linux send

Linux send是一个命令行工具，用于发送电子邮件。它可以通过SMTP服务器发送邮件，支持多种身份验证方式和加密协议。使用Linux send可以方便地在脚本中自动发送邮件，也可以手动发送邮件。它是Linux系统中非常常用的邮件发送工具之一。

相关问题

linux socket send函数

send函数是Linux中用于发送数据的函数，它可以将数据从一个socket发送到另一个socket。send函数的参数包括发送数据的socket描述符、要发送的数据、数据的长度、发送标志等。send函数返回值为成功发送的字节数，如果出现错误则返回-1。在使用send函数时需要注意数据的正确性和完整性，以及网络连接的稳定性。

linux epoll send recv 实例

下面是一个使用 epoll 实现的简单的 TCP 服务器和客户端的例子。服务器和客户端都是非阻塞的，使用 epoll 监听和处理文件描述符事件。其中，服务器使用了多线程技术，每个线程负责处理一个客户端连接。

服务器代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <netinet/in.h>
#include <sys/epoll.h>
#include <pthread.h>

#define MAX_EVENTS 1024
#define BUF_SIZE 1024
#define THREAD_NUM 4

int listen_fd;
int epoll_fd;
pthread_t thread_pool[THREAD_NUM];

void setnonblocking(int fd) {
    int flags = fcntl(fd, F_GETFL, 0);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}

void add_event(int fd, int events) {
    struct epoll_event ev;
    ev.events = events;
    ev.data.fd = fd;
    epoll_ctl(epoll_fd, EPOLL_CTL_ADD, fd, &ev);
}

void del_event(int fd, int events) {
    struct epoll_event ev;
    ev.events = events;
    ev.data.fd = fd;
    epoll_ctl(epoll_fd, EPOLL_CTL_DEL, fd, &ev);
}

void mod_event(int fd, int events) {
    struct epoll_event ev;
    ev.events = events;
    ev.data.fd = fd;
    epoll_ctl(epoll_fd, EPOLL_CTL_MOD, fd, &ev);
}

void *worker(void *arg) {
    int client_fd = *(int*)arg;
    char buf[BUF_SIZE];
    int nread;

    while (1) {
        nread = recv(client_fd, buf, BUF_SIZE, 0);
        if (nread == -1) {
            if (errno == EAGAIN) {
                printf("recv EAGAIN\n");
                break;
            } else {
                perror("recv");
                break;
            }
        } else if (nread == 0) {
            printf("client close\n");
            break;
        } else {
            printf("recv: %s\n", buf);
            if (send(client_fd, buf, nread, 0) == -1) {
                perror("send");
                break;
            }
        }
    }

    close(client_fd);
    pthread_exit(NULL);
}

void *accepter(void *arg) {
    struct sockaddr_in client_addr;
    socklen_t client_len = sizeof(client_addr);
    int client_fd;
    int i;

    while (1) {
        client_fd = accept(listen_fd, (struct sockaddr*)&client_addr, &client_len);
        if (client_fd == -1) {
            if (errno == EAGAIN) {
                printf("accept EAGAIN\n");
                continue;
            } else {
                perror("accept");
                break;
            }
        } else {
            setnonblocking(client_fd);
            add_event(client_fd, EPOLLIN|EPOLLET);
            printf("new client: %d\n", client_fd);
        }
    }

    close(listen_fd);
    pthread_exit(NULL);
}

int main(int argc, char *argv[]) {
    struct sockaddr_in server_addr;
    int port = 8888;
    struct epoll_event events[MAX_EVENTS];
    int nready;
    int i, j;

    if (argc > 1) {
        port = atoi(argv[1]);
    }

    listen_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (listen_fd == -1) {
        perror("socket");
        exit(1);
    }

    setnonblocking(listen_fd);

