即使客户端未发送任何内容，recvfrom() 也会得到空缓冲区
recvfrom() gets empty buffer even though the client sent nothing
client: argv[1]: ip地址, argv[2]: 端口号, argv[3]: 文件名
客户端首先向服务器发送 argv[3] 并在 UDP 连接中以数据包的形式发送文件。一旦发现没有数据读取，它就会跳出循环并终止。
服务器：argv[1]：端口号
这是迭代的，因此会一直重复接收，直到系统获得 ^C。首先是接收文件名并进入循环获取数据。实际上我仍然不知道我到底对逃逸条件做了什么。我认为当最后一个数据包大小与 BUFFER_SIZE 相同时会产生一些问题。无论如何，到目前为止它工作没有问题，所以这部分不是要处理的最大任务。
我遇到的问题是接收文件名的recvfrom()得到的是空数据。我所期望的是该函数等待从客户端发送文件名。下面添加两个源代码和终端显示的结果。谁能帮我阻止 recvfrom() 获取空缓冲区？
服务器：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <fcntl.h>
#define BUFFER_SIZE 50
int main(int argc, char *argv[]){
int sockfd;//socket file descriptor
int byteRcvd;//gets received bytes when recvfrom() is called
int addr_size = sizeof(struct sockaddr);//used to bind
int fp;//to handle file
int i;
struct sockaddr_in addr;//contains address information
char fileName[20];//gets file name
char buf[BUFFER_SIZE];//buffer
//create a socket
sockfd = socket(PF_INET, SOCK_DGRAM, 0);
//set and addr
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_ANY);//address here
addr.sin_port = htons(atoi(argv[1]));//port # here
bind(sockfd, (struct sockaddr*)&addr, sizeof(addr));
//repetition of receiving files
while(1){
//get file name and open
memset(buf, 0, sizeof(buf));
byteRcvd = recvfrom(sockfd, buf, sizeof(buf), 0,
(struct sockaddr*)&addr, &addr_size);
fp = open(buf, O_RDWR | O_CREAT, 0644);
printf("file \"%s\" is opened\n", buf);
//get file
memset(buf, 0, sizeof(buf));//reset buffer
//byteRcvd = recvfrom(sockfd, buf, sizeof(buf), 0,
//(struct sockaddr*)&addr, &addr_size);
byteRcvd = BUFFER_SIZE;
while(byteRcvd){
if(byteRcvd != BUFFER_SIZE)
break;
//rcv data and show its size
if((byteRcvd = recvfrom(sockfd, buf, sizeof(buf), 0,
(struct sockaddr*)&addr, &addr_size)) == EOF){
printf("Out of loop by EOF\n");
break;
}
printf("%dB Rcvd ", byteRcvd);
//printf rcvd data
for(i = 0; i < BUFFER_SIZE; i++)
if(buf[i] == '\n')
printf("#", buf[i]);
else
printf("%c", buf[i]);
printf("\n");
//getchar();
write(fp, buf, byteRcvd);
memset(buf, 0, sizeof(buf));
}
printf("byteRcvd: %d\n", byteRcvd);
close(sockfd);
close(fp);
fp = 0;
printf("Continue??\n");
getchar();
}
return 0;
}
客户：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <fcntl.h>
#define BUFFER_SIZE 50
int sockfd;//socket file descriptor
struct sockaddr_in addr;//variable to contain IPv4 and port#
//argv[1]: IP address
//argv[2]: port #
//argv[3]: file name to be sent
int main(int argc, char *argv[]){
int i, n;
int byteSent = 0;//size of data sent at each time
int addr_size = sizeof(struct sockaddr);
int fp = open(argv[3], O_RDONLY);
char buf[BUFFER_SIZE];//buffer to contain data
char temp[BUFFER_SIZE];
//check argument number
if(argc != 4)
exit(1);
//create a socket
if((sockfd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
exit(1);
//set addr
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(argv[1]);
addr.sin_port = htons(atoi(argv[2]));
//send the file name to the server
