xref: /trunk/main/desktop/source/deployment/registry/dp_backenddb.cxx (revision 79aad27f)

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 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 *
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// MARKER(update_precomp.py): autogen include statement, do not remove
#include "precompiled_desktop.hxx"

#include "rtl/string.h"
#include "rtl/strbuf.hxx"
#include "rtl/bootstrap.hxx"
#include "cppuhelper/exc_hlp.hxx"
#include "osl/file.hxx"
#include "com/sun/star/uno/XComponentContext.hpp"
#include "com/sun/star/xml/dom/XDocumentBuilder.hpp"
#include "com/sun/star/xml/xpath/XXPathAPI.hpp"
#include "com/sun/star/io/XActiveDataSource.hpp"
#include "com/sun/star/io/XActiveDataControl.hpp"
#include "dp_ucb.h"
#include "dp_misc.h"
#include "ucbhelper/content.hxx"
#include "xmlscript/xml_helper.hxx"
#include "dp_backenddb.hxx"


namespace css = ::com::sun::star;
using namespace ::com::sun::star::uno;
using ::rtl::OUString;


namespace dp_registry {
namespace backend {

BackendDb::BackendDb(
    Reference<css::uno::XComponentContext> const &  xContext,
    ::rtl::OUString const & url):
    m_xContext(xContext)
{
    m_urlDb = dp_misc::expandUnoRcUrl(url);
}

void BackendDb::save()
{
    const Reference<css::io::XActiveDataSource> xDataSource(m_doc,css::uno::UNO_QUERY_THROW);
    ::rtl::ByteSequence bytes;
    xDataSource->setOutputStream(::xmlscript::createOutputStream(&bytes));
    const Reference<css::io::XActiveDataControl> xDataControl(m_doc,css::uno::UNO_QUERY_THROW);
    xDataControl->start();

    const Reference<css::io::XInputStream> xData(
        ::xmlscript::createInputStream(bytes));
    ::ucbhelper::Content ucbDb(m_urlDb, 0);
    ucbDb.writeStream(xData, true /*replace existing*/);
}

css::uno::Reference<css::xml::dom::XDocument> BackendDb::getDocument()
{
    if (!m_doc.is())
    {
        const Reference<css::xml::dom::XDocumentBuilder> xDocBuilder(
            m_xContext->getServiceManager()->createInstanceWithContext(
                OUSTR("com.sun.star.xml.dom.DocumentBuilder"),
                m_xContext ), css::uno::UNO_QUERY);
        if (!xDocBuilder.is())
            throw css::uno::RuntimeException(
                OUSTR(" Could not create service com.sun.star.xml.dom.DocumentBuilder"), 0);

        ::osl::DirectoryItem item;
        ::osl::File::RC err = ::osl::DirectoryItem::get(m_urlDb, item);
        if (err == ::osl::File::E_None)
        {
            ::ucbhelper::Content descContent(
                m_urlDb, css::uno::Reference<css::ucb::XCommandEnvironment>());
            Reference<css::io::XInputStream> xIn = descContent.openStream();
            m_doc = xDocBuilder->parse(xIn);
        }
        else if (err == ::osl::File::E_NOENT)
        {
            //Create a new document and insert some basic stuff
            m_doc = xDocBuilder->newDocument();
            const Reference<css::xml::dom::XElement> rootNode =
                m_doc->createElementNS(getDbNSName(), getNSPrefix() +
                                       OUSTR(":") + getRootElementName());

            m_doc->appendChild(Reference<css::xml::dom::XNode>(
                                   rootNode, UNO_QUERY_THROW));
            save();
        }
        else
            throw css::uno::RuntimeException(
                OUSTR("Extension manager could not access database file:" )
                + m_urlDb, 0);

        if (!m_doc.is())
            throw css::uno::RuntimeException(
                OUSTR("Extension manager could not get root node of data base file: ")
                      + m_urlDb, 0);
    }

    return m_doc;
}

Reference<css::xml::xpath::XXPathAPI> BackendDb::getXPathAPI()
{
    if (!m_xpathApi.is())
    {
        m_xpathApi = Reference< css::xml::xpath::XXPathAPI >(
            m_xContext->getServiceManager()->createInstanceWithContext(
                OUSTR("com.sun.star.xml.xpath.XPathAPI"),
                m_xContext), css::uno::UNO_QUERY);

        if (!m_xpathApi.is())
            throw css::uno::RuntimeException(
                OUSTR(" Could not create service com.sun.star.xml.xpath.XPathAPI"), 0);

