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"""Key-Value store server.
The request takes "key=" and "value=" URL parameters. The key must be UUID
generated by token().
- When only the "key=" is specified, serves a 200 response whose body contains
the stored value specified by the key. If the stored value doesn't exist,
serves a 200 response with an empty body.
- When both the "key=" and "value=" are specified, stores the pair and serves
a 200 response without body.
"""
def main(request, response):
key = request.GET.get(b"key")
value = request.GET.get(b"value")
# Store the value.
# We have two ways to check the truthiness of `value`:
# 1. `if value`
# 2. `if value != None`
# While (1) is the most intuitive, we actually need (2), which is a looser
# check. We need the looser check so that if the URL contains `&value=` to
# set the value equal to the empty string (a case we need to support), this
# condition still evaluates to true and we enter this branch.
if value != None:
# We opted for (2) above which is the looser of the truthiness tests
# that lets empty strings into this branch. So you might think that when
# the URL contains `&value=`, then the `value` variable here would be
# equal `""`, but instead it equals the empty byte string. If you just
# store that empty byte string into the stash and retrieve it later, you
# actually get <Not set> because it doesn't recognize the empty byte
# string as a real value, so we instead have to override it to the empty
# normal string, and then we can store it for later use. This is
# because we have to support storage and retrieval of empty strings.
if type(value) is bytes and value == b'':
value = ""
request.server.stash.put(key, value)
return (200, [], b"")
# Get the value.
data = request.server.stash.take(key)
if not data and data != "":
return (200, [], b"<Not set>")
return (200, [], data)