前沿：下面这段代码是tftp实现的客户端源码，通常为了项目需要，你需要在远程的开发板上实现一段tftp代码，用于从远程tftp server端来得到数据或者文件（因为使用tftp命令如：
），其中要加入错误检测等，下段代码是我从csdn上下载来的一整套源码中，提取其中的客户端代码，并且添加上自己的一些东西，使其更加简单些，最终实现了从server端下载一个文件的功能（注意，并没有上传功能）
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
//add zyf
#define tftp_debug 1
#define ERROR -1
#define TIMEOUT 2000 /*amount of time to wait for an ACK/Data Packet in 1000microseconds 1000 = 1 second*/
#define MAXDATASIZE 1024 /* Maximum data size allowed */
int datasize = 512;
unsigned short int ackfreq = 1;
#define RETRIES 3 /* Number of times to resend a data OR ack packet beforing giving up */
#define DEFAULT_TFTP_HOST "192.168.1.140"
//end
/*
*This function is called when the client would like to download a file from the server.
*/
void
tget (char *pFilename, struct sockaddr_in server, char *pMode, int sock)
{
/* local variables */
int len, server_len, opcode, i, j, n, tid = 0, flag = 1;
unsigned short int count = 0, rcount = 0;
unsigned char filebuf[MAXDATASIZE + 1];
unsigned char packetbuf[MAXDATASIZE + 12];
extern int errno;
char filename[128], mode[12], *bufindex, ackbuf[512];
struct sockaddr_in data;
FILE *fp; /* pointer to the file we will be getting */
strcpy (filename, pFilename); //copy the pointer to the filename into a real array
strcpy (mode, pMode); //same as above
if (tftp_debug)
printf ("branched to file receive function\n");
fp = fopen (filename, "w"); /* open the file for writing */
if (fp == NULL)
{ //if the pointer is null then the file can't be opened - Bad perms
if (tftp_debug)
printf ("Client requested bad file: cannot open for writing (%s)\n",
filename);
return;
}
else /* File is open and ready to be written to */
{
if (tftp_debug)
printf ("Getting file... (destination: %s) \n", filename);
}
/* zero the buffer before we begin */
memset (filebuf, 0, sizeof (filebuf));
n = datasize + 4;
do
{
/* zero buffers so if there are any errors only NULLs will be exposed */
memset (packetbuf, 0, sizeof (packetbuf));
memset (ackbuf, 0, sizeof (ackbuf));
printf ("enter %d \n",count);
if (n != (datasize + 4)) /* remember if our datasize is less than a full packet this was the last packet to be received */
{
if (tftp_debug)
printf
("Last chunk detected (file chunk size: %d). exiting while loop\n",
n - 4);
len = sprintf (ackbuf, "%c%c%c%c", 0x00, 0x04, 0x00, 0x00);
ackbuf[2] = (count & 0xFF00) >> 8; //fill in the count (top number first)
ackbuf[3] = (count & 0x00FF); //fill in the lower part of the count
if (tftp_debug)
printf ("Sending ack # %04d (length: %d)\n", count, len);
if (sendto
(sock, ackbuf, len, 0, (struct sockaddr *) &server,
sizeof (server)) != len)
{
if (tftp_debug)
printf ("Mismatch in number of sent bytes\n");
return;
}
if (tftp_debug)
printf ("The Client has sent an ACK for packet\n");
goto done; /* gotos are not optimal, but a good solution when exiting a multi-layer loop */
}
count++;
for (j = 0; j < RETRIES; j++) /* this allows us to loop until we either break out by getting the correct ack OR time out because we've looped more than RETRIES times */
{
server_len = sizeof (data);
errno = EAGAIN; /* this allows us to enter the loop */
n = -1;
for (i = 0; errno == EAGAIN && i <= TIMEOUT && n < 0; i++) /* this for loop will just keep checking the non-blocking socket until timeout */
{
n =
recvfrom (sock, packetbuf, sizeof (packetbuf) - 1,
MSG_DONTWAIT, (struct sockaddr *) &data,
(socklen_t *) & server_len);
usleep (1000);
}
/*if(tftp_debug)
ip_port (data); print the vlaue recived from the server */
if (!tid)
{
tid = ntohs (data.sin_port); //get the tid of the server.
