44 lines
1.4 KiB
Plaintext
44 lines
1.4 KiB
Plaintext
This is the description of the regex used previously for topic/subscription
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matching. It is reproduced here for posterity.
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When a message is ready to be published at the broker, we need to check all
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of the subscriptions to see which ones the message should be sent to. This
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would be easy without wildcards, but requires a bit more work with them.
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The regex used to do the matching is of the form below for a topic of a/b/c:
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^(?:(?:(a|\+)(?!$))(?:(?:/(?:(b|\+)(?!$)))(?:(?:/(?:c|\+))|/#)?|/#)?|#)$
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In general, we're matching (a or +) followed by (the next levels of
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hierarchy or #).
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More specifically, all the levels of hierarchy must match, unless the last
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level is #.
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^(?: # Must start at beginning of string
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(?: # (Level 1 hierarchy)
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(a|\+)(?!$) # Match a or +, but only if not EOL.
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) # AND
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(?:
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(?: # (Level 2 hierarchy)
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/ # Match /
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(?: # AND
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(b|\+)(?!$) # Match b or +, but only if not EOL.
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)
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) # AND
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(?:
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(?: # (Level 3 hierarchy)
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/ # Match /
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(?: # AND
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c|\+ # Match c or +.
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)
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)
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| # OR (instead of level 3)
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/# # Match /# at level 3
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)? # Level 3 exist 1/0 times
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| # OR (instead of level 2)
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/# # Match /# at level 2
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)? # Level 2 exist 1/0 times
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| # OR (instead of level 1)
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# # Match # at level 1
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)$ # Must end on EOL.
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