Internet Engineering Task Force (IETF) P. McManus
Request for Comments: 8441 Mozilla
Updates: 6455 September 2018
Category: Standards Track
Bootstrapping WebSockets with HTTP/2
This document defines a mechanism for running the WebSocket Protocol
(RFC 6455) over a single stream of an HTTP/2 connection.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 22. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 33. The SETTINGS_ENABLE_CONNECT_PROTOCOL SETTINGS Parameter . . . 34. The Extended CONNECT Method . . . . . . . . . . . . . . . . . 45. Using Extended CONNECT to Bootstrap the WebSocket Protocol . 45.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 66. Design Considerations . . . . . . . . . . . . . . . . . . . . 67. About Intermediaries . . . . . . . . . . . . . . . . . . . . 68. Security Considerations . . . . . . . . . . . . . . . . . . . 79. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 79.1. A New HTTP/2 Setting . . . . . . . . . . . . . . . . . . 79.2. A New HTTP Upgrade Token . . . . . . . . . . . . . . . . 710. Normative References . . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 81. Introduction
The Hypertext Transfer Protocol (HTTP) [RFC7230] provides compatible
resource-level semantics across different versions, but it does not
offer compatibility at the connection-management level. Other
protocols that rely on connection-management details of HTTP, such as
WebSockets, must be updated for new versions of HTTP.
The WebSocket Protocol [RFC6455] uses the HTTP/1.1 Upgrade mechanism
(Section 6.7 of [RFC7230]) to transition a TCP connection from HTTP
into a WebSocket connection. A different approach must be taken with
HTTP/2 [RFC7540]. Due to its multiplexing nature, HTTP/2 does not
allow connection-wide header fields or status codes, such as the
Upgrade and Connection request-header fields or the 101 (Switching
Protocols) response code. These are all required by the [RFC6455]
Being able to bootstrap WebSockets from HTTP/2 allows one TCP
connection to be shared by both protocols and extends HTTP/2's more
efficient use of the network to WebSockets.
This document extends the HTTP CONNECT method, as specified for
HTTP/2 in Section 8.3 of [RFC7540]. The extension allows the
substitution of a new protocol name to connect to rather than the
external host normally used by CONNECT. The result is a tunnel on a
single HTTP/2 stream that can carry data for WebSockets (or any other
protocol). The other streams on the connection may carry more
extended CONNECT tunnels, traditional HTTP/2 data, or a mixture of
This tunneled stream will be multiplexed with other regular streams
on the connection and enjoys the normal priority, cancellation, and
flow-control features of HTTP/2.
Streams that successfully establish a WebSocket connection using a
tunneled stream and the modifications to the opening handshake
defined in this document then use the traditional WebSocket Protocol,
treating the stream as if it were the TCP connection in that
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 SETTINGS_ENABLE_CONNECT_PROTOCOL SETTINGS Parameter
This document adds a new SETTINGS parameter to those defined by
[RFC7540], Section 6.5.2.
The new parameter name is SETTINGS_ENABLE_CONNECT_PROTOCOL. The
value of the parameter MUST be 0 or 1.
Upon receipt of SETTINGS_ENABLE_CONNECT_PROTOCOL with a value of 1, a
client MAY use the Extended CONNECT as defined in this document when
creating new streams. Receipt of this parameter by a server does not
have any impact.
A sender MUST NOT send a SETTINGS_ENABLE_CONNECT_PROTOCOL parameter
with the value of 0 after previously sending a value of 1.
Using a SETTINGS parameter to opt into an otherwise incompatible
protocol change is a use of "Extending HTTP/2" defined by Section 5.5
of [RFC7540]. Specifically, the addition a new pseudo-header field,
":protocol", and the change in meaning of the :authority pseudo-
header field in Section 4 require opt-in negotiation. If a client
were to use the provisions of the extended CONNECT method defined in
this document without first receiving a
SETTINGS_ENABLE_CONNECT_PROTOCOL parameter, a non-supporting peer
would detect a malformed request and generate a stream error
(Section 22.214.171.124 of [RFC7540]).
4. The Extended CONNECT Method
Usage of the CONNECT method in HTTP/2 is defined by Section 8.3 of
[RFC7540]. This extension modifies the method in the following ways:
o A new pseudo-header field :protocol MAY be included on request
HEADERS indicating the desired protocol to be spoken on the tunnel
created by CONNECT. The pseudo-header field is single valued and
contains a value from the "Hypertext Transfer Protocol (HTTP)
Upgrade Token Registry" located at
o On requests that contain the :protocol pseudo-header field, the
:scheme and :path pseudo-header fields of the target URI (see
Section 5) MUST also be included.
o On requests bearing the :protocol pseudo-header field, the
:authority pseudo-header field is interpreted according to
Section 126.96.36.199 of [RFC7540] instead of Section 8.3 of that
document. In particular, the server MUST NOT create a tunnel to
the host indicated by the :authority as it would with a CONNECT
method request that was not modified by this extension.
