package Rinci::function; # just to make PodWeaver happy

# DATE
# VERSION

1;
# ABSTRACT: Metadata for your functions/methods

__END__

=pod

=encoding UTF-8

=head1 NAME

Rinci::function - Metadata for your functions/methods

=head1 SPECIFICATION VERSION

 1.1

=head1 VERSION

This document describes version 1.1.94 of Rinci::function (from Perl distribution Rinci), released on 2020-09-23.

=head1 INTRODUCTION

This document describes metadata for functions/methods. Since the metadata
properties describe features and the way a function works, this document also
describes how a function should support those properties.

This specification is part of L<Rinci>. Please do a read up on it first, if you
have not already done so.

=head1 SPECIFICATION

B<Result envelope>. Function should return an enveloped result to express error
code/message as well as actual result. The envelope can be produced by the
function itself, or added by a wrapper tool. Result envelope is modeled after
HTTP or L<PSGI> response; it is an array in the following format:

 [STATUS*, MESSAGE, RESULT, META]

STATUS is a 3-digit integer and is the only required element, much like HTTP
response status code and is explained further in L</"Envelope status codes">.
MESSAGE is a string containing error message. RESULT (or PAYLOAD) is the actual
content to be returned and can be omitted or set to undef if the function does
not need to return anything. META is called result metadata, a defhash
containing extra data, analogous to HTTP response headers. Result metadata is
specified further in L<Rinci::resmeta>.

Some example of an enveloped results:

 [200]
 [200, "OK", 42]
 [404, "Not found"]
 [200, "Account created", {id=>9323}, {}]
 [500, "Can't delete foo: permission denied", undef,
  {"cmdline.exit_code"=>300, perm_err=>1}]

As mentioned, an enveloped result can contain error code/message as well as the
actual result. It can also be easily converted to HTTP response message. And it
can also contain extra data, useful for things like the transaction protocol
(explained in L<Rinci::Transaction>).

B<Special arguments>. Special arguments are some known arguments that start with
dash (C<->) and serve special purposes. You need not specify them in the C<args>
metadata property. Examples of special arguments include C<-dry_run>,
C<-tx_action>, C<-action>, C<-confirm/*>, C<-arg_part_start>, C<-arg_part_len>,
C<-res_part_start>, C<-res_part_len>. They will be explained in other related
sections/documents.

B<Functions vs methods>. Since in many programming languages (like Perl 5,
Python, Ruby, PHP) static functions are not that differentiated from methods,
functions and methods share the same Rinci spec. But there are certain
properties that can be used to declare if a function is (also) a method or not.
See C<is_func>, C<is_meth>, C<is_class_meth> properties below for details.

B<Multiple dispatch>. This specification also does not (yet) have any
recommendation on how to best handle functions in languages that support
multiple dispatch, like Perl 6: whether we should create multiple metadata or
just one. It is more up to the tool and what you want to do with the metadata.

=head2 Envelope status codes

In general, status codes map directly to HTTP response status codes. Below are
the suggestion on which codes to use (or avoid). An asterisk (C<*>) marks which
codes are not defined in HTTP specification and introduced by this
specification.

=over 4

=item * 1xx code

Currently not used. Some tools like L<Perinci::CmdLine> assumes that status code
is always C<< >= 200 >>, so you should perhaps never used status less than 200.

=item * 2xx code - success

200 should be used to mean success.

201 (created) can be used to signal success when creating something.

204 (no content) can also be used when there is no content to show. In HTTP,
browsers won't clear current page if response is 206 (instead of showing a blank
page if response is 200). Currently in Rinci there is no difference between 200
and 204.

206 (partial content) can be used to signal partial content. See C<partial>
property in the C<result> function property.

207 (multistatus) can be used to signal partial success, for example a function
which processed 5 items wanted to report that it successfully processed 2 items
but failed to process the rest 3 items. For each item's statuses, you can use
result metadata property C<results>. Note: 207 is used by WebDAV. Note: When all
functions instead of only some/partial items fail, you might want to return 4xx
or 5xx instead of 207.

=item * 3xx code - further actions needs to be taken by user agent (caller)

301 (moved) can be used to redirect callers to alternate location, although this
is very rare.

304 (not modified, nothing done). Used for example by setup functions to
indicate that nothing is being modified or no modifying action has been
performed (see Setup::* modules in CPAN).

331* (confirmation required). Function requires confirmation, for example if
action to be taken is dangerous or requires user's attention. Confirmation
message/prompt from function can be returned in the message, or in the
C<confirm_prompt> property (e.g. to provide translations). Confirmation from
caller is in the form of special argument C<-confirm> with boolean value of true
(TODO: A more detailed confirmation for different actions can be specified later
in the form of C<-confirm_XXX> special arguments.) For an example of application
of this, see L<Perinci::Tx::Manager>.

=item * 4xx code - client (caller) side error

400 (bad request, bad arguments) should be returned when the function encounters
invalid input. A function wrapper can return this code when the function
arguments fail the argument schema validation (specified in the C<args>
property).

401 (authentication required).

403 (forbidden, access denied, authorization failed).

404 (not found). Can be used for example by an object-retrieval functions (like
C<get_user()>) and the object is not found.

For object-listing functions (like C<list_users()>), when there are no users
found matching the requested criteria, 200 code should still be returned with an
empty result (like an empty array or hash).

Also in general, an object-deletion function (like C<delete_user()>) should also
return 200 (or perhaps 304, but 200 is preferred) instead of 404 when the object
specified to be deleted is not found, since the goal of the delete function is
reached anyway.

408 (request timeout).

409 (conflict). Can be used for example by a C<create_user()> function when
receiving an already existing username.

