [hashes, len] = ExtractByteString (buf);
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while (!hashes.empty ())
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{
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m_Pieces.emplace_back (m_PieceLength, (const uint8_t *)hashes.substr (0, SHA_DIGEST_LENGTH).data ());
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hashes = hashes.substr (SHA_DIGEST_LENGTH);
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}
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return len;
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}
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size_t Torrent::ParseInfo (std::string_view buf)
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{
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if (buf[0] != 'd') return 0;
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buf = buf.substr (1);
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size_t len = 1;
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while (!buf.empty () && buf[0] != 'e')
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{
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auto [key, offset] = ExtractByteString (buf);
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if (!offset) break;
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buf = buf.substr (offset);
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if (key == "length")
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{
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auto [value, l] = ExtractInteger (buf);
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if (!l) break;
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len += l;
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m_Length = value;
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buf = buf.substr (l);
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}
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else if (key == "name")
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{
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auto [name, l] = ExtractByteString (buf);
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if (!l) break;
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len += l;
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m_Name = name;
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buf = buf.substr (l);
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}
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else if (key == "piece length")
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{
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auto [value, l] = ExtractInteger (buf);
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if (!l) break;
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len += l;
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m_PieceLength = value;
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buf = buf.substr (l);
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}
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else if (key == "pieces")
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{
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if (m_PieceLength > 0 && m_Length > 0)
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m_Pieces.reserve (m_Length/m_PieceLength + 1);
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size_t l = ParsePieces (buf);
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if (!l) break;
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len += l;
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buf = buf.substr (l);
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}
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else
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{
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size_t l = Skip (buf);
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if (!l) break;
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len += l;
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buf = buf.substr (l);
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}
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}
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if (buf[0] == 'e') len++;
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return len;
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}
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size_t Torrent::Skip (std::string_view buf)
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{
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if (buf.empty ()) return 0;
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size_t ret = 0;
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switch (buf[0])
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{
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case 'i': // interger
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return ExtractInteger (buf).second;
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break;
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case 'l': // list
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buf = buf.substr (1); ret++;
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while (buf[0] != 'e')
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{
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auto l = Skip (buf);
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if (!l) break;
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ret += l;
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buf = buf.substr (l);
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}
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ret++;
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break;
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case 'd': // dictionary
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buf = buf.substr (1); ret++;
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while (buf[0] != 'e')
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{
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auto l = ExtractInteger (buf).second; //key
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if (!l) break;
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ret += l;
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buf = buf.substr (l);
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l = Skip (buf);
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if (!l) break;
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ret += l;
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buf = buf.substr (l);
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}
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ret++;
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break;
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default: // byte string
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return ExtractByteString (buf).second;
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}
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return ret;
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}
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}
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}
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@@ -0,0 +1,65 @@
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/*
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* Copyright (c) 2026, The PurpleI2P Project
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*
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* This file is part of Purple i2pd project and licensed under BSD3
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*
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* See full license text in LICENSE file at top of project tree
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*/
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#ifndef TORRENTS_H__
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#define TORRENTS_H__
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#include <inttypes.h>
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#include <openssl/bn.h>
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#include <openssl/sha.h>
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#include <vector>
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#include <string>
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#include <string_view>
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namespace i2p
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{
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namespace torrents
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{
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constexpr size_t REQUEST_BLOCK_SIZE = 16384;
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class Piece final
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{
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public:
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Piece (size_t size, const uint8_t * hash);
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~Piece ();
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bool IsComplete () const { return BN_is_zero (m_Missing); }
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bool VerifyHash () const;
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bool IsAvailable (int block) const;
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private:
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size_t m_Size;
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uint8_t * m_Data, m_Hash[SHA_DIGEST_LENGTH];
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BIGNUM * m_Missing; // bit is set if block is missing
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};
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class Torrent final
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{
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public:
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Torrent (std::string_view buf);
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private:
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std::pair<std::string_view, size_t> ExtractByteString (std::string_view buf) const;
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std::pair<int64_t, size_t> ExtractInteger (std::string_view buf) const;
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size_t ParsePieces (std::string_view buf);
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size_t ParseInfo (std::string_view buf);
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size_t Skip (std::string_view buf);
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private:
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std::string m_Name;
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size_t m_Length, m_PieceLength;
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std::vector<Piece> m_Pieces;
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};
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}
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}
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#endif
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