Nevermind, I'm stupid: Memory Overright problem.

Nevermind, I'm stupid: Memory Overright problem.

[John T. Williams]

Anyone who wondering, for some reason (probably blind habit) I was using the 
sizeof() function in my malloc call, when I shouldn't have been, consiquently i was
makeing a bunch of arrays 4 bytes long

>>shakes head, hits self on forhead


While trying to write a function to parse a http url, I ran accross a
strange problem, which is that when I malloc some memory, suddenly some
memory already allocated changes its contents.  I can't figure out where
the problem is so I was hoping someone might point me at it.  

I'm including the code here, and as an attachment 


The problem line is pointed out with at 

***************here********************
***************end here ***************
and its affecting the memory pointed at by http_addr->abspath

#####################################################
#include <string.h>

#ifndef NULL
#define NULL (void*) 0
#endif


typedef struct _http {
  char* query;	// query string
  int  port;	// port number if other then 80
  char* abspath;// absolute path of file on serve
  char* host; 	// domain ex: www.something.com

} http_url;

int parsehttp( http_url*, char* );
int initurl(http_url*);
int cleanurl(http_url*);

int
initurl( http_url* url)
{
  if( !url ) return -1;
  url->host = NULL;
  url->query = NULL;
  url->abspath = NULL;
  url->port = 80;
}

int cleanurl(http_url* url) {
  if( !url ) return -1;
  if(url->host) {
    free(url->host);
    url->host = NULL;
  }
  if(url->query) {
    free(url->query);
    url->query = NULL;
  }
  if(url->abspath) {
    free(url->abspath);
    url->abspath = NULL;
  }
  url->port = 80;
}

int
parsehttp( http_url* http_addr, char* urlstr )
{
  char* host_ptr;
  char* abspath_ptr;
  char* port_ptr;
  char* query_ptr;

  int host_len,
    abspath_len,
    port_len,
    query_len,
    total_len;


  //check for null parameters:
  if( !http_addr || !urlstr ) {
    perror("error called parsehttp with NULL\n");
    return -1;
  }

  //check for http:// head
  if( strncmp(urlstr, "http://", 7) ) {
    perror("url not propperly formatted: %s\n", urlstr);
    return -2;
  }

  // find the starting point for each string
  // if there indicating character is missing *ptr == NULL;
  port_ptr = abspath_ptr = query_ptr = host_ptr = &urlstr[7];
  while(port_ptr && *port_ptr != ':') port_ptr++; //search for ':'
indicating
  //					      		a port in this url
  while(abspath_ptr && *abspath_ptr != '/') abspath_ptr++;
  //					     	search for a '/' indicating
  //						a absolute path listed
  while(query_ptr && *query_ptr != '?') query_ptr++;
  //						search for a '?' indicating
  //						a query is listed

  // Parse out the query if any and record its length
  if(*query_ptr) {
    query_len = strlen(query_ptr);
    http_addr->query = (char*) malloc( sizeof( query_len + 128 ) );
    strncpy(http_addr->query, &query_ptr[1], query_len - 1 );
    http_addr->query[query_len - 1] = '\0';
  } else query_len = 0;

  // Parse out the abspath if any and record its length
  if(*abspath_ptr) {
    abspath_len = strlen(abspath_ptr) - query_len;
    http_addr->abspath = (char*) malloc( sizeof( abspath_len + 128 ) );
    strncpy(http_addr->abspath, abspath_ptr, abspath_len);
    http_addr->abspath[abspath_len] = '\0';
  } else abspath_len = 0;

  // Parse out the port number if any
  if(*port_ptr) {  // if a port was found
    port_len = strlen( port_ptr) - abspath_len - query_len;
    port_ptr++; //move past ':'
    http_addr->port = atoi(port_ptr);
  } else port_len = 0;
  printf("port length: %i\n", port_len);

  // Parse out the host str if any
  if(*host_ptr) {
    host_len = strlen(host_ptr) - port_len - abspath_len - query_len;

/***************here********************/
    http_addr->host = (char*) malloc( sizeof( host_len + 128 ) );
/***************end here ***************/

    strncpy(http_addr->host, host_ptr, host_len );
    http_addr->host[host_len] = '\0';
  }


  return 0;
}


int
main(int argC, char** argV, char** envp)
{
  http_url  url;

  initurl( &url );
  parsehttp( &url,
"http://www.vt.edu:23/users/jowillia/index.html?t=12");


  printf("http://");
  //  if(url.host) printf("%s", url.host);
  if(url.port != 80) printf(":%i", url.port);
  if(url.abspath) printf("%s", url.abspath);
  if(url.query) printf("?%s", url.query);
  printf("\n");

  cleanurl( &url );


  return 0;
}

Re: Nevermind, I'm stupid: Memory Overright problem.

[Christoph Bussenius]

Hi,

there is at least one more problem with your program.

>   while(port_ptr && *port_ptr != ':') port_ptr++; //search for ':'

This line will increment port_ptr until it becomes NULL. I guess this is
not what you wanted.

However you should not use perror() all the time to report errors, for
it will print the error string of the most recent system call, which is
--again-- not what you want.

Regards
Christoph

-- 
``There's no dark side of the moon, really
Matter of fact, it's all dark''

--Pink Floyd