Hypertext Transfer Protocol Working Group C. Benfield
Internet-Draft Hewlett Packard Enterprise
Intended status: Informational B. Fitzpatrick
Expires: January 29, 2017 Google, Inc.
July 28, 2016
HTTP/2 Implementation Debug State
draft-benfield-http2-debug-state-00
Abstract
This document defines a standard format and well-known URI for HTTP/2
server implementations to expose their internal state for the
purposes of debugging and interoperability work.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Debug Output . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Settings . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Peer Settings . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Outbound Flow Control Window . . . . . . . . . . . . . . 4
2.4. Inbound Flow Control Window. . . . . . . . . . . . . . . 4
2.5. Streams . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.6. HPACK . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.7. Sent GoAway . . . . . . . . . . . . . . . . . . . . . . . 7
2.8. Additional Fields . . . . . . . . . . . . . . . . . . . . 8
3. Debug Headers . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Flow In . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Flow Out . . . . . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
4.1. Well-known URI . . . . . . . . . . . . . . . . . . . . . 9
5. Normative References . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The HTTP/2 [RFC7540] specification provides an alternative framing
layer for the semantics of HTTP/1.1 [RFC7231]. This alternative
framing layer includes substantially greater quantities of state to
be stored by all implementations. Disagreements on the state of the
connection are the cause of the vast majority of interoperability
errors in HTTP/2 implementations.
In general it is not possible for implementations to query the
internal state of their peer, and those implementations that do
expose their internal state do it using a number of different
interfaces, in different places, and in different formats. This
makes it hard to debug interoperability problems, particularly when
those problems arise on the open web with implementations that have
unknown configuration and that may not identify themselves clearly.
This document defines a standard format and well-known URI for HTTP/2
server implementations to make their internal state available for
introspection. This allows both new and established implementers to
do more effective testing of their implementations, as well as to
enable them to more effectively diagnose and report subtle bugs in
both their own and other implementations.
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1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Debug Output
An implementation that wishes to support the HTTP/2 debug state
information does so by publishing a JSON document at a well-known URI
([RFC5785]): specifically, at .well-known/h2interop/state. This JSON
document reveals aspects of the state of the specific HTTP/2
connection as seen by the implementation in question at the time of
response generation.
This JSON document is represented as a single JSON object with
multiple keys. The object has several mandatory keys, as well as
several optional ones. The fields are outlined below.
2.1. Settings
The "settings" key in the state object is associated with a JSON
object that contains the remote implementation's active settings.
These are the settings that are actually in force for the connection
at this time. This means that if the implementation has emitted a
SETTINGS frame but has not yet received an ACK, the changes in that
SETTINGS frame MUST NOT be reflected in the object.
Each setting is published along with its value. The name of each
setting MUST be the same as its name in [RFC7540] Section 6.5.2: for
example, "SETTINGS_ENABLE_PUSH". The values MUST be sent as JSON
integers.
An implementation MAY omit a setting from this object if it has never
been emitted by the implementation. In this situation it should be
assumed that the default value is in force.
A conforming implementation MUST emit this field.
Sample output:
"settings": {
"SETTINGS_MAX_CONCURRENT_STREAMS": 250,
"SETTINGS_MAX_FRAME_SIZE": 1048576,
"SETTINGS_MAX_HEADER_LIST_SIZE": 1048896
}
Figure 1: Example output for settings key
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2.2. Peer Settings
The "peerSettings" key in the state object is associated with a JSON
object that contains the remote implementation's view of the local
implementation's settings. These are the settings that are actually
in force for the connection at this time.
The value of this key is exactly symmetrical with the value of the
"settings" key: see Section 2.1 for more.
A conforming implementation MUST emit this field.
Sample output:
"peerSettings": {
"SETTINGS_HEADER_TABLE_SIZE": 4096,
"SETTINGS_ENABLE_PUSH": 1,
"SETTINGS_INITIAL_WINDOW_SIZE": 6291456,
"SETTINGS_MAX_FRAME_SIZE": 16384,
"SETTINGS_MAX_CONCURRENT_STREAMS": 1000
}
Figure 2: Example output for peerSettings key
2.3. Outbound Flow Control Window
The "connFlowOut" key in the state object is associated with a JSON
integer that reflects the remote peer's outbound connection window
size. This represents the number of flow controlled bytes the remote
implementation believes it can emit before the entire connection is
blocked behind flow control.
A conforming implementation MUST emit this field.
Sample output:
"connFlowOut": 15724175,
Figure 3: Example output for connFlowOut key
2.4. Inbound Flow Control Window.
The "connFlowIn" key in the state object is associated with a JSON
integer that reflects the remote peer's inbound connection window
size. This represents the number of flow controlled bytes the remote
implementation believes it can receive before the entire connection
is blocked behind flow control.
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A conforming implementation MUST emit this field.
Sample output:
"connFlowIn": 65535,
Figure 4: Example output for connFlowIn key
2.5. Streams
The "streams" key in the state object is associated with a JSON
object containing state about all the active streams on the
connection. A stream MUST be represnted in this JSON object if it is
in any state other than IDLE or CLOSED.
