1、简介

socket顾名思义就是套接字的意思，用于描述地址和端口，是一个通信链的句柄。应用程序通过socket向网络发出请求或者回应。

socket编程有三种，流式套接字（SOCK_STREAM）,数据报套接字(SOCK_DGRAM),原始套接字(SOCK_RAW),前两者较常用。基于TCP的socket编程是流式套接字。

2、TCP方式

Server

Initialize Winsock.
Create a socket.
Bind the socket.
Listen on the socket for a client.
Accept a connection from a client.
Receive and send data.
Disconnect.

Client

Initialize Winsock.
Create a socket.
Connect to the server.
Send and receive data.
Disconnect.

2.1 服务端

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#pragma comment(lib, "Ws2_32.lib")

#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "27015"

int __cdecl main(void) 
{
    WSADATA wsaData;
    SOCKET ListenSocket = INVALID_SOCKET,
           ClientSocket = INVALID_SOCKET;
    struct addrinfo *result = NULL,
                    hints;
    char recvbuf[DEFAULT_BUFLEN];
    int iResult, iSendResult;
    int recvbuflen = DEFAULT_BUFLEN;
    

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed: %d\n", iResult);
        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    // Resolve the server address and port
    iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
    if ( iResult != 0 ) {
        printf("getaddrinfo failed: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // Create a SOCKET for connecting to server
    ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
    if (ListenSocket == INVALID_SOCKET) {
        printf("socket failed: %ld\n", WSAGetLastError());
        freeaddrinfo(result);
        WSACleanup();
        return 1;
    }

    // Setup the TCP listening socket
    iResult = bind( ListenSocket, result->ai_addr, (int)result->ai_addrlen);
    if (iResult == SOCKET_ERROR) {
        printf("bind failed: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    freeaddrinfo(result);

    iResult = listen(ListenSocket, SOMAXCONN);
    if (iResult == SOCKET_ERROR) {
        printf("listen failed: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    // Accept a client socket
    ClientSocket = accept(ListenSocket, NULL, NULL);
    if (ClientSocket == INVALID_SOCKET) {
        printf("accept failed: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    // No longer need server socket
    closesocket(ListenSocket);

    // Receive until the peer shuts down the connection
    do {

        iResult = recv(ClientSocket, recvbuf, recvbuflen, 0);
        if (iResult > 0) {
            printf("Bytes received: %d\n", iResult);

        // Echo the buffer back to the sender
            iSendResult = send( ClientSocket, recvbuf, iResult, 0 );
            if (iSendResult == SOCKET_ERROR) {
                printf("send failed: %d\n", WSAGetLastError());
                closesocket(ClientSocket);
                WSACleanup();
                return 1;
            }
            printf("Bytes sent: %d\n", iSendResult);
        }
        else if (iResult == 0)
            printf("Connection closing...\n");
        else  {
            printf("recv failed: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }

    } while (iResult > 0);

    // shutdown the connection since we're done
    iResult = shutdown(ClientSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }

    // cleanup
    closesocket(ClientSocket);
    WSACleanup();

    return 0;
}

2.2 客户端

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#pragma comment(lib, "Ws2_32.lib")

#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "27015"

int __cdecl main(int argc, char **argv) 
{
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct addrinfo *result = NULL,
                    *ptr = NULL,
                    hints;
    char *sendbuf = "this is a test";
    char recvbuf[DEFAULT_BUFLEN];
    int iResult;
    int recvbuflen = DEFAULT_BUFLEN;
    
    // Validate the parameters
    if (argc != 2) {
        printf("usage: %s server-name\n", argv[0]);
        return 1;
    }

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed: %d\n", iResult);
        return 1;
    }

    ZeroMemory( &hints, sizeof(hints) );
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    // Resolve the server address and port
    iResult = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result);
    if ( iResult != 0 ) {
        printf("getaddrinfo failed: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // Attempt to connect to an address until one succeeds
    for(ptr=result; ptr != NULL ;ptr=ptr->ai_next) {

