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File Caching


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Message-Id: <31742528.41C6@aic.lockheed.com>
Date: Tue, 16 Apr 1996 15:54:32 -0700
From: Sandeep Tewari <tewari@aic.lockheed.com>
Organization: Lockheed Martin
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To: libwww@w3.org
Cc: tewari@aic.lockheed.com
Subject: File Caching
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Hi,

  I am using CERN 4.0D and seem to be having a problem with File
Caching. The basic caching is working fine for me. I am having a 
problem in trying to find out if a file on the server has been modified
and to load it only if it was modified. There is a function that does
this check for expires header (HTCache_isValid()). I could not find
a similar function for checking if a file has been modified. Going by
the documentation I set the reload mode as HT_CACHE_REFRESH. This
should lead to a conditional GET with If-Modified-Since. This is not
working. Even if the file is not modified the cache still gets
updated. 

   All I want to do is find out if a file has been modified at the
server and load it over the n/w only if it has been modified. Has
anybody done this using CERN 4.0D ? If this feature in the library is
working I would appreciate details on how to get it to work.

   Thanks for your help.

regards,

Sandeep.
- -- 
// Sandeep Tewari  tewari@aic.lockheed.com       Orgn 9620 Bldg 255
// 415.424.2676  fax: 415.354.5235             3251 Hanover Street 
// Lockheed Martin Advanced Technology Center  Palo Alto, CA 94304-1187
// http://vet.parl.com/~vet/people/tewari/

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Sender: tewari@aic.lockheed.com
Message-Id: <3175237C.15FB@aic.lockheed.com>
Date: Wed, 17 Apr 1996 09:59:40 -0700
From: Sandeep Tewari <tewari@aic.lockheed.com>
Organization: Lockheed Martin
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To: libwww@w3.org
Cc: tewari@aic.lockheed.com
Subject: File Caching bug !!
X-Url: http://www.w3.org/pub/WWW/Library/User/Patch/
Content-Type: multipart/mixed; boundary="------------59E21CFB3F54"

This is a multi-part message in MIME format.

- --------------59E21CFB3F54
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Hi,

 I am using the File Caching feature of CERN 4.0D and found the
following bug :

 The Cache directory would not get created the first time but the second
time it would get created. I use a proxy and discovered that this was
because of a double '//' after the access scheme. In the file HTCache.c
the function "create_cache_place" is the one which creates the cache
directory. The function searches for '/' and creates the directory one
level at a time. A double '//' means that it tries to create the same
directory twice (sincle Unix ignores multiple forward slashes). I just
put in code to ignore multiple forward slashes.

 The modified file is attached to this email. Do a search on "Sandeep"
to find out what I did.

Sandeep.

- -- 
// Sandeep Tewari  tewari@aic.lockheed.com       Orgn 9620 Bldg 255
// 415.424.2676  fax: 415.354.5235             3251 Hanover Street 
// Lockheed Martin Advanced Technology Center  Palo Alto, CA 94304-1187
// http://vet.parl.com/~vet/people/tewari/

- --------------59E21CFB3F54
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Content-Disposition: inline; filename="HTCache.c"

/*							       	    HTCache.c
**	CACHE WRITER
**
**	(c) COPYRIGHT MIT 1995.
**	Please first read the full copyright statement in the file COPYRIGH.
**
**	This modules manages the cache
**
**      History:
**         HFN: spawned from HTFwrite
**         HWL: converted the caching scheme to be hierachical by taking
**              AL code from Deamon
**
*/

/* Library include files */
#include "tcp.h"
#include "HTUtils.h"
#include "HTString.h"
#include "HTFormat.h"
#include "HTFWrite.h"
#include "HTAccess.h"
#include "HTBind.h"
#include "HTList.h"
#include "HTReqMan.h"
#include "HTParse.h"
#include "HTCache.h"					 /* Implemented here */

/*
** The cache limit is the number of files which are kept. Yes, I know,
** the amount of disk space would be more relevant. So this may change.
** Currently it is preset to 100 but may be changed by the application by
** writing into this variable.
*/
#define CACHE_LIMIT	100				  /* Number of files */

