Code that relies on gRPC metadata formatting should be fixed

[dfawley]

Bug report criteria

• This bug report is not security related, security issues should be disclosed privately via etcd maintainers.
• This is not a support request or question, support requests or questions should be raised in the etcd discussion forums.
• You have read the etcd bug reporting guidelines.
• Existing open issues along with etcd frequently asked questions have been checked and this is not a duplicate.

What happened?

This code:

etcd/client/v3/watch.go

Lines 1038 to 1043 in 21e5876

	func streamKeyFromCtx(ctx context.Context) string {
	if md, ok := metadata.FromOutgoingContext(ctx); ok {
	return fmt.Sprintf("%+v", md)
	}
	return ""
	}

expects consistent ordering from gRPC as well as expecting all metadata to be included.

However, metadata can contain PII, so we would like to change gRPC's behavior to not print any potential PII. grpc/grpc-go#7395

What did you expect to happen?

Code correctness to not rely upon gRPC's metadata.MD.String method.

How can we reproduce it (as minimally and precisely as possible)?

Look at the code.

Anything else we need to know?

No response

Etcd version (please run commands below)

master

Etcd configuration (command line flags or environment variables)

No response

Etcd debug information (please run commands below, feel free to obfuscate the IP address or FQDN in the output)

No response

Relevant log output

No response

[dfawley]

One trivial fix would be forcing the Go builtin formatting for the raw, underlying map type:

return fmt.Sprint(map[string][]string(md))

[ahrtr]

Thanks @dfawley for raising this ticket. We should raise it long time ago.

Please read clarification below In case anyone gets confused.

• fmt.Sprintf("%+v", md) will call (md MD) String(), which iterates over a map, but the iteration order over maps is not specified and is not guaranteed to be the same from one iteration to the next.
• Golang fmt package guarantees that Maps are printed in a consistent order, sorted by the values of the keys.

[ahrtr]

• Golang fmt package guarantees that Maps are printed in a consistent order, sorted by the values of the keys.

It's exactly the reason why #18303 (comment) can resolve this issue.

[JabulaniNgcobo]

#18308

[JabulaniNgcobo]

#18289

[ahrtr]

@mohamedawnallah Please update changelog for both 3.5 and 3.4. thx

[mohamedawnallah]

@ahrtr Sounds good! Updated the change log for releases 3.4 and 3.5 in the following PRs:

• CHANGELOG-3.4.md: CHANGELOG/CHANGELOG-3.4.md: update changelog for gRPC metadata printing #18316
• CHANGELOG-3.5.md: CHANGELOG/CHANGELOG-3.5.md: update changelog for gRPC metadata printing #18317

[ahrtr]

@ahrtr Sounds good! Updated the change log for releases 3.4 and 3.5 in the following PRs:

• CHANGELOG-3.4.md: CHANGELOG/CHANGELOG-3.4.md: update changelog for gRPC metadata printing #18316
• CHANGELOG-3.5.md: CHANGELOG/CHANGELOG-3.5.md: update changelog for gRPC metadata printing #18317

Thanks. Actually one PR should be good, there is no need to raise two separate PRs to update changelog. But not a big problem, so I won't insist on it.

[mohamedawnallah]

Thanks for the clarification! Combining into a single PR makes sense. I'll follow that approach in the future. Thanks for the flexibility on this one!

[ahrtr]

All done!

Thanks @mohamedawnallah and @dfawley

[dfawley]

Thank you for the quick fixes!