Linux network programming notes

Linux network programming notes-general Linux technology-Linux programming and kernel information. The following is a detailed description. There are three types of sockets:

1. Streaming socket (SOCKET_STREAM)
Provides reliable connection-oriented data transmission services. Data is considered as a byte stream with no length restrictions. For example, FTP uses this protocol.

2. datagram socket (SOCKET_DGRAM)
Provides a connectionless data transmission service, which does not guarantee reliability.

3. original socket (SOCKET_RAW)
This interface allows direct access to lower-level protocols, such as IP and ICMP.

II. The basic socket system has the following calls:

Create a socket: socket ()
Bind local port: bind ()
Establish a connection: connect (), accept ()
Listening port: listen ()
Data transmission: send (), recv ()
Input/Output multiplexing: select ()
Disable socket only: closesocket ()

Three Data Types

Struct sockaddr
{
Unsigned short sa_family; // address family, generally AF_INET
Char sa_data [14]; // 14-byte Protocol address
}

Struct sockaddr_in
{
Short int sin_family; // address family
Unsigned short int sin_port; // port number
Struct in_addr; // ip address
Unsigned char sin_zero [8]; // fill
}

Four common functions

1 socket ()
Header file:
# Include
# Include
Function prototype:
Int socket (int domain, int type, int protocol)
Domain: protocol type, generally AF_INET
Type: socket type
Protocol: used to specify the number of the transport protocol used by the socket. It is usually set to 0.

2 bind ()
Header file:
# Include
# Include
Function prototype:
Int bind (int sockfd, struct sockaddr * my_addr, int addrlen)
Sockfd: socket Descriptor
My_addr: A sockaddr pointer pointing to information including the local IP address and port number.
Addrlen: usually set to sizeof (struct sockaddr)

3 connect ()
Header file:
# Include
# Include
Function prototype:
Int connect (int sockfd, struct sockaddr * serv_addr, int addrlen)
Sockfd: socket descriptor of the target server
Serv_addr: pointer containing the IP address and port number of the target machine
Addrlen: sizeof (struct sockaddr)

4 listen ()
Header file:
# Include
Function prototype:
Int listen (int sockfd, int backlog );
Sockfd: socket descriptor returned by the socket () system call
Backlog: specify the maximum number of requests in the Request queue. incoming connection requests will wait for accept () in the queue.

5 accept ()
Header file:
# Include
# Inlcude
Function prototype:
Int accept (int sockfd, void * addr, int addrlen)
Sockfd: indicates the socket descriptor to be monitored.
Addr: Usually a pointer to the sockaddr_in variable, which is used to store the information of the host requesting the Connection Service.
Addrlen: sizeof (struct sockaddr_in)

6 send ()
Header file:
# Include
Function prototype:
Int send (int sockfd, const void * msg, int len, int flags );
Sockfd: socket descriptor used to transmit data
Msg: pointer to send data
Flags: 0

7 recv ()
Header file:
# Include
# Include
Function prototype:
Int recv (int sockfd, void * buf, int len, unsigned int flags)
Sockfd: socket descriptor for receiving data
Buf: buffer for storing data
Len: Buffer Length
Flags: 0

8 sendto ()
Header file:
# Include
# Include
Function prototype:
Int sendto (int sockfd, const void * msg, int len, unsigned int flags, const struct sockaddr * to, int tolen );


9 recvfrom ()
Header file:
# Include
# Include
Function prototype:
Int recvfrom (int sockfd, void * buf, int len, unsigned int flags, struct sockaddr * from, int fromlen)


10 read () write ()
Int read (int fd, char * buf, int len)
Int write (int fd, char * buf, int len)

11 shutdown ()
Close (sockfd)
Int shutdown (int sockfd, int how)