The CLIENT_SETUP and SERVER_SETUP messages are the first messages exchanged
by the client and the server; they allow the endpoints to establish the mutually
supported version and agree on the initial configuration before any objects are
exchanged. It is a sequence of key-value pairs called Setup parameters; the
semantics and format of which can vary based on whether the client or server is
sending. To ensure future extensibility of MOQT, endpoints MUST ignore unknown
setup parameters. TODO: describe GREASE for those.
The wire format of the Setup messages are as follows:
CLIENT_SETUP Message {
Type (i) = 0x40,
Length (i),
Number of Supported Versions (i),
Supported Version (i) ...,
Number of Parameters (i) ...,
Setup Parameters (..) ...,
}
SERVER_SETUP Message {
Type (i) = 0x41,
Length (i),
Selected Version (i),
Number of Parameters (i) ...,
Setup Parameters (..) ...,
}
The available versions and Setup parameters are detailed in the next sections.
8.2.1. Versions
MoQ Transport versions are a 32-bit unsigned integer, encoded as a varint. This version of the specification is identified by the number 0x00000001. Versions with the most significant 16 bits of the version number cleared are reserved for use in future IETF consensus documents.
The client offers the list of the protocol versions it supports; the server MUST reply with one of the versions offered by the client. If the server does not support any of the versions offered by the client, or the client receives a server version that it did not offer, the corresponding peer MUST close the session.
[[RFC editor: please remove the remainder of this section before publication.]]
The version number for the final version of this specification (0x00000001), is reserved for the version of the protocol that is published as an RFC. Version numbers used to identify IETF drafts are created by adding the draft number to 0xff000000. For example, draft-ietf-moq-transport-13 would be identified as 0xff00000D.
8.2.2. Setup Parameters
8.2.2.1. PATH
The PATH parameter (Parameter Type 0x01) allows the client to specify the path of the MoQ URI when using native QUIC ([QUIC]). It MUST NOT be used by the server, or when WebTransport is used. If the peer receives a PATH parameter from the server, or when WebTransport is used, it MUST close the connection. It follows the URI formatting rules [RFC3986].
When connecting to a server using a URI with the "moqt" scheme, the
client MUST set the PATH parameter to the path-abempty portion of the
URI; if query is present, the client MUST concatenate ?, followed by
the query portion of the URI to the parameter.
8.2.2.2. MAX_SUBSCRIBE_ID
The MAX_SUBSCRIBE_ID parameter (Parameter Type 0x02) communicates an initial value for the Maximum Subscribe ID to the receiving subscriber. The default value is 0, so if not specified, the peer MUST NOT create subscriptions.