Send POST multipart/form-data request using restbed C++

I am working on a C++ rest client using restbed lib that will send a base64 encoded image using a POST request. The code I wrote so far is :

auto request = make_shared< Request >(Uri("http://127.0.0.1:8080/ProcessImage"));
request->set_header("Accept", "*/*");
request->set_header("Content-Type", "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW");
request->set_header("Cache-Control", "no-cache");
request->set_method("POST");
string test = "------WebKitFormBoundary7MA4YWxkTrZu0gW"
    "Content-Disposition:form-data;name=\"image\""
    ""
    "testMessage"
    "------WebKitFormBoundary7MA4YWxkTrZu0gW--";
request->set_body(imgContent);
auto response = Http::sync(request)

I am not sure how I should set the request body. I tried with simple image="blabla" and also with this long version message I took from postman. But in every case I received a "error 400 Bad request" answer.

Update: Tested also with this version of code but with no success:

auto request = make_shared< Request >(Uri("http://127.0.0.1:8080/ProcessImage"));
    request->set_header("Accept", "*/*");
    request->set_header("Host","127.0.0.1:8080");
    request->set_method("POST");
    request->set_header("Content-Type", "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW");
    request->set_header("Cache-Control", "no-cache");
    string imgContent = "------WebKitFormBoundary7MA4YWxkTrZu0gW\r\n"
        "Content-Disposition: form-data; name=\"image\"\r\n"
        "\r\n"
        "test\r\n"
        "------WebKitFormBoundary7MA4YWxkTrZu0gW--\r\n";
    request->set_body(imgContent
    auto response = Http::sync(request);

The response I get from the server:

    *** Response ***
Status Code:    400
Status Message: BAD REQUEST
HTTP Version:   1.0
HTTP Protocol:  HTTP
Header 'Content-Length' > '192'
Header 'Content-Type' > 'text/html'
Header 'Date' > 'Sun, 04 Feb 2018 21:09:45 GMT'
Header 'Server' > 'Werkzeug/0.14.1 Python/3.5.4'
Body:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>400 Bad Request</title>
<h1>Bad Request</h1>
<p>The browser (or proxy) sent a request that this server could not understand.</p>
²²²²∩x...

Also on the server side (which is using python flask) I added: encoded_img = request.form.get('image') and printed the string. The print result was: "None"

Solution

Your body content is missing explicit line break characters at the end of each line. C++ does not insert them automatically for you.

Also, if you are going to send base64 data, you should include a Content-Transfer-Encoding header, too.

Try this:

string imgContent = "------WebKitFormBoundary7MA4YWxkTrZu0gW\r\n"
    "Content-Disposition: form-data; name=\"image\"\r\n"
    "Content-Transfer-Encoding: base64\r\n"     
    "\r\n"
    "<base64 image data here>\r\n"
    "------WebKitFormBoundary7MA4YWxkTrZu0gW--\r\n";
request->set_body(imgContent);