The Proxy-Status HTTP Response Header Field
draft-ietf-httpbis-proxy-status-08
| Document | Type | Active Internet-Draft (httpbis WG) | |
|---|---|---|---|
| Authors | Mark Nottingham , Piotr Sikora | ||
| Last updated | 2021-10-14 (latest revision 2021-10-13) | ||
| Replaces | draft-nottingham-proxy-status | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | plain text html xml pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication (wg milestone: - Submit Proxy-Status ... ) | |
| Document shepherd | Tommy Pauly | ||
| Shepherd write-up | Show (last changed 2021-08-27) | ||
| IESG | IESG state | IESG Evaluation | |
| Action Holders |
|
||
| Consensus Boilerplate | Yes | ||
| Telechat date |
Has enough positions to pass. |
||
| Responsible AD | Francesca Palombini | ||
| Send notices to | tpauly@apple.com | ||
| IANA | IANA review state | Version Changed - Review Needed | |
HTTP M. Nottingham
Internet-Draft Fastly
Intended status: Standards Track P. Sikora
Expires: 16 April 2022 Google
13 October 2021
The Proxy-Status HTTP Response Header Field
draft-ietf-httpbis-proxy-status-08
Abstract
This document defines the Proxy-Status HTTP field to convey the
details of intermediary response handling, including generated
errors.
Note to Readers
_RFC EDITOR: please remove this section before publication_
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/
(https://lists.w3.org/Archives/Public/ietf-http-wg/).
Working Group information can be found at https://httpwg.org/
(https://httpwg.org/); source code and issues list for this draft can
be found at https://github.com/httpwg/http-extensions/labels/proxy-
status (https://github.com/httpwg/http-extensions/labels/proxy-
status).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 16 April 2022.
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4
2. The Proxy-Status HTTP Field . . . . . . . . . . . . . . . . . 4
2.1. Proxy-Status Parameters . . . . . . . . . . . . . . . . . 6
2.1.1. error . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.2. next-hop . . . . . . . . . . . . . . . . . . . . . . 8
2.1.3. next-protocol . . . . . . . . . . . . . . . . . . . . 8
2.1.4. received-status . . . . . . . . . . . . . . . . . . . 8
2.1.5. details . . . . . . . . . . . . . . . . . . . . . . . 9
2.2. Defining New Proxy-Status Parameters . . . . . . . . . . 9
2.3. Proxy Error Types . . . . . . . . . . . . . . . . . . . . 10
2.3.1. DNS Timeout . . . . . . . . . . . . . . . . . . . . . 10
2.3.2. DNS Error . . . . . . . . . . . . . . . . . . . . . . 10
2.3.3. Destination Not Found . . . . . . . . . . . . . . . . 11
2.3.4. Destination Unavailable . . . . . . . . . . . . . . . 11
2.3.5. Destination IP Prohibited . . . . . . . . . . . . . . 11
2.3.6. Destination IP Unroutable . . . . . . . . . . . . . . 12
2.3.7. Connection Refused . . . . . . . . . . . . . . . . . 12
2.3.8. Connection Terminated . . . . . . . . . . . . . . . . 12
2.3.9. Connection Timeout . . . . . . . . . . . . . . . . . 13
2.3.10. Connection Read Timeout . . . . . . . . . . . . . . . 13
2.3.11. Connection Write Timeout . . . . . . . . . . . . . . 13
2.3.12. Connection Limit Reached . . . . . . . . . . . . . . 14
2.3.13. TLS Protocol Error . . . . . . . . . . . . . . . . . 14
2.3.14. TLS Certificate Error . . . . . . . . . . . . . . . . 14
2.3.15. TLS Alert Received . . . . . . . . . . . . . . . . . 15
2.3.16. HTTP Request Error . . . . . . . . . . . . . . . . . 15
2.3.17. HTTP Request Denied . . . . . . . . . . . . . . . . . 16
2.3.18. HTTP Incomplete Response . . . . . . . . . . . . . . 16
2.3.19. HTTP Response Header Section Too Large . . . . . . . 16
2.3.20. HTTP Response Header Field Line Too Large . . . . . . 17
2.3.21. HTTP Response Body Too Large . . . . . . . . . . . . 17
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2.3.22. HTTP Response Trailer Section Too Large . . . . . . . 18
2.3.23. HTTP Response Trailer Field Line Too Large . . . . . 18
2.3.24. HTTP Response Transfer-Coding Error . . . . . . . . . 18
2.3.25. HTTP Response Content-Coding Error . . . . . . . . . 19
2.3.26. HTTP Response Timeout . . . . . . . . . . . . . . . . 19
