用C语言实现利用TCP协议编写一个简单的文件服务器和客户端。 支持功能： 1. list：列表远端目录下的文件和目录信息（目录用方括号括起以示区分） 2. pwd: 查看远端当前目录 3. lpwd: 查看本地当前目录 4. cd xxxxx: 切换远端当前目录为xxxxx 5. lcd xxxxx: 切换本地当前目录为xxxxx 6. down xxxxx: 下载远端当前目录下的文件xxxxx到客户端的当前目录下 7. exit：断开连接并退出。

以下是一个简单的文件服务器和客户端的实现，使用TCP协议。

服务器端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <dirent.h>
#include <fcntl.h>

#define PORT 8080
#define MAX_CLIENTS 10
#define BUFFER_SIZE 1024

char current_dir[BUFFER_SIZE];

void list_files(int sock) {
    DIR *dir;
    struct dirent *ent;
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, BUFFER_SIZE);
    dir = opendir(current_dir);
    if (dir != NULL) {
        while ((ent = readdir(dir)) != NULL) {
            if (ent->d_type == DT_DIR) {
                strcat(buffer, "[");
            }
            strcat(buffer, ent->d_name);
            if (ent->d_type == DT_DIR) {
                strcat(buffer, "]");
            }
            strcat(buffer, "\n");
        }
        closedir(dir);
    } else {
        strcpy(buffer, "Error: cannot open directory.\n");
    }
    send(sock, buffer, strlen(buffer), 0);
}

void get_pwd(int sock) {
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, BUFFER_SIZE);
    getcwd(buffer, BUFFER_SIZE);
    strcat(buffer, "\n");
    send(sock, buffer, strlen(buffer), 0);
}

void change_dir(char *directory, int sock) {
    int result = chdir(directory);
    if (result == 0) {
        get_pwd(sock);
    } else {
        char buffer[BUFFER_SIZE];
        memset(buffer, 0, BUFFER_SIZE);
        strcpy(buffer, "Error: cannot change directory.\n");
        send(sock, buffer, strlen(buffer), 0);
    }
}

void download(char *filename, int sock) {
    char path[BUFFER_SIZE];
    memset(path, 0, BUFFER_SIZE);
    strcat(path, current_dir);
    strcat(path, "/");
    strcat(path, filename);
    int fd = open(path, O_RDONLY);
    if (fd == -1) {
        char buffer[BUFFER_SIZE];
        memset(buffer, 0, BUFFER_SIZE);
        strcpy(buffer, "Error: cannot open file.\n");
        send(sock, buffer, strlen(buffer), 0);
        return;
    }
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, BUFFER_SIZE);
    int bytes_read;
    while ((bytes_read = read(fd, buffer, BUFFER_SIZE)) != 0) {
        send(sock, buffer, bytes_read, 0);
        memset(buffer, 0, BUFFER_SIZE);
    }
    close(fd);
}

int main() {
    int server_fd, client_fd, address_len;
    struct sockaddr_in server_addr, client_addr;
    char buffer[BUFFER_SIZE];

    // Create socket
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("Error creating socket");
        exit(EXIT_FAILURE);
    }

    // Set server address
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);

    // Bind socket to address
    if (bind(server_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        perror("Error binding socket");
        exit(EXIT_FAILURE);
    }

    // Listen for connections
    if (listen(server_fd, MAX_CLIENTS) == -1) {
        perror("Error listening for connections");
        exit(EXIT_FAILURE);
    }

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

    while (1) {
        // Accept client connection
        address_len = sizeof(client_addr);
        if ((client_fd = accept(server_fd, (struct sockaddr *)&client_addr, &address_len)) == -1) {
            perror("Error accepting connection");
            continue;
        }

        printf("New client connected\n");

        // Send welcome message
        strcpy(buffer, "Welcome to the file server!\n");
        send(client_fd, buffer, strlen(buffer), 0);

        // Set current directory
        memset(current_dir, 0, BUFFER_SIZE);
        getcwd(current_dir, BUFFER_SIZE);

        while (1) {
            // Receive command from client
            memset(buffer, 0, BUFFER_SIZE);
            int bytes_received = recv(client_fd, buffer, BUFFER_SIZE, 0);
            if (bytes_received == -1) {
                perror("Error receiving data");
                break;
            } else if (bytes_received == 0) {
                printf("Client disconnected\n");
                break;
            }