This JSON object has keys that are the stream IDs for the active
streams. Each key has an object associated with it, with the
following keys:
o "state": This key maps to a string value representing the stream
state. The stream states are represented as all-caps ASCII text
with all parentheses stripped and spaces replaced with
underscores. For example, "OPEN" or "HALF_CLOSED_LOCAL". This
field MUST be present.
o "flowIn": The remote peer's inbound stream window size as a JSON
integer. This represents the number of flow controlled bytes the
remote implementation believes it can receive on this stream
before this stream is blocked behind flow control. This field
MUST be present.
o "flowOut": The remote peer's outbound stream window size as a JSON
integer. This represents the number of flow controlled bytes the
remote implementation believes it can send on this stream before
this stream is blocked behind flow control. This field MUST be
present.
o "dataIn": The number of bytes of data the remote implementation
has received on this stream. This excludes padding bytes. This
field MAY be present, but is optional.
o "dataOut": The number of bytes of data the remote implementation
has sent on this stream. This excludes padding bytes. This field
MAY be present, but is optional.
A conforming implementation MUST emit this field, but MAY omit any of
the optional sub-fields.
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Sample output:
"streams": {
"5": {
"state": "HALF_CLOSED_REMOTE",
"flowIn": 65535,
"flowOut": 6291456,
"dataIn": 0,
"dataOut": 0
},
"7": {
"state": "OPEN",
"flowIn": 65535,
"flowOut": 6291456
}
},
Figure 5: Example output for streams key
2.6. HPACK
The "hpack" key contains information about the HPACK compression
state for the connection. It maps to a JSON object that represents
this compression state.
This JSON object contains the following fields:
o "inbound_table_size": The current size of the HPACK dynamic header
table for the headers emitted by the local implementation, as an
integer. This field MUST be present.
o "outbound_table_size": The current size of the HPACK dynamic
header table for the headers emitted by the remote implementation,
as an integer. Note that this value MUST include the headers
added to the compression context as part of serving this response.
This field MUST be present.
o "inbound_dynamic_header_table": The entries added to the HPACK
dynamic header table by the local implementation. This is
formatted as a JSON array of two-element JSON arrays, the first
element of which contains the header name and the second element
of which contains the header value. This field MAY be omitted.
o "outbound_dynamic_header_table": The entries added to the HPACK
dynamic header table by the remote implementation. This is
formatted in the same manner as "inbound_dynamic_header_table".
This field MAY be omitted.
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A conforming implementation MAY omit this field. If it does include
this field, it MAY omit any optional sub-fields.
Sample output:
"hpack": {
"inbound_table_size": 340,
"inbound_dynamic_header_table": [
[
"accept-encoding",
"gzip, deflate, sdch, br"
],
[
"upgrade-insecure-requests",
"1"
],
[
"cache-control",
"max-age=0"
],
[
":authority",
"shootout.lukasa.co.uk"
]
],
"outbound_table_size": 137,
"outbound_dynamic_header_table": [
[
"content-type",
"application/json"
],
[
"server",
"TwistedWeb/16.3.0"
]
]
}
Figure 6: Example output for hpack key
2.7. Sent GoAway
The "sentGoAway" field tracks whether or not a GOAWAY frame
([RFC7540] Section 6.8) has been sent on the connection by the remote
implementation. The value of this field is boolean.
A conforming implementation MAY omit this field.
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Sample output:
"sentGoAway": false,
Figure 7: Example output for sentGoAway key
2.8. Additional Fields
In addition to these fields, implementations MAY add their own
debugging information, as appropriate, to the JSON object. These
MUST be keyed off keys other than the ones defined in this document.
For example, some implementations are known to expose the number of
threads they currently have active in the "threads" field.
3. Debug Headers
One of the most common issues when implementing HTTP/2 is to have
problems with flow control windows. This is why the "connFlowOut"
(Section 2.3) and "connFlowIn" (Section 2.4) fields are defined in
the JSON document.
However, it's possible that the two implementations disagree on the
size of this window, and that the server believes that it cannot send
the response body because it's blocked behind flow control. For this
reason, a small amount of debugging data MUST be inserted into the
response headers for this JSON document. This ensures that it is
possible for implementations to discover that they have inadvertently
blocked the debug response behind flow control, and to take action to
widen the flow control window so that the response can be delivered.
The following header fields MUST be emitted by implementations.
3.1. Flow In
The "conn-flow-in" header field contains the size of the remote
implementation's inbound flow control window. The field value
contains only the size of that window in octets. This MUST be
calculated the same way that the implementation calculates
"connFlowIn" (Section 2.4).
3.2. Flow Out
The "conn-flow-out" header field contains the size of the remote
implementation's outbound flow control window. The field value
contains only the size of that window in octets. This MUST be
calculated the same way that the implementation calculates
"connFlowOut" (Section 2.3).
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4. IANA Considerations
4.1. Well-known URI
This document establishes a single well-known URI, with the suffix
"h2interop/state".
5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
DOI 10.17487/RFC5785, April 2010,
<http://www.rfc-editor.org/info/rfc5785>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
Appendix A. Acknowledgements
We would like to thank the attendees of the 2016 HTTP Workshop in
Stockholm for their feedback on early prototype implementations of
this debugging feature.
Appendix B. Changelog
(This appendix to be deleted by the RFC editor.)
Authors' Addresses
Cory Benfield
Hewlett Packard Enterprise
Email: cory@lukasa.co.uk
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Brad Fitzpatrick
Google, Inc.
Email: brad@danga.com
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