C++ LibCurl GET from Socket - c++

Question

I would like to convert this code (using a scripting language with a Sockets extension) over to C++ using LibCurl. I have only used LibCurl once previously, so I am at a bit of a loss as to what else I am going to need. My main point of confusing is wether I should be able to just use curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers); to send this, or if I am going to need to extract the socket, then send it over that.
Here is the relevant snippet from the script...
public OnSocketConnected(Handle:socket, any:friendId)
{
decl String:CommunityId[32];
FriendIDToCommunityId(friendId, CommunityId, sizeof(CommunityId));
decl String:query[2048];
decl String:cookieString[100];
decl String:inviterString[32];
decl String:groupString[32];
GetConVarString(cookie, cookieString, sizeof(cookieString));
GetConVarString(inviter, inviterString, sizeof(inviterString));
GetConVarString(group, groupString, sizeof(groupString));
Format(query, sizeof(query), "GET /actions/GroupInvite?type=groupInvite&inviter=%s&invitee=%s&group=%s HTTP/1.1\r\nHost: steamcommunity.com\r\nConnection: close\r\nCookie: steamLogin=%s\r\n\r\n", inviterString, CommunityId, groupString, cookieString);
SocketSend(socket, query);
LogMessage("%s", query);
}
and here is what I have in C++ so far. It is looking like I am going to need to extract the socket first, but I am not proficient with network coding, so I am not exactly sure where I need to go from here.
void InviteToGroup(const char *szUserSteamID, const char *szInviterSteamID, const char *steamUser, const char *steamPass)
{
CURL *curl;
CURLcode res, result;
//int sockfd; /* socket */
char errorBuffer[CURL_ERROR_SIZE];
const char *szUserID = GetCommunityID(szUserSteamID); // User's Steam Community ID
const char *szInviterID = GetCommunityID(szInviterSteamID); // Inviter's Steam Community ID
char *szGroupID = "";
GetGroupCommunityID(1254745, &szGroupID); // Group Steam Community ID
const char *szCookie = "76561198018111441%7C%7CC7D70E74A3F592F3E130CCF4CAACD4A7B9CAD993"; // Steam Community Login Cookie
char *buffer = new char[512];
// Create the GET request
struct curl_slist *headers = NULL;
headers = curl_slist_append(headers, "GET /actions/GroupInvite?type=groupInvite&inviter=");
snprintf(buffer, sizeof(buffer), "%s&invitee=%s&group=%s ", szInviterID, szUserID, szGroupID);
headers = curl_slist_append(headers, buffer);
headers = curl_slist_append(headers, "HTTP/1.1\r\nHost: steamcommunity.com\r\nConnection: close\r\nCookie: ");
snprintf(buffer, sizeof(buffer), "steamLogin=%s\r\n\r\n", szCookie);
headers = curl_slist_append(headers, buffer);
delete buffer;
// Init CURL
curl = curl_easy_init();
if(curl)
{
curl_easy_setopt(curl, CURLOPT_URL, "https://www.steamcommunity.com");
curl_easy_setopt(curl, CURLOPT_PORT, 443); // Check this before using
curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errorBuffer);
//curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1); // No transfer, just extract the socket
// Find out if we need to use Proxy stuff here
char *userpass = new char[64];
snprintf(userpass, sizeof(userpass), "%s:%s", steamUser, steamPass);
curl_easy_setopt(curl, CURLOPT_USERPWD, userpass);
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
// Attempt to Connect the Steam Community Server
res = curl_easy_perform(curl);
if (res == CURLE_OK)
Msg("Connected Successfully!\n");
else
Msg("Connection Failed! Error: %s\n", errorBuffer);
// Close the connection
curl_easy_cleanup(curl);
}
}

Answer 1

So corrections here as your C++ is incorrect which will mean your code won't work.
sizeof( char * ) is the size of a pointer, not the length of the string. So your snprintf will print up to 4 characters on a 32-bit system which will include the null terminator so you will actually get only a string of length 3.
If you are going to use a "should be big enough" buffer do not allocate it with new. You could use std::vector if you want to use snprintf, then check the return value of snprintf which is the length of the actual string that would be written and then increase the buffer size if necessary (to the return value + 1).
vector<char> buffer;
size_t required = 511;
do
{
buffer.resize( required + 1 );
required = snprintf( &buffer[0], buffer.size(), formatstr, ... );
}
while( required >= buffer.size() );
There is no need to "free" the buffer at the end (which incidentally you did incorrectly) as vector will do that automatically.
You now pass &buffer[0] to the function, it will point to a null-terminated string and will be writable if the API requires a char* rather than a const char*. (libcurl though takes ... as the 3rd parameter to curl_easy_setopt so you can pass in "anything". You therefore do have to be careful as you won't get warned by the compiler if you accidentally pass in a std::string or std::vector).