Hei alle sammen, jeg er en nybegynner i UNIX / Linux socket programmering. Dette er en klasse prosjekt som jeg hadde problemer med.

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Jeg prøvde å gjøre "Keep-alive" HTTP tilkoblinger til serveren på en liten robotsøkeprogram prosjektet. Her er problemet: Når jeg prøvde å recv () den første siden, det lyktes. Men 2. påfølgende recv () får null byte, som jeg egentlig ikke har noen ide. Jeg hadde sett et "Keep-alive"-feltet i forespørselen melding når jeg ringte send ().

Jeg ikke helt vet hvordan de skal iverksette HTTP vedvarende forbindelse med Keep-Alive. Jeg hentet socket-relatert kode i et lite program som vedlegg.

Kan du ta en titt på koden og forklare hva som var galt med det til meg? Det ville være til stor hjelp siden jeg har fast på dette problemet i flere dager.

For øvrig, programmet ble utarbeidet under SunOS bruker g + + og lsocket.
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#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>

#include <string>
#include <iostream>

using namespace std;

// ------------------------------------------------------
const short SOCKET_ERROR = -1;

const short RECV_BUFFER_SIZE = 20;
const short REQUEST_BUFFER_SIZE = 255;

int sock;
char recv_buf [RECV_BUFFER_SIZE + 1];
char req_buf [REQUEST_BUFFER_SIZE + 1];

const static char REQUEST_TEMPLATE [] = 
{
	"GET %s HTTP/1.1\r\n"
	"Host: xxx.xxx.xxx\r\n" // should be replaced with a really host
	"Connection: Keep-Alive\r\n"
	"\r\n"
};

// ------------------------------------------------------
void create_socket ();
void download (const string& path, string& response);

// ------------------------------------------------------

int main (void)
{
	string first_addr = "/~pdu/index.html"; // should be replaced with a really URL
	string second_addr = "/~pdu/a.html"; // should be replaced with a really URL
	string response;

	create_socket ();
	download (first_addr, response);
	cout << response << endl << endl;
	response = "";
	download (second_addr, response);
	if (response.size() > 0)
	{
		cout << response << endl;
	}
	else
	{
		cout << "### The 2nd recv() failed to receive any bytes from the socket!" << endl << endl;
	}
	
	close (sock);

	return 0;
}

void create_socket ()
{
	struct sockaddr_in addr;

	// ------------------------------------------------------
	sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if(sock == SOCKET_ERROR)
    {
        perror ("Could not make a socket.\n");
		exit (-1);
    }

	cout << ">>> Socket created!" << endl;

	// ------------------------------------------------------
	struct hostent* host_info = gethostbyname("cse.unl.edu");	
	
	cout << ">>> DNS done!" << endl;

	long host_addr;

	/* copy address into long */
	memcpy(&host_addr, host_info->h_addr,
		host_info->h_length);

	/* fill address struct */
	addr.sin_addr.s_addr = host_addr;
	addr.sin_port = htons(80);
	addr.sin_family = AF_INET;

	// ------------------------------------------------------
	if( connect(sock, (struct sockaddr*)(&addr),
		sizeof(addr)) == SOCKET_ERROR )
    {
        perror("Could not connect to HTTP server.\n");
		exit (-1);
    }

	cout << ">>> Connection established!" << endl;
}

void download (const string& path, string& response) 
{
	size_t nBytes = snprintf(
		req_buf, 
		REQUEST_BUFFER_SIZE, 
		REQUEST_TEMPLATE, 
		path.c_str());

	if (nBytes >= REQUEST_BUFFER_SIZE)
	{
        cerr << "Buffer is too small for making a request message" << endl;
		exit (-1);
	}

	if (send(sock, req_buf, nBytes, 0) != nBytes)
	{
        perror("Could not send request to the HTTP server.\n");
		exit (-1);
	}
	cout << ">>> Request sent! -> " << path << endl << req_buf << endl;
	
	ssize_t size = 0;
	
	while ((size = recv(sock, recv_buf, 
		RECV_BUFFER_SIZE, 0)) > 0) 
	{
		recv_buf[size] = '\0';
		response.append(recv_buf);
    }

	cout << ">>> Response received!" << endl;
}