How do you upload a file using Emscripten in C++? - c++

Question

I'm trying to upload a file to a server. I have been successful in downloading data using Emscripten's Fetch API with a GET request, but so far have been unsuccessful with POST requests.
Here is my current implementation: (the file is being opened and read as expected, but the server is not receiving the file)
void uploadSucceeded(emscripten_fetch_t* fetch)
{
printf("Successful upload of %llu bytes to %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 uploadFailed(emscripten_fetch_t* fetch)
{
printf("Failed upload to %s - HTTP failure status code: %d.\n", fetch->url, fetch->status);
emscripten_fetch_close(fetch); // Also free data on failure.
}
bool UploadFile(const std::string& url, const std::string& file_name)
{
emscripten_fetch_attr_t attr;
emscripten_fetch_attr_init(&attr);
strcpy(attr.requestMethod, "POST");
attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY;
attr.onsuccess = uploadSucceeded;
attr.onerror = uploadFailed;
// Set headers:
const char* headers[] = { "Content-Type", "application/x-www-form-urlencoded", 0 };
attr.requestHeaders = headers;
// Read file data:
std::ifstream in_file(file_name.c_str(), std::ios::binary);
//
in_file.seekg(0, std::ios::end);
int file_size = in_file.tellg();
//
in_file.seekg(0, std::ios::beg);
std::stringstream buffer;
buffer << in_file.rdbuf();
//
char *cstr = new char[buffer.str().length() + 1];
strcpy(cstr, buffer.str().c_str());
//
attr.requestData = cstr;
attr.requestDataSize = file_size;
// Send HTTP request:
emscripten_fetch(&attr, url.c_str());
return true;
}

Answer 1

You need to make sure that the request header has:
"Content-Type", "multipart/form-data; boundary=[custom-boundary]\r\n"
...where [custom-boundary] is a string of your choice.
Then in the request data, you start with that custom boundary, followed by "\r\n", then you have another header, such as:
"Content-Disposition: form-data; name=\"myFile\" filename=\"G0000U00000R01.html\"\r\n"
"Content-Transfer-Encoding: binary\r\n"
"Content-Type: text/html\r\n\r\n"
...followed by the file contents, followed by "\r\n" again, and finally followed by the same custom boundary as before.