lib/Net/AS2.pm - metacpan.org

package Net::AS2;
use strict;
use warnings qw(all);

=head1 NAME

Net::AS2 - AS2 Protocol implementation (RFC 4130) used in Electronic Data Exchange (EDI)

=head1 SYNOPSIS

    ### Create an AS2 handler
    my $as2 = Net::AS2->new(
            MyId => 'alice', 
            MyKey => '...RSA KEY in PEM...', 
            MyCert => '...X509 Cert in PEM...'
            PartnerId => 'bob', PartnerCert => '...X509 Cert in PEM...'
        );

    ### Sending Message (Sync MDN)
    my $mdn = $as2->send($body, Type => 'application/xml', MessageId => 'my-message-id-12345@localhost')

    ### Receiving MDN (Async MDN)
    my $mdn = $as2->decode_mdn($headers, $body);

    ### Receiving Message and sending MDN
    my $message = $as2->decode_message($headers, $post_body);

    if ($message->is_success) {
        print $message->content;
    }

    if ($message->is_mdn_async) {
        # ASYNC MDN is expected

        # stored the state for later use
        my $state = $message->serialized_state;

        # ...in another perl instance...
        my $message = Net::AS2::Message->create_from_serialized_state($state);
        $as2->send_async_mdn(
                $message->is_success ?
                    Net::AS2::MDN->create_success($message) :
                    Net::AS2::MDN->create_from_unsuccessful_message($message),
                'id-23456@localhost'
            );
    } else 
    {
        # SYNC MDN is expected
        my ($new_headers, $mdn_body) = $as2->prepare_sync_mdn(
                $message->is_success ?
                    Net::AS2::MDN->create_success($message) :
                    Net::AS2::MDN->create_from_unsuccessful_message($message),
                'id-23456@localhost'
            );

        # ... Send headers and body ...
    }

=head1 DESCRIPTION

This is a class for handling AS2 (RFC-4130) communication - sending
message (optionally sign and encrypt), decoding MDN. Receving message
and produce corresponding MDN.

=head2 Protocol Introduction

AS2 is a protocol that defines communication over HTTP(s), and 
optionally using SMIME as payload container, plus a mandated
multipart/report machine readable Message Disposition Notification 
response (MDN). 

When encryption and signature are used in SMIME payload (agree between 
parties), as well as a signed MDN, the protocol offers data 
confidentiality, data integrity/authenticity, non-repudiation of
origin, and non-repudiation of receipt over HTTP.

In AS2, MDN can only be signed but not encrypted, some MIME headers
are also exposed in the HTTP headers when sending. Use HTTPS if this 
is a concerns.

Encryption and Signature are done in PKCS7/SMIME favor. The certifacate
are usually exchanged out of band before establishing communication.
The certificates could be self-signed.

=head1 PUBLIC INTERFACE

=cut

use Net::AS2::MDN;
use Net::AS2::Message;
use Carp;
use Crypt::SMIME;
use LWP::UserAgent;
use HTTP::Request;
use Digest::SHA1;
use MIME::Base64;
use MIME::Parser;
use Encode;
use MIME::Entity;
use Sys::Hostname;

my $crlf = "\x0d\x0a";

our $VERSION = "0.02";

=head2 Constructor

=over 4

=item $as2 = Net::AS2->new(%ARGS)

Create an AS2 handler. For preparing keys and certificates, see L<Preparing Certificates|Net::AS2::FAQ/Preparing Certificates>

The arguments are:

=over 4

=item MyId

I<Required.> 
Your AS2 name. This will be used in the AS2-From header.

=item PartnerId

I<Required.> 
The AS2 name of the partner. This will be used in the AS2-To header.

=item PartnerUrl

I<Required.> 
The Url of partner where message would be sent to.

=item MyKey

I<Required.>
Our private key in PEM format. 
Please includes the C<-----BEGIN RSA PRIVATE KEY-----> and C<-----END RSA PRIVATE KEY-----> line.

