doc/man7/property.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 property - Properties, a selection mechanism for algorithm implementations

 =head1 DESCRIPTION

 As of OpenSSL 3.0, a new method has been introduced to decide which of
 multiple implementations of an algorithm will be used.
 The method is centered around the concept of properties.
 Each implementation defines a number of properties and when an algorithm
 is being selected, filters based on these properties can be used to
 choose the most appropriate implementation of the algorithm.

 Properties are like variables, they are referenced by name and have a value
 assigned.

 =head2 Property Names

 Property names fall into two categories: those reserved by the OpenSSL
 project and user defined names.
 A I<reserved> property name consists of a single C-style identifier
 (except for leading underscores not being permitted), which begins
 with a letter and can be followed by any number of letters, numbers
 and underscores.
 Property names are case-insensitive, but OpenSSL will only use lowercase
 letters.

 A I<user defined> property name is similar, but it B<must> consist of
 two or more C-style identifiers, separated by periods.
 The last identifier in the name can be considered the 'true' property
 name, which is prefixed by some sort of 'namespace'.
 Providers for example could include their name in the prefix and use
 property names like

   <provider_name>.<property_name>
   <provider_name>.<algorithm_name>.<property_name>

 =head2 Properties

 A I<property> is a I<name=value> pair.
 A I<property definition> is a sequence of comma separated properties.
 There can be any number of properties in a definition, however each name must
 be unique.
 For example: "" defines an empty property definition (i.e., no restriction);
 "my.foo=bar" defines a property named I<my.foo> which has a string value I<bar>
 and "iteration.count=3" defines a property named I<iteration.count> which
 has a numeric value of I<3>.
 The full syntax for property definitions appears below.

 =head2 Implementations

 Each implementation of an algorithm can define any number of
 properties.
 For example, the default provider defines the property I<provider=default>
 for all of its algorithms.
 Likewise, OpenSSL's FIPS provider defines I<provider=fips> and the legacy
 provider defines I<provider=legacy> for all of their algorithms.

 =head2 Queries

 A I<property query clause> is a single conditional test.
 For example, "fips=yes", "provider!=default" or "?iteration.count=3".
 The first two represent mandatory clauses, such clauses B<must> match
 for any algorithm to even be under consideration.
 The third clause represents an optional clause.
 Matching such clauses is not a requirement, but any additional optional
 match counts in favor of the algorithm.
 More details about that in the B<Lookups> section.
 A I<property query> is a sequence of comma separated property query clauses.
 It is an error if a property name appears in more than one query clause.
 The full syntax for property queries appears below, but the available syntactic
 features are:

 =over 4

 =item *

 B<=> is an infix operator providing an equality test.

 =item *

 B<!=> is an infix operator providing an inequality test.

 =item *

 B<?> is a prefix operator that means that the following clause is optional
 but preferred.

 =item *

 B<-> is a prefix operator that means any global query clause involving the
 following property name should be ignored.

 =item *

 B<"..."> is a quoted string.
 The quotes are not included in the body of the string.

 =item *

 B<'...'> is a quoted string.
 The quotes are not included in the body of the string.

 =back

 =head2 Lookups

 When an algorithm is looked up, a property query is used to determine
 the best matching algorithm.
 All mandatory query clauses B<must> be present and the implementation
 that additionally has the largest number of matching optional query
 clauses will be used.
 If there is more than one such optimal candidate, the result will be
 chosen from amongst those in an indeterminate way.
 Ordering of optional clauses is not significant.

 =head2 Shortcut

 In order to permit a more concise expression of boolean properties, there
 is one short cut: a property name alone (e.g. "my.property") is
 exactly equivalent to "my.property=yes" in both definitions and queries.

 =head2 Global and Local

 Two levels of property query are supported.
 A context based property query that applies to all fetch operations and a local
 property query.
 Where both the context and local queries include a clause with the same name,
 the local clause overrides the context clause.

 It is possible for a local property query to remove a clause in the context
 property query by preceding the property name with a '-'.
 For example, a context property query that contains "fips=yes" would normally
 result in implementations that have "fips=yes".

 However, if the setting of the "fips" property is irrelevant to the
 operations being performed, the local property query can include the
 clause "-fips".
 Note that the local property query could not use "fips=no" because that would
 disallow any implementations with "fips=yes" rather than not caring about the
 setting.

 =head1 SYNTAX

 The lexical syntax in EBNF is given by:

  Definition     ::= PropertyName ( '=' Value )?
                         ( ',' PropertyName ( '=' Value )? )*
  Query          ::= PropertyQuery ( ',' PropertyQuery )*
  PropertyQuery  ::= '-' PropertyName
                   | '?'? ( PropertyName (( '=' | '!=' ) Value)?)
  Value          ::= NumberLiteral | StringLiteral
  StringLiteral  ::= QuotedString | UnquotedString
  QuotedString   ::= '"' [^"]* '"' | "'" [^']* "'"
  UnquotedString ::= [^{space},]+
  NumberLiteral  ::= '0' ( [0-7]* | 'x' [0-9A-Fa-f]+ ) | '-'? [1-9] [0-9]+
  PropertyName   ::= [A-Z] [A-Z0-9_]* ( '.' [A-Z] [A-Z0-9_]* )*

 =head1 HISTORY

 Properties were added in OpenSSL 3.0

 =head1 COPYRIGHT

 Copyright 2019-2020 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
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=head1 NAME

	property - Properties, a selection mechanism for algorithm implementations

	=head1 DESCRIPTION

	As of OpenSSL 3.0, a new method has been introduced to decide which of
	multiple implementations of an algorithm will be used.
	The method is centered around the concept of properties.
	Each implementation defines a number of properties and when an algorithm
	is being selected, filters based on these properties can be used to
	choose the most appropriate implementation of the algorithm.

