Original text:
single underlying transport connection where possible.  This is not a strict requirement.  The default is to not have this option. <del> 5.2.6. </del>  Type: Boolean

Reviewer comments:
This closed As we have no methods on a connection object that query properties, cansend/canreceive also became connection properties. As with all the other connection properties, these are indeed a little underspecified. I want to keep it that way till we fix it for all connection properties with and
Aehm… that comes surprising – NAME why didn't you bring this up in ? Do you think this pull-request is the right place to discuss this issue? I would prefer we merge it now and make a new issue for the question whether the uni-directional connection should be more reflected in the connection. I am not particularly found on keeping it a selection property but would like to have the concept of unidirectional connections rather sooner than later. Our consensus in was that unidirectional connection should use the same abstraction for QUIC unidirectional streams, multicast sources/sinks, and half-closed connections – despite they are constructed in completely different ways. The Selection property is just for the QUIC style ones…

Aehm… that comes surprising – NAME why didn't you bring this up in ? Do you think this pull-request is the right place to discuss this issue? Happy to move the discussion back over to the issue if you like. Will continue the thread here for now though since you've got points to address below. fine, but keep open then, because adding the selection property is possibly-necessary but definitely-not-sufficient to fully address unidirectional connection semantics. good, I agree with this. then I'm confused why this PR purports to since it only addresses part of the issue...?
NAME agreed. The question (and discussion) was about support for including some support for unidirectional connections (with focus on QUIC and half-closed), but omitted details on multicast, as this has not laned yet. So indeed, this pull-requests does everything requested by , but does not fully capture the topic. I will move the open issues (Multicast support, is the Selection Property enough, find some place for more explanation of Uni/Bidi Streams) to once this PR is merged.
In Section 9 – "Setting and Querying of Connection Properties" – the properties of an established connection and path are heavily underspecified. Should be fixed along with .
I'm working on this issue within our pull request for , using the terminology as simplified there. For Section 9, I'm proposing the following: An application can query Connection Properties on a connection. Connection Properties include the status of the connection and whether it is possible to send and to receive data on it. (One of them might not be possible, e.g., in a unidirectional connection.) Additionally, Connection Properties include the Connection's Transport Properties. Transport Properties include Selection Properties, so the application can know which Protocol Selection Properties had been specified, and which ones are actually supported by the protocol that has been chosen. For Establishing connections (i.e., we are not done racing yet, the final protocols have not been selected yet), the application gets the Selection Properties that had been specified on the Preconnection earlier. For Established, Closing, or Closed connections (i.e., the protocols have been selected), the application learns whether the Selection Properties are actually provided by the selected protocols. For example, if the application specified earlier, "Control Checksum Coverage: Prefer", now it will get "Control checksum coverage: True", indicating that on this connection it can indeed control the checksum coverage. Transport Properties also include Protocol Properties (Generic and Specific). These Protocol Properties can still be modified by the application. Basically, Protocol Properties are the only thing that the application can still set, everything else it can only query at this point. Finally, the application can query properties of the path. Not sure how well we have to specify them, probably this part will be implementation-specific just like, e.g., the Interface Instance or Type. Does everyone agree, or is there anything to discuss here? For me this is not a big change, it's just putting what was already there in terms of . The only thing I'm wondering if whether the Protocol Selection Properties of the finally chosen protocols are still "Selection Properties", as the selection is already done. That's why they were called "Transport Features" before, but now I want less terms and they're almost the same thing...
OK - so I commented on these things before - but in these things I think I agree. I'd personally prefer to keep the features as attributes implemented in the transport (etc) and the properties as the things requested. Indeed this begs the question about what to call the resulting transport when you selected properties and now get a transport. I think still calling them (for consistency) properties seems really good to me. :-).
As QUIC has unidirectional streams, we might want to be able to accommodate them in our transport API. Do we want to handle them fundamentally different from a half-closed connection? This should match the decisions made in .
Side note: we don't support half-closed connections to begin with. As for unidirectional streams, is this the final decision in QUIC's design, or might it change? I'd suggest postponing this until we can be sure.
NAME regarding half-closed connections: we don't have any top-level state in the connection for being half-closed. However, being able to express that a message is final in a given direction when sending allows the same functionality. As I've discussed before, we absolutely need the ability to express sending a TCP FIN, but I whole-heartedly agree it doesn't need to be a top level concept. I think this is somewhat different from half-closing, since a unidirectional stream never allows sending on one end. You could imagine that it is a connection object that returns an error if you ever try to send on it, etc. If you wanted it to look like half-closing, you could open a connection (stream), and then mark it complete in a direction immediately? But that's a bit odd.
All ok, I agree with your suggestion to fin-mark a message
I agreee with NAME regarding half-closed. My suggestion is to explicitly state that connections can be uni- or bi-directional and to add a method to query that (cansend / canrecv). This aligns nicely with final messages after which can_send becomes false. I can do a PR for that.
Thanks! I like this
Still missing unidirectional stream for multicast. – please continue discussion of multicast aspects in The connection properties (can send/receive data) are still a little under-specified - please discuss in details in – we should fix this together with .
We need unidirectional connections. You know, for multicast. And ICN. And unidirectional streaming protocols.
This is a dup of , which has more discussion
I am re-opening this ticket as only dealt with unidirectional streams in unicast context (added with PR ): Current status: The current model for unidirectional streams supports half-closed connections and QUIC style unidirectional streams so far. We don't know yet whether it is sufficient to have canread/canwrite property on the connection level to model unidirectional connections We don't have pre-connection methods to create multicast sessions yet
there's a selection property for this, tagged discuss, which we haven't discussed yet. I'm moving this down to the appendix as part of my restructuring in my work on
If help is still wanted here, I'm maybe up for an attempt or 2 at adding multicast support. Has there been some prior discussion I can review about rough ideas on pre-connection methods for multicast sessions, or should I just try making something up?

ok, with the caveat that we need to keep multicast as an open issueLGTM About the multicast concern: I agree that it would be good if this could function for multicast reception too, and I couldn't tell if this is suitable for multicast. I suspect that multicast support is much harder anyway - see RFC 3678... so for now, this is a good step forward IMO, and let's discuss how this relates to multicast when we see a concrete text proposal that addresses it.

Revised text:
single underlying transport connection where possible.  This is not a strict requirement.  The default is to not have this option.  <ins> 5.2.7. </ins> Type: Boolean