Linux下利用Socket抓取网页内容

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 %dn", Ret);
return FALSE;
}

头文件：
--WinSock--
#include //header
#pragma comment (lib, "ws2_32.lib") //lib
--Linux--
#include
#include
#include
#include
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
#include
#include

#include
#include
#include
#include

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 hostn");
   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/1.1rn");
strcat(message, "Host:www.hao123.comrn");
strcat(message, "Accept: */*rn");
strcat(message, "User-Agent: Mozilla/4.0(compatible)rn");
strcat(message, "connection:Keep-Alivern");
strcat(message, "rnrn");

printf("%s",message);

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

if( send(isock, message, strlen(message), 0) == -1)
{
   printf("Error in sendn");
   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;
}