OpenTracing::WrapScope - Automatically add spans to selected subroutines


    use OpenTracing::WrapScope qw/foo Foo::bar/;
    use Foo;
    sub foo { ... }
    package Foo {
        sub bar { ... }


    use OpenTracing::WrapScope;


which is roughly equivalent to:

    use OpenTracing::AutoScope;
    sub foo {
    package Foo {
        sub bar {


import takes subroutine names (with optional signatures) as arguments, these need to be fully qualified if they are not in the current package. All specified subroutines will have spans attached to them. Context and caller frames will be preserved.

The following tags will be automatically added to each span:

caller.file - filename where the subroutine was called
caller.line - line number on which the subroutine was called
caller.package - the calling package
caller.subname - the name of the calling subroutine (won't be added if there is none)
source.file - filename where the subroutine is defined
source.line - line on which the subroutine is defined
source.package - package in which the subroutine is located
source.subname - the name of the subroutine

Additionally, if a wrapped subroutine dies, an additional error tag (set to a true value) and message tag, containing ($@) will be added to the span.


If a signature is used, tags containing the argument values will be added to the span. The syntax is similar to the built-in signatures, although simplified. A signature is a parenthesised list of arguments:

  use OpenTracing::WrapScope 'Foo::bar($arg, \%config)'

In this example, calling

  Foo::bar('test', { date => '2020-01-01', limit => 16 })

will produce the following tags:

 arguments.arg = 'test' = '2020-01-01'
 arguments.config.limit = 10

The following argument types are supported:


Captures a single argument and assigns it to a tag with the specified name.

  use OpenTracing::WrapScope 'foo($bar)';


Produces: = 'username'

Causes an argument to be skipped.

  use OpenTracing::WrapScope 'foo($first, undef, $third)';

  foo(1, 2, 3)


  arguments.first = 1
  arguments.third = 3

Captures all remaining arguments and puts them into indexed tags.

  use OpenTracing::WrapScope 'foo(@args)';

  foo('a', 'b', 'c')


  arguments.args.0 = 'a'
  arguments.args.1 = 'b'
  arguments.args.2 = 'c'

Optionally, slices can be used to limit which elements are to be captured:

  use OpenTracing::WrapScope 'foo(@args[ 0, 2 ])';
  use OpenTracing::WrapScope 'foo(@args[ 3, 5..8 ])';

Note: Only literal integers and ranges can be used for slicing.


Captures a single array reference argument and puts it into indexed tags.

  use OpenTracing::WrapScope 'foo(\@args)';

  foo([ 'x', 'y', 'z' ])


  arguments.args.0 = 'x'
  arguments.args.1 = 'y'
  arguments.args.2 = 'z'

It supports slicing in the same way as the regular Array.

  use OpenTracing::WrapScope 'foo(\@args[ 0, 2 ])';
  use OpenTracing::WrapScope 'foo(\@args[ 3, 5..8 ])';

Note: If at the time of the call, the specified argument is not an array reference, it will be silently ignored and no tags will be produced for that argument.

Hash (or key-value pairs)

Captures all remaining arguments and treats them as a hash.

  use OpenTracing::WrapScope 'foo(%args)';

  foo(x => 1, y => 2, z => 3)

Produces: = 1 = 2 = 3

Optionally, slices can be used to limit which elements are to be captured:

  use OpenTracing::WrapScope 'foo(%args{"x", "y"})';

Note: Only single or double quoted strings can be used for slicing.


Captures a single hash reference argument and puts it into tags.

  use OpenTracing::WrapScope 'foo(\%args)';

  foo( { x => 1, y => 2, z => 3 } )

Produces: = 1 = 2 = 3

It supports slicing in the same way as the regular Hash.

  use OpenTracing::WrapScope 'foo(\%args{"x", "y"})';

Note: If at the time of the call, the specified argument is not a hash reference, it will be silently ignored and no tags will be produced for that argument.


List of subroutine names can be read from text files. Only a simple list of subroutines is supported with each line containing a single subroutine name, the subroutine needs to be fully qualified, regardless of where OpenTracing::WrapScope is used. The effect is the same as using the subroutine names directly. Multiple files can be specified at once.

Comments are supported, any line starting with # will be skipped, trailing comments beginning with # will be ignored.

Suppose you have a file called wrapscope.conf with the following contents:


You could wrap these subroutines by using:

  use OpenTracing::WrapScope -file => 'wrapscope.conf';

Mutiple filenames can be specified by using an arrayref:

  use OpenTracing::WrapScope -file => [ 'config/wrap_base.conf', 'config/wrap_extra.conf' ];

or a shell glob (expanded using the glob builtin):

  use OpenTracing::WrapScope -file => 'config/wrap*.conf';


If this argument is specified, arguments for -file will be read from OPENTRACING_WRAPSCOPE_FILE. This environment variable can contain a single filename/glob or multiple ones separated by colons:



Normally, if any of the requested subs (either directly or through a file) is not found, a warning will be issued at the end of the programs runtime. Passing this option will disable that warning.



Replaces the specified subroutine with a span-handling version. $sub needs to be a fully qualified subroutine name or an unqualified name from the current package, it can optionally include a signature (see Signatures).

The subroutine needs to be defined or a warning will be thrown. This warning can be made fatal with:

  use warnings FATAL => 'OpenTracing::WrapScope';

or disabled with:

  no warnings 'OpenTracing::WrapScope';

wrapped($code_ref, $signature)

Returns a version of the given code reference with span handling attached. Useful for adding spans to anonymous subroutines.

A signature may be optionally included to track the arguments, it should not include parentheses:

  my $coderef = OpenTracing::WrapScope::wrapped(sub { ... }, '$arg1, $arg2, @others')

See Signatures for details.


Read a list of subroutines from $filename and install scope handlers in them. The file should contain a list of subroutines (identical to the one accepted by -file in import()).



Because this module overrides caller, it's best to use it as soon as possible, before caller-using code is compiled. It likely won't work well with other modules which override caller themselves.


Subroutines exported using Exporter or a similar module could split into two versions. If the export happens before the span handling is applied to a subroutine, only the original version will have a span, the exported version will be unmodified.

In order to wrap subroutines in modules utilising Exporter, use OpenTracing::WrapScope directly in those modules.


Since OpenTracing::WrapScope works by replacing subroutines with modified versions, it's not possible to apply to Moose classes which have been made immutable.


Szymon Nieznanski <>


'OpenTracing::WrapScope' is Copyright (C) 2020, Perceptyx Inc

This library is free software; you can redistribute it and/or modify it under the terms of the Artistic License 2.0.

This package is distributed in the hope that it will be useful, but it is provided "as is" and without any express or implied warranties.

For details, see the full text of the license in the file LICENSE.