server.sin_port = htons (tid); //set the tid for rest of the transfer
}
if (n < 0 && errno != EAGAIN) /* this will be true when there is an error that isn't the WOULD BLOCK error */
{
if (tftp_debug)
printf
("The server could not receive from the client (errno: %d n: %d)\n",
errno, n);
//resend packet
}
else if (n < 0 && errno == EAGAIN) /* this is true when the error IS would block. This means we timed out */
{
if (tftp_debug)
printf ("Timeout waiting for data (errno: %d == %d n: %d)\n",
errno, EAGAIN, n);
//resend packet
}
else
{
if (server.sin_addr.s_addr != data.sin_addr.s_addr) /* checks to ensure get from ip is same from ACK IP */
{
if (tftp_debug)
printf
("Error recieving file (data from invalid address)\n");
j--;
continue; /* we aren't going to let another connection spoil our first connection */
}
if (tid != ntohs (server.sin_port)) /* checks to ensure get from the correct TID */
{
if (tftp_debug)
printf ("Error recieving file (data from invalid tid)\n");
len = sprintf ((char *) packetbuf,
"%c%c%c%cBad/Unknown TID%c",
0x00, 0x05, 0x00, 0x05, 0x00);
if (sendto (sock, packetbuf, len, 0, (struct sockaddr *) &server, sizeof (server)) != len) /* send the data packet */
{
printf
("Mismatch in number of sent bytes while trying to send mode error packet\n");
}
j--;
continue; /* we aren't going to let another connection spoil our first connection */
}
/* this formatting code is just like the code in the main function */
bufindex = (char *) packetbuf; //start our pointer going
if (bufindex++[0] != 0x00)
printf ("bad first nullbyte!\n");
opcode = *bufindex++;
rcount = *bufindex++ << 8;
rcount &= 0xff00;
rcount += (*bufindex++ & 0x00ff);
memcpy ((char *) filebuf, bufindex, n - 4); /* copy the rest of the packet (data portion) into our data array */
if (tftp_debug)
printf
("Remote host sent data packet #%d (Opcode: %d packetsize: %d filechunksize: %d)\n",
rcount, opcode, n, n - 4);
if (flag)
{
if (n > 516)
datasize = n - 4;
else if (n < 516)
datasize = 512;
flag = 0;
}
if (opcode != 3) /* ack packet should have code 3 (data) and should be ack+1 the packet we just sent */
{
if (tftp_debug)
printf
("Badly ordered/invalid data packet (Got OP: %d Block: %d) (Wanted Op: 3 Block: %d)\n",
opcode, rcount, count);
/* sending error message */
if (opcode > 5)
{
len = sprintf ((char *) packetbuf,
"%c%c%c%cIllegal operation%c",
0x00, 0x05, 0x00, 0x04, 0x00);
if (sendto (sock, packetbuf, len, 0, (struct sockaddr *) &server, sizeof (server)) != len) /* send the data packet */
{
printf
("Mismatch in number of sent bytes while trying to send mode error packet\n");
}
}
}
else
{
len = sprintf (ackbuf, "%c%c%c%c", 0x00, 0x04, 0x00, 0x00);
ackbuf[2] = (count & 0xFF00) >> 8; //fill in the count (top number first)
ackbuf[3] = (count & 0x00FF); //fill in the lower part of the count
if (tftp_debug)
printf ("Sending ack # %04d (length: %d)\n", count, len);
if (((count - 1) % ackfreq) == 0)
{
if (sendto
(sock, ackbuf, len, 0, (struct sockaddr *) &server,
sizeof (server)) != len)
{
if (tftp_debug)
printf ("Mismatch in number of sent bytes\n");
return;
}
if (tftp_debug)
printf ("The client has sent an ACK for packet %d\n",
count);
} //check for ackfreq
else if (count == 1)
{
if (sendto
(sock, ackbuf, len, 0, (struct sockaddr *) &server,
sizeof (server)) != len)
{
if (tftp_debug)
printf ("Mismatch in number of sent bytes\n");
return;
}
if (tftp_debug)
printf ("The Client has sent an ACK for packet 1\n");
}
break;
} //end of else
}
}
if (j == RETRIES)
{
if (tftp_debug)
printf ("Data recieve Timeout. Aborting transfer\n");
fclose (fp);
return;
}
}
while (fwrite (filebuf, 1, n - 4, fp) == n - 4); /* if it doesn't write the file the length of the packet received less 4 then it didn't work */
fclose (fp);
sync ();
if (tftp_debug)
printf
("fclose and sync unsuccessful. File failed to recieve properly\n");
return;
done:
fclose (fp);
sync ();
if (tftp_debug)
printf ("fclose and sync successful. File received successfully\n");
return;
}
int req_packet (int opcode, char *filename, char *mode, char buf[])
{
int len;
len =
sprintf (buf, "%c%c%s%c%s%c", 0x00, opcode, filename, 0x00, mode, 0x00);
if (len == 0)
{
printf ("Error in creating the request packet\n"); /*could not print to the client buffer */
exit (ERROR);
}
return len;
}
int tftp_get_file(char *hostip,char *filename ,char *buf){
char mode[12] = "octet";
int port = 69;
char opcode =1;
int sock, server_len, len, opt; //,n;
//struct hostent *host; /*for host information */
struct sockaddr_in server; //, client; /*the address structure for both the server and client */
/*Create the socket, a -1 will show us an error */
if ((sock = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
{
printf ("Client: Socket could not be created");
return 0;
}
printf ("tftp_get_file\n");
/*set the address values for the server */
memset (&server, 0, sizeof (server)); /*Clear the structure */
server.sin_family = AF_INET; /*address family for TCP and UDP */
server.sin_addr.s_addr=inet_addr(hostip);
//server.sin_addr.s_addr = htonl (INADDR_ANY); /*use any address */
server.sin_port = htons (port); /*pick a free port */
server_len = sizeof (server); /*get the length of the server address */
//memset (buf, 0, BUFSIZ); /*clear the buffer */
/* this is the first request message */
len = req_packet (opcode, filename, mode, buf);
printf ("the len is %d\n",len);
//printf ("the server.sin_addr is %s\n",server.sin_addr.s_addr);
if (sendto (sock, buf, len, 0, (struct sockaddr *) &server, server_len) != len)
{
perror ("Client: sendto has returend an error");
exit (ERROR);
}
strncpy (mode, "octet", sizeof (mode) - 1);
tget (filename, server, mode, sock);
}
int main(void){
#if 1
char hostip[128] ;
char filename[128];
char buf[1024];
strcpy(hostip,DEFAULT_TFTP_HOST);
strcpy(filename,"/aaa.bin");
#endif
printf ("main\n");
tftp_get_file( hostip, filename, buf);
return 0;
}
//其中tget()函数其中的内容我也不懂，我只是封装了源码里面的一个函数，如果你使用这个源码不能实现你的功能，说明你的tftp的server端没有配置成功，你可以现在命令行下输入tftp ip，然后在>符号下先tget下一下试试能否成功。
