Provided by: librinci-perl_1.1.93-1_all bug

NAME

       Rinci::function - Metadata for your functions/methods

SPECIFICATION VERSION

        1.1

VERSION

       This document describes version 1.1.93 of Rinci::function (from Perl distribution Rinci),
       released on 2019-07-19.

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 Rinci. Please do a read up on it first, if you have not
       already done so.

SPECIFICATION

       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 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 "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 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
       Rinci::Transaction).

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

       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 "is_func", "is_meth", "is_class_meth" properties
       below for details.

       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.

   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 ("*") marks which codes are not
       defined in HTTP specification and introduced by this specification.

       ·   1xx code

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

       ·   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 "partial" property in
           the "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 "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.

       ·   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 "confirm_prompt" property (e.g. to
           provide translations). Confirmation from caller is in the form of special argument
           "-confirm" with boolean value of true (TODO: A more detailed confirmation for
           different actions can be specified later in the form of "-confirm_XXX" special
           arguments.) For an example of application of this, see Perinci::Tx::Manager.

       ·   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 "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
           "get_user()") and the object is not found.

           For object-listing functions (like "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 "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 "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 "partial" property in "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).

       ·   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 "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 Perinci::CmdLine).

   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

   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

   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

   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:

       schema (argument property)

       Data::Sah schema for argument value.

       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
       "ticket_status" schema. In "create_ticket" function you want the default "status" argument
       to be "new", while in "reply_ticket" you want the default "status" to be "answered".

       summary (argument property)

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

       req

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

       description (argument property)

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

       tags (argument property)

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

       pos

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

       slurpy

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

       Old alias: "greedy"

       greedy

       Old alias for "slurpy". Will be removed in Rinci 1.2.

       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. "str" where the unit is character, "buf" where
       the unit is byte, and "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 "-arg_len" (total argument
       length), "-arg_part_start" (start position of the part that is being sent),
       "-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);

       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.

       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:
       "summary" (a string, optional), "schema" (optional, defaults to argument's schema),
       "is_flag" (bool, optional, if set to 1 then it is a shortcut for specifying "schema" to
       "["bool", {"is":1}]"), "code" (a code to set argument value, optional, will be given
       "(\%args, $val)"); if not set, the default behavior is simply to set the argument value).

       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: "arg" (str, argument
       name), "value" (str, option value), "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 "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 "mod1" won't search in
       "dir2" as that directory has not been added by -I).

       completion (argument property)

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

       index_completion

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

       hash: for completing hash pair keys. (See also "element_completion" for completing hash
       pair values).

       See examples for how to use this property.

       element_completion

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

       array: for completing array element values.

       hash: for completing hash pair values. (See also "index_completion" for completing hash
       keys).

       See examples for how to use this property.

       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 "****" when logging.

       cmdline_src

       Str. Normally in a command-line program, command-line options and arguments will map to
       function arguments, e.g. "--arg 2" will set the "foo" argument to 2 and positional
       arguments (argument which specifies the "pos" property and optionally also a "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 "cmdline_src" property
       can be set to one of the following value for this purpose:

       ·   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).

       ·   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 "stdin" or "stdin_or_file" or
           "stdin_or_files" or "stdin_or_args".

       ·   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.

       ·   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 "<>" (diamond operator) in Perl.

       ·   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.

       ·   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 "cmdline_src" of "stdin_line" will be processed before
           "stdin"/"stdin_or_file"/"stdin_or_files"/"stdin_or_args".

       Other sources might be defined in the future.

       TODO: Define "web_src" property?

       TODO: A way to define record separator?

       cmdline_prompt

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

       TODO: cmdline_prompt_template?

       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.

       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.

       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 "deps (function property)"
       property. It is a hash or dep types and values.  The most important dep type is "arg"
       (dependency to another argument). Some dep types are special: "all", "any", "none".
       Example:

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

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

        % prog --delete --force

       Specifying "--force" without "--delete" doesn't make sense.

       filters

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

       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 "value" property (so if your sample argument is a
       hash like "{}" (in JSON), you have to specify it as "{"value":{}, "summary":"Optional
       summary..."}" (in JSON).

