那recv函数呢

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#include <sys/types.h>
#include <sys/socket.h>

ssize_t recv(int sockfd, void *buf, size_t len, int flags);

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#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>

int receive_data(int sockfd) {
    char buffer[1024];
    ssize_t received_bytes = recv(sockfd, buffer, sizeof(buffer), 0);
    if (received_bytes < 0) {
        perror("recv failed");
        return -1;
    } else if (received_bytes == 0) {
        printf("Connection closed by peer.\n");
        return 0;
    } else {
        // 处理接收到的数据
        buffer[received_bytes] = '\0'; // 确保字符串以空字符结尾
        printf("Received %zd bytes: %s\n", received_bytes, buffer);
    }
    return received_bytes;
}

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ssize_t peek_data(int sockfd, void *buf, size_t len) {
    return recv(sockfd, buf, len, MSG_PEEK);
}

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ssize_t receive_exact(int sockfd, void *buf, size_t len) {
    return recv(sockfd, buf, len, MSG_WAITALL);
}

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#include <sys/select.h>

int recv_with_timeout(int sockfd, void *buf, size_t len, int timeout_sec) {
    fd_set readfds;
    struct timeval tv;

    FD_ZERO(&readfds);
    FD_SET(sockfd, &readfds);

    tv.tv_sec = timeout_sec;
    tv.tv_usec = 0;

    int ret = select(sockfd + 1, &readfds, NULL, NULL, &tv);
    if (ret > 0) {
        // 套接字可读
        return recv(sockfd, buf, len, 0);
    } else if (ret == 0) {
        // 超时
        fprintf(stderr, "recv timeout\n");
        return -2;
    } else {
        // 错误
        perror("select failed");
        return -1;
    }
}

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ssize_t recv_oob_data(int sockfd, void *buf, size_t len) {
    return recv(sockfd, buf, len, MSG_OOB);
}

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#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define SERVER_PORT 8080

int main() {
    int listenfd, connfd;
    struct sockaddr_in server_addr, client_addr;
    socklen_t client_len = sizeof(client_addr);
    char buffer[1024];

    // 忽略 SIGPIPE 信号
    signal(SIGPIPE, SIG_IGN);

    // 创建套接字
    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    if (listenfd < 0) {
        perror("socket creation failed");
        return -1;
    }

    // 设置服务器地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;          // IPv4
    server_addr.sin_addr.s_addr = INADDR_ANY;  // 监听所有接口
    server_addr.sin_port = htons(SERVER_PORT); // 端口

    // 绑定地址
    if (bind(listenfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("bind failed");
        close(listenfd);
        return -1;
    }

    // 开始监听
    if (listen(listenfd, 5) < 0) {
        perror("listen failed");
        close(listenfd);
        return -1;
    }

    printf("Server is listening on port %d...\n", SERVER_PORT);

    // 接受连接
    connfd = accept(listenfd, (struct sockaddr *)&client_addr, &client_len);
    if (connfd < 0) {
        perror("accept failed");
        close(listenfd);
        return -1;
    }

    printf("Client connected.\n");

    // 接收数据
    while (1) {
        ssize_t received = recv(connfd, buffer, sizeof(buffer) - 1, 0);
        if (received < 0) {
            if (errno == EINTR) {
                continue; // 被信号中断，重新接收
            } else {
                perror("recv failed");
                break;
            }
        } else if (received == 0) {
            printf("Client disconnected.\n");
            break;
        } else {
            buffer[received] = '\0'; // 确保字符串以空字符结尾
            printf("Received %zd bytes: %s\n", received, buffer);
            // 可以在此处处理数据，或发送响应
        }
    }

    // 关闭套接字
    close(connfd);
    close(listenfd);
    return 0;
}