Some special usages of TCP/UDP and transceiver interfaces

1.UDP the difference between using the Connect function and not using the Connect function

* No longer use sendto/recvfrom, but only write/read or SEND/RECV, which means that the destination IP cannot be specified when sending and receiving data

* Asynchronous errors raised by connected UDP are returned to the process in which they are located, while non-connected UDP does not receive asynchronous errors

* Connected UDP has high transceiver efficiency. Because the non-connected UDP is sending and receiving data, the connection process needs to be performed before the data is sent and received, and then the connection is unblocked.

* UDP can call connect multiple times to specify a new IP address and port, or it can be disconnected

2.3 Ways to control timeout for all blocking ports such as Recvfrom/sendto,read/write,recv/send,accept,connect

* Select Timeout exit Select.io can be driven not only with Select, but also with signal Sigio (asynchronous IO), which is emitted when any event occurs on Io

* The alarm timeout will receive the SIGALRM signal while the current blocking port returns a ERRNO==EINTR error

* setsockopt setting socket option: So_rcvtimeo/so_sndtimeo

Non-blocking settings:

int Val=fcntl (fd,f_getfl,0);

Fcntl (fd,f_setfl,val| O_nonblock);

3. Parameters for Recvfrom/sendto,read/write,recv/send read-write interface flags flags

* 0 does not have any special meaning

* Msg_dontroute send and receive data, do not need to perform a route lookup, tell the route is within the LAN

* Msg_dontwait perform non-blocking send and receive operations only this time

* Msg_oob indicates that data is sent or received out of band, only one byte on the TCP connection can be transmitted as out-of-band data

* Msg_peek is only useful for receiving data, see how much data is already readable in the cache

* Msg_waitall only useful for receiving data, reading to a specified number of data will return 000

4. Aggregation and dispersion Readv/writev functions: Any file descriptor can be manipulated

#include <sys/uio.h>

size_t readv (int fd,const struct IOVEC *iov,int iovcnt);

size_t writev (int fd,const struct IOVEC *iov,int iovcnt); If successful, returns the number of bytes read and written, failing to return 1

struct iovec{

void *iov_base; //starting Address of buffer

size_t Iov_len; //sizeof of buffer

}

This article from "Tech record" blog, declined reprint!

Some special usages of TCP/UDP and transceiver interfaces