Socket API 详解

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

#define MAX_EVENTS 64
#define BUF_SIZE   4096

static int setnonblock(int fd)
{
    int flags = fcntl(fd, F_GETFL);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);
    return flags;
}

typedef struct conn {
    int fd;
    char buf[BUF_SIZE];
    int len;
} conn_t;

conn_t *conn_new(int fd) {
    conn_t *c = calloc(1, sizeof(*c));
    c->fd = fd;
    return c;
}
void conn_free(conn_t *c) { free(c); }

int main(void)
{
    int lfd = socket(AF_INET, SOCK_STREAM, 0);
    int yes = 1;
    setsockopt(lfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));

    struct sockaddr_in addr = {
        .sin_family = AF_INET,
        .sin_port = htons(8080),
        .sin_addr.s_addr = htonl(INADDR_ANY),
    };
    bind(lfd, (struct sockaddr*)&addr, sizeof(addr));
    listen(lfd, 128);

    int epfd = epoll_create1(0);
    struct epoll_event ev = { .events = EPOLLIN, .data.ptr = NULL };
    epoll_ctl(epfd, EPOLL_CTL_ADD, lfd, &ev);

    struct epoll_event events[MAX_EVENTS];

    for (;;) {
        int n = epoll_wait(epfd, events, MAX_EVENTS, -1);
        for (int i = 0; i < n; i++) {
            if (events[i].data.ptr == NULL) {
                // listen socket
                struct sockaddr_in cli;
                socklen_t clilen = sizeof(cli);
                int cfd = accept(lfd, (struct sockaddr*)&cli, &clilen);
                if (cfd < 0) continue;
                setnonblock(cfd);
                conn_t *c = conn_new(cfd);
                struct epoll_event e = { .events = EPOLLIN|EPOLLET, .data.ptr = c };
                epoll_ctl(epfd, EPOLL_CTL_ADD, cfd, &e);
                char ip[INET_ADDRSTRLEN];
                printf("connected: %s:%d\n", inet_ntop(AF_INET, &cli.sin_addr, ip, sizeof(ip)), ntohs(cli.sin_port));
            } else {
                conn_t *c = events[i].data.ptr;
                if (events[i].events & (EPOLLERR | EPOLLHUP)) {
                    goto close;
                }
                if (events[i].events & EPOLLIN) {
                    while (1) {
                        ssize_t r = read(c->fd, c->buf + c->len, sizeof(c->buf) - c->len);
                        if (r > 0) {
                            c->len += r;
                            // 处理：HTTP 解析、回显等
                            write(c->fd, c->buf, c->len);
                            c->len = 0;
                        } else if (r == 0) {
                            goto close;
                        } else {
                            if (errno == EAGAIN) break;
                            if (errno == EINTR) continue;
                            goto close;
                        }
                    }
                }
            close:
                epoll_ctl(epfd, EPOLL_CTL_DEL, c->fd, NULL);
                close(c->fd);
                conn_free(c);
            }
        }
    }
}

int fd = socket(AF_INET, SOCK_STREAM, 0);
struct sockaddr_in srv = { .sin_family = AF_INET, .sin_port = htons(80) };
inet_pton(AF_INET, "192.168.1.10", &srv.sin_addr);
connect(fd, (struct sockaddr*)&srv, sizeof(srv));

char *req = "GET / HTTP/1.0\r\nHost: example.com\r\n\r\n";
write(fd, req, strlen(req));

char buf[4096];
ssize_t n;
while ((n = read(fd, buf, sizeof(buf)-1)) > 0) {
    buf[n] = 0;
    printf("%s", buf);
}
close(fd);

int fd = socket(AF_INET, SOCK_DGRAM, 0);
struct sockaddr_in addr = { .sin_family = AF_INET, .sin_port = htons(5000), .sin_addr.s_addr = htonl(INADDR_ANY) };
bind(fd, (struct sockaddr*)&addr, sizeof(addr));

for (;;) {
    char buf[1024];
    struct sockaddr_in cli;
    socklen_t clilen = sizeof(cli);
    ssize_t n = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr*)&cli, &clilen);
    if (n > 0) {
        sendto(fd, buf, n, 0, (struct sockaddr*)&cli, clilen);
    }
}

// server
int fd = socket(AF_UNIX, SOCK_STREAM, 0);
struct sockaddr_un addr = { .sun_family = AF_UNIX };
strcpy(addr.sun_path, "/tmp/my.sock");
unlink("/tmp/my.sock");
bind(fd, (struct sockaddr*)&addr, sizeof(addr));
listen(fd, 5);
int cfd = accept(fd, NULL, NULL);

int yes = 1;
setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));
setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &yes, sizeof(yes));
setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &yes, sizeof(yes));

int idle = 30, intvl = 5, cnt = 3;
setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &idle, sizeof(idle));
setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &intvl, sizeof(intvl));
setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, &cnt, sizeof(cnt));

#include <sys/sendfile.h>
sendfile(out_fd, in_fd, &offset, count);

#include <sys/uio.h
struct iovec iov[2];
iov[0].iov_base = header;
iov[0].iov_len = header_len;
iov[1].iov_base = body;
iov[1].iov_len = body_len;
writev(fd, iov, 2);

splice(fd_in, NULL, fd_out, NULL, count, 0);

// OpenSSL
SSL_library_init();
SSL_CTX *ctx = SSL_CTX_new(TLS_server_method());
SSL_CTX_use_certificate_file(ctx, "cert.pem", SSL_FILETYPE_PEM);
SSL_CTX_use_PrivateKey_file(ctx, "key.pem", SSL_FILETYPE_PEM);

SSL *ssl = SSL_new(ctx);
SSL_set_fd(ssl, cfd);
SSL_accept(ssl);
SSL_read(ssl, buf, sizeof(buf));
SSL_write(ssl, buf, len);
SSL_free(ssl);