        m_xpathApi->registerNS(
            getNSPrefix(), getDbNSName());
    }

    return m_xpathApi;
}

void BackendDb::removeElement(::rtl::OUString const & sXPathExpression)
{
    try
    {
        const Reference<css::xml::dom::XDocument> doc = getDocument();
        const Reference<css::xml::dom::XNode> root = doc->getFirstChild();
        const Reference<css::xml::xpath::XXPathAPI> xpathApi = getXPathAPI();
        //find the extension element that is to be removed
        const Reference<css::xml::dom::XNode> aNode =
            xpathApi->selectSingleNode(root, sXPathExpression);

        if (aNode.is())
        {
            root->removeChild(aNode);
            save();
        }

#if    OSL_DEBUG_LEVEL > 0
        //There must not be any other entry with the same url
        const Reference<css::xml::dom::XNode> nextNode =
            xpathApi->selectSingleNode(root, sXPathExpression);
        OSL_ASSERT(! nextNode.is());
#endif
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to write data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

void BackendDb::removeEntry(::rtl::OUString const & url)
{
    const OUString sKeyElement = getKeyElementName();
    const OUString sPrefix = getNSPrefix();
    ::rtl::OUStringBuffer sExpression(500);
    sExpression.append(sPrefix);
    sExpression.appendAscii(":");
    sExpression.append(sKeyElement);
    sExpression.append(OUSTR("[@url = \""));
    sExpression.append(url);
    sExpression.appendAscii("\"]");

    removeElement(sExpression.makeStringAndClear());
}

void BackendDb::revokeEntry(::rtl::OUString const & url)
{
    try
    {
        Reference<css::xml::dom::XElement> entry = Reference<css::xml::dom::XElement>(getKeyElement(url), UNO_QUERY);
        if (entry.is())
        {
            entry->setAttribute(OUSTR("revoked"), OUSTR("true"));
            save();
        }
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to revoke data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

bool BackendDb::activateEntry(::rtl::OUString const & url)
{
    try
    {
        bool ret = false;
        Reference<css::xml::dom::XElement> entry = Reference<css::xml::dom::XElement>(getKeyElement(url), UNO_QUERY);
        if (entry.is())
        {
            //no attribute "active" means it is active, that is, registered.
            entry->removeAttribute(OUSTR("revoked"));
            save();
            ret = true;
        }
        return ret;
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to revoke data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

bool BackendDb::hasActiveEntry(::rtl::OUString const & url)
{
    try
    {
        bool ret = false;
        Reference<css::xml::dom::XElement> entry = Reference<css::xml::dom::XElement>(getKeyElement(url), UNO_QUERY);
        if (entry.is())
        {
            OUString sActive = entry->getAttribute(OUSTR("revoked"));
            if (!sActive.equals(OUSTR("true")))
                ret = true;
        }
        return ret;

    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to determine an active entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

Reference<css::xml::dom::XNode> BackendDb::getKeyElement(
    ::rtl::OUString const & url)
{
    try
    {
        const OUString sPrefix = getNSPrefix();
        const OUString sKeyElement = getKeyElementName();
        ::rtl::OUStringBuffer sExpression(500);
        sExpression.append(sPrefix);
        sExpression.appendAscii(":");
        sExpression.append(sKeyElement);
        sExpression.append(OUSTR("[@url = \""));
        sExpression.append(url);
        sExpression.appendAscii("\"]");

        const Reference<css::xml::dom::XDocument> doc = getDocument();
        const Reference<css::xml::dom::XNode> root = doc->getFirstChild();
        const Reference<css::xml::xpath::XXPathAPI> xpathApi = getXPathAPI();
        return xpathApi->selectSingleNode(root, sExpression.makeStringAndClear());
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to read key element in backend db: ") +
            m_urlDb, 0, exc);
    }
}

