Connection::post() seems to send deformed data #181

Expected behaviour

I was experiencing some issues authenticating with the Reddit API using this client, so I tried to isolate the problem in a blank C++ file, and I believe it is because the library is sending deformed data to the server.

I have a simple test.cpp with the following contents:

#include <restclient-cpp/restclient.h>
#include <restclient-cpp/connection.h>

int main () {
    RestClient::init();
    RestClient::Connection * connection = new RestClient::Connection ("http://localhost:3000");
    RestClient::Response response = connection->post("/post", "{\"foo\": \"bar\"}");
    delete connection;
    RestClient::disable();
}

...and I spun up a simple web server in Express.js that just repeats back what it receives with the following contents:

'use strict';
const PORT = 3000;
const express = require("express");
const app = express();
app.use(express.static('public'));
app.use(express.urlencoded({
    extended: true
}));

app.post("/post", (req, res) => {
    console.log(req.body)
    res.send({})
})

app.listen(PORT, () => {
    console.log(`Server listening on port ${PORT}...`);
});

I expected the Express server to print this:

Server listening on port 3000...
{ foo: 'bar' }

...which was generated by sending the following request with Python requests:

requests.post("http://localhost:3000/post", {"foo": "bar"})

Actual behaviour

Server listening on port 3000...
{ '{"foo": "bar"}': '' }

Environment and debugging details

• compiler and version: g++ (Ubuntu 11.2.0-19ubuntu1) 11.2.0
• operating system: Ubuntu 22.04 LTS amd64
• version of restclient-cpp: master
• how did you install restclient-cpp? (via packages, git, tarball): git
• libcurl version and compile flags: libcurl4-openssl-dev/jammy-updates,jammy-security,now 7.81.0-1ubuntu1.3 amd64

(some of these things might not apply but the more you can provide the easier
it will be to fix this bug. Thanks!)