Module draft20 

MoQT wire codec for draft-20.

Key changes from draft-19:

• FETCH (0x16) is rewritten. The Fetch Type field, the Standalone Fetch and Joining Fetch structures and the Fetch Type registry are all gone. Track Namespace and Track Name are inline fields of FETCH itself, in the positions they occupied inside the old Standalone Fetch, and the range travels in the LOCATION_FILTER message parameter. The codepoint did not change, so a draft-19 decoder reads the Number of Track Namespace Fields count as a Fetch Type and mis-parses in silence; there is no in-band version signal to catch it (Section 10.13)
• PUBLISH_STATE_NOTIFY (0x22) is new. A publisher-only, unilateral report that a subscription’s state changed for a reason other than a subscriber-sent REQUEST_UPDATE. It has no Request ID field — the message is identified by the bidirectional request stream it arrives on, like SUBSCRIBE_OK, PUBLISH_DONE and FETCH_OK (Section 10.10)
• LOCATION_FILTER (0x21) is restructured. The Filter Type enum (draft-19’s 0x1 Next Group Start / 0x2 Largest Object / 0x3 AbsoluteStart / 0x4 AbsoluteRange) is gone; the filter’s shape now comes from how many vi64 fields its value holds (Section 5.1.2)
• Ranges are inclusive at both ends, on subscriptions and on fetches. Draft-19’s fetch end was “the last Object, plus 1; or 0 to indicate the entire Group”; both conventions are deleted. This change is absent from the draft’s own change log, and a draft-19 encoder ported forward with its end-location arithmetic intact fetches one object too many (Sections 5.1.2, 10.13, 10.14)
• FILL_PARAMETERS (0x23) is new: a length-prefixed parameter whose value is a nested parameter block, and whose mere presence on a SUBSCRIBE or a REQUEST_UPDATE asks the publisher to open a fill fetch stream (Section 10.2.15)
• INCLUDE_PROPERTIES (0x35) is new: a uint8 opt-out from Track Properties on the responding OK, default 1 (Section 10.2.21)
• Three code points are removed: SUBSCRIPTION_ENDED (PUBLISH_DONE 0x3), VERSION_NEGOTIATION_FAILED (session 0x15) and INVALID_JOINING_REQUEST_ID (REQUEST_ERROR 0x32). Two whole enumerations go with them: the Fetch Type registry and the Location Filter Type enum
• PUBLISH_DONE.Stream Count’s “unknown” sentinel moves from 2^62 - 1 to 2^64 - 1, and the count now includes fill fetch streams (Section 10.12)
• Subscription parameters moved off PUBLISH_OK. Six parameter definitions dropped it from their “MAY appear in” list and several gained PUBLISH; EXPIRES (0x08) is the only one that still names it (Section 10.2)
• The data-plane headers rename their leading field Type to Type Flags and move the validity rules out of the figure into prose. The field list, order, widths and the set of valid values are all unchanged; what changed is the receive path. Sections 11.3.1 and 11.4.2 give different rule sets — subgroup’s reserved bit 4 must be 1, datagram’s must be 0, and subgroup has no “unspecified bit” clause because bits 0-6 are all specified for it
• A fetch stream gains a third End of Range marker, End of Timed-Out Range (Serialization Flags 0x20C), for the Objects a relay abandoned when its FILL_TIMEOUT budget ran out. Draft-19 reported those as Unknown gaps (Section 11.4.4, Table 7)
• Section numbering: everything from Section 10.10 on shifted by one, because PUBLISH_STATE_NOTIFY was inserted there. Range Filters moved 5.1.3 to 5.1.4, and five parameter subsections shifted (EXPIRES 10.2.15 to 10.2.16, LARGEST_OBJECT 10.2.16 to 10.2.17, FORWARD 10.2.17 to 10.2.18, NEW_GROUP_REQUEST 10.2.18 to 10.2.19, TRACK_NAMESPACE_PREFIX 10.2.19 to 10.2.20). Every section reference in this module is draft-20’s own

Where this codec had to choose

Draft-20 leaves several wire questions open. Each decision is recorded at the encode or decode site that makes it, and each says that the draft does not state it. They are, with the site that carries the comment:

• FILL_PARAMETERS’s value begins with a Number of Parameters count — message::decode_fill_parameters
• the Type Delta chain restarts inside FILL_PARAMETERS and the outer chain is unaffected — message::decode_fill_parameters
• a LOCATION_FILTER’s field count comes from parsing, never from the byte length — message::decode_location_filter
• a non-minimally encoded Type Flags is accepted on receive and never emitted — data_stream::SubgroupHeader::decode and data_stream::DatagramHeader::decode
• PUBLISH_DONE.Stream Count’s 2^64 - 1 sentinel is indistinguishable from a well-formed exact count — message::publish_done_codes::STREAM_COUNT_UNKNOWN
• PUBLISH_STATE_NOTIFY’s parameter allow-list is treated as closed — message::parameter_in_scope
• Object Payload Length is present on an End-of-Range marker record, encoded as 0, and the ordinary delta arithmetic applies to the marker’s two fields — data_stream::FetchObjectHeader

Modules

data_stream

Draft-20 data stream header encoding and decoding.

error_codes

Error, status and stream-reset code registries defined by draft-ietf-moq-transport-20.

fields

This draft’s field names for a decoded control message.

message

Draft-20 control message encoding and decoding.

types

Draft-20 object status values.