semxx.c

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

const char RESP[] = "HTTP/1.1 200 OK\r\nConnection: close\r\nContent-Length: 0\r\n\r\n";

int server() {
    int fd = socket(AF_INET, SOCK_STREAM, 0);
    if (fd == -1) {
        return 1;
    }

    struct sockaddr_in addr = {0};
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY); // 0.0.0.0
    addr.sin_port = htons(1337); // 32768-60999

    int rc = bind(fd, (struct sockaddr*)&addr, sizeof(addr));
    if (rc != 0) {
        close(fd);
        return 1;
    }

    struct sockaddr_in l_addr = {0};
    int l_addr_len = sizeof(l_addr);
    getsockname(fd, (struct sockaddr*)&l_addr, &l_addr_len);
    printf("bind address: %s:%d\n", inet_ntoa(l_addr.sin_addr), (int)ntohs(l_addr.sin_port));

    rc = listen(fd, 16);
    if (rc != 0) {
        close(fd);
        return 1;
    }

    char buf[512];    
    for (;;) {
        printf("ready for accept\n");
        struct sockaddr_in r_addr = {0};
        int r_addr_len = sizeof(r_addr);
        int c_fd = accept(fd, (struct sockaddr*)&r_addr, &r_addr_len);
        printf("accepted connection from: %s:%d\n", inet_ntoa(r_addr.sin_addr), (int)ntohs(r_addr.sin_port));

        int n_read = recv(c_fd, &buf, sizeof(buf), 0);
        if (n_read == 0) {
            printf("closed from remote\n");
            close(c_fd);
            break;
        }

        int n_sent = send(c_fd, &RESP, sizeof(RESP), 0);
        // EINPROGRESS | EAGAIN
        printf("sent %d bytes\n", n_sent);

        close(c_fd);
    }

    close(fd);

    return 0;
}

int client() {
    int fd = socket(AF_INET, SOCK_STREAM, 0);
    if (fd == -1) {
        return 1;
    }

    struct sockaddr_in addr = {0};
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(0x7f000001); // 127.0.0.1 | 127 0 0 1 | 0x7f, 0x00, 0x00, 0x01
    addr.sin_port = htons(1337); // 32768-60999

    int rc = connect(fd, (struct sockaddr*)&addr, sizeof(addr));
    if (rc == -1) {
        close(fd);
        return 1;
    }

    printf("CONNECTED\n");
    send(fd, "Hi", 3, 0);

    return 0;
}

int epoll_server() {
    int fd = socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);
    if (fd == -1) {
        return 1;
    }

    struct sockaddr_in addr = {0};
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(1337);

    int rc = bind(fd, (struct sockaddr*)&addr, sizeof(addr));
    if (rc != 0) {
        return 1;
    }

    struct sockaddr_in l_addr;
    socklen_t l_addr_len = sizeof(l_addr);
    getsockname(fd, (struct sockaddr*)&l_addr, &l_addr_len);
    printf("bind address: %s:%d\n", inet_ntoa(l_addr.sin_addr), (int)ntohs(l_addr.sin_port));

    rc = listen(fd, 16);
    if (rc != 0) {
        return 1;
    }

    int efd = epoll_create1(0);
    if (efd == -1) {
        return 1;
    }
        
    struct epoll_event event;
    event.data.fd = fd;
    event.events = EPOLLIN | EPOLLET;
    rc = epoll_ctl(efd, EPOLL_CTL_ADD, fd, &event);
    if (rc == -1) {
        return 1;
    }

    struct epoll_event *events = calloc(1024, sizeof event);
    for (;;) {
        int n = epoll_wait(efd, events, 1024, -1);
        for (int i = 0; i < n; i++) {
	    if ((events[i].events & EPOLLERR) || (events[i].events & EPOLLHUP) || (!(events[i].events & EPOLLIN))) {
	        close (events[i].data.fd);
	        continue;
        } else if (fd == events[i].data.fd) {
              // We have a notification on the listening socket, which means one or more incoming connections.
              while (1) {
                    struct sockaddr in_addr;
                    socklen_t in_len = sizeof in_addr;
                    int infd = accept4(fd, &in_addr, &in_len, SOCK_NONBLOCK);
                    if (infd == -1) {
                        if ((errno == EAGAIN) || (errno == EWOULDBLOCK)) {
                            // It's ok.
                            break;
                        } else {
                            // Not OK :(
                            break;
                        }
                    }

                    event.data.fd = infd;
                    event.events = EPOLLIN | EPOLLET;
                    rc = epoll_ctl(efd, EPOLL_CTL_ADD, infd, &event);
                    if (rc == -1) {
                        return 1;
                    }
                }
            } else {
                int done = 0;

                while (1) {
                    char buf[512];

                    int n_read = recv(events[i].data.fd, buf, sizeof buf, 0);
                    if (n_read == -1) {
                        if (errno != EAGAIN) {
                            done = 1;
                        }
                        break;
                    } else if (n_read == 0) {
                        // EOF.
                        done = 1;
                        break;
                    }
                
                    int n_sent = send(events[i].data.fd, RESP, sizeof(RESP), 0);
                    if (n_sent == -1) {
                        if (errno != EAGAIN) {
                            done = 1;
                        }
                        break;
                    }
                    done = 1;
                    break;                    
                }

                if (done) {
                    close(events[i].data.fd);
                }
            }
        }
    }

    return 0;
}

int main(int argc, char** argv) {
    if (argc == 1) {
        return server();
    } else if (argc == 2) {
        return epoll_server();
    } else {
        return client();
    }
}