Question

Help Parsing a URL

Asked by: kinko899

I was wondering if anyone can provide me with some C code on how I can parse a URL containing an IP address and path name provided in the program argument into the IP address, and object path:

for example if someone was to execute my program as follows

./program  http://1.2.3.4/file.htm

I would like to parse the URL http://1.2.3.4/file.htm into an IP address and object path

I figured out how to implement my program if the user just simply specifies an IP address but I am stumbled on how to implement it if the user enters a URL with an IP address and path.  

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Asked On
2005-05-18 at 18:53:53ID21429240
Tags

programing

Topic

C Programming Language

Participating Experts
8
Points
500
Comments
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Answers

 

by: KdoPosted on 2005-05-18 at 19:15:32ID: 14033112

Hi kinko899,

Basically, you want to generate three strings from the first one.

http://1.2.3.4/file.htm

The three strings are:

http:
1.2.3.4
file.htm

There are quite a few ways to do this.  Here's a simple way that should server you well.

char *p1, *p2, *p3;

char *String = "http://1.2.3.4/file.htm";

  p1 = strtok (String, "/");   /*  returns http:  */
  strtok (NULL, "/");    /*  there are back-to-back slashes.  Skip this one.  */
  p2 = strok (NULL, "/");     /*  returns 1.2.3.4  */
  p3 = strtok (NULL, "/");    /*  returns file.htm  */



That's all there is to it.

Good Luck!
Kent

 

by: loser5745Posted on 2005-05-18 at 19:15:54ID: 14033114

This is a skeleton of something I am currently using.  I got it from bejee's socket programming tutorial.  Google it.  anyways, this should pretty much compile and run (if I didn't miss any errors.  I don't have a compiler here), at least is linux eviroment.  If you are using windows, google that tutorial and you can learn the differences.  Hope this helps.



Here is the basic layout:

#define FILESIZE 100000  /* size of download -- change as needed */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <netdb.h>  /* Important to gethostname */
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>



int main(int argc, char **argv)
{
  int sockfd;
  struct sockaddr_in dest_addr;
  struct hostent *host;

  char *stream;

  /* Don't forget to check the args */
 
  /* Build the GET command for the download */

  b_send = (char *)malloc(31*sizeof(char));
  strcpy(b_send, "GET file.html\r\n");  /* file.html is the your file.html */

  /* Resolve the Hostname */

  if((host = gethostbyname(argv[1])) == NULL )
  {
    herror("gethostbyname()");
    exit(1);
  }

  /* Open the socket */

  sockfd = socket(host->h_addrtype, SOCK_STREAM, 0);
  if (sockfd == -1)
  {
    printf("socket() failed.\n");
    exit(1);
  }


  /* Build the Destination Address Struct */

  memset(&(dest_addr.sin_family), '\0', sizeof(struct sockaddr_in));
  dest_addr.sin_family = AF_INET;
  dest_addr.sin_port = htons(DEST_PORT);
  memcpy(&dest_addr.sin_addr.s_addr, host->h_addr, host->h_length);


  /* Connect to destination Address */

  if ((connect(sockfd, (struct sockaddr *)&dest_addr, sizeof(dest_addr))) == -1)
  {
      perror("connect()");
        printf("      %s : %d\n", sys_errlist[errno], errno);
      exit(1);
  }


  /* Send GET /..... */

  if((bytes_sent = send(sockfd, b_send, strlen(b_send), 0)) == -1)
  {
    perror("send()");
  }


  /* Allocate the receive memory and open the out file */

  b_recv = malloc(1500);
  stream = malloc(FILESIZE);
  strcpy(stream, "");
 
  /* Receive the information in blocks of 1500 bytes */

  while((bytes_recv = recv(sockfd, b_recv, 1500, 0)) > 0)
  {
    strcat(b_recv, sizeof(char), bytes_recv, ofp);
  }

  if(bytes_recv == -1)
  {
    perror("recv()");
  }

  close(sockfd);
  free(b_send);
  free(b_recv);
  free(stream);

  return 0;
}

 

by: loser5745Posted on 2005-05-18 at 19:22:52ID: 14033137

oops, guess you did't want all that.  i should read the question more carefully.  good job kdo.

