Client streaming methods should send routing headers

[busunkim96]

Clients streaming methods should send routing headers on the initial RPC that opens the stream. Field headers are currently ignored for these methods
https://github.com/googleapis/gapic-generator-python/blob/eaa6f3622ccf3f51a73635d8190ae2a07f036d89/gapic/templates/%25namespace/%25name_%25version/%25sub/services/%25service/client.py.j2#L329-L341

As far as I know this isn't currently an issue for any libraries on the microgenerator.

[arithmetic1728]

any updates as we are out of slo

[hkdevandla]

@busunkim96 , can you clarify why this isn't an issue for libraries using micro-generator?

is this a feature gap between micro-generator and the legacy (monolith) that we need to support i.e adding routing headers to the streaming requests? If not, we should mark this bug as feature request or mark with appropriate priority so we can fix it. Please advice. Thanks!

P.S: This issue triggered OO-SLO.

[busunkim96]

@hkdevandla None of the currently published APIs have a streaming method that requires a routing header be sent.

I opened this after discussion googleapis/gapic-generator-python#443 which added routing headers for all the http verbs. The current behavior may be correct, but I opened this to make sure this comment was followed up on:

I was under the impression that headers for streaming methods don't make a lot of sense because they're not tightly bound to http semantics. If that's not correct, then I think we would need to ask someone who knows better.

Originally posted by @software-dov in googleapis/gapic-generator-python#443 (comment)

[hkdevandla]

Thanks @busunkim96, making this as P3 in that case if it is not an issue but needs some follow up/investigation.