More encryption fixes.
[libdcp.git] / src / cpl.cc
index 10a83078ed1c1ca40c4a273ed30134e3a57b794a..a3d2ecfa9fbbaa831f5597ce3a0cd1f5d9b618db 100644 (file)
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2012 Carl Hetherington <cth@carlh.net>
+    Copyright (C) 2012-2013 Carl Hetherington <cth@carlh.net>
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
 */
 
 #include <fstream>
+#include <libxml/parser.h>
 #include "cpl.h"
-#include "cpl_file.h"
+#include "parse/cpl.h"
 #include "util.h"
 #include "picture_asset.h"
 #include "sound_asset.h"
 #include "subtitle_asset.h"
-#include "asset_map.h"
+#include "parse/asset_map.h"
 #include "reel.h"
 #include "metadata.h"
+#include "signer.h"
+#include "exceptions.h"
+#include "compose.hpp"
 
 using std::string;
 using std::stringstream;
 using std::ofstream;
 using std::ostream;
 using std::list;
+using std::pair;
+using std::make_pair;
 using boost::shared_ptr;
+using boost::lexical_cast;
+using boost::optional;
 using namespace libdcp;
 
-CPL::CPL (string directory, string name, ContentKind content_kind, int length, int frames_per_second)
+CPL::CPL (boost::filesystem::path directory, string name, ContentKind content_kind, int length, int frames_per_second)
        : _directory (directory)
        , _name (name)
        , _content_kind (content_kind)
        , _length (length)
        , _fps (frames_per_second)
 {
-       _uuid = make_uuid ();
+       _id = make_uuid ();
 }
 
 /** Construct a CPL object from a XML file.
  *  @param directory The directory containing this CPL's DCP.
  *  @param file The CPL XML filename.
- *  @param asset_map The corresponding asset map.
+ *  @param asset_maps AssetMaps to look for assets in.
  *  @param require_mxfs true to throw an exception if a required MXF file does not exist.
  */
-CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, bool require_mxfs)
+CPL::CPL (boost::filesystem::path directory, string file, list<PathAssetMap> asset_maps, bool require_mxfs)
        : _directory (directory)
        , _content_kind (FEATURE)
        , _length (0)
        , _fps (0)
 {
        /* Read the XML */
-       shared_ptr<CPLFile> cpl;
+       shared_ptr<parse::CPL> cpl;
        try {
-               cpl.reset (new CPLFile (file));
+               cpl.reset (new parse::CPL (file));
        } catch (FileError& e) {
                boost::throw_exception (FileError ("could not load CPL file", file));
        }
@@ -71,9 +79,12 @@ CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, b
        _name = cpl->annotation_text;
        _content_kind = cpl->content_kind;
 
-       for (list<shared_ptr<CPLReel> >::iterator i = cpl->reels.begin(); i != cpl->reels.end(); ++i) {
+       /* Trim urn:uuid: off the front */
+       _id = cpl->id.substr (9);
 
-               shared_ptr<Picture> p;
+       for (list<shared_ptr<parse::Reel> >::iterator i = cpl->reels.begin(); i != cpl->reels.end(); ++i) {
+
+               shared_ptr<parse::Picture> p;
 
                if ((*i)->asset_list->main_picture) {
                        p = (*i)->asset_list->main_picture;
@@ -96,15 +107,21 @@ CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, b
 
                if (!(*i)->asset_list->main_stereoscopic_picture && p->edit_rate == p->frame_rate) {
 
+                       pair<string, shared_ptr<const parse::AssetMapAsset> > asset = asset_from_id (asset_maps, p->id);
+
                        try {
                                picture.reset (new MonoPictureAsset (
-                                                      _directory,
-                                                      asset_map->asset_from_id (p->id)->chunks.front()->path
+                                                      asset.first,
+                                                      asset.second->chunks.front()->path
                                                       )
                                        );
 
                                picture->set_entry_point (p->entry_point);
                                picture->set_duration (p->duration);
+                               if (p->key_id.length() > 9) {
+                                       /* Trim urn:uuid: */
+                                       picture->set_key_id (p->key_id.substr (9));
+                               }
                        } catch (MXFFileError) {
                                if (require_mxfs) {
                                        throw;
@@ -113,9 +130,11 @@ CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, b
                        
