/* hgen+ */
/*
 * $Id: askkey-pinentry.c,v 1.3 2008/08/20 02:59:27 az Exp $
 * 
 * File:		askkey-pinentry.c
 * Date:		Wed Apr 11 14:54:15 2007
 * Author:		Alexander Zangerl (az)
 * 
 * Abstract:
 *	interface to pinentry programs for key requesting
 *
 */
/* hgen- */
/*
 * Modifications:
 *	$Log: askkey-pinentry.c,v $
 *	Revision 1.3  2008/08/20 02:59:27  az
 *	added dehexing
 *
 *	Revision 1.2  2007/04/11 07:08:25  az
 *	added passing of display variables to the pinentry
 *
 *	Revision 1.1  2007/04/11 06:37:00  az
 *	Initial revision
 *
 */

#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <alloca.h>
#include <ctype.h>


#define BAILOUT(x,...) (fprintf(stderr,x,## __VA_ARGS__),exit(1))
#define BAILSTD(x) (perror(x),exit(1))
#define USAGE "Usage: %s <uid> <gid> <secretinfo> <displayvars>\ndisplayvars is a SINGLE arg, form key=value|key=value...\n",argv[0]

#define PE "/usr/bin/pinentry","pinentry"
#define LB 4096
#define FALLBACKCTYPE "iso-8859-1"

/* %-unescape instring, inplace (safe as it gets only shorter) 
   this does not touch a solo % or otherwise badly hexed stuff. */
char *dehex(char instring[])
{
   char *s,*d,cbuf[]="0xaa";
   int n;

   for (s=d=instring;*s;)
   {
      if (*s=='%' && *(s+1) && *(s+2) 
	  && isxdigit(*(s+1)) && isxdigit(*(s+2)))
      {
	 cbuf[2]=*(s+1); cbuf[3]=*(s+2);
	 n=(int)strtol(cbuf,NULL,16);
	 *d=n;			/* 2 hexbytes, n can be only one byte */
	 s=s+3;			/* past the % and the two chars */
	 ++d;			/* only one step */
      }
      else
      {
	 /* no change, but copy from source to dest only if needed */
	 if (s!=d) 
	    *d=*s;
	 ++d; ++s;
      }
   }
   /* terminate the output cleanly */
   *d=0;
   return instring;
}

int main(int argc,char *argv[])
{
   int uid,gid,pid,res;
   char *info,*display,*pin,*p,*q,linebuffer[LB];
   int dn[2],up[2];
   FILE *cmd,*rsp;

   
   if (argc!=5)
      BAILOUT(USAGE);
   uid=atoi(argv[1]); gid=atoi(argv[2]);
   if (uid<=0 || gid<=0)
      BAILOUT(USAGE);

   info=argv[3];
   display=argv[4];

   /* setup pipes */
   if (pipe(up) || pipe(dn))
      BAILSTD("pipe failed");

   if ((pid=fork())<0)
      BAILSTD("fork failed");

   /* child runs pinentry as the given user and with given 
      display envvars; i/o into pipes */
   if (!pid)
   {
      if (setgid(gid))
	 BAILSTD("setgid failed");
      if (setuid(uid))
	 BAILSTD("setuid failed");

      for(p=display;p && *p;p=q)
      {
	 if ((q=strchr(p,'|')))
	    *(q++)=0;
	 if (putenv(p))
	    BAILSTD("putenv failed");
      }

      if (dup2(dn[0],0)<0)
	 BAILSTD("dup2 failed");
      if (dup2(up[1],1)<0)
	 BAILSTD("dup2 failed");
      
      close(dn[1]); close(up[0]);

      execl(PE,NULL);
      BAILSTD("exec failed");
   }


   /* parent needs to talk to pinentry */
   close(dn[0]); close(up[1]);
   cmd=fdopen(dn[1],"w"); rsp=fdopen(up[0],"r");
   if (!cmd || !rsp)
      BAILSTD("fdopen failed");

   if (!fgets(linebuffer,sizeof(linebuffer),rsp)
       || strncmp(linebuffer,"OK",2))
      BAILOUT("no greeting from pinentry\n");
   
   fprintf(cmd,"SETDESC Enter secret for %s\n",info);
   fflush(cmd);
   if (!fgets(linebuffer,sizeof(linebuffer),rsp)
       || strncmp(linebuffer,"OK",2))
      BAILOUT("setting description failed\n");

   p=getenv("LC_CTYPE");
   if (!p)
      p=FALLBACKCTYPE;
   
   fprintf(cmd,"OPTION lc-ctype=%s\n",p);
   fflush(cmd);
   if (!fgets(linebuffer,sizeof(linebuffer),rsp)
       || strncmp(linebuffer,"OK",2))
      BAILOUT("setting ctype option failed\n");

   fprintf(cmd,"GETPIN\n");
   fflush(cmd);

   if (!fgets(linebuffer,sizeof(linebuffer),rsp)
       || strncmp(linebuffer,"D ",2))
      BAILOUT("getting pin failed\n");
   pin=linebuffer+2;

   fclose(cmd);
   fclose(rsp);
   wait(&res);

   p=strchr(pin,'\n');
   if (p)
      *p=0;
   /* this is necessary because the pinentry tools 
      are expecting to work within the gnupg/assuan framework,
      where passphrases are %- or hex-escaped on output... */
   dehex(pin);
   printf("%s",pin);
   return WEXITSTATUS(res);
}