byteSent = sendto(sockfd, argv[3], sizeof(argv[3]), 0,
(struct sockaddr*)&addr, addr_size);
memset(buf, 0, sizeof(buf));
//while((byteSent = read(fp, buf, BUFFER_SIZE))){
byteSent = read(fp, buf, BUFFER_SIZE);
while(byteSent){
getchar();
sendto(sockfd, buf, byteSent, 0,
(struct sockaddr*)&addr, addr_size);
printf("%d byte sent\n", byteSent);
for(i = 0; i < BUFFER_SIZE; i++){
if(i == 0)
printf("[");
if(buf[i] == '\n')
printf("@");
else
printf("%c", buf[i]);
if(i == 39)
printf("]");}
printf("\n");
memset(buf, 0, sizeof(buf));
byteSent = read(fp, buf, BUFFER_SIZE);
printf("Next byteSent is to be %d\n", byteSent);
}
close(sockfd);
close(fp);
return 0;
}
l.txt:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat。 Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur。 Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
服务器端：
[21100610@localhost server]$ ./s 70000
file "l.txt" is opened
50B Rcvd Lorem ipsum dolor sit amet, consectetur adipiscing
50B Rcvd elit, sed do eiusmod tempor incididunt ut labore
50B Rcvd et dolore magna aliqua. Ut enim ad minim veniam, q
50B Rcvd uis nostrud exercitation ullamco laboris nisi ut a
50B Rcvd liquip ex ea commodo consequat. Duis aute irure do
50B Rcvd lor in reprehenderit in voluptate velit esse cillu
50B Rcvd m dolore eu fugiat nulla pariatur. Excepteur sint
50B Rcvd occaecat cupidatat non proident, sunt in culpa qui
46B Rcvd officia deserunt mollit anim id est laborum.#
byteRcvd: 46
Continue?? <=== at this point I typed enter
file "" is opened
Out of loop by EOF
byteRcvd: -1
Continue?? <=== at this point I typed enter
file "" is opened
Out of loop by EOF
byteRcvd: -1
Continue?? <=== at this point I typed enter
file "" is opened
Out of loop by EOF
byteRcvd: -1
Continue??
^C
[21100610@localhost server]$
客户端终端：
[21100610@localhost client]$ ./c 127.0.0.1 70000 l.txt
50 byte sent
[Lorem ipsum dolor sit amet, consectetur ]adipiscing
Next byteSent is to be 50
50 byte sent
[ elit, sed do eiusmod tempor incididunt ]ut labore
Next byteSent is to be 50
50 byte sent
[et dolore magna aliqua. Ut enim ad minim] veniam, q
Next byteSent is to be 50
50 byte sent
[uis nostrud exercitation ullamco laboris] nisi ut a
Next byteSent is to be 50
50 byte sent
[liquip ex ea commodo consequat. Duis aut]e irure do
Next byteSent is to be 50
50 byte sent
[lor in reprehenderit in voluptate velit ]esse cillu
Next byteSent is to be 50
50 byte sent
[m dolore eu fugiat nulla pariatur. Excep]teur sint
Next byteSent is to be 50
50 byte sent
[occaecat cupidatat non proident, sunt in] culpa qui
Next byteSent is to be 46
46 byte sent
[ officia deserunt mollit anim id est lab]orum.@
Next byteSent is to be 0
[21100610@localhost client]$
这里有问题吗？
您调用recvfrom接收文件内容，直到您收到一个小于50字节的数据包。发生这种情况时，您关闭套接字并返回尝试读取更多数据（另一个文件？），但是 recvfrom 将始终 return -1（错误）和 EBADF，因为套接字已关闭。
您正在将 recvfrom 的 return 值与 EOF 进行比较，这是胡说八道 -- EOF 用于 函数，而不是套接字功能。碰巧 EOF 是 -1，而套接字函数 return -1 是错误的，所以通过检查 EOF，你实际上是在检查错误...
