packer.c

-

/*
 * $Id: Packer.c,v 1.11 1999/01/19 02:24:20 wessels Exp $
 *
 * DEBUG: section 60    Packer: A uniform interface to store-like modules
 * AUTHOR: Alex Rousskov
 *
 * SQUID Internet Object Cache  http://squid.nlanr.net/Squid/
 * ----------------------------------------------------------
 *
 *  Squid is the result of efforts by numerous individuals from the
 *  Internet community.  Development is led by Duane Wessels of the
 *  National Laboratory for Applied Network Research and funded by the
 *  National Science Foundation.  Squid is Copyrighted (C) 1998 by
 *  Duane Wessels and the University of California San Diego.  Please
 *  see the COPYRIGHT file for full details.  Squid incorporates
 *  software developed and/or copyrighted by other sources.  Please see
 *  the CREDITS file for full details.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *  
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *  
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
 *
 */

/*
 * Rationale:
 * ----------
 * 
 * OK, we have to major interfaces comm.c and store.c.
 * 
 * Store.c has a nice storeAppend[Printf] capability which makes "storing"
 * things easy and painless. 
 * 
 * Comm.c lacks commAppend[Printf] because comm does not handle its own
 * buffers (no mem_obj equivalent for comm.c).
 * 
 * Thus, if one wants to be able to store _and_ comm_write an object, s/he
 * has to implement two almost identical functions.
 * 
 * Packer
 * ------
 * 
 * Packer provides for a more uniform interface to store and comm modules.
 * Packer has its own append and printf routines that "know" where to send
 * incoming data. In case of store interface, Packer sends data to
 * storeAppend.  Otherwise, Packer uses a MemBuf that can be flushed later to
 * comm_write.
 * 
 * Thus, one can write just one function that will either "pack" things for
 * comm_write or "append" things to store, depending on actual packer
 * supplied.
 * 
 * It is amazing how much work a tiny object can save. :)
 * 
 */


/*
 * To-Do:
 */


#include "squid.h"

/* local types */

/* local routines */

/* local constants and vars */

/*
 * We do have one potential problem here. Both append_f and vprintf_f types
 * cannot match real functions precisely (at least because of the difference in
 * the type of the first parameter). Thus, we have to use type cast. If somebody
 * changes the prototypes of real functions, Packer will not notice that because
 * of the type cast.
 *
 * Solution: we use the constants below to *hard code* current prototypes of
 * real functions. If real prototypes change, these constants will produce a
 * warning (e.g., "warning: assignment from incompatible pointer type").
 */

/* append()'s */
static void (*const store_append) (StoreEntry *, const char *, int) = &storeAppend;
static void (*const memBuf_append) (MemBuf *, const char *, mb_size_t) = &memBufAppend;

/* vprintf()'s */
static void (*const store_vprintf) (StoreEntry *, const char *, va_list ap) = &storeAppendVPrintf;
static void (*const memBuf_vprintf) (MemBuf *, const char *, va_list ap) = &memBufVPrintf;


/* init/clean */

/* init with this to forward data to StoreEntry */
void
packerToStoreInit(Packer * p, StoreEntry * e)
{
    assert(p && e);
    p->append = (append_f) store_append;
    p->vprintf = (vprintf_f) store_vprintf;
    p->real_handler = e;
}

/* init with this to accumulate data in MemBuf */
void
packerToMemInit(Packer * p, MemBuf * mb)
{
    assert(p && mb);
    p->append = (append_f) memBuf_append;
    p->vprintf = (vprintf_f) memBuf_vprintf;
    p->real_handler = mb;
}

/* call this when you are done */
void
packerClean(Packer * p)
{
    assert(p);
    /* it is not really necessary to do this, but, just in case... */
    p->append = NULL;
    p->vprintf = NULL;
    p->real_handler = NULL;
}

void
packerAppend(Packer * p, const char *buf, int sz)
{
    assert(p);
    assert(p->real_handler && p->append);
    p->append(p->real_handler, buf, sz);
}

#if STDC_HEADERS
void
packerPrintf(Packer * p, const char *fmt,...)
{
    va_list args;
    va_start(args, fmt);
#else
void
packerPrintf(va_alist)
     va_dcl
{
    va_list args;
    Packer *p = NULL;
    const char *fmt = NULL;
    int sz = 0;
    va_start(args);
    p = va_arg(args, Packer *);
    fmt = va_arg(args, char *);
#endif
    assert(p);
    assert(p->real_handler && p->vprintf);
    p->vprintf(p->real_handler, fmt, args);
    va_end(args);
}