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Plack::Util − Utility subroutines for Plack server and framework developers



  my $true  = Plack::Util::TRUE;
  my $false = Plack::Util::FALSE;

Utility constants to include when you specify boolean variables in $env hash (e.g. "psgi.multithread").


  my $class = Plack::Util::load_class($class [, $prefix ]);

Constructs a class name and "require" the class. Throws an exception if the .pm file for the class is not found, just with the built-in "require".

If $prefix is set, the class name is prepended to the $class unless $class begins with "+" sign, which means the class name is already fully qualified.

  my $class = Plack::Util::load_class("Foo");                   # Foo
  my $class = Plack::Util::load_class("Baz", "Foo::Bar");       # Foo::Bar::Baz
  my $class = Plack::Util::load_class("+XYZ::ZZZ", "Foo::Bar"); # XYZ::ZZZ

Note that this function doesn’t validate (or "sanitize") the passed string, hence if you pass a user input to this function (which is an insecure thing to do in the first place) it might lead to unexpected behavior of loading files outside your @INC path. If you want a generic module loading function, you should check out CPAN modules such as Module::Runtime.


  if ( Plack::Util::is_real_fh($fh) ) { }

returns true if a given $fh is a real file handle that has a file descriptor. It returns false if $fh is PerlIO handle that is not really related to the underlying file etc.


  my $cl = Plack::Util::content_length($body);

Returns the length of content from body if it can be calculated. If $body is an array ref it’s a sum of length of each chunk, if $body is a real filehandle it’s a remaining size of the filehandle, otherwise returns undef.


  Plack::Util::set_io_path($fh, "/path/to/foobar.txt");

Sets the (absolute) file path to $fh filehandle object, so you can call "$fh−>path" on it. As a side effect $fh is blessed to an internal package but it can still be treated as a normal file handle.

This module doesn’t normalize or absolutize the given path, and is intended to be used from Server or Middleware implementations. See also IO::File::WithPath.


  Plack::Util::foreach($body, $cb);

Iterate through $body which is an array reference or IO::Handle−like object and pass each line (which is NOT really guaranteed to be a line) to the callback function.

It internally sets the buffer length $/ to 65536 in case it reads the binary file, unless otherwise set in the caller’s code.


  my $app = Plack::Util::load_psgi $psgi_file_or_class;

Load "app.psgi" file or a class name (like "MyApp::PSGI") and require the file to get PSGI application handler. If the file can’t be loaded (e.g. file doesn’t exist or has a perl syntax error), it will throw an exception.

Security: If you give this function a class name or module name that is loadable from your system, it will load the module. This could lead to a security hole:

  my $psgi = ...; # user−input: consider ""
  $app = Plack::Util::load_psgi($psgi); # this does 'require ""'!

Generally speaking, passing an external input to this function is considered very insecure. But if you really want to do that, be sure to validate the argument passed to this function. Also, if you do not want to accept an arbitrary class name but only load from a file path, make sure that the argument $psgi_file_or_class begins with "/" so that Perl’s built-in do function won’t search the include path.


  my $res = Plack::Util::run_app $app, $env;

Runs the $app by wrapping errors with eval and if an error is found, logs it to "$env−>{'psgi.errors'}" and returns the template 500 Error response.

header_get, header_exists, header_set, header_push, header_remove

  my $hdrs = [ 'Content−Type' => 'text/plain' ];
  my $v = Plack::Util::header_get($hdrs, $key); # First found only
  my @v = Plack::Util::header_get($hdrs, $key);
  my $bool = Plack::Util::header_exists($hdrs, $key);
  Plack::Util::header_set($hdrs, $key, $val);   # overwrites existent header
  Plack::Util::header_push($hdrs, $key, $val);
  Plack::Util::header_remove($hdrs, $key);

Utility functions to manipulate PSGI response headers array reference. The methods that read existent header value handles header name as case insensitive.

  my $hdrs = [ 'Content−Type' => 'text/plain' ];
  my $v = Plack::Util::header_get($hdrs, 'content−type'); # 'text/plain'


  my $headers = [ 'Content−Type' => 'text/plain' ];
  my $h = Plack::Util::headers($headers);
  if ($h−>exists($key)) { ... }
  $h−>set($key => $val);
  $h−>push($key => $val);
  $h−>headers; # same reference as $headers

Given a header array reference, returns a convenient object that has an instance methods to access "header_*" functions with an OO interface. The object holds a reference to the original given $headers argument and updates the reference accordingly when called write methods like "set", "push" or "remove". It also has "headers" method that would return the same reference.


  if (status_with_no_entity_body($res−>[0])) { }

Returns true if the given status code doesn’t have any Entity body in HTTP response, i.e. it’s 100, 101, 204 or 304.


  my $o = Plack::Util::inline_object(
      write => sub { $h−>push_write(@_) },
      close => sub { $h−>push_shutdown },

Creates an instant object that can react to methods passed in the constructor. Handy to create when you need to create an IO stream object for input or errors.


  my $encoded_string = Plack::Util::encode( $string );

Entity encodes "<", ">", "&", """ and "'" in the input string and returns it.


See " RESPONSE CALLBACK " in Plack::Middleware for details.