Core concepts and models of network programming

Keywords: network

Core concepts and models of network programming

1. Question

How to program network?

2. The essence of network programming

Using the interface function provided by the operating system, the application has the ability to send and receive network data.

  • The network interface is a function provided by the operating system at the code level
    • Network programming is just a fancy way to play a series of system functions
  • Applications use the networking capabilities of the operating system through network interfaces
    • Network programming is a domain specific C language programming

3. Core concepts of network programming

  • Protocol: predefined data rules for data communication
  • Address: an integer value used to identify a device in network communication
  • Port number:
    • The value specified by the device for sending and receiving data, which is used to identify the specific connection
    • It can be understood as: the data channel used for network communication in the device
  • role
    • Server: the device waiting for connection
    • Client: the device that initiates the connection
  • Network knowledge charging station
    • Is the web address the IP address? What is the URL? What is the domain name?
      • The web address is not an IP address, but the address of network information resources (such as the address of specific web pages), i.e. URL
      • Domain name is an alias of IP address. Multiple domain names can point to the same IP address
    • Must the protocol be binary data that you can't understand?
      • Agreement is a kind of agreement, that is, predefined rules
      • Protocols can be defined based on text or binary
    • Small end system
      • The system adopts small end mode, that is, the low byte of data is placed in the low address of memory
    • Big end system
      • The system adopts the big end mode, that is, the low byte of data is placed in the high address of memory
    • Network byte order
      • The network byte order adopts the large end mode, so the byte order conversion is required in the small segment system.

4. Network programming mode

1. Prepare network connection
2. Connecting remote devices
3. Send and receive data
4. Close connection
  • Discussion on network programming interface
#include<sys/types.h>
#include<sys/socket.h>
Function prototypeFunction description
int socket(int domain, int type, int protocol);Create sockets to prepare for network connections
int connect(SOCKET s, const struct sockaddr * name, int namelen);Connect to a remote device at the specified address
ssize_t send(int s,const void* buf,size_t len,int flags);Send data to remote device
ssize_t recv(int sockfd, void *buf, size_t nbytes, int flags);Receive data from remote device
int close(int fd);Close the connection and destroy the socket

5. Programming experiment

//1-1.c

#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdio.h>
#include<unistd.h>
#include<string.h>

int main()
{
    int sock = 0;
    struct sockaddr_in addr = {0};  
    char* tosend = "GET /index.html HTTP/1.1\nHOST: www.dt4sw.com\nUser-Agent: TEST\nConnection: close\n\n";
    int len = 0;
    int r = 0;
    char buf[128] = {0};

    sock = socket(PF_INET,SOCK_STREAM,0);
    if(sock == -1)
    {
        printf("socket err\n");
        return -1;
    }

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr("47.99.217.175");
    addr.sin_port = htons(80);

    if(connect(sock,(struct sockaddr*)&addr,sizeof(addr)) == -1)
    {
        printf("connect err\n");
        return -1;
    }

    printf("connect success\n");

    len = send(sock,tosend,strlen(tosend),0);
    printf("send bytes = %d\n",len);

    do
    {
        int i = 0;

        r = recv(sock, buf, sizeof(buf), 0);

        if( r > 0)
        {
            len += r;
        }

        for( i = 0; i < r; i++)
        {
            printf("%c",buf[i]);
        }
    } while ( r > 0);

    printf("\n");
    printf("recv bytes = %d\n",len);

    close(sock);

    return 0;
}

Operation results:

connect success
send bytes = 81
HTTP/1.1 200 OK
Content-Type: text/html
Last-Modified: Wed, 19 May 2021 14:09:18 GMT
Accept-Ranges: bytes
ETag: "0bb8c8eb84cd71:0"
Server: Microsoft-IIS/7.5
Date: Mon, 01 Nov 2021 13:59:57 GMT
Connection: close
Content-Length: 22138

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Posted by g00fy_m on Mon, 01 Nov 2021 20:08:24 -0700