source: trunk/src/xmlpatterns/api/qxmlquery.cpp@ 1036

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#include <QtCore/QBuffer>
#include <QtCore/QStringList>
#include <QtXmlPatterns/QXmlFormatter>

#include "qacceltreeresourceloader_p.h"
#include "qcommonvalues_p.h"
#include "qxmlresultitems.h"
#include "qxmlresultitems_p.h"
#include "qxmlserializer.h"
#include "qxpathhelper_p.h"

#include "qxmlquery.h"
#include "qxmlquery_p.h"

QT_BEGIN_NAMESPACE

/*!
  \class QXmlQuery

  \brief The QXmlQuery class performs XQueries on XML data, or on non-XML data modeled to look like XML.

  \reentrant
  \since 4.4
  \ingroup xml-tools

  The QXmlQuery class compiles and executes queries written in the
  \l {http://www.w3.org/TR/xquery/}{XQuery language}. QXmlQuery is
  typically used to query XML data, but it can also query non-XML
  data that has been modeled to look like XML.

  Using QXmlQuery to query XML data, as in the snippet below, is
  simple because it can use the built-in \l {QAbstractXmlNodeModel}
  {XML data model} as its delegate to the underlying query engine for
  traversing the data. The built-in data model is specified in \l
  {http://www.w3.org/TR/xpath-datamodel/} {XQuery 1.0 and XPath 2.0
  Data Model}.

  \snippet doc/src/snippets/code/src_xmlpatterns_api_qabstractxmlreceiver.cpp 0

  The example uses QXmlQuery to match the first paragraph of an XML
  document and then \l {QXmlSerializer} {output the result} to a
  device as XML.

  Using QXmlQuery to query \e {non-XML} data requires writing a
  subclass of QAbstractXmlNodeModel to use as a replacement for the
  built-in XML data model. The custom data model will be able to
  traverse the non-XML data as required by the QAbstractXmlNodeModel
  interface. An instance of this custom data model then becomes the
  delegate used by the query engine to traverse the non-XML data. For
  an example of how to use QXmlQuery to query non-XML data, see the
  documentation for QAbstractXmlNodeModel.

  \section1 Running XQueries

  To run a query set up with QXmlQuery, call one of the evaluation
  functions.

  \list

  \o evaluateTo(QAbstractXmlReceiver *) is called with a pointer to an
  XML \l {QAbstractXmlReceiver} {receiver}, which receives the query
  results as a sequence of callbacks. The receiver callback class is
  like the callback class used for translating the output of a SAX
  parser. QXmlSerializer, for example, is a receiver callback class
  for translating the sequence of callbacks for output as unformatted
  XML text.

  \endlist

  \list

  \o evaluateTo(QXmlResultItems *) is called with a pointer to an
  iterator for an empty sequence of query \l {QXmlResultItems} {result
  items}.  The Java-like iterator allows the query results to be
  accessed sequentially.

  \endlist

  \list

  \o evaluateTo(QStringList *) is like evaluateTo(QXmlResultItems *),
  but the query must evaluate to a sequence of strings.

  \endlist

  \section1 Running XPath Expressions

  The XPath language is a subset of the XQuery language, so
  running an XPath expression is the same as running an XQuery
  query. Pass the XPath expression to QXmlQuery using setQuery().

  \section1 Running XSLT stylesheets

  Running an XSLT stylesheet is like running an XQuery, except that
  when you construct your QXmlQuery, you must pass QXmlQuery::XSLT20
  to tell QXmlQuery to interpret whatever it gets from setQuery() as
  an XSLT stylesheet instead of as an XQuery. You must also set the
  input document by calling setFocus().

  \snippet doc/src/snippets/code/src_xmlpatterns_api_qxmlquery.cpp 7

  \note Currently, setFocus() must be called \e before setQuery() when
  using XSLT.

  Another way to run an XSLT stylesheet is to use the \c xmlpatterns
  command line utility.

  \code
  xmlpatterns myStylesheet.xsl myInput.xml
  \endcode

  \note For the current release, XSLT support should be considered
  experimental. See section \l{XQuery#XSLT 2.0} {XSLT conformance} for
  details.