#define CACHE_INFO	".cache_info"
#define INDEX_FILE	".cache_dirindex"
#define WELCOME_FILE	".cache_welcome"
#define TMP_SUFFIX	".cache_tmp"
#define LOCK_SUFFIX	".cache_lock"

/* This is the default cache directory: */
#ifndef HT_CACHE_ROOT
#define HT_CACHE_ROOT	"/tmp"
#endif

typedef struct _HTCache {
    HTFormat		format;		/* May have many formats per anchor */
    char *		filename;
    time_t		start_time;
    time_t		load_delay;
    int			reference_count;
} HTCache;

struct _HTStream {
    CONST HTStreamClass *	isa;
    FILE *			fp;
    HTCache *			cache;
    HTRequest *			request;
};

PRIVATE BOOL		HTCacheEnable = NO;
PRIVATE char *		HTCacheRoot = NULL;  	    /* Destination for cache */
PRIVATE HTList *	HTCacheList = NULL;	  /* List of cached elements */
PRIVATE int		HTCacheLimit = CACHE_LIMIT;

PRIVATE HTExpiresMode HTExpMode = HT_EXPIRES_IGNORE;
PRIVATE char *HTExpNotify = NULL;

PRIVATE HTMemoryCacheHandler *HTMemoryCache = NULL;  /* Memory cache handler 
*/

/* ------------------------------------------------------------------------- 
*/
/*  			      GARBAGE COLLECTOR				     */
/* ------------------------------------------------------------------------- 
*/

/*
**  Removes cache item from disk and corresponding object from list in memory
*/
PRIVATE void HTCache_remove (HTCache * item)
{
    if (HTCacheList && item) {
	if (CACHE_TRACE)
	    TTYPrint(TDEST, "Cache....... Removing %s\n", item->filename);
	HTList_removeObject(HTCacheList, item);
	REMOVE(item->filename);
	
	/* HWL 22/9/94: Clean up hierachical file structure */
	{
	    char * p;
	    while ((p = strrchr(item->filename,'/')) && (p != NULL)){
		item->filename[p-item->filename] = 0;
		if (strcmp(item->filename, HTCacheRoot) != 0) {
		    if (CACHE_TRACE) 
			TTYPrint(TDEST, "rmdir....... %s\n", item->filename);
		    RMDIR(item->filename); /* fails if directory isn't empty */
		}
	    }
	}
	HT_FREE(item->filename);
	HT_FREE(item);
    }
}


/*
**  Remove a file from the cache to prevent too many files from being cached
*/
PRIVATE void limit_cache (HTList * list)
{
    HTList * cur = list;
    HTCache * item;
    time_t best_delay = 0;   /* time_t in principle can be any arith type */
    HTCache* best_item = NULL;

    if (HTList_count(list) < HTCacheLimit) return;   /* Limit not reached */

    while (NULL != (item = (HTCache*)HTList_nextObject(cur))) {
        if (best_delay == 0  ||  item->load_delay < best_delay) {
            best_delay = item->load_delay;
            best_item = item;
        }
    }
    if (best_item) HTCache_remove(best_item);
}

/*
**	Check that the name we're about to generate doesn't
**	clash with anything used by the caching system.
*/
PRIVATE BOOL reserved_name (char * url)
{
    char * name = strrchr(url, '/');
    char * suff = NULL;

    if (name) name++;
    else name = url;

    if (!strcmp(name, CACHE_INFO) ||
	!strcmp(name, INDEX_FILE) ||
	!strcmp(name, WELCOME_FILE))
	return YES;

    suff = strrchr(name, TMP_SUFFIX[0]);
    if (suff && !strcmp(suff, TMP_SUFFIX))
	return YES;

    suff = strrchr(name, LOCK_SUFFIX[0]);
    if (suff && !strcmp(suff, LOCK_SUFFIX))
	return YES;

    return NO;
}

/*
**  Removes all cache entries in memory
*/
PUBLIC void HTCache_clearMem (void)
{
    HTList *cur=HTCacheList;
    HTCache *pres;
    if (cur) {
	while ((pres = (HTCache *) HTList_nextObject(cur))) {
	    HT_FREE(pres->filename);
	    HT_FREE(pres);
	}
	HTList_delete(HTCacheList);
	HTCacheList = NULL;
    }
}

