Golang Socket Programming

This is a creation in Article, where the information may have evolved or changed.

The OSI reference model divides the computer network structure into 7 levels, but in the actual development application, we more recognize the TCP/IP family protocol five layer structure, namely Application layer (HTTP, FTP, DNS), Transport layer (UDP, TCP), Network layer (IP), link layer (Ethernet), physical layer.

Socket programming as a network layer and transport layer based data IO mode is mainly divided into two kinds, TCP sockets and UDP sockets, that is, the connection-oriented streaming socket and non-connected datagram socket.

Today mostly talk about Golang's TCP socket programming. Let's start with a simple example.

Server.go

Impersonation server-side func main () {tcpserver, _: = Net. RESOLVETCPADDR ("Tcp4", ": 8080") listener, _: = Net. LISTENTCP ("TCP", TCPServer) for {//when there is a new client request coming, get the connection to the client conn, err: = Listener. Accept () if err! = Nil {fmt.        PRINTLN (ERR) continue}//processing logic GO handle (conn) }}FUNC HANDLE (conn net. Conn) {defer Conn.                                                                                                                                                                                                                                             Close () Read the message sent by the client go func () {response, _: = Ioutil. ReadAll (conn) fmt. PRINTLN (String (response))} ()//sends a message to the client time. Sleep (1 * time. Second) Now: = time. Now (). String () Conn. Write ([]byte (now)})

Client.go

 //Impersonation client func main () {if Len (OS. Args) < 2 {fmt. fprintf (OS. Stderr, "Usage:%s host:port", OS. Args[0])}//Get command line parameters for socket address server: = OS. Args[1] addr, err: = Net. RESOLVETCPADDR ("TCP4", server) CheckError (ERR)//Establish TCP connection conn, err: = Net. Dialtcp ("TCP4", nil, addr) checkerror (ERR)//Send data to the server _, err = conn. Write ([]byte ("head/http/1.0\r\n\r\n")) CheckError (ERR)//Receive response response, _: = Ioutil. ReadAll (conn) fmt. PRINTLN (String (response)) OS.                                                                                                                                                                                                                                             Exit (0) }func checkerror (err error) {if err! = Nil {fmt. PRINTLN (ERR) OS. Exit (1)}}  

The overall approximate flow is:

Server-side first listens to port 8080 through the TCP protocol, then when there is a client to access it can read the information and write the response information, note here conn, err: = Listener. The Accept () statement is used to get the next call to the connection, and if it has not been connected, it will be in a blocked state.

The client attempts to establish a connection with the server through DIALTCP, sends the data to and receives the response after the connection succeeds, and in the above code, the connection is invalidated only after the connection is closed by the server side, otherwise the connection will remain in the established state. If the author will defer Conn. After the Close () comment is dropped, the connection to the 8080 port is viewed, and a connection is found to exist: