C++/CLR post HTTP

Question

Hello all,

Using Visual Studio 2019 I am trying to write a small windows desktop application with C++ CLR (.NET Framework).

After a lot of trial an error I managed to get a HTTP GET request working.

    System::String^ HTTP_GET(System::String^ link) {  
    		System::Net::HttpWebRequest^ request = dynamic_cast<System::Net::HttpWebRequest^>(System::Net::WebRequest::Create(link));  
    		System::Net::HttpWebResponse^ response = dynamic_cast<System::Net::HttpWebResponse^>(request->GetResponse());  
    		Stream^ dataStream = response->GetResponseStream();  
    		StreamReader^ reader = gcnew StreamReader(dataStream);  
    		System::String^ responseFromServer = reader->ReadToEnd();  
    		response->Close();  
    		return System::Convert::ToString(responseFromServer);  
    	}  
  
  

Having no experience in C++, I spend almost 2 days trying to build the POST equivalent (based on what i have found online) with no success. Here is what I managed to build so far:

	System::String^ HTTP_POST(System::String^ link, System::String^ param) {  
		array<Byte>^ buffer = Encoding::UTF8->GetBytes(param); // <== error: too few arguments for class template "std::array"  
		System::Net::HttpWebRequest^ request = dynamic_cast<System::Net::HttpWebRequest^>(System::Net::WebRequest::Create(link));  
		request->Method = "POST";  
		System::IO::Stream^ stream = request->GetRequestStream();  
		stream->Write(buffer, 0, buffer->Length);  
		stream->Flush();  
		stream->Close();  
  
		//read the response  
		System::Net::HttpWebResponse^ response = dynamic_cast<System::Net::HttpWebResponse^>(request->GetResponse());  
		Stream^ dataStream = response->GetResponseStream();  
		StreamReader^ reader = gcnew StreamReader(dataStream);  
		System::String^ responseFromServer = reader->ReadToEnd();  
		response->Close();  
		return System::Convert::ToString(responseFromServer);  
	}  

The following line is blocking me as I have no ideea how to correct it.

array<Byte>^ buffer = Encoding::UTF8->GetBytes(param);  

If I change the line to:

array<Byte,1>^ buffer = Encoding::UTF8->GetBytes(param);  

i get the error: a handle to a non-managed class is not allowed.

If I chanage the line to:

System: Array^ buffer = Encoding::UTF8->GetBytes(param);  

Then the line:

stream->Write(buffer, 0, buffer->Length);  

Errors with: function "System::IO::Stream::Write" cannot be called with the given argument list
function type is IO::Stream^ but arguments are System::Array^, int, int ...

Can anyone help me with fixing the code so that will POST and retrive the response from server?

Thank you.

P.S: I also tried with curl but again, with no success in resolving the error I get and retreving the response:

static size_t Callback(void* contents, size_t size, size_t nmemb, std::string* userp) {  
	userp->append((char*)contents, size * nmemb);  
	return size * nmemb;  
}  

CURL* curl;  
CURLcode res;  
curl_global_init(CURL_GLOBAL_ALL);  

curl = curl_easy_init();  
if (curl) {  
	string readBuffer{};  
	  
	curl_easy_setopt(curl, CURLOPT_URL, "https://some-link/test-post.php");  
	curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "param=something");  
	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, Callback); // <== error: can't take address of 'CLRproject::MyForm::Callback' unless creating delegate instance  
	curl_easy_setopt(curl, CURLOPT_WRITEDATA, readBuffer);  

	res = curl_easy_perform(curl);  

	if (res != CURLE_OK)  
		label2->Text = System::Convert::ToString(curl_easy_strerror(res));  

	curl_easy_cleanup(curl);  
	//System::String^ x = gcnew System::String(readBuffer.data());  
	label2->Text = System::Convert::ToString(curl_easy_strerror(res));  
}  
curl_global_cleanup();	  

Answer 1

To solve the compilation problem, try this:

cli::array<Byte>^ buffer = Encoding::UTF8->GetBytes( param );  

Answer 2

Thanks Viorel!

Changing to that line indeed solved the compilation problem (thank you so much for that!!!), but this revealed a new problem:

The post parameter "param" supplied to the function is a string formated as "key1=value1&key2=value2", but for some reason it is not processed server side.
It seems the server does not see the parameter keys.

I don't know if my code is wrong and does not send to server the parameters... (post is processed as i get a result from the server as if no parameter was sent)