imaplib: search/sort/thread don't encode criteria to the declared CHARSET #153494

IMAP4.search(charset, *criteria) (and sort, thread, and the uid SORT/THREAD variants) send a CHARSET <name> token but serialize the criteria strings with the connection encoding (bytes(arg, self._encoding), ASCII by default). So the declared charset and the actual byte-encoding of the criteria are decoupled: a non-ASCII str criterion with a charset raises UnicodeEncodeError, and the only way to search non-ASCII text today is to pass the criteria as pre-encoded bytes and remember to match them to the charset by hand.

This is a Python 2 legacy. The module was written when str was 8-bit and search criteria were byte strings passed straight through to the socket -- no encoding step was needed, and CHARSET was just an opaque label forwarded to the server. Under Python 3 that model leaves str criteria unencoded (or failing), so the CHARSET argument no longer does what it appears to.

str criteria should be encoded to the declared charset. bytes criteria -- necessary for server-only charsets that Python has no codec for (e.g. the ones this module has always forwarded blindly) -- should pass through unchanged.

Linked PRs

• gh-153494: Encode imaplib search criteria to the declared CHARSET #153495