                } else {
                        try {
+                               pair<string, shared_ptr<const parse::AssetMapAsset> > asset = asset_from_id (asset_maps, p->id);
+
                                picture.reset (new StereoPictureAsset (
-                                                      _directory,
-                                                      asset_map->asset_from_id (p->id)->chunks.front()->path,
+                                                      asset.first,
+                                                      asset.second->chunks.front()->path,
                                                       _fps,
                                                       p->duration
                                                       )
@@ -123,6 +142,10 @@ CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, b
 
                                picture->set_entry_point (p->entry_point);
                                picture->set_duration (p->duration);
+                               if (p->key_id.length() > 9) {
+                                       /* Trim urn:uuid: */
+                                       picture->set_key_id (p->key_id.substr (9));
+                               }
                                
                        } catch (MXFFileError) {
                                if (require_mxfs) {
@@ -135,14 +158,22 @@ CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, b
                if ((*i)->asset_list->main_sound) {
                        
                        try {
+                               pair<string, shared_ptr<const parse::AssetMapAsset> > asset = asset_from_id (asset_maps, (*i)->asset_list->main_sound->id);
+                       
                                sound.reset (new SoundAsset (
-                                                    _directory,
-                                                    asset_map->asset_from_id ((*i)->asset_list->main_sound->id)->chunks.front()->path
+                                                    asset.first,
+                                                    asset.second->chunks.front()->path
                                                     )
                                        );
 
-                               sound->set_entry_point ((*i)->asset_list->main_sound->entry_point);
-                               sound->set_duration ((*i)->asset_list->main_sound->duration);
+                               shared_ptr<parse::MainSound> s = (*i)->asset_list->main_sound;
+
+                               sound->set_entry_point (s->entry_point);
+                               sound->set_duration (s->duration);
+                               if (s->key_id.length() > 9) {
+                                       /* Trim urn:uuid: */
+                                       sound->set_key_id (s->key_id.substr (9));
+                               }
                        } catch (MXFFileError) {
                                if (require_mxfs) {
                                        throw;
@@ -152,9 +183,11 @@ CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, b
 
                if ((*i)->asset_list->main_subtitle) {
                        
+                       pair<string, shared_ptr<const parse::AssetMapAsset> > asset = asset_from_id (asset_maps, (*i)->asset_list->main_subtitle->id);
+
                        subtitle.reset (new SubtitleAsset (
-                                               _directory,
-                                               asset_map->asset_from_id ((*i)->asset_list->main_subtitle->id)->chunks.front()->path
+                                               asset.first,
+                                               asset.second->chunks.front()->path
                                                )
                                );
 
@@ -167,65 +200,77 @@ CPL::CPL (string directory, string file, shared_ptr<const AssetMap> asset_map, b
 }
 
 void
-CPL::add_reel (shared_ptr<const Reel> reel)
+CPL::add_reel (shared_ptr<Reel> reel)
 {
        _reels.push_back (reel);
 }
 
 void
-CPL::write_xml (XMLMetadata const & metadata) const
+CPL::write_xml (bool interop, XMLMetadata const & metadata, shared_ptr<const Signer> signer) const
 {
        boost::filesystem::path p;
        p /= _directory;
        stringstream s;
-       s << _uuid << "_cpl.xml";
+       s << _id << "_cpl.xml";
        p /= s.str();
-       ofstream os (p.string().c_str());
+
+       xmlpp::Document doc;
+       xmlpp::Element* root;
+       if (interop) {
+               root = doc.create_root_node ("CompositionPlaylist", "http://www.digicine.com/PROTO-ASDCP-CPL-20040511#");
+       } else {
+               root = doc.create_root_node ("CompositionPlaylist", "http://www.smpte-ra.org/schemas/429-7/2006/CPL");
+       }
+
+       if (signer) {
+               root->set_namespace_declaration ("http://www.w3.org/2000/09/xmldsig#", "dsig");
+       }
        
