ftp_client.c

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

#define BUF_SIZE 1024

void prompt() {
    printf("ftp> ");
    fflush(stdout);
}

int recv_response(int sock, char *buf, int size) {
    memset(buf, 0, size);
    int len = recv(sock, buf, size - 1, 0);
    if (len > 0) {
        buf[len] = '\0';
        printf("%s", buf);
    }
    return len;
}

int parse_pasv_response(const char *response, char *ip, int *port) {
    int h1,h2,h3,h4,p1,p2;
    if (sscanf(response, "227 Entering Passive Mode (%d,%d,%d,%d,%d,%d)",
               &h1,&h2,&h3,&h4,&p1,&p2) == 6) {
        sprintf(ip, "%d.%d.%d.%d", h1,h2,h3,h4);
        *port = p1 * 256 + p2;
        return 0;
    }
    return -1;
}

int connect_data(const char *ip, int port) {
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock < 0) return -1;

    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    inet_pton(AF_INET, ip, &addr.sin_addr);

    if (connect(sock, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        close(sock);
        return -1;
    }
    return sock;
}

int main(int argc, char *argv[]) {
    if (argc < 3) {
        fprintf(stderr, "Usage: %s <server_ip> <server_port>\n", argv[0]);
        exit(1);
    }

    const char *server_ip = argv[1];
    int server_port = atoi(argv[2]);

    int ctrl_sock = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(server_port);
    inet_pton(AF_INET, server_ip, &server_addr.sin_addr);

    if (connect(ctrl_sock, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
        perror("connect");
        exit(1);
    }

    char buf[BUF_SIZE];
    recv_response(ctrl_sock, buf, sizeof(buf));

    char user[64], pass[64];
    printf("Username: ");
    fgets(user, sizeof(user), stdin);
    user[strcspn(user, "\n")] = 0;

    printf("Password: ");
    fgets(pass, sizeof(pass), stdin);
    pass[strcspn(pass, "\n")] = 0;

    char login_cmd[128];
    snprintf(login_cmd, sizeof(login_cmd), "USER %s\r\n", user);
    send(ctrl_sock, login_cmd, strlen(login_cmd), 0);
    recv_response(ctrl_sock, buf, sizeof(buf));

    snprintf(login_cmd, sizeof(login_cmd), "PASS %s\r\n", pass);
    send(ctrl_sock, login_cmd, strlen(login_cmd), 0);
    recv_response(ctrl_sock, buf, sizeof(buf));

    printf("Commands:\n");
    printf("pwd         - print working directory\n");
    printf("dir         - list files\n");
    printf("cd <dir>    - change directory\n");
    printf("mkdir <dir> - make directory\n");
    printf("rmdir <dir> - remove directory\n");
    printf("get <file>  - download file\n");
    printf("put <file>  - upload file\n");
    printf("?           - help\n");
    printf("quit        - exit\n");

    while (1) {
        prompt();
        char line[256], cmd[64], arg[128];
        int n = 0;
        if (fgets(line, sizeof(line), stdin))
            n = sscanf(line, "%s %s", cmd, arg);
        else break;

        if (n <= 0) continue;

        if (strcasecmp(cmd, "quit") == 0) {
            send(ctrl_sock, "QUIT\r\n", 6, 0);
            recv_response(ctrl_sock, buf, sizeof(buf));
            break;

        } else if (strcasecmp(cmd, "?") == 0) {
            printf("Commands:\n");
            printf("pwd         - print working directory\n");
            printf("dir         - list files\n");
            printf("cd <dir>    - change directory\n");
            printf("mkdir <dir> - make directory\n");
            printf("rmdir <dir> - remove directory\n");
            printf("get <file>  - download file\n");
            printf("put <file>  - upload file\n");
            printf("?           - help\n");
            printf("quit        - exit\n");

        } else if (strcasecmp(cmd, "pwd") == 0) {
            send(ctrl_sock, "PWD\r\n", 5, 0);
            recv_response(ctrl_sock, buf, sizeof(buf));

        } else if (strcasecmp(cmd, "cd") == 0 && n == 2) {
            char cmdline[256];
            snprintf(cmdline, sizeof(cmdline), "CWD %s\r\n", arg);
            send(ctrl_sock, cmdline, strlen(cmdline), 0);
            recv_response(ctrl_sock, buf, sizeof(buf));

