telme.c

// Author: Jason Larsen
// Project: A program that downloads a webpage using an HTTP GET request. I probably
// will never use this because I'll just use curl -I anyway... but it was fun

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

#define SOCKET_ERROR        -1
#define LARGE_BUFFER        4096
#define HOST_NAME_SIZE      255
#define HOST				argv[argc - 3]
#define PORT				argv[argc - 2]
#define PATH				argv[argc - 1]

void fatal(char *message) {
	char error_message[100];
	strcpy(error_message, "[!!] Fatal Error ");
	strncat(error_message, message, 83);
	perror(error_message);
	exit(-1);
}

int send_string(int sockfd, unsigned char *buffer) {
   int sent_bytes, bytes_to_send;
   bytes_to_send = strlen(buffer);
   while(bytes_to_send > 0) {
      sent_bytes = send(sockfd, buffer, bytes_to_send, 0);
      if(sent_bytes == -1)
         return 0; // return 0 on send error
      bytes_to_send -= sent_bytes;
      buffer += sent_bytes;
   }
   return 1; // return 1 on success
}

int recv_line(int sockfd, unsigned char *dest_buffer) {
#define EOL "\r\n" // End-Of-Line byte sequence
#define EOL_SIZE 2
   unsigned char *ptr;
   int eol_matched = 0;

   ptr = dest_buffer;
   while(recv(sockfd, ptr, 1, 0) == 1) { // read a single byte
      if(*ptr == EOL[eol_matched]) { // does this byte match terminator
         eol_matched++;
         if(eol_matched == EOL_SIZE) { // if all bytes match terminator,
            *(ptr+1-EOL_SIZE) = '\0'; // terminate the string
            return strlen(dest_buffer); // return bytes recevied
         }
      } else {
         eol_matched = 0;
      }   
      ptr++; // increment the pointer to the next byter;
   }
   return 0; // didn't find the end of line characters
}

// Reads in an HTTP header, filling the buffer passed in and returning
// the number of bytes (Content-Length) that should be read
int recv_header(int sockfd, unsigned char *dest_buffer) {
	int bytes_to_recv = 0;
	char buffer[LARGE_BUFFER];
	while(recv_line(sockfd, buffer)) {
		strncat(dest_buffer, buffer, strlen(buffer));
		strncat(dest_buffer, "\n", 1);
		if(strncasecmp(buffer, "Content-Length:", 15) == 0) {
			// copy into dest_buffer
			bytes_to_recv = atoi(buffer+15);
		}
	}
	return bytes_to_recv;
}

void usage(char * program_name) {
	printf("Usage: %s [-d] <hostname> <port> <path>\n", program_name);
	exit(1);
}

int main(int argc, char *argv[]) {
	int sockfd, port;
	struct hostent *host_info;
	struct in_addr *address;
	struct sockaddr_in target_addr;
	int recv_length=1, yes=1;
	unsigned char buffer[LARGE_BUFFER];
	int dflag = 0;
	
	// USAGE and param checking
	int ch;
	while((ch = getopt(argc, argv, "d:")) != -1)
		if(ch == 'd') dflag = 1;
		else usage(argv[0]);
		
	if( argc - dflag != 4 ) usage(argv[0]); // make sure we have either 4 or 5
	
	int i; // make sure we're getting a valid port
	for(i = 0; PORT[i]; i++)
		if(!isnumber(PORT[i])) usage(argv[0]);
	port = atoi(PORT);

	if((host_info = gethostbyname(HOST)) == NULL)
		fatal("looking up hostname");

	if ((sockfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) == SOCKET_ERROR)
        fatal("Making socket");
		
	// is this only for when you're binding?
	// if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
	// 	fatal("setting socket option SO_REUSEADDR");
	
	target_addr.sin_family = AF_INET;
	target_addr.sin_port = htons(port);	
	target_addr.sin_addr = *((struct in_addr *)host_info->h_addr);
	memset(&(target_addr.sin_zero), '\0', 8); // zero the rest of the struct
	
	// send GET request
	if (connect(sockfd, (struct sockaddr *)&target_addr, sizeof(struct sockaddr)) == -1)
		fatal("connecting to target server");

	char request[100];
	strcpy(request,"GET ");
	strncat(request,PATH,strlen(PATH));
	strncat(request," HTTP/1.0\r\n\r\n",13);
	printf("%s\n", request);
	
	if(!send_string(sockfd, request))
		fatal("sending GET REQUEST");
		
	int bytes_to_recv = recv_header(sockfd, buffer);
	if(dflag) printf("%s\n",buffer);
	// if(bytes_to_recv == 0) fatal("no Content-Length tag or value of 0");
	
	if(bytes_to_recv == 0) bytes_to_recv = 1024;
	char body[bytes_to_recv + 1];
	int bytes_read;
	while((bytes_read = recv(sockfd, body, bytes_to_recv, 0)) > 0) {
		// printf("bytes read: %d", bytes_read);
		body[bytes_read] = '\0';
		printf("%s\n", body);
	}
	
	close(sockfd);
	return 0;
}