412 (precondition failed). Similar to 409, but can be used to indicate lack of
resources, like disk space or bandwidth. For lacking authentication and
authorization, use 401 and 403 respectively.

413 (request range not satisfiable). When client requests partial result outside
the range of available. See the C<partial> property in C<result> property for
examples.

429 (too many requests).

(EXPERIMENTAL) 44x* codes are reserved for function-specific codes. Each
function is free to define what each number means. However, this is not really
encouraged and should only be used if necessary. Function should perhaps stick
to predefined codes here. To return more detailed status, result metadata can be
used.

480* is general transaction error, e.g. transaction status is aborted so further
requests for this transaction is ignored until transaction is aborted.

484* (no such transaction).

=item * 5xx code - server (callee) side error

500 is the general code to use when a failure occurs during the execution of a
function. for example when a C<delete_file()> function fails to delete specified
file (though in this case it can also choose to return 403 instead, which is
more specific).

501 (not implemented)

503 (service unavailable). You can use this when service is temporarily
unavailable, e.g. when system load is too high, a required service is down, etc.
Users should try again at a later time.

507 (insufficient storage)

521 (maximum retries reached)

531* (bad metadata) is used when there is something wrong with the metadata.

532* (failure in recording transaction) when there is a failure in updating
transaction status or in preparing/committing/rolling back the transaction.

(EXPERIMENTAL) 54x* codes are reserved for function-specific codes. Each
function is free to define what each number means. However, this is not really
encouraged and should only be used if necessary. Function should perhaps stick
to predefined codes here. To return more detailed status, result metadata can be
used.

Try not to use code greater than 555, as some tools use (CODE-300) for error
codes that must fit in one unsigned byte (like L<Perinci::CmdLine>).

=back

=head2 is_func

Bool. Specify that the function can be called as a static function (i.e.
procedural, not as a method). Default is true if unspecified, but becomes false
if is_meth or is_class_meth is set to true.

Example:

 # specify that function can be called a method *as well as* a static function
 is_meth => 1
 is_func => 1 # if not specified, will default to false after is_meth set to 1

=head2 is_meth

Bool. Specify that the function can be called as an instance (object) method.
Default is false.

Example:

 # specify that function is a method
 is_meth => 1

=head2 is_class_meth

Bool. Specify that the function can be called as a class method. Examples of
class methods include the constructor, but there are others. Default is false.

Example:

 # specify that function is a class method
 is_class_meth => 1

=head2 args (function property)

Hash. Specify arguments. Property value is defhash of argument names and
argument specification. Argument name must only contain letters, numbers, and
underscores (and do not start with a number).

Argument specification is a hash containing these keys:

=head3 schema (argument property)

L<Data::Sah> schema for argument value.

=head3 default

Any. Give default value for argument. This takes precedence over schema, which
can also specify default value. This is useful if you want to share a common
schema over several arguments but want to have different default for each
argument. For example, you have a C<ticket_status> schema. In C<create_ticket>
function you want the default C<status> argument to be C<new>, while in
C<reply_ticket> you want the default C<status> to be C<answered>.

=head3 summary (argument property)

Str. From DefHash. A one-line plaintext summary, much like the C<summary>
property in variable metadata.

=head3 req

Bool. Specify that argument is required (although its value can be undef/null).
Default is false.

=head3 description (argument property)

Str. From DefHash. A longer description of marked up text, much like the
C<description> property. It is suggested to format the text to 74 columns.

=head3 tags (argument property)

Array of (str|hash). From DefHash. An array of tags, can be used by tools to
categorize arguments. Not unlike the C<tags> property.

=head3 pos

Non-negative integer. Argument position when specified in an ordered fashion,
e.g. in an array. Starts from zero.

=head3 slurpy

Bool. Only relevant if B<pos> is specified, specify whether argument should
gobble up all remaining values in an ordered argument list into an array.

Old alias: L</greedy>

=head3 greedy

Old alias for L</slurpy>. Will be removed in Rinci 1.2.

=head3 partial (argument property)

Bool. Whether or not argument value can be sent partially. Only argument types
that have a length notion can be set as partial (e.g. C<str> where the unit is
character, C<buf> where the unit is byte, and C<array> where the unit is
element).

There should at most be one argument with this property set to true.

To send partial argument, you can use the special arguments C<-arg_len> (total
argument length), C<-arg_part_start> (start position of the part that is being
sent), C<-arg_part_len> (length of part that is being sent). Example (in Perl):

 # function metadata
 {
     v => 1.1,
     summary => "Upload a file",
     args => {
         name => {schema=>"str*", req=>1},
         data => {schema=>"buf*", req=>1, partial=>1},
     },
 }

 # function usage example: send the first 10MiB of data
 upload_file(name=>"myvideo.mp4", data=>substr($data, 0, 10_000_000),
             -arg_len        => 24_500_000,
             -arg_part_start =>          0,
             -arg_part_len   => 10_000_000);
 # send the next 10MiB
 upload_file(name=>"myvideo.mp4", data=>substr($data, 10_000_000, 10_000_000),
             -arg_len        => 24_500_000,
             -arg_part_start => 10_000_000,
             -arg_part_len   => 10_000_000);
 # send the last 4.5 MiB
 upload_file(name=>"myvideo.mp4", data=>substr($data, 20_000_000),
             -arg_len        => 24_500_000,
             -arg_part_start => 20_000_000,
             -arg_part_len   =>  4_500_000);

=head3 stream (argument property)

Bool. By setting this property to true, function can specify that it accepts
streaming data for this argument. It is useful when argument value is large or
of undetermined/infinite length. To send value as a stream, caller must send a
subroutine reference (callback) instead which the function will call repeatedly
until it gets undef to signify exhaustion of data.

