Default exchange in v3 documentation

[andreleblanc11]

In v2, when exchange is omitted from a config it resolves to xpublic -> https://github.com/MetPX/sarracenia/blob/v2_stable/doc/sr_subscribe.1.rst#exchange-name-default-xpublic-and-exchange_suffix

In v3, the behaviour is a bit different.
But the v3 docs don't reflect this, and states that it also resolves to xpublic
https://metpx.github.io/sarracenia/Reference/sr3_options.7.html#exchange-name-default-xpublic-and-exchangesuffix

It's only when a broker user isn't specified or when the user is anonymous that xpublic is defaulted.

sarracenia/sarracenia/config/__init__.py

Lines 1362 to 1374 in a3f30e2

	def _resolve_exchange(self):
	"""
	based on the given configuration, fill in with defaults or guesses.
	sets self.exchange.
	"""
	if not hasattr(self, 'exchange') or self.exchange is None:
	#if hasattr(self, 'post_broker') and self.post_broker is not None and self.post_broker.url is not None:
	# self.exchange = 'xs_%s' % self.post_broker.url.username
	#else:
	if not hasattr(self.broker.url,'username') or ( self.broker.url.username == 'anonymous' ):
	self.exchange = 'xpublic'
	else:
	self.exchange = 'xs_%s' % self.broker.url.username

[petersilva]

I remember thinking about this for a long time... I can't recall if the change of default is an intentional change or a bug... have to go rummage through old logs and docs.

obviously:

• this arises when converting... we could have sr3 convert add an exchange directive to make the conversion result reflect the v2 intent.
• we could change the default in sr3.

dunno which to do atm...

[andreleblanc11]

I think what we set now makes sense. Most client will be pulling data through the anonymous user so performing an sr3 convert and omitting the exchange would still be fine.

Some other clients did specify other broker users but would still not specify the exchange in v2. I think for that case using convert to reflect v2 behavior would be the way to go.