C++ File Download - DNS HTTP GET

#include <stdio.h>
#include <memory.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>
 
#include <string>
#include <iostream>
#include <fstream>
 
using std::string;
using std::vector;
using std::cout;
using std::endl;
using std::ofstream;
using std::stringstream;
 
vector<string> dns_lookup(const string &host_name, int ipv=4); //ipv: default=4
bool is_ipv6_address(const string& str);
bool is_ipv4_address(const string& str);
int socket_connect(string ip_address, int port);
int http_get(const string& request, const string& ip_address, int port, const string& fname);
void download(const string& url, const string& filename);
 
 
int main(int argc, char* argv[])
{
    download("http://code.jquery.com/jquery-1.11.1.js", "./jquery-1.11.1.js");
    return 0;
}
 
//----------------------------------------------------------------------
vector<string> dns_lookup(const string &host_name, int ipv) //ipv: default=4
{
    vector<string> output;
 
    struct addrinfo hints, *res, *p;
    int status, ai_family;
    char ip_address[INET6_ADDRSTRLEN];
 
    ai_family = ipv==6 ? AF_INET6 : AF_INET; //v4 vs v6?
    ai_family = ipv==0 ? AF_UNSPEC : ai_family; // AF_UNSPEC (any), or chosen
    memset(&hints, 0, sizeof hints);
    hints.ai_family = ai_family; 
    hints.ai_socktype = SOCK_STREAM;
 
    if ((status = getaddrinfo(host_name.c_str(), NULL, &hints, &res)) != 0) {
        //cerr << "getaddrinfo: "<< gai_strerror(status) << endl;
        return output;
    }
 
    //cout << "DNS Lookup: " << host_name << " ipv:" << ipv << endl;
 
    for(p = res;p != NULL; p = p->ai_next) {
        void *addr;
        if (p->ai_family == AF_INET) { // IPv4
            struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
            addr = &(ipv4->sin_addr);
        } else { // IPv6
            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
            addr = &(ipv6->sin6_addr);
        }
 
        // convert the IP to a string
        inet_ntop(p->ai_family, addr, ip_address, sizeof ip_address);
        output.push_back(ip_address);
    }
 
    freeaddrinfo(res); // free the linked list
 
    return output;
}
//----------------------------------------------------------------------
bool is_ipv6_address(const string& str)
{
    struct sockaddr_in6 sa;
    return inet_pton(AF_INET6, str.c_str(), &(sa.sin6_addr))!=0;
}
//----------------------------------------------------------------------
bool is_ipv4_address(const string& str)
{
    struct sockaddr_in sa;
    return inet_pton(AF_INET, str.c_str(), &(sa.sin_addr))!=0;
}
//----------------------------------------------------------------------
int socket_connect(string ip_address, int port)
{
    int err=-1,sd=-1;
    struct sockaddr_in sa;
 
    memset (&sa, '\0', sizeof(sa));
    sa.sin_family      = AF_INET;
    sa.sin_addr.s_addr = inet_addr (ip_address.c_str());   /* Server IP */
    sa.sin_port        = htons     (port);   /* Server Port number */
 
    sd = ::socket(AF_INET, SOCK_STREAM, 0);
    if (sd)
    {
        err = ::connect(sd, (struct sockaddr*) &sa, sizeof(sa));
    }
    if (err!=-1)//success
    {
        return sd;
    }
    cout << "socket connect error: " << endl;
    return -1;
    //if (errno==EINPROGRESS) { return 0; }//errno is a global set by connect
}
//----------------------------------------------------------------------
void download(const string& url, const string& filename)
{
    int ipv,r,port;
    string protocol, domain, path, query, url_port;
    vector<string> ip_addresses;
 
