qpdf/libqpdf/QPDF_optimization.cc

// See the "Optimization" section of the manual.

#include <qpdf/QPDF.hh>

#include <qpdf/QTC.hh>
#include <qpdf/QPDFExc.hh>
#include <qpdf/QPDF_Dictionary.hh>
#include <qpdf/QPDF_Array.hh>
#include <assert.h>

QPDF::ObjUser::ObjUser() :
    ou_type(ou_bad),
    pageno(0)
{
}

QPDF::ObjUser::ObjUser(user_e type) :
    ou_type(type),
    pageno(0)
{
    assert(type == ou_root);
}

QPDF::ObjUser::ObjUser(user_e type, int pageno) :
    ou_type(type),
    pageno(pageno)
{
    assert((type == ou_page) || (type == ou_thumb));
}

QPDF::ObjUser::ObjUser(user_e type, std::string const& key) :
    ou_type(type),
    pageno(0),
    key(key)
{
    assert((type == ou_trailer_key) || (type == ou_root_key));
}

bool
QPDF::ObjUser::operator<(ObjUser const& rhs) const
{
    if (this->ou_type < rhs.ou_type)
    {
	return true;
    }
    else if (this->ou_type == rhs.ou_type)
    {
	if (this->pageno < rhs.pageno)
	{
	    return true;
	}
	else if (this->pageno == rhs.pageno)
	{
	    return (this->key < rhs.key);
	}
    }

    return false;
}

void
QPDF::optimize(std::map<int, int> const& object_stream_data,
	       bool allow_changes)
{
    if (! this->obj_user_to_objects.empty())
    {
	// already optimized
	return;
    }

    // The PDF specification indicates that /Outlines is supposed to
    // be an indirect reference.  Force it to be so if it exists and
    // is direct.  (This has been seen in the wild.)
    QPDFObjectHandle root = getRoot();
    if (root.getKey("/Outlines").isDictionary())
    {
        QPDFObjectHandle outlines = root.getKey("/Outlines");
        if (! outlines.isIndirect())
        {
            QTC::TC("qpdf", "QPDF_optimization indirect outlines");
            root.replaceKey("/Outlines", makeIndirectObject(outlines));
        }
    }

    // Traverse pages tree pushing all inherited resources down to the
    // page level.  This also initializes this->all_pages.
    pushInheritedAttributesToPage(allow_changes, false);

    // Traverse pages
    int n = this->all_pages.size();
    for (int pageno = 0; pageno < n; ++pageno)
    {
        updateObjectMaps(ObjUser(ObjUser::ou_page, pageno),
                         this->all_pages[pageno]);
    }

    // Traverse document-level items
    std::set<std::string> keys = this->trailer.getKeys();
    for (std::set<std::string>::iterator iter = keys.begin();
	 iter != keys.end(); ++iter)
    {
	std::string const& key = *iter;
	if (key == "/Root")
	{
	    // handled separately
	}
	else
	{
	    updateObjectMaps(ObjUser(ObjUser::ou_trailer_key, key),
			     this->trailer.getKey(key));
	}
    }

    keys = root.getKeys();
    for (std::set<std::string>::iterator iter = keys.begin();
	 iter != keys.end(); ++iter)
    {
	// Technically, /I keys from /Thread dictionaries are supposed
	// to be handled separately, but we are going to disregard
	// that specification for now.  There is loads of evidence
	// that pdlin and Acrobat both disregard things like this from
	// time to time, so this is almost certain not to cause any
	// problems.

	std::string const& key = *iter;
	updateObjectMaps(ObjUser(ObjUser::ou_root_key, key),
			 root.getKey(key));
    }

    ObjUser root_ou = ObjUser(ObjUser::ou_root);
    QPDFObjGen root_og = QPDFObjGen(root.getObjGen());
    obj_user_to_objects[root_ou].insert(root_og);
    object_to_obj_users[root_og].insert(root_ou);

    filterCompressedObjects(object_stream_data);
}

void
QPDF::pushInheritedAttributesToPage()
{
    // Public API should not have access to allow_changes.
    pushInheritedAttributesToPage(true, false);
}

void
QPDF::pushInheritedAttributesToPage(bool allow_changes, bool warn_skipped_keys)
{
    // Traverse pages tree pushing all inherited resources down to the
    // page level.