=item MyEncryptionKey, MySignatureKey

I<Optional.> 
Different private keys could be used for encryption and signing. L<MyKey> will be used if not independently supplied.

=item MyCertificate

I<Required.> 
Our corresponding certificate in PEM format.
Please includes the C<-----BEGIN CERTIFICATE-----> and C<-----END CERTIFICATE-----> line.

=item MyEncryptionKey, MySignatureKey

I<Optional.> 
Different certificate could be used for encryption and signing. L<MyCertificate> will be used if not independently supplied.

=item PartnerCertificate

I<Required.>
Partner's certificate in PEM format. 
Please includes the C<-----BEGIN CERTIFICATE-----> and C<-----END CERTIFICATE-----> line.

=item PartnerEncryptionCertificate, PartnerSignatureCertificate

I<Optional.> 
Different certificate could be used for encryption and signing. If so, load them here. 
L<PartnerCertificate> will be used if not independently supplied.

=item Encryption

I<Optional.> 
Encryption alogrithm used in SMIME encryption operation. Only C<3des> is supported at this moment.

If left undefined, encryption is enabled and C<3des> would be used. 
A false value must be specified to disable encryption.

If enabled, encryption would also be required for receiving. 
Otherwise, encryption would be optional for receiving.

=item Signature

I<Optional.> 
Signing alogrithm used in SMIME signing operation. Only C<sha1> is supported at this moment.

If left undefined, signing is enabled and C<sha1> would be used. 
A false value must be specified to disable signature.

If enabled, signature would also be required for receiving. 
Otherwise, signature would be optional for receiving.

Also, if enabled, signed MDN would be requested.

=item Mdn

I<Optional.> 
The preferred MDN method - C<sync> or C<async>. The default is C<sync>.

=item MdnAsyncUrl

i<Required if Mdn is async>. 
The Url where the parten should send the async MDN to.

=item Timeout

i<Optional.>
The timeout in seconds for HTTP communication. The default is 30.

This is passed to LWP::UserAgent.

=item UserAgent

I<Optional.>
User Agent name used in HTTP communication.

This is passed to LWP::UserAgent.

=back

=cut

sub new
{
    my ($class, %opts) = @_;

    $class = ref($class) || $class;
    my $self = { %opts };
    bless ($self, $class);

    $self->_validations();

    my $s_e = $self->{_smime_enc} = Crypt::SMIME->new();
    
    eval { $s_e->setPrivateKey($self->{MyEncryptionKey}, $self->{MyEncryptionCertificate}); };
    croak "Unable to load private key/certificate for encryption: $@" if $@;

    eval { $s_e->setPublicKey($self->{PartnerEncryptionCertificate}); };
    croak "Unable to load public certificate for encryption: $@" if $@;

    if (
        $self->{MyEncryptionKey} eq $self->{MySignatureKey} &&
        $self->{MyEncryptionCertificate} eq $self->{MySignatureCertificate} &&
        $self->{PartnerEncryptionCertificate} eq $self->{PartnerSignatureCertificate}
    ) {
        $self->{_smime_sign} = $self->{_smime_enc};
    } else 
    {
        my $s_s = $self->{_smime_sign} = Crypt::SMIME->new();
        
        eval { $s_s->setPrivateKey($self->{MySignatureKey}, $self->{MySignatureCertificate}); };
        croak "Unable to load private key/certificate for signature: $@" if $@;

        eval { $s_s->setPublicKey($self->{PartnerSignatureCertificate}); };
        croak "Unable to load public certificate for signature: $@" if $@;
    }
    
    return $self;
}

sub _validations
{
    my ($self) = @_;

    $self->{Encryption} = lc($self->{Encryption} // '3des');
    croak sprintf("encryption %s is not supported", $self->{Encryption})
        unless !$self->{Encryption} || $self->{Encryption} ~~ ['3des'];

    $self->{Signature} = lc($self->{Signature} // 'sha1');
    croak sprintf("signature %s is not supported", $self->{Signature})
        unless !$self->{Signature} || $self->{Signature} ~~ ['sha1'];