        // Create a SOCKET for connecting to server
        ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype, 
            ptr->ai_protocol);
        if (ConnectSocket == INVALID_SOCKET) {
            printf("Error at socket(): %ld\n", WSAGetLastError());
            freeaddrinfo(result);
            WSACleanup();
            return 1;
        }

        // Connect to server.
        iResult = connect( ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
        if (iResult == SOCKET_ERROR) {
            closesocket(ConnectSocket);
            ConnectSocket = INVALID_SOCKET;
            continue;
        }
        break;
    }

    freeaddrinfo(result);

    if (ConnectSocket == INVALID_SOCKET) {
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }

    // Send an initial buffer
    iResult = send( ConnectSocket, sendbuf, (int)strlen(sendbuf), 0 );
    if (iResult == SOCKET_ERROR) {
        printf("send failed: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    printf("Bytes Sent: %ld\n", iResult);

    // shutdown the connection since no more data will be sent
    iResult = shutdown(ConnectSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    // Receive until the peer closes the connection
    do {

        iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
        if ( iResult > 0 )
            printf("Bytes received: %d\n", iResult);
        else if ( iResult == 0 )
            printf("Connection closed\n");
        else
            printf("recv failed: %d\n", WSAGetLastError());

    } while( iResult > 0 );

    // cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

3、UDP方式

3.1 接收端

#include <stdio.h>
#include "winsock2.h"
#pragma comment(lib, "Ws2_32.lib")

void main() {

  WSADATA wsaData;
  SOCKET RecvSocket;
  sockaddr_in RecvAddr;
  int Port = 27015;
  char RecvBuf[1024];
  int  BufLen = 1024;
  sockaddr_in SenderAddr;
  int SenderAddrSize = sizeof(SenderAddr);

  //-----------------------------------------------
  // Initialize Winsock
  WSAStartup(MAKEWORD(2,2), &wsaData);

  //-----------------------------------------------
  // Create a receiver socket to receive datagrams
  RecvSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

  //-----------------------------------------------
  // Bind the socket to any address and the specified port.
  RecvAddr.sin_family = AF_INET;
  RecvAddr.sin_port = htons(Port);
  RecvAddr.sin_addr.s_addr = htonl(INADDR_ANY);

  bind(RecvSocket, (SOCKADDR *) &RecvAddr, sizeof(RecvAddr));

  //-----------------------------------------------
  // Call the recvfrom function to receive datagrams
  // on the bound socket.
  printf("Receiving datagrams...\n");
  recvfrom(RecvSocket, 
    RecvBuf, 
    BufLen, 
    0, 
    (SOCKADDR *)&SenderAddr, 
    &SenderAddrSize);

  //-----------------------------------------------
  // Close the socket when finished receiving datagrams
  printf("Finished receiving. Closing socket.\n");
  closesocket(RecvSocket);

  //-----------------------------------------------
  // Clean up and exit.
  printf("Exiting.\n");
  WSACleanup();
  return;
}

3.2 发送端

#include <stdio.h>
#include "winsock2.h"
#pragma comment(lib, "Ws2_32.lib")

void main() {
  
  WSADATA wsaData;
  SOCKET SendSocket;
  sockaddr_in RecvAddr;
  int Port = 27015;
  char SendBuf[1024];
  int BufLen = 1024;

  //---------------------------------------------
  // Initialize Winsock
  WSAStartup(MAKEWORD(2,2), &wsaData);

  //---------------------------------------------
  // Create a socket for sending data
  SendSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

  //---------------------------------------------
  // Set up the RecvAddr structure with the IP address of
  // the receiver (in this example case "123.456.789.1")
  // and the specified port number.
  RecvAddr.sin_family = AF_INET;
  RecvAddr.sin_port = htons(Port);
  RecvAddr.sin_addr.s_addr = inet_addr("123.456.789.1");

  //---------------------------------------------
  // Send a datagram to the receiver
  printf("Sending a datagram to the receiver...\n");
  sendto(SendSocket, 
    SendBuf, 
    BufLen, 
    0, 
    (SOCKADDR *) &RecvAddr, 
    sizeof(RecvAddr));

