Discovery: Scan stream includes services advertised by the same discovery client.

[aghassemi]

Maybe we should excludes services that are advertised by the same discovery client? I expect the common case to be the advertiser ignoring their own advertisements since they would be handling those differently than services from others.

@bjornick @asadovsky @jhahn21

[jhahn21]

This is on our todo: https://docs.google.com/document/d/1RkN5ndOfVh728OHXEb4fYaXL1hWaHBEQPrhnBMdT5og/edit#heading=h.ide9lpycot1z

But it's not clear how to identify the same discovery client, since there may be multiple clients for a single discovery instance in a device.

@asimshankar

[asadovsky]

A couple ideas:

• Provide a client library, where each client stub instance stores a session id which is included in the discovery payload
• If you don't want to force clients to instantiate a stub object, you could use the process pid or somesuch as an implicit session id

(Of course, each of these has drawbacks.)

[jhahn21]

I was thinking a similar way like putting a session id to context.

myCtx = context.WithNewSession(ctx)
(or myCtx = context.WithSession(ctx, sessionId) ?)
...

ctxForAd = context.WithCancel(myCtx)
discovery.Advertise(ctxForAd, ...)
...

ctxForScan = context.WithCancel(myCtx)
discovery.Scan(ctxForScan, ...)  // Scan will filter out all the advertisements from the same session
...

But I'm not sure whether we want to put this WithSession() into context (@mattr-google) :), although I think it's clearer than providing as a discovery util function.

[monopole]

My 'moments' app ignores its own ads by storing the ad's ID in a table when advertising is on, and consulting that table on the scan side - dropping self adverts on the floor.

Ken's 'syncslides' app sends a "device UUID" as an advertising attribute, and uses that to drop the ad on the floor on the scan side.

First option is more bookkeeping, the second option adds the string encoding of a 128 bit ID to each ad.

Would like this to be opaque, e.g. my app makes an advertiser, and from it creates a scanner 'child' that knows to ignore ads made by its parent. An app that made a scanner with no parent wouldn't have this built in filter thingie.

[jhahn21]

I'm not sure yet whether it's a good idea to add WithSession to context until we have more general use cases for it. So I'll add WithSession() to discovery.T for now like

ctx, session = discovery.WithNewSession(ctx)

Please let me know if you have any better idea.

[jhahn21]

And we also have Service and Mojo interface for discovery, which have no context. So, we need to pass a SessionId or something like that to Advertise() and Scan()