        } else if (strcasecmp(cmd, "mkdir") == 0 && n == 2) {
            char cmdline[256];
            snprintf(cmdline, sizeof(cmdline), "MKD %s\r\n", arg);
            send(ctrl_sock, cmdline, strlen(cmdline), 0);
            recv_response(ctrl_sock, buf, sizeof(buf));
            if (strstr(buf, "550")) {
                printf("Failed to create directory: %s\n", arg);
            }

        } else if (strcasecmp(cmd, "rmdir") == 0 && n == 2) {
            char cmdline[256];
            snprintf(cmdline, sizeof(cmdline), "RMD %s\r\n", arg);
            send(ctrl_sock, cmdline, strlen(cmdline), 0);
            recv_response(ctrl_sock, buf, sizeof(buf));
            if (strstr(buf, "550")) {
                printf("Failed to remove directory: %s\n", arg);
            }

        } else if (strcasecmp(cmd, "dir") == 0) {
            send(ctrl_sock, "PASV\r\n", 6, 0);
            recv_response(ctrl_sock, buf, sizeof(buf));
            if (strstr(buf, "227") == NULL) {
                printf("PASV failed\n");
                continue;
            }

            char data_ip[64];
            int data_port;
            if (parse_pasv_response(buf, data_ip, &data_port) < 0) {
                printf("Failed to parse PASV response\n");
                continue;
            }

            int data_sock = connect_data(data_ip, data_port);
            if (data_sock < 0) {
                perror("connect data");
                continue;
            }

            send(ctrl_sock, "LIST\r\n", 6, 0);
            recv_response(ctrl_sock, buf, sizeof(buf));

            while ((n = recv(data_sock, buf, sizeof(buf) - 1, 0)) > 0) {
                buf[n] = '\0';
                printf("%s", buf);
            }
            close(data_sock);
            recv_response(ctrl_sock, buf, sizeof(buf));

        } else if (strcasecmp(cmd, "get") == 0 && n == 2) {
            send(ctrl_sock, "PASV\r\n", 6, 0);
            recv_response(ctrl_sock, buf, sizeof(buf));
            if (strstr(buf, "227") == NULL) {
                printf("PASV failed\n");
                continue;
            }

            char data_ip[64];
            int data_port;
            if (parse_pasv_response(buf, data_ip, &data_port) < 0) {
                printf("Failed to parse PASV response\n");
                continue;
            }

            int data_sock = connect_data(data_ip, data_port);
            if (data_sock < 0) {
                perror("connect data");
                continue;
            }

            char cmdline[256];
            snprintf(cmdline, sizeof(cmdline), "RETR %s\r\n", arg);
            send(ctrl_sock, cmdline, strlen(cmdline), 0);
            recv_response(ctrl_sock, buf, sizeof(buf));

            FILE *fp = fopen(arg, "wb");
            if (!fp) {
                perror("fopen");
                close(data_sock);
                continue;
            }

            while ((n = recv(data_sock, buf, sizeof(buf), 0)) > 0) {
                fwrite(buf, 1, n, fp);
            }
            fclose(fp);
            close(data_sock);
            recv_response(ctrl_sock, buf, sizeof(buf));

        } else if (strcasecmp(cmd, "put") == 0 && n == 2) {
            FILE *fp = fopen(arg, "rb");
            if (!fp) {
                perror("fopen");
                continue;
            }

            send(ctrl_sock, "PASV\r\n", 6, 0);
            recv_response(ctrl_sock, buf, sizeof(buf));
            if (strstr(buf, "227") == NULL) {
                printf("PASV failed\n");
                fclose(fp);
                continue;
            }

            char data_ip[64];
            int data_port;
            if (parse_pasv_response(buf, data_ip, &data_port) < 0) {
                printf("Failed to parse PASV response\n");
                fclose(fp);
                continue;
            }

            int data_sock = connect_data(data_ip, data_port);
            if (data_sock < 0) {
                perror("connect data");
                fclose(fp);
                continue;
            }

            char cmdline[300];
            snprintf(cmdline, sizeof(cmdline), "STOR %s\r\n", arg);
            send(ctrl_sock, cmdline, strlen(cmdline), 0);
            recv_response(ctrl_sock, buf, sizeof(buf));

            int r;
            while ((r = fread(buf, 1, sizeof(buf), fp)) > 0) {
                send(data_sock, buf, r, 0);
            }
            fclose(fp);
            close(data_sock);
            recv_response(ctrl_sock, buf, sizeof(buf));

        } else {
            printf("Unknown or malformed command. Type '?' for help.\n");
        }
    }

    close(ctrl_sock);
    return 0;
}