-       os << "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
-          << "<CompositionPlaylist xmlns=\"http://www.smpte-ra.org/schemas/429-7/2006/CPL\">\n"
-          << "  <Id>urn:uuid:" << _uuid << "</Id>\n"
-          << "  <AnnotationText>" << _name << "</AnnotationText>\n"
-          << "  <IssueDate>" << metadata.issue_date << "</IssueDate>\n"
-          << "  <Creator>" << metadata.creator << "</Creator>\n"
-          << "  <ContentTitleText>" << _name << "</ContentTitleText>\n"
-          << "  <ContentKind>" << content_kind_to_string (_content_kind) << "</ContentKind>\n"
-          << "  <ContentVersion>\n"
-          << "    <Id>urn:uri:" << _uuid << "_" << metadata.issue_date << "</Id>\n"
-          << "    <LabelText>" << _uuid << "_" << metadata.issue_date << "</LabelText>\n"
-          << "  </ContentVersion>\n"
-          << "  <RatingList/>\n"
-          << "  <ReelList>\n";
+       root->add_child("Id")->add_child_text ("urn:uuid:" + _id);
+       root->add_child("AnnotationText")->add_child_text (_name);
+       root->add_child("IssueDate")->add_child_text (metadata.issue_date);
+       root->add_child("Issuer")->add_child_text (metadata.issuer);
+       root->add_child("Creator")->add_child_text (metadata.creator);
+       root->add_child("ContentTitleText")->add_child_text (_name);
+       root->add_child("ContentKind")->add_child_text (content_kind_to_string (_content_kind));
+       {
+               xmlpp::Node* cv = root->add_child ("ContentVersion");
+               cv->add_child ("Id")->add_child_text ("urn:uri:" + _id + "_" + metadata.issue_date);
+               cv->add_child ("LabelText")->add_child_text (_id + "_" + metadata.issue_date);
+       }
+       root->add_child("RatingList");
+
+       xmlpp::Element* reel_list = root->add_child ("ReelList");
        
-       for (list<shared_ptr<const Reel> >::const_iterator i = _reels.begin(); i != _reels.end(); ++i) {
-               (*i)->write_to_cpl (os);
+       for (list<shared_ptr<Reel> >::const_iterator i = _reels.begin(); i != _reels.end(); ++i) {
+               (*i)->write_to_cpl (reel_list, interop);
        }
 
-       os << "  </ReelList>\n"
-          << "</CompositionPlaylist>\n";
+       if (signer) {
+               signer->sign (root, interop);
+       }
 
-       os.close ();
+       doc.write_to_file_formatted (p.string (), "UTF-8");
 
-       _digest = make_digest (p.string ());
+       _digest = make_digest (p.string (), 0);
        _length = boost::filesystem::file_size (p.string ());
 }
 
 void
-CPL::write_to_pkl (ostream& s) const
+CPL::write_to_pkl (xmlpp::Node* node) const
 {
-       s << "    <Asset>\n"
-         << "      <Id>urn:uuid:" << _uuid << "</Id>\n"
-         << "      <Hash>" << _digest << "</Hash>\n"
-         << "      <Size>" << _length << "</Size>\n"
-         << "      <Type>text/xml</Type>\n"
-         << "    </Asset>\n";
+       xmlpp::Node* asset = node->add_child ("Asset");
+       asset->add_child("Id")->add_child_text ("urn:uuid:" + _id);
+       asset->add_child("Hash")->add_child_text (_digest);
+       asset->add_child("Size")->add_child_text (lexical_cast<string> (_length));
+       asset->add_child("Type")->add_child_text ("text/xml");
 }
 
 list<shared_ptr<const Asset> >
 CPL::assets () const
 {
        list<shared_ptr<const Asset> > a;
-       for (list<shared_ptr<const Reel> >::const_iterator i = _reels.begin(); i != _reels.end(); ++i) {
+       for (list<shared_ptr<Reel> >::const_iterator i = _reels.begin(); i != _reels.end(); ++i) {
                if ((*i)->main_picture ()) {
                        a.push_back ((*i)->main_picture ());
                }
@@ -241,19 +286,16 @@ CPL::assets () const
 }
 
