Question

I am working on a function that will (when it’s finished) return the output of an html page. I just got help from StackOverFlow with understanding how recv works, and I am now at a point where I am finishing up the function. The problem I am having right now is that it appears that the socket is not opening properly. The recv function just returns -1 (which indicates a socket error I believe)

Here is the code:

#include <stdio.h>
#include <stdlib.h>
#include <winsock2.h>
#include <windows.h>
#define BUFFERSIZE 4096

char *readsite(const char *url, const char *ip, const int port)
{
    char *req, *ret, *tmp, tmpbuff[256];
    int c, i, q;
    SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    struct sockaddr_in sa = { 0 };
    sa.sin_port = htons(port);
    sa.sin_addr.s_addr = inet_addr(ip);

    for(i = 0; url[i] != 0x00; i++);
    req = malloc((i + 18) * sizeof(char));
    if(!req) return NULL;
    req[0] = 'G';
    req[1] = 'E';
    req[2] = 'T';
    req[3] = ' ';
    for(c = 4, q = 0; q <= i; c++, q++) req[c] = url[q];
    req[c - 1] = ' ';
    req[c + 0] = 'H';
    req[c + 1] = 'T';
    req[c + 2] = 'T';
    req[c + 3] = 'P';
    req[c + 4] = '/';
    req[c + 5] = '1';
    req[c + 6] = '.';
    req[c + 7] = '0';
    req[c + 8] = '\r';
    req[c + 9] = '\n';
    req[c + 10] = '\r';
    req[c + 11] = '\n';
    req[c + 12] = '\0';
    connect(sock, (struct sockaddr*)&sa, sizeof(sa));
    for(i = 0; req[i] != 0x00; i++);
    send(sock, req, i, 0);
    printf("%s %s", req, ip);
    free(req);
    ret = malloc(BUFFERSIZE);
    if(!ret) return NULL;
    c = 0;             // recv value
    i = BUFFERSIZE;    // buffer size
    q = 0;             // loaded bytes
    while((c = recv(sock, tmpbuff, sizeof(tmpbuff), 0)) > 0)
    {
        if((q + c + 1) > i)
        {
                i += BUFFERSIZE;
                if(!(tmp = realloc(ret, i))) return NULL;
                ret = tmp;
        }
    }
 }

int main(void)
{
        readsite("http://www.google.com/", "74.125.226.226", 80);
    return 0;
}

Answer 1

Use the error code in errno to figure out what went wrong; perror() is a great function for this, call it after a check for error code != 0. Here is a suggested way of doing so in your code:

while(1)
{
    if ((c = recv(sock, tmpbuff, sizeof(tmpbuff), 0)) < 0) {
        perror("Receive error");
    }
    else if (c == 0) { 
        break;
    }
    if((q + c + 1) > i)
    {
            i += BUFFERSIZE;
            if(!(tmp = realloc(ret, i))) return NULL;
            ret = tmp;
    }
}