2.3.27. HTTP Upgrade Failed . . . . . . . . . . . . . . . . . 19
2.3.28. HTTP Protocol Error . . . . . . . . . . . . . . . . . 20
2.3.29. Proxy Internal Response . . . . . . . . . . . . . . . 20
2.3.30. Proxy Internal Error . . . . . . . . . . . . . . . . 20
2.3.31. Proxy Configuration Error . . . . . . . . . . . . . . 21
2.3.32. Proxy Loop Detected . . . . . . . . . . . . . . . . . 21
2.4. Defining New Proxy Error Types . . . . . . . . . . . . . 21
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
4. Security Considerations . . . . . . . . . . . . . . . . . . . 23
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.1. Normative References . . . . . . . . . . . . . . . . . . 23
5.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
HTTP intermediaries (see Section 3.7 of [HTTP]) -- including both
forward proxies and gateways (also known as "reverse proxies") --
have become an increasingly significant part of HTTP deployments. In
particular, reverse proxies and Content Delivery Networks (CDNs) form
part of the critical infrastructure of many Web sites.
Typically, HTTP intermediaries forward requests towards the origin
server (inbound) and then forward their responses back to clients
(outbound). However, if an error occurs before a response is
obtained from an inbound server, the response is often generated by
the intermediary itself.
HTTP accommodates these types of errors with a few status codes; for
example, 502 Bad Gateway and 504 Gateway Timeout. However,
experience has shown that more information is necessary to aid
debugging and communicate what's happened to the client.
Additionally, intermediaries sometimes want to convey additional
information about their handling of a response, even if they did not
generate it.
To enable these uses, Section 2 defines a new HTTP response field to
allow intermediaries to convey details of their handling of a
response. Section 2.1 enumerates the information that can be added
to the field by intermediaries, which can be extended as per
Section 2.2. Section 2.3 defines a set of error types for use when a
proxy encounters an issue when obtaining a response for the request;
these can likewise be extended as per Section 2.4.
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1.1. Notational Conventions
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.
This specification uses Structured Fields [STRUCTURED-FIELDS] to
specify syntax and parsing, and ABNF [RFC5234] as a shorthand for
that syntax. The terms sf-list, sf-item, sf-string, sf-token, sf-
integer and key refer to the structured types defined therein.
Note that in this specification, "proxy" is used to indicate both
forward and reverse proxies, otherwise known as gateways. "Next hop"
indicates the connection in the direction leading to the origin
server for the request.
2. The Proxy-Status HTTP Field
The Proxy-Status HTTP response field allows an intermediary to convey
additional information about its handling of a response and its
associated request. The syntax of this header field conforms to
[STRUCTURED-FIELDS].
It is a List ([STRUCTURED-FIELDS], Section 3.1):
Proxy-Status = sf-list
Each member of the list represents an intermediary that has handled
the response. The first member of the list represents the
intermediary closest to the origin server, and the last member of the
list represents the intermediary closest to the user agent.
For example:
Proxy-Status: revproxy1.example.net, ExampleCDN
indicates that this response was handled first by
revproxy1.example.net (a reverse proxy adjacent to the origin server)
and then ExampleCDN.
Intermediaries determine when it is appropriate to add the Proxy-
Status field to a response. Some might decide to append to it to all
responses, whereas others might only do so when specifically
configured to, or when the request contains a header field that
activates a debugging mode.
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Each member of the list identifies the intermediary that inserted the
value, and MUST have a type of either sf-string or sf-token.
