[processing] Add method to encode and decode a combined provider key and uri

to a single string

We need this to allow processing inputs to load non gdal/ogr/mdal sources, such
as being able to directly read postgis layers without loading them into a project first

python/core/auto_generated/processing/qgsprocessingutils.sip.in

@@ -90,6 +90,28 @@ value.
 .. seealso:: :py:func:`compatibleRasterLayers`
 
 .. seealso:: :py:func:`compatibleVectorLayers`
+%End
+
+    static QString encodeProviderKeyAndUri( const QString &providerKey, const QString &uri );
+%Docstring
+Encodes a provider key and layer ``uri`` to a single string, for use with
+decodeProviderKeyAndUri()
+
+.. versionadded:: 3.14
+%End
+
+    static bool decodeProviderKeyAndUri( const QString &string, QString &providerKey /Out/, QString &uri /Out/ );
+%Docstring
+Decodes a provider key and layer ``uri`` from an encoded string, for use with
+encodeProviderKeyAndUri()
+
+:param string: encoded string, as returned by encodeProviderKeyAndUri()
+:param uri: decoded layer uri
+
+:return: - ``True`` if ``string`` was successfully decoded
+         - providerKey: ID key for corresponding data provider
+
+.. versionadded:: 3.14
 %End
 
     enum class LayerHint

src/core/processing/qgsprocessingutils.cpp

@@ -133,6 +133,25 @@ QList<QgsMapLayer *> QgsProcessingUtils::compatibleLayers( QgsProject *project,
   return layers;
 }
 
+QString QgsProcessingUtils::encodeProviderKeyAndUri( const QString &providerKey, const QString &uri )
+{
+  return QStringLiteral( "%1://%2" ).arg( providerKey, uri );
+}
+
+bool QgsProcessingUtils::decodeProviderKeyAndUri( const QString &string, QString &providerKey, QString &uri )
+{
+  QRegularExpression re( QStringLiteral( "^(\\w+?):\\/\\/(.+)$" ) );
+  const QRegularExpressionMatch match = re.match( string );
+  if ( !match.hasMatch() )
+    return false;
+
+  providerKey = match.captured( 1 );
+  uri = match.captured( 2 );
+
+  // double check that provider is valid
+  return QgsProviderRegistry::instance()->providerMetadata( providerKey );
+}
+
 QgsMapLayer *QgsProcessingUtils::mapLayerFromStore( const QString &string, QgsMapLayerStore *store, QgsProcessingUtils::LayerHint typeHint )
 {
   if ( !store || string.isEmpty() )

src/core/processing/qgsprocessingutils.h

@@ -105,6 +105,27 @@ class CORE_EXPORT QgsProcessingUtils
      */
     static QList< QgsMapLayer * > compatibleLayers( QgsProject *project, bool sort = true );
 
+    /**
+     * Encodes a provider key and layer \a uri to a single string, for use with
+     * decodeProviderKeyAndUri()
+     *
+     * \since QGIS 3.14
+     */
+    static QString encodeProviderKeyAndUri( const QString &providerKey, const QString &uri );
+
+    /**
+     * Decodes a provider key and layer \a uri from an encoded string, for use with
+     * encodeProviderKeyAndUri()
+     *
+     * \param string encoded string, as returned by encodeProviderKeyAndUri()
+     * \param providerKey ID key for corresponding data provider
