如何获取并理解FTP服务器的C语言源代码？

由于FTP服务器源代码较长，我将为您提供一个简单的C语言实现的FTP服务器示例，这个示例仅用于演示目的，实际应用中需要考虑更多的安全性和功能。

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#define PORT 8080
#define BUFFER_SIZE 1024
void handle_client(int client_socket) {
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, sizeof(buffer));
    ssize_t bytes_read = recv(client_socket, buffer, sizeof(buffer), 0);
    if (bytes_read > 0) {
        printf("Received: %s
", buffer);
        send(client_socket, buffer, bytes_read, 0);
    }
    close(client_socket);
}
int main() {
    int server_socket, client_socket;
    struct sockaddr_in server_addr, client_addr;
    socklen_t addr_len = sizeof(client_addr);
    server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket == 1) {
        perror("socket");
        exit(EXIT_FAILURE);
    }
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) == 1) {
        perror("bind");
        exit(EXIT_FAILURE);
    }
    if (listen(server_socket, 5) == 1) {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    printf("Server is listening on port %d...
", PORT);
    while (1) {
        client_socket = accept(server_socket, (struct sockaddr *)&client_addr, &addr_len);
        if (client_socket == 1) {
            perror("accept");
            continue;
        }
        printf("New connection from %s:%d
", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
        handle_client(client_socket);
    }
    close(server_socket);
    return 0;
}

这个示例创建了一个简单的TCP服务器，监听8080端口，当客户端连接时，服务器会接收客户端发送的数据，并将其原样发送回客户端，这个示例没有实现FTP协议的任何部分，只是一个简单的回显服务器，要实现一个完整的FTP服务器，您需要实现FTP协议的各种命令和响应，以及处理文件传输等功能。