Mercurial > repos > shellac > sam_consensus_v3

annotate env/lib/python3.9/site-packages/cachecontrol/heuristics.py @ 0:4f3585e2f14b draft default tip

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"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"
author shellac
date Mon, 22 Mar 2021 18:12:50 +0000
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1 import calendar
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2 import time
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3
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4 from email.utils import formatdate, parsedate, parsedate_tz
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5
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6 from datetime import datetime, timedelta
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7
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8 TIME_FMT = "%a, %d %b %Y %H:%M:%S GMT"
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9
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10
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11 def expire_after(delta, date=None):
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12 date = date or datetime.now()
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13 return date + delta
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14
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15
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16 def datetime_to_header(dt):
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17 return formatdate(calendar.timegm(dt.timetuple()))
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18
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19
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20 class BaseHeuristic(object):
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21
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22 def warning(self, response):
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23 """
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24 Return a valid 1xx warning header value describing the cache
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25 adjustments.
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26
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27 The response is provided too allow warnings like 113
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28 http://tools.ietf.org/html/rfc7234#section-5.5.4 where we need
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29 to explicitly say response is over 24 hours old.
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30 """
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31 return '110 - "Response is Stale"'
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32
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33 def update_headers(self, response):
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34 """Update the response headers with any new headers.
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35
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36 NOTE: This SHOULD always include some Warning header to
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37 signify that the response was cached by the client, not
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38 by way of the provided headers.
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39 """
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40 return {}
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41
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42 def apply(self, response):
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43 updated_headers = self.update_headers(response)
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44
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45 if updated_headers:
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46 response.headers.update(updated_headers)
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47 warning_header_value = self.warning(response)
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48 if warning_header_value is not None:
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49 response.headers.update({'Warning': warning_header_value})
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50
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51 return response
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52
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53
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54 class OneDayCache(BaseHeuristic):
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55 """
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56 Cache the response by providing an expires 1 day in the
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57 future.
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58 """
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59 def update_headers(self, response):
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60 headers = {}
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61
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62 if 'expires' not in response.headers:
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63 date = parsedate(response.headers['date'])
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64 expires = expire_after(timedelta(days=1),
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65 date=datetime(*date[:6]))
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66 headers['expires'] = datetime_to_header(expires)
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67 headers['cache-control'] = 'public'
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68 return headers
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69
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70
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71 class ExpiresAfter(BaseHeuristic):
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72 """
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73 Cache **all** requests for a defined time period.
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74 """
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75
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76 def __init__(self, **kw):
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77 self.delta = timedelta(**kw)
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78
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79 def update_headers(self, response):
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80 expires = expire_after(self.delta)
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81 return {
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82 'expires': datetime_to_header(expires),
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83 'cache-control': 'public',
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84 }
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85
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86 def warning(self, response):
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87 tmpl = '110 - Automatically cached for %s. Response might be stale'
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88 return tmpl % self.delta
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89
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90
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91 class LastModified(BaseHeuristic):
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92 """
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93 If there is no Expires header already, fall back on Last-Modified
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94 using the heuristic from
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95 http://tools.ietf.org/html/rfc7234#section-4.2.2
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96 to calculate a reasonable value.
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97
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98 Firefox also does something like this per
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99 https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching_FAQ
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100 http://lxr.mozilla.org/mozilla-release/source/netwerk/protocol/http/nsHttpResponseHead.cpp#397
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101 Unlike mozilla we limit this to 24-hr.
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102 """
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103 cacheable_by_default_statuses = set([
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104 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, 501
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105 ])
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106
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107 def update_headers(self, resp):
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108 headers = resp.headers
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109
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110 if 'expires' in headers:
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111 return {}
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112
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113 if 'cache-control' in headers and headers['cache-control'] != 'public':
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114 return {}
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115
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116 if resp.status not in self.cacheable_by_default_statuses:
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117 return {}
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118
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119 if 'date' not in headers or 'last-modified' not in headers:
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120 return {}
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121
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122 date = calendar.timegm(parsedate_tz(headers['date']))
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123 last_modified = parsedate(headers['last-modified'])
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124 if date is None or last_modified is None:
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125 return {}
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126
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127 now = time.time()
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128 current_age = max(0, now - date)
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shellac
parents:
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129 delta = date - calendar.timegm(last_modified)
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shellac
parents:
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130 freshness_lifetime = max(0, min(delta / 10, 24 * 3600))
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shellac
parents:
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131 if freshness_lifetime <= current_age:
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shellac
parents:
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132 return {}
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shellac
parents:
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133
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shellac
parents:
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134 expires = date + freshness_lifetime
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shellac
parents:
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135 return {'expires': time.strftime(TIME_FMT, time.gmtime(expires))}
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shellac
parents:
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136
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shellac
parents:
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137 def warning(self, resp):
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shellac
parents:
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138 return None