Linux下socket实现网页抓取

 主要用来和WinSock进行下比较：

--WinSock--
需要初始化：
if( (Ret = WSAStartup(MAKEWORD(1,1), &wsaData) ) != 0 )
{
 printf("WSAStartup failed with error %d/n", Ret);
 return FALSE;
}

头文件：
--WinSock--
#include <winsock2.h> //header
#pragma comment (lib, "ws2_32.lib") //lib
--Linux--
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
各个头文件的作用还需要进一步研究

gethostbyname(host)：//从主机名返回地址
这个都是一样的，返回一个struct hostent *的指针。

地址结构：
--WinSock--
SOCKADDR_IN
--Linux--
sockaddr_in
实际上是一样的都是
struct sockaddr_in{
   shortsin_family;
   unsigned short sin_port;
   struct in_addr sin_addr;
   charsin_zero[8];
};
(
  这个结构是sockaddr的等价结构
  struct sockaddr
  {
   unsigned short sa_family; // address family, AF_XXX
 char sa_data[14];   //14 bytes of protocol address
  };
)
其中IP地址结构struct in_addr定义如下：
struct   in_addr {
    union   {
         struct{
             unsigned  char   s_b1,
                              s_b2,
                              s_b3,
                              s_b4;
        }  S_un_b;
             struct  {
             unsigned  short  s_w1,
                              s_w2;
              }  S_un_w;
               unsigned long  S_addr;
     } S_un;
};

Socket:
--WinSock--
返回句柄SOCKET，就是socket描述符
--Linux--
比较直接返回int型socket描述符

函数接口都一样
函数例子：
socket (AF_INET, SOCK_STREAM, 0); //TCP

connect(sock, (const sockaddr * )&tcpaddr, sizeof(tcpaddr)); //返回值有不同
--WinSock--
If no error occurs, connect returns zero. Otherwise, it returns SOCKET_ERROR, and a specific error code can be retrieved by calling

WSAGetLastError.
--Linux--
错误返回-1

send(sock_description, message, strlen(message), 0); //返回值不同
--WinSock--
If no error occurs, send returns the total number of bytes sent, which can be less than the number indicated by len. Otherwise, a value of

SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.
--Linux--
错误返回-1

recv(sock_description, buffer, sizeof(buffer), 0);//返回值不同
--WinSock--
If no error occurs, recv returns the number of bytes received. If the connection has been gracefully closed, the return value is zero. Otherwise, a

value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.
--Linux--
错误返回-1

结束：
--WinSock--
closesocket(sock);
if( WSACleanup() == SOCKET_ERROR )
{
 printf("WSACleanup failed with error %d /n", WSAGetLastError() );
}
--Linux--
close(sock);

下面是一个Linux下socket一个HTTP协议GET方法的应用：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

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

char* host = "www.hao123.com";
int port = 80;

int main(void)
{
 char buffer[512];
 int isock;
 struct sockaddr_in pin;
 struct hostent * remoteHost;
 char message[512];
 int done = 0;
 int chars = 0;
 int l = 0;

 if( (remoteHost = gethostbyname(host)) == 0 )
 {
  printf("Error resolving host/n");
  exit(1);
 }

 bzero(message,sizeof(message));
 bzero(&pin,sizeof(pin));
 pin.sin_family = AF_INET;
 pin.sin_port = htons(port);
 pin.sin_addr.s_addr = ( (struct in_addr *)(remoteHost->h_addr) )->s_addr;
 
 if( (isock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
 {
  printf("Error opening socket!/n");
  exit(1);
 }
 sprintf(message, "GET / HTTP/1.1/r/n");
 strcat(message, "Host:www.hao123.com/r/n");
 strcat(message, "Accept: */*/r/n");
 strcat(message, "User-Agent: Mozilla/4.0(compatible)/r/n");
 strcat(message, "connection:Keep-Alive/r/n");
 strcat(message, "/r/n/r/n");

 printf("%s",message);

 if( connect(isock, (void *)&pin, sizeof(pin)) == -1 )
 {
  printf("Error connecting to socket/n");
  exit(1);
 }

 if( send(isock, message, strlen(message), 0) == -1)
 {
  printf("Error in send/n");
  exit(1);
 }
 
 while(done == 0)
 {
  l = recv(isock, buffer, 1, 0);
  if( l < 0 )
   done = 1;
  switch(*buffer)
  {
   case '/r':
    break;
   case '/n':
    if(chars == 0)
     done = 1;
    chars = 0;
    break;
   default:
    chars++;
    break;
  }
   printf("%c",*buffer);
 }

 do
 {
  l = recv(isock, buffer, sizeof(buffer) - 1, 0);
  if( l < 0 )
   break;
  *(buffer + l) = 0;
  fputs(buffer, stdout);
 }while( l > 0 );

 close(isock);
 return 0;
}