    // The record of whether we've done this is cleared by
    // updateAllPagesCache().  If we're warning for skipped keys,
    // re-traverse unconditionally.
    if (this->pushed_inherited_attributes_to_pages && (! warn_skipped_keys))
    {
        return;
    }

    // key_ancestors is a mapping of page attribute keys to a stack of
    // Pages nodes that contain values for them.
    std::map<std::string, std::vector<QPDFObjectHandle> > key_ancestors;
    this->all_pages.clear();
    pushInheritedAttributesToPageInternal(
        this->trailer.getKey("/Root").getKey("/Pages"),
        key_ancestors, this->all_pages, allow_changes, warn_skipped_keys);
    assert(key_ancestors.empty());
    this->pushed_inherited_attributes_to_pages = true;
}

void
QPDF::pushInheritedAttributesToPageInternal(
    QPDFObjectHandle cur_pages,
    std::map<std::string, std::vector<QPDFObjectHandle> >& key_ancestors,
    std::vector<QPDFObjectHandle>& pages,
    bool allow_changes, bool warn_skipped_keys)
{
    // Extract the underlying dictionary object
    std::string type = cur_pages.getKey("/Type").getName();

    if (type == "/Pages")
    {
	// Make a list of inheritable keys.  Any key other than /Type,
	// /Parent, Kids, or /Count is an inheritable attribute.  Push
	// this object onto the stack of pages nodes that have values
	// for this attribute.

	std::set<std::string> inheritable_keys;
	std::set<std::string> keys = cur_pages.getKeys();
	for (std::set<std::string>::iterator iter = keys.begin();
	     iter != keys.end(); ++iter)
	{
	    std::string const& key = *iter;
            if ( (key == "/MediaBox") || (key == "/CropBox") ||
                 (key == "/Resources") || (key == "/Rotate") )
	    {
		if (! allow_changes)
		{
		    throw QPDFExc(qpdf_e_internal, this->file->getName(),
				  this->last_object_description,
				  this->file->getLastOffset(),
				  "optimize detected an "
                                  "inheritable attribute when called "
				  "in no-change mode");
		}

		// This is an inheritable resource
		inheritable_keys.insert(key);
		QPDFObjectHandle oh = cur_pages.getKey(key);
		QTC::TC("qpdf", "QPDF opt direct pages resource",
			oh.isIndirect() ? 0 : 1);
		if (! oh.isIndirect())
		{
		    if (! oh.isScalar())
		    {
			// Replace shared direct object non-scalar
			// resources with indirect objects to avoid
			// copying large structures around.
			cur_pages.replaceKey(key, makeIndirectObject(oh));
			oh = cur_pages.getKey(key);
		    }
		    else
		    {
			// It's okay to copy scalars.
			QTC::TC("qpdf", "QPDF opt inherited scalar");
		    }
		}
		key_ancestors[key].push_back(oh);
		if (key_ancestors[key].size() > 1)
		{
		    QTC::TC("qpdf", "QPDF opt key ancestors depth > 1");
		}
		// Remove this resource from this node.  It will be
		// reattached at the page level.
		cur_pages.removeKey(key);
	    }
            else if (! ((key == "/Type") || (key == "/Parent") ||
                       (key == "/Kids") || (key == "/Count")))
            {
                // Warn when flattening, but not if the key is at the top
                // level (i.e. "/Parent" not set), as we don't change these;
                // but flattening removes intermediate /Pages nodes.
                if ( (warn_skipped_keys) && (cur_pages.hasKey("/Parent")) )
                {
                    QTC::TC("qpdf", "QPDF unknown key not inherited");
                    setLastObjectDescription("Pages object",
                                             cur_pages.getObjectID(),
                                             cur_pages.getGeneration());
                    warn(QPDFExc(qpdf_e_pages, this->file->getName(),
                                 this->last_object_description, 0,
                                 "Unknown key " + key + " in /Pages object"
                                 " is being discarded as a result of"
                                 " flattening the /Pages tree"));
                }
            }
	}

	// Visit descendant nodes.
	QPDFObjectHandle kids = cur_pages.getKey("/Kids");
	int n = kids.getArrayNItems();
	for (int i = 0; i < n; ++i)
	{
            pushInheritedAttributesToPageInternal(
                kids.getArrayItem(i), key_ancestors, pages,
                allow_changes, warn_skipped_keys);
	}

	// For each inheritable key, pop the stack.  If the stack
	// becomes empty, remove it from the map.  That way, the
	// invariant that the list of keys in key_ancestors is exactly
	// those keys for which inheritable attributes are available.

	if (! inheritable_keys.empty())
	{
	    QTC::TC("qpdf", "QPDF opt inheritable keys");
	    for (std::set<std::string>::iterator iter =
		     inheritable_keys.begin();
		 iter != inheritable_keys.end(); ++iter)
	    {
		std::string const& key = (*iter);
		key_ancestors[key].pop_back();
		if (key_ancestors[key].empty())
		{
		    QTC::TC("qpdf", "QPDF opt erase empty key ancestor");
		    key_ancestors.erase(key);
		}
	    }
	}
	else
	{
	    QTC::TC("qpdf", "QPDF opt no inheritable keys");
	}
    }
    else if (type == "/Page")
    {
	// Add all available inheritable attributes not present in
	// this object to this object.
	for (std::map<std::string, std::vector<QPDFObjectHandle> >::iterator
		 iter = key_ancestors.begin();
	     iter != key_ancestors.end(); ++iter)
	{
	    std::string const& key = (*iter).first;
	    if (! cur_pages.hasKey(key))
	    {
		QTC::TC("qpdf", "QPDF opt resource inherited");
		cur_pages.replaceKey(key, (*iter).second.back());
	    }
	    else
	    {
		QTC::TC("qpdf", "QPDF opt page resource hides ancestor");
	    }
	}
        pages.push_back(cur_pages);
    }
    else
    {
	throw QPDFExc(qpdf_e_damaged_pdf, this->file->getName(),
		      this->last_object_description,
		      this->file->getLastOffset(),
		      "invalid Type " + type + " in page tree");
    }
}

