我有两台机器，我希望它们都能在 C 编程语言下使用套接字进行通信。
我开发了两个样本来代表双方，但我注意到如果它们小于某个数字，我就可以成功发送数据。
我测试过但不起作用的大小是发送和接收 2048 字节，相反，对于其他较小的大小，例如 258 字节、1KByte，它工作正常。
经过一番调查，我发现发送操作没有错误，而接收操作却什么也没得到。
我已经检查了两台机器上的发送和接收缓冲区大小，我想它们是足够的。
这是我的代码的第一面:
/* UDP client in the internet domain */
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
#define BUFF_SIZE 1800
#define MOBIPASS_L2_IP_ADDRESS "192.168.13.53"
#define MOBIPASS_L2_PORT_NUM 12001
#define BRIDGE_IP_ADDRESS "192.168.13.30"
#define BRIDGE_PORT_NUM 12000
#define RESTRICT_SRC_DST_NUM 1
#define TEN_MSEC 10000
void error(const char *);
void adjustSockParam (int sockFD);
int main(int argc, char *argv[])
{
#if RESTRICT_SRC_DST_NUM
int bridge_sock_fd = -1, n =-1;
struct sockaddr_in server_mobipass, client_bridge;
char buffer[BUFF_SIZE];
char* choice = NULL;
size_t size = 1;
/* create socket descriptor at client machine*/
bridge_sock_fd= socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (bridge_sock_fd < 0) error("socket");
/* *********************************************************
* prepare source information of the socket file descriptor
* *********************************************************
*/
client_bridge.sin_family = AF_INET;
client_bridge.sin_addr.s_addr=inet_addr(BRIDGE_IP_ADDRESS) ;
client_bridge.sin_port = htons(BRIDGE_PORT_NUM);
if( bind( bridge_sock_fd, (struct sockaddr *) &client_bridge, sizeof ( client_bridge ) ) < 0 )
{
error( "bind" );
}
/* *********************************************************
* prepare destination information of the socket file descriptor
* *********************************************************
*/
server_mobipass.sin_family = AF_INET;
server_mobipass.sin_addr.s_addr=inet_addr(MOBIPASS_L2_IP_ADDRESS) ;
server_mobipass.sin_port = htons(MOBIPASS_L2_PORT_NUM);
if( connect( bridge_sock_fd, (struct sockaddr *) &server_mobipass, sizeof ( server_mobipass ) ) < 0 ) {
error("connect");
}
adjustSockParam(bridge_sock_fd);
do
{
printf("sending traffic?[y/n]\n");
getline(&choice,&size,stdin);
if(*choice=='n')
break;
strncpy( buffer,
"Hello Mobipass, this is bridge :)\n",
sizeof(buffer));
n = send( bridge_sock_fd, buffer, sizeof(buffer), MSG_CONFIRM );
if( n < 0 )
{
error( "send" );
}
assert(n == sizeof(buffer));
usleep(TEN_MSEC);
/*memset(buffer,0 , sizeof(buffer));
if( recv( bridge_sock_fd, buffer, sizeof(buffer), 0 ) < 0 )
{
error( "recv" );
}
else
{
printf("Msg received from mobipass is:\n%s",buffer);
}*/
}while(*choice == 'y' || *choice == 'Y');
close( bridge_sock_fd );
#else
int tx_sock, n, rx_sock;
unsigned int srv_length;
struct sockaddr_in server_mobipass, from, server_bridge;
char buffer[256];
/* create socket descriptor at client machine*/
tx_sock= socket(AF_INET, SOCK_DGRAM, 0);
if (tx_sock < 0) error("socket");
srv_length=sizeof(struct sockaddr_in);
/*prepare server (peer entity) of UDP connection*/
server_mobipass.sin_family = AF_INET;
server_mobipass.sin_addr.s_addr=inet_addr(MOBIPASS_L2_IP_ADDRESS) ;
server_mobipass.sin_port = htons(MOBIPASS_L2_PORT_NUM);
printf("Please enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n=sendto(tx_sock,buffer,
strlen(buffer),0,(const struct sockaddr *)&server_mobipass,srv_length);
if (n < 0) error("Sendto");
rx_sock= socket(AF_INET, SOCK_DGRAM, 0);
if (rx_sock < 0) error("socket");
server_bridge.sin_family = AF_INET;
server_bridge.sin_addr.s_addr = inet_addr(BRIDGE_IP_ADDRESS);
server_bridge.sin_port = htons(BRIDGE_PORT_NUM);
if (bind(rx_sock,(struct sockaddr *)&server_bridge,srv_length)<0)