            // Process command
            char *command = strtok(buffer, " ");
            char *argument = strtok(NULL, " ");
            if (strcmp(command, "list") == 0) {
                list_files(client_fd);
            } else if (strcmp(command, "pwd") == 0) {
                get_pwd(client_fd);
            } else if (strcmp(command, "cd") == 0) {
                if (argument == NULL) {
                    char buffer[BUFFER_SIZE];
                    memset(buffer, 0, BUFFER_SIZE);
                    strcpy(buffer, "Usage: cd directory\n");
                    send(client_fd, buffer, strlen(buffer), 0);
                    continue;
                }
                change_dir(argument, client_fd);
            } else if (strcmp(command, "down") == 0) {
                if (argument == NULL) {
                    char buffer[BUFFER_SIZE];
                    memset(buffer, 0, BUFFER_SIZE);
                    strcpy(buffer, "Usage: down filename\n");
                    send(client_fd, buffer, strlen(buffer), 0);
                    continue;
                }
                download(argument, client_fd);
            } else if (strcmp(command, "exit") == 0) {
                break;
            } else {
                char buffer[BUFFER_SIZE];
                memset(buffer, 0, BUFFER_SIZE);
                strcpy(buffer, "Invalid command\n");
                send(client_fd, buffer, strlen(buffer), 0);
            }
        }

        // Close client connection
        close(client_fd);
    }

    // Close server socket
    close(server_fd);

    return 0;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>

#define SERVER_IP "127.0.0.1"
#define PORT 8080
#define BUFFER_SIZE 1024

void print_prompt() {
    char cwd[BUFFER_SIZE];
    memset(cwd, 0, BUFFER_SIZE);
    getcwd(cwd, BUFFER_SIZE);
    printf("%s> ", cwd);
    fflush(stdout);
}

void handle_list(int sock) {
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, BUFFER_SIZE);
    int bytes_received;
    while ((bytes_received = recv(sock, buffer, BUFFER_SIZE, 0)) != 0) {
        printf("%s", buffer);
        memset(buffer, 0, BUFFER_SIZE);
    }
}

void handle_pwd(int sock) {
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, BUFFER_SIZE);
    int bytes_received = recv(sock, buffer, BUFFER_SIZE, 0);
    if (bytes_received != -1) {
        printf("%s", buffer);
    }
}

void handle_cd(char *directory, int sock) {
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, BUFFER_SIZE);
    sprintf(buffer, "cd %s", directory);
    send(sock, buffer, strlen(buffer), 0);
    int bytes_received = recv(sock, buffer, BUFFER_SIZE, 0);
    if (bytes_received != -1) {
        printf("%s", buffer);
    }
}

void handle_down(char *filename, int sock) {
    char buffer[BUFFER_SIZE];
    memset(buffer, 0, BUFFER_SIZE);
    sprintf(buffer, "down %s", filename);
    send(sock, buffer, strlen(buffer), 0);
    memset(buffer, 0, BUFFER_SIZE);
    int fd = open(filename, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
    int bytes_received;
    while ((bytes_received = recv(sock, buffer, BUFFER_SIZE, 0)) != 0) {
        write(fd, buffer, bytes_received);
        memset(buffer, 0, BUFFER_SIZE);
    }
    close(fd);
}

int main() {
    int sock;
    struct sockaddr_in server_addr;
    char buffer[BUFFER_SIZE];

    // Create socket
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("Error creating socket");
        exit(EXIT_FAILURE);
    }

    // Set server address
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);
    server_addr.sin_port = htons(PORT);

    // Connect to server
    if (connect(sock, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        perror("Error connecting to server");
        exit(EXIT_FAILURE);
    }

    // Receive welcome message
    int bytes_received = recv(sock, buffer, BUFFER_SIZE, 0);
    if (bytes_received != -1) {
        printf("%s", buffer);
    }

    while (1) {
        print_prompt();

        // Read command from user
        memset(buffer, 0, BUFFER_SIZE);
        fgets(buffer, BUFFER_SIZE, stdin);
        buffer[strlen(buffer) - 1] = '\0';

        // Process command
        char *command = strtok(buffer, " ");
        char *argument = strtok(NULL, " ");
        if (strcmp(command, "list") == 0) {
            send(sock, "list", strlen("list"), 0);
            handle_list(sock);
        } else if (strcmp(command, "pwd") == 0) {
            send(sock, "pwd", strlen("pwd"), 0);
            handle_pwd(sock);
        } else if (strcmp(command, "cd") == 0) {
            if (argument == NULL) {
                printf("Usage: cd directory\n");
                continue;
            }
            handle_cd(argument, sock);
        } else if (strcmp(command, "down") == 0) {
            if (argument == NULL) {
                printf("Usage: down filename\n");
                continue;
            }
            handle_down(argument, sock);
        } else if (strcmp(command, "lcd") == 0) {
            if (argument == NULL) {
                printf("Usage: lcd directory\n");
                continue;
            }
            int result = chdir(argument);
            if (result == -1) {
                printf("Error: cannot change directory.\n");
            }
        } else if (strcmp(command, "exit") == 0) {
            break;
        } else {
            printf("Invalid command\n");
        }
    }

    // Close socket
    close(sock);

    return 0;
}