//Only writes the data if there is at least one entry
void BackendDb::writeVectorOfPair(
    ::std::vector< ::std::pair< ::rtl::OUString, ::rtl::OUString > > const & vecPairs,
    OUString const & sVectorTagName,
    OUString const & sPairTagName,
    OUString const & sFirstTagName,
    OUString const & sSecondTagName,
    css::uno::Reference<css::xml::dom::XNode> const & xParent)
{
    try{
        if (vecPairs.size() == 0)
            return;
        const OUString sNameSpace = getDbNSName();
        OSL_ASSERT(sNameSpace.getLength());
        const OUString sPrefix(getNSPrefix() + OUSTR(":"));
        const Reference<css::xml::dom::XDocument> doc = getDocument();
        const Reference<css::xml::dom::XNode> root = doc->getFirstChild();

        const Reference<css::xml::dom::XElement> vectorNode(
            doc->createElementNS(sNameSpace, sPrefix + sVectorTagName));

        xParent->appendChild(
            Reference<css::xml::dom::XNode>(
                vectorNode, css::uno::UNO_QUERY_THROW));
        typedef ::std::vector< ::std::pair< OUString, OUString > >::const_iterator CIT;
        for (CIT i = vecPairs.begin(); i != vecPairs.end(); i++)
        {
            const Reference<css::xml::dom::XElement> pairNode(
                doc->createElementNS(sNameSpace, sPrefix + sPairTagName));

            vectorNode->appendChild(
                Reference<css::xml::dom::XNode>(
                    pairNode, css::uno::UNO_QUERY_THROW));

            const Reference<css::xml::dom::XElement> firstNode(
                doc->createElementNS(sNameSpace, sPrefix + sFirstTagName));

            pairNode->appendChild(
                Reference<css::xml::dom::XNode>(
                    firstNode, css::uno::UNO_QUERY_THROW));

            const Reference<css::xml::dom::XText> firstTextNode(
                doc->createTextNode( i->first));

            firstNode->appendChild(
                Reference<css::xml::dom::XNode>(
                    firstTextNode, css::uno::UNO_QUERY_THROW));

            const Reference<css::xml::dom::XElement> secondNode(
                doc->createElementNS(sNameSpace, sPrefix + sSecondTagName));

            pairNode->appendChild(
                Reference<css::xml::dom::XNode>(
                    secondNode, css::uno::UNO_QUERY_THROW));

            const Reference<css::xml::dom::XText> secondTextNode(
                doc->createTextNode( i->second));

            secondNode->appendChild(
                Reference<css::xml::dom::XNode>(
                    secondTextNode, css::uno::UNO_QUERY_THROW));
        }
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to write data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

::std::vector< ::std::pair< OUString, OUString > >
BackendDb::readVectorOfPair(
    Reference<css::xml::dom::XNode> const & parent,
    OUString const & sListTagName,
    OUString const & sPairTagName,
    OUString const & sFirstTagName,
    OUString const & sSecondTagName)
{
    try
    {
        OSL_ASSERT(parent.is());
        const OUString sPrefix(getNSPrefix() + OUSTR(":"));
        const Reference<css::xml::xpath::XXPathAPI> xpathApi = getXPathAPI();
        const OUString sExprPairs(
            sPrefix + sListTagName + OUSTR("/") + sPrefix + sPairTagName);
        const Reference<css::xml::dom::XNodeList> listPairs =
            xpathApi->selectNodeList(parent, sExprPairs);

        ::std::vector< ::std::pair< OUString, OUString > > retVector;
        sal_Int32 length = listPairs->getLength();
        for (sal_Int32 i = 0; i < length; i++)
        {
            const Reference<css::xml::dom::XNode> aPair = listPairs->item(i);
            const OUString sExprFirst(sPrefix + sFirstTagName + OUSTR("/text()"));
            const Reference<css::xml::dom::XNode> first =
                xpathApi->selectSingleNode(aPair, sExprFirst);

            const OUString sExprSecond(sPrefix + sSecondTagName + OUSTR("/text()"));
            const Reference<css::xml::dom::XNode> second =
                xpathApi->selectSingleNode(aPair, sExprSecond);
            OSL_ASSERT(first.is() && second.is());

            retVector.push_back(::std::make_pair(
                                    first->getNodeValue(), second->getNodeValue()));
        }
        return retVector;
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to read data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

//Only writes the data if there is at least one entry
void BackendDb::writeSimpleList(
    ::std::list< ::rtl::OUString> const & list,
    OUString const & sListTagName,
    OUString const & sMemberTagName,
    Reference<css::xml::dom::XNode> const & xParent)
{
    try
    {
        if (list.size() == 0)
            return;
        const OUString sNameSpace = getDbNSName();
        const OUString sPrefix(getNSPrefix() + OUSTR(":"));
        const Reference<css::xml::dom::XDocument> doc = getDocument();

        const Reference<css::xml::dom::XElement> listNode(
            doc->createElementNS(sNameSpace, sPrefix + sListTagName));

