TFTP客户端开源代码分析

wxmtwfx

479人浏览 · 2026-03-12 13:58:08

wxmtwfx · 2026-03-12 13:58:08 发布

TFTP客户端开源代码分析

本文件详细分析TFTP客户端的实现，包括数据结构、层次关系和工作流程。

1. 文件结构

client.c - 客户端主应用逻辑文件
client_comm.c - 通信模块的实现文件
client_comm.h - 通信模块的头文件
tftpx.h - 通用TFTP协议定义

2. 数据结构

2.1 struct tftpx_packet (tftpx.h)

struct tftpx_packet {
    uint16_t cmd;      // 操作码
    uint16_t block;    // 块编号
    char data[512];    // 数据内容
};

cmd: 操作码，取值为RRQ(1)、WRQ(2)、DATA(3)、ACK(4)、ERROR(5)
block: 数据块编号，从1开始递增
data: 数据内容，最大512字节

2.2 struct sockaddr_in (client_comm.c)

struct sockaddr_in server;
server.sin_family = AF_INET;
server.sin_port = htons(port);
inet_pton(AF_INET, server_ip, &(server.sin_addr.s_addr));

sin_family: 地址族，固定为AF_INET（IPv4）
sin_port: 端口号，使用htons()转换为网络字节序
sin_addr: IP地址，使用inet_pton()转换为二进制格式

3. 层次关系

+-------------------+
|    client.c       |
+-------------------+
|  业务逻辑层       |
|  - 命令解析       |
|  - 流程控制       |
+-------------------+
          |
          v
+-------------------+
|  client_comm.c    |
+-------------------+
|  通信层           |
|  - 套接字操作     |
|  - 数据包发送     |
|  - 数据包接收     |
+-------------------+

3.1 层次说明

client.c: 业务逻辑层，负责命令解析和流程控制
client_comm.c: 通信层，实现底层套接字操作，向上提供封装好的接口

4. 初始化流程

4.1 命令行参数解析 (client.c:main)

if(argc < 3){
    printf("Usage: %s <server> <port> <get|put> <file>\n", argv[0]);
    return 0;
}

const char *server_ip = argv[1];
unsigned short port = atoi(argv[2]);
const char *cmd = argv[3];
const char *file = argv[4];

4.2 套接字初始化 (client_comm.c:client_comm_init)

int client_comm_init(const char *server_ip, unsigned short port) {
    addr_len = sizeof(struct sockaddr_in);
    sender_len = sizeof(struct sockaddr_in);
    memset(&sender, 0, sizeof(struct sockaddr_in));
    
    if((sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0){
        printf("Server socket could not be created.\n");
        return -1;
    }
    
    // 初始化服务器地址
    server.sin_family = AF_INET;
    server.sin_port = htons(port);
    inet_pton(AF_INET, server_ip, &(server.sin_addr.s_addr));
    
    return 0;
}

4.3 流程分支 (client.c:main)

if(strcmp(cmd, "get") == 0){
    do_get(server_ip, port, file);
} else if(strcmp(cmd, "put") == 0){
    do_put(server_ip, port, file);
} else {
    printf("Unknown command: %s\n", cmd);
    return 0;
}

5. 发送文件流程（PUT操作）

5.1 准备WRQ数据包 (client.c:do_put)

struct tftpx_packet snd_packet;
snd_packet.cmd = htons(CMD_WRQ);
sprintf(snd_packet.data, "%s\0%s\0", file, "octet");

5.2 发送WRQ数据包 (client.c:do_put)

client_comm_send(&snd_packet, sizeof(struct tftpx_packet));

5.3 等待ACK响应 (client.c:do_put)

struct tftpx_packet rcv_packet;
int r_size = client_comm_recvfrom(&rcv_packet, sizeof(struct tftpx_packet));
if(r_size >= 4 && rcv_packet.cmd == htons(CMD_ACK)){
    printf("Received ACK for block 0\n");
}

5.4 分块发送文件数据 (client.c:do_put)

FILE *fp = fopen(file, "rb");
if(fp == NULL){
    printf("Can't open file: %s\n", file);
    return;
}

char buffer[512];
int block = 1;
while(!feof(fp)){
    int bytes_read = fread(buffer, 1, 512, fp);
    struct tftpx_packet data_packet;
    data_packet.cmd = htons(CMD_DATA);
    data_packet.block = htons(block);
    memcpy(data_packet.data, buffer, bytes_read);
    
    if(client_comm_send(&data_packet, bytes_read + 4) == -1){
        printf("Error sending block %d\n", block);
        break;
    }
    
    // 等待ACK
    int ack_received = 0;
    while(!ack_received){
        struct tftpx_packet ack_packet;
        int r_size = client_comm_recvfrom(&ack_packet, sizeof(struct tftpx_packet));
        if(r_size >= 4 && ack_packet.cmd == htons(CMD_ACK) && ack_packet.block == htons(block)){
            ack_received = 1;
        }
    }
    
    block++;
}

fclose(fp);

6. 接收文件流程（GET操作）

6.1 准备RRQ数据包 (client.c:do_get)

struct tftpx_packet snd_packet;
snd_packet.cmd = htons(CMD_RRQ);
sprintf(snd_packet.data, "%s\0%s\0", file, "octet");

6.2 发送RRQ数据包 (client.c:do_get)

client_comm_send(&snd_packet, sizeof(struct tftpx_packet));

6.3 接收DATA数据包 (client.c:do_get)

FILE *fp = fopen(file, "wb");
if(fp == NULL){
    printf("Can't create file: %s\n", file);
    return;
}

struct tftpx_packet rcv_packet;
int block = 1;
while(1){
    int r_size = client_comm_recvfrom(&rcv_packet, sizeof(struct tftpx_packet));
    if(r_size < 4){
        printf("Error receiving data\n");
        break;
    }
    
    if(rcv_packet.cmd == htons(CMD_DATA) && ntohs(rcv_packet.block) == block){
        // 写入文件
        fwrite(rcv_packet.data, 1, r_size - 4, fp);
        
        // 发送ACK
        struct tftpx_packet ack_packet;
        ack_packet.cmd = htons(CMD_ACK);
        ack_packet.block = rcv_packet.block;
        client_comm_send_to(&ack_packet, sizeof(struct tftpx_packet));
        
        // 检查是否为最后一个块
        if(r_size - 4 < 512){
            printf("Received final block\n");
            break;
        }
        
        block++;
    }
}

fclose(fp);