  Stylesheet parameters are bound using bindVariable().

  \section1 Binding A Query To A Starting Node

  When a query is run on XML data, as in the snippet above, the
  \c{doc()} function returns the node in the built-in data model where
  the query evaluation will begin. But when a query is run on a custom
  node model containing non-XML data, one of the bindVariable()
  functions must be called to bind a variable name to a starting node
  in the custom model.  A $variable reference is used in the XQuery
  text to access the starting node in the custom model. It is not
  necessary to declare the variable name external in the query. See
  the example in the documentation for QAbstractXmlNodeModel.

  \section1 Reentrancy and Thread-Safety

  QXmlQuery is reentrant but not thread-safe. It is safe to use the
  QxmlQuery copy constructor to create a copy of a query and run the
  same query multiple times. Behind the scenes, QXmlQuery will reuse
  resources such as opened files and compiled queries to the extent
  possible. But it is not safe to use the same instance of QXmlQuery
  in multiple threads.

  \section1 Error Handling

  Errors can occur during query evaluation. Examples include type
  errors and file loading errors. When an error occurs:

  \list

  \o The error message is sent to the messageHandler().

  \o QXmlResultItems::hasError() will return \c{true}, or
  evaluateTo() will return \c{false};

  \o The results of the evaluation are undefined.

  \endlist

  \section1 Resource Management

  When a query runs, it parses documents, allocating internal data
  structures to hold them, and it may load other resources over the
  network. It reuses these allocated resources when possible, to
  avoid having to reload and reparse them.

  When setQuery() is called, the query text is compiled into an
  internal data structure and optimized. The optimized form can
  then be reused for multiple evaluations of the query. Since the
  compile-and-optimize process can be expensive, repeating it for
  the same query should be avoided by using a separate instance of
  QXmlQuery for each query text.

  Once a document has been parsed, its internal representation is
  maintained in the QXmlQuery instance and shared among multiple
  QXmlQuery instances.

  An instance of QCoreApplication must exist before QXmlQuery can be
  used.

  \section1 Event Handling

  When QXmlQuery accesses resources (e.g., calling \c fn:doc() to load a file,
  or accessing a device via a bound variable), the event loop is used, which
  means events will be processed. To avoid processing events when QXmlQuery
  accesses resources, create your QXmlQuery instance in a separate thread.
 */

/*!
 \enum QXmlQuery::QueryLanguage
 \since 4.5

 Specifies whether you want QXmlQuery to interpret the input to
 setQuery() as an XQuery or as an XSLT stylesheet.

 \value XQuery10 XQuery 1.0.
 \value XSLT20 XSLT 2.0
 \omitvalue XmlSchema11IdentityConstraintSelector The selector, the restricted
            XPath pattern found in W3C XML Schema 1.1 for uniqueness
            contraints. Apart from restricting the syntax, the type check stage
            for the expression assumes a sequence of nodes to be the focus.
 \omitvalue XmlSchema11IdentityConstraintField The field, the restricted
            XPath pattern found in W3C XML Schema 1.1 for uniqueness
            contraints. Apart from restricting the syntax, the type check stage
            for the expression assumes a sequence of nodes to be the focus.
 \omitvalue XPath20 Signifies XPath 2.0. Has no effect in the public API, it's
            used internally. As With XmlSchema11IdentityConstraintSelector and
            XmlSchema11IdentityConstraintField, the type check stage
            for the expression assumes a sequence of nodes to be the focus.

 \sa setQuery()
 */

// ### Qt5: Merge constructor overloads
/*!
  Constructs an invalid, empty query that cannot be used until
  setQuery() is called.

  \note This constructor must not be used if you intend to use
  this QXmlQuery to process XSL-T stylesheets. The other constructor
  must be used in that case.
 */
QXmlQuery::QXmlQuery() : d(new QXmlQueryPrivate())
{
}

/*!
  Constructs a QXmlQuery that is a copy of \a other. The new
  instance will share resources with the existing query
  to the extent possible.
 */
QXmlQuery::QXmlQuery(const QXmlQuery &other) : d(new QXmlQueryPrivate(*other.d))
{
    /* First we have invoked QXmlQueryPrivate's synthesized copy constructor.
     * Keep this section in sync with QXmlQuery::operator=(). */
    d->detach();
}

/*!
  Constructs a query that will use \a np as its name pool. The query
  cannot be evaluated until setQuery() has been called.
 */
QXmlQuery::QXmlQuery(const QXmlNamePool &np) : d(new QXmlQueryPrivate(np))
{
}

/*!