    int offset = 0;
    size_t pos1,pos2,pos3,pos4;
    offset = offset==0 && url.compare(0, 8, "https://")==0 ? 8 : offset;
    offset = offset==0 && url.compare(0, 7, "http://" )==0 ? 7 : offset;
    pos1 = url.find_first_of('/', offset+1 );
    path = pos1==string::npos ? "" : url.substr(pos1);
    domain = string( url.begin()+offset, pos1 != string::npos ? url.begin()+pos1 : url.end() );
    path = (pos2 = path.find("#"))!=string::npos ? path.substr(0,pos2) : path;
    url_port = (pos3 = domain.find(":"))!=string::npos ? domain.substr(pos3+1) : "";
    domain = domain.substr(0, pos3!=string::npos ? pos3 : domain.length());
    protocol = offset > 0 ? url.substr(0,offset-3) : "";
    query = (pos4 = path.find("?"))!=string::npos ? path.substr(pos4+1) : "";
    path = pos4!=string::npos ? path.substr(0,pos4) : path;
 
    if (query.length()>0)
    {
        path.reserve( path.length() + 1 + query.length() );
        path.append("?").append(query);
    }
    if (url_port.length()==0 && protocol.length()>0)
    {
        url_port = protocol=="http" ? "80" : "443";
    }
    if (domain.length()>0 && !is_ipv6_address(domain))
    {
        if (is_ipv4_address(domain))
        {
            ip_addresses.push_back(domain);
        }
        else //if (!is_ipv4_address(domain))
        {
            ip_addresses = dns_lookup(domain, ipv=4);
        }
    }
    if (ip_addresses.size()>0)
    {
        stringstream(url_port) >> port;//string to int
        stringstream request;
        request << "GET " << path << " HTTP/1.1\r\n";
        request << "Host: " << domain << "\r\n\r\n";
 
        for(int i=0,r=0, ix=ip_addresses.size(); i<ix && r==0; i++)
        {
            r = http_get(request.str(), ip_addresses[i], port, filename);
        }
    }
}
//----------------------------------------------------------------------
string header_value(const string& full_header, const string& header_name)
{
    size_t pos = full_header.find(header_name);//case sensitive but probably shouldn't be
    string r;
    if (pos!=string::npos)
    {
        size_t begin = full_header.find_first_not_of(": ", pos + header_name.length());
        size_t until = full_header.find_first_of("\r\n\t ", begin + 1);
        if (begin!=string::npos && until!=string::npos)
        {
            r = full_header.substr(begin,until-begin);
        }
    }
    return r;
}
//----------------------------------------------------------------------
int http_get(const string& request, const string& ip_address, int port, const string& fname)
{
    stringstream header;
    char delim[] = "\r\n\r\n";
    char buffer[16384];
    int sd, bytes_received=-1,bytes_sofar=0,bytes_expected=-1,i,state=0;
 
    ofstream fd(fname.c_str());
    if (fd.good() && (sd = socket_connect(ip_address, port)) )
    {
        ::send(sd, request.c_str(), request.length(), 0);
        while (bytes_sofar!=bytes_expected && (bytes_received = ::recv(sd, buffer, sizeof(buffer), 0))>0)
        {
            if (state<sizeof(delim)-1)//read header
            {
                for(i=0; i<bytes_received && state<sizeof(delim)-1; i++)
                {
                    header << buffer[i];
                    state = buffer[i]==delim[state] ? state+1 : 0;
                }
                bytes_received = state==sizeof(delim)-1 ? bytes_received-i : bytes_received;
            }
            if (bytes_expected==-1 && state==sizeof(delim)-1)//parse header
            {
                bytes_expected=-2;
                string h = header.str();
                stringstream(header_value(h, "Content-Length"))>>bytes_expected;
            }
            if (state==sizeof(delim)-1)//read body
            {
                bytes_sofar+=bytes_received;
                fd.write(buffer, bytes_received);
            }
        }
        //cout << header.str() << endl;//OUTPUT header
        ::close(sd);
        fd.close();
    }
    return bytes_sofar;
}
//----------------------------------------------------------------------