Depending on the deployment, this might be a service name (but not a
software or hardware product name; e.g., "Example CDN"is appropriate,
but "ExampleProxy" is not, because it doesn't identify the
deployment), a hostname ("proxy-3.example.com"), an IP address, or a
generated string.
Parameters on each member (as per Section 3.1.2 of
[STRUCTURED-FIELDS]) convey additional information about that
intermediary's handling of the response and its associated request;
see Section 2.1. While all of these parameters are OPTIONAL,
intermediaries are encouraged to provide as much information as
possible (but see Section 4 for security considerations in doing so).
When adding a value to the Proxy-Status field, intermediaries SHOULD
preserve the existing members of the field to allow debugging of the
entire chain of intermediaries handling the request, unless
explicitly configured to remove them (e.g., to prevent internal
network details from leaking; see Section 4).
Origin servers MUST NOT generate the Proxy-Status field.
Proxy-Status MAY be sent as a HTTP trailer field. For example, if an
intermediary is streaming a response and the inbound connection
suddenly terminates, Proxy-Status can only be appended to the trailer
section of the outbound message, since the header section has already
been sent. However, because it might be silently discarded along the
path to the user agent (as is the case for all trailer fields; see
Section 6.5 of [HTTP]), Proxy-Status SHOULD NOT be sent as a trailer
field unless it is not possible to send it in the header section.
To allow recipients to reconstruct the relative ordering of Proxy-
Status members conveyed in trailer fields with those conveyed in
header fields, an intermediary MUST NOT send Proxy-Status as a
trailer field unless it has also generated a Proxy-Status header
field with the same member (although potentially different
parameters) in that message.
For example, a proxy identified as 'ThisProxy' that receives a
response bearing a header field:
Proxy-Status: SomeOtherProxy
would add its own entry to the header field:
Proxy-Status: SomeOtherProxy, ThisProxy
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thus allowing it to append a trailer field:
Proxy-Status: ThisProxy; error=read_timeout
... which would thereby allow a downstream recipient to understand
that processing by 'SomeOtherProxy' occurred before 'ThisProxy'.
A client MAY promote the Proxy-Status trailer field into a header
field by following these steps:
1. For each member trailer_member of the Proxy-Status trailer field
value:
1. Let header_member be the first (left-most) value of the
Proxy-Status header field value, comparing the sf-token or
sf-string character-by-character and without consideration of
parameters.
2. If no matching header_member is found, continue processing
the next trailer_member.
3. Replace header_member with trailer_member in its entirety,
including any parameters.
2. Remove the Proxy-Status trailer field, if empty.
2.1. Proxy-Status Parameters
This section lists parameters that can be used on the members of the
Proxy-Status field. Unrecognised parameters MUST be ignored.
2.1.1. error
The error parameter's value is an sf-token that is a Proxy Error
Type. When present, it indicates that the intermediary encountered
an issue when obtaining this response.
The presence of some Proxy Error Types indicates that the response
was generated by the intermediary itself, rather than being forwarded
from the origin server. This is the case when, for example, the
origin server can't be contacted, so the proxy has to create its own
response.
Other Proxy Error Types can be added to (potentially partial)
responses that were generated by the origin server or some other
inbound server. For example, if the forward connection abruptly
closes, an intermediary might add Proxy-Status with an appropriate
error as a trailer field.
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Proxy Error Types that are registered with a 'Response only generated
by intermediaries' value of 'true' indicate that they can only occur
on responses generated by the intermediary. If the value is 'false',
the response might be generated by the intermediary or an inbound
server.
Section 2.3 lists the Proxy Error Types defined in this document; new
ones can be defined using the procedure outlined in Section 2.4.
For example:
HTTP/1.1 504 Gateway Timeout
Proxy-Status: ExampleCDN; error=connection_timeout
indicates that this 504 response was generated by ExampleCDN, due to
a connection timeout when going forward.
Or:
HTTP/1.1 429 Too Many Requests
Proxy-Status: r34.example.net; error=http_request_error, ExampleCDN
indicates that this 429 Too Many Requests response was generated by
r34.example.net, not the CDN or the origin.
