How do you make a HTTP request with C++?

Question

Is there any way to easily make a HTTP request with C++? Specifically, I want to download the contents of a page (an API) and check the contents to see if it contains a 1 or a 0. Is it also possible to download the contents into a string?

Answer 1

Here is some (relatively) simple C++11 code that uses libCURL to download a URL's content into a std::vector<char>:

http_download.hh

# pragma once

#include <string>
#include <vector>

std::vector<char> download(std::string url, long* responseCode = nullptr);

http_download.cc

#include "http_download.hh"

#include <curl/curl.h>
#include <sstream>
#include <stdexcept>

using namespace std;

size_t callback(void* contents, size_t size, size_t nmemb, void* user)
{
  auto chunk = reinterpret_cast<char*>(contents);
  auto buffer = reinterpret_cast<vector<char>*>(user);

  size_t priorSize = buffer->size();
  size_t sizeIncrease = size * nmemb;

  buffer->resize(priorSize + sizeIncrease);
  std::copy(chunk, chunk + sizeIncrease, buffer->data() + priorSize);

  return sizeIncrease;
}

vector<char> download(string url, long* responseCode)
{
  vector<char> data;

  curl_global_init(CURL_GLOBAL_ALL);
  CURL* handle = curl_easy_init();
  curl_easy_setopt(handle, CURLOPT_URL, url.c_str());
  curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, callback);
  curl_easy_setopt(handle, CURLOPT_WRITEDATA, &data);
  curl_easy_setopt(handle, CURLOPT_USERAGENT, "libcurl-agent/1.0");
  CURLcode result = curl_easy_perform(handle);
  if (responseCode != nullptr)
    curl_easy_getinfo(handle, CURLINFO_RESPONSE_CODE, responseCode);
  curl_easy_cleanup(handle);
  curl_global_cleanup();

  if (result != CURLE_OK)
  {
    stringstream err;
    err << "Error downloading from URL \"" << url << "\": " << curl_easy_strerror(result);
    throw runtime_error(err.str());
  }

  return move(data);
}

Answer 2

I had the same problem. libcurl is really complete. There is a C++ wrapper curlpp that might interest you as you ask for a C++ library. neon is another interesting C library that also support WebDAV.

curlpp seems natural if you use C++. There are many examples provided in the source distribution. To get the content of an URL you do something like that (extracted from examples) :

// Edit : rewritten for cURLpp 0.7.3
// Note : namespace changed, was cURLpp in 0.7.2 ...

#include <curlpp/cURLpp.hpp>
#include <curlpp/Options.hpp>

// RAII cleanup

curlpp::Cleanup myCleanup;

// Send request and get a result.
// Here I use a shortcut to get it in a string stream ...

std::ostringstream os;
os << curlpp::options::Url(std::string("http://www.wikipedia.org"));

string asAskedInQuestion = os.str();

See the examples directory in curlpp source distribution, there is a lot of more complex cases, as well as a simple complete minimal one using curlpp.

my 2 cents ...

Answer 3

libCURL is a pretty good option for you. Depending on what you need to do, the tutorial should tell you what you want, specifically for the easy handle. But, basically, you could do this just to see the source of a page:

CURL* c;
c = curl_easy_init();
curl_easy_setopt( c, CURL_URL, "www.google.com" );
curl_easy_perform( c );
curl_easy_cleanup( c );

I believe this will cause the result to be printed to stdout. If you want to handle it instead -- which, I assume, you do -- you need to set the CURL_WRITEFUNCTION. All of that is covered in the curl tutorial linked above.

Answer 4

You may want to check C++ REST SDK (codename "Casablanca"). http://msdn.microsoft.com/en-us/library/jj950081.aspx

With the C++ REST SDK, you can more easily connect to HTTP servers from your C++ app.

Usage example:

#include <iostream>
#include <cpprest/http_client.h>

using namespace web::http;                  // Common HTTP functionality
using namespace web::http::client;          // HTTP client features

int main(int argc, char** argv) {
    http_client client("http://httpbin.org/");

    http_response response;
    // ordinary `get` request
    response = client.request(methods::GET, "/get").get();
    std::cout << response.extract_string().get() << "\n";

    // working with json
    response = client.request(methods::GET, "/get").get();
    std::cout << "url: " << response.extract_json().get()[U("url")] << "\n";
}

The C++ REST SDK is a Microsoft project for cloud-based client-server communication in native code using a modern asynchronous C++ API design.

Answer 5

Here is my minimal wrapper around cURL to be able just to fetch a webpage as a string. This is useful, for example, for unit testing. It is basically a RAII wrapper around the C code.

Install "libcurl" on your machine yum install libcurl libcurl-devel or equivalent.

Usage example:

CURLplusplus client;
string x = client.Get("http://google.com");
string y = client.Get("http://yahoo.com");

Class implementation:

#include <curl/curl.h>


class CURLplusplus
{
private:
    CURL* curl;
    stringstream ss;
    long http_code;
public:
    CURLplusplus()
            : curl(curl_easy_init())
    , http_code(0)
    {

    }
    ~CURLplusplus()
    {
        if (curl) curl_easy_cleanup(curl);
    }
    std::string Get(const std::string& url)
    {
        CURLcode res;
        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
        curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, this);

        ss.str("");
        http_code = 0;
        res = curl_easy_perform(curl);
        if (res != CURLE_OK)
        {
            throw std::runtime_error(curl_easy_strerror(res));
        }
        curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);
        return ss.str();
    }
    long GetHttpCode()
    {
        return http_code;
    }
private:
    static size_t write_data(void *buffer, size_t size, size_t nmemb, void *userp)
    {
        return static_cast<CURLplusplus*>(userp)->Write(buffer,size,nmemb);
    }
    size_t Write(void *buffer, size_t size, size_t nmemb)
    {
        ss.write((const char*)buffer,size*nmemb);
        return size*nmemb;
    }
};

Answer 6

As you want a C++ solution, you could use Qt. It has a QHttp class you can use.

You can check the docs:

http->setHost("qt.nokia.com");
http->get(QUrl::toPercentEncoding("/index.html"));

Qt also has a lot more to it that you could use in a common C++ app.