/*
**  Removes all cache entries in memory and on disk
*/
PUBLIC void HTCache_deleteAll (void)
{
    HTList *cur=HTCacheList;
    HTCache * pres;
    if (cur) {
	while ((pres = (HTCache *) HTList_lastObject(cur)))
	    HTCache_remove(pres);
	HTList_delete(HTCacheList);
	HTCacheList = NULL;
    }
}

/* ------------------------------------------------------------------------- 
*/
/*  				 NAMING SCHEME				     */
/* ------------------------------------------------------------------------- 
*/

/*
**	Map url to cache file name.
*/
PRIVATE char * cache_file_name (char * url)
{
    char * access = NULL;
    char * host = NULL;
    char * path = NULL;
    char * cfn = NULL;
    BOOL welcome = NO;
    BOOL res = NO;

    if (!url ||  strchr(url, '?')  ||  (res = reserved_name(url))  ||
	!(access = HTParse(url, "", PARSE_ACCESS)) ||
	(0 != strcmp(access, "http") &&
	 0 != strcmp(access, "ftp")  &&
	 0 != strcmp(access, "gopher"))) {

	if (access) HT_FREE(access);

	if (res && CACHE_TRACE)
	    TTYPrint(TDEST,
		    "Cache....... Clash with reserved name (\"%s\")\n",url);

	return NULL;
    }

    host = HTParse(url, "", PARSE_HOST);
    path = HTParse(url, "", PARSE_PATH | PARSE_PUNCTUATION);
    if (path && path[strlen(path)-1] == '/')
	welcome = YES;

    if ((cfn = (char *) HT_MALLOC(strlen(HTCacheRoot) + strlen(access) + 
(host ? strlen(host) : 0) + (path ? strlen(path) : 0) + (welcome ? 
strlen(WELCOME_FILE) : 0) + 3)) == NULL)
        HT_OUTOFMEM("cache_file_name");

    /* Removed extra slash - HF May2,95 */
    sprintf(cfn, "%s%s/%s%s%s", HTCacheRoot, access, host, path,
	    (welcome ? WELCOME_FILE : ""));

    HT_FREE(access);
    HT_FREE(host);
    HT_FREE(path);

    /*
    ** This checks that the last component is not too long.
    ** It could check all the components, but the last one
    ** is most important because it could later blow up the
    ** whole gc when reading cache info files.
    ** Operating system handles other cases.
    ** 64 = 42 + 22  and  22 = 42 - 20  :-)
    ** In other words I just picked some number, it doesn't
    ** really matter that much.
    */
    {
	char * last = strrchr(cfn, '/');
	if (!last) last = cfn;
	if ((int)strlen(last) > 64) {
	    if (CACHE_TRACE)
		TTYPrint(TDEST, "Too long.... cache file name \"%s\"\n", cfn);
	    HT_FREE(cfn);
	    cfn = NULL;
	}
    }
    return cfn;
}


/*
**	Create directory path for cache file
**
** On exit:
**	return YES
**		if directories created -- after that caller
**		can rely on fopen(cfn,"w") succeeding.
**
*/
PRIVATE BOOL create_cache_place (char * cfn)
{
    struct stat stat_info;
    char * cur = NULL;
    BOOL create = NO;

    if (!cfn  ||  (int)strlen(cfn) <= (int)strlen(HTCacheRoot) + 1)
	return NO;

    cur = cfn + strlen(HTCacheRoot) + 1;

    while ((cur = strchr(cur, '/'))) {
          if(*(cur+1) != '/') /* Sandeep added to ignore multiple '/' */
	    {
	     *cur = 0;
	     if (create || HT_STAT(cfn, &stat_info) == -1) {
	      create = YES;	/* To avoid doing stat()s in vain */
	      if (CACHE_TRACE)
		TTYPrint(TDEST,"Cache....... creating cache dir \"%s\"\n",cfn);
	      if (MKDIR(cfn, 0777) < 0) {
		if (CACHE_TRACE)
		  TTYPrint(TDEST,"Cache....... can't create dir `%s\'\n",cfn);
		return NO;
	      }
	} else {
	    if (S_ISREG(stat_info.st_mode)) {
		int len = strlen(cfn);
		char * tmp1;
		char * tmp2;
		if ((tmp1 = (char *) HT_MALLOC(len + strlen(TMP_SUFFIX) + 1)) == NULL)
		    HT_OUTOFMEM("tmp1");

