How do I access the request data POSTed by client?

jayashrik · 03-03-2005, 06:45 AM

Hello

How do I access the request data POSTed by client?I want to write input filter in "c" which will access the request data POSTed by client?Could anyone please help me in this?

Thanking You

Jayashri

Mara · 03-03-2005, 10:23 AM

It depends what it will be a filter for. I understand you want to write an extenstion for a program, so you need to read its docs to see how the program is storing POST data. Because when received it's up to the program author.

itsme86 · 03-03-2005, 10:53 AM

I wrote a CGI library in C once. Hopefully this will help you out:

Code:

// cgi.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>

typedef struct cgi_opts
{
  char *name;
  char *val;
  struct cgi_opts *next;
} CGIOPT;

static CGIOPT *optlist = NULL;

typedef struct cookie
{
  char *name;
  char *val;
  struct cookie *next;
} COOKIE;

static COOKIE *cookielist = NULL;

static int hex_to_dec(char *str)
{
  char vals[] = "0123456789ABCDEF";
  unsigned int num;
  char *p, *q;

  p = strchr(vals, *str);
  q = strchr(vals, *(str+1));

  if(p && q)
  {
    num = (p - vals) << 4;
    num += q - vals;
  }
  else
    num = 0;

  return num;
}

static void cgi_decode(char *str, size_t maxlen)
{
  char buf[4096], *p, *b = buf;

  for(p = str;*p && b-buf < sizeof(buf)-2;p++, b++)
  {
    switch(*p)
    {
      case '+': *b = ' '; break;
      case '%': *b = hex_to_dec(p+1); p += 2; break;
      default:
        *b = *p;
    }
  }

  *b = '\0';
  strncpy(str, buf, maxlen);
  str[maxlen] = '\0';
}

void get_cgi_opts(void)
{
  CGIOPT *opt;
  char buf[4096], buf2[4096], *p = buf, *q = buf;

  fgets(buf, sizeof(buf), stdin);
  if(!*buf)
    strncpy(buf, getenv("QUERY_STRING"), sizeof(buf)-1);

  while(*p && *p != '\n')
    p++;
  if(*p == '\n')
    *p = '\0';
  p = buf;

  while((p = strchr(q, '=')))
  {
    if(!(opt = malloc(sizeof(CGIOPT))))
      return;
    opt->next = optlist;
    optlist = opt;

    strncpy(buf2, q, p-q);
    buf2[p-q] = '\0';
    cgi_decode(buf2, sizeof(buf2));
    if(!(opt->name = malloc(strlen(buf2)+1)))
    {
      optlist = opt->next;
      free(opt);
      return;
    }
    strcpy(opt->name, buf2);

    p++;
    q = strchr(p, '&');
    if(!q)
      q = p+strlen(p);
    strncpy(buf2, p, q-p);
    buf2[q-p] = '\0';
    cgi_decode(buf2, sizeof(buf2));
    if(!(opt->val = malloc(strlen(buf2)+1)))
    {
      optlist = opt->next;
      free(opt->name);
      free(opt);
      return;
    }
    strcpy(opt->val, buf2);

    if(q)
      q++;
  }
}

char *opt_val(char *name)
{
  CGIOPT *opt;

  for(opt = optlist;opt;opt = opt->next)
    if(!strcmp(opt->name, name))
      return opt->val;

  return "";
}

void get_cookies(void)
{
  char buf[4096], *p, *q;
  COOKIE *c;

  if(!(p = getenv("HTTP_COOKIE")))
    return;
  strcpy(buf, p);

  p = buf;
  do
  {
    if(!(c = malloc(sizeof(COOKIE))))
      return;

    while(isspace(*p))
      p++;
    if(!(q = strchr(p, '=')))
      return;
    *q++ = '\0';
    if(!(c->name = malloc(q-p)))
    {
      free(c);
      return;
    }
    strcpy(c->name, p);
    p = q;

    if(!(q = strchr(p, ';')))
      q = p+strlen(p);
    *q++ = '\0';
    if(!(c->val = malloc(q-p)))
    {
      free(c->name);
      free(c);
      return;
    }
    strcpy(c->val, p);
    p = q;

    c->next = cookielist;
    cookielist = c;
  } while(*p);
}

char *cookie_val(char *name)
{
  COOKIE *c;

  for(c = cookielist;c;c = c->next)
    if(!strcmp(c->name, name))
      return c->val;

  return "";
}

char *cgi_header(char *title)
{
  static char buf[4096];

  sprintf(buf, "Content-type: text/html\n\n<html>\n");
  if(title)
    sprintf(buf+strlen(buf), "<title>%s</title>\n", title);

  return buf;
}

Code:

// cgi.h
#ifndef CGI_H_
#define CGI_H_

void get_cgi_opts(void);
char *opt_val(char *);
char *cgi_header(char *);
void get_cookies(void);
char *cookie_val(char *);

#endif //CGI_H_

Mara · 03-04-2005, 04:13 PM

Here you've got examplanation and code: http://www.cs.tut.fi/~jkorpela/forms/cgic.html