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Transport QUIC Internet-Draft QUIC () defines a RESET_STREAM frame to reset a stream. When a sender resets a stream, it stops retransmitting STREAM frames for this stream. On the receiver side, there is no guarantee that any of the data sent on that stream is delivered to the application. This document defines a new QUIC frame, the CLOSE_STREAM frame, that allows closing and resetting of a stream, while guaranteeing reliable delivery of stream data up to a certain byte offset. Discussion Venues Discussion of this document takes place on the QUIC Working Group mailing list (quic@ietf.org), which is archived at . Source for this draft and an issue tracker can be found at .

Introduction QUIC v1 () allows streams to be reset. When a stream is reset, the sender doesn't retransmit stream data for the respective stream. On the receiver side, the QUIC stack is free to surface the stream reset to the application immediately, even if it has already received stream data for that stream. Applications running on top of QUIC might need to send an identifier at the beginning of the stream in order to associate that stream with a specific subpart of the application. For example, WebTransport () uses a variable-length-encoded integer (as defined in QUIC v1) to transmit the ID of the WebTransport session to the receiver. It is desirable that the receiver is able to associate incoming streams with their respective subpart of the application, even if the QUIC stream is reset before the identifier at the beginning of the stream was read. Another use-case is relaying data from an external data source. When a relay is sending data being read from an external source and encounters an error, it might want to use a stream reset to signal that error, at the same time making sure that all data being read previously is delivered to the peer. This document describes a QUIC extension defining a new frame type, the CLOSE_STREAM frame. This frame allows an endpoint to mark a portion at the beginning of the stream which will then be guaranteed to be delivered to receiver's application, even if the stream was reset.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Negotiating Extension Use Endpoints advertise their support of the extension described in this document by sending the close_stream (0x17f7586d2cb570) transport parameter (Section 7.4 of ) with an empty value. An implementation that understands this transport parameter MUST treat the receipt of a non-empty value as a connection error of type TRANSPORT_PARAMETER_ERROR. In order to allow reliable stream resets in 0-RTT packets, the client MUST remember the value of this transport parameter. If 0-RTT data is accepted by the server, the server MUST not disable this extension on the resumed connection.

CLOSE_STREAM Frame Conceptually, the CLOSE_STREAM frame is a RESET_STREAM frame with an added Reliable Size field. The CLOSE_STREAM frames contain the following fields: Stream ID: A variable-length integer encoding of the stream ID of the stream being terminated. Application Protocol Error Code: A variable-length integer containing the application protocol error code (see Section 20.2) that indicates why the stream is being closed. If the Type is 0x20, this field is not included. Final Size: A variable-length integer indicating the final size of the stream by the RESET_STREAM sender, in units of bytes; see (Section 4.5 of ). Reliable Size: A variable-length integer indicating the amount of data that needs to be delivered to the application even though the stream is reset. If the Reliable Size is larger than the Final Size, the receiver MUST close the connection with a connection error of type FRAME_ENCODING_ERROR. CLOSE_STREAM frames are ack-eliciting. When lost, they MUST be retransmitted, unless the stream state has transitioned to "Data Recvd" or "Reset Recvd" due to transmission and acknowledgement of other frames (see ).

Closing Streams

Without an Error When closing a stream with an error, the node has the choise between a STREAM frame that carries the FIN bit and a CLOSE_STREAM frame of type 0x20. The CLOSE_STREAM frame can be used to reduce the reliable offset after a STREAM frame with a FIN bit has been sent. If STREAM frames containing data up to that byte offset are lost, the initiator MUST retransmit this data, as described in (Section 13.3 of ). Data sent beyond that byte offset SHOULD NOT be retransmitted.

Using an Error Code When resetting a stream, the node has the choice between using a RESET_STREAM frame and a CLOSE_STREAM frame of type 0x21. When using a RESET_STREAM frame, the behavior is unchanged from the behavior described in (). When using the CLOSE_STREAM frame, the initiator MUST guarantee reliable delivery of stream data of at least Reliable Size bytes. If STREAM frames containing data up to that byte offset are lost, the initiator MUST retransmit this data, as described in (Section 13.3 of ). Data sent beyond that byte offset SHOULD NOT be retransmitted. As described in (Section 3.2 of ), it MAY deliver data beyond that offset to the application.

Multiple CLOSE_STREAM / RESET_STREAM frames The initiator MAY send multiple CLOSE_STREAM frames for the same stream in order to reduce the Reliable Size. It MAY also send a RESET_STREAM frame, which is equivalent to sending a CLOSE_STREAM frame with a Reliable Size of 0. When sending multiple frames for the same stream, the initiator MUST NOT increase the Reliable Size. When receiving a CLOSE_STREAM frame with a lower Reliable Size, the receiver only needs to deliver data up the lower Reliable Size to the application. It MUST NOT expect the delivery of any data beyond that byte offset. Reordering of packets might lead to a CLOSE_STREAM frame with a higher Reliable Size being received after a CLOSE_STREAM frame with a lower Reliable Size. The receiver MUST ignore any CLOSE_STREAM frame that increases the Reliable Size. When sending another CLOSE_STREAM, RESET_STREAM or STREAM frame carrying a FIN bit for the same stream, the initiator MUST NOT change the Application Error Code or the Final Size. This also means that sending CLOSE_STREAM frames of different types is not permitted. If the receiver detects a change in those fields, it MUST close the connection with a connection error of type STREAM_STATE_ERROR.

Security Considerations TODO Security

IANA Considerations This document has no IANA actions.

Normative References This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. Facebook Apple Inc. Google WebTransport [OVERVIEW] is a protocol framework that enables clients constrained by the Web security model to communicate with a remote server using a secure multiplexed transport. This document describes a WebTransport protocol that is based on HTTP/3 [HTTP3] and provides support for unidirectional streams, bidirectional streams and datagrams, all multiplexed within the same HTTP/3 connection. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.

Acknowledgments TODO acknowledge.