Fix/quadratic backtracking in email scan - #91
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August 25, 2026 14:45
This change limits the length of the local part in the email regex to 64 characters (the maximum allowed). This solves the problem that `email_regex.findall(string)` takes time that grows quadratically with the length of the string.
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This change improves the asymptotic performance when parsing an e-mail with a very long
Receive:header from quadratic to linear.The constant factor is still pretty large; for example, parsing a Receive header of 1MB still takes ~2.5s on my machine. OTH before this change, it would have taken multiple minutes.
This is achieved by modifying the regex used to parse e-mail addresses to impose a maximum length of 128 characters on the local part of the e-mail address (the part before the @-sign). Legal e-mail addresses should not have local parts with more than 64 characters.