NAME
    Perinci::Sub::Wrapper - A multi-purpose subroutine wrapping framework

VERSION
    version 0.58

SYNOPSIS
    For dynamic usage:

     use Perinci::Sub::Wrapper qw(wrap_sub);
     my $res = wrap_sub(sub_name => "mysub", meta=>{...});
     my ($wrapped_sub, $meta) = ($res->[2]{sub}, $res->[2]{meta});
     $wrapped_sub->(); # call the wrapped function

DESCRIPTION
    Perinci::Sub::Wrapper (PSW for short) is an extensible subroutine
    wrapping framework. It generates code to do stuffs before calling your
    subroutine, like validate arguments, convert arguments from
    positional/array to named/hash or vice versa, etc; as well as generate
    code to do stuffs after calling your subroutine, like retry calling for
    a number of times if subroutine returns a non-success status, check
    subroutine result against a schema, etc). Some other things it can do:
    apply a timeout, currying, and so on.

    PSW differs from other function composition or decoration system like
    Python decorators (or its Perl equivalent Python::Decorator) in a couple
    of ways:

    *   Single wrapper

        Instead of multiple/nested wrapping for implementing different
        features, PSW is designed to generate a single large wrapper around
        your code, i.e.:

         sub _wrapper_for_your_sub {
             ...
             # do various stuffs before calling:

             # e.g. start timer
             # e.g. convert, prefill, validate arguments
             my @args = ...;
             ...
             your_sub(@args);
             ...
             # do various stuffs after calling
             ...
             # e.g. report times
             # e.g. perform retry
             # e.g. convert or envelope results

             # return result
         }

        Multiple functionalities will be added and combined in this single
        wrapper subroutine in the appropriate location. This is done to
        reduce function call overhead or depth of nested call levels. And
        also to make it easier to embed the wrapping code to your source
        code (see Dist::Zilla::Plugin::Rinci::Wrap).

        Of course, you can still wrap multiple times if wanted.

    *   Rinci

        The wrapper code is built according to the Rinci metadata you
        provide. Rinci allows you to specify various things for your
        function, e.g. list of arguments including the expected data type of
        each argument and whether an argument is required or optional. PSW
        can then be used to generate the necessary code to enforce this
        specification, e.g. generate validator for the function arguments.

        Since Rinci specification is extensible, you can describe additional
        stuffs for your function and write a PSW plugin to generate the
        necessary code to implement your specification. An example is
        "timeout" to specify execution time limit, implemented by
        Perinci::Sub::Property::timeout which generates code to call
        function inside an "eval()" block and use "alarm()" to limit the
        execution. Another example is "retry" property, implemented by
        Perinci::Sub::Property::retry which generates code to call function
        inside a simple retry loop.

    Normally you do not use PSW directly in your applications. You might
    want to check out Perinci::Access::Perl and Perinci::Exporter on
    examples of wrapping function dynamically (during runtime), or
    Dist::Zilla::Plugin::Rinci::Wrap on an example of embedding the
    generated wrapping code to source code during build.

FUNCTIONS
  wrap_sub(%args) -> [status, msg, result, meta]
    Wrap subroutine to do various things, like enforcing Rinci properties.

    Arguments ('*' denotes required arguments):

    *   compile => *bool* (default: 1)

        Whether to compile the generated wrapper.

        Can be set to 0 to not actually wrap but just return the generated
        wrapper source code.

    *   convert => *hash*

        Properties to convert to new value.

        Not all properties can be converted, but these are a partial list of
        those that can: v (usually do not need to be specified when
        converting from 1.0 to 1.1, will be done automatically), args*as,
        result*naked, default_lang.

    *   debug => *bool* (default: 0)

        Generate code with debugging.

        If turned on, will produce various debugging in the generated code.
        Currently what this does:

        *   add more comments (e.g. for each property handler)

    *   meta* => *hash*

        The function metadata.

    *   meta_name => *str*

        Where to find the metadata, e.g. "$SPEC{foo}".

        Some wrapper code (e.g. handler for "dep" property) needs to refer
        to the function metadata. If not provided, the wrapper will store
        the function metadata in a unique variable (e.g.
        $Perinci::Sub::Wrapped::meta34127816).

    *   sub => *str*

        The code to be wrapped.

        At least one of "sub" or "sub_name" must be specified.

    *   sub_name => *str*

        The name of the subroutine, e.g. func or Foo::func (qualified).

        At least one of "sub" or "sub_name" must be specified.

    *   validate_args => *bool*

        Whether wrapper should validate arguments.

        If set to true, will validate arguments. Validation error will cause
        status 400 to be returned. The default is to enable this unless
        previous wrapper(s) have already done this.

    *   validate_result => *bool*

        Whether wrapper should validate arguments.

        If set to true, will validate sub's result. Validation error will
        cause wrapper to return status 500 instead of sub's result. The
        default is to enable this unless previous wrapper(s) have already
        done this.

    Return value:

    Returns an enveloped result (an array).

    First element (status) is an integer containing HTTP status code (200
    means OK, 4xx caller error, 5xx function error). Second element (msg) is
    a string containing error message, or 'OK' if status is 200. Third
    element (result) is optional, the actual result. Fourth element (meta)
    is called result metadata and is optional, a hash that contains extra
    information.

EXTENDING
    The framework is simple and extensible. Please delve directly into the
    source code for now. Some notes:

    The internal uses OO.

