version 1 .
embeddedType EntityRef.Cap .

# ---------------------------------------------------------------------------
# Protocol at *gatekeeper* entities

# Assertion. Gatekeeper will attempt to resolve `step`, responding with a `Resolved` to
# `observer`.
Resolve = <resolve @step Step @observer #:Resolved> .
Resolved = <accepted @responderSession #:any> / Rejected .
Step = <<rec> @stepType symbol [@detail any]> .

# ---------------------------------------------------------------------------
# Protocol at dataspaces *associated* with gatekeeper entities

# ## Handling `Resolve` requests
#
# When the gatekeeper entity receives a `Resolve` assertion (call it R1), it
#
#  1. asserts a `Resolve` (call it R2) into its associated dataspace that
#     is the same as R1 except it has a different `observer`; and
#
#  2. observes a `Bind` with `description` matching the `step` of R1/R2
#     according to `stepType` (e.g. treatment of SturdyStepType is not the
#     same as treatment of NoiseStepType).
#
# Normally, an appropriate `Bind` is expected to exist. If the gatekeeper
# sees the `Bind` first, it takes the `target` from it and does whatever
# `stepType` mandates before replying to R1's observer.
#
# However, if a `Resolved` is asserted to R2's observer before a `Bind`
# appears, that resolution is relayed on to R1's observer directly, be it
# positive or negative, and the gatekeeper stops waiting for a `Bind`.
#
# This way, entities can keep an eye out for `Resolve` requests that will
# never complete, and answer `Rejected` to them even when no matching
# `Bind` exists. Entities could also use `Resolve` requests to synthesize a
# `Bind` in a "just-in-time" fashion.
#
# ## General treatment of `Bind` assertions
#
# When the gatekeeper sees a `Bind`, independently of any potential
# `Resolve` requests, it computes an appropriate PathStep from
# `description` pointing at `target`, and responds with a `Bound` to
# `observer` (if supplied).
#
Bind = <bind @description Description @target #:any @observer BindObserver> .
Description = <<rec> @stepType symbol [@detail any]> .
BindObserver = @present #:Bound / @absent #f .
Bound = <bound @pathStep PathStep> / Rejected .

# ---------------------------------------------------------------------------
# Protocol at client-side dataspaces, for resolution utilities

# Assertion. In response to observation of this with appropriate captures/wildcards in `addr`
# and `resolved`, respondent will follow `route.pathSteps` starting from one of the
# `route.transports`, asserting `ResolvePath` with the final `Resolved` as well as the selected
# transport `addr` and a `control` for it.
ResolvePath = <resolve-path @route Route @addr any @control #:TransportControl @resolved Resolved> .

TransportConnection = <connect-transport @addr any @control #:TransportControl @resolved Resolved> .
ResolvedPathStep = <path-step @origin #:Resolve @pathStep PathStep @resolved Resolved> .
PathStep = <<rec> @stepType symbol [@detail any]> .

# A `Route` describes a network path that can be followed to reach some target entity.
#
# It starts with a set of zero or more possible non-Syndicate `transports`. These could be
# `transportAddress.Tcp` values or similar. They are just suggestions; it's quite possible the
# endpoint is reachable by some means not listed. The network outside Syndicate is, after all,
# pretty diverse! In particular, *zero* `transports` may be provided, in which case some
# out-of-band means has to be used to make that first connection.
#
# The `transports` give instructions for contacting the first entity in the `Route` path. Often
# this will be a `gatekeeper`, or a `noise` protocol endpoint, or both. Occasionally, it may
# even be the desired target entity. Subsequent `pathSteps` describe how to proceed from the
# initial entity to the target.
#
# (`transports` should by rights be a set, not a sequence, but that opens up a Can Of Worms
# regarding dataspace patterns including literal sets that I can't deal with right now.)
Route = <route @transports [any ...] @pathSteps PathStep ...> .

TransportControl = ForceDisconnect .
ForceDisconnect = <force-disconnect> .

# ---------------------------------------------------------------------------

Rejected = <rejected @detail any> .