void
QPDF::updateObjectMaps(ObjUser const& ou, QPDFObjectHandle oh)
{
    std::set<QPDFObjGen> visited;
    updateObjectMapsInternal(ou, oh, visited, true);
}

void
QPDF::updateObjectMapsInternal(ObjUser const& ou, QPDFObjectHandle oh,
			       std::set<QPDFObjGen>& visited, bool top)
{
    // Traverse the object tree from this point taking care to avoid
    // crossing page boundaries.

    bool is_page_node = false;

    if (oh.isDictionary() && oh.hasKey("/Type"))
    {
	std::string type = oh.getKey("/Type").getName();
	if (type == "/Page")
	{
	    is_page_node = true;
	    if (! top)
	    {
		return;
	    }
	}
    }

    if (oh.isIndirect())
    {
	QPDFObjGen og(oh.getObjGen());
	if (visited.count(og))
	{
	    QTC::TC("qpdf", "QPDF opt loop detected");
	    return;
	}
	this->obj_user_to_objects[ou].insert(og);
	this->object_to_obj_users[og].insert(ou);
	visited.insert(og);
    }

    if (oh.isArray())
    {
	int n = oh.getArrayNItems();
	for (int i = 0; i < n; ++i)
	{
	    updateObjectMapsInternal(ou, oh.getArrayItem(i), visited, false);
	}
    }
    else if (oh.isDictionary() || oh.isStream())
    {
	QPDFObjectHandle dict = oh;
	if (oh.isStream())
	{
	    dict = oh.getDict();
	}

	std::set<std::string> keys = dict.getKeys();
	for (std::set<std::string>::iterator iter = keys.begin();
	     iter != keys.end(); ++iter)
	{
	    std::string const& key = *iter;
	    if (is_page_node && (key == "/Thumb"))
	    {
		// Traverse page thumbnail dictionaries as a special
		// case.
		updateObjectMaps(ObjUser(ObjUser::ou_thumb, ou.pageno),
				 dict.getKey(key));
	    }
	    else if (is_page_node && (key == "/Parent"))
	    {
		// Don't traverse back up the page tree
	    }
	    else
	    {
		updateObjectMapsInternal(ou, dict.getKey(key),
					 visited, false);
	    }
	}
    }
}

void
QPDF::filterCompressedObjects(std::map<int, int> const& object_stream_data)
{
    if (object_stream_data.empty())
    {
	return;
    }

    // Transform object_to_obj_users and obj_user_to_objects so that
    // they refer only to uncompressed objects.  If something is a
    // user of a compressed object, then it is really a user of the
    // object stream that contains it.

    std::map<ObjUser, std::set<QPDFObjGen> > t_obj_user_to_objects;
    std::map<QPDFObjGen, std::set<ObjUser> > t_object_to_obj_users;

    for (std::map<ObjUser, std::set<QPDFObjGen> >::iterator i1 =
	     this->obj_user_to_objects.begin();
	 i1 != this->obj_user_to_objects.end(); ++i1)
    {
	ObjUser const& ou = (*i1).first;
	std::set<QPDFObjGen> const& objects = (*i1).second;
	for (std::set<QPDFObjGen>::const_iterator i2 = objects.begin();
	     i2 != objects.end(); ++i2)
	{
	    QPDFObjGen const& og = (*i2);
	    std::map<int, int>::const_iterator i3 =
		object_stream_data.find(og.getObj());
	    if (i3 == object_stream_data.end())
	    {
		t_obj_user_to_objects[ou].insert(og);
	    }
	    else
	    {
		t_obj_user_to_objects[ou].insert(QPDFObjGen((*i3).second, 0));
	    }
	}
    }

    for (std::map<QPDFObjGen, std::set<ObjUser> >::iterator i1 =
	     this->object_to_obj_users.begin();
	 i1 != this->object_to_obj_users.end(); ++i1)
    {
	QPDFObjGen const& og = (*i1).first;
	std::set<ObjUser> const& objusers = (*i1).second;
	for (std::set<ObjUser>::const_iterator i2 = objusers.begin();
	     i2 != objusers.end(); ++i2)
	{
	    ObjUser const& ou = (*i2);
	    std::map<int, int>::const_iterator i3 =
		object_stream_data.find(og.getObj());
	    if (i3 == object_stream_data.end())
	    {
		t_object_to_obj_users[og].insert(ou);
	    }
	    else
	    {
		t_object_to_obj_users[QPDFObjGen((*i3).second, 0)].insert(ou);
	    }
	}
    }

    this->obj_user_to_objects = t_obj_user_to_objects;
    this->object_to_obj_users = t_object_to_obj_users;
}