    $self->{MyEncryptionKey} //= $self->{MyKey};
    $self->{MyEncryptionCertificate} //= $self->{MyCertificate};
    $self->{MySignatureKey} //= $self->{MyKey};
    $self->{MySignatureCertificate} //= $self->{MyCertificate};
    $self->{PartnerEncryptionCertificate} //= $self->{PartnerCertificate};
    $self->{PartnerSignatureCertificate} //= $self->{PartnerCertificate};
    delete $self->{MyKey};
    delete $self->{MyCertificate};
    delete $self->{PartnerCertificate};

    foreach my $t (qw(
        MyId
        MyEncryptionKey MyEncryptionCertificate
        MySignatureKey MySignatureCertificate
        PartnerId 
        PartnerEncryptionCertificate PartnerSignatureCertificate
        ))
    {
        croak "$t is not valid"
            unless defined $self->{$t} && $self->{$t} =~ /^[\r\n\x20-\x7E]+$/;
    }
    croak "PartnerUrl is invalid"
        unless defined $self->{PartnerUrl} && $self->{PartnerUrl} =~ m{^https?://[\x20-\x7E]+$};

    $self->{Mdn} = lc($self->{Mdn} // 'sync');
    croak sprintf("mdn %s is not supported", $self->{Mdn})
        unless lc($self->{Mdn}) ~~ [qw(sync async)];

    croak "mdn_async_url is invalid"
        unless 
            !defined $self->{MdnAsyncUrl} && $self->{Mdn} eq 'sync' || 
            defined $self->{MdnAsyncUrl} && $self->{MdnAsyncUrl} =~ m{^https?://[\x20-\x7E]+$} &&
                $self->{Mdn} eq 'async';

    $self->{Timeout} //= 30;
    croak "timeout is invalid"
        unless $self->{Timeout} =~ /^[0-9]+$/;

    $self->{UserAgent} //= "Perl AS2/$VERSION";
}

=back

=head2 Methods

=over 4

=item $message = $as2->decode_message($headers, $content)

Decode the incoming HTTP request as AS2 Message.

Headers is an hash ref and should be supplied in PSGI format, or C<\%ENV> in CGI mode.
Content is the raw POST body of the request.

This method always returns a C<Net::AS2::Message> object and never dies.
The message could be successfully parsed, or contains corresponding error message.

Check the C<$message-E<gt>is_async> property and send the MDN accordingly. 

If ASYNC MDN is requested, it should be sent after this HTTP request is returned
or in another thread - some AS2 server might block otherwise, YMMV. How to handle
this is out of topic.

=cut

sub decode_message
{
    my ($self, $headers, $content) = @_;
    croak "headers must be an hash reference"
        unless ref $headers eq 'HASH';
    croak "content is undefined"
        unless defined $content;

    my $message_id = $headers->{HTTP_MESSAGE_ID};
    my $async_url = $headers->{HTTP_RECEIPT_DELIVERY_OPTION};
    my @new_prefix = ($message_id, $async_url, 0);

    unless (!defined $async_url || $async_url =~ m{^https?://}) {
        $new_prefix[1] = undef;
        return Net::AS2::Message->create_failure_message(@new_prefix, 'Async transport other than http/https is not supported');
    }

    if ($headers->{HTTP_DISPOSITION_NOTIFICATION_OPTIONS}) {
        my $status = Net::AS2::Message::notification_options_check($headers->{HTTP_DISPOSITION_NOTIFICATION_OPTIONS});
        return Net::AS2::Message->create_failure_message(@new_prefix, $status)
            if defined $status;
        $new_prefix[2] = 1;
    }
    
    unless (
        defined $headers->{CONTENT_TYPE} &&
        defined $headers->{HTTP_MESSAGE_ID} &&
        defined $headers->{HTTP_AS2_VERSION} &&
        defined $headers->{HTTP_AS2_FROM} &&
        defined $headers->{HTTP_AS2_TO})
    {
        return Net::AS2::Message->create_error_message(@new_prefix, 'unexpected-processing-error', 'Malformed AS2 Message, crucial headers are missing.');
    }

