--- index.cgi	2011-09-06 17:47:32.000000000 -0500
+++ index-cache.cgi	2011-09-07 06:37:51.000000000 -0500
@@ -136,15 +136,34 @@
 # Encode parameters in utf-8 before passing to standard functions.
 
 def utf8_exists(filename):
-    return path.exists(filename.encode('utf-8'))
+    # If the item exists, depend on it
+    # If the item does not exist, dependon the directory
+    # cache.cgi requires that the thing listed in dep exist, and for the file
+    # that didn't exist to start existing, the directory must change
+    result = path.exists(filename.encode('utf-8'))
+    if result:
+        dependencies[filename.encode('utf-8')] = 1
+    else:
+        filename = os.path.dirname(filename)
+        dependencies[filename.encode('utf-8')] = 1
+    return result
 
 def utf8_isdir(filename):
+    # Depend on the containing directory
+    # If item doesn't exist, this is necessary---cache.cgi requires that things
+    # listed in dep exist.  If it does exist, it's OK, because something can't
+    # change from existing as one kind of thing to not existing without changing
+    # the directory timestamp, and likewise for changing between file and
+    # directory.
+    dependencies[os.path.dirname(filename.encode('utf-8'))] = 1
     return path.isdir(filename.encode('utf-8'))
 
 def utf8_isfile(filename):
+    dependencies[os.path.dirname(filename).encode('utf-8')] = 1
     return path.isfile(filename.encode('utf-8'))
 
 def utf8_listdir(filename):
+    dependencies[filename.encode('utf-8')] = 1
     result = os.listdir(filename.encode('utf-8'))
     
     for i in xrange(len(result)):
@@ -165,9 +184,11 @@
     os.rmdir(dir.encode('utf-8'))
 
 def utf8_open(filename, mode):
+    dependencies[filename.encode('utf-8')] = 1
     return __builtins__.open(filename.encode('utf-8'), mode)
 
 def utf8_gzip_open(filename, *args):
+    dependencies[filename.encode('utf-8')] = 1
     import gzip
     return gzip.open(filename.encode('utf-8'), *args)
 
@@ -180,7 +201,13 @@
         Do not communicate with Apache while the lock is held,
             as network traffic can take arbitrary time. """
 
-    filename = (data_dir+u'/_lock').encode('utf-8')
+    lockdir =  (data_dir+u'/_lock').encode('utf-8')
+    filename = lockdir + "/lock"
+
+    try:
+        os.mkdir(lockdir)
+    except:
+        pass
 
     try:
         begin = os.stat(filename).st_mtime
@@ -208,7 +235,9 @@
 def unlock():
     """ Release lock on access to files. """
 
-    utf8_rmdir(data_dir+u'/_lock')
+    lockdir =  (data_dir+u'/_lock').encode('utf-8')
+    filename = lockdir + "/lock"
+    utf8_rmdir(filename)
 
 
 
@@ -235,6 +264,8 @@
     """ Ensure a directory exists, move file out of way if necessary.
         (rename to dir/_index). """
 
+    dir = dir.rstrip("/")
+
     if utf8_isdir(dir):
         return
 
@@ -1982,7 +2013,17 @@
     fields = cgi.FieldStorage()
     query = decode_fields(fields)
 
-    sys.stdout.write(perform_request(name, query).encode('utf-8'))
+    result = perform_request(name, query).encode('utf-8')
+
+    if (os.environ.get('REQUEST_METHOD', '') in ['GET', 'HEAD']  and
+            (not os.environ.get('QUERY_STRING'))
+            and (result.startswith("Status: 200\n") or not result.startswith("Status:"))):
+        depstr = "\0".join(dependencies.keys())
+        depdir = os.path.join( cache_dir, (name or '__index__').strip("/") )
+        ensure_dir_exists( depdir )
+
+        open(os.path.join(depdir, "_cache"), "wb").write(depstr + "\0\0" + result)
+    sys.stdout.write( result )
 
 
 if __name__ == '__main__':
@@ -2008,11 +2053,14 @@
 
         script_filename = path.join(os.getcwd().decode('utf-8'), 
                                     sys.argv[0].decode('utf-8'))
-        file_dir = '/var/www/emergent/index.cgi-files'
-        data_dir = '/var/www/emergent/index.cgi-data'
+        aether_base = os.environ.get('AETHER_BASE', script_filename)
+        data_dir = aether_base + u'-data'
+        file_dir = aether_base + u'-files'
+        cache_dir = aether_base + u'-cache'
+        dependencies = {}
 
         host_url = 'http://' + os.environ.get('HTTP_HOST','').decode('utf-8') 
 
         media_url = 'http://media.unpythonic.net/emergent-files/'
         script_base = os.environ.get('SCRIPT_NAME','').decode('utf-8') or "/"
         file_base = '/files'