Thu Nov 17 03:10:28 UTC 2005  Alberto Bertogli <albertogli@telpin.com.ar>
  * Implement a simple cache.
  
  This patch implements a very simple but effective cache, so darcsweb can avoid
  regenerating everything all the time.
  
  Based on an idea from Alexandre Rossi.
diff -rN -u old-darcsweb/config.py.sample new-darcsweb/config.py.sample
--- old-darcsweb/config.py.sample	2016-02-07 22:12:59.000000000 +0000
+++ new-darcsweb/config.py.sample	2016-02-07 22:12:59.000000000 +0000
@@ -29,6 +29,17 @@
 	# alternative footer here; it's optional, of course
 	#footer = "I don't like shoes"
 
+	# It is possible to have a cache where darcsweb will store the pages
+	# it generates; entries are automatically updated when the repository
+	# changes. This will speed things up significatively, specially for
+	# popular sites.
+	# It's recommended that you clean the directory with some regularity,
+	# to avoid having too many unused files. A simple rm will do just
+	# fine.
+	# If you leave the entry commented, no cache will be ever used;
+	# otherwise the directory is assumed to exist and be writeable.
+	#cachedir = '/tmp/darcsweb-cache'
+
 
 #
 # From now on, every class is a repo configuration, with the same format
diff -rN -u old-darcsweb/darcsweb.cgi new-darcsweb/darcsweb.cgi
--- old-darcsweb/darcsweb.cgi	2016-02-07 22:12:59.000000000 +0000
+++ new-darcsweb/darcsweb.cgi	2016-02-07 22:12:59.000000000 +0000
@@ -13,6 +13,7 @@
 import string
 import time
 import stat
+import sha
 import cgi
 import cgitb; cgitb.enable()
 import urllib
@@ -384,6 +385,91 @@
 	print "Content-type: text/plain; charset=utf-8\n"
 
 
+
+#
+# basic caching
+#
+
+class Cache:
+	def __init__(self, basedir, url):
+		self.basedir = basedir
+		self.url = url
+		self.fname = sha.sha(url).hexdigest()
+		self.file = None
+		self.mode = None
+		self.real_stdout = sys.stdout
+
+	def open(self):
+		"Returns 1 on hit, 0 on miss"
+		fname = self.basedir + '/' + self.fname
+
+		if not os.access(fname, os.R_OK):
+			# the file doesn't exist, direct miss
+			pid = str(os.getpid())
+			fname = self.basedir + '/.' + self.fname + '-' + pid
+			self.file = open(fname, 'w')
+			self.mode = 'w'
+
+			# step over stdout so when "print" tries to write
+			# output, we get it first
+			sys.stdout = self
+			return 0
+
+		inv = config.repodir + '/_darcs/inventory'
+		cache_lastmod = os.stat(fname).st_mtime
+		repo_lastmod = os.stat(inv).st_mtime
+
+		if repo_lastmod > cache_lastmod:
+			# the entry is too old, remove it and return a miss
+			close(self.file)
+			os.unlink(fname)
+
+			pid = str(os.getpid())
+			fname = self.basedir + '/.' + self.fname + '-' + pid
+			self.file = open(fname, 'w')
+			self.mode = 'w'
+			sys.stdout = self
+			return 0
+
+		# the entry is still valid, hit!
+		self.file = open(fname, 'r')
+		self.mode = 'r'
+		return 1
+
+
+	def dump(self):
+		for l in self.file:
+			self.real_stdout.write(l)
+
+	def write(self, s):
+		# this gets called from print, because we replaced stdout with
+		# ourselves
+		self.file.write(s)
+		self.real_stdout.write(s)
+
+	def close(self):
+		if self.file:
+			self.file.close()
+		sys.stdout = self.real_stdout
+		if self.mode == 'w':
+			pid = str(os.getpid())
+			fname1 = self.basedir + '/.' + self.fname + '-' + pid
+			fname2 = self.basedir + '/' + self.fname
+			os.rename(fname1, fname2)
+			self.mode = 'c'
+
+	def cancel(self):
+		"Like close() but don't save the entry."
+		if self.file:
+			self.file.close()
+		sys.stdout = self.real_stdout
+		if self.mode == 'w':
+			pid = str(os.getpid())
+			fname = self.basedir + '/.' + self.fname + '-' + pid
+			os.unlink(fname)
+			self.mode = 'c'
+
+
 #
 # darcs repo manipulation
 #
@@ -1693,7 +1779,6 @@
 	print_header()
 	print "<p><font color=red>Error! Malformed query</font></p>"
 	print_footer()
-	sys.exit(1)
 
 
 def do_listrepos():
@@ -1860,6 +1945,11 @@
 These are all the available repositories.<br/>
 		"""
 
+	if "cachedir" in dir(base):
+		config.cachedir = base.cachedir
+	else:
+		config.cachedir = None
+
 	if name and "footer" in dir(c):
 		config.footer = c.footer
 	elif "footer" in dir(base):
@@ -1869,6 +1959,7 @@
 				+ "crece desde el pie"
 
 
+
 #
 # main
 #
@@ -1892,6 +1983,18 @@
 else:
 	action = filter_act(form["a"].value)
 
+# check if we have the page in the cache
+if config.cachedir:
+	url_request = os.environ['QUERY_STRING']
+	cache = Cache(config.cachedir, url_request)
+	if cache.open():
+		# we have a hit, dump and run
+		cache.dump()
+		cache.close()
+		sys.exit(0)
+	# if there is a miss, the cache will step over stdout, intercepting
+	# all "print"s and writing them to the cache file automatically
+
 
 # see what should we do according to the received action
 if action == "summary":
@@ -2021,6 +2124,9 @@
 else:
 	action = "invalid query"
 	do_die()
+	cache.cancel()
 
 
+if config.cachedir:
+	cache.close()