 

by: kinko899Posted on 2005-05-18 at 19:40:29ID: 14033188

Hi Kent...thanks for the reply.....I tried implementing the following simple program but it does not seem to work.  Do you have any more suggestions:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main (int argc, char **argv)
(

char *p1;
char *p2;
char *p3;
char *String;

if (argc != 2)
{
    printf("usage: <URL containing IP address and Path>
    exit(1);
}

String = argv[1];


p1 = strtok (String, "/");
p2 = strtok (NULL, "/");
p3 = strtok (NULL, "/");

printf("P1 is %s\n", p1);
printf("P2 is %s\n", p2);
printf("P3 is %s\n", p3);

exit(0);
)

 

by: dr_countryPosted on 2005-05-18 at 21:18:21ID: 14033508

String = argv[0];

Try it, I'm not 100% sure though....

 

by: sunnycoderPosted on 2005-05-18 at 22:34:55ID: 14033725

int main (int argc, char **argv)
(              >>>>>>>>>>>>
.....
)              >>>>>>>>>>>>    these should be curly braces { } ... rest of the code works fine ...

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main (int argc, char **argv)
{

char *p1;
char *p2;
char *p3;
char String[] = "http://1.2.3.4/abc.html";

/*
if (argc != 2)
{
    printf("usage: <URL containing IP address and Path>
    exit(1);
}

String = argv[1];
*/

p1 = strtok (String, "/");
p2 = strtok (NULL, "/");
p3 = strtok (NULL, "/");

printf("P1 is %s\n", p1);
printf("P2 is %s\n", p2);
printf("P3 is %s\n", p3);

exit(0);
}

Output:
P1 is http:
P2 is 1.2.3.4
P3 is abc.html
Press any key to continue

 

by: Infinity08Posted on 2005-05-19 at 00:14:12ID: 14034057

Also :

printf("usage: <URL containing IP address and Path>

should be :

printf("usage: <URL containing IP address and Path>");

btw : you should know that the strtok() function modifies its first argument (in this case argv[1]). If you don't want that to happen, do this :

int length = strlen(argv[1]) + 1;
String = (char*) malloc(length*sizeof(char));
strncpy(String, argv[1],length);

instead of :

String = argv[1];

 

by: PaulCaswellPosted on 2005-05-19 at 00:40:06ID: 14034141

>>btw ...
Yes! I came across this one a while ago. On Windoze 32 the 'argv' array passed to main is actually in protected memory space so its better to copy it. However, 'strdup' might be a tidier function to use:

char * string = strdup(argv[1]);

Paul

 

by: Shan_rocksPosted on 2005-05-19 at 06:07:53ID: 14035843

Hi Kinko,

Just copy and paste the below code, compile it.  This works fine for me. I've compiled and run in my linux box.


Program :
------------

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main (int argc, char **argv)
{

char *p1;
char *p2;
char *p3;
char *String;

if (argc != 2)
{
    printf("usage: <URL containing IP address and Path>");
    exit(1);
}

String = argv[1];


p1 = strtok (String, "/");
p2 = strtok (NULL, "/");
p3 = strtok (NULL, "/");

printf("P1 is %s\n", p1);
printf("P2 is %s\n", p2);
printf("P3 is %s\n", p3);

exit(0);

}

Output
--------

[root@localhost Shans]# gcc httpparse.c
[root@localhost Shans]# ./a.out http://123.123.123.123/shan.htm
P1 is http:
P2 is 123.123.123.123
P3 is shan.htm
[root@localhost Shans]#

Regards
Shan

 

by: makerpPosted on 2005-05-19 at 11:54:57ID: 14039347

here you go... you need to pass allocated buffers

/* cracks a URL into component parts */
void parse_url(char *url,char *svr,int *prt,char *res)
{
      char *fs = NULL, temp;

      strcpy(svr,"");
      *prt = 80;
      strcpy(res,"/");

      /* its got http, therefore it has a server */
      if(_strnicmp(url,"http://",7) == 0 && strlen(url) > 7)
      {
            url += 7;
            /* get the port */
            if(fs = strstr(url,":"))
            {
                  *prt = atoi(fs + 1);
                  if(*prt == 0) *prt = 80;
            }
            /* get the first : or / */
            if(fs = strpbrk(url,":/"))
            {
                  temp = *fs;
                  *fs = '\0';
                  strcpy(svr,url);
                  *fs = temp;
                  if(*fs == ':') fs = strstr(fs,"/");
                  if(fs) strcpy(res,fs);
            }
            else strcpy(svr,url);
      }
      else strcpy(res,url);
}

 

by: kinko899Posted on 2005-05-22 at 12:02:05ID: 14056226

Thanks everyone for you help.  I decided the most fair way to accept an answer was to split it 4 ways among KDO, Sunny Coder, Shan_Rock, and Makerp.  Thanks again for the help :-)

20120131-EE-VQP-002

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