client: argv[1]: ip地址, argv[2]: 端口号, argv[3]: 文件名 客户端首先向服务器发送 argv[3] 并在 UDP 连接中以数据包的形式发送文件。一旦发现没有数据读取，它就会跳出循环并终止。
服务器：argv[1]：端口号 这是迭代的，因此会一直重复接收，直到系统获得 ^C。首先是接收文件名并进入循环获取数据。实际上我仍然不知道我到底对逃逸条件做了什么。我认为当最后一个数据包大小与 BUFFER_SIZE 相同时会产生一些问题。无论如何，到目前为止它工作没有问题，所以这部分不是要处理的最大任务。
我遇到的问题是接收文件名的recvfrom()得到的是空数据。我所期望的是该函数等待从客户端发送文件名。下面添加两个源代码和终端显示的结果。谁能帮我阻止 recvfrom() 获取空缓冲区？
服务器：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <fcntl.h>
#define BUFFER_SIZE 50
int main(int argc, char *argv[]){
int sockfd;//socket file descriptor
int byteRcvd;//gets received bytes when recvfrom() is called
int addr_size = sizeof(struct sockaddr);//used to bind
int fp;//to handle file
int i;
struct sockaddr_in addr;//contains address information
char fileName[20];//gets file name
char buf[BUFFER_SIZE];//buffer
//create a socket
sockfd = socket(PF_INET, SOCK_DGRAM, 0);
//set and addr
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_ANY);//address here
addr.sin_port = htons(atoi(argv[1]));//port # here
bind(sockfd, (struct sockaddr*)&addr, sizeof(addr));
//repetition of receiving files
while(1){
//get file name and open
memset(buf, 0, sizeof(buf));
byteRcvd = recvfrom(sockfd, buf, sizeof(buf), 0,
(struct sockaddr*)&addr, &addr_size);
fp = open(buf, O_RDWR | O_CREAT, 0644);
printf("file \"%s\" is opened\n", buf);
//get file
memset(buf, 0, sizeof(buf));//reset buffer
//byteRcvd = recvfrom(sockfd, buf, sizeof(buf), 0,
//(struct sockaddr*)&addr, &addr_size);
byteRcvd = BUFFER_SIZE;
while(byteRcvd){
if(byteRcvd != BUFFER_SIZE)
break;
//rcv data and show its size
if((byteRcvd = recvfrom(sockfd, buf, sizeof(buf), 0,
(struct sockaddr*)&addr, &addr_size)) == EOF){
printf("Out of loop by EOF\n");
break;
}
printf("%dB Rcvd ", byteRcvd);
//printf rcvd data
for(i = 0; i < BUFFER_SIZE; i++)
if(buf[i] == '\n')
printf("#", buf[i]);
else
printf("%c", buf[i]);
printf("\n");
//getchar();
write(fp, buf, byteRcvd);
memset(buf, 0, sizeof(buf));
}
printf("byteRcvd: %d\n", byteRcvd);
close(sockfd);
close(fp);
fp = 0;
printf("Continue??\n");
getchar();
}
return 0;
}
客户：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <fcntl.h>
#define BUFFER_SIZE 50
int sockfd;//socket file descriptor
struct sockaddr_in addr;//variable to contain IPv4 and port#
//argv[1]: IP address
//argv[2]: port #
//argv[3]: file name to be sent
int main(int argc, char *argv[]){
int i, n;
int byteSent = 0;//size of data sent at each time
int addr_size = sizeof(struct sockaddr);
int fp = open(argv[3], O_RDONLY);
char buf[BUFFER_SIZE];//buffer to contain data
char temp[BUFFER_SIZE];
//check argument number
if(argc != 4)
exit(1);
//create a socket
if((sockfd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
exit(1);
//set addr
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(argv[1]);
addr.sin_port = htons(atoi(argv[2]));
//send the file name to the server
byteSent = sendto(sockfd, argv[3], sizeof(argv[3]), 0,