 void
-CPL::write_to_assetmap (ostream& s) const
+CPL::write_to_assetmap (xmlpp::Node* node) const
 {
-       s << "    <Asset>\n"
-         << "      <Id>urn:uuid:" << _uuid << "</Id>\n"
-         << "      <ChunkList>\n"
-         << "        <Chunk>\n"
-         << "          <Path>" << _uuid << "_cpl.xml</Path>\n"
-         << "          <VolumeIndex>1</VolumeIndex>\n"
-         << "          <Offset>0</Offset>\n"
-         << "          <Length>" << _length << "</Length>\n"
-         << "        </Chunk>\n"
-         << "      </ChunkList>\n"
-         << "    </Asset>\n";
+       xmlpp::Node* asset = node->add_child ("Asset");
+       asset->add_child("Id")->add_child_text ("urn:uuid:" + _id);
+       xmlpp::Node* chunk_list = asset->add_child ("ChunkList");
+       xmlpp::Node* chunk = chunk_list->add_child ("Chunk");
+       chunk->add_child("Path")->add_child_text (_id + "_cpl.xml");
+       chunk->add_child("VolumeIndex")->add_child_text ("1");
+       chunk->add_child("Offset")->add_child_text("0");
+       chunk->add_child("Length")->add_child_text(lexical_cast<string> (_length));
 }
        
        
@@ -261,8 +303,10 @@ CPL::write_to_assetmap (ostream& s) const
 bool
 CPL::equals (CPL const & other, EqualityOptions opt, boost::function<void (NoteType, string)> note) const
 {
-       if (_name != other._name) {
-               note (ERROR, "names differ");
+       if (_name != other._name && !opt.cpl_names_can_differ) {
+               stringstream s;
+               s << "names differ: " << _name << " vs " << other._name << "\n";
+               note (ERROR, s.str ());
                return false;
        }
 
@@ -272,22 +316,22 @@ CPL::equals (CPL const & other, EqualityOptions opt, boost::function<void (NoteT
        }
 
        if (_fps != other._fps) {
-               note (ERROR, "frames per second differ");
+               note (ERROR, String::compose ("frames per second differ (%1 vs %2)", _fps, other._fps));
                return false;
        }
 
        if (_length != other._length) {
-               note (ERROR, "lengths differ");
-               return false;
+               stringstream s;
+               note (ERROR, String::compose ("lengths differ (%1 vs %2)", _length, other._length));
        }
 
        if (_reels.size() != other._reels.size()) {
-               note (ERROR, "reel counts differ");
+               note (ERROR, String::compose ("reel counts differ (%1 vs %2)", _reels.size(), other._reels.size()));
                return false;
        }
        
-       list<shared_ptr<const Reel> >::const_iterator a = _reels.begin ();
-       list<shared_ptr<const Reel> >::const_iterator b = other._reels.begin ();
+       list<shared_ptr<Reel> >::const_iterator a = _reels.begin ();
+       list<shared_ptr<Reel> >::const_iterator b = other._reels.begin ();
        
        while (a != _reels.end ()) {
                if (!(*a)->equals (*b, opt, note)) {
@@ -299,3 +343,187 @@ CPL::equals (CPL const & other, EqualityOptions opt, boost::function<void (NoteT
 