    if (
        _parse_as2_id($headers->{HTTP_AS2_FROM}) ne $self->{PartnerId} ||
        _parse_as2_id($headers->{HTTP_AS2_TO}) ne $self->{MyId}
    ) {
        return Net::AS2::Message->create_error_message(@new_prefix, 'authentication-failed', 'AS2-From or AS2-To is not expected');
    }

    my $is_content_raw = 1;

    my $raw_content = $content;
    my $merged_headers =
        join($crlf, map {
            if (/^HTTP_/ || /^CONTENT_TYPE$/) {
                my $key = $_; 
                $key =~ s/^HTTP_//;
                $key =~ s/_/-/g;
                "$key: ". $headers->{$_};
            } else { (); }
        } keys %{$headers}) . "$crlf$crlf";

    if ($self->{_smime_enc}->isEncrypted($merged_headers . $content))
    {
        # OpenSSL (Crypt::SMIME) in Windows cannot handle binary content, 
        # convert the data to base64
        $content = 
            "Content-Transfer-Encoding: base64$crlf" .
            $merged_headers .
            encode_base64($content);
        $is_content_raw = 0;

        $content = eval { $self->{_smime_enc}->decrypt($content); };
        return Net::AS2::Message->create_error_message(@new_prefix, 
            'decryption-failed', 'Unable to decrypt the message')
            if $@;
    } else {
        return Net::AS2::Message->create_error_message(@new_prefix, 
            'insufficient-message-security', 'Encryption is expected but the message is not encrypted')
            if $self->{Encryption};
    }

    if ($self->{_smime_sign}->isSigned($is_content_raw ? $merged_headers . $content : $content))
    {
        if ($is_content_raw) {
            $content = 
                $merged_headers .
                $content;
            $is_content_raw = 0;
        }
        $content = eval { $self->{_smime_sign}->check($content); };

        return Net::AS2::Message->create_error_message(@new_prefix,
            'insufficient-message-security', 'Unable to verify the signature')
            if $@;
    } else {
        return Net::AS2::Message->create_error_message(@new_prefix, 
            'insufficient-message-security', 'Signature is expected but the message is not signed')
            if $self->{Signature};
    }

    my $mic = Digest::SHA1::sha1_base64($content) . '=';

    my $parser = new MIME::Parser;
    $parser->output_to_core(1);
    $parser->tmp_to_core(1);
    my $entity = $parser->parse_data($is_content_raw ? $merged_headers . $content : $content);
    my $bh = $entity->bodyhandle;

    return Net::AS2::Message->create_failure_message(@new_prefix, 
        'unexpected-processing-error', 
        'MIME has no body (multipart message is not supported)')
        unless defined $bh;

    $content = $bh->as_string;
    return Net::AS2::Message->new(@new_prefix, $mic, $content);
}

=item $mdn = $as2->decode_mdn($headers, $content)

I<Instance method.> 
Decode the incoming HTTP request as AS2 MDN.

Headers is an hash ref and should be supplied in PSGI format, or C<\%ENV> in CGI mode.
Content is the raw POST body of the request.

This method always returns a C<Net::AS2::MDN> object and never dies.
The MDN could be successfully parsed, or contains unparsable error details 
if it is malformed, or signature could not be verified.

C<$mdn-E<gt>match_mic($content_mic)> should be called afterward with the 
pre-calculated MIC from the outgoing message to verify the correctness 
of the MIC.

