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    if ($header =~ /Sampled=([^;]+)/) {
        $sampled = $1;
    }
    return ($trace_id, $segment_id, $sampled);
}

sub add_capture {
    my ($class, $package, @methods) = @_;
    no warnings 'redefine';
    no strict 'refs';
    for my $method (@methods) {
        my $orig = $package->can($method) or next;
        *{"${package}::${method}"} = sub {
            my @args = @_;
            capture(
                $package,
                sub {
                    my $segment = shift;
                    $segment->{metadata}->{method}  = $method;
                    $segment->{metadata}->{package} = $package;
                    $orig->(@args);
                },
            );
        };
    }
}

if ($ENV{LAMBDA_TASK_ROOT}) {
    # AWS::XRay is loaded in AWS Lambda worker.
    # notify the Lambda Runtime that initialization is complete.
    unless (mkdir '/tmp/.aws-xray') {
        # ignore the error if the directory is already exits or other process created it.
        my $err = $!;
        unless (-d '/tmp/.aws-xray') {
            warn "failed to make directory: $err";
        }
    }
    open my $fh, '>', '/tmp/.aws-xray/initialized' or warn "failed to create file: $!";
    close $fh;
    utime undef, undef, '/tmp/.aws-xray/initialized' or warn "failed to touch file: $!";

    # patch the capture
    no warnings 'redefine';
    no strict 'refs';
    my $org = \&capture;
    *capture = sub {
        my ($trace_id, $segment_id, $sampled) = parse_trace_header($ENV{_X_AMZN_TRACE_ID});
        local $AWS::XRay::SAMPLED = $sampled // $SAMPLER->();
        local $AWS::XRay::ENABLED = $AWS::XRay::SAMPLED;
        local ($AWS::XRay::TRACE_ID, $AWS::XRay::SEGMENT_ID) = ($trace_id, $segment_id);
        local *capture = $org;
        local *trace   = $org;
        capture(@_);
    };
    *trace = \&capture;
}

1;
__END__

=encoding utf-8

=head1 NAME

AWS::XRay - AWS X-Ray tracing library

=head1 SYNOPSIS

    use AWS::XRay qw/ capture /;

    capture "myApp", sub {
        capture "remote", sub {
            # do something ...
            capture "nested", sub {
                # ...
            };
        };
        capture "myHTTP", sub {
            my $segment = shift;
            # ...
            $segment->{http} = { # modify segment document
                request => {
                    method => "GET",
                    url    => "http://localhost/",
                },
                response => {
                    status => 200,
                },
            };
        };
    };

    my $header;
    capture "source", sub {
        my $segment = shift;
        $header = $segment->trace_header;
    };
    capture_from $header, "dest", sub {
        my $segment = shift;  # is a child of "source" segment
        # ...
    };

=head1 DESCRIPTION

AWS::XRay is a tracing library with AWS X-Ray.

AWS::XRay sends segment data to L<AWS X-Ray Daemon|https://docs.aws.amazon.com/xray/latest/devguide/xray-daemon.html>.

=head1 FUNCTIONS

=head2 new_trace_id

Generate a Trace ID. (e.g. "1-581cf771-a006649127e371903a2de979")

L<Document|https://docs.aws.amazon.com/xray/latest/devguide/xray-api-sendingdata.html#xray-api-traceids>

=head2 capture($name, $code)

capture() executes $code->($segment) and send the segment document to X-Ray daemon.

$segment is a AWS::XRay::Segment object.