  //---------------------------------------------
  // When the application is finished sending, close the socket.
  printf("Finished sending. Closing socket.\n");
  closesocket(SendSocket);

  //---------------------------------------------
  // Clean up and quit.
  printf("Exiting.\n");
  WSACleanup();
  return;
}

4、HTTP

无论是Http还是Https都是基于TCP进行传输的，因此使用SOCKET模拟HTTP访问web站点的方式，就是将头部数据拼接成数据包，发送给服务端，然后接收返回再解析就可以了。

这里通过socket访问如下网易新闻api接口网址获取对应数据：
http://data.live.126.net/livechannel/classifylist.json


#define _WINSOCK_DEPRECATED_NO_WARNINGS
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#pragma comment(lib, "Ws2_32.lib")

#define DEFAULT_BUFLEN 4086
#define DEFAULT_PORT 80
#define DEFAULT_URL "/livechannel/classifylist.json"
#define DEFAULT_DOMAIN "data.live.126.net" 

void get_ip_addr(const char *domain, char *ip_addr)
{
	/*通过域名得到相应的ip地址*/
	struct hostent *host = gethostbyname(domain);
	if (!host)
	{
		ip_addr = NULL;
		return;
	}

	for (int i = 0; host->h_addr_list[i]; i++)
	{
		strcpy(ip_addr, inet_ntoa(*(struct in_addr*) host->h_addr_list[i]));
		break;
	}
}

int __cdecl main(int argc, char **argv)
{
	WSADATA wsaData;
	SOCKET ConnectSocket = INVALID_SOCKET;
	const char *sendbuf = "this is a test";
	char recvbuf[DEFAULT_BUFLEN];
	int iResult;
	int recvbuflen = DEFAULT_BUFLEN;

	// Initialize Winsock
	iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
	if (iResult != 0) {
		printf("WSAStartup failed: %d\n", iResult);
		return 1;
	}

	char szRemoteIPAddr[128];
	get_ip_addr(DEFAULT_DOMAIN, szRemoteIPAddr);

	// Create a SOCKET for connecting to server
	ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (ConnectSocket == INVALID_SOCKET) {
		printf("Error at socket(): %ld\n", WSAGetLastError());
		WSACleanup();
		return 1;
	}

	struct sockaddr_in serverAddr;
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_port = htons(DEFAULT_PORT);
	serverAddr.sin_addr.s_addr = inet_addr(szRemoteIPAddr);

	// Connect to server.
	iResult = connect(ConnectSocket, (struct sockaddr *)&serverAddr, sizeof(serverAddr));
	if (iResult == SOCKET_ERROR) {
		closesocket(ConnectSocket);
		ConnectSocket = INVALID_SOCKET;
		return 1;
	}

	// Send an initial buffer
	std::string head = "GET " DEFAULT_URL " HTTP/1.1\r\n";
	head.append("Host: " DEFAULT_DOMAIN "\r\n");//请求的域名
	head.append("Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8\r\n");
	head.append("User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36\r\n");
	head.append("Accept-Language: zh-cn,zh;q=0.8,en-us;q=0.5,en;q=0.3\r\n");
	head.append("Accept-Charset: GB2312,utf-8;q=0.7,*;q=0.7");
	head.append("Accept-Encoding: gzip,deflate\r\n");
	head.append("\r\n");//表明请求头结束了

	iResult = send(ConnectSocket, head.c_str(), (int)head.size(), 0);
	if (iResult == SOCKET_ERROR) {
		printf("send failed: %d\n", WSAGetLastError());
		closesocket(ConnectSocket);
		WSACleanup();
		return 1;
	}

	printf("Bytes Sent: %ld\n", iResult);

	// Receive until the peer closes the connection
	do {
		memset(recvbuf, 0, sizeof(recvbuf));
		iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
		if (iResult > 0) {
			printf("Bytes received: %d\n", iResult);
			printf(recvbuf);
		}
		else if (iResult == 0)
			printf("Connection closed\n");
		else
			printf("recv failed: %d\n", WSAGetLastError());

	} while (iResult > 0);

	// cleanup
	closesocket(ConnectSocket);
	WSACleanup();

	return 0;
}