error("binding");
n = recvfrom(rx_sock,buffer,256,0,(struct sockaddr *)&from, &srv_length);
if (n < 0) error("recvfrom");
/*print to stdout what have been received*/
write(1,"Got an ack: ",12);
write(1,buffer,n);
/* close sockets */
close(rx_sock);
close(tx_sock);
#endif /* RESTRICT_SRC_DST_NUM */
return 0;
}
void error(const char *msg)
{
perror(msg);
exit(0);
}
void adjustSockParam (int sockFD)
{
int option_value;
socklen_t option_len = sizeof(option_value);
/** Adjust Send Buffer Size**/
if( getsockopt(sockFD, SOL_SOCKET, SO_SNDBUF,
&option_value, &option_len)< 0)
{
error("get Socket Option error:");
}
printf("Initial SO_SNDBUF: option_len = %d option_value = %d\n",option_len,option_value);
/*option_value = 2048;
if( setsockopt(sockFD, SOL_SOCKET, SO_SNDBUF,
&option_value, option_len)< 0)
{
error("get Socket Option error:");
}
if( getsockopt(sockFD, SOL_SOCKET, SO_SNDBUF,
&option_value, &option_len)< 0)
{
error("get Socket Option error:");
}
printf("Final SO_SNDBUF: option_len = %d option_value = %d\n",option_len,option_value);*/
/** Adjust Receiver Buffer Size **/
if( getsockopt(sockFD, SOL_SOCKET, SO_RCVBUF,
&option_value, &option_len)< 0)
{
error("get Socket Option error:");
}
printf("Initial SO_RCVBUF: option_len = %d option_value = %d\n",option_len,option_value);
}
这是我的代码的第二面:
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <netdb.h>
#include <stdio.h>
#include <assert.h>
#define BUFF_SIZE 1800
#define MOBIPASS_L2_IP_ADDRESS "192.168.13.53"
#define MOBIPASS_L2_PORT_NUM 12001
#define BRIDGE_IP_ADDRESS "192.168.13.30"
#define BRIDGE_PORT_NUM 12000
#define DUMP 0
#define ACT_AS_STRING 0
#define RESTRICT_SRC_DST_NUM 1
#define TEN_MSEC 10000
#if DUMP
#define DUMP_BUFFER(buf,len) \
{ \
int i; \
for(i = 0; i < len; i++) \
printf("buf[%d] = 0x%x",i,buf[i]); \
}
#else
#define DUMP_BUFFER(buf,len) printf("received len=%d\n",len)
#endif
void adjustSockParam (int sockFD);
void error(const char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
#if RESTRICT_SRC_DST_NUM
int mobipass_sock_fd = -1;
struct sockaddr_in server_mobipass, client_bridge;
char buffer[BUFF_SIZE];
int recivedBytes=-1;
printf("size of buffer = %d\n",sizeof(buffer));
/* create socket descriptor at client machine*/
mobipass_sock_fd= socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (mobipass_sock_fd < 0) error("socket");
/* *********************************************************
* prepare source information of the socket file descriptor
* *********************************************************
*/
client_bridge.sin_family = AF_INET;
client_bridge.sin_addr.s_addr=inet_addr(MOBIPASS_L2_IP_ADDRESS) ;
client_bridge.sin_port = htons(MOBIPASS_L2_PORT_NUM);
if( bind( mobipass_sock_fd, (struct sockaddr *) &client_bridge, sizeof ( client_bridge ) ) < 0 )
{
error( "bind" );
}
/* *********************************************************
* prepare destination information of the socket file descriptor
* *********************************************************
*/
server_mobipass.sin_family = AF_INET;
server_mobipass.sin_addr.s_addr=inet_addr(BRIDGE_IP_ADDRESS) ;
server_mobipass.sin_port = htons(BRIDGE_PORT_NUM);
if( connect( mobipass_sock_fd, (struct sockaddr *) &server_mobipass, sizeof ( server_mobipass ) ) < 0 ) {
error("connect");
}
adjustSockParam(mobipass_sock_fd);
printf("waiting for message from bridge:\n");
do{
memset(buffer,0 , sizeof(buffer));
