Server setup (TCP socket)-Basic version (client)

1. socket

1.1. vim man view socket

:!man socket

1.2. Dependent header files

 #include <sys/types.h>     
 #include <sys/socket.h>

1.3. Prototype

int socket(int domain, int type, int protocol);

domain	illustrate
OF_INET	IPv4 protocol
AF_INET6	IPv6 protocol
AF_LOCAL	Unix Domain Protocol

type	illustrate
SOCK_STREAM	Byte stream socket (TCP/SCTP)
SOCK_DGRAM	Datagram socket (UDP)
SOCK_RAM	Raw sockets (IPv4/IPv6)
SOCK_SEQPACKET	Ordered Packet Sockets (SCTP)

protocol	illustrate
IPPROTO_CP	TCP transport protocol
IPPROTO_UDP	UDP transport protocol
IPPROTO_SCTP	SCTP transfer protocol

The socket function will return a small non-negative integer value when successful , which is similar to a file descriptor, so it is called a socket descriptor . Just specify the protocol family (IPV4, IPV6 or Unix) and socket type

• Code

socket_fd=socket(AF_INET,SOCK_STREAM,0);

2. connect

2.1. Prototype

int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);

The connect() function is used in client applications to establish a connection with the server. Note that the connect() function may block until the connection is successfully established or an error occurs . Therefore, you can use appropriate timeout mechanisms or non-blocking Socket settings to control the behavior of the connection process.

Enter:

• sockfd: The file descriptor of the client Socket to be connected.
• addr: Pointer to the server address structure, which contains the server's IP address and port number.
• addrlen: The length of the server address structure.

return value:

• 0 means the connection is successful
• A return value of -1 indicates that the connection failed, and the corresponding error code is set (you can use the perror() function to print error information).

2.2. Code

#define SERVER_PORT 8596 
#define MESSAGE_LENGTH 1024

int ret = -1;
int socket_fd;
//server addr
struct sockaddr_in serverAddr;

serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(SERVER_PORT);
//inet_addr()函数，将点分十进制IP转换成网络字节序IP
serverAddr.sin_addr.s_addr = inet_addr(args[1]);
if(connect(socket_fd, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) < 0){
    
    
    perror("connect error");
    return 1;
}

3. send

3.1. Prototype

ssize_t send(int sockfd, const void *buf, size_t len, int flags);

send is a function used in network programming to send data to a connected socket or send datagrams to a socket.

Enter:

• sockfd: Integer parameter, indicating the file descriptor of the socket to send data.
• buf: Pointer to the buffer to send data to.
• len: unsigned integer parameter, indicating the length of the data to be sent.
• flags: Integer parameter used to specify optional flags for the send operation. Common flags include 0 (no special flag) and MSG_DONTWAIT (non-blocking mode transmission).

return value

• If the data is sent successfully, send returns the number of bytes sent.
• If the connection is closed (for a stream socket) or the send times out (for a datagram socket), send returns 0.
• If an error occurs, send returns -1 and sets the corresponding error code. You can obtain specific error information through the errno global variable.

3.2. Source code

#define MESSAGE_LENGTH 1024

char sendbuf[MESSAGE_LENGTH];

 while(1)
  {
    
    
    memset(sendbuf, 0, MESSAGE_LENGTH);

    printf("send message:");

    fgets(sendbuf,MESSAGE_LENGTH,stdin);
    //printf("\n");
    ret = send(socket_fd, sendbuf, strlen(sendbuf), 0);
    if(ret <= 0 ){
    
    
      printf("the connection is disconnection!\n");
      break;
    }

  }

4. recv

4.1. Prototype

ssize_t recv(int sockfd, void *buf, size_t len, int flags);

recv is a function used in network programming to receive data from a connected socket or to receive datagrams from a socket.

It should be noted that the recv function is a blocking call , that is, it will wait until no data arrives. If non-blocking operations are required, non-blocking I/O or multi-thread/multi-process methods can be used to handle receive operations.

Enter:

• sockfd: Integer parameter, indicating the file descriptor of the socket to receive data.
• buf: Pointer to the receive data buffer, used to store received data.
• len: unsigned integer parameter, indicating the length of the receive data buffer.
• flags: Integer parameter used to specify optional flags for the receive operation. Common flags include 0 (no special flag), MSG_DONTWAIT (non-blocking mode reception) and MSG_WAITALL (blocking mode reception until data of the specified length is received), etc.

return value:

• If data is received successfully, recv returns the number of bytes received.
• recv returns 0 if the connection is closed (for a stream socket) or the receive times out (for a datagram socket).
• If an error occurs, recv returns -1 and sets the corresponding error code. Specific error information can be obtained through the errno global variable.

5. Complete code

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#include <errno.h>
#include <netdb.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define SERVER_PORT 8596 
#define MESSAGE_LENGTH 1024

int main(int argc,char* args[])
{
    
    

  int ret = -1;
  int socket_fd;

  //server addr
  struct sockaddr_in serverAddr;

  char sendbuf[MESSAGE_LENGTH];
  char recvbuf[MESSAGE_LENGTH];

  int data_len;

  if((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
  {
    
    
    perror("socket");
    return 1;
  }

  serverAddr.sin_family = AF_INET;
  serverAddr.sin_port = htons(SERVER_PORT);

  //inet_addr()函数，将点分十进制IP转换成网络字节序IP
  serverAddr.sin_addr.s_addr = inet_addr(args[1]);

  if(connect(socket_fd, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) < 0)
  {
    
    
    perror("connect");
    return 1;
  }

  printf("success to connect server...\n");

  while(1)
  {
    
    
    memset(sendbuf, 0, MESSAGE_LENGTH);

    printf("send message:");

    fgets(sendbuf,MESSAGE_LENGTH,stdin);
    //printf("\n");
    ret = send(socket_fd, sendbuf, strlen(sendbuf), 0);
    if(ret <= 0 ){
    
    
      printf("the connection is disconnection!\n");
      break;
    }

    if(strcmp(sendbuf, "quit") == 0){
    
    
      break;
    }

    printf("receive message:");

    recvbuf[0] = '\0';
    data_len = recv(socket_fd, recvbuf, MESSAGE_LENGTH, 0);

    recvbuf[data_len] = '\0';

    printf("%s\n", recvbuf);

  }

  close(socket_fd);

  return 0;

}