  Constructs a query that will be used to run Xqueries or XSL-T
  stylesheets, depending on the value of \a queryLanguage. It will use
  \a np as its name pool.

  \note If your QXmlQuery will process XSL-T stylesheets, this
  constructor must be used. The default constructor can only
  create instances of QXmlQuery for running XQueries.

  \note The XSL-T support in this release is considered experimental.
  See the \l{XQuery#XSLT 2.0} {XSLT conformance} for details.

 \since 4.5
 \sa queryLanguage()
 */
QXmlQuery::QXmlQuery(QueryLanguage queryLanguage,
                     const QXmlNamePool &np) : d(new QXmlQueryPrivate(np))
{
    d->queryLanguage = queryLanguage;
}

/*!
  Destroys this QXmlQuery.
 */
QXmlQuery::~QXmlQuery()
{
    delete d;
}

/*!
  Assigns \a other to this QXmlQuery instance.
 */
QXmlQuery &QXmlQuery::operator=(const QXmlQuery &other)
{
    /* Keep this section in sync with QXmlQuery::QXmlQuery(const QXmlQuery &).
     */
    if(d != other.d)
    {
        *d = *other.d;
        d->detach();
    }

    return *this;
}

/*!
  Changes the \l {QAbstractMessageHandler}{message handler} for this
  QXmlQuery to \a aMessageHandler. The query sends all compile and
  runtime messages to this message handler. QXmlQuery does not take
  ownership of \a aMessageHandler.

  Normally, the default message handler is sufficient. It writes
  compile and runtime messages to \e stderr. The default message
  handler includes color codes if \e stderr can render colors.

  Note that changing the message handler after the query has been
  compiled has no effect, i.e. the query uses the same message handler
  at runtime that it uses at compile time.

  When QXmlQuery calls QAbstractMessageHandler::message(),
  the arguments are as follows:

  \table
  \header
    \o message() argument
    \o Semantics
  \row
    \o QtMsgType type
    \o Only QtWarningMsg and QtFatalMsg are used. The former
       identifies a compile or runtime warning, while the
       latter identifies a dynamic or static error.
  \row
    \o const QString & description
    \o An XHTML document which is the actual message. It is translated
       into the current language.
  \row
    \o const QUrl &identifier
    \o Identifies the error with a URI, where the fragment is
       the error code, and the rest of the URI is the error namespace.
  \row
    \o const QSourceLocation & sourceLocation
    \o Identifies where the error occurred.
  \endtable

 */
void QXmlQuery::setMessageHandler(QAbstractMessageHandler *aMessageHandler)
{
    d->messageHandler = aMessageHandler;
}

/*!
    Returns the message handler that handles compile and runtime
    messages for this QXmlQuery.
 */
QAbstractMessageHandler *QXmlQuery::messageHandler() const
{
    return d->messageHandler;
}

/*!
  Sets this QXmlQuery to an XQuery read from the \a sourceCode
  device.  The device must have been opened with at least
  QIODevice::ReadOnly.

  \a documentURI represents the query obtained from the \a sourceCode
  device. It is the base URI of the static context, as defined in the
  \l {http://www.w3.org/TR/xquery/}{XQuery language}. It is used
  internally to resolve relative URIs that appear in the query, and
  for message reporting. \a documentURI can be empty. If it is empty,
  the \l{QCoreApplication::applicationFilePath()} {application file
  path} is used. If it is not empty, it may be either relative or
  absolute. If it is relative, it is resolved itself against the
  \l {QCoreApplication::applicationFilePath()} {application file
  path} before it is used. If \a documentURI is neither a valid URI
  nor empty, the result is undefined.

