cache.c

harvest是一个下载html网页得机器人

	/* See if we have room, if not delete an object */
	while (1) {
		if (ndeletes > 3) {	/* Try 3 times to reduce cache size */
			release_access();
			return;	/* RELEASE and give up */
		}
		current_size = get_cachesize();
		Debug(22, 1, ("add_cache: Current Cache Size is %d\n",
			current_size));
		if (sb.st_size + current_size > max_cache_size) {
			delete_cache_entry();
			ndeletes++;
		} else {
			break;	/* We're ready to add */
		}
	}

	/* Cache the file; by link'ing it */
	cfile = get_cache_filename();
	Debug(22, 1, ("add_cache: Linking %s to %s\n", cfile, filename));
	if (link(filename, cfile) < 0) {
		/* must copy the file */
		int n;
		char *buf = NULL;
		int rfd, wfd;
		if ((wfd = open(cfile, O_WRONLY | O_CREAT, 0666)) < 0) {
			log_errno2(__FILE__, __LINE__, cfile);
			release_access();	/* RELEASE  and give up */
			xfree(cfile);
			return;
		}
		if ((rfd = open(filename, O_RDONLY)) < 0) {
			log_errno2(__FILE__, __LINE__, filename);
			release_access();	/* RELEASE  and give up */
			xfree(cfile);
			close(wfd);             /* Close the file handle */
			return;
		}
		buf = (char *) xmalloc(4096);
		while ((n = read(rfd, buf, 4096)) > 0)
			write(wfd, buf, n);
		close(rfd);
		close(wfd);
		xfree(buf);
	}
	/* Add the file to the cache */
	k.dptr = xstrdup(url);
	k.dsize = strlen(k.dptr) + 1;
	d.dptr = xstrdup(cfile);
	d.dsize = strlen(d.dptr) + 1;

	Debug(22, 1, ("add_cache: Adding %s -> %s\n", k.dptr, d.dptr));

	status = gdbm_store(dbf, k, d, GDBM_INSERT);
	if (status) {
		/* already an entry for URL */
		Debug(22, 1, ("add_cache: GDBM_ERROR: gdbm_store: key (%s): %s: %s\n", k.dptr, cfile, gdbm_strerror(gdbm_errno)));
		(void) unlink(cfile);
		xfree(k.dptr);
		xfree(d.dptr);
		xfree(cfile);
		release_access();	/* RELEASE */
		return;
	}
	xfree(k.dptr);
	xfree(d.dptr);
	xfree(cfile);
	change_cachesize(sb.st_size);

	/* Add the LMT */
	k.dptr = xstrdup(url);
	k.dsize = strlen(k.dptr) + 1;
	d.dptr = (char *) &lmt;
	d.dsize = sizeof(lmt);

	Debug(22, 5, ("Storing LMT=%d for %s\n", lmt, url));

	status = gdbm_store(lm_dbf, k, d, GDBM_INSERT);
	if (status) {
		/* already an entry for URL */
		Debug(22, 1, ("add_cache: GDBM_ERROR: gdbm_store: url=%s LMT=%ld: %s\n", k.dptr, lmt, gdbm_strerror(gdbm_errno)));
#if 0
		/* don't need this kjl/24feb2002 */
		release_access();	/* RELEASE */
		return;
#endif
	}
	xfree(k.dptr);

	release_access();	/* RELEASE */
}


/*
 *  lookup_cache() - Checks to see if the URL is already cached on the
 *  local disk.  If it is, then it returns a pointer to a copy of the file.
 */
char *lookup_cache(url)
     char *url;
{
	static char *filecopy;
	datum k, d;
	struct stat sb;

