version 1 .
embeddedType EntityRef.Cap .

# https://noiseprotocol.org/

# ---------------------------------------------------------------------------
# Binding and connection

NoiseStepType = =noise .

# In a gatekeeper.Step, use ServiceSelector as detail.
NoiseStepDetail = ServiceSelector .

# In a gatekeeper.PathStep, use a NoiseSpec as detail.
NoisePathStepDetail = NoiseSpec .

# In a gatekeeper.Description, use a NoiseServiceSpec as detail.
NoiseDescriptionDetail = NoiseServiceSpec .

# ---------------------------------------------------------------------------
# Specification of target and bind addresses

ServiceSelector = any .

NoiseSpec = {
  # The `serviceSelector` to use in a `NoiseStep` for `gatekeeper.Resolve`.
  service: ServiceSelector,
  # The responder's static public key. If not required (uncommon!), supply the empty ByteString.
  key: bytes,
}
& @protocol NoiseProtocol
& @preSharedKeys NoisePreSharedKeys
.

NoiseServiceSpec = @base NoiseSpec & @secretKey SecretKeyField .
SecretKeyField = @present { secretKey: bytes } / @invalid { secretKey: any } / @absent {} .

# If absent, a default of DefaultProtocol is used. Most services will speak the default.
NoiseProtocol = @present { protocol: string } / @invalid { protocol: any } / @absent {} .
DefaultProtocol = "Noise_NK_25519_ChaChaPoly_BLAKE2s" .

# If present, Noise pre-shared-keys (PSKs) are drawn from the sequence as required; if the
# sequence is exhausted or not supplied, an all-zeros key is used each time a PSK is needed.
NoisePreSharedKeys = @present { preSharedKeys: [bytes ...] } / @invalid { preSharedKeys: any } / @absent {} .

# ---------------------------------------------------------------------------
# Handshaking and running a session

# 1. initiator asserts <resolve <noise ServiceSelector> #:A> at Gatekeeper
# 2. gatekeeper asserts <accepted #:B> at #:A
# 3. initiator asserts <initiator #:C> at #:B and then sends `Packet`s to #:B
# 4. responder sends `Packet`s to #:C
#
# Sessions begin with introduction of initiator (#:C) and responder (#:B) to each other, and
# then proceed by sending `Packet`s (from #:C) to #:B and (from #:B) to #:C according to
# the Noise protocol definition. Each `Packet` represents a complete logical unit of
# communication; for example, a complete Turn when layering the Syndicate protocol over Noise.
# Note well the restriction on Noise messages: no individual complete packet or packet fragment
# may exceed 65535 bytes (N.B. not 65536!). When `fragmented`, each portion of a `Packet` is a
# complete Noise "transport message"; when `complete`, the whole thing is likewise a complete
# "transport message".
#
# Retraction of the `Initiator` ends the session from the initiator-side; retraction of the
# `<accepted ...>` assertion ends the session from the responder-side.

SessionItem = Initiator / Packet .
# Assertion
Initiator = <initiator @initiatorSession #:Packet> .
# Message
Packet = @complete bytes / @fragmented [bytes ...] .

# When layering Syndicate protocol over noise,
#
#  - the canonical encoding of the serviceSelector is the prologue
#  - protocol.Packets MUST be encoded using the machine-oriented Preserves syntax
#  - zero or more Turns are permitted per noise.Packet
#  - each Turn must fit inside a single noise.Packet (fragment if needed)
#  - payloads inside a noise.Packet may be padded at the end with byte 0x80 (128), which
#    encodes `#f` in the machine-oriented Preserves syntax.
#
# In summary, each noise.Packet, once (reassembled and) decrypted, will be a sequence of zero
# or more machine-encoded protocol.Packets, followed by zero or more 0x80 bytes.
.