  If the query contains a static error (e.g. syntax error), an error
  message is sent to the messageHandler(), and isValid() will return
  \e false.

  Variables must be bound before setQuery() is called.

  The encoding of the XQuery in \a sourceCode is detected internally
  using the rules for setting and detecting encoding of XQuery files,
  which are explained in the \l {http://www.w3.org/TR/xquery/}
  {XQuery language}.

  If \a sourceCode is \c null or not readable, or if \a documentURI is not
  a valid URI, behavior is undefined.
  \sa isValid()
 */
void QXmlQuery::setQuery(QIODevice *sourceCode, const QUrl &documentURI)
{
    if(!sourceCode)
    {
        qWarning("A null QIODevice pointer cannot be passed.");
        return;
    }

    if(!sourceCode->isReadable())
    {
        qWarning("The device must be readable.");
        return;
    }

    d->queryURI = QPatternist::XPathHelper::normalizeQueryURI(documentURI);
    d->expression(sourceCode);
}

/*!
  \overload
  The behavior and requirements of this function are the same as for
  setQuery(QIODevice*, const QUrl&), after the XQuery has been read
  from the IO device into a string. Because \a sourceCode is already
  a Unicode string, detection of its encoding is unnecessary.
*/
void QXmlQuery::setQuery(const QString &sourceCode, const QUrl &documentURI)
{
    Q_ASSERT_X(documentURI.isEmpty() || documentURI.isValid(), Q_FUNC_INFO,
               "The document URI must be valid.");

    QByteArray query(sourceCode.toUtf8());
    QBuffer buffer(&query);
    buffer.open(QIODevice::ReadOnly);

    setQuery(&buffer, documentURI);
}

/*!
  Sets this QXmlQuery to the XQuery read from the \a queryURI.  Use
  isValid() after calling this function. If an error occurred reading
  \a queryURI, e.g., the query does not exist, cannot be read, or is
  invalid, isValid() will return \e false.

  The supported URI schemes are the same as those in the XQuery
  function \c{fn:doc}, except that queryURI can be the object of
  a variable binding.

  \a baseURI is the Base URI of the static context, as defined in the
  \l {http://www.w3.org/TR/xquery/}{XQuery language}. It is used
  internally to resolve relative URIs that appear in the query, and
  for message reporting. If \a baseURI is empty, \a queryURI is used.
  Otherwise, \a baseURI is used, and it is resolved against the \l
  {QCoreApplication::applicationFilePath()} {application file path} if
  it is relative.

  If \a queryURI is empty or invalid, or if \a baseURI is invalid,
  the behavior of this function is undefined.
 */
void QXmlQuery::setQuery(const QUrl &queryURI, const QUrl &baseURI)
{
    Q_ASSERT_X(queryURI.isValid(), Q_FUNC_INFO, "The passed URI must be valid.");

    const QUrl canonicalURI(QPatternist::XPathHelper::normalizeQueryURI(queryURI));
    Q_ASSERT(canonicalURI.isValid());
    Q_ASSERT(!canonicalURI.isRelative());
    Q_ASSERT(baseURI.isValid() || baseURI.isEmpty());

    d->queryURI = QPatternist::XPathHelper::normalizeQueryURI(baseURI.isEmpty() ? queryURI : baseURI);

    QPatternist::AutoPtr<QIODevice> result;

    try
    {
        result.reset(QPatternist::AccelTreeResourceLoader::load(canonicalURI, d->m_networkAccessDelegator,
                                                                d->staticContext()));
    }
    catch(const QPatternist::Exception)
    {
        /* We do nothing, result will be 0. */
    }

    if(result)
    {
        setQuery(result.data(), d->queryURI);
        result->close();
    }
    else
        d->recompileRequired();
}

/*!
  Binds the variable \a name to the \a value so that $\a name can be
  used from within the query to refer to the \a value.

  \a name must not be \e null. \a {name}.isNull() must return false.
  If \a name has already been bound by a previous bindVariable() call,
  its previous binding will be overridden.

  If \a {value} is null so that \a {value}.isNull() returns true, and
  \a {name} already has a binding, the effect is to remove the
  existing binding for \a {name}.

