WinInet : How to send multiple http get request with C++

Question

I'm trying to write a program that download some things from a remote server,

#include <iostream>
#include <string>
#include <Windows.h>
#include <WinInet.h>
#pragma comment(lib,"wininet.lib")

using namespace std;

string Get(){
    DWORD size = 0;
    DWORD wrt;
    string msg = "";
    HINTERNET io=InternetOpen("Downloader",INTERNET_OPEN_TYPE_DIRECT,NULL,NULL,0);
    HINTERNET ic=InternetConnect(io,"192.168.1.15",8080,NULL,NULL,INTERNET_SERVICE_HTTP,0,0);
    HINTERNET hreq=HttpOpenRequest(ic,NULL,"/cgi-bin/cmd.py","HTTP/1.0",NULL,NULL,0,0);
    HttpSendRequest(hreq,NULL,0,NULL,0);
    InternetQueryDataAvailable(hreq,&size,0,0);
    char* buffer = new char[size+1];
    memset(buffer,0,size+1);
    InternetReadFile(hreq,buffer,size,&wrt);
    msg += buffer;
    free(buffer);
    InternetCloseHandle(io);
    InternetCloseHandle(ic);
    InternetCloseHandle(hreq);
    return msg;
}


int main(){
    while(TRUE){
        string msg=Get();
        if(msg.length()>1){
            cout<<msg<<endl;
        }
        Sleep(2000);
    }
return 0;
}

In the other side (on server ) I run a python CGI script , to send the text. The problem is that the program send the GET request just one time, even if there is a loop and the msg.length() is equal to 0 , in the other side I can see that I just recieved one GET request . Can someone solve my problem, or any idea ....

What insights could you gather from running the application under a debugger? — IInspectable, Sep 13 '16 at 17:49
Is the code you show the actual code you're running? If not, then in your actual you do check for error from all the functions you call? Many of them can fail and you don't seem to be checking for that (if the code you show is your actual code). — Some programmer dude, Sep 13 '16 at 17:50
@JoachimPileborg it's my actual code , so I will see what fonctions return ... , but even if the program don't crash ? — Tarek Radah, Sep 13 '16 at 17:55
If you call a function that can fail, then you need to check for failure. Failure will always happen when you least expect it. — Some programmer dude, Sep 13 '16 at 17:56
...lest you violate [Henry Spencer's 6th Commandment](https://www.lysator.liu.se/c/ten-commandments.html). — WhozCraig, Sep 13 '16 at 17:57
@JoachimPileborg now the code look like : if(!HttpSendRequest(hreq,NULL,0,NULL,0))cout< — Tarek Radah, Sep 13 '16 at 18:13
`char* buffer = new char[size+1];` followed by `free(buffer)` is wrong. Either `new` and `delete`, or `malloc` and `free`. — user58697, Sep 13 '16 at 20:51
@user58697 I agree with you , but it's not the source of my problem — Tarek Radah, Sep 13 '16 at 23:20
@TarekRadah How do you know the mismatch in allocation/freeing is not the cause? What you do leads to *undefined behavior* and after that all bets are off. To *seemingly* work is one of the possible outcomes of undefined behavior. — Some programmer dude, Sep 14 '16 at 05:44

score 2 · Accepted Answer · edited Oct 15 '19 at 06:56

You need to add error handling to each WinInet API call.

You also need to loop InternetReadFile(), as it may take multiple reads to receive the full response. And you need to take into account the number of bytes actually read when appending each buffer to your std::string.

Try something more like this:

#include <iostream>
#include <string>
#include <sstream>
#include <stdexcept>

#pragma comment(lib, "wininet.lib")

struct sHINTERNET
{
    HINTERNET hInet;

    sHINTERNET(HINTERNET AInet = NULL) : hInet(AInet) {}
    ~sHINTERNET() { InternetCloseHandle(hInet); }

    operator HINTERNET() { return hInet; }
    bool operator!() const { return !hInet; }
}

void WinInetError(const char *FuncName)
{
    DWORD dwErr = GetLastError();

    std::ostringstream oss;
    oss << FuncName << " failed!";

    if (dwErr != ERROR_INTERNET_EXTENDED_ERROR)
        oss << " Error: " << dwErr;
    else
    {
        DWORD dwLen = 0;
        InternetGetLastResponseInfo(&dwErr, NULL, &dwLen);

        if (GetLastError() == ERROR_INSUFFICIENT_BUFFER)
        {
            std::basic_string<TCHAR> msg;

            ++dwLen;
            msg.resize(dwLen);

            if (InternetGetLastResponseInfo(&dwErr, &msg[0], &dwLen))
            {
                msg.resize(dwLen);
                oss << " Error: " << msg;
            }
        }
    }

    throw std::runtime_error(oss.str());
}

std::string Download()
{
    sHINTERNET io = InternetOpen("Downloader", INTERNET_OPEN_TYPE_DIRECT, NULL, NULL, 0);
    if (!io)
        WinInetError("InternetOpen");

    sHINTERNET ic = InternetConnect(io, "192.168.1.15", 8080, NULL, NULL, INTERNET_SERVICE_HTTP, 0, 0);
    if (!ic)
        WinInetError("InternetConnect");

    sHINTERNET hreq = HttpOpenRequest(ic, NULL, "/cgi-bin/cmd.py", "HTTP/1.0", NULL, NULL, 0, 0);
    if (!hreq)
        WinInetError("HttpOpenRequest");

    if (!HttpSendRequest(hreq, NULL, 0, NULL, 0))
        WinInetError("HttpSendRequest");

    std::string data;
    char buffer[1024];
    DWORD wrt;

    do
    {
        if (!InternetReadFile(hreq, buffer, sizeof(buffer), &wrt))
            WinInetError("InternetReadFile");

        if (wrt == 0)
            break; 

        data.append(buffer, wrt);
    }
    while (true);

    return data;
}

int main()
{
    while (true)
    {
        try
        {
            std::string data = Download();
            std::cout << data << std::endl;
        }
        catch (const std::exception &e)
        {
            std::cerr << "Error! " << e.what() << std::endl;
        }

        Sleep(2000);
    }

    return 0;
}

Tnks!!! actualy my problem is to verify each time if there is some things in the other side to download — Tarek Radah, Sep 14 '16 at 00:44
it's okey for the loop and the error handling but I don't understand this : struct sHINTERNET {HINTERNET hInet; sHINTERNET(HINTERNET AInet = NULL) : hInet(AInet) {} ~sHINTERNET() { InternetCloseHandle(hInet); } operator HINTERNET() { return hInet; } bool operator!() const { return !hInet; } } — Tarek Radah, Sep 14 '16 at 12:29
It is similar to a smart pointer (`std::auto_ptr`, `std::unique_ptr`, etc). It uses RAII to automate the calling of `InternetCloseHandle()`, thus allowing for cleaner and exception-safe code. If you are using C++11 or later, you can use `std::unique_ptr` instead of defining a custom struct. The end effect is the same. — Remy Lebeau, Sep 14 '16 at 14:59

WinInet : How to send multiple http get request with C++

1 Answers1