[svn] New option --random-wait.

Submitted by Alan Eldridge in
<200111042106.fA4L63b75804@wwweasel.geeksrus.net>.

doc/ChangeLog

@@ -1,3 +1,7 @@
+2001-11-04  Alan Eldridge  <alane@geeksrus.net>
+
+	* wget.texi: Document --random-wait, randomwait=on/off.
+
 2001-11-23  Hrvoje Niksic  <hniksic@arsdigita.com>
 
 	* wget.texi (Download Options): Document the new `--progress'

doc/wget.texi

@@ -701,6 +701,26 @@ seconds per file.
 Note that this option is turned on by default in the global
 @file{wgetrc} file.
 
+@cindex wait, random
+@cindex random wait
+@itemx --random-wait
+Some web sites may perform log analysis to identify retrieval programs
+such as Wget by looking for statistically significant similarities in
+the time between requests. This option causes the time between requests
+to vary between 0 and 2 * @var{wait} seconds, where @var{wait} was
+specified using the @samp{-w} or @samp{--wait} options, in order to mask
+Wget's presence from such analysis.
+
+A recent article in a publication devoted to development on a popular
+consumer platform provided code to perform this analysis on the fly.
+Its author suggested blocking at the class C address level to ensure
+automated retrieval programs were blocked despite changing DHCP-supplied
+addresses.
+
+The @samp{--random-wait} option was inspired by this ill-advised
+recommendation to block many unrelated users from a web site due to the
+actions of one.
+
 @cindex proxy
 @item -Y on/off
 @itemx --proxy=on/off
@@ -2168,6 +2188,10 @@ Wait @var{n} seconds between retrievals---the same as @samp{-w}.
 Wait up to @var{n} seconds between retries of failed retrievals
 only---the same as @samp{--waitretry}.  Note that this is turned on by
 default in the global @file{wgetrc}.
+
+@item randomwait = on/off
+Turn random between-request wait times on or off. The same as 
+@samp{--random-wait}.
 @end table
 
 @node Sample Wgetrc,  , Wgetrc Commands, Startup File

src/ChangeLog

@@ -1,3 +1,17 @@
+2001-11-04  Alan Eldridge  <alane@geeksrus.net>
+
+	* config.h.in: added HAVE_RANDOM.
+
+	* options.h: added random_wait to struct options.
+
+	* main.c (print_help [HAVE_RANDOM], main): added arg parsing, help
+	for --random-wait.
+
+	* retr.c (sleep_between_retrievals) [HAVE_RANDOM]: added
+	implementation of random wait times.
+
+	* init.c (commands): added "randomwait" keyword.
+
 2001-11-25  Hrvoje Niksic  <hniksic@arsdigita.com>
 
 	* recur.c (descend_url_p): Be more conservative with blacklisting

src/init.c

@@ -160,6 +160,7 @@ static struct {
   { "proxyuser",	&opt.proxy_user,	cmd_string },
   { "quiet",		&opt.quiet,		cmd_boolean },
   { "quota",		&opt.quota,		cmd_bytes },
+  { "randomwait",	&opt.random_wait,	cmd_boolean },
   { "reclevel",		&opt.reclevel,		cmd_number_inf },
   { "recursive",	NULL,			cmd_spec_recursive },
   { "referer",		&opt.referer,		cmd_string },

src/main.c

@@ -161,9 +161,14 @@ Download:\n\
   -T,  --timeout=SECONDS        set the read timeout to SECONDS.\n\
   -w,  --wait=SECONDS           wait SECONDS between retrievals.\n\
        --waitretry=SECONDS      wait 1...SECONDS between retries of a retrieval.\n\
+       --random-wait            wait from 0...2*WAIT secs between retrievals.\n\
   -Y,  --proxy=on/off           turn proxy on or off.\n\
   -Q,  --quota=NUMBER           set retrieval quota to NUMBER.\n\
 \n"), stdout);
+#ifdef HAVE_RANDOM
+  fputs (_("\
+\n"), stdout);
+#endif
   fputs (_("\
 Directories:\n\
   -nd  --no-directories            don\'t create directories.\n\
@@ -261,6 +266,7 @@ main (int argc, char *const *argv)
     { "passive-ftp", no_argument, NULL, 139 },
     { "page-requisites", no_argument, NULL, 'p' },
     { "quiet", no_argument, NULL, 'q' },
+    { "random-wait", no_argument, NULL, 165 },
     { "recursive", no_argument, NULL, 'r' },
     { "relative", no_argument, NULL, 'L' },
     { "retr-symlinks", no_argument, NULL, 137 },
@@ -395,6 +401,9 @@ hpVqvdkKsxmNWrHSLcFbEY:G:g:T:U:O:l:n:i:o:a:t:D:A:R:P:B:e:Q:X:I:w:C:",
 	case 156:
 	  setval ("httpkeepalive", "off");
 	  break;
+	case 165:
+	  setval ("randomwait", "on");
+	  break;
 	case 'b':
 	  setval ("background", "on");
 	  break;

src/options.h

@@ -99,6 +99,7 @@ struct options
   long timeout;			/* The value of read timeout in
 				   seconds. */
 #endif
+  int random_wait;		/* vary from 0 .. wait secs by random()? */
   long wait;			/* The wait period between retrievals. */
   long waitretry;		/* The wait period between retries. - HEH */
   int use_robots;		/* Do we heed robots.txt? */

src/retr.c

@@ -560,8 +560,18 @@ sleep_between_retrievals (int count)
 	    sleep (opt.waitretry);
 	}
       else if (opt.wait)
+	{
 	  /* Otherwise, check if opt.wait is specified.  If so, sleep.  */
+	  if (count > 1 || !opt.random_wait)
 	    sleep (opt.wait);
+	  else
+	    {
+	      int waitsecs = random() % (opt.wait * 2 + 1);
+	      DEBUGP(("sleep_between_retrievals: norm=%ld,random=%ld,sleep=%d\n",
+		      opt.wait, waitsecs - opt.wait, waitsecs));
+	      sleep(waitsecs);
+	    }
+	}
     }
   if (first_retrieval)
     first_retrieval = 0;