	Debug(22, 1, ("lookup_cache: %s\n", url));

	k.dptr = xstrdup(url);
	k.dsize = strlen(url) + 1;

	get_access(GDBM_READER);	/* LOCK */

	d = gdbm_fetch(dbf, k);
	xfree(k.dptr);

	if (d.dptr == NULL) {
		release_access();	/* RELEASE */
		xfree(d.dptr);
		return (NULL);
	}
	/* make sure its really there */
	if (stat(d.dptr, &sb) < 0) {
		release_access();	/* RELEASE */
		delete_cache_url(d.dptr);
		xfree(d.dptr);
		return NULL;
	}
	filecopy = tempnam(cachedir, "cache");
	Debug(22, 1, ("lookup_cache: CACHE HIT: Linking %s to %s\n",
		filecopy, d.dptr));
	if (link(d.dptr, filecopy) < 0) {
		if (symlink(d.dptr, filecopy) < 0) {	/* try symlink(2) */
			log_errno(filecopy);
			xfree(filecopy);
			filecopy = NULL;
		}
	}
	release_access();	/* RELEASE */
	xfree(d.dptr);
	return (filecopy);
}

/*
 *  delete_cache_url() - deletes the cache entry for the URL.
 */
static void delete_cache_url(url)
     char *url;
{
	datum k, d;
	struct stat sb;

	Debug(22, 1, ("delete_cache_url: %s\n", url));
	k.dptr = xstrdup(url);
	k.dsize = strlen(k.dptr) + 1;

	d = gdbm_fetch(dbf, k);
	if (d.dptr == NULL) {
		errorlog("URL %s is not in the cache.\n", url);
		return;
	}
	if (stat(d.dptr, &sb) < 0) {
		log_errno(d.dptr);
		sb.st_size = 0;
	}
	(void) unlink(d.dptr);
	xfree(d.dptr);
	change_cachesize(-sb.st_size);
	(void) gdbm_delete(dbf, k);
	xfree(k.dptr);

	Debug(22, 1, ("delete_cache_url (LMT): %s\n", url));
	k.dptr = xstrdup(url);
	k.dsize = strlen(k.dptr) + 1;

	d = gdbm_fetch(lm_dbf, k);
	if (d.dptr == NULL) {
		errorlog("not in LMT.gdbm: %s\n", url);
		return;
	}
	(void) gdbm_delete(dbf, k);
	xfree(d.dptr);
	xfree(k.dptr);

}

/*
 *  delete_cache_entry() - remove the file that was accessed last.
 *  ASSUMES that get_access() has already been called.
 */
static void delete_cache_entry()
{
	datum k, nk;

	Debug(22, 1, ("delete_cache_entry: deleting...\n"));

	/* Randomly select an entry to delete */
	k = gdbm_firstkey(dbf);
	while (k.dptr) {
		nk = gdbm_nextkey(dbf, k);
#if   defined(HAVE_SRAND48)
		if (lrand48() % 13 == 0) {	/* delete a random entry */
#elif defined(HAVE_SRANDOM)
			if (random() % 13 == 0) {	/* delete a random entry */
#else
		if (rand() % 13 == 0) {		/* delete a random entry */
#endif
			delete_cache_url(k.dptr);
		}
		xfree(k.dptr);
		k = nk;
	}

	/*
	 *  Oops, we didn't select any during the random traversal,
	 *  so just delete the first one
	 */
	k = gdbm_firstkey(dbf);
	if (k.dptr) {
		delete_cache_url(k.dptr);
		xfree(k.dptr);
	}
}

/*
 *  get_cachesize() - Returns the number of bytes in the cache
 */
static int get_cachesize()
{
	FILE *fp;
	int sz = 0;

	if ((fp = fopen(cachesize, "r")) == NULL) {
		return (0);
	}
	if (fscanf(fp, "%d", &sz) != 1) {
		fclose(fp);
		return (0);
	}
	fclose(fp);
	return (sz < 0 ? 0 : sz);
}

/*
 *  change_cachesize() - Changes the cache size by n bytes;
 */
static void change_cachesize(n)
     int n;
{
	FILE *fp;
	int sz = get_cachesize();

	if ((fp = fopen(cachesize, "w+")) == NULL) {
		log_errno(cachesize);
		die();
	}
	fprintf(fp, "%d", sz + n);
	fclose(fp);
}

