http server (c) - send command doesn't work (empty reply from server)

Question

I got a task to implement a http server in c code. it should include handling several connections, but for now I just want to make sure it works with just a single connection. first, here is my code:

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>

#define BUF_SIZE 1025

int main(int argc, char **argv)
{

    uint16_t portNum = 80;   
    int connfd = 0, listenFd;
    struct sockaddr_in serv_addr, peer_addr;

    if ((listenFd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("socket syscall failed: %s.\nExiting...\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    memset(&serv_addr, 0, sizeof(serv_addr));


    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); 
    serv_addr.sin_port = htons(portNum);

    if (bind(listenFd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)))
    {
        printf("bind syscall failed: %s\nExiting...\n", strerror(errno));
        exit(EXIT_FAILURE);
    }

    if (listen(listenFd, 5))
    {
        printf("listen syscall failed: %s\nExiting...\n", strerror(errno));
        exit(EXIT_FAILURE);
    }

    while (1)
    {
        /* new connection */
        socklen_t addrsize = sizeof(struct sockaddr_in);
        connfd = accept(listenFd, (struct sockaddr *) &peer_addr, &addrsize);
        if (connfd < 0)
        {
            printf("\n Error : Accept Failed. %s \n", strerror(errno));
            return 1;
        }

        char httpRequest[BUF_SIZE] = {0};       
        if ((recv(connfd, httpRequest, BUF_SIZE, 0)) == -1)
        {
            printf("recv syscall failed: %s\nExiting...\n", strerror(errno));
            exit(EXIT_FAILURE);
        }

        char msg[BUF_SIZE] = {0};
        strcpy(msg, "200 OK THIS IS A TEST");
        printf("sending message...\n");
        int len = strlen(msg);
        if (send(connfd, msg, len, 0) < 0)
        {
            printf("SEND ERROR\n");
            exit(EXIT_FAILURE);
        }
        printf("message sent!\n");
        close(connfd);
        close(listenFd);
        // THIS IS FOR DEBUG - ignore...
        return 0;

    }

    return EXIT_SUCCESS;
}

here's my problem: to test my code I ran the following command in another linux terminal:

curl -v loaclhost:80/~/ex.txt

(where ex.txt is simply a test file...) here is the problem: I see the http request both in the server and in the curl output, but it seems like the "send" command of the server doesn't work - in the curl window beneath the http rquest it says:

* Empty reply from server
* Connection #0 to host localhost left intact
curl: (52) Empty reply from server

any ideas?

Answer 1

1. Buffer of 1024 is too small for anything serious. For just playing locally it will work OK. If you ever want to do some serious work buffer of 8192 bytes works fine even for heavy loads.

2. recv() is in most implementations blocking function, which means that it will block until it receives the entered number of bytes or a client closes the connection after sending data. I didn't see your socket being defined and treated as non-blocking. So that part is up to curl to overcome.

3. Your HTTP response is wrong.

The header should look like:

"HTTP/1.1 200 OK\r\nStatus: 200 OK\r\nContent-Type: text/plain\r\n\r\n"

You may also add a header:

"Content-Length: 0"

as you aren't sending any data back except the header.

Also, if you continue using HTTP/0.9 or switch to HtTP/1.0, you should close the connection with a client after sending the data to him.

HTTP/1.1 supports opened connection, but it is usually controlled via Keep-Alive and Connection headers.

Answer 2

ok, -1 for me, it didn't work due to the missing '\n' character in strcpy..