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(port);

    if (bind(listen_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
        perror("bind");
        exit(1);
    }

    if (listen(listen_fd, 1024) == -1) {
        perror("listen");
        exit(1);
    }

    epoll_fd = epoll_create(MAX_EVENTS);
    if (epoll_fd == -1) {
        perror("epoll_create");
        exit(1);
    }

    add_event(listen_fd, EPOLLIN|EPOLLET);

    for (i = 0; i < THREAD_NUM; i++) {
        if (pthread_create(&thread_pool[i], NULL, accepter, NULL) == -1) {
            perror("pthread_create");
            exit(1);
        }
    }

    while (1) {
        nready = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);
        if (nready == -1) {
            if (errno == EINTR) {
                continue;
            } else {
                perror("epoll_wait");
                break;
            }
        }

        for (i = 0; i < nready; i++) {
            if (events[i].data.fd == listen_fd) {
                continue;
            }

            if (events[i].events & EPOLLIN) {
                pthread_t thread_id;
                int client_fd = events[i].data.fd;
                del_event(client_fd, EPOLLIN|EPOLLET);
                if (pthread_create(&thread_id, NULL, worker, (void*)&client_fd) == -1) {
                    perror("pthread_create");
                }
            }
        }
    }

    for (i = 0; i < THREAD_NUM; i++) {
        if (pthread_join(thread_pool[i], NULL) == -1) {
            perror("pthread_join");
        }
    }

    close(epoll_fd);

    return 0;
}

客户端代码：

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

#define MAX_EVENTS 1024
#define BUF_SIZE 1024

void setnonblocking(int fd) {
    int flags = fcntl(fd, F_GETFL, 0);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}

void add_event(int fd, int events) {
    struct epoll_event ev;
    ev.events = events;
    ev.data.fd = fd;
    epoll_ctl(epoll_fd, EPOLL_CTL_ADD, fd, &ev);
}

void del_event(int fd, int events) {
    struct epoll_event ev;
    ev.events = events;
    ev.data.fd = fd;
    epoll_ctl(epoll_fd, EPOLL_CTL_DEL, fd, &ev);
}

void mod_event(int fd, int events) {
    struct epoll_event ev;
    ev.events = events;
    ev.data.fd = fd;
    epoll_ctl(epoll_fd, EPOLL_CTL_MOD, fd, &ev);
}

int main(int argc, char *argv[]) {
    struct sockaddr_in server_addr;
    char *ip = "127.0.0.1";
    int port = 8888;
    int sockfd;
    struct epoll_event events[MAX_EVENTS];
    int nready;
    char buf[BUF_SIZE];
    int nread, nwrite;
    int i;

    if (argc > 1) {
        ip = argv[1];
    }

    if (argc > 2) {
        port = atoi(argv[2]);
    }

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        perror("socket");
        exit(1);
    }

    setnonblocking(sockfd);

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr(ip);
    server_addr.sin_port = htons(port);

    if (connect(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
        if (errno != EINPROGRESS) {
            perror("connect");
            exit(1);
        }
    }

    epoll_fd = epoll_create(MAX_EVENTS);
    if (epoll_fd == -1) {
        perror("epoll_create");
        exit(1);
    }

    add_event(sockfd, EPOLLOUT);

    while (1) {
        nready = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);
        if (nready == -1) {
            if (errno == EINTR) {
                continue;
            } else {
                perror("epoll_wait");
                break;
            }
        }

        for (i = 0; i < nready; i++) {
            if (events[i].events & EPOLLOUT) {
                del_event(sockfd, EPOLLOUT);
                printf("connected\n");
                break;
            }
        }
    }

    while (1) {
        scanf("%s", buf);
        if (strcmp(buf, "quit") == 0) {
            break;
        }
        nwrite = send(sockfd, buf, strlen(buf), 0);
        if (nwrite == -1) {
            perror("send");
            break;
        }
        nread = recv(sockfd, buf, BUF_SIZE, 0);
        if (nread == -1) {
            if (errno == EAGAIN) {
                printf("recv EAGAIN\n");
                continue;
            } else {
                perror("recv");
                break;
            }
        } else if (nread == 0) {
            printf("server close\n");
            break;
        } else {
            printf("recv: %s\n", buf);
        }
    }

    close(sockfd);
    close(epoll_fd);

    return 0;
}