Method readBigAt

src/IO/ReadWriteBufferFromHTTP.cpp:527–587

}

size_t ReadWriteBufferFromHTTP::readBigAt(char * to, size_t n, size_t offset, const std::function<bool(size_t)> & progress_callback) const
{
    /// Caller must have checked supportsReadAt().
    /// This ensures we've sent at least one HTTP request and populated current_uri.
    chassert(file_info && file_info->seekable);

    size_t initial_n = n;
    size_t total_bytes_copied = 0;
    size_t bytes_copied = 0;
    bool is_canceled = false;

    doWithRetries(
        /*callable=*/ [&] ()
        {
            auto range = HTTPRange{offset, offset + n - 1};

            Poco::Net::HTTPResponse response;
            auto result = callImpl(response, method, range, false);

            if (response.getStatus() != Poco::Net::HTTPResponse::HTTPStatus::HTTP_PARTIAL_CONTENT &&
                (offset != 0 || offset + n < *file_info->file_size))
            {
                String explanation = fmt::format(
                    "When reading with readBigAt {}."
                    "Cannot read with range: [{}, {}] (response status: {}, reason: {}), will retry",
                    initial_uri.toString(),
                    *range.begin, *range.end,
                    toString(response.getStatus()), response.getReason());

                throw HTTPException(
                    ErrorCodes::HTTP_RANGE_NOT_SATISFIABLE,
                    current_uri.toString(),
                    Poco::Net::HTTPResponse::HTTP_REQUESTED_RANGE_NOT_SATISFIABLE,
                    response.getReason(),
                    explanation);
            }

            copyFromIStreamWithProgressCallback(*result.response_stream, to, n, progress_callback, &bytes_copied, &is_canceled);

            ProfileEvents::increment(ProfileEvents::ReadWriteBufferFromHTTPBytes, bytes_copied);

            offset += bytes_copied;
            total_bytes_copied += bytes_copied;
            to += bytes_copied;
            n -= bytes_copied;
            bytes_copied = 0;
        },
        /*on_retry=*/ [&] ()
        {
            ProfileEvents::increment(ProfileEvents::ReadWriteBufferFromHTTPBytes, bytes_copied);

            offset += bytes_copied;
            total_bytes_copied += bytes_copied;
            to += bytes_copied;
            n -= bytes_copied;
            bytes_copied = 0;
        });