#define myabs(a)	((a) < 0 ? -(a) : (a))

/*
 *  expire_cache() - Removes any cached files that are older than CACHE_TTL.
 */
void expire_cache()
{
	datum k, nk, d;
	struct stat sb;
	time_t now = time(0);

	Debug(22, 1, ("expire_cache: Deleting expired entries...\n"));
	Debug(22, 1, ("expire_cache: local-disk cache in %s...\n", cachedir));

	get_access(GDBM_WRITER);	/* LOCK */

	/* Walk each cache file and delete if necessary */
	k = gdbm_firstkey(dbf);
	while (k.dptr) {
		nk = gdbm_nextkey(dbf, k);
		d = gdbm_fetch(dbf, k);
		if (d.dptr == NULL) {
			errorlog("Internal Error: %s not in cache table\n",
			    k.dptr);
			die();
		}
		if (stat(d.dptr, &sb) < 0) {
			log_errno(d.dptr);
			delete_cache_url(k.dptr);
		} else if (myabs(now - sb.st_mtime) > cache_ttl) {
			delete_cache_url(k.dptr);
		}
		xfree(d.dptr);
		xfree(k.dptr);
		k = nk;
	}

	release_access(GDBM_WRITER);	/* RELEASE */
}
#undef myabs

static char *topdir = NULL;

static void init_next_filename(dirname)
     char *dirname;		/* name of top level directory to store files */
{
	if (dirname == NULL)
		return;
	topdir = xstrdup(dirname);
#if   defined(HAVE_SRAND48)
	(void) srand48((long) time(NULL));
#elif defined(HAVE_SRANDOM)
	(void) srandom((unsigned) time(NULL));
#else
	(void) srand(time(NULL));
#endif
}

static char *next_filename()
{
	static char p[BUFSIZ];
#if   defined(HAVE_SRAND48)
	unsigned n = lrand48() % 100000000;	/* 8 digits */
#elif defined(HAVE_SRANDOM)
	unsigned n = random() % 100000000;	/* 8 digits */
#else
	unsigned n = rand() % 100000000;	/* 8 digits */
#endif

	sprintf(p, "%s/%02d", topdir, (int) n / 1000000);	/* first 2 digits */
	if (mkdir(p, 0755) < 0) {
		if (errno != EEXIST) {
			log_errno(p);
			return (NULL);
		}
	}
	/* Entire filename uses directory (2 digits) and 6 digits for name */
	sprintf(p, "%s/%02d/%06d", topdir, (int) n / 1000000, (int) n % 1000000);
	return (xstrdup(p));
}

/*
 *  lmt_cache() - Returns the Last-Modification-Time for the cache hit.
 */
time_t lmt_cache(url)
     char *url;
{
	datum k, d;
	char *filename;
	struct stat sb;
	time_t t;

	Debug(22, 1, ("lmt_cache: %s\n", url));

	k.dptr = xstrdup(url);
	k.dsize = strlen(url) + 1;

	get_access(GDBM_READER);	/* LOCK */

	Debug(22, 5, ("Looking up LMT: %s\n", url));
	d = gdbm_fetch(lm_dbf, k);
	xfree(k.dptr);
	if (d.dptr != NULL) {
		t = *((time_t *) d.dptr);
		Debug(22, 5, ("--> Found LMT=%d in LMT.gdbm.\n", t));
		release_access();	/* RELEASE */
		xfree(d.dptr);
		return t;
	}
	d = gdbm_fetch(dbf, k);
	xfree(k.dptr);

	if (d.dptr == NULL) {
		release_access();	/* RELEASE */
		xfree(d.dptr);
		return ((time_t) NULL);
	}
	filename = xstrdup(d.dptr);
	xfree(d.dptr);
	release_access();	/* RELEASE */

	t = (stat(filename, &sb) < 0) ? 0 : sb.st_mtime;
	xfree(filename);
	return (t);
}