	Properties are like variables, they are referenced by name and have a value
	assigned.

	=head2 Property Names

	Property names fall into two categories: those reserved by the OpenSSL
	project and user defined names.
	A I<reserved> property name consists of a single C-style identifier
	(except for leading underscores not being permitted), which begins
	with a letter and can be followed by any number of letters, numbers
	and underscores.
	Property names are case-insensitive, but OpenSSL will only use lowercase
	letters.

	A I<user defined> property name is similar, but it B<must> consist of
	two or more C-style identifiers, separated by periods.
	The last identifier in the name can be considered the 'true' property
	name, which is prefixed by some sort of 'namespace'.
	Providers for example could include their name in the prefix and use
	property names like

	<provider_name>.<property_name>
	<provider_name>.<algorithm_name>.<property_name>

	=head2 Properties

	A I<property> is a I<name=value> pair.
	A I<property definition> is a sequence of comma separated properties.
	There can be any number of properties in a definition, however each name must
	be unique.
	For example: "" defines an empty property definition (i.e., no restriction);
	"my.foo=bar" defines a property named I<my.foo> which has a string value I<bar>
	and "iteration.count=3" defines a property named I<iteration.count> which
	has a numeric value of I<3>.
	The full syntax for property definitions appears below.

	=head2 Implementations

	Each implementation of an algorithm can define any number of
	properties.
	For example, the default provider defines the property I<provider=default>
	for all of its algorithms.
	Likewise, OpenSSL's FIPS provider defines I<provider=fips> and the legacy
	provider defines I<provider=legacy> for all of their algorithms.

	=head2 Queries

	A I<property query clause> is a single conditional test.
	For example, "fips=yes", "provider!=default" or "?iteration.count=3".
	The first two represent mandatory clauses, such clauses B<must> match
	for any algorithm to even be under consideration.
	The third clause represents an optional clause.
	Matching such clauses is not a requirement, but any additional optional
	match counts in favor of the algorithm.
	More details about that in the B<Lookups> section.
	A I<property query> is a sequence of comma separated property query clauses.
	It is an error if a property name appears in more than one query clause.
	The full syntax for property queries appears below, but the available syntactic
	features are:

	=over 4

	=item *

	B<=> is an infix operator providing an equality test.

	=item *

	B<!=> is an infix operator providing an inequality test.

	=item *

	B<?> is a prefix operator that means that the following clause is optional
	but preferred.

	=item *

	B<-> is a prefix operator that means any global query clause involving the
	following property name should be ignored.

	=item *

	B<"..."> is a quoted string.
	The quotes are not included in the body of the string.

	=item *

	B<'...'> is a quoted string.
	The quotes are not included in the body of the string.

	=back

	=head2 Lookups

	When an algorithm is looked up, a property query is used to determine
	the best matching algorithm.
	All mandatory query clauses B<must> be present and the implementation
	that additionally has the largest number of matching optional query
	clauses will be used.
	If there is more than one such optimal candidate, the result will be
	chosen from amongst those in an indeterminate way.
	Ordering of optional clauses is not significant.

	=head2 Shortcut

	In order to permit a more concise expression of boolean properties, there
	is one short cut: a property name alone (e.g. "my.property") is
	exactly equivalent to "my.property=yes" in both definitions and queries.

	=head2 Global and Local

	Two levels of property query are supported.
	A context based property query that applies to all fetch operations and a local
	property query.
	Where both the context and local queries include a clause with the same name,
	the local clause overrides the context clause.

	It is possible for a local property query to remove a clause in the context
	property query by preceding the property name with a '-'.
	For example, a context property query that contains "fips=yes" would normally
	result in implementations that have "fips=yes".

	However, if the setting of the "fips" property is irrelevant to the
	operations being performed, the local property query can include the
	clause "-fips".
	Note that the local property query could not use "fips=no" because that would
	disallow any implementations with "fips=yes" rather than not caring about the
	setting.

	=head1 SYNTAX

	The lexical syntax in EBNF is given by:

	Definition ::= PropertyName ( '=' Value )?
	( ',' PropertyName ( '=' Value )? )*
	Query ::= PropertyQuery ( ',' PropertyQuery )*
	PropertyQuery ::= '-' PropertyName
	\| '?'? ( PropertyName (( '=' \| '!=' ) Value)?)
	Value ::= NumberLiteral \| StringLiteral
	StringLiteral ::= QuotedString \| UnquotedString
	QuotedString ::= '"' [^"]* '"' \| "'" [^']* "'"
	UnquotedString ::= [^{space},]+
	NumberLiteral ::= '0' ( [0-7]* \| 'x' [0-9A-Fa-f]+ ) \| '-'? [1-9] [0-9]+
	PropertyName ::= [A-Z] [A-Z0-9_]* ( '.' [A-Z] [A-Z0-9_]* )*

	=head1 HISTORY

	Properties were added in OpenSSL 3.0

	=head1 COPYRIGHT

	Copyright 2019-2020 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
	L<https://www.openssl.org/source/license.html>.

	=cut