Unable to connect to host using getaddrinfo()

Question

Note: This is a project for homework, I will try to write the remaining code, but cannot figure out why this is unable to connect to an input URL.

I was given skeleton code that I modified a bit to receive an input URL. Expected usage could be: ./a.out http://google.com

For whatever reason it never succeeds in connecting. The error message "could not connect" always is printed. Later I will need to take a file from the URL and save it to the local directory but I will try to figure out how to do that (my guess is that it has to do with recv() in the code below). In the case of "http://google.com" I would be expected to take "index.html".

The skeleton code is using connect() but the man page for getaddrinfo() uses bind() which seems to be much faster but also is not working. Using connect() it never seems to leave the for loop (Edit: It never leaves because it seems to be stuck trying to connect):

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char** argv) {
        // Alex: Input usage (expecting one URL)
        if (argc != 2) {
                printf("Usage: ./hw1 URL\n");
                exit(1);
        }

        // Alex: Set noHttp as argv[1] and remove "http://"
        char* noHttp = argv[1];
        char http[] = "http://";
        if (strlen(noHttp) > 7 && !strncmp(noHttp, http, 7)) noHttp += 7;
        else {
                printf("Invalid URL, expecting http://host/path\n");
                exit(1);
        }
        printf("%s\n", noHttp);

        struct addrinfo hints;
        struct addrinfo* result, * rp;
        int sock_fd, s;

        // Alex: I moved assigning hints.ai_socktype after memset()
        memset(&hints, 0, sizeof(struct addrinfo));
        //hints.ai_socktype = SOCK_STREAM;

        s = getaddrinfo(noHttp, "8080", &hints, &result); // To Stack Overflow: This changed to "80", I am leaving it here because there are comments about it
        if (0 != s) {
                perror("Error populating address structure");
                exit(1);
        }

        int i = 0;
        for (rp = result; rp != NULL; rp = rp->ai_next) {
                printf("i = %d\n", i);
                i++;

                //printf("rp->ai_flags = %d\n", rp->ai_flags);
                printf("rp->ai_family = %d\n", rp->ai_family);
                printf("rp->ai_socktype = %d\n", rp->ai_socktype);
                printf("rp->ai_protocol = %d\n", rp->ai_protocol);

                sock_fd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
                printf("sock_fd = %d\n", sock_fd);
                if (sock_fd == -1) continue;

                // Success
                if (connect(sock_fd, rp->ai_addr, rp->ai_addrlen) != -1) break;
                close(sock_fd);
        }

        if (rp == NULL) {
                fprintf(stderr, "could not connect\n");
                exit(1);
        }

        freeaddrinfo(result);

        char buf[255];
        memset(&buf, 0, sizeof(buf));

        int recv_count = recv(sock_fd, buf, 255, 0);
        if (recv_count < 0) {
                perror("Receive failed");
                exit(1);
        }

        printf("%s",buf);
        shutdown(sock_fd, SHUT_RDWR);
        return 0;
}

Edit: I replaced "8080" with "80" as Uku Loskit recommended.

Answer 1

Your program looks OK to me, run netcat on port 8080 and connet to the host:

$ echo "Hello" | ncat -l 8080

will return:

$ gcc -Wall sample.c 
$ ./a.out http://127.0.0.1
127.0.0.1
i = 0
rp->ai_family = 2
rp->ai_socktype = 1
rp->ai_protocol = 6
sock_fd = 3
Hello
$ 

in order to connect to HTTP, you need to send HTTP request first or it will block, add after the line 64:

    freeaddrinfo(result);

    send(sock_fd, "GET / HTTP/1.1\n\n", 16, 0); // HTTP request

    char buf[255];
    memset(&buf, 0, sizeof(buf));

this will send the request:

GET / HTTP/1.1

and change the port to 80, it should work:

$ ./a.out http://google.com
google.com
i = 0
rp->ai_family = 2
rp->ai_socktype = 1
rp->ai_protocol = 6
sock_fd = 3
HTTP/1.1 200 OK
Date: Sun, 01 Sep 2013 21:05:16 GMT
Expires: -1
Cache-Control: private, max-age=0
Content-Type: text/html; charset=ISO-8859-1
P3P: CP="This is not a P3P policy! See http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=151
$ 

Answer 2

You should be connecting on port 80, not 8080. Port 80 is the default for HTTP.

Answer 3

When you change your port number to 80 and connect to http://google.com, it'll work as expected, but hangs on the recv() call because an HTTP server won't send anything to you until you ask it for something. Sp.'s answer gives you an example of how to do this by adding a send() call before your recv() call.

What's happening right now is you're connecting to it, and it's waiting for you to tell it what you want. What you are doing is just waiting for it to send you something with your recv() call, so you're both going to just wait until it times out.