When sending the error parameter, the most specific Proxy Error Type
SHOULD be sent, provided that it accurately represents the error
condition. If an appropriate Proxy Error Type is not defined, there
are a number of generic error types (e.g., proxy_internal_error,
http_protocol_error) that can be used. If they are not suitable,
consider registering a new Proxy Error Type (see Section 2.4).
Each Proxy Error Type has a Recommended HTTP Status Code. When
generating a HTTP response containing error, its HTTP status code
SHOULD be set to the Recommended HTTP Status Code. However, there
may be circumstances (e.g., for backwards compatibility with previous
behaviours, a status code has already been sent) when another status
code might be used.
Proxy Error Types can also define any number of extra parameters for
use with that type. Their use, like all parameters, is optional. As
a result, if an extra parameter is used with a Proxy Error Type for
which it is not defined, it will be ignored.
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2.1.2. next-hop
The next-hop parameter's value is an sf-string or sf-token that
identifies the intermediary or origin server selected (and used, if
contacted) to obtain this response. It might be a hostname, IP
address, or alias.
For example:
Proxy-Status: cdn.example.org; next-hop=backend.example.org:8001
indicates that cdn.example.org used backend.example.org:8001 as the
next hop for this request.
2.1.3. next-protocol
The next-protocol parameter's value indicates the ALPN protocol
identifier [RFC7301] of the protocol used by the intermediary to
connect to the next hop when obtaining this response.
The value MUST be either an sf-token or sf-binary, representing a TLS
Application-Layer Protocol Negotiation (ALPN) Protocol ID (see
https://www.iana.org/assignments/tls-extensiontype-values/tls-
extensiontype-values.xhtml#alpn-protocol-ids
(https://www.iana.org/assignments/tls-extensiontype-values/tls-
extensiontype-values.xhtml#alpn-protocol-ids)). If the protocol
identifier is able to be expressed as an sf-token using ASCII
encoding, that form MUST be used.
For example:
Proxy-Status: "proxy.example.org"; next-protocol=h2
Note that the APLN identifier is being used here to identify the
protocol in use; it may or may not have been actually used in the
protocol negotiation.
2.1.4. received-status
The received-status parameter's value indicates the HTTP status code
that the intermediary received from the next hop server when
obtaining this response.
The value MUST be an sf-integer.
For example:
Proxy-Status: ExampleCDN; received-status=200
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2.1.5. details
The details parameter's value is an sf-string containing additional
information not captured anywhere else. This can include
implementation-specific or deployment-specific information.
For example:
Proxy-Status: proxy.example.net; error="http_protocol_error";
details="Malformed response header: space before colon"
2.2. Defining New Proxy-Status Parameters
New Proxy-Status Parameters can be defined by registering them in the
HTTP Proxy-Status Parameters registry.
Registration requests are reviewed and approved by Expert Review, as
per [RFC8126], Section 4.5. A specification document is appreciated,
but not required.
The Expert(s) should consider the following factors when evaluating
requests:
* Community feedback
* If the value is sufficiently well-defined
* Generic parameters are preferred over vendor-specific,
application-specific or deployment-specific values. If a generic
value cannot be agreed upon in the community, the parameter's name
should be correspondingly specific (e.g., with a prefix that
identifies the vendor, application or deployment).
* Parameter names should not conflict with registered extra
parameters in the Proxy Error Type Registry.
Registration requests should use the following template:
* Name: [a name for the Proxy-Status Parameter that matches key]
* Description: [a description of the parameter semantics and value]
* Reference: [to a specification defining this parameter; optional]
See the registry at https://iana.org/assignments/http-proxy-status
(https://iana.org/assignments/http-proxy-status) for details on where
to send registration requests.
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2.3. Proxy Error Types
This section lists the Proxy Error Types defined by this document.
See Section 2.4 for information about defining new Proxy Error Types.
Note that implementations might not produce all Proxy Error Types.
The set of types below is designed to map to existing states in
implementations, and so may not be applicable to some.
