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Fix documentation around Expires header #1909

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Fix documentation around Expires header #1909

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330c039
Refer to current RFC in documentation
menelaos Feb 26, 2026
fddd347
Fix documentation for `neverExpires`
menelaos Feb 26, 2026
994d670
Update ChangeLog.md
menelaos Feb 26, 2026
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4 changes: 4 additions & 0 deletions yesod-core/ChangeLog.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,9 @@
# ChangeLog for yesod-core

## Unreleased

* Fix documentation around `Expires` header [#1909](https://github.com/yesodweb/yesod/pull/1909)

## 1.6.29.1

* Fix compilation error for text >= 2.1.2 [#1905](https://github.com/yesodweb/yesod/pull/1905)
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4 changes: 2 additions & 2 deletions yesod-core/src/Yesod/Core/Handler.hs
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Expand Up @@ -889,8 +889,8 @@ cacheSeconds i = setHeader "Cache-Control" $ T.concat
, ", public"
]

-- | Set the Expires header to some date in 2037. In other words, this content
-- is never (realistically) expired.
-- | Set the Expires header to a date one year from now. In other words, this
-- content is never (realistically) expired.
neverExpires :: MonadHandler m => m ()
neverExpires = do
setHeader "Expires" . rheMaxExpires =<< askHandlerEnv
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2 changes: 1 addition & 1 deletion yesod-core/src/Yesod/Core/Internal/Util.hs
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Expand Up @@ -47,7 +47,7 @@ formatRFC822 :: UTCTime -> T.Text
formatRFC822 = T.pack . formatTime defaultTimeLocale "%a, %d %b %Y %H:%M:%S %z"

{- | Get the time 365 days from now in RFC 1123 format. For use as an expiry
date on a resource that never expires. See RFC 2616 section 14.21 for details.
date on a resource that never expires. See RFC 9111 section 5.3 for details.
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@menelaos menelaos Feb 26, 2026

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RFC 2616 has been obsoleted by RFC 7234, which in turn has been obsoleted by RFC 9111.

Side note:
Initially, the expiry date was set to the year 2037. This was changed in #870.

The newer standard theoretically permits longer lifetimes but I think it doesn't hurt to keep the current behaviour. The relevant passage:

Historically, HTTP required the Expires field value to be no more than a year in the future. While longer freshness lifetimes are no longer prohibited, extremely large values have been demonstrated to cause problems (e.g., clock overflows due to use of 32-bit integers for time values), and many caches will evict a response far sooner than that.

-}
getCurrentMaxExpiresRFC1123 :: IO T.Text
getCurrentMaxExpiresRFC1123 = fmap (formatRFC1123 . addUTCTime (60*60*24*365)) getCurrentTime
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