120 lines
3.5 KiB
C++
120 lines
3.5 KiB
C++
// This file Copyright © 2008-2022 Mnemosyne LLC.
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// It may be used under GPLv2 (SPDX: GPL-2.0), GPLv3 (SPDX: GPL-3.0),
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// or any future license endorsed by Mnemosyne LLC.
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// License text can be found in the licenses/ folder.
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#pragma once
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#ifndef __TRANSMISSION__
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#error only libtransmission should #include this header.
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#endif
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#include <cstddef>
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#include <vector>
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/**
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* @brief Implementation of the BitTorrent spec's Bitfield array of bits.
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*
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* This is for tracking the pieces a peer has. Its functionality is like
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* a bitset or vector<bool> with some added use cases:
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*
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* - It needs to be able to read/write the left-to-right bitfield format
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* specified in the bittorrent spec. This is what raw() and getRaw()
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* are for.
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*
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* - "Have all" is a special case where we know the peer has all the
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* pieces and don't need to check the bit array. This is useful since
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* (a) it's very common (i.e. seeds) and saves memory and work of
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* allocating a bit array and doing lookups, and (b) if we have a
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* magnet link and haven't gotten the metainfo yet, we may not know
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* how many pieces there are -- but we can still know "this peer has
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* all of them".
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*
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* - "Have none" is another special case that has the same advantages
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* and motivations as "Have all".
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*/
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class tr_bitfield
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{
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public:
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explicit tr_bitfield(size_t bit_count);
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void setHasAll();
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void setHasNone();
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// set one or more bits
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void set(size_t bit, bool value = true);
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void setSpan(size_t begin, size_t end, bool value = true);
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void unset(size_t bit)
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{
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set(bit, false);
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}
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void unsetSpan(size_t begin, size_t end)
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{
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setSpan(begin, end, false);
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}
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void setFromBools(bool const* bytes, size_t n);
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// "raw" here is in BEP0003 format: "The first byte of the bitfield
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// corresponds to indices 0 - 7 from high bit to low bit, respectively.
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// The next one 8-15, etc. Spare bits at the end are set to zero.
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void setRaw(uint8_t const* bits, size_t byte_count);
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std::vector<uint8_t> raw() const;
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[[nodiscard]] constexpr bool hasAll() const
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{
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return have_all_hint_ || (bit_count_ > 0 && bit_count_ == true_count_);
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}
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[[nodiscard]] constexpr bool hasNone() const
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{
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return have_none_hint_ || (bit_count_ > 0 && true_count_ == 0);
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}
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[[nodiscard]] bool test(size_t bit) const
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{
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return hasAll() || (!hasNone() && testFlag(bit));
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}
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[[nodiscard]] constexpr size_t count() const
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{
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return true_count_;
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}
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[[nodiscard]] size_t count(size_t begin, size_t end) const;
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[[nodiscard]] constexpr size_t size() const
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{
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return bit_count_;
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}
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[[nodiscard]] constexpr size_t empty() const
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{
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return size() == 0;
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}
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bool isValid() const;
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private:
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std::vector<uint8_t> flags_;
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[[nodiscard]] size_t countFlags() const;
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[[nodiscard]] size_t countFlags(size_t begin, size_t end) const;
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[[nodiscard]] bool testFlag(size_t bit) const;
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void ensureBitsAlloced(size_t n);
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[[nodiscard]] bool ensureNthBitAlloced(size_t nth);
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void freeArray();
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void setTrueCount(size_t n);
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void rebuildTrueCount();
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void incrementTrueCount(size_t inc);
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void decrementTrueCount(size_t dec);
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size_t bit_count_ = 0;
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size_t true_count_ = 0;
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/* Special cases for when full or empty but we don't know the bitCount.
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This occurs when a magnet link's peers send have all / have none */
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bool have_all_hint_ = false;
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bool have_none_hint_ = false;
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};
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