win32 HTTP GET

win32_net.cpp

#include "win32_net.h"

#include <windows.h>
#include <wininet.h>
#pragma comment (lib, "Wininet.lib")
#include <stdio.h>
#include <wchar.h>
#include <cwctype>
#include <algorithm>

namespace net {

std::string HttpGet(std::wstring url, std::wstring headers) {
  std::string response;
  
  if (url.empty()) {
    return response;
  }

  // to lowercase
  std::wstring urlLower(url);
  std::transform(
    urlLower.begin(), urlLower.end(),
    urlLower.begin(),
    std::towlower);

  bool ssl;
  size_t schemeLen;
  if (urlLower.find(L"http://") == 0) {
    ssl = false;
    schemeLen = 7;
  }
  else if (urlLower.find(L"https://") == 0) {
    ssl = true;
    schemeLen = 8;
  }
  else {
    return response; // invalid url
  }

  // get host
  std::wstring host(url.substr(schemeLen, url.length() - schemeLen));
  size_t posSlash = host.find(L"/");
  size_t posQuestion = host.find(L"?");
  size_t posEnd = host.length();
  if (posSlash != std::string::npos && posQuestion != std::string::npos) {
    posEnd = std::min(posSlash, posQuestion);
  } else if (posSlash != std::string::npos) {
    posEnd = posSlash;
  } else if (posQuestion != std::string::npos) {
    posEnd = posQuestion;
  }
  host = host.substr(0, posEnd);

  // get port if exists (and remove it from host name)
  INTERNET_PORT port = ssl ? INTERNET_DEFAULT_HTTPS_PORT : INTERNET_DEFAULT_HTTP_PORT;
  size_t colonAndPortLen = 0;
  size_t posColon = host.find(L":");
  if (posColon != std::string::npos) {
    colonAndPortLen = 1;
    if (posColon + 1 < host.length()) {
      std::wstring sPort(host.substr(posColon + 1));
      colonAndPortLen += sPort.length();
      int iPort = _wtoi(sPort.c_str());
      if (iPort != 0) {
        port = (INTERNET_PORT)iPort;
        if (port == INTERNET_DEFAULT_HTTPS_PORT) {
          ssl = true;
        }
      }
    }

    // remove from host name
    host = host.substr(0, posColon);
  }

  if (host.empty()) {
    return response;
  }

  // get the rest (everything after host and port)
  std::wstring rest;
  if (url.length() > schemeLen + host.length() + colonAndPortLen)
    rest = url.substr(schemeLen + host.length() + colonAndPortLen);

  // TODO: parameterize useragent
  HINTERNET hIntSession = 
    ::InternetOpenW(L"MyGreatAppName", // useragent
      INTERNET_OPEN_TYPE_PRECONFIG, nullptr, nullptr, 0);
  if (!hIntSession) {
    return response;
  }

  HINTERNET hHttpSession = 
    ::InternetConnectW(hIntSession, host.c_str(),
        port,
        nullptr, nullptr, INTERNET_SERVICE_HTTP, 0, 0);
  if (!hHttpSession) {
    ::InternetCloseHandle(hIntSession);
    return response;
  }

  DWORD dwOpenFlags = INTERNET_FLAG_RELOAD | INTERNET_FLAG_NO_UI | INTERNET_FLAG_NO_COOKIES | INTERNET_FLAG_NO_CACHE_WRITE;
  if (ssl) {
    dwOpenFlags |= INTERNET_FLAG_SECURE;
  }

  HINTERNET hHttpRequest = HttpOpenRequestW(
    hHttpSession,
    L"GET",
    rest.empty() ? L"/" : rest.c_str(), // if lpszObjectName is empty string, must pass "/", otherwise no request will be made to the server (and there is no error).
    0, 0, 0, dwOpenFlags, 0);
  if (!hHttpRequest) {
    ::InternetCloseHandle(hHttpSession);
    ::InternetCloseHandle(hIntSession);
    return response;
  }

  if(!::HttpSendRequestW(hHttpRequest,
      headers.empty() ? nullptr : headers.c_str(),
      headers.empty() ? -1 : headers.length(),
      nullptr, 0)) {
    ::InternetCloseHandle(hHttpRequest);
    ::InternetCloseHandle(hHttpSession);
    ::InternetCloseHandle(hIntSession);
    return response;
  }

  char szBuffer[1025];
  DWORD dwRead=0;
  while(::InternetReadFile(hHttpRequest, szBuffer, sizeof(szBuffer)-1, &dwRead) && dwRead) {
    szBuffer[dwRead] = 0;
    //OutputDebugStringA(szBuffer);
    dwRead=0;
  }

  ::InternetCloseHandle(hHttpRequest);
  ::InternetCloseHandle(hHttpSession);
  ::InternetCloseHandle(hIntSession);
  
  return response;
}

} // namespace net

win32_net.h

#ifndef WIN32_NET_H_
#define WIN32_NET_H_

#include <string>

namespace net {

// headers = L"Content-Type: text/html\nMySpecialHeder: whatever"
std::string HttpGet(std::wstring url, std::wstring headers = L"");

}

#endif // WIN32_NET_H_