(struct sockaddr*)&addr, addr_size);
memset(buf, 0, sizeof(buf));
//while((byteSent = read(fp, buf, BUFFER_SIZE))){
byteSent = read(fp, buf, BUFFER_SIZE);
while(byteSent){
getchar();
sendto(sockfd, buf, byteSent, 0,
(struct sockaddr*)&addr, addr_size);
printf("%d byte sent\n", byteSent);
for(i = 0; i < BUFFER_SIZE; i++){
if(i == 0)
printf("[");
if(buf[i] == '\n')
printf("@");
else
printf("%c", buf[i]);
if(i == 39)
printf("]");}
printf("\n");
memset(buf, 0, sizeof(buf));
byteSent = read(fp, buf, BUFFER_SIZE);
printf("Next byteSent is to be %d\n", byteSent);
}
close(sockfd);
close(fp);
return 0;
}
l.txt:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat。 Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur。 Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
服务器端：
[21100610@localhost server]$ ./s 70000
file "l.txt" is opened
50B Rcvd Lorem ipsum dolor sit amet, consectetur adipiscing
50B Rcvd elit, sed do eiusmod tempor incididunt ut labore
50B Rcvd et dolore magna aliqua. Ut enim ad minim veniam, q
50B Rcvd uis nostrud exercitation ullamco laboris nisi ut a
50B Rcvd liquip ex ea commodo consequat. Duis aute irure do
50B Rcvd lor in reprehenderit in voluptate velit esse cillu
50B Rcvd m dolore eu fugiat nulla pariatur. Excepteur sint
50B Rcvd occaecat cupidatat non proident, sunt in culpa qui
46B Rcvd officia deserunt mollit anim id est laborum.#
byteRcvd: 46
Continue?? <=== at this point I typed enter
file "" is opened
Out of loop by EOF
byteRcvd: -1
Continue?? <=== at this point I typed enter
file "" is opened
Out of loop by EOF
byteRcvd: -1
Continue?? <=== at this point I typed enter
file "" is opened
Out of loop by EOF
byteRcvd: -1
Continue??
^C
[21100610@localhost server]$
客户端终端：
[21100610@localhost client]$ ./c 127.0.0.1 70000 l.txt
50 byte sent
[Lorem ipsum dolor sit amet, consectetur ]adipiscing
Next byteSent is to be 50
50 byte sent
[ elit, sed do eiusmod tempor incididunt ]ut labore
Next byteSent is to be 50
50 byte sent
[et dolore magna aliqua. Ut enim ad minim] veniam, q
Next byteSent is to be 50
50 byte sent
[uis nostrud exercitation ullamco laboris] nisi ut a
Next byteSent is to be 50
50 byte sent
[liquip ex ea commodo consequat. Duis aut]e irure do
Next byteSent is to be 50
50 byte sent
[lor in reprehenderit in voluptate velit ]esse cillu
Next byteSent is to be 50
50 byte sent
[m dolore eu fugiat nulla pariatur. Excep]teur sint
Next byteSent is to be 50
50 byte sent
[occaecat cupidatat non proident, sunt in] culpa qui
Next byteSent is to be 46
46 byte sent
[ officia deserunt mollit anim id est lab]orum.@
Next byteSent is to be 0
[21100610@localhost client]$
这里有问题吗？
您调用recvfrom接收文件内容，直到您收到一个小于50字节的数据包。发生这种情况时，您关闭套接字并返回尝试读取更多数据（另一个文件？），但是 recvfrom 将始终 return -1（错误）和 EBADF，因为套接字已关闭。
您正在将 recvfrom 的 return 值与 EOF 进行比较，这是胡说八道 -- EOF 用于 EOF 是 -1，而套接字函数 return -1 是错误的，所以通过检查 EOF，你实际上是在检查错误...