=head3 cmdline_aliases

Hash. Specify aliases for use in command-line options (or other possibly
suitable situation where arguments are parsed from command-line-like options).
Keys are alias names, values are itself hashes (alias specification). Valid
alias specification keys: C<summary> (a string, optional), C<schema> (optional,
defaults to argument's schema), C<is_flag> (bool, optional, if set to 1 then it
is a shortcut for specifying C<schema> to C<< ["bool", {"is":1}] >>), C<code> (a
code to set argument value, optional, will be given C<< (\%args, $val) >>); if
not set, the default behavior is simply to set the argument value).

=head3 cmdline_on_getopt

Code. A hook that will be called when argument is specified as a command-line
option. In Perl, hook will be called with a hash argument containing this key:
C<arg> (str, argument name), C<value> (str, option value), C<args> (hash, the
argument hash defined so far).

This can be useful if you want to process a command-line option directly on a
per-option basis instead of getting the final resulting argument value. For
example (in Perl):

 args => {
     library => {
         schema            => ['array*' => of => 'str*'],
         cmdline_aliases   => { I => {} },
         cmdline_on_getopt => sub {
             my %args = @_;
             require lib;
             lib->import($args{value});
         },
     },
     module => {
         schema            => ['array*' => of => 'str*'],
         cmdline_aliases   => { M => {} },
         cmdline_on_getopt => sub {
             my %args = @_;
             require Module::Load;
             Module::Load::load($args{value});
         },
     },
 }

With command-line argument like this:

 -I dir1 -M mod1 -I dir2 -M mod2

Without any C<cmdline_on_getopt> hooks, the function will receive this argument
hash:

 { library => ['dir1', 'dir2'], module => ['mod1', 'mod2'] }

but there is no way to know the order of options being specified in the
command-line. With the hooks, the function can load modules correctly (e.g.
loading C<mod1> won't search in C<dir2> as that directory has not been added by
-I).

=head3 completion (argument property)

Code. A code to supply argument value completion. Will be explained in the
examples.

=head3 index_completion

Code. A code to supply argument element index completion. Applicable to the
following argument types:

B<hash>: for completing hash pair keys. (See also C<element_completion> for
completing hash pair values).

See examples for how to use this property.

=head3 element_completion

Code. A code to supply argument element value completion. Applicable to the
following argument types:

B<array>: for completing array element values.

B<hash>: for completing hash pair values. (See also C<index_completion> for
completing hash keys).

See examples for how to use this property.

=head3 is_password

Experimental. Bool. Describe that argument holds password. Programs can react to
this in several ways, for example they can turn off echoing to terminal when
asking value from standard input. Or they can redact values to C<****> when
logging.

=head3 cmdline_src

Str. Normally in a command-line program, command-line options and arguments will
map to function arguments, e.g. C<--arg 2> will set the C<foo> argument to C<2>
and positional arguments (argument which specifies the C<pos> property and
optionally also a C<slurpy> property with true value) will get or slurp
command-line arguments.

In some cases, this is not convenient. When supplying larger amount of data, a
complex structures, or a stream, we might want to use other sources. The
C<cmdline_src> property can be set to one of the following value for this
purpose:

=over

=item * file

Command-line option/argument value will be treated as filename and function
argument will be set to content of the file (or in the case of streaming
argument, to a callback which can be used to get the file's content).

=item * stdin

This means that program should get function argument from the whole standard
input until EOF.

Note that only one argument can have its source set to C<stdin> or
C<stdin_or_file> or C<stdin_or_files> or C<stdin_or_args>.

=item * stdin_or_file

This means that program should get argument value from content of file (the name
of which is given from the first remaining command-line argument after all other
arguments/options have been processed), or, if none is provided, from standard
input.

=item * stdin_or_files

This means that program should get argument value from content of files (the
names of which are taken from the remaining command-line arguments after all
other arguments/options have been processed), or, or if no command-line argument
remains, from standard input. This behavior is similar to the C<< <> >> (diamond
operator) in Perl.

=item * stdin_or_args

This means that program should get argument value from remaining command-line
argument(s), or if no command-line argument remains, from standard input.

=item * stdin_line

This means that program should get argument value from a line of standard input;
newline ending will be removed from the argument value.

Arguments with C<cmdline_src> of C<stdin_line> will be processed before
C<stdin>/C<stdin_or_file>/C<stdin_or_files>/C<stdin_or_args>.

=back

Other sources might be defined in the future.

TODO: Define C<web_src> property?

TODO: A way to define record separator?

=head3 cmdline_prompt

Str. String to display when asking for argument value from stdin (if
C<cmdline_src> property value is C<stdin_line>.

TODO: cmdline_prompt_template?

=head3 meta

Experimental. Hash. This allows specifying argument submetadata, used e.g. when
dealing with forms (a form field/widget can be a subform). Value is Rinci
function metadata.

=head3 element_meta

Experimental. Hash. This allows specifying argument element submetadata, used
e.g. when dealing with forms (a form field/widget can contain an array of
records/subforms). Value is Rinci function metadata.

=head3 deps (argument property)

Hash. This property specifies argument's dependencies to other arguments (but
possibly to other things too, in the future). This is similar to function's
L</"deps (function property)"> property. It is a hash or dep types and values.
The most important dep type is C<arg> (dependency to another argument). Some dep
types are special: C<all>, C<any>, C<none>. Example:

 args => {
     delete => {
         schema=>'bool',
     },
     force => {
         summary => 'Force deletion',
         schema => 'bool',
         deps => {arg=>'delete'},
     },

The above example states that argument C<force> "depends on" C<delete>. What it
means (usually) is that specifying C<force> only makes sense when C<delete> is
also specified. In a CLI context:

 % prog --delete --force

Specifying C<--force> without C<--delete> doesn't make sense.

=head3 filters

Experimental. Array of string, or code. Filters to apply before argument is
converted from text and validated.