Upon receiving a CONNECT request bearing the :protocol pseudo-header
field, the server establishes a tunnel to another service of the
protocol type indicated by the pseudo-header field. This service may
or may not be co-located with the server.
5. Using Extended CONNECT to Bootstrap the WebSocket Protocol
The :protocol pseudo-header field MUST be included in the CONNECT
request, and it MUST have a value of "websocket" to initiate a
WebSocket connection on an HTTP/2 stream. Other HTTP request and
response-header fields, such as those for manipulating cookies, may
be included in the HEADERS with the CONNECT method as usual. This
request replaces the GET-based request in [RFC6455] and is used to
process the WebSockets opening handshake.
The scheme of the target URI (Section 5.1 of [RFC7230]) MUST be
"https" for "wss"-schemed WebSockets and "http" for "ws"-schemed
WebSockets. The remainder of the target URI is the same as the
WebSocket URI. The WebSocket URI is still used for proxy
autoconfiguration. The security requirements for the HTTP/2
connection used by this specification are established by [RFC7540]
for https requests and [RFC8164] for http requests.
[RFC6455] requires the use of Connection and Upgrade header fields
that are not part of HTTP/2. They MUST NOT be included in the
CONNECT request defined here.
[RFC6455] requires the use of a Host header field that is also not
part of HTTP/2. The Host information is conveyed as part of the
:authority pseudo-header field, which is required on every HTTP/2
Implementations using this extended CONNECT to bootstrap WebSockets
do not do the processing of the Sec-WebSocket-Key and Sec-WebSocket-
Accept header fields of [RFC6455] as that functionality has been
superseded by the :protocol pseudo-header field.
The Origin [RFC6454], Sec-WebSocket-Version, Sec-WebSocket-Protocol,
and Sec-WebSocket-Extensions header fields are used in the CONNECT
request and response-header fields as defined in [RFC6455]. Note
that HTTP/1 header field names were case insensitive, whereas HTTP/2
requires they be encoded as lowercase.
After successfully processing the opening handshake, the peers should
proceed with the WebSocket Protocol [RFC6455] using the HTTP/2 stream
from the CONNECT transaction as if it were the TCP connection
referred to in [RFC6455]. The state of the WebSocket connection at
this point is OPEN, as defined by [RFC6455], Section 4.1.
The HTTP/2 stream closure is also analogous to the TCP connection
closure of [RFC6455]. Orderly TCP-level closures are represented as
END_STREAM flags ([RFC7540], Section 6.1). RST exceptions are
represented with the RST_STREAM frame ([RFC7540], Section 6.4) with
the CANCEL error code ([RFC7540], Section 7).
[[ From Client ]] [[ From Server ]]
SETTINGS_ENABLE_CONNECT_[..] = 1
HEADERS + END_HEADERS
:method = CONNECT
:protocol = websocket
:scheme = https
:path = /chat
:authority = server.example.com
sec-websocket-protocol = chat, superchat
sec-websocket-extensions = permessage-deflate
sec-websocket-version = 13
origin = http://www.example.com
HEADERS + END_HEADERS
:status = 200
sec-websocket-protocol = chat
DATA + END_STREAM
DATA + END_STREAM
6. Design Considerations
A more native integration with HTTP/2 is certainly possible with
larger additions to HTTP/2. This design was selected to minimize the
solution complexity while still addressing the primary concern of
running HTTP/2 and WebSockets concurrently.
7. About Intermediaries
This document does not change how WebSockets interacts with HTTP
forward proxies. If a client wishing to speak WebSockets connects
via HTTP/2 to an HTTP proxy, it should continue to use a traditional
CONNECT (i.e., not with a :protocol pseudo-header field) to tunnel
through that proxy to the WebSocket server via HTTP.
The resulting version of HTTP on that tunnel determines whether
WebSockets is initiated directly or via a modified CONNECT request
described in this document.
8. Security Considerations
[RFC6455] ensures that non-WebSockets clients, especially
XMLHttpRequest-based clients, cannot make a WebSocket connection.
Its primary mechanism for doing that is the use of Sec-prefixed
request-header fields that cannot be created by XMLHttpRequest-based
clients. This specification addresses that concern in two ways:
o XMLHttpRequest also prohibits use of the CONNECT method in
addition to Sec-prefixed request-header fields.
o The use of a pseudo-header field is something that is connection
specific, and HTTP/2 never allows a pseudo-header to be created
outside of the protocol stack.
The security considerations of [RFC6455], Section 10 continue to
apply to the use of the WebSocket Protocol when using this
specification, with the exception of 10.8. That section is not
relevant, because it is specific to the bootstrapping handshake that
is changed in this document.
9. IANA Considerations
9.1. A New HTTP/2 Setting
This document registers an entry in the "HTTP/2 Settings" registry
that was established by Section 11.3 of [RFC7540].
Initial Value: 0
Specification: This document
9.2. A New HTTP Upgrade Token
This document registers an entry in the "HTTP Upgrade Tokens"
registry that was established by [RFC7230].
Description: The Web Socket Protocol
Expected Version Tokens:
References: [RFC6455] [RFC8441]