    The main wrapper building mechanism is in the "wrap()" method.

    For each Rinci property, it will call "handle_NAME()" wrapper handler
    method. The "handlemeta_NAME()" methods are called first, to determine
    order of processing. You can supply these methods either by subclassing
    the class or, more simply, monkeypatching the method in the
    "Perinci::Sub::Wrapper" package.

    The wrapper handler method will be called with a hash argument,
    containing these keys: value (property value), new (this key will exist
    if "convert" argument of "wrap()" exists, to convert a property to a new
    value).

    For properties that have name in the form of "NAME1.NAME2.NAME3" (i.e.,
    dotted) only the first part of the name will be used (i.e.,
    "handle_NAME1()").

VARIABLES
  $Log_Wrapper_Code (BOOL)
    Whether to log wrapper result. Default is from environment variable
    LOG_PERINCI_WRAPPER_CODE, or false. Logging is done with Log::Any at
    trace level.

METHODS
    The OO interface is only used internally or when you want to extend the
    wrapper.

ENVIRONMENT
  LOG_PERINCI_WRAPPER_CODE (bool)
    If set to 1, will log the generated wrapper code. This value is used to
    set $Log_Wrapper_Code if it is not already set.

PERFORMANCE NOTES
    The following numbers are produced on an Intel Core i5-2400 3.1GHz
    desktop using PSW v0.51 and Perl v5.18.2. Operating system is Debian sid
    (64bit).

    For perspective, empty subroutine ("sub {}") as well as "sub { [200,
    "OK"] }" can be called around 5.3 mil/sec.

    Wrapping this subroutine "sub { [200, "OK"] }" and this simple metadata
    "{v=>1.1}" using default options yields call performance for "$sub->()"
    of about 0.9 mil/sec. With "validate_args=>0" and "validate_result=>0",
    it's 1.5 mil/sec.

    As more (and more complex) arguments are introduced and validated,
    overhead will increase. The significant portion of the overhead is in
    argument validation. For example, this metadata "{v=>1.1,
    args=>{a=>{schema=>"int"}}}" yields 0.5 mil/sec.

FAQ
  General
    *   What is a function wrapper?

        A wrapper function calls the target function but with additional
        behaviors. The goal is similar to function composition or decorator
        system like in Python (or its Perl equivalent Python::Decorator)
        where you use a higher-order function which accepts another function
        and modifies it.

        It is used to add various functionalities, e.g.: cache/memoization,
        singleton, adding benchmarking/timing around function call, logging,
        argument validation (parameter checking), checking
        pre/post-condition, authentication/authorization checking, etc. The
        Python folks use decorators quite a bit; see discussions on the
        Internet on those.

    *   How is PSW different from Python::Decorator?

        PSW uses dynamic code generation (it generates Perl code on the
        fly). It also creates a single large wrapper instead of nested
        wrappers. It builds wrapper code according to Rinci specification.

    *   Why use code generation?

        Mainly because Data::Sah, which is the module used to do argument
        validation, also uses code generation. Data::Sah allows us to do
        data validation at full Perl speed, which can be one or two orders
        of magnitude faster than "interpreter" modules like
        Data::FormValidator.

    *   Why use a single large wrapper?

        This is just a design approach. It can impose some restriction for
        wrapper code authors, since everything needs to be put in a single
        subroutine, but has nice properties like less stack trace depth and
        less function call overhead.

  Debugging
    *   How to display the wrapper code being generated?

        If environment variable LOG_PERINCI_WRAPPER_CODE or package variable
        $Log_Perinci_Wrapper_Code is set to true, generated wrapper source
        code is logged at trace level using Log::Any. It can be displayed,
        for example, using Log::Any::App:

         % LOG_PERINCI_WRAPPER_CODE=1 TRACE=1 \
           perl -MLog::Any::App -MPerinci::Sub::Wrapper=wrap_sub \
           -e 'wrap_sub(sub=>sub{}, meta=>{v=>1.1, args=>{a=>{schema=>"int"}}});'

        Note that Data::Sah (the module used to generate validator code)
        observes "LOG_SAH_VALIDATOR_CODE", but during wrapping this
        environment flag is currently disabled by this module, so you need
        to set LOG_PERINCI_WRAPPER_CODE instead.

  caller() doesn't work from inside my wrapped code!
    Wrapping adds at least one or two levels of calls: one for the wrapper
    subroutine itself, the other is for the eval trap when necessary.

    This poses a problem if you need to call caller() from within your
    wrapped code; it will also be off by at least one or two.

    The solution is for your function to use the caller() replacement,
    provided by Perinci::Sub::Util. Or use embedded mode, where the wrapper
    code won't add extra subroutine calls.

SEE ALSO
    Perinci, Rinci

    Python::Decorator

    Dist::Zilla::Plugin::Rinci::Wrap

    Dist::Zilla::Plugin::Rinci::Validate

HOMEPAGE
    Please visit the project's homepage at
    <https://metacpan.org/release/Perinci-Sub-Wrapper>.

SOURCE
    Source repository is at
    <https://github.com/sharyanto/perl-Perinci-Sub-Wrapper>.

BUGS
    Please report any bugs or feature requests on the bugtracker website
    <https://rt.cpan.org/Public/Dist/Display.html?Name=Perinci-Sub-Wrapper>

    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.

AUTHOR
    Steven Haryanto <stevenharyanto@gmail.com>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2014 by Steven Haryanto.

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