recivedBytes = recv( mobipass_sock_fd, buffer, sizeof(buffer), 0 );
if( recivedBytes < 0 )
{
error( "recv" );
}
else
{
assert(recivedBytes == sizeof(buffer));
DUMP_BUFFER(buffer,recivedBytes);
#if ACT_AS_STRING
printf("Msg received from bridge is:\n%s",buffer);
#endif
}
usleep(TEN_MSEC);
#if ACT_AS_STRING
strncpy( buffer,
"Hello Bridge, this is mobipass :)\n",
sizeof(buffer));
if( send( mobipass_sock_fd, buffer, sizeof(buffer), 0 ) < 0 )
{
error( "send" );
}
#endif
}while(1);
close( mobipass_sock_fd );
#else
int tx_sock, n, rx_sock;
unsigned int srv_length;
socklen_t fromlen;
struct sockaddr_in server_mobipass, from, server_bridge;
char buf[1024];
rx_sock=socket(AF_INET, SOCK_DGRAM, 0);
if (rx_sock < 0) error("Opening socket");
else printf("Creating rx udp socket\n");
srv_length = sizeof(server_mobipass);
bzero(&server_mobipass,srv_length);
server_mobipass.sin_family=AF_INET;
server_mobipass.sin_addr.s_addr=inet_addr(MOBIPASS_L2_IP_ADDRESS);
server_mobipass.sin_port=htons(MOBIPASS_L2_PORT_NUM);
if (bind(rx_sock,(struct sockaddr *)&server_mobipass,srv_length)<0)
error("binding");
else
printf("Binding a socket to a server IP address\n");
fromlen = sizeof(struct sockaddr_in);
tx_sock=socket(AF_INET, SOCK_DGRAM, 0);
if (tx_sock < 0) error("Opening socket");
else printf("Creating tx udp socket\n");
server_bridge.sin_family=AF_INET;
server_bridge.sin_addr.s_addr=inet_addr(BRIDGE_IP_ADDRESS);
server_bridge.sin_port=htons(BRIDGE_PORT_NUM);
while (1)
{
printf("waiting for a message from client side:\n");
n = recvfrom(rx_sock,buf,1024,0,(struct sockaddr *)&from,&fromlen);
if (n < 0) error("recvfrom");
write(1,"Message received from eNB machince:\n",36);
write(1,buf,n);
n = sendto(tx_sock,"hello eNB, I am mobipass\n",27,
0,(struct sockaddr *)&server_bridge,fromlen);
if (n < 0) error("sendto");
}
#endif
return 0;
}
void adjustSockParam (int sockFD)
{
int option_value;
socklen_t option_len = sizeof(option_value);
/** Adjust Send Buffer Size**/
if( getsockopt(sockFD, SOL_SOCKET, SO_SNDBUF,
&option_value, &option_len)< 0)
{
error("get Socket Option error:");
}
printf("Initial SO_SNDBUF: option_len = %d option_value = %d\n",option_len,option_value);
/* option_value = 2048;
if( setsockopt(sockFD, SOL_SOCKET, SO_SNDBUF,
&option_value, option_len)< 0)
{
error("get Socket Option error:");
}
if( getsockopt(sockFD, SOL_SOCKET, SO_SNDBUF,
&option_value, &option_len)< 0)
{
error("get Socket Option error:");
}
printf("Final SO_SNDBUF: option_len = %d option_value = %d\n",option_len,option_value);*/
/** Adjust Receiver Buffer Size **/
if( getsockopt(sockFD, SOL_SOCKET, SO_RCVBUF,
&option_value, &option_len)< 0)
{
error("get Socket Option error:");
}
printf("Initial SO_RCVBUF: option_len = %d option_value = %d\n",option_len,option_value);
}
这是第一面的输出:
Initial SO_SNDBUF: option_len = 4 option_value = 112640
Initial SO_RCVBUF: option_len = 4 option_value = 112640
sending traffic?[y/n]
y
sending traffic?[y/n]
y
这是第二面的输出:
size of buffer = 1800
Initial SO_SNDBUF: option_len = 4 option_value = 1048576
Initial SO_RCVBUF: option_len = 4 option_value = 1048576
waiting for message from bridge:
我不确定我在这里做错了什么。您有什么建议吗？
最佳答案
虽然 UDP 数据报包大小可达 64K(16 位数据长度字段)，但通常的底层数据链路技术 - 以太网 - 的帧大小为 1500 字节。 IP header 至少少 20 个字节，UDP header 少 8 个字节，这样就只剩下 1472 个字节用于 UDP 有效负载，可以在没有 IP 分段的情况下发送，这通常会导致问题，例如您的情况，数据包只是在某处丢失。
正是出于这个原因，大多数基于 UDP 的协议(protocol)都会限制数据报大小。
关于c - Linux 上的 UDP 套接字；发送成功但无法接收大缓冲区，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14122056/