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pyfisch / httpdate

HTTP date parsing and formatting
Apache License 2.0
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Looser case parsing (Postel's Law)? #15

Open cbiffle opened 7 months ago

cbiffle commented 7 months ago

Hi! What's your feeling on accepting lowercase variations of the date format?

I'm currently using httpdate to parse and compare modified dates for resources in my webserver. Strictly speaking, the HTTP standard says that clients should send back the exact date I previously served them, but in practice I see many clients who don't. In cases where I can figure out what they mean, I'd like to be flexible to increase the chances of a 304 Not Modified. Thus my use of httpdate rather than an exact string compare.

However, I'm seeing clients in practice that send all headers lowercased, including the contents of if-modified-since. This means I receive a date that would be otherwise valid, except for letter case. httpdate's parser is strict and it rejects these dates. Per Postel's Law I'm going to modify the server to accept lowercase, and I'm trying to figure out if that means I need to fork this crate.

Thanks!

pyfisch commented 7 months ago

Hi! Thanks for raising this issue. RFC9111 notes that the Date format is case-sensitive but recommends that caches accept lowercased variants.

Although all date formats are specified to be case-sensitive, a cache recipient SHOULD match the field value case-insensitively.

https://www.rfc-editor.org/rfc/rfc9111.html#name-freshness

I'm glad to review a patch.