[英]reliable data transfer using udp in c
我正在编写一个使用 udp 进行可靠数据传输的套接字程序。 我正在以 1024 字节的块将图像文件从客户端发送到服务器。 下面是我的代码。它们对于大字符串和较小的图像文件工作正常。但是当我传输 2.3 MB 的图像时,服务器只会接收到 2 MB。 假设发送的数据包总数为 2271。服务器只会接收到 2211 或更少,并且会突然终止。 我不知道原因。 你能解释一下吗? 并提出任何解决方案。 下面是我的客户端代码
#include<stdio.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<netdb.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<arpa/inet.h>
char *itoa(long i,char *s,int dummy_radix)
{
sprintf(s,"%ld",i);
return s;
}
int main(int argc, int *argv[])
{
int sock,length,n;
struct sockaddr_in server,from;
struct hostent *hp;
long int packets =0;
unsigned char buff[1024] = {0};
// checking if hostname and the port address is provided //
if(argc!=3)
{
printf("insufficient arguments\n");
exit(1);
}
//create a socket//
sock = socket(AF_INET,SOCK_DGRAM,0);
if(sock<0)
{
printf("error in opening socket\n");
return 1;
}
//to get the hostname of the system or the machine//
hp= gethostbyname(argv[1]);
if(hp==0)
{
printf("Unknown host\n");
return 1;
}
//build the server's IP address //
bzero((char *)&server,sizeof(server));
bcopy((char*)hp->h_addr,(char *)&server.sin_addr,hp->h_length);
server.sin_family = AF_INET;
server.sin_port = htons(atoi(argv[2]));
length = sizeof(server);
/*open the file that we wish to transfer*/
FILE *fp = fopen("landscape.jpeg","rb");
if(fp==NULL)
{
printf("file open error");
return 1;
}
fseek(fp,0,SEEK_END); //if exists read the size of the file
size_t file_size = ftell(fp);
fseek(fp,0,SEEK_SET);
printf("size of the file is %d\n", file_size);
/*find the number of packets*/
packets = (file_size/1024)+1 ;
/*send the number of packets to the server*/
itoa(packets,buff,10);
n= sendto(sock,buff,strlen(buff),0,(struct sockaddr *)&server,sizeof(struct sockaddr));
if(n<0)
{
printf("error in sending message to the serveR");
return 1;
}
/*Read data from file and send it*/
int packetNum = 0;
while(1)
{
/*First read file in chunks of 1024 bytes */
int nread = fread(buff,1,1024,fp);
//printf("Bytes read %d\n",nread);
/*if read was success ,send data*/
if(nread>0)
{
//printf("data sent now is %s\n",buff);
n= sendto(sock,buff,strlen(buff),0,(struct sockaddr *)&server,sizeof(struct sockaddr));
printf("Sending %d, numBytes sent: %d\n", packetNum, n);
packetNum++;
if(n<0)
{
printf("error in sending message to the server");
fclose(fp);
return 1;
}
}
/*There is something tricky going on with the read..
* Either there was error ,or we reached end of file.
*/
if(nread<1024)
{
if(feof(fp))
printf("End of file\n");
if(ferror(fp))
printf("Error reading\n");
break;
}
}
close(sock);
fclose(fp);
return 0;
}
还有我的服务器代码:
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<netdb.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<arpa/inet.h>
int main(int argc, char *argv[])
{
int sock,length,fromlen,n;
struct sockaddr_in server;
struct sockaddr_in from;
char buf[1024];
char file_buf[1024];
int packets = 0;
int received = 0;
FILE *newfp;
newfp = fopen("output.jpeg","wb");
if(newfp==NULL)
{
printf("error opening the file\n");
return 1;
}
if(argc<2)
{
fprintf(stderr, "no port number specified\n");
exit(0);
}
sock = socket(AF_INET,SOCK_DGRAM,0);
if(sock<0)
{
printf("error in opening socket\n");
return 1;
}
length = sizeof(server);
bzero(&server,length);
server.sin_family= AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(atoi(argv[1]));
if(bind(sock,(struct sockaddr*)&server,length)<0)
{
printf("cannot bind\n");
return 1;
}
fromlen =sizeof(struct sockaddr_in);
n = recvfrom(sock,buf,1024,0,(struct sockaddr *)&from,&fromlen);
if(n<0)
{
printf("recvfrom error\n");
return 1;
}
packets = atoi(buf);
printf("Num packets expected: %d\n", packets);
while(received<packets)
{
n = recvfrom(sock,buf,sizeof (buf),0,(struct sockaddr *)&from,&fromlen);
//printf ("%d\n", n);
printf("Packet num %d, numBytes received: %d\n", received, n);
if(n<0)
{
printf("recvfrom error\n");
return 1;
}
//printf("%s",buf);
if((fwrite(buf,1,n,newfp)) < n)
{
printf("error in writing to the file\n");
return 1;
}
received++;
}
printf("Finished\n");
fclose(newfp);
return 0;
}
n= sendto(sock,buff,strlen(buff),0,(struct sockaddr *)&server,sizeof(struct sockaddr));
您正在传输二进制数据,即可能包含\\0
。 strlen
不能用于二进制数据,因为它只是通过查找数据中的\\0
来确定数据的长度。 如果\\0
在buff
的中间,则只会发送直到但不包括此\\0
的部分。
除此之外:
在c中使用udp进行可靠的数据传输
在进行数据传输时,您根本不关心可靠性。 数据包可能会被重新排序、复制或丢失,并且在大多数情况下您不会注意到。 与 TCP 不同,UDP 本身根本不提供任何可靠性。
如果需要可靠传输,则建议使用 TCP 套接字。
但是,如果你想使用 UDP 套接字,那么你必须实现某种自定义协议,你必须等到接收器没有确认接收到数据包。
在您的客户端和服务器代码中,客户端盲目地向服务器发送数据,而不关心当前在服务器端发生的丢失数据包。
对于一个简单的解决方法,您可以添加一个recvfrom(sock,buf,sizeof (buf),0,(struct sockaddr *)&server,sizeof(struct sockaddr));
紧随其后n= sendto(sock,buff,strlen(buff),0,(struct sockaddr *)&server,sizeof(struct sockaddr));
在您的client.c和n= sendto(sock,"ACK",strlen("ACK"),0,(struct sockaddr *)&from,&fromlen);
紧随其后n = recvfrom(sock,buf,sizeof (buf),0,(struct sockaddr *)&from,&fromlen);
在server.c 中
并且您必须注意正确处理文件,因为不正确的文件处理会导致输入和输出文件不匹配。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.