crawler: more code comments

pictuga 2020-05-12 20:44:25 +02:00
parent 36e2a1c3fd
commit 5dac4c69a1
1 changed files with 37 additions and 6 deletions

View File

@ -387,12 +387,28 @@ default_cache = {}
class CacheHandler(BaseHandler):
" Cache based on etags/last-modified "
private_cache = False # False to behave like a CDN (or if you just don't care), True like a PC
private_cache = False # Websites can indicate whether the page should be
# cached by CDNs (e.g. shouldn't be the case for
# private/confidential/user-specific pages.
# With this setting, decide whether (False) you want
# the cache to behave like a CDN (i.e. don't cache
# private pages), or (True) to behave like a end-cache
# private pages. If unsure, False is the safest bet.
handler_order = 499
def __init__(self, cache=None, force_min=None):
self.cache = cache or default_cache
self.force_min = force_min # force_min (seconds) to bypass http headers, -1 forever, 0 never, -2 do nothing if not in cache
self.force_min = force_min
# Servers indicate how long they think their content is "valid".
# With this parameter (force_min, expressed in seconds), we can
# override the validity period (i.e. bypassing http headers)
# Special values:
# -1: valid forever, i.e. use the cache no matter what (and fetch
# the page online if not present in cache)
# 0: valid zero second, i.e. force refresh
# -2: same as -1, i.e. use the cache no matter what, but do NOT
# fetch the page online if not present in cache, throw an
# error instead
def load(self, url):
@ -422,6 +438,10 @@ class CacheHandler(BaseHandler):
return req
def http_open(self, req):
# Reminder of how/when this function is called by urllib2:
# If 'None' is returned, try your chance with the next-available handler
# If a 'resp' is returned, stop there, and proceed with 'http_response'
(code, msg, headers, data, timestamp) = self.load(req.get_full_url())
# some info needed to process everything
@ -444,6 +464,7 @@ class CacheHandler(BaseHandler):
# raise an error, via urllib handlers
headers['Morss'] = 'from_cache'
resp = addinfourl(BytesIO(), headers, req.get_full_url(), 409)
resp.msg = 'Conflict'
@ -462,14 +483,18 @@ class CacheHandler(BaseHandler):
return None
elif code == 301 and cache_age < 7*24*3600:
# "301 Moved Permanently" has to be long as we want (awesome HTTP specs), let's say a week (why not?)
# use force_min=0 if you want to bypass this (needed for a proper refresh)
# "301 Moved Permanently" has to be long as we want
# (awesome HTTP specs), let's say a week (why not?). Use force_min=0
# if you want to bypass this (needed for a proper refresh)
elif self.force_min is None and ('no-cache' in cc_list
or 'no-store' in cc_list
or ('private' in cc_list and not self.private_cache)):
# kindly follow web servers indications, refresh
# if the same settings are used all along, this section shouldn't be
# of any use, since the page woudln't be cached in the first place
# the check is only performed "just in case"
return None
elif 'max-age' in cc_values and int(cc_values['max-age']) > cache_age:
@ -484,7 +509,7 @@ class CacheHandler(BaseHandler):
# according to the www, we have to refresh when nothing is said
return None
# return the cache as a response
# return the cache as a response. This code is reached with 'pass' above
headers['morss'] = 'from_cache' # TODO delete the morss header from incoming pages, to avoid websites messing up with us
resp = addinfourl(BytesIO(data), headers, req.get_full_url(), code)
resp.msg = msg
@ -515,6 +540,8 @@ class CacheHandler(BaseHandler):
data =, resp.code, resp.msg, resp.headers, data, time.time())
# the below is only needed because of '' above, as we can't
# seek(0) on arbitraty file-like objects (e.g. sockets)
fp = BytesIO(data)
old_resp = resp
resp = addinfourl(fp, old_resp.headers, old_resp.url, old_resp.code)
@ -534,10 +561,14 @@ class CacheHandler(BaseHandler):
new.add_unredirected_header('Morss', 'from_304')
# create a "fake" new request to just re-run through the various
# handlers
return, timeout=req.timeout)
return None
return None # when returning 'None', the next-available handler is used
# the 'HTTPRedirectHandler' has no 'handler_order', i.e.
# uses the default of 500, therefore executed after this
https_request = http_request
https_open = http_open