tessesframework/src/BitTorrent/TorrentStream.cpp

/*
    TessesFramework a library to make C++ easier for me, used in CrossLang:
    https://git.tesses.org/tesses50/crosslang

    Copyright (C) 2026 Mike Nolan
    SPDX-License-Identifier: GPL-3.0-or-later WITH TessesFramework-Exception-1.0

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#include "TessesFramework/BitTorrent/TorrentStream.hpp"

namespace Tesses::Framework::BitTorrent {
TorrentFileEntry::TorrentFileEntry() {}
TorrentFileEntry::TorrentFileEntry(Tesses::Framework::Filesystem::VFSPath path,
                                   int64_t length)
    : path(path), length(length) {}

ReadWriteAt::~ReadWriteAt() {}

TorrentFileStream::TorrentFileStream(
    std::shared_ptr<Tesses::Framework::Filesystem::VFS> vfs,
    Tesses::Framework::Filesystem::VFSPath path, uint64_t length)
    : vfs(vfs), path(path), length(length) {}
bool TorrentFileStream::ReadBlockAt(uint64_t offset, uint8_t *data,
                                    size_t len) {
    if (!vfs->FileExists(path))
        return false;
    auto strm = vfs->OpenFile(path, "rb");
    strm->Seek((int64_t)offset, Streams::SeekOrigin::Begin);
    strm->ReadBlock(data, len);
    return true;
}
void TorrentFileStream::WriteBlockAt(uint64_t offset, const uint8_t *data,
                                     size_t len) {
    len =
        (size_t)std::min((int64_t)len, (int64_t)this->length - (int64_t)offset);
    if (len == 0)
        return;

    mtx.Lock();
    auto strm = vfs->OpenFile(path, "wb");
    strm->Seek((int64_t)offset, Streams::SeekOrigin::Begin);
    strm->WriteBlock(data, len);
    mtx.Unlock();
}

TorrentDirectoryStream::TorrentDirectoryStream(
    std::shared_ptr<Tesses::Framework::Filesystem::VFS> vfs,
    Tesses::Framework::Filesystem::VFSPath path,
    std::vector<TorrentFileEntry> entries)
    : vfs(vfs), path(path), entries(entries) {
    if (!vfs->DirectoryExists(path))
        this->vfs->CreateDirectory(path);
    this->mtxs.resize(entries.size());
}

// From https://www.seanjoflynn.com/research/bittorrent.html , which is licensed
// under MIT based on code repo
bool TorrentDirectoryStream::ReadBlockAt(uint64_t offset, uint8_t *data,
                                         size_t len) {
    uint64_t currentOffset = 0;
    uint64_t end = offset + len;
    for (size_t i = 0; i < this->entries.size(); i++) {
        if (offset < currentOffset && end < currentOffset) {
            currentOffset += this->entries[i].length;
            continue;
        }

        if (offset > currentOffset + this->entries[i].length &&
            end > currentOffset + this->entries[i].length) {
            currentOffset += this->entries[i].length;
            continue;
        }

        auto path = this->path / this->entries[i].path;
        if (!vfs->FileExists(path))
            return false;

        int64_t fstart =
            std::max((int64_t)0, (int64_t)offset - (int64_t)currentOffset);
        int64_t fend = std::min((int64_t)end - (int64_t)currentOffset,
                                (int64_t)this->entries[i].length);
        int flength = (int)(fend - fstart);
        int bstart =
            std::max((int)0, (int)((int64_t)currentOffset - (int64_t)offset));
        auto strm = vfs->OpenFile(path, "rb");
        strm->Seek(fstart, Streams::SeekOrigin::Begin);
        strm->ReadBlock(data + bstart, flength);

        currentOffset += this->entries[i].length;
    }
    return true;
}

// From https://www.seanjoflynn.com/research/bittorrent.html , which is licensed
// under MIT based on code repo
void TorrentDirectoryStream::WriteBlockAt(uint64_t offset, const uint8_t *data,
                                          size_t len) {
    uint64_t currentOffset = 0;
    uint64_t end = offset + len;
    for (size_t i = 0; i < this->entries.size(); i++) {
        if (offset < currentOffset && end < currentOffset) {
            currentOffset += this->entries[i].length;
            continue;
        }

        if (offset > currentOffset + this->entries[i].length &&
            end > currentOffset + this->entries[i].length) {
            currentOffset += this->entries[i].length;
            continue;
        }

        auto path = this->path / this->entries[i].path;
        auto parent = path.GetParent();
        if (!vfs->DirectoryExists(parent))
            vfs->CreateDirectory(parent);

        int64_t fstart =
            std::max((int64_t)0, (int64_t)offset - (int64_t)currentOffset);
        int64_t fend = std::min((int64_t)end - (int64_t)currentOffset,
                                (int64_t)this->entries[i].length);
        int flength = (int)(fend - fstart);
        int bstart =
            std::max((int)0, (int)((int64_t)currentOffset - (int64_t)offset));

        this->mtxs[i].Lock();
        {
            auto strm = vfs->OpenFile(path, "wb");
            strm->Seek(fstart, Streams::SeekOrigin::Begin);
            strm->WriteBlock(data + bstart, flength);
        }
        this->mtxs[i].Unlock();

        currentOffset += this->entries[i].length;
    }
}
} // namespace Tesses::Framework::BitTorrent