        xParent->appendChild(
            Reference<css::xml::dom::XNode>(
                listNode, css::uno::UNO_QUERY_THROW));

        typedef ::std::list<OUString>::const_iterator ITC_ITEMS;
        for (ITC_ITEMS i = list.begin(); i != list.end(); i++)
        {
            const Reference<css::xml::dom::XNode> memberNode(
                doc->createElementNS(sNameSpace, sPrefix + sMemberTagName), css::uno::UNO_QUERY_THROW);

            listNode->appendChild(memberNode);

            const Reference<css::xml::dom::XNode> textNode(
                doc->createTextNode( *i), css::uno::UNO_QUERY_THROW);

            memberNode->appendChild(textNode);
        }
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to write data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

//Writes only the element if is has a value.
//The prefix is automatically added to the element name
void BackendDb::writeSimpleElement(
    OUString const & sElementName, OUString const & value,
    Reference<css::xml::dom::XNode> const & xParent)
{
    try
    {
        if (value.getLength() == 0)
            return;
        const OUString sPrefix = getNSPrefix();
        const Reference<css::xml::dom::XDocument> doc = getDocument();
        const OUString sNameSpace = getDbNSName();
        const Reference<css::xml::dom::XNode> dataNode(
            doc->createElementNS(sNameSpace, sPrefix + OUSTR(":") + sElementName),
            UNO_QUERY_THROW);
        xParent->appendChild(dataNode);

        const Reference<css::xml::dom::XNode> dataValue(
            doc->createTextNode(value), UNO_QUERY_THROW);
        dataNode->appendChild(dataValue);
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to write data entry(writeSimpleElement) in backend db: ") +
            m_urlDb, 0, exc);
    }

}

/** The key elements have an url attribute and are always children of the root
    element.
*/
Reference<css::xml::dom::XNode> BackendDb::writeKeyElement(
    ::rtl::OUString const & url)
{
    try
    {
        const OUString sNameSpace = getDbNSName();
        const OUString sPrefix = getNSPrefix();
        const OUString sElementName = getKeyElementName();
        const Reference<css::xml::dom::XDocument> doc = getDocument();
        const Reference<css::xml::dom::XNode> root = doc->getFirstChild();

        //Check if there are an entry with the same url. This can be the case if the
        //the status of an XPackage is ambiguous. In this case a call to activateExtension
        //(dp_extensionmanager.cxx), will register the package again. See also
        //Package::processPackage_impl in dp_backend.cxx.
        //A package can become
        //invalid after its successful registration, for example if a second extension with
        //the same service is installed.
        const OUString sExpression(
            sPrefix + OUSTR(":") + sElementName + OUSTR("[@url = \"") + url + OUSTR("\"]"));
        const Reference<css::xml::dom::XNode> existingNode =
            getXPathAPI()->selectSingleNode(root, sExpression);
        if (existingNode.is())
        {
            OSL_ASSERT(0);
            //replace the existing entry.
            removeEntry(url);
        }

        const Reference<css::xml::dom::XElement> keyElement(
            doc->createElementNS(sNameSpace, sPrefix +  OUSTR(":") + sElementName));

        keyElement->setAttribute(OUSTR("url"), url);

        const Reference<css::xml::dom::XNode> keyNode(
            keyElement, UNO_QUERY_THROW);
        root->appendChild(keyNode);
        return keyNode;
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to write key element in backend db: ") +
            m_urlDb, 0, exc);
    }
}

OUString BackendDb::readSimpleElement(
    OUString const & sElementName, Reference<css::xml::dom::XNode> const & xParent)
{
    try
    {
        const OUString sPrefix = getNSPrefix();
        const OUString sExpr(sPrefix + OUSTR(":") + sElementName + OUSTR("/text()"));
        const Reference<css::xml::xpath::XXPathAPI> xpathApi = getXPathAPI();
        const Reference<css::xml::dom::XNode> val =
            xpathApi->selectSingleNode(xParent, sExpr);
        if (val.is())
            return val->getNodeValue();
        return OUString();
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to read data (readSimpleElement) in backend db: ") +
            m_urlDb, 0, exc);
    }
}


::std::list< OUString> BackendDb::readList(
    Reference<css::xml::dom::XNode> const & parent,
    OUString const & sListTagName,
    OUString const & sMemberTagName)
{
    try
    {
        OSL_ASSERT(parent.is());
        const OUString sPrefix(getNSPrefix() + OUSTR(":"));
        const Reference<css::xml::xpath::XXPathAPI> xpathApi = getXPathAPI();
        const OUString sExprList(
            sPrefix + sListTagName + OUSTR("/") + sPrefix + sMemberTagName + OUSTR("/text()"));
        const Reference<css::xml::dom::XNodeList> list =
            xpathApi->selectNodeList(parent, sExprList);