2.3.1. DNS Timeout
* Name: dns_timeout
* Description: The intermediary encountered a timeout when trying to
find an IP address for the next hop hostname.
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.2. DNS Error
* Name: dns_error
* Description: The intermediary encountered a DNS error when trying
to find an IP address for the next hop hostname.
* Extra Parameters:
- rcode: A sf-string conveying the DNS RCODE that indicates the
error type. See [RFC8499], Section 3.
- info-code: A sf-integer conveying the Extended DNS Error Code
info-code. See [RFC8914].
* Recommended HTTP status code: 502
* Response only generated by intermediaries: true
* Reference: [this document]
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2.3.3. Destination Not Found
* Name: destination_not_found
* Description: The intermediary cannot determine the appropriate
next hop to use for this request; for example, it may not be
configured. Note that this error is specific to gateways, which
typically require specific configuration to identify the "backend"
server; forward proxies use in-band information to identify the
origin server.
* Extra Parameters: None.
* Recommended HTTP status code: 500
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.4. Destination Unavailable
* Name: destination_unavailable
* Description: The intermediary considers the next hop to be
unavailable; e.g., recent attempts to communicate with it may have
failed, or a health check may indicate that it is down.
* Extra Parameters: None.
* Recommended HTTP status code: 503
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.5. Destination IP Prohibited
* Name: destination_ip_prohibited
* Description: The intermediary is configured to prohibit
connections to the next hop IP address.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: true
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* Reference: [this document]
2.3.6. Destination IP Unroutable
* Name: destination_ip_unroutable
* Description: The intermediary cannot find a route to the next hop
IP address.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.7. Connection Refused
* Name: connection_refused
* Description: The intermediary's connection to the next hop was
refused.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.8. Connection Terminated
* Name: connection_terminated
* Description: The intermediary's connection to the next hop was
closed before complete response was received.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
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2.3.9. Connection Timeout
* Name: connection_timeout
* Description: The intermediary's attempt to open a connection to
the next hop timed out.
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.10. Connection Read Timeout
* Name: connection_read_timeout
* Description: The intermediary was expecting data on a connection
(e.g., part of a response), but did not receive any new data in a
configured time limit.
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.11. Connection Write Timeout
* Name: connection_write_timeout
* Description: The intermediary was attempting to write data to a
connection, but was not able to (e.g., because its buffers were
full).
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Response only generated by intermediaries: false
* Reference: [this document]
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2.3.12. Connection Limit Reached
* Name: connection_limit_reached
* Description: The intermediary is configured to limit the number of
connections it has to the next hop, and that limit has been
passed.
* Extra Parameters: None.
* Recommended HTTP status code: 503
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.13. TLS Protocol Error
* Name: tls_protocol_error
* Description: The intermediary encountered a TLS error when
communicating with the next hop, either during handshake or
afterwards.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
* Notes: Not appropriate when a TLS alert is received; see
tls_alert_received
2.3.14. TLS Certificate Error
* Name: tls_certificate_error
* Description: The intermediary encountered an error when verifying
the certificate presented by the next hop.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: true
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* Reference: [this document]
2.3.15. TLS Alert Received
* Name: tls_alert_received
* Description: The intermediary received a TLS alert from the next
hop.
* Extra Parameters:
- alert-id: an sf-integer containing the applicable value from
the TLS Alerts registry. See {!RFC8446}}.
- alert-message: an sf-token or sf-string containing the
applicable description string from the TLS Alerts registry.
See [RFC8446].
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.16. HTTP Request Error
* Name: http_request_error
* Description: The intermediary is generating a client (4xx)
response on the origin's behalf. Applicable status codes include
(but are not limited to) 400, 403, 405, 406, 408, 411, 413, 414,
415, 416, 417, 429.
* Extra Parameters:
- status-code: an sf-integer containing the generated status
code.
- status-phrase: an sf-string containing the generated status
phrase.
* Recommended HTTP status code: The applicable 4xx status code
* Response only generated by intermediaries: true
* Reference: [this document]
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* Notes: This type helps distinguish between responses generated by
intermediaries from those generated by the origin.