=cut

sub decode_mdn
{
    my ($self, $headers, $content) = @_;
    croak "headers must be an hash reference"
        unless ref $headers eq 'HASH';
    croak "content is undefined"
        unless defined $content;

    unless (
        defined $headers->{CONTENT_TYPE} &&
        defined $headers->{HTTP_MESSAGE_ID} &&
        defined $headers->{HTTP_AS2_VERSION} &&
        defined $headers->{HTTP_AS2_FROM} &&
        defined $headers->{HTTP_AS2_TO})
    {
        return Net::AS2::MDN->create_unparsable_mdn('Malformed AS2 MDN, crucial headers are missing.')
    }

    if (
        _parse_as2_id($headers->{HTTP_AS2_FROM}) ne $self->{PartnerId} ||
        _parse_as2_id($headers->{HTTP_AS2_TO}) ne $self->{MyId}
    ) {
        return Net::AS2::MDN->create_unparsable_mdn('AS2-From or AS2-To is not expected')
    }

    my $merged_headers =
        join($crlf, map {
            if (/^HTTP_/ || /^CONTENT_TYPE$/) {
                my $key = $_; 
                $key =~ s/^HTTP_//;
                $key =~ s/_/-/g;
                "$key: ". $headers->{$_};
            } else { (); }
        } keys %{$headers}) . "$crlf$crlf";

    $content = 
        $merged_headers .
        $content;

    return $self->_parse_mdn($content);
}

=item ($headers, $content) = $as2->prepare_sync_mdn($mdn, $message_id)

Returns the headers and content to be sent in a HTTP response for a sync MDN.

The MDN is usually created after an incoming message is received, with 
C<Net::AS2::MDN-E<gt>create_success> or C<Net::AS2::MDN-E<gt>create_from_unsuccessful_message>.

The headers are in arrayref format in PSGI response format.
The content is raw and ready to be sent.

For CGI, it should be sent like this:

    my ($headers, $content) = $as2->prepare_sync_mdn($mdn, $message_id);

    my $mh = '';
    for (my $i = 0; $i < scalar @{$headers}; $i += 2)
    {
        $mh .= $headers->[$i] . ': ' . $headers->[$i+1] . "\x0d\x0a";
    }

    binmode(STDOUT);
    print $mh . "\x0d\x0a" . $content;    

If message id not specified, a random one will be generated.

=cut

sub prepare_sync_mdn
{
    my ($self, $mdn, $message_id) = @_;

    $mdn->recipient($self->{MyId});

    $message_id = 
        defined $message_id && $message_id =~ /@/ ? $message_id :
        sprintf('<%s@%s>', ($message_id || time + rand()), hostname);
    my ($headers, $payload) = 
        $self->_send_preprocess($mdn->as_mime->stringify, $message_id, undef, undef, 
            1, $mdn->should_sign);

    return ($headers, $payload);
}

=item $resp = $as2->send_async_mdn($mdn, $message_id)

Send an ASYNC MDN requested by partner. Returns a L<HTTP::Response>.

The MDN is usually created after an incoming message is received, with 
C<Net::AS2::MDN-E<gt>create_success> or C<Net::AS2::MDN-E<gt>create_from_unsuccessful_message>.

If message id is not specified, a random one will be generated.

Note that the destination URL is passed by the partner in its request, 
but not specified during construction.

=cut

sub send_async_mdn
{
    my ($self, $mdn, $message_id) = @_;

    $mdn->recipient($self->{MyId});
    my $target_url = $mdn->async_url;

    croak "MDN async url is not defined" unless $target_url;
    croak "MDN async url is not valid" unless $target_url =~ m{^https?://};    

    $message_id = 
        defined $message_id && $message_id =~ /@/ ? $message_id :
        sprintf('<%s@%s>', ($message_id || time + rand()), hostname);
    my ($headers, $payload) = 
        $self->_send_preprocess($mdn->as_mime->stringify, $message_id, $target_url, undef, 
            1, $mdn->should_sign);

    my $req = HTTP::Request->new(POST => $target_url, \@$headers);
    $req->content($payload);

    my $ua = $self->create_useragent;
    my $resp = $ua->request($req);

    return $resp;
}


=item ($mdn, $mic) = $as2->send($data, %MIMEHEADERS)

Send a message to the partner. Returns a C<Net::AS2::MDN> object and calculated SHA-1 MIC.

The data should be encoded (or assumed to be UTF-8 encoded).

The mime headers should be listed in a hash. 
It will be passed to C<MIME::Entity> almost transparently with some defaults dedicated for AS2,
at least the following must also be supplied

=over 4

=item MessageId

Message id of this request should be supplied, or a random one would be generated.

