我正在创建一个简单的服务器/客户端UDP套接字程序,并且遇到了问题。recvfrom重新读取套接字上的数据
问题是recvfrom()函数不断重新读取最后发送的数据。
所以,如果我送两包从客户机到服务器,然后recvfrom的()将读取第一个数据包,并打印其数据,然后它就会不断地一遍又一遍读第二个数据包。
据我所知,数据包应该从套接字中删除一旦成功的读取操作已经执行,但似乎并没有发生。
我知道客户端没有重发数据,因为客户端发送数据时会写入一个控制台输出。
这里的发件人
int sendPacket(int socketFd, int type, char *typeString, char *data, int seq, int windowSize, struct sockaddr_in serverName) {
struct packet *sendPacketPtr, sendPacket;
fd_set writeFdSet;
sendPacketPtr = &sendPacket;
sendPacket.flags = type;
sendPacket.windowsize = windowSize;
sendPacket.seq = seq;
sendPacket.id = getpid();
if (type == NORMAL)
strcpy(sendPacket.data, data);
FD_ZERO(&writeFdSet);
FD_SET(socketFd, &writeFdSet);
if(select(FD_SETSIZE, NULL, &writeFdSet, NULL, NULL) > 0) {
if(sendto(socketFd, sendPacketPtr, sizeof(sendPacket), 0, (struct sockaddr *)&serverName, sizeof(serverName)) < 0) {
printf("%s packet was not sent\n", typeString);
perror("Send error");
} else {
printf("%s packet was sent\n", typeString);
}
}
return 0;
}
被称为具有该环路这对于其给定值的两倍运行的功能。
for (int i = seqBase; i <= seqMax && i < packetNum; i++) {
sendPacket(socketFd, NORMAL, "DATA", dataArray[i], i, 0, serverName);
}
和接收功能
struct packet receivePacket (int socketFd, struct sockaddr_in *address, int timeout, int useTimeout) {
struct packet buffer;
fd_set readFdSet;
struct sockaddr_in dest_addr;
struct timeval selectTimeout;
selectTimeout.tv_usec = 0;
selectTimeout.tv_sec = timeout;
FD_ZERO(&readFdSet);
FD_SET(socketFd, &readFdSet);
socklen_t len = sizeof(dest_addr);
if(useTimeout == 0) {
if(select(FD_SETSIZE, &readFdSet, NULL, NULL, NULL) > 0) {
if(recvfrom(socketFd, &buffer, sizeof(buffer), 0, (struct sockaddr *)&dest_addr, &len) < 0) {
perror("Read error");
}else {
*address = dest_addr;
}
}
}else {
if(select(FD_SETSIZE, &readFdSet, NULL, NULL, &selectTimeout) > 0) {
if(recvfrom(socketFd, &buffer, sizeof(buffer), 0, (struct sockaddr *)&dest_addr, &len) < 0) {
perror("Read error");
}else {
*address = dest_addr;
}
}
}
return buffer;
}
被称为与这个循环从服务器
receivedPacket = receivePacket(socketFd, &destAddress, 0, 0);
while (receivedPacket.flags == NORMAL) {
printf("Data received: \"%s\", sequence: %d\n", receivedPacket.data, receivedPacket.seq);
receivedPacket = receivePacket(socketFd, &destAddress, TIMEOUT, 1);
}
和它一直运行(因为它保留重新读最后输出数据包)是:
Data received: "Packet 0", sequence: 0
Data received: "Packet 1", sequence: 1
Data received: "Packet 1", sequence: 1
Data received: "Packet 1", sequence: 1
Data received: "Packet 1", sequence: 1
........
在执行print()调用的任何其他系统调用(如write()之前,必须调用perror()。否则,错误值可能会更改,并且会显示误导性错误消息。 – EJP