		if ((tmp2 = (char *) HT_MALLOC(len + strlen(INDEX_FILE) + 2)) == NULL)
		    HT_OUTOFMEM("tmp2");
		/* time_t t1,t2,t3,t4,t5; */


		sprintf(tmp1, "%s%s", cfn, TMP_SUFFIX);
		sprintf(tmp2, "%s/%s", cfn, INDEX_FILE);

		if (CACHE_TRACE) {
		    TTYPrint(TDEST,"Cache....... moving \"%s\" to \"%s\"\n",
			    cfn,tmp1);
		    TTYPrint(TDEST,"and......... creating dir \"%s\"\n",
			    cfn);
		    TTYPrint(TDEST,"and......... moving \"%s\" to \"%s\"\n",
			    tmp1,tmp2);
		}
		rename(cfn,tmp1);
		(void) MKDIR(cfn, 0777);
		rename(tmp1,tmp2);
		HT_FREE(tmp1);
		HT_FREE(tmp2);
	      }
	    else {
		if (CACHE_TRACE)
		    TTYPrint(TDEST,"Cache....... dir \"%s\" already exists\n",
			    cfn);
	    }
	}
	*cur = '/';
	   }
	cur++;
    }
    return YES;
}


/*	Create a cache path
**	-------------------
**	Find a full path name for the cache file and create the path if it
**	does not already exist. Returns name or NULL
**	HWL 22/9/94
**	HWL added support for hierachical structure
*/
PRIVATE char *HTCache_getName (char * url)
{
    char *filename = cache_file_name(url);
    if (!filename)
	return NULL;
    if (create_cache_place(filename))
	return(filename);
    return NULL;
}

/*
**  Make a WWW name from a cache name and returns it if OK, else NULL.
**  The string returned must be freed by the caller.
**  We keep this function private as we might change the naming scheme for
**  cache files. Right now it follows the file hierarchi.
*/
PRIVATE char *HTCache_wwwName  (char * name)
{
    char * result = NULL;
    if (name && *name) {
	StrAllocCopy(result, "file:");	     /* We get an absolute file name */
#ifdef VMS 
	/* convert directory name to Unix-style syntax */
	{
	    char * disk = strchr (name, ':');
	    char * dir = strchr (name, '[');
	    if (disk) {
		*disk = '\0';
		StrAllocCat(result, "/"); /* needs delimiter */
		StrAllocCat(result, name);
	    }
	    if (dir) {
		char *p;
		*dir = '/';	/* Convert leading '[' */
		for (p = dir ; *p != ']'; ++p)
		    if (*p == '.') *p = '/';
		*p = '\0';	/* Cut on final ']' */
		StrAllocCat(result, dir);
	    }
	}
#else  /* not VMS */
#ifdef WIN32
	{
	    char * p = name;					  /* a colon */
	    while( *p != 0 ) { 
		if (*p == '\\')		         /* change to one true slash */
		    *p = '/' ;
		p++;
	    }
	    StrAllocCat(result, name);
	}
#else /* not WIN32 */
	StrAllocCat (result, name);
#endif /* not WIN32 */
#endif /* not VMS */
    }
    return result;
}

/* ------------------------------------------------------------------------- 
*/
/*  			      CACHE PARAMETERS				     */
/* ------------------------------------------------------------------------- 
*/

/*	Enable Cache
**	------------
**	If `cache_root' is NULL then reuse old value or use HT_CACHE_ROOT.
**	An empty string will make '/' as cache root
**	We can only enable the cache if the HTSecure flag is not set. This
**	is for example the case if using an application as a telnet shell.
*/
PUBLIC BOOL HTCache_enable (CONST char * cache_root)
{
    if (!HTLib_secure()) {
	HTCache_setRoot(cache_root);
	HTCacheEnable = YES;
	return YES;
    }
    return NO;
}


