Before this patch, the TLS verification fails with an exception if the client uses a fully-qualified domain name with a trailing dot, like https://github.com./ :

aiohttp.client_exceptions.ClientConnectorCertificateError: Cannot connect to host github.com.:443 ssl:True
[SSLCertVerificationError: (1, "[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: Hostname mismatch,
certificate is not valid for 'github.com.'. (_ssl.c:1051)")]

The reason is that TLS certificates do not contain the trailing dot, as per RFC 6066:

"HostName" contains the fully qualified DNS hostname of the server,
as understood by the client. The hostname is represented as a byte
string using ASCII encoding without a trailing dot.

This change makes aiohttp strip the trailing dot for TLS context and Host header, where trailing dots are not present.
For DNS resolution, we include the trailing dot as it signifies a fully-qualified domain name (FQDN).
DNS lookups of FQDNs are faster as the resolver does not need to check DNS search path, like for relative DNS names.

This effectively allows clients to connect to server if URL has dot at the end of the hostname, e.g. `https://example.com./.

Fixes #3636
PR #7364

Co-authored-by: Sviatoslav Sydorenko [email protected]
(cherry picked from commit d84fcf7)

What do these changes do?

Backport #7364 into 3.9

Are there changes in behavior for the user?

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
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