c需要 实现tftp
时间: 2024-03-14 10:44:20 浏览: 23
要在C语言中实现TFTP(Trivial File Transfer Protocol)客户端,您需要进行以下步骤:
1. 创建一个UDP套接字,用于与TFTP服务器进行通信。
2. 构造TFTP请求报文(Read Request或Write Request),并通过UDP套接字发送给TFTP服务器。
3. 接收TFTP服务器的响应报文,并解析其中的数据和错误码。
4. 根据TFTP服务器的响应报文构造相应的TFTP请求报文,并继续发送给TFTP服务器。
5. 当接收到TFTP服务器发送的数据块时,将数据块写入本地文件中。
6. 当接收到TFTP服务器发送的最后一个数据块时,关闭UDP套接字,结束TFTP传输。
以下是一个简单的TFTP客户端的示例代码:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define TFTP_SERVER_PORT 69
#define TFTP_BLOCK_SIZE 512
#define TFTP_OPCODE_RRQ 1
#define TFTP_OPCODE_WRQ 2
#define TFTP_OPCODE_DATA 3
#define TFTP_OPCODE_ACK 4
#define TFTP_OPCODE_ERROR 5
#define TFTP_ERROR_UNDEFINED 0
#define TFTP_ERROR_NOT_FOUND 1
#define TFTP_ERROR_ACCESS_VIOLATION 2
#define TFTP_ERROR_DISK_FULL 3
#define TFTP_ERROR_ILLEGAL_OPERATION 4
#define TFTP_ERROR_UNKNOWN_TRANSFER_ID 5
#define TFTP_ERROR_FILE_EXISTS 6
struct tftp_rrq_packet {
uint16_t opcode;
char filename_and_mode[1];
};
struct tftp_data_packet {
uint16_t opcode;
uint16_t block_number;
char data[TFTP_BLOCK_SIZE];
};
struct tftp_ack_packet {
uint16_t opcode;
uint16_t block_number;
};
struct tftp_error_packet {
uint16_t opcode;
uint16_t error_code;
char error_message[1];
};
int tftp_send_request(int sockfd, const char *filename, const char *mode, const struct sockaddr *addr, socklen_t addrlen)
{
struct tftp_rrq_packet *packet;
char *buf;
int len;
len = sizeof(struct tftp_rrq_packet) + strlen(filename) + 1 + strlen(mode) + 1;
buf = malloc(len);
packet = (struct tftp_rrq_packet *)buf;
packet->opcode = htons(TFTP_OPCODE_RRQ);
strcpy(packet->filename_and_mode, filename);
strcpy(packet->filename_and_mode + strlen(filename) + 1, mode);
return sendto(sockfd, buf, len, 0, addr, addrlen);
}
int tftp_receive_data(int sockfd, FILE *fp, struct sockaddr *addr, socklen_t *addrlen)
{
struct tftp_data_packet *packet;
struct tftp_ack_packet ack_pkt;
char *buf;
int block_number = 1;
int ret;
buf = malloc(sizeof(struct tftp_data_packet) + TFTP_BLOCK_SIZE);
do {
ret = recvfrom(sockfd, buf, sizeof(struct tftp_data_packet) + TFTP_BLOCK_SIZE, 0, addr, addrlen);
if (ret < 0) {
perror("recvfrom");
break;
}
packet = (struct tftp_data_packet *)buf;
if (ntohs(packet->opcode) == TFTP_OPCODE_ERROR) {
struct tftp_error_packet *err_pkt = (struct tftp_error_packet *)packet;
fprintf(stderr, "TFTP error: %s\n", err_pkt->error_message);
ret = -1;
break;
} else if (ntohs(packet->opcode) != TFTP_OPCODE_DATA) {
fprintf(stderr, "Invalid TFTP opcode: %d\n", ntohs(packet->opcode));
ret = -1;
break;
}
if (ntohs(packet->block_number) != block_number) {
fprintf(stderr, "Invalid TFTP block number: %d (expected %d)\n", ntohs(packet->block_number), block_number);
ret = -1;
break;
}
fwrite(packet->data, 1, ret - sizeof(struct tftp_data_packet), fp);
ack_pkt.opcode = htons(TFTP_OPCODE_ACK);
ack_pkt.block_number = packet->block_number;
if (sendto(sockfd, &ack_pkt, sizeof(ack_pkt), 0, addr, *addrlen) < 0) {
perror("sendto");
ret = -1;
break;
}
block_number++;
} while (ret == TFTP_BLOCK_SIZE + sizeof(struct tftp_data_packet));
free(buf);
return ret;
}
int tftp_receive_file(const char *filename, const char *mode, const char *server_addr_str)
{
int sockfd;
struct sockaddr_in server_addr;
socklen_t addrlen;
FILE *fp;
int ret;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0) {
perror("socket");
return -1;
}
memset(&server_addr, 0, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(server_addr_str);
server_addr.sin_port = htons(TFTP_SERVER_PORT);
ret = tftp_send_request(sockfd, filename, mode, (struct sockaddr *)&server_addr, sizeof(server_addr));
if (ret < 0) {
perror("sendto");
close(sockfd);
return ret;
}
fp = fopen(filename, "wb");
if (fp == NULL) {
perror("fopen");
close(sockfd);
return -1;
}
addrlen = sizeof(server_addr);
ret = tftp_receive_data(sockfd, fp, (struct sockaddr *)&server_addr, &addrlen);
fclose(fp);
close(sockfd);
return ret;
}
```
该示例代码可通过调用`tftp_receive_file`函数来从TFTP服务器下载文件。在该函数中,我们首先创建了一个UDP套接字,然后发送TFTP读请求报文。接着,我们在循环中接收TFTP数据块,并将其写入本地文件中。每当接收到一个数据块时,我们都会发送一个确认报文(ACK)告知TFTP服务器已经成功接收到该数据块。当接收到的数据块大小不足TFTP块大小时,表示文件传输结束,我们退出循环,关闭套接字,结束TFTP传输。