=head3 examples (argument property)

Array. Each element is sample argument values. But if it is a hash, will be
assumed as a DefHash with the actual value put in the C<value> property (so if
your sample argument is a hash like C<{}> (in JSON), you have to specify it as
C<< {"value":{}, "summary":"Optional summary..."} >> (in JSON).

Note that a Sah schema can also have an L<examples|Sah::Type/"examples"> clause
which you can use to put examples in. And Rinci function metadata also has
L<examples|/"examples (function property)"> property too.

Example function metadata and its implementation in Perl:

 $SPEC{multiply2} = {
     v => 1.1,
     summary => 'Multiple two numbers',
     args => {
         a => {
             summary => 'The first operand',
             description => '... a longer description ...',
             schema=>['float*', {
                 examples => [1, -10, 0, 3.333],
             }],
             pos => 0,
             tags => ['category:operand'],
         },
         b => {
             summary => 'The second operand',
             description => '... a longer description ...',
             schema => 'float*',
             pos => 1,
             tags => ['category:operand'],
             examples => [
                 1, -10, 0, 3.333,
                 {value => 1e-10, summary => 'Blah blah'},
             ],
         },
         round => {
             summary => 'Whether to round result',
             description => '... a longer description ...',
             schema => [bool => {default=>0}],
             pos => 2,
             tags => ['category:options'],
             cmdline_aliases => {
                 r=>{},
                 R=>{summary=>'Equivalent to --round=0',
                     code=>sub { my ($args, $val) = @_; $args->{round}=0 }},
             },
         },
     }
 };
 sub multiply2 {
     my %args = @_;
     my $res = $args{a} * $args{b};
     $res = int($res) if $round;
     [200, "OK", $res];
 }

By default, without any wrapper, the function is called with a named hash style:

 multiply2(a=>4, b=>3);  # 12

But with the information from the metadata, a wrapper tool like
Perinci::Sub::Wrapper is able to change the calling style to positional:

 multiply2(4, 3.1, 1);  # 12

A command-line tool will also enable the function to be called named options as
well as positional arguments:

 % multiply2 --a 2 --b 3
 % multiply2 2 --b 3
 % multiply2 2 3

As mentioned earlier, C<cmdline_alises> is parsed by command-line option parser:

 % multiply2 2 3.5 -r ; # equivalent to multiply2 2 3 --round
 % multiply2 2 3.5 -R ; # equivalent to multiply2 2 3 --noround (--round=0)

Aliases in C<cmdline_aliases> are not recognized as real arguments:

 multiply2(a=>4, b=>3, r=>0);  # unknown argument r

Another example (demonstrates C<cmdline_aliases>):

 $SPEC{smtpd} = {
     v => 1.1,
     summary => 'Control SMTP daemon',
     args    => {
         action => {
             schema => ['str*' => {in=>[qw/status start stop restart/]}],
             pos    => 0,
             req    => 1,
             cmdline_aliases => {
                 status => {
                     schema    => [bool=>{is=>1}],
                     summary   => 'Alias for setting action=status',
                     code      => sub { $_[0]{action} = 'status' },
                 },
                 start => {
                     schema    => [bool=>{is=>1}],
                     summary   => 'Alias for setting action=start',
                     code      => sub { $_[0]{action} = 'start' },
                 },
                 stop => {
                     schema    => [bool=>{is=>1}],
                     summary   => 'Alias for setting action=stop',
                     code      => sub { $_[0]{action} = 'stop' },
                 },
                 restart => {
                     schema    => [bool=>{is=>1}],
                     summary   => 'Alias for setting action=restart',
                     code      => sub { $_[0]{action} = 'restart' },
                 },
             },
         },
         force => {
             schema => 'bool',
         },
     },
 };

Another example (demonstrates B<slurpy>):

 $SPEC{multiply_many} = {
     v => 1.1,
     summary => 'Multiple numbers',
     args    => {
         nums   => {
             schema => ['array*' => {of=>'num*', min_len=>1}],
             pos    => 0,
             slurpy => 1
         },
     },
 };
 sub multiply_many {
     my %args = @_;
     my $nums = $args{nums};

     my $ans = 1;
     $ans *= $_ for @$nums;
     [200, "OK", $ans];
 }

After wrapping, in positional mode it can then be called:

 multiply_many(2, 3, 4);  # 24

which is the same as (in normal named-argument style):

 multiply_many(nums => [2, 3, 4]);  # 24

In command-line:

 % multiply-many 2 3 4

in addition to the normal:

 % multiply-many --nums '[2, 3, 4]'

B<completion>. This argument specification key specifies how to complete
argument value (e.g. in shell or L<Riap::HTTP>) and is supplied an anonymous
function as value. The function will be called with arguments: word=>... (which
is the formed word so far, ci=>0|1 (whether completion should be done
case-insensitively). The function should return an array containing a list of
possible candidates, or a hash containing these keys: C<completion> (array, list
of possible candidates) and extra keys for formatting hints e.g. C<is_path>
(bool, whether the list of completion is path-like, meaning it can be
traversed/dug to multiple levels) C<path_sep> (string, path separator
character), C<type> (string, either C<filename>, C<env>, or other types). For an
example of implementation for this, see L<Perinci::Sub::Complete> in Perl which
provides tab completion for argument values. Example:

 $SPEC{delete_user} = {
     v => 1.1,
     args => {
         username => {
             schema     => 'str*',
             pos        => 0,
             completion => sub {
                 my %args = @_;
                 my $word = $args{word} // "";

                 # find users beginning with $word
                 local $CWD = "/home";
                 return [grep {-d && $_ ~~ /^\Q$word/} <*>];
             },
         },
         force => {schema=>[bool => {default=>0}]},
     },
 };

When C<delete_user> is executed over the command line and the Tab key is
pressed:

 $ delete-user --force --username fo<tab>
 $ delete-user fo<tab>

then B<bash> will try to complete with usernames starting with C<fo>.