        ::std::list<OUString > retList;
        sal_Int32 length = list->getLength();
        for (sal_Int32 i = 0; i < length; i++)
        {
            const Reference<css::xml::dom::XNode> member = list->item(i);
            retList.push_back(member->getNodeValue());
        }
        return retList;
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to read data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

::std::list<OUString> BackendDb::getOneChildFromAllEntries(
    OUString const & name)
{
    try
    {
        ::std::list<OUString> listRet;
        Reference<css::xml::dom::XDocument> doc = getDocument();
        Reference<css::xml::dom::XNode> root = doc->getFirstChild();

        Reference<css::xml::xpath::XXPathAPI> xpathApi = getXPathAPI();
        const OUString sPrefix = getNSPrefix();
        const OUString sKeyElement = getKeyElementName();
        ::rtl::OUStringBuffer buf(512);
        buf.append(sPrefix);
        buf.appendAscii(":");
        buf.append(sKeyElement);
        buf.appendAscii("/");
        buf.append(sPrefix);
        buf.appendAscii(":");
        buf.append(name);
        buf.append(OUSTR("/text()"));

        Reference<css::xml::dom::XNodeList> nodes =
            xpathApi->selectNodeList(root, buf.makeStringAndClear());
        if (nodes.is())
        {
            sal_Int32 length = nodes->getLength();
            for (sal_Int32 i = 0; i < length; i++)
                listRet.push_back(nodes->item(i)->getNodeValue());
        }
        return listRet;
    }
    catch (css::deployment::DeploymentException& )
    {
        throw;
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to read data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}



//================================================================================
RegisteredDb::RegisteredDb(
    Reference<XComponentContext> const &  xContext,
    ::rtl::OUString const & url):BackendDb(xContext, url)
{

}

void RegisteredDb::addEntry(::rtl::OUString const & url)
{
    try{
        if (!activateEntry(url))
        {
            const OUString sNameSpace = getDbNSName();
            const OUString sPrefix = getNSPrefix();
            const OUString sEntry = getKeyElementName();

            Reference<css::xml::dom::XDocument> doc = getDocument();
            Reference<css::xml::dom::XNode> root = doc->getFirstChild();

#if    OSL_DEBUG_LEVEL > 0
            //There must not be yet an entry with the same url
            OUString sExpression(
                sPrefix + OUSTR(":") + sEntry + OUSTR("[@url = \"") + url + OUSTR("\"]"));
            Reference<css::xml::dom::XNode> _extensionNode =
                getXPathAPI()->selectSingleNode(root, sExpression);
            OSL_ASSERT(! _extensionNode.is());
#endif
            Reference<css::xml::dom::XElement> helpElement(
                doc->createElementNS(sNameSpace, sPrefix +  OUSTR(":") + sEntry));

            helpElement->setAttribute(OUSTR("url"), url);

            Reference<css::xml::dom::XNode> helpNode(
                helpElement, UNO_QUERY_THROW);
            root->appendChild(helpNode);

            save();
        }
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to write data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}

bool RegisteredDb::getEntry(::rtl::OUString const & url)
{
    try
    {
        const OUString sPrefix = getNSPrefix();
        const OUString sEntry = getKeyElementName();
        const OUString sExpression(
            sPrefix + OUSTR(":") + sEntry + OUSTR("[@url = \"") + url + OUSTR("\"]"));
        Reference<css::xml::dom::XDocument> doc = getDocument();
        Reference<css::xml::dom::XNode> root = doc->getFirstChild();

        Reference<css::xml::xpath::XXPathAPI> xpathApi = getXPathAPI();
        //find the extension element that is to be removed
        Reference<css::xml::dom::XNode> aNode =
            xpathApi->selectSingleNode(root, sExpression);
        if (!aNode.is())
        {
            return false;
        }
        return true;
    }
    catch(css::uno::Exception &)
    {
        Any exc( ::cppu::getCaughtException() );
        throw css::deployment::DeploymentException(
            OUSTR("Extension Manager: failed to read data entry in backend db: ") +
            m_urlDb, 0, exc);
    }
}


} // namespace backend
} // namespace dp_registry