Method readFromFile

src/common/file_system/local_file_system.cpp:420–477

}

void LocalFileSystem::readFromFile(FileInfo& fileInfo, void* buffer, uint64_t numBytes,
    uint64_t position) const {
    auto localFileInfo = fileInfo.constPtrCast<LocalFileInfo>();
    DASSERT(localFileInfo->getFileSize() >= position + numBytes);
    auto outputBuffer = static_cast<uint8_t*>(buffer);
    uint64_t remainingNumBytesToRead = numBytes;
    uint64_t bufferOffset = 0;
    // Keep reads below common OS syscall transfer limits.
    constexpr uint64_t maxBytesToReadAtOnce = 1ull << 30;
    while (remainingNumBytesToRead > 0) {
        const auto numBytesToRead = (std::min)(remainingNumBytesToRead, maxBytesToReadAtOnce);
#if defined(_WIN32)
        DWORD numBytesRead;
        OVERLAPPED overlapped = {};
        overlapped.Offset = position & 0xffffffff;
        overlapped.OffsetHigh = position >> 32;
        if (!ReadFile((HANDLE)localFileInfo->handle, outputBuffer + bufferOffset, numBytesToRead,
                &numBytesRead, &overlapped)) {
            auto error = GetLastError();
            throw IOException(
                std::format("Cannot read from file: {} handle: {} "
                            "numBytesRead: {} numBytesToRead: {} position: {}. Error {}: {}",
                    fileInfo.path, (intptr_t)localFileInfo->handle, numBytesRead, numBytesToRead,
                    position, error, std::system_category().message(error)));
        }
        if (numBytesRead != numBytesToRead && fileInfo.getFileSize() != position + numBytesRead) {
            throw IOException(std::format("Cannot read from file: {} handle: {} "
                                          "numBytesRead: {} numBytesToRead: {} position: {}",
                fileInfo.path, (intptr_t)localFileInfo->handle, numBytesRead, numBytesToRead,
                position));
        }
#else
        auto numBytesRead =
            pread(localFileInfo->fd, outputBuffer + bufferOffset, numBytesToRead, position);
        if (numBytesRead < 0) {
            // LCOV_EXCL_START
            throw IOException(std::format("Cannot read from file: {} fileDescriptor: {} "
                                          "numBytesRead: {} numBytesToRead: {} position: {}",
                fileInfo.path, localFileInfo->fd, numBytesRead, numBytesToRead, position));
            // LCOV_EXCL_STOP
        }
        if (static_cast<uint64_t>(numBytesRead) != numBytesToRead &&
            localFileInfo->getFileSize() != position + numBytesRead) {
            // LCOV_EXCL_START
            throw IOException(std::format("Cannot read from file: {} fileDescriptor: {} "
                                          "numBytesRead: {} numBytesToRead: {} position: {}",
                fileInfo.path, localFileInfo->fd, numBytesRead, numBytesToRead, position));
            // LCOV_EXCL_STOP
        }
#endif
        if (numBytesRead == 0) {
            break;
        }
        remainingNumBytesToRead -= numBytesRead;
        position += numBytesRead;
        bufferOffset += numBytesRead;
    }
}