B<element_completion>. This is like B<completion>, but for array or hash
elements. Argument type must be C<array> or C<hash>. Example for array:

 $SPEC{delete_users} = {
     v => 1.1,
     args => {
         usernames => {
             schema     => ['array*' => of => 'str*'],
             req        => 1,
             pos        => 0,
             slurpy     => 1,
             element_completion => sub {
                 my %args = @_;
                 my $word = $args{word} // "";

                 # find users beginning with $word
                 local $CWD = "/home";
                 my $res = [grep {-d && $_ ~~ /^\Q$word/} <*>];

                 # exclude users already mentioned by user
                 my $ary = $args{args}{usernames};
                 $res = [grep {!($_ ~~ @$ary)}] @$res;

                 return $res;
             },
         },
     },
 };

When C<delete_users> is executed over the command line:

 $ delete-users c<tab> ; # will complete with all users beginning with c
 $ delete-users charlie c<tab> ; # will complete with users but exclude charlie
 $ delete-users charlie chucky <tab> ; # and so on

Example for hash (as well as B<index_completion> property to complete hash
keys):

 $SPEC{create_file} = {
     v => 1.1,
     args => {
         filename => {
             schema => 'str*',
             req => 1,
             pos => 0,
         },
         content => {
             schema => 'buf*',
             req => 1,
             pos => 1,
         },
         mode => {
             summary => 'Permission mode',
             schema => 'posint*',
         },
         extra_attrs => {
             'x.name.is_plural' => 1,
             'x.name.singular' => 'extra_attr',
             schema     => ['hash*' => of => 'str*'],
             index_completion => sub {
                 # complete with list of known attributes
                 my %args = @_;
                 require Complete::Util;
                 Complete::Util::complete_array_elem(
                     word => $args{word},
                     array => [qw/mtime ctime owner group/],
                 );
             },
             element_completion => sub {
                 my %args = @_;
                 my $word  = $args{word} // "";
                 my $index = $args{index};

                 if ($index eq 'owner') {
                     require Complete::Unix;
                     return Complete::Unix::complete_user(word=>$word);
                 } elsif ($index eq 'group') {
                     require Complete::Unix;
                     return Complete::Unix::complete_group(word=>$word);
                 } else {
                     return undef;
                 }
             },
         },
     },
 };

When C<create_file> is executed over the command line:

 $ create-file file1 "hello filesystem" --extra-attr <tab>; # will complete with list of known attributes
 $ create-file file1 "hello filesystem" --extra-attr owner=<tab>; # will complete with list of Unix users

=head2 args_rels

Hash. This property is used to expression relationships between arguments. The
value is actually L<Sah> schema hash clause set (see hash type in L<Sah::Type>).
The arguments are represented as a hash, and you can use the various Sah clauses
to express relationships between the arguments (hash keys) because the Sah hash
type supports such clauses, e.g. C<choose_one>, C<choose_all>, C<req_one>,
C<req_all>, C<dep_any>, C<dep_all>, C<req_dep_any>, C<req_dep_all>.

Examples:

 args_rels => {
     choose_one => ['delete', 'add', 'edit'],
     choose_all => ['red', 'green', 'blue'],
 }

The above example says that only one of C<delete>, C<add>, C<edit> can be
specified. And if any of C<red>, C<green>, C<blue> is specified then all must be
specified. In CLI context this translates to:

 % prog --delete item
 % prog --delete --add item ; # error, both --delete and --add specified

 % prog --red 255 --green 255 --blue 0
 % prog --red 255 --blue 0 ; # error, --green is missing

Another example:

 XXX

=head2 args_as

Str. Specify in what form the function expects the arguments. The value is
actually implementation-specific since it describes the function implementation.
For example in L<Perinci> for Perl, these values are recognized: C<array>,
C<hash>, C<arrayref>, C<hashref>. This property is useful for wrapper to be able
to convert one form to another.

The default value is also left to the implementation.

For interimplementation communication (e.g. via L<Riap::HTTP> or L<Riap::TCP>),
named arguments are always used so this property is irrelevant.

=head2 result

DefHash. Specify function return value. It is a defhash containing keys:

=over 4

=item * summary (result property)

From DefHash. Like the C<summary> property in variable metadata.

=item * description (result property)

From DefHash. Like the C<description> property. Suggested to be formatted to 78
columns.

=item * schema (result property)

A Sah schema to validate the result (the third element in the envelope result).
This schema should only be tested if status is 200. See also: C<statuses>.

=item * statuses

Hash. Can be used to specify different result schema for different statuses. For
example:

 statuses => {
     206 => {
         schema => 'str*',
     },
 }

=item * stream (result property)

Bool. Specify that function returns streaming output. Note that function can
also signify streaming output by setting result metadata property C<stream> to
true.

Function must then return a subroutine reference (callback) as its actual result
which the caller can call repeatedly until it gets undef to signify exhaustion.

