Function pj_emscripten_read_range

src/networkfilemanager.cpp:2011–2165

#endif

static size_t pj_emscripten_read_range(PJ_CONTEXT *ctx,
                                       PROJ_NETWORK_HANDLE *raw_handle,
                                       unsigned long long offset,
                                       size_t size_to_read, void *buffer,
                                       size_t error_string_max_size,
                                       char *out_error_string, void *) {
    auto handle = reinterpret_cast<EmscriptenFileHandle *>(raw_handle);

    double oldDelay = MIN_RETRY_DELAY_MS;

    char szBuffer[128];
    sqlite3_snprintf(sizeof(szBuffer), szBuffer, "bytes=%llu-%llu", offset,
                     offset + size_to_read - 1);

    // To work in the browser, we need to run the fetch part in Web Worker,
    // otherwise we cannot run it synchronous. (at least with my tests)
    // It is easier running all PROJ in the Web Worker (that is the test done).
    // Documentation says compiling with pthread flag is needed.
    // https://emscripten.org/docs/api_reference/fetch.html#synchronous-fetches
    // We encapsulate the code related to empscripten_fetch in a lamda.
    // Some tests running this lambda in a thread were partially successful.
    size_t real_read = 0;
    const std::string url = handle->m_url;
    auto fetching = [&]() {
        emscripten_fetch_t *fetch = nullptr;
        while (true) {

            emscripten_fetch_attr_t attr;
            emscripten_fetch_attr_init(&attr);
            strcpy(attr.requestMethod, "GET");
            const char *requestHeaders[] = {"Range", szBuffer, nullptr};
            attr.requestHeaders = requestHeaders;
            attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY |
                              EMSCRIPTEN_FETCH_SYNCHRONOUS |
                              EMSCRIPTEN_FETCH_REPLACE;
            if (fetch) {
                emscripten_fetch_close(fetch);
            }

            TRACE_FETCH("Pre-fetch, url: " << url << ", range: " << szBuffer);
            fetch = emscripten_fetch(&attr, url.c_str());
            // emscripten_fetch_wait(fetch, -1); // This is deprecated
            TRACE_FETCH("Post-fetch");

            if (!fetch) {
                snprintf(out_error_string, error_string_max_size,
                         "Cannot init emscripten_fetch for url %s",
                         url.c_str());
                return;
            }
            const auto response_code = fetch->status;
            TRACE_FETCH("Received HTTP response code: " << response_code);
            if (response_code == 0 || response_code >= 300) {
                const double delay =
                    GetNewRetryDelay(static_cast<int>(response_code), oldDelay,
                                     fetch->data, fetch->statusText);
                if (delay != 0 && delay < MAX_RETRY_DELAY_MS) {
                    pj_log(ctx, PJ_LOG_TRACE,