       Note that a Sah schema can also have an examples clause which you can use to put examples
       in. And Rinci function metadata also has examples 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, "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 "cmdline_aliases" are not recognized as real arguments:

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

       Another example (demonstrates "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 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]'

       completion. This argument specification key specifies how to complete argument value (e.g.
       in shell or 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: "completion"
       (array, list of possible candidates) and extra keys for formatting hints e.g. "is_path"
       (bool, whether the list of completion is path-like, meaning it can be traversed/dug to
       multiple levels) "path_sep" (string, path separator character), "type" (string, either
       "filename", "env", or other types). For an example of implementation for this, see
       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 "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 bash will try to complete with usernames starting with "fo".

       element_completion. This is like completion, but for array or hash elements. Argument type
       must be "array" or "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 "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 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 "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

   args_rels
       Hash. This property is used to expression relationships between arguments. The value is
       actually Sah schema hash clause set (see hash type in 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.
       "choose_one", "choose_all", "req_one", "req_all", "dep_any", "dep_all", "req_dep_any",
       "req_dep_all".

       Examples:

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

       The above example says that only one of "delete", "add", "edit" can be specified. And if
       any of "red", "green", "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

   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
       Perinci for Perl, these values are recognized: "array", "hash", "arrayref", "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 Riap::HTTP or Riap::TCP), named arguments
       are always used so this property is irrelevant.

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

       ·   summary (result property)

           From DefHash. Like the "summary" property in variable metadata.

       ·   description (result property)

           From DefHash. Like the "description" property. Suggested to be formatted to 78
           columns.

       ·   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: "statuses".

       ·   statuses

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

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

       ·   stream (result property)

           Bool. Specify that function returns streaming output. Note that function can also
           signify streaming output by setting result metadata property "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.

       ·   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.

       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/]} ]
            }]
        }

   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.

   examples (function property)
       Array. This property allows you to put examples in a detailed and structured way, as an
       alternative to putting everything in "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:

       ·   args (function example property)

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

       ·   argv

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

       ·   src

           Str. An alternative to "args" or "argv", to provide raw source code. See also:
           "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 "args", "argv", or "src" must be specified.

       ·   src_plang

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

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

           Required if "src" is specified.

       ·   status

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

       ·   result

           Any. Expected result.

       ·   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 "args" alone.

       ·   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.

       ·   tags (function example property)

           From DefHash.

       ·   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 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).

       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 "src" for a function called "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',
            },
        ],

   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.

       ·   reverse

           Bool. Default: false. If set to true, specifies that function supports reverse
           operation. To reverse, caller can add special argument "-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

       ·   tx

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

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

       ·   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: "<{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 "-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:

           ·   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.

       ·   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:

           ·   it can safely be inculded in transaction without recording in journal;

           ·   it can safely be included during dry run;

       ·   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 "sub { $_[0]+$_[1] }" where its
           results only depend on the arguments. Example of a mutable function would be "rand()"
           or "read()" that reads contents from a file.

       ·   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.

       ·   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 "-action" special argument with the value of "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.

   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: "all", "any", and "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.

       ·   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'

       ·   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

       ·   pkg

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

            pkg => '/Foo/'

       ·   func

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

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

       ·   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

       ·   tmp_dir

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

       ·   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 "-trash_dir".

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

       ·   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'},
            ],

       ·   any

           Array of deps. Like "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'},
            ],

       ·   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.

       If you add a new language-specific dependency type, please prefix it with the language
       code, e.g. "perl_module", "perl_func", "ruby_gem", "python_egg".  These dependency types
       have also been defined by some existing tools: "deb" (dependency to a Debian package),
       "rpm" (dependency to an RPM package), "js_url" (loading a remote JavaScript script URL),
       "file" (existence of a), "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.

FAQ

   What is the difference between "summary" or "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 "summary" and "description", but the schema for each
       argument also has a "summary" and "description" schema clauses. What is the difference and
       which should be put into which?

       The argument specification's "summary" (and "description") describe the argument itself,
       in this example it says that "src" means "The source path" and "dest" means "The target
       path". The argument schema's "summary" (and "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, "src" and "dest" are probably of the same type ("Unix
       path") and can share schema.

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

   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 "b" and "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" 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

   Should I add a new metadata property, or add a new feature name to the "features" property, or
       add a new dependency type to the "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 "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, "reverse" is a feature name, because it just states that if we pass
       "-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, "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).

HOMEPAGE

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

SOURCE

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

BUGS

       Please report any bugs or feature requests on the bugtracker website
       <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.

SEE ALSO

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

       Rinci

AUTHOR

       perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

       This software is copyright (c) 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.