=item * partial (result property)

Bool. If set to true, specify that it is possible to request partial result. An
example is in a function that reads contents from (potentially large) files:

 # function metadata
 {
     v => 1.1,
     summary => 'Read file contents',
     args => {
         name => {
             summary => 'File name',
             schema  => 'str*',
             req     => 1,
         },
     },
     result => {schema=>'buf*', partial=>1},
 }

 # example function usage: request to read first 10MiB of file content,
 # -result_part_start defaults to 0.
 my $res = read_file(name=>'myvideo.mp4', -res_part_len=>10000000);
 # => [206, "Partial content", "data...", {len=>24500000, part_start=>0, part_len=>10000000}]

 # request the next 10MiB
 my $res = read_file(name=>'myvideo.mp4', -res_part_start=>10000000, -res_part_len=>10000000);
 # => [206, "Partial content", "data...", {len=>24500000, part_start=>10000000, part_len=>10000000}]

 # request the next 10MiB, since this actual file size is only 24500000,
 # function should return 416 status
 my $res = read_file(name=>'myvideo.mp4', -res_part_start=>20000000, -res_part_len=>10000000);
 # => [416, "Request range not satisfiable, file size is only 24500000"]

 # request the next 4.5MiB, this time succeeds
 my $res = read_file(name=>'myvideo.mp4', -res_part_start=>20000000, -res_part_len=>4500000);
 # => [206, "Partial content", "data...", {len=>24500000, part_start=>20000000, part_len=>4500000}]

Partial result request to a function which does not support partial result might
have the effect of the whole content being returned (status 200) or status 416.

=back

Note that since functions normally return enveloped result, instead of
returning:

 RESULT

your functions normally have to return an enveloped result:

 [STATUS, MESSAGE, RESULT, METADATA]

Examples:

 # result is an integer
 result => {schema => 'int*'}

 # result is an integer starting from zero
 result => {schema => ['int*' => {ge=>0}]}

 # result is an array of records
 result => {
     summary => 'Matching addressbook entries',
     schema => ['array*' => {
         summary => 'blah blah blah ...',
         of      => ['hash*' => {allowed_keys=>[qw/name age address/]} ]
     }]
 }

=head2 result_naked

Bool. If set to true, specify that function does not envelope its results. The
default is false, to encourage functions to create envelopes. However, wrapper
should be able to create or strip envelope if needed. For example, if you have
"traditional" functions which does not do envelopes, you can set this property
to true, and the wrapper can generate the envelope for the functions.

=head2 examples (function property)

Array. This property allows you to put examples in a detailed and structured
way, as an alternative to putting everything in C<description>.

Each example is a defhash, it specifies what arguments are used, what the
results are, and some description. It can be used when generating API/usage
documentation, as well as for testing data. It can also be used for testing
(function will be run with specified arguments and the result will be matched
against expected result). Known properties:

=over 4

=item * args (function example property)

Hash. Arguments used to produce result. Can be converted to C<argv> by tool,
e.g. when displaying command-line examples.

=item * argv

Array. An alternative to C<args>, for example when function is run from the
command-line. Can be converted to C<args> most of the time when wanting to
display examples in Perl instead of command-line.

=item * src

Str. An alternative to C<args> or C<argv>, to provide raw source code. See also:
C<src_plang>. This can be used to show more general examples. For example, you
can show how a function is used in an expression or code block, or how a
command-line program is used in a shell script.

Exactly one of C<args>, C<argv>, or C<src> must be specified.

=item * src_plang

Str. The programming language the examples source code C<src> is written in.
Valid values include: C<perl>, C<bash>.

Command-line interface tools will typically only show examples written in
C<bash> or other shells, while Perl module tools will typically only show
C<perl> examples.

Required if C<src> is specified.

=item * status

Int. Status from envelope. If unspecified, assumed to be 200.

=item * result

Any. Expected result.

=item * env_result

Array. Expected enveloped result.

=item * naked_result

Any. Expected naked result (payload).

=item * summary (function example property)

From DefHash. A one-line summary of the example You should describe, in one
phrase or sentence, what the example tries to demonstrate. You can skip the
summary if the example is pretty basic or things are already clear from the
C<args> alone.

=item * description (function example property)

From DefHash. Longer marked up text about the example (e.g. discussion or things
to note), suggested to be formatted to 72 columns.

=item * tags (function example property)

From DefHash.

=item * test

Bool. Defaults to true. Whether to actually test example or not. Examples are by
default run as tests by a test module (e.g. Perl module L<Test::Rinci>. Setting
this to 0 disables this example from being included in a test.

TODO: more detailed testing instruction (e.g. only test in release candidate,
or under certain environment flag, etc).

=back

Example:

 # part of metadata for Math::is_prime function
 examples => [
     {
         args => {num=>10},
         result => 0,
         # summary no needed here, already clear.
     },
     {
         args => {},
         result => 400,
         summary => 'Num argument is required',
     },

     {
         argv => [-5],
         result => 1,
         summary => 'Also works for negative integers',
     },
 ],

Another example demonstrating C<src> for a function called C<list_countries>:

 examples => [
     {
         src => 'for c in `list-countries`; do wget http://flags.org/country/$c; done',
         src_plang => 'bash',
     },
     {
         src => <<'EOT',
 my $res = list_countries(detail => 1, sort=>['-popsize']);
 die "Can't list countries: $res->[0] - $res->[1]" unless $res->[0] == 200;
 my $i = 0;
 for my $c (@{ $res->[2] }) { $i++; say "$i. $_->{name}'s population: $_->{popsize}";
 EOT
         src_plang => 'perl',
     },
 ],

=head2 features

DefHash. Allows functions to express their features. Each hash key contains
feature name, which must only contain letters/numbers/underscores.

Below is the list of defined features. New feature names may be defined by
extension.

=over 4

=item * reverse

Bool. Default: false. If set to true, specifies that function supports reverse
operation. To reverse, caller can add special argument C<-reverse>. For example:

 $SPEC{triple} = {
     v => 1.1,
     args     => {num=>{schema=>'num*'}},
     features => {reverse=>1}
 };
 sub triple {
     my %args = @_;
     my $num  = $args{num};
     [200, "OK", $args{-reverse} ? $num/3 : $num*3];
 }

 triple(num=>12);              # => 36
 triple(num=>12, -reverse=>1); # =>  4

=item * tx

Hash. Default is none. Specify transactional support, as specified in
L<Rinci::Transaction>. Value is a hash containing these keys: C<v> (int,
protocol version, default if not specified is 1).