/*	Disable Cache
**	------------
**	Turns off the cache. Note that the cache can be disabled and enabled
**	at any time. The cache root is kept and can be reused during the
**	execution.
*/
PUBLIC BOOL HTCache_disable (void)
{
    HTCacheEnable = NO;
    return YES;
}

/*	Is Cache Enabled
**	----------------
**	Returns YES or NO. Also makes sure that we have a root value
**	(even though it might be invalid)
*/
PUBLIC BOOL HTCache_isEnabled (void)
{
    return HTCacheEnable;
}


/*	Set Cache Root
**	--------------
**	If `cache_root' is NULL then the current value (might be a define)
**	Should we check if the cache_root is actually OK? I think not!
*/
PUBLIC BOOL HTCache_setRoot (CONST char * cache_root)
{
    StrAllocCopy(HTCacheRoot, cache_root ? cache_root : HT_CACHE_ROOT);
    if (*(HTCacheRoot+strlen(HTCacheRoot)-1) != '/')
	StrAllocCat(HTCacheRoot, "/");
    if (CACHE_TRACE)
	TTYPrint(TDEST, "Cache Root.. Root set to `%s\'\n", HTCacheRoot);
    return YES;
}


/*	Get Cache Root
**	--------------
*/
PUBLIC CONST char * HTCache_getRoot (void)
{
    return HTCacheRoot;
}

/*	Free Cache Root
**	--------------
**	For clean up memory
*/
PUBLIC void HTCache_freeRoot (void)
{
    HT_FREE(HTCacheRoot);
}

/* ------------------------------------------------------------------------- 
*/
/*  				 MEMORY CACHE				     */
/* ------------------------------------------------------------------------- 
*/

/*
**  Register a Memory Cache Handler. This function is introduced in order to
**  avoid having references to HText module outside HTML.
*/
PUBLIC BOOL HTMemoryCache_register (HTMemoryCacheHandler * cbf)
{
    return (HTMemoryCache = cbf) ? YES : NO;
}

PUBLIC BOOL HTMemoryCache_unRegister (void)
{
    HTMemoryCache = NULL;
    return YES;
}

PUBLIC int HTMemoryCache_check (HTRequest * request)
{
    return HTMemoryCache ? HTMemoryCache(request,HTExpMode,HTExpNotify) : 0;
}

/*
**  Set the mode for how we handle Expires header from the local history
**  list. The following modes are available:
**
**	HT_EXPIRES_IGNORE : No update in the history list
**	HT_EXPIRES_NOTIFY : The user is notified but no reload
**	HT_EXPIRES_AUTO   : Automatic reload
**
**  The notify only makes sense when HT_EXPIRES_NOTIFY. NULL is valid.
*/
PUBLIC void HTCache_setExpiresMode (HTExpiresMode mode, char * notify)
{
    HTExpMode = mode;
    HTExpNotify = notify;
}

PUBLIC HTExpiresMode HTCache_expiresMode (char ** notify)
{
    *notify = HTExpNotify ? HTExpNotify : "This version has expired!";
    return HTExpMode;
}

/* ------------------------------------------------------------------------- 
*/
/*  				 CACHE MANAGER				     */
/* ------------------------------------------------------------------------- 
*/

/*
**  Verifies if a cache object exists for this URL and if so returns a URL
**  for the cached object. It does not verify whether the object is valid or
**  not, for example it might have expired.
**
**  Returns: file name	If OK (must be freed by caller)
**	     NULL	If no cache object found
*/
PUBLIC char * HTCache_getReference (char * url)
{
    if (url && HTCache_isEnabled()) {
	char *fnam = cache_file_name(url);
	if (fnam) {
	    FILE *fp = fopen(fnam, "r");
	    if (fp) {
		char *url = HTCache_wwwName(fnam);
		fclose(fp);
		if (CACHE_TRACE)
		    TTYPrint(TDEST, "Cache....... Object found `%s\'\n", url);
		HT_FREE(fnam);
		return url;
	    } else
		HT_FREE(fnam);
	}
    }
    return NULL;
}