  To bind a value of type QString or QUrl, wrap the value in a
  QVariant such that QXmlItem's QVariant constructor is called.

  All strings processed by the query must be valid XQuery strings,
  which means they must contain only XML 1.0 characters. However,
  this requirement is not checked. If the query processes an invalid
  string, the behavior is undefined.

  \sa QVariant::isValid(), {QtXDM}{How QVariant maps to XQuery's Data Model},
   QXmlItem::isNull()
 */
void QXmlQuery::bindVariable(const QXmlName &name, const QXmlItem &value)
{
    if(name.isNull())
    {
        qWarning("The variable name cannot be null.");
        return;
    }

    const QPatternist::VariableLoader::Ptr vl(d->variableLoader());
    const QVariant variant(qVariantFromValue(value));

    /* If the type of the variable changed(as opposed to only the value),
     * we will have to recompile. */
    if(vl->invalidationRequired(name, variant) || value.isNull())
        d->recompileRequired();

    vl->addBinding(name, variant);
}

/*!
  \overload

  This function constructs a QXmlName from \a localName using the
  query's \l {QXmlNamePool} {namespace}. The function then behaves as
  the overloaded function. It is equivalent to the following snippet.

  \snippet doc/src/snippets/code/src_xmlpatterns_api_qxmlquery.cpp 0
 */
void QXmlQuery::bindVariable(const QString &localName, const QXmlItem &value)
{
    bindVariable(QXmlName(d->namePool, localName), value);
}

/*!
  Binds the variable \a name to the \a device so that $\a name can be
  used from within the query to refer to the \a device. The QIODevice
  \a device is exposed to the query as a URI of type \c{xs:anyURI},
  which can be passed to the \c{fn:doc()} function to be read. E.g.,
  this function can be used to pass an XML document in memory to
  \c{fn:doc}.

  \snippet doc/src/snippets/code/src_xmlpatterns_api_qxmlquery.cpp 1

  The caller must ensure that \a device has been opened with at least
  QIODevice::ReadOnly prior to this binding. Otherwise, behavior is
  undefined.

  If the query will access an XML document contained in a QString, use
  a QBuffer as shown in the following snippet. Suppose \e myQString
  contains \c{<document>content</document>}

  \snippet doc/src/snippets/qxmlquery/bindingExample.cpp 0

  \a name must not be \e null. \a {name}.isNull() must return false.
  If \a name has already been bound, its previous binding will be
  overridden. The URI that \a name evaluates to is arbitrary and may
  change.

  If the type of the variable binding changes (e.g., if a previous
  binding by the same name was a QVariant, or if there was no previous
  binding), isValid() will return \c{false}, and recompilation of the
  query text is required. To recompile the query, call setQuery(). For
  this reason, bindVariable() should be called before setQuery(), if
  possible.

  \note \a device must not be deleted while this QXmlQuery exists.
*/
void QXmlQuery::bindVariable(const QXmlName &name, QIODevice *device)
{
    if(device && !device->isReadable())
    {
        qWarning("A null, or readable QIODevice must be passed.");
        return;
    }

    if(name.isNull())
    {
        qWarning("The variable name cannot be null.");
        return;
    }

    const QPatternist::VariableLoader::Ptr vl(d->variableLoader());

    if(device)
    {
        const QVariant variant(qVariantFromValue(device));

        if(vl->invalidationRequired(name, variant))
            d->recompileRequired();

        vl->addBinding(name, variant);

        /* We need to tell the resource loader to discard its document, because
         * the underlying QIODevice has changed, but the variable name is the
         * same which means that the URI is the same, and hence the resource
         * loader will return the document for the old QIODevice.
         */
        d->resourceLoader()->clear(QUrl(QLatin1String("tag:trolltech.com,2007:QtXmlPatterns:QIODeviceVariable:") + d->namePool.d->stringForLocalName(name.localName())));
    }
    else
    {
        vl->removeBinding(name);
        d->recompileRequired();
    }
}

/*!
  \overload

  If \a localName is a valid \l {QXmlName::isNCName()} {NCName}, this
  function is equivalent to the following snippet.