Please see Rinci::Transaction for more details on transaction.

=item * dry_run

Bool, or hash. If set to a true value, specifies that function supports dry-run
(simulation) mode. Can also be set to a hash like this: C<<{default=>1}>> to
mean that function supports dry-run and the default is dry-run mode. Example:

 use Log::ger;

 $SPEC{rmre} = {
     summary  => 'Delete files in curdir matching a regex',
     args     => {re=>{schema=>'str*'}},
     features => {dry_run=>1}
 };
 sub rmre {
     my %args    = @_;
     my $re      = qr/$args{re}/;
     my $dry_run = $args{-dry_run};

     opendir my($dir), ".";
     while (my $f = readdir($dir)) {
         next unless $f =~ $re;
         log_info "Deleting $f ...";
         next if $dry_run;
         unlink $f;
     }
     [200, "OK"];
 }

The above Perl function delete files, but if passed argument C<-dry_run> => 1
(simulation mode), will not actually delete files, only display what files match
the criteria and would have be deleted.

Specifying a function as supporting dry_run means, among others:

=over 4

=item * If dry_run is requested, function will have no side effects

It will behave like a pure function, and thus have the properties of a pure
function.

=back

=item * pure

Bool. Default: false. If set to true, specifies that function is "pure" and has
no "side effects" (these are terms from functional programming / computer
science). Having a side effect means changing something, somewhere (e.g. setting
the value of a global variable, modifies its arguments, writing some data to
disk, changing system date/time, etc.) Specifying a function as pure means,
among others:

=over 4

=item * it can safely be inculded in transaction without recording in journal;

=item * it can safely be included during dry run;

=back

=item * immutable

Bool. Default is false. If set to true, specifies that function always returns
the same result when given the same argument values. This enables optimization
like memoization. An example of an immutable function is C<sub { $_[0]+$_[1] }>
where its results only depend on the arguments. Example of a mutable function
would be C<rand()> or C<read()> that reads contents from a file.

=item * idempotent

Bool. Default is false. If set to true, specifies that function is idempotent.
Idempotency means that repeated invocation of a function (each with the same
arguments) will have the same effect as a single invocation. In other words,
extra invocation will not have any effect.

Some operations, like reading a database row or a file's content, is inherently
idempotent (or to be exact nullipotent). Another example is setting or updating
an entity to some specific value, or deleting some entity. Repeated invocation
of the operation will still sets the entity to the same value, or still deletes
the entity.

Some other operations are inherently non-idempotent, for example sending an
email. Repeated invocation will cause multiple emails to be sent.

Yet some other operations are non-idempotent, but can be made idempotent simply
by checking whether the target object(s) has (have) reached the final desired
state, (optionally additionally also checking whether they are in the correct
original state to begin with). For example, a function that renames a file can
record the original file that was renamed (its MD5 checksum, size, or what not)
or perhaps record the action in a history database or flag file, and refuse to
rename again if the file to be renamed is not the original file.

=item * check_arg

Bool. Default is false. If set to true, specifies that function supports the
action of checking only a single argument. Usually useful when doing form
processing, where we want to check only a single form field (function argument).
To check a single argument, one passes C<-action> special argument with the
value of C<check_arg> and also passes the argument she wants to check. Function
should check that argument and immediately return 200 status upon success, or
400 upon validation failure.

=back

=head2 deps (function property)

Hash. This property specifies function's dependencies to various things. It is a
hash of dep types and values. Some dep types are special: C<all>, C<any>, and
C<none>.

 deps => {
     DEPTYPE => DEPVALUE,
     ...,
     all => [
         {DEPTYPE=>DEPVALUE, ...},
         ...,
     },
     any => [
         {DEPTYPE => DEPVALUE, ...},
         ...,
     ],
     none => [
         {DEPTYPE => DEPVALUE, ...},
         ....,
     ],
 }

A dependency can be of any type: another function, environment variables,
programs, OS software packages, etc. It is up to the dependency checker library
to make use of this information.

For the dependencies to be declared as satisfied, all of the clauses must be
satisfied.

Below is the list of defined dependency types. New dependency type may be
defined by an extension.

=over 4

=item * env

Str. Require that an environment variable exists and is true, where true is in
the Perl sense (not an empty string or "0"; " " and "0.0" are both true).
Example:

 env => 'HTTPS'

=item * prog

Str. Require that a program exists. If STR doesn't contain path separator
character '/' it will be searched in PATH. Windows filesystem should also use
Unix-style path, e.g. "C:/Program Files/Foo/Bar.exe".

 prog => 'rsync'   # any rsync found on PATH
 prog => '/bin/su' # won't accept any other su

=item * pkg

Str. Specify dependency on a L<Riap> package. STR must be a valid Riap package
URI string. Checker can check that requesting C<info> on this URI succeeds and
the type is indeed C<package>. Example:

 pkg => '/Foo/'

=item * func

Str. Specify dependency on a L<Riap> function. STR must be a valid Riap function
URI string. Checker can check that requesting C<info> on this URI succeeds and
the type is indeed C<package>. Example:

 pkg => '/Foo/somefunc'
 pkg => 'http://gudangapi.com/ga/list_ubuntu_releases'

=item * code

Code. Require that anonymous function returns a true value after called, where
the notion of true depends on the host language. Example in Perl:

 code => sub {$>}  # i am not being run as root

Example in Ruby:

 "code" => Proc.new { Process.euid > 0 }  # i am not being run as root

=item * tmp_dir

Bool. If set to 1, specify that function requires temporary directory. Caller
should provide path to this using special argument C<-tmp_dir>.

