HTTP/3 on Streams

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Table of Contents

1. Introduction

As of 2023, HTTP/2 [HTTP2] remains the most widely used version of HTTP across the Internet, although the adoption rate of HTTP/3 [HTTP3] is increasing rapidly.¶

HTTP/3 has several advantages over HTTP/2, primarily due to its use of QUIC [QUIC] as the transport layer protocol, which provides features like stream multiplexing without head-of-line blocking and low-latency connection establishment.¶

However, given that QUIC's availability and accessibility are not as universal as TCP's, a complete migration of all HTTP/2 traffic to QUIC-based HTTP/3 seems unlikely.¶

This situation necessitates HTTP deployments to support both transport protocols and their respective HTTP versions for the foreseeable future.¶

Maintaining dual support is costly, as the two protocols differ in many aspects such as wire-encoding, flow control and stream multiplexing machinery, and HTTP header compression. Extensions operating at the HTTP wire encoding layer must be developed and implemented for both HTTP/2 and HTTP/3, and both protocol stacks require ongoing maintenance to address bugs, performance issues, and vulnerabilities.¶

To address this redundancy, this specification defines the method of running HTTP/3 over TCP, utilizing QUIC on Streams [QUIC-ON-STREAMS] as the basis. QUIC on Streams, acting as a polyfill of QUIC atop bi-directional byte streams, enables the operation of HTTP/3 over TCP without any modifications.¶

Consequently, design, implementation, and maintenance efforts can concentrate on a single HTTP version: HTTP/3.¶

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. The Protocol

HTTP/3 functions over QUIC version 1, employing the set of operations (i.e., API) defined in Section 2.4 and Section 5.3 of [QUIC]. Conversely, HTTP/3 on Streams utilizes the same set of operations but functions over QUIC on Streams instead.¶

4. Starting HTTP/3 on Streams

HTTP/3 on Streams can be used for “http” and “https” URI schemes defined in Section 4.2 of [HTTP-SEMANTICS] with the same default port numbers as HTTP/1.1 [HTTP1].¶

When starting HTTP/3 on Streams for “https” URIs, clients use the TLS [TLS13] with the ALPN [ALPN] extension: “h3s”.¶

Also, clients may learn that a particular server supports HTTP/3 on Streams by other means. A client that knows that a server supports HTTP/3 on Streams can establish a TCP connection and start exchanging HTTP/3 frames using QUIC on Streams.¶

The latter is the only way to discover HTTP/3 on Streams for “http” URIs.¶

When used in cleartext, servers can determine if or not the client is speaking HTTP/3 on Streams by comparing the first eight bytes to the encoded form of the QS_TRANSPORT_PARAMETERS frame type (Section 4.2 of [QUIC-ON-STREAMS]).¶

5. Support for Extended CONNECT

Servers speaking HTTP/3 on Streams MUST implement the Extended CONNECT scheme defined in [EXT-CONNECT3].¶

6. Security Considerations

TODO Security¶

7. IANA Considerations

This document has no IANA actions.¶

Acknowledgments

TODO acknowledge.¶

Authors' Addresses