        return true;
 }
+
+shared_ptr<xmlpp::Document>
+CPL::make_kdm (
+       shared_ptr<const Signer> signer,
+       shared_ptr<const Certificate> recipient_cert,
+       Key key,
+       boost::posix_time::ptime from,
+       boost::posix_time::ptime until,
+       bool interop,
+       MXFMetadata const & mxf_metadata,
+       XMLMetadata const & xml_metadata
+       ) const
+{
+       assert (recipient_cert);
+       
+       shared_ptr<xmlpp::Document> doc (new xmlpp::Document);
+       xmlpp::Element* root = doc->create_root_node ("DCinemaSecurityMessage");
+       root->set_namespace_declaration ("http://www.smpte-ra.org/schemas/430-3/2006/ETM", "");
+       root->set_namespace_declaration ("http://www.w3.org/2000/09/xmldsig#", "ds");
+       root->set_namespace_declaration ("http://www.w3.org/2001/04/xmlenc#", "enc");
+
+       {
+               xmlpp::Element* authenticated_public = root->add_child("AuthenticatedPublic");
+               authenticated_public->set_attribute("Id", "ID_AuthenticatedPublic");
+               xmlAddID (0, doc->cobj(), (const xmlChar *) "ID_AuthenticatedPublic", authenticated_public->get_attribute("Id")->cobj());
+               
+               authenticated_public->add_child("MessageId")->add_child_text ("urn:uuid:" + make_uuid());
+               /* XXX: this should probably be different if interop == true */
+               authenticated_public->add_child("MessageType")->add_child_text ("http://www.smpte-ra.org/430-1/2006/KDM#kdm-key-type");
+               authenticated_public->add_child("AnnotationText")->add_child_text (mxf_metadata.product_name);
+               authenticated_public->add_child("IssueDate")->add_child_text (xml_metadata.issue_date);
+
+               {
+                       xmlpp::Element* xml_signer = authenticated_public->add_child("Signer");
+                       xml_signer->add_child("X509IssuerName", "ds")->add_child_text (signer->certificates().leaf()->issuer());
+                       xml_signer->add_child("X509SerialNumber", "ds")->add_child_text (signer->certificates().leaf()->serial());
+               }
+
+               {
+                       xmlpp::Element* required_extensions = authenticated_public->add_child("RequiredExtensions");
+
+                       {
+                               xmlpp::Element* kdm_required_extensions = required_extensions->add_child("KDMRequiredExtensions");
+                               kdm_required_extensions->set_namespace_declaration ("http://www.smpte-ra.org/schemas/430-1/2006/KDM");
+                               {
+                                       xmlpp::Element* recipient = kdm_required_extensions->add_child("Recipient");
+                                       {
+                                               xmlpp::Element* serial_element = recipient->add_child("X509IssuerSerial");
+                                               serial_element->add_child("X509IssuerName", "ds")->add_child_text (recipient_cert->issuer());
+                                               serial_element->add_child("X509SerialNumber", "ds")->add_child_text (recipient_cert->serial());
+                                       }
+
+                                       recipient->add_child("X509SubjectName")->add_child_text (recipient_cert->subject());
+                               }
+
+                               kdm_required_extensions->add_child("CompositionPlaylistId")->add_child_text("urn:uuid:" + _id);
+                               kdm_required_extensions->add_child("ContentTitleText")->add_child_text(_name);
+                               kdm_required_extensions->add_child("ContentAuthenticator")->add_child_text(signer->certificates().leaf()->thumbprint());
+                               kdm_required_extensions->add_child("ContentKeysNotValidBefore")->add_child_text(ptime_to_string (from));
+                               kdm_required_extensions->add_child("ContentKeysNotValidAfter")->add_child_text(ptime_to_string (until));
+
+                               {
+                                       xmlpp::Element* authorized_device_info = kdm_required_extensions->add_child("AuthorizedDeviceInfo");
+                                       authorized_device_info->add_child("DeviceListIdentifier")->add_child_text("urn:uuid:" + make_uuid());
+                                       authorized_device_info->add_child("DeviceListDescription")->add_child_text(recipient_cert->subject());
+                                       {
+                                               xmlpp::Element* device_list = authorized_device_info->add_child("DeviceList");
+                                               device_list->add_child("CertificateThumbprint")->add_child_text(recipient_cert->thumbprint());
+                                       }
+                               }
+
+                               {
+                                       xmlpp::Element* key_id_list = kdm_required_extensions->add_child("KeyIdList");
+                                       list<shared_ptr<const Asset> > a = assets();
+                                       for (list<shared_ptr<const Asset> >::iterator i = a.begin(); i != a.end(); ++i) {
+                                               /* XXX: non-MXF assets? */
+                                               shared_ptr<const MXFAsset> mxf = boost::dynamic_pointer_cast<const MXFAsset> (*i);