  \snippet doc/src/snippets/code/src_xmlpatterns_api_qxmlquery.cpp 2

  A QXmlName is constructed from \a localName, and is passed
  to the appropriate overload along with \a device.

  \sa QXmlName::isNCName()
 */
void QXmlQuery::bindVariable(const QString &localName, QIODevice *device)
{
    bindVariable(QXmlName(d->namePool, localName), device);
}

/*!
  Evaluates this query and sends the result as a sequence of callbacks
  to the \l {QAbstractXmlReceiver} {receiver} \a callback. QXmlQuery
  does not take ownership of \a callback.

  If an error occurs during the evaluation, error messages are sent to
  messageHandler() and \c false is returned.

  If this query \l {isValid()} {is invalid}, \c{false} is returned
  and the behavior is undefined. If \a callback is null,
  behavior is undefined.

  \sa QAbstractXmlReceiver, isValid()
 */
bool QXmlQuery::evaluateTo(QAbstractXmlReceiver *callback) const
{
    if(!callback)
    {
        qWarning("A non-null callback must be passed.");
        return false;
    }

    if(isValid())
    {
        try
        {
            /*
             * This order is significant. expression() might cause
             * query recompilation, and as part of that it recreates
             * the static context. However, if we create the dynamic
             * context before the query recompilation has been
             * triggered, it will use the old static context, and
             * hence old source locations.
             */
            const QPatternist::Expression::Ptr expr(d->expression());
            const QPatternist::DynamicContext::Ptr dynContext(d->dynamicContext(callback));
            callback->startOfSequence();
            expr->evaluateToSequenceReceiver(dynContext);
            callback->endOfSequence();
            return true;
        }
        catch(const QPatternist::Exception)
        {
            return false;
        }
    }
    else
        return false;
}

/*!
  Attempts to evaluate the query and returns the results in the
  \a target \l {QStringList} {string list}.

  If the query \l {isValid()} {is valid} and the evaluation succeeds,
  true is returned. Otherwise, false is returned and the contents of
  \a target are undefined.

  The query must evaluate to a sequence of \c{xs:string} values. If
  the query does not evaluate to a sequence of strings, the values can
  often be converted by adding a call to \c{string()} at the end of
  the XQuery.

  If \a target is null, the behavior is undefined.
 */
bool QXmlQuery::evaluateTo(QStringList *target) const
{
    if(!target)
    {
        qWarning("A non-null callback must be passed.");
        return false;
    }

    if(isValid())
    {
        try
        {
            /*
             * This order is significant. expression() might cause
             * query recompilation, and as part of that it recreates
             * the static context. However, if we create the dynamic
             * context before the query recompilation has been
             * triggered, it will use the old static context, and
             * hence old source locations.
             */
            const QPatternist::Expression::Ptr expr(d->expression());
            if(!expr)
                return false;

            QPatternist::DynamicContext::Ptr dynContext(d->dynamicContext());

            if(!QPatternist::BuiltinTypes::xsString->xdtTypeMatches(expr->staticType()->itemType()))
                return false;

            const QPatternist::Item::Iterator::Ptr it(expr->evaluateSequence(dynContext));
            QPatternist::Item next(it->next());

            while(!next.isNull())
            {
                target->append(next.stringValue());
                next = it->next();
            }

            return true;
        }
        catch(const QPatternist::Exception)
        {
            return false;
        }
    }
    else
        return false;
}

/*!
  Evaluates the query or stylesheet, and writes the output to \a target.

  QXmlSerializer is used to write the output to \a target. In a future
  release, it is expected that this function will be changed to
  respect serialization options set in the stylesheet.

  If an error occurs during the evaluation, error messages are sent to
  messageHandler() and \c false is returned.

  If \a target is \c null, or is not opened in at least
  QIODevice::WriteOnly mode, the behavior is undefined.  QXmlQuery
  does not take ownership of \a target.

  \since 4.5
  \overload
 */
bool QXmlQuery::evaluateTo(QIODevice *target) const
{
    if(!target)
    {
        qWarning("The pointer to the device cannot be null.");
        return false;
    }

    if(!target->isWritable())
    {