How can I start a download from c++ code compiled web assembly? - c++

Question

I've been trying to not do this javascript side and I haven't found anything satisfying yet.
Fetch API seems to be a good lead, but I can't seem to find a way to start the download in the browser so it can download a zip file.
This is emscripten code snippet, but it seems to be a local file of some sort.
#include <stdio.h>
#include <string.h>
#include <emscripten/fetch.h>
void downloadSucceeded(emscripten_fetch_t *fetch) {
printf("Finished downloading %llu bytes from URL %s.\n", fetch->numBytes, fetch->url);
// The data is now available at fetch->data[0] through fetch->data[fetch->numBytes-1];
emscripten_fetch_close(fetch); // Free data associated with the fetch.
}
void downloadFailed(emscripten_fetch_t *fetch) {
printf("Downloading %s failed, HTTP failure status code: %d.\n", fetch->url, fetch->status);
emscripten_fetch_close(fetch); // Also free data on failure.
}
int main() {
emscripten_fetch_attr_t attr;
emscripten_fetch_attr_init(&attr);
strcpy(attr.requestMethod, "GET");
attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY;
attr.onsuccess = downloadSucceeded;
attr.onerror = downloadFailed;
emscripten_fetch(&attr, "myfile.dat");
}

Answer 1

Add this to your cpp file.
EM_JS(void, DownloadUrl, (const char* str),
{
url = UTF8ToString(str);
var hiddenIFrameID = 'hiddenDownloader';
var iframe = document.getElementById(hiddenIFrameID);
if (iframe === null)
{
iframe = document.createElement('iframe');
iframe.id = hiddenIFrameID;
iframe.style.display = 'none';
document.body.appendChild(iframe);
}
iframe.src = url;
});
And an example on how to use it.
void Device::DrawContent()
{
ImGui::Begin("DW Store");
if (ImGui::Button("Download"))
{
DownloadUrl("https://dotnet.microsoft.com/download/dotnet/thank-you/sdk-5.0.402-macos-x64-installer");
}
ImGui::End();
}