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.