mirror of
https://github.com/chubin/wttr.in
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101 lines
2.7 KiB
Python
101 lines
2.7 KiB
Python
"""
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LRU-Cache implementation for formatted (`format=`) answers
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"""
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import datetime
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import re
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import time
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import os
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import hashlib
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import pytz
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import pylru
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from globals import LRU_CACHE
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CACHE_SIZE = 10000
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CACHE = pylru.lrucache(CACHE_SIZE)
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# strings longer than this are stored not in ram
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# but in the file cache
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MIN_SIZE_FOR_FILECACHE = 80
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def _update_answer(answer):
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def _now_in_tz(timezone):
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return datetime.datetime.now(pytz.timezone(timezone)).strftime("%H:%M:%S%z")
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if "%{{NOW(" in answer:
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answer = re.sub(r"%{{NOW\(([^}]*)\)}}", lambda x: _now_in_tz(x.group(1)), answer)
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return answer
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def get_signature(user_agent, query_string, client_ip_address, lang):
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"""
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Get cache signature based on `user_agent`, `url_string`,
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`lang`, and `client_ip_address`
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"""
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timestamp = int(time.time() / 1000)
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signature = "%s:%s:%s:%s:%s" % \
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(user_agent, query_string, client_ip_address, lang, timestamp)
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print(signature)
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return signature
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def get(signature):
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"""
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If `update_answer` is not True, return answer as it is
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stored in the cache. Otherwise update it, using
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the `_update_answer` function.
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"""
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value = CACHE.get(signature)
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if value:
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if value.startswith("file:"):
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sighash = value[5:]
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value = _read_from_file(signature, sighash=sighash)
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if not value:
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return None
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return _update_answer(value)
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return None
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def store(signature, value):
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"""
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Store in cache `value` for `signature`
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"""
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if len(value) < MIN_SIZE_FOR_FILECACHE:
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CACHE[signature] = value
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else:
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sighash = _store_in_file(signature, value)
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CACHE[signature] = "file:%s" % sighash
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return _update_answer(value)
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def _hash(signature):
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return hashlib.md5(signature.encode("utf-8")).hexdigest()
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def _store_in_file(signature, value):
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"""Store `value` for `signature` in cache file.
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Return file name (signature_hash) as the result.
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"""
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signature_hash = _hash(signature)
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filename = os.path.join(LRU_CACHE, signature_hash)
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if not os.path.exists(LRU_CACHE):
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os.makedirs(LRU_CACHE)
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with open(filename, "w") as f_cache:
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f_cache.write(value)
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return signature_hash
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def _read_from_file(signature, sighash=None):
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"""Read value for `signature` from cache file,
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or return None if file is not found.
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If `sighash` is specified, do not calculate file name
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from signature, but use `sighash` instead.
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"""
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signature_hash = sighash or _hash(signature)
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filename = os.path.join(LRU_CACHE, signature_hash)
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if not os.path.exists(filename):
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return None
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with open(filename, "r") as f_cache:
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return f_cache.read()
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