Reliable QUIC Stream Resets

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Table of Contents

1. Introduction

QUIC version 1 ([RFC9000]) allows streams to be reset. When a stream is reset, the sender doesn't retransmit stream data for the respective stream. On the receiving side, the QUIC stack is free to surface the stream reset to the application immediately, without providing any stream data it has received for that stream.¶

Some applications running on top of QUIC use bytes at the beginning of the stream to communicate critical information related to that stream. For example, WebTransport ([WEBTRANSPORT]) uses a variable-length encoded integer to associate a stream with a particular WebTransport session.¶

Since QUIC does not provide guaranteed delivery of steam data for reset streams, it is possible that a receiver is unable to read critical information. In the example above, a reset stream can cause the receiver to fail to associate incoming streams with their respective subcomponent of the application. Therefore, it is desirable that the receiver can rely on the delivery of critical information to applications, even if the QUIC stream is reset before data is read by the application.¶

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, while at the same time guaranteeing that all data received from the source is delivered to the peer.¶

This document describes a QUIC extension defining a new frame type, the RESET_STREAM_AT frame. This frame allows an endpoint to mark a portion at the beginning of the stream which will then be reliably delivered, even if the stream was reset.¶

2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. Negotiating Extension Use

Endpoints advertise their support of the extension described in this document by sending the reliable_stream_reset (0x17f7586d2cb570) transport parameter (Section 7.4 of [RFC9000]) 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.¶

When using 0-RTT, both endpoints MUST remember the value of this transport parameter. This allows use of this extension in 0-RTT packets. When the server accepts 0-RTT data, the server MUST NOT disable this extension on the resumed connection.¶

4. RESET_STREAM_AT Frame

Conceptually, the RESET_STREAM_AT frame is a RESET_STREAM frame with an added Reliable Size field.¶

RESET_STREAM_AT Frame {
  Type (i) = 0x20,
  Stream ID (i),
  Application Protocol Error Code (i),
  Final Size (i),
  Reliable Size (i),
}

The RESET_STREAM_AT frame contains 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 (Section 20.2 of [RFC9000]) that indicates why the stream is being closed.¶

Final Size:

A variable-length integer indicating the final size of the stream by the sender, in units of bytes; see Section 4.5 of [RFC9000].¶

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.¶

RESET_STREAM_AT frames are ack-eliciting, and MUST only be sent in the application data packet number space. 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 Section 5.1).¶

5. Resetting Streams

A sender that wants to reset a stream but also deliver some bytes to the receiver sends a RESET_STREAM_AT frame with the Reliable Size field specifying the amount of data to be delivered.¶

When using a RESET_STREAM_AT 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 [RFC9000]. Data sent beyond that byte offset SHOULD NOT be retransmitted.¶

As described in Section 3.2 of [RFC9000], a stream reset signal might be suppressed or withheld, and the same applies to a stream reset signal carried in a RESET_STREAM_AT frame. Similarly, the Reliable Size of the RESET_STREAM_AT frame does not prevent a QUIC stack from delivering data beyond the specified offset to the receiving application.¶

Note that a Reliable Size value of zero is valid. A RESET_STREAM_AT frame with this value is logically equivalent to a RESET_STREAM frame (Section 3.2 of [RFC9000]). When resetting a stream without the intent to deliver any data to the receiver, the sender MAY use either RESET_STREAM or RESET_STREAM_AT with a Reliable Size of zero.¶

6. Implementation Guidance

In terms of transport machinery, the RESET_STREAM_AT frame is more akin to the FIN bit than to the RESET_STREAM frame (see Section 5.2). By sending a RESET_STREAM_AT frame, the sender commits to delivering all bytes up to the Reliable Size.¶

To the endpoints, the main differences from closing a stream by using the FIN bit are:¶

• the offset up to which the sender commits to sending might be smaller than Final Size,¶

• this offset might get reduced by subsequent RESET_STREAM_AT frames, and¶

• the closure is accompanied by an error code.¶

7. Security Considerations

As the RESET_STREAM_AT frame is an extension to the stream machinery defined in QUIC version 1, the security considerations of [RFC9000] apply accordingly. Specifically, given that RESET_STREAM_AT frames indicate the offset up to which data is reliably transmitted, endpoints SHOULD remain vigilant against resource commitment and exhaustion attacks even after sending or receiving RESET_STREAM_AT frames, until the stream reaches the terminal state.¶

8. IANA Considerations

Acknowledgments

TODO acknowledge.¶

Authors' Addresses