使用 curlpp 在 C++ 中发出 POST 请求

Question

I am attempting to make a POST request using curlpp in C++ to Statistics Canada with their getDataFromVectorsAndLatestNPeriods . I can't seem to get a result from the request.

#include <stdlib.h>
#include <stdio.h>
#include <curlpp/cURLpp.hpp>
#include <curlpp/Easy.hpp>
#include <curlpp/Options.hpp>

int main()
{
    curlpp::Cleanup cleanup;
    curlpp::Easy request;
    curlpp::Forms form;

    request.setOpt(curlpp::options::Url(std::string("https://www150.statcan.gc.ca/t1/wds/rest/getDataFromVectorsAndLatestNPeriods")));
    request.setOpt(curlpp::options::Verbose(true));

    form.push_back(new curlpp::FormParts::Content("vectorID:54325508","latestN:1"));
    request.setOpt(new curlpp::options::HttpPost(form));

    request.setOpt(new curlpp::options::WriteStream(&std::cout));

    request.perform();

    return 0;
}

I compiled it with g++ -std=gnu++11 -lcurl -lcurlpp cry.cpp

And when the output when verbose is set to true is:

*   Trying 205.193.226.160...
* TCP_NODELAY set
* Connected to www150.statcan.gc.ca (205.193.226.160) port 443 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*   CAfile: /etc/ssl/cert.pem
  CApath: none
* SSL connection using TLSv1.2 / ECDHE-RSA-AES256-GCM-SHA384
* ALPN, server did not agree to a protocol
* Server certificate:
*  subject: C=CA; ST=Ontario; L=Ottawa; jurisdictionCountryName=CA; O=Statistics Canada; businessCategory=Government Entity; serialNumber=1970-01-01; CN=www150.statcan.gc.ca
*  start date: Oct  4 16:33:01 2019 GMT
*  expire date: Jan  3 17:02:58 2022 GMT
*  subjectAltName: host "www150.statcan.gc.ca" matched cert's "www150.statcan.gc.ca"
*  issuer: C=US; O=Entrust, Inc.; OU=See www.entrust.net/legal-terms; OU=(c) 2014 Entrust, Inc. - for authorized use only; CN=Entrust Certification Authority - L1M
*  SSL certificate verify ok.
> POST /t1/wds/rest/getDataFromVectorsAndLatestNPeriods HTTP/1.1
Host: www150.statcan.gc.ca
Accept: */*
Content-Length: 161
Content-Type: multipart/form-data; boundary=------------------------8fe530d4d57d4b83

* We are completely uploaded and fine
< HTTP/1.1 415 
< Date: Sat, 06 Nov 2021 03:39:47 GMT
< Content-Length: 0
< Connection: keep-alive
< X-Content-Type-Options: nosniff
< X-XSS-Protection: 1; mode=block
< Content-Security-Policy: default-src 'self' 'unsafe-inline' *.statcan.gc.ca *.statcan.ca *.stc.ca  *.demdex.net *.omtrdc.net *.everesttech.net blob:; style-src 'self' 'unsafe-inline' *.statcan.gc.ca *.statcan.ca https://fonts.googleapis.com blob:; script-src 'self' 'unsafe-inline' 'unsafe-eval' *.statcan.gc.ca *.statcan.ca *.googletagmanager.com *.adobedtm.com *.jsdelivr.net *.mathjax.org cdnjs.cloudflare.com blob:; connect-src 'self' *.statcan.gc.ca *.statcan.ca *.stc.ca  *.demdex.net *.omtrdc.net https://api.mapbox.com/ https://events.mapbox.com/; img-src 'self' *.statcan.gc.ca *.statcan.ca *.stc.ca  *.demdex.net *.omtrdc.net *.everesttech.net *.jsdelivr.net data: blob:; font-src 'self' *.statcan.gc.ca *.statcan.ca https://fonts.gstatic.com; worker-src 'self' 'unsafe-inline' 'unsafe-eval' *.statcan.gc.ca *.statcan.ca blob:; frame-src 'self' 'unsafe-inline' *.statcan.gc.ca *.statcan.ca *.stc.ca https://dv-vd.shinyapps.io *.demdex.net blob:;
< Strict-Transport-Security: max-age=31536000; includeSubDomains
< Strict-Transport-Security: max-age=31536000
< 
* Connection #0 to host www150.statcan.gc.ca left intact

* Closing connection 0

What is happening and how can I get it to do what I actually want?

Answer 1

I haven't used libcurlpp , but for libcurl a natural way of making a POST request is through the CURLOPT_POST and CURLOPT_POST_FIELDS options, see for example How to use libcurl for HTTP post? . This leas to this simple main:

int main()
{
  curlpp::Cleanup cleanup;
  curlpp::Easy request;

  request.setOpt(curlpp::options::Url(std::string("https://www150.statcan.gc.ca/t1/wds/rest/getDataFromVectorsAndLatestNPeriods")));
//  request.setOpt(curlpp::options::Verbose(true));

  std::list<std::string> header = 
  {
    "Content-Type: application/json",
    "accept: application/json"
  }; 
  request.setOpt(new curlpp::options::HttpHeader(header)); 

  std::string query = "[{\"vectorId\":54325508, \"latestN\":1}]";
  request.setOpt(new curlpp::options::PostFields(query)); 
  request.setOpt(new curlpp::options::WriteStream(&std::cout));

  request.perform();
}

The part setting the HTTP header can actually be skipped for the server you connect with. The solution is in complete agreement with example 12 from curlpp documentation, https://github.com/jpbarrette/curlpp/blob/master/examples/example12.cpp .