+                                               if (mxf) {
+                                                       mxf->add_typed_key_id (key_id_list);
+                                               }
+                                       }
+                               }
+
+                               {
+                                       xmlpp::Element* forensic_mark_flag_list = kdm_required_extensions->add_child("ForensicMarkFlagList");
+                                       forensic_mark_flag_list->add_child("ForensicMarkFlag")->add_child_text ( 
+                                               "http://www.smpte-ra.org/430-1/2006/KDM#mrkflg-picture-disable"
+                                               );
+                                       forensic_mark_flag_list->add_child("ForensicMarkFlag")->add_child_text ( 
+                                               "http://www.smpte-ra.org/430-1/2006/KDM#mrkflg-audio-disable"
+                                               );
+                               }
+                       }
+               }
+                                        
+               authenticated_public->add_child("NonCriticalExtensions");
+       }
+
+       {
+               xmlpp::Element* authenticated_private = root->add_child("AuthenticatedPrivate");
+               authenticated_private->set_attribute ("Id", "ID_AuthenticatedPrivate");
+               xmlAddID (0, doc->cobj(), (const xmlChar *) "ID_AuthenticatedPrivate", authenticated_private->get_attribute("Id")->cobj());
+
+               xmlpp::Element* encrypted_key = authenticated_private->add_child ("EncryptedKey", "enc");
+               xmlpp::Element* encryption_method = encrypted_key->add_child ("EncryptionMethod", "enc");
+               encryption_method->set_attribute ("Algorithm", "http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p");
+               encryption_method->add_child("DigestMethod", "ds")->set_attribute("Algorithm", "http://www.w3.org/2000/09/xmldsig#sha1");
+               xmlpp::Element* cipher_data = authenticated_private->add_child ("CipherData", "enc");
+               cipher_data->add_child("CipherValue", "enc")->add_child_text(key.hex());
+       }
+       
+       {
+               xmlpp::Element* signature = root->add_child("Signature", "ds");
+               
+               {
+                       xmlpp::Element* signed_info = signature->add_child("SignedInfo", "ds");
+                       signed_info->add_child("CanonicalizationMethod", "ds")->set_attribute(
+                               "Algorithm", "http://www.w3.org/TR/2001/REC-xml-c14n-20010315#WithComments"
+                               );
+
+                       if (interop) {
+                               signed_info->add_child("SignatureMethod", "ds")->set_attribute(
+                                       "Algorithm", "http://www.w3.org/2000/09/xmldsig#rsa-sha1"
+                                       );
+                       } else {
+                               signed_info->add_child("SignatureMethod", "ds")->set_attribute(
+                                       "Algorithm", "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"
+                                       );
+                       }
+                       
+                       {
+                               xmlpp::Element* reference = signed_info->add_child("Reference", "ds");
+                               reference->set_attribute("URI", "#ID_AuthenticatedPublic");
+                               reference->add_child("DigestMethod", "ds")->set_attribute("Algorithm", "http://www.w3.org/2001/04/xmlenc#sha256");
+                               reference->add_child("DigestValue", "ds");
+                       }
+                       
+                       {                               
+                               xmlpp::Element* reference = signed_info->add_child("Reference", "ds");
+                               reference->set_attribute("URI", "#ID_AuthenticatedPrivate");
+                               reference->add_child("DigestMethod", "ds")->set_attribute("Algorithm", "http://www.w3.org/2001/04/xmlenc#sha256");
+                               reference->add_child("DigestValue", "ds");
+                       }
+               }
+               
+               signer->add_signature_value (signature, "ds");
+       }
+
+       return doc;
+}
+
+/** @return true if we have any encrypted content */
+bool
+CPL::encrypted () const
+{
+       for (list<shared_ptr<Reel> >::const_iterator i = _reels.begin(); i != _reels.end(); ++i) {
+               if ((*i)->encrypted ()) {
+                       return true;
+               }
+       }
+
+       return false;
+}
+
+void
+CPL::add_kdm (KDM const & kdm)
+{
+       for (list<shared_ptr<Reel> >::const_iterator i = _reels.begin(); i != _reels.end(); ++i) {
+               (*i)->add_kdm (kdm);
+       }
+}
+
+pair<string, shared_ptr<const parse::AssetMapAsset> >
+CPL::asset_from_id (list<PathAssetMap> asset_maps, string id) const
+{
+       for (list<PathAssetMap>::const_iterator i = asset_maps.begin(); i != asset_maps.end(); ++i) {
+               shared_ptr<parse::AssetMapAsset> a = i->second->asset_from_id (id);
+               if (a) {
+                       return make_pair (i->first, a);
+               }
+       }
+
+       return make_pair ("", shared_ptr<const parse::AssetMapAsset> ());
+}