=item Type

Content type of the message should be supplied.

=back

In case of HTTP failure, the MDN object will be marked with C<$mdn-E<gt>is_error>.

In case ASYNC MDN is expected, the MDN object returned will most likely be marked with
C<$mdn-E<gt>is_unparsable> and should be ignored. A misbehave AS2 server could returns
a valid MDN even if async was requested - in this case the C<$mdn-E<gt>is_success> would 
be true.

=cut

sub send
{
    my ($self, $data, %opts) = @_;

    croak "data is not defined" 
        unless defined $data;

    $data = utf8::is_utf8($data) ? encode("utf8", $data) : $data;
    my $mic;
    $mic = Digest::SHA1::sha1_base64($data) . '='
        unless $self->{Signature} || $self->{Encryption};

    my $message_id = $opts{MessageId} // '';
    $message_id = 
        $message_id =~ /@/ ? $message_id :
        sprintf('<%s@%s>', ($message_id || time + rand()), hostname);

    $opts{Encoding} = 'base64';
    $opts{Disposition} //= 'attachment';
    $opts{Subject} //= 'AS2 Message';
    $opts{'X-Mailer'} = undef;

    my $mime = new MIME::Entity->build(Data => $data, %opts);
    return $self->_send($mime->stringify, $message_id, $mic);
}

sub _send_preprocess
{
    my ($self, $data, $message_id, $target_url, $pre_mic, $is_mdn, $should_mdn_signed) = @_;
    
    $data =~ s/(?:$crlf|\n)/$crlf/g;
    my $mic = $is_mdn ? undef : ($pre_mic // Digest::SHA1::sha1_base64($data) . '=');

    if ($is_mdn && $should_mdn_signed || !$is_mdn && $self->{Signature}) {
        $data = $self->{_smime_sign}->sign($data);
    }
    if ($self->{Encryption} && !$is_mdn) {
        $data = $self->{_smime_enc}->encrypt($data);
    }

    my ($header, $payload) = $data =~ /^(.*?)$crlf$crlf(.*)$/s;
    
    $header =~ //;

    my @header;
    my ($prev_head, $prev_value);
    my $is_base64 = 0;
    foreach my $line (split(/$crlf/, $header))
    {
        if ($line =~ m/^([^:]+):\s*(.*)/) {
			my ($key, $value) = ($1, $2);
            push @header, ($prev_head => $prev_value)
                if defined $prev_head;
            if (lc($key) eq 'content-type') {
                $value =~ s{application/x-pkcs7}{application/pkcs7};
            } elsif (lc($key) eq 'content-transfer-encoding') {
                $is_base64 = 1 if lc($value) eq 'base64';
                $key = undef;
            }
			$prev_head = $key;
            $prev_value = $value;
		} elsif (defined $prev_head) {
            $prev_value .= " $line";
		}
    }
    push @header, ($prev_head => $prev_value)
        if defined $prev_head;

    push @header, (
        defined $target_url ? ('Recipient-Address' => $target_url) : (),
        'Message-Id' => $message_id,
        'AS2-Version' => '1.0',
        'AS2-From' => _encode_as2_id($self->{MyId}), 'AS2-To' => _encode_as2_id($self->{PartnerId}), 
        $is_mdn ? () : (
            'Disposition-notification-To' => 'example@example.com',
            ($self->{Signature} ? (
                'Disposition-Notification-Options' => 'signed-receipt-protocol=required, pkcs7-signature; signed-receipt-micalg=required, sha1'
            ) : ()),
            ($self->{MdnAsyncUrl} ? (
                'Receipt-Delivery-Option' => $self->{MdnAsyncUrl}
            ) : ())
        ),
    );
    $payload = decode_base64($payload) 
        if $is_base64;
    return (\@header, $payload, $mic);
}

=back

=head2 Test Hooks

=over 4

=item $as2->create_useragent()

This should return a C<LWP::UserAgent> usable for handling HTTP request.

This allows test code to monitor the HTTP request sending out.

