我正在编写一个套接字程序，以使用udp进行可靠的数据传输。我正在以1024个字节的块从客户端向服务器发送图像文件。下面是我的代码，它们适用于较大的字符串和较小的图像文件，但是当我传输2.3 MB的图像时，服务器只能接收到2 MB的内存。假设发送的数据包总数为2271。服务器将只接收到2211或更短的时间，并且会突然终止。我不知道原因。你能给我解释一下吗？并提出任何解决方案。
下面是我的客户代码
#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;
}
和我的服务器代码：
#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;
}
最佳答案
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的数据。 strlen不能与二进制数据一起使用，因为它只能通过在数据内部查找\0来确定数据的长度。如果\0位于buff的中间，则仅发送直到（但不包括）该部分的部分。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。数据包可能会重新排序，重复或丢失，在大多数情况下您不会注意到它。与TCP相反，UDP完全不提供任何可靠性。
关于c - 在C中使用udp进行可靠的数据传输，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/46558412/