#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <netdb.h>

#define WCBS 0x1000
#define WCEL 0x0400
#define MYPORT 8088

typedef uint32_t in_addr_t;

in_addr_t get_ip_by_name(char *hostname) {
	struct hostent *he;
	if((he=gethostbyname(hostname))==NULL)
		{ herror(hostname); return -1; }
	else return *(in_addr_t *)he->h_addr;
}

void fill_sa_in(struct sockaddr_in *sai, in_addr_t addr,unsigned short port) {
	sai->sin_family=AF_INET; sai->sin_port=htons(port);
	sai->sin_addr.s_addr=addr;
	memset(sai->sin_zero,0,sizeof(sai->sin_zero));
}

struct sockaddr_in www_in,me_in;

int www_init(char *hostname, char *portname) {
	int c,port; in_addr_t ip;
	if((ip=get_ip_by_name(hostname))==-1) return -1;
	if(portname==NULL || sscanf(portname,"%u%n",&port,&c)!=1
	|| portname[c]!=0) port=80; fill_sa_in(&www_in,ip,port);
	return 0;
}

int www_client(int rs) {
	int i,sk,rl,wr; char *es,*s1,*s2,*cp,buf[WCBS];

	/* read, log, and check request */
	for(rl=0; (i=read(rs,buf+WCEL+rl,sizeof(buf)-WCEL-rl))>0; )
		if((rl+=i)>4) {
			cp=buf+WCEL+rl; if(*--cp!='\n') continue;
			if((i=*--cp)=='\r') i=*--cp; if(i=='\n') break;
		}
	write(1,buf+WCEL,rl);
	if(rl<=0 || rl>=sizeof(buf)-WCEL) goto brq; buf[WCEL+rl]=0;
	if((s2=strchr(buf+WCEL,'\n'))==NULL
	|| (s1=strchr(buf+WCEL,'/'))==NULL
	|| (cp=strchr(s1+1,' '))==NULL || cp>s2
	|| (s2=strchr(s1+1,'/'))==NULL || s2>cp) goto brq;
	*s2=0; if((cp=strchr(s2,':'))!=NULL) *cp++=0;
	if(www_init(s1+1,cp)<0) goto brq; if(cp!=NULL) *--cp=':';
	for(i=0; i<WCEL && buf+WCEL+i<=s1; i++) buf[i]=buf[i+WCEL];
	do {	while(*++s2!=0 && (buf[i++]=*s2)!='\n');
		if(strncmp(s2+1,"Host:",5)!=0) continue;
		strncpy(buf+i,s2+1,5); i+=5; buf[i++]=' ';
		while(*++s1) buf[i++]=*s1; buf[i++]='\n';
		s2=strchr(s2+1,'\n');
	} while(s2!=NULL && *s2!=0);

	if((sk=socket(AF_INET,SOCK_STREAM,0))==-1)
		{ es="www_socket"; goto err; }
	if(connect(sk, (struct sockaddr *)&www_in, sizeof(www_in))==-1)
		{ es="www_connect"; goto err; }

	write(1,buf,i); write(sk,buf,i);

	/* read reply and forward it back */
	for(wr=3; (rl=read(sk,buf,sizeof(buf)))>0;) {
		if(wr>0) {
			for(i=0; wr!=0 && i<rl; i++)
				if(buf[i]=='\n') if(wr==3) wr=1; else wr=0;
				else if(buf[i]!='\r') wr=3; else wr+=wr<3;
			if(i) write(1,buf,i);
		}
		write(rs,buf,rl);
	}

	/* close connections on both sides and return */
	close(sk); close(rs); return 0;
brq:	es="request";
err:	sprintf(buf,"%s: %s\r\n",es,strerror(errno));
	write(rs,buf,strlen(buf)); close(rs);
	if(sk!=-1) close(sk); return -1;
}

void show_ip_and_port(struct sockaddr_in *in) {
	typedef unsigned char byte;
	char buf[64];
	sprintf(buf,"\n\n=== request from %u.%u.%u.%u:%u ===\n",
		((byte *)&in->sin_addr.s_addr)[0],
		((byte *)&in->sin_addr.s_addr)[1],
		((byte *)&in->sin_addr.s_addr)[2],
		((byte *)&in->sin_addr.s_addr)[3],
		ntohs(in->sin_port));
	write(1, buf, strlen(buf));
}

int www_server() {
	int s,c,l; char *es; struct sockaddr_in rem_in;
	if((s=socket(AF_INET,SOCK_STREAM,0))==-1)
		{ es="www_socket"; goto err; }
	if(bind(s, (struct sockaddr *)&me_in, sizeof(me_in))==-1)
		{ es="www_bind"; goto err; }
	if(listen(s,5)==-1) { es="www_listen"; goto err; }
next:	l=sizeof(rem_in); c=accept(s, (struct sockaddr *)&rem_in, &l);
	if(c==-1) perror("www_accept"); else {
		show_ip_and_port(&rem_in);
		www_client(c);
	}
	goto next;
err:	perror(es); return -1;
}

char usage[]=	"Usage: %s port\n"
		"redirects HTTP from the specified port\n";

int main(int ac, char **av /**/) {
	int myport,vfy;
	if(ac==1 || sscanf(av[1],"%u%n",&myport,&vfy)!=1 || av[1][vfy]!=0)
		{ fprintf(stderr,usage,av[0]); return -1; }
	fill_sa_in(&me_in,htonl(INADDR_ANY),myport);
	www_server(); dup2(2,1); show_ip_and_port(&me_in);
	return -1;
}