=cut

sub create_useragent
{
    my $self = shift;
    my $ua = new LWP::UserAgent(timeout => $self->{Timeout}, agent => $self->{UserAgent});
    return $ua;
}

sub _send
{
    my ($self, $data, $message_id, $pre_mic) = @_;

    my $target_url = $self->{PartnerUrl};
    my ($headers, $payload, $mic) =
        $self->_send_preprocess($data, $message_id, $target_url, $pre_mic);

    my $req = HTTP::Request->new(POST => $target_url, \@$headers);
    $req->content($payload);

    my $test = $req->as_string;

    my $ua = $self->create_useragent;
    my $resp = $ua->request($req);

    my $mdn;
    if ($resp->is_success)
    {
        my $content = $resp->as_string;
        # Remove the status line
        $content =~ s{^.*?\r?\n}{};
        $mdn = $self->_parse_mdn($content);
        $mdn->match_mic($mic, 'sha1');

    } else {
        $mdn = 
            Net::AS2::MDN->create_error_mdn(sprintf('HTTP failure: %s', $resp->status_line));
    }
    return wantarray ? ($mdn, $mic) : $mdn;
}

sub _parse_mdn
{
    my ($self, $content) = @_;

    if ($self->{_smime_sign}->isSigned($content))
    {
        # OpenSSL (Crypt::SMIME) in Windows cannot handle binary content, 
        # convert signature part to base64
        $content = _pkcs7_base64($content);
        $content = eval { $self->{_smime_sign}->check($content); };
        return Net::AS2::MDN->create_unparsable_mdn('MDN signature failed verification: ' . $@)
            if $@;
    } else {
        return Net::AS2::MDN->create_unparsable_mdn('MDN is not signed')
            if $self->{Signature};
    }
    return Net::AS2::MDN->parse_mdn($content);
}


sub _parse_as2_id {
    my $as2_id = shift;
    $as2_id =~ /^ (?: ([!\x23-\x5B\x5D-\x7E]+) | "((?:\\\\|\\"|[!\x23-\x5B\x5D-\x7E ])+)" ) $/x;
    if (defined $1) {
        return $1;
    } elsif (defined $2) {
        $as2_id = $2;
        $as2_id =~ s/\\(\\|")/$1/g;
        return $as2_id;
    }
    return undef;
}

sub _encode_as2_id {
    my $as2_id = shift;
    if ($as2_id =~ s/(\\|")/\\$1/g || $as2_id =~ / /) {
        return qq{"$as2_id"};
    } else {
        return $as2_id;
    }
}

sub _pkcs7_base64
{
    my ($content) = @_;
    my $parser = new MIME::Parser;

    $parser->output_to_core(1);
    $parser->tmp_to_core(1);
    my $entity = $parser->parse_data($content);

    if ($entity->parts == 2)
    {
        my $p = $entity->parts(1);
        if (defined $p && $p->head &&
            $p->head->get('Content-type') =~ m{^application/(x-)?pkcs7-signature($|;)} &&
            ($p->head->get('Content-transfer-encoding') // '') ne 'base64'
        ) {
            $p->head->replace('Content-transfer-encoding', 'base64');
            return $entity->stringify;
        }
    }

    return $content;
}

1;

=back

=head1 BUGS

=over 4

=item *

A bug in L<Crypt::SMIME> will caused test to fail - specifically failed to add public key after decryption failure.
I applied the fixes and fork it to L<github|https://github.com/sam0737/perl-crypt-smime>.

=back

=head1 SEE ALSO

L<Net::AS2::FAQ>, L<Net::AS2::Message>, L<Net::AS2::MDN>, L<MIME::Entity>

Source code is maintained here at L<https://github.com/sam0737/perl-net-as2>. Patches are welcome.

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2012 by Sam Wong.

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

=head1 DISCLAIMER OF WARRANTY

This module is not certificated by any AS2 body. This module generates MDN on behave of you.  
When using this module, you must have reviewed and responsible for all the actions and in-actions caused by this module.

More legal jargon follows:

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
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