=item * trash_dir

Bool. If set to 1, specify that function requires trash directory. Trash is not
unlike a temporary directory. Caller should provide path to trash directory
using special argument C<-trash_dir>.

Trash directory can be provided, e.g. by transaction manager (see
L<Rinci::Transaction>).

=item * all

Array of deps. A "meta" type that allows several dependencies to be joined
together in a logical-AND fashion. All dependency hashes must be satisfied. For
example, to declare a dependency to several programs and an environment
variable:

 all => [
     {prog => 'rsync'},
     {prog => 'tar'},
     {env  => 'FORCE'},
 ],

=item * any

Array of deps. Like C<all>, but specify a logical-OR relationship. Any one of
the dependencies will suffice. For example, to specify requirement to
alternative Perl modules:

 or => [
     {perl_module => 'HTTP::Daemon'},
     {perl_module => 'HTTP::Daemon::SSL'},
 ],

=item * none

Array of deps. Specify that none of the dependencies must be satisfied for this
type to be satisfied. Example, to specify that the function not run under SUDO
or by root:

 none => [
     {env  => 'SUDO_USER'   },
     {code => sub {$> != 0} },
 ],

Note that the above is not equivalent to below:

 none => [
     {env => 'SUDO_USER', code => sub {$> != 0} },
 ],

which means that if none or only one of 'env'/'code' is satisfied, the whole
dependency becomes a success (since it is negated by 'none'). Probably not what
you want.

=back

If you add a new language-specific dependency type, please prefix it with the
language code, e.g. C<perl_module>, C<perl_func>, C<ruby_gem>, C<python_egg>.
These dependency types have also been defined by some existing tools: C<deb>
(dependency to a Debian package), C<rpm> (dependency to an RPM package),
C<js_url> (loading a remote JavaScript script URL), C<file> (existence of a),
C<perl_run_func> (running a Perl subroutine and getting a successful enveloped
result). Some of these might be declared as part of the core dependency types in
the future.

=head1 FAQ

=head2 What is the difference between C<summary> or C<description> in the Sah schema and arg specification?

Example:

 {
     args => {
         src => {
             summary => "Source path",
             description => "...",
             schema => ["str*", {
                 summary => "...",
                 description => "...",
                 ...
             }],
             ...
         },
         dest => {
             summary => "Target path",
             description => "...",
             schema => ["str*", {
                 summary => "...",
                 description => "...",
                 ...
             }],
             ...
         },
         ...
     },
 }

As you can see, each argument has a C<summary> and C<description>, but the
schema for each argument also has a C<summary> and C<description> schema
clauses. What is the difference and which should be put into which?

The argument specification's C<summary> (and C<description>) describe the
argument itself, in this example it says that C<src> means "The source path" and
C<dest> means "The target path". The argument schema's C<summary> (and
C<description>) describe the data type and valid values. In this example it
could say, e.g., "a Unix-path string with a maximum length of 255 characters".
In fact, C<src> and C<dest> are probably of the same type ("Unix path") and can
share schema.

 {
     ...
     args => {
         src => {
             ...
             schema => "unix_path",
         },
         dest => {
             ...
             schema => "unix_path",
         },
         ...
     },
 }

=head2 What is the difference between setting req=>1 in the argument specification and req=>1 in schema?

Example:

 # Note: remember that in Sah, str* is equivalent to [str => {req=>1}]
 args => {
     a => {         schema=>"str"  },
     b => {         schema=>"str*" },
     c => { req=>1, schema=>"str"  },
     d => { req=>1, schema=>"str*" },
 }

In particular look at C<b> and C<c>. C<b> is not a required argument (no req=>1
in the argument spec) but if it is specified, than it cannot be undef/null
(since the schema says [str=>{req=>1}], a.k.a "str*"). On the other hand, C<c>
is a required argument (req=>1 in the argument spec) but you can specify
undef/null as the value. The following are valid:

 func(c=>undef, d=>1);

But the following are not:

 func(b=>1, d=>1);  # c is not specified
 func(b=>undef, c=>1, d=>1);  # b has undef value
 func(b=>1, c=>1, d=>undef);  # d has undef value

=head2 Should I add a new metadata property, or add a new feature name to the C<features> property, or add a new dependency type to the C<deps> property?

If your property describes a dependency to something, it should definitely be a
new dependency type. If your property only describes what the function can do
and does not include any wrapper code, then it probably goes into C<features>.
Otherwise, it should probably become a new metadata property.

For example, if you want to declare that your function can only be run under a
certain moon phase (e.g. full moon), it should definitely go as a new dependency
type, so it becomes: deps => { moon_phase => 'full' }.

Another example, C<reverse> is a feature name, because it just states that if we
pass C<-reverse> => 1 special argument to a reversible function, it can do a
reverse operation. It doesn't include any wrapper code, all functionality is
realized by the function itself. On the other hand, C<timeout> is a metadata
property because it involves adding adding some wrapping code (a timeout
mechanism, e.g. an eval() block and alarm() in Perl).

=head1 HOMEPAGE

Please visit the project's homepage at L<https://metacpan.org/release/Rinci>.

=head1 SOURCE

Source repository is at L<https://github.com/perlancar/perl-Rinci>.

=head1 BUGS

Please report any bugs or feature requests on the bugtracker website L<https://rt.cpan.org/Public/Dist/Display.html?Name=Rinci>

When submitting a bug or request, please include a test-file or a
patch to an existing test-file that illustrates the bug or desired
feature.

=head1 SEE ALSO

Related specifications: L<Sah>, HTTP/1.1 (RFC 2068)

L<Rinci>

=head1 AUTHOR

perlancar <perlancar@cpan.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2020, 2019, 2018, 2017, 2016, 2015, 2014, 2013, 2012 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
