Ubuntu Manpage: openssl-qlog - OpenSSL qlog tracing functionality

Provided by: openssl_3.4.1-1ubuntu3_amd64

NAME

       openssl-qlog - OpenSSL qlog tracing functionality

DESCRIPTION

       OpenSSL has unstable support for generating logs in the qlog logging format, which can be used to obtain
       diagnostic data for QUIC connections. The data generated includes information on packets sent and
       received and the frames contained within them, as well as loss detection and other events.

       The qlog output generated by OpenSSL can be used to obtain diagnostic visualisations of a given QUIC
       connection using tools such as qvis.

       WARNING: The output of OpenSSL's qlog functionality uses an unstable format based on a draft
       specification. qlog output is not subject to any format stability or compatibility guarantees at this
       time, and will change in incompatible ways in future versions of OpenSSL. See FORMAT STABILITY below for
       details.

USAGE

       When OpenSSL is built with qlog support, qlog is enabled at run time by setting the standard QLOGDIR
       environment variable to point to a directory where qlog files should be written. Once set, any QUIC
       connection established by OpenSSL will have a qlog file written automatically to the specified directory.

       Log files are generated in the .sqlog format based on JSON-SEQ (RFC 7464).

       The filenames of generated log files under the specified QLOGDIR use the following structure:

           {connection_odcid}_{vantage_point_type}.sqlog

       where {connection_odcid} is the lowercase hexadecimal encoding of a QUIC connection's Original
       Destination Connection ID, which is the Destination Connection ID used in the header of the first Initial
       packet sent as part of the connection process, and {vantage_point_type} is either "client" or "server",
       reflecting the perspective of the endpoint producing the qlog output.

       The qlog functionality can be disabled at OpenSSL build time using the no-unstable-qlog configure flag.

SUPPORTED EVENT TYPES

       The following event types are currently supported:

       connectivity:connection_started
       connectivity:connection_state_updated
       connectivity:connection_closed
       transport:parameters_set
       transport:packet_sent
       transport:packet_received
       recovery:packet_lost

FILTERS

By default, all supported event types are logged. The OSSL_QFILTER environment variable can be used to
configure a filter specification which determines which event types are to be logged. Each event type can
be turned on and off individually. The filter specification is a space-separated list of terms listing
event types to enable or disable. The terms are applied in order, thus the effects of later terms
override the effects of earlier terms.

Examples
Here are some example filter specifications:

"*" (or "+*")
Enable all supported qlog event types.

"-*"
Disable all qlog event types.

"* -transport:packet_received"
Enable all qlog event types, but disable the transport:packet_received event type.

"-* transport:packet_sent"
Disable all qlog event types, except for the transport:packet_sent event type.

"-* connectivity:* transport:parameters_set"
Disable all qlog event types, except for transport:parameters_set and all supported event types in
the connectivity category.

Filter Syntax Specification
Formally, the format of the filter specification in ABNF is as follows:

filter = *filter-term

filter-term = add-sub-term

add-sub-term = ["-" / "+"] specifier

specifier = global-specifier / qualified-specifier

global-specifier = wildcard

qualified-specifier = component-specifier ":" component-specifier

component-specifier = name / wildcard

wildcard = "*"

name = 1*(ALPHA / DIGIT / "_" / "-")

Filter terms are interpreted as follows:

"+*" (or "*")
Enables all event types.

"-*"
Disables all event types.

"+foo:*" (or "foo:*")
Enables all event types in the foo category.

"-foo:*"
Disables all event types in the foo category.

"+foo:bar" (or "foo:bar")
Enables a specific event type foo:bar.

"-foo:bar"
Disables a specific event type foo:bar.

Partial wildcard matches are not supported at this time.

Default Configuration
If the OSSL_QFILTER environment variable is not set or set to the empty string, this is equivalent to
enabling all event types (i.e., it is equivalent to a filter of "*"). Note that the QLOGDIR environment
variable must also be set to enable qlog.

FORMAT STABILITY

The OpenSSL qlog functionality currently implements a draft version of the qlog specification. Future
revisions to the qlog specification in advance of formal standardisation are expected to introduce
incompatible and breaking changes to the qlog format. The OpenSSL qlog functionality will transition to
producing output in this format in the future once standardisation is complete.

Because of this, the qlog output of OpenSSL will change in incompatible and breaking ways in the future,
including in non-major releases of OpenSSL. The qlog output of OpenSSL is considered unstable and not
subject to any format stability or compatibility guarantees at this time.

Users of the OpenSSL qlog functionality must be aware that the output may change arbitrarily between
releases and that the preservation of compatibility with any given tool between releases is not
guaranteed.

Aims
The OpenSSL draft qlog functionality is primarily intended for use in conjunction with the qvis tool
<https://qvis.quictools.info/>. In terms of format compatibility, the output format of the OpenSSL qlog
functionality is expected to track what is supported by qvis. As such, future changes to the output of
the OpenSSL qlog functionality are expected to track changes in qvis as they occur, and reflect the
versions of qlog currently supported by qvis.

This means that prior to the finalisation of the qlog standard, in the event of a disparity between the
current draft and what qvis supports, the OpenSSL qlog functionality will generally aim for qvis
compatibility over compliance with the latest draft.

As such, OpenSSL's qlog functionality currently implements qlog version 0.3 as defined in
draft-ietf-quic-qlog-main-schema-05 and draft-ietf-quic-qlog-quic-events-04. These revisions are
intentionally used instead of more recent revisions due to their qvis compatibility.

LIMITATIONS

       The OpenSSL implementation of qlog currently has the following limitations:

       •   Not all event types defined by the draft specification are implemented.

       •   Only the JSON-SEQ (.sqlog) output format is supported.

       •   Only the QLOGDIR environment variable is supported for configuring the  qlog  output  directory.  The
           standard QLOGFILE environment variable is not supported.

       •   There is no API for programmatically enabling or controlling the qlog functionality.

HISTORY

       This functionality was added in OpenSSL 3.3.

COPYRIGHT

       Copyright 2024 The OpenSSL Project Authors. All Rights Reserved.

       Licensed  under  the  Apache License 2.0 (the "License").  You may not use this file except in compliance
       with the License.  You can obtain  a  copy  in  the  file  LICENSE  in  the  source  distribution  or  at
       <https://www.openssl.org/source/license.html>.

3.4.1                                              2025-04-03                                 OPENSSL-QLOG(7SSL)