/*
**  This function checks whether a document has expired or not.
**  The check is based on the metainformation passed in the anchor object
**  The function returns YES or NO.
*/
PUBLIC BOOL HTCache_isValid (HTParentAnchor * anchor)
{
    time_t cur = time(NULL);
    time_t expires = HTAnchor_expires(anchor);
    return (expires>0 && cur>0 && expires<cur) ? NO : YES;
}

/* ------------------------------------------------------------------------- 
*/
/*  			     CACHE WRITER STREAM			     */
/* ------------------------------------------------------------------------- 
*/

PRIVATE int HTCache_flush (HTStream * me)
{
    return (fflush(me->fp) == EOF) ? HT_ERROR : HT_OK;
}

PRIVATE int HTCache_putBlock (HTStream * me, CONST char * s, int  l)
{
    int status = (fwrite(s, 1, l, me->fp) != l) ? HT_ERROR : HT_OK;
    if (l > 1 && status == HT_OK)
	(void) HTCache_flush(me);
    return status;
}

PRIVATE int HTCache_putChar (HTStream * me, char c)
{
    return HTCache_putBlock(me, &c, 1);
}

PRIVATE int HTCache_putString (HTStream * me, CONST char * s)
{
    return HTCache_putBlock(me, s, (int) strlen(s));
}

PRIVATE int HTCache_free (HTStream * me)
{
    me->cache->load_delay = time(NULL) - me->cache->start_time;
    fclose(me->fp);
    HT_FREE(me);
    return HT_OK;
}

PRIVATE int HTCache_abort (HTStream * me, HTList * e)
{
    if (CACHE_TRACE)
	TTYPrint(TDEST, "Cache....... ABORTING\n");
    if (me->fp)
	fclose(me->fp);
    if (me->cache)
	HTCache_remove(me->cache);
    HT_FREE(me);
    return HT_ERROR;
}

PRIVATE CONST HTStreamClass HTCacheClass =
{		
    "Cache",
    HTCache_flush,
    HTCache_free,
    HTCache_abort,
    HTCache_putChar,
    HTCache_putString,
    HTCache_putBlock
};


/*	Cache Writer
**	------------------
**
*/
PUBLIC HTStream* HTCacheWriter (HTRequest *	request,
				void *		param,
				HTFormat	input_format,
				HTFormat	output_format,
				HTStream *	output_stream)
{
    char *fnam;
    HTStream *me;
    if (!HTCacheEnable) {
	if (CACHE_TRACE) TTYPrint(TDEST, "Cache....... Not enabled\n");
	return HTBlackHole();
    }

    /* Get a file name and open file */
    if ((fnam = HTCache_getName(HTAnchor_physical(request->anchor))) == NULL)
	return HTBlackHole();

    /* Set up the stream */
    if ((me = (HTStream *) HT_CALLOC(sizeof(*me), 1)) == NULL)
        HT_OUTOFMEM("Cache");
    me->isa = &HTCacheClass;
    me->request = request;
    if ((me->fp = fopen(fnam, "wb")) == NULL) {
	if (CACHE_TRACE)
	    TTYPrint(TDEST, "Cache....... Can't open %s for writing\n", fnam);
	HT_FREE(fnam);
	return HTBlackHole();
    } else
	if (CACHE_TRACE)
	    TTYPrint(TDEST, "Cache....... Creating file %s\n", fnam);

    /* Set up a cache record */
    if ((me->cache = (HTCache *) HT_CALLOC(sizeof(*me->cache), 1)) == NULL)
        HT_OUTOFMEM("Cache");
    me->cache->filename = fnam;
    me->cache->start_time = time(NULL);
    me->cache->format = input_format;

    /* Keep a global list of all cache items */
    if (!HTCacheList) HTCacheList = HTList_new();
    HTList_addObject(HTCacheList, me->cache);
    limit_cache(HTCacheList);		 /* Limit number (not size) of files */
    return me;
}

- --------------59E21CFB3F54--

------- End of Forwarded Messages


-- 
Henrik Frystyk Nielsen, <frystyk@w3.org>
World-Wide Web Consortium, MIT/LCS NE43-356
545 Technology Square, Cambridge MA 02139, USA