2.3.17. HTTP Request Denied
* Name: http_request_denied
* Description: The intermediary rejected the HTTP request based on
its configuration and/or policy settings. The request wasn't
forwarded to the next hop.
* Extra Parameters: None.
* Recommended HTTP status code: 403
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.18. HTTP Incomplete Response
* Name: http_response_incomplete
* Description: The intermediary received an incomplete response to
the request from the next hop.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.19. HTTP Response Header Section Too Large
* Name: http_response_header_section_size
* Description: The intermediary received a response to the request
whose header section was considered too large.
* Extra Parameters:
- header-section-size: an sf-integer indicating how large the
headers received were. Note that they might not be complete;
i.e., the intermediary may have discarded or refused additional
data.
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* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.20. HTTP Response Header Field Line Too Large
* Name: http_response_header_size
* Description: The intermediary received a response to the request
containing an individual header field line that was considered too
large.
* Extra Parameters:
- header-name: an sf-string indicating the name of the header
field that triggered the error.
- header-size: an sf-integer indicating the size of the header
field that triggered the error.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.21. HTTP Response Body Too Large
* Name: http_response_body_size
* Description: The intermediary received a response to the request
whose body was considered too large.
* Extra Parameters:
- body-size: an sf-integer indicating how large the body received
was. Note that it may not have been complete; i.e., the
intermediary may have discarded or refused additional data.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
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2.3.22. HTTP Response Trailer Section Too Large
* Name: http_response_trailer_section_size
* Description: The intermediary received a response to the request
whose trailer section was considered too large.
* Extra Parameters:
- trailer-section-size: an sf-integer indicating how large the
trailers received were. Note that they might not be complete;
i.e., the intermediary may have discarded or refused additional
data.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.23. HTTP Response Trailer Field Line Too Large
* Name: http_response_trailer_size
* Description: The intermediary received a response to the request
containing an individual trailer field line that was considered
too large.
* Extra Parameters:
- trailer-name: an sf-string indicating the name of the trailer
field that triggered the error.
- trailer-size: an sf-integer indicating the size of the trailer
field that triggered the error.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.24. HTTP Response Transfer-Coding Error
* Name: http_response_transfer_coding
* Description: The intermediary encountered an error decoding the
transfer-coding of the response.
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* Extra Parameters:
- coding: an sf-token containing the specific coding (from the
HTTP Transfer Coding Registry) that caused the error.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.25. HTTP Response Content-Coding Error
* Name: http_response_content_coding
* Description: The intermediary encountered an error decoding the
content-coding of the response.
* Extra Parameters:
- coding: an sf-token containing the specific coding (from the
HTTP Content Coding Registry) that caused the error.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.26. HTTP Response Timeout
* Name: http_response_timeout
* Description: The intermediary reached a configured time limit
waiting for the complete response.
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.27. HTTP Upgrade Failed
* Name: http_upgrade_failed
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* Description: The HTTP Upgrade between the intermediary and the
next hop failed.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.28. HTTP Protocol Error
* Name: http_protocol_error
* Description: The intermediary encountered a HTTP protocol error
when communicating with the next hop. This error should only be
used when a more specific one is not defined.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: false
* Reference: [this document]
2.3.29. Proxy Internal Response
* Name: proxy_internal_response
* Description: The intermediary generated the response locally,
without attempting to connect to the next hop (e.g. in response to
a request to a debug endpoint terminated at the intermediary).
* Extra Parameters: None.
* Recommended HTTP status code: The most appropriate status code for
the response
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.30. Proxy Internal Error
* Name: proxy_internal_error
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* Description: The intermediary encountered an internal error
unrelated to the origin.
* Extra Parameters: None
* Recommended HTTP status code: 500
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.31. Proxy Configuration Error
* Name: proxy_configuration_error
* Description: The intermediary encountered an error regarding its
configuration.
* Extra Parameters: None
* Recommended HTTP status code: 500
* Response only generated by intermediaries: true
* Reference: [this document]
2.3.32. Proxy Loop Detected
* Name: proxy_loop_detected
* Description: The intermediary tried to forward the request to
itself, or a loop has been detected using different means (e.g.
[RFC8586]).
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Response only generated by intermediaries: true
* Reference: [this document]
2.4. Defining New Proxy Error Types
New Proxy Error Types can be defined by registering them in the HTTP
Proxy Error Types registry.
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Registration requests are reviewed and approved by Expert Review, as
per [RFC8126], Section 4.5. A specification document is appreciated,
but not required.
The Expert(s) should consider the following factors when evaluating
requests:
* Community feedback
* If the value is sufficiently well-defined
* Generic types are preferred over vendor-specific, application-
specific or deployment-specific values. If a generic value cannot
be agreed upon in the community, the types's name should be
correspondingly specific (e.g., with a prefix that identifies the
vendor, application or deployment).
* Extra Parameters should not conflict with registered Proxy-Status
parameters.
Registration requests should use the following template:
* Name: [a name for the Proxy Error Type that matches sf-token]
* Description: [a description of the conditions that generate the
Proxy Error Type]
* Extra Parameters: [zero or more optional parameters, along with
their allowable type(s)]
* Recommended HTTP status code: [the appropriate HTTP status code
for this entry]
* Response only generated by intermediaries: ['true' or 'false']
* Reference: [to a specification defining this error type; optional]
* Notes: [optional]
If the Proxy Error Type might occur in responses that are not
generated by the intermediary -- for example, when an error is
detected as the response is streamed from a forward connection,
causing a Proxy-Status trailer field to be appended -- the 'Response
only generated by intermediaries' should be 'false'. If the Proxy
Error Type only occurs in responses that are generated by the
intermediary, it should be 'true'.
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See the registry at https://iana.org/assignments/http-proxy-status
(https://iana.org/assignments/http-proxy-status) for details on where
to send registration requests.
3. IANA Considerations
Upon publication, please create the HTTP Proxy-Status Parameters
registry and the HTTP Proxy Error Types registry at
https://iana.org/assignments/http-proxy-status
(https://iana.org/assignments/http-proxy-status) and populate them
with the types defined in Section 2.1 and Section 2.3 respectively;
see Section 2.2 and Section 2.4 for its associated procedures.
Additionally, please register the following entry in the Hypertext
Transfer Protocol (HTTP) Field Name Registry:
* Field name: Proxy-Status
* Status: permanent
* Specification document(s): [this document]
* Comments:
4. Security Considerations
One of the primary security concerns when using Proxy-Status is
leaking information that might aid an attacker. For example,
information about the intermediary's configuration and back-end
topology can be exposed, allowing attackers to directly target back-
end services that are not prepared for high traffic volume or
malformed inputs. Some information might only be suitable to reveal
to authorized parties.
As a result, care needs to be taken when deciding to generate a
Proxy-Status field and what information to include in it. Note that
intermediaries are not required to generate a Proxy-Status field in
any response, and can conditionally generate them based upon request
attributes (e.g., authentication tokens, IP address).
Likewise, generation of all parameters is optional, as is generation
of the field itself. Also, the field's content is not verified; an
intermediary can claim certain actions (e.g., sending a request over
an encrypted channel) but fail to actually do that.
5. References
5.1. Normative References
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[HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-19>.
[STRUCTURED-FIELDS]
Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/rfc/rfc8499>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
Lawrence, "Extended DNS Errors", RFC 8914,
DOI 10.17487/RFC8914, October 2020,
<https://www.rfc-editor.org/rfc/rfc8914>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
5.2. Informative References
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[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC8586] Ludin, S., Nottingham, M., and N. Sullivan, "Loop
Detection in Content Delivery Networks (CDNs)", RFC 8586,
DOI 10.17487/RFC8586, April 2019,
<https://www.rfc-editor.org/rfc/rfc8586>.
Authors' Addresses
Mark Nottingham
Fastly
Prahran
Australia
Email: mnot@mnot.net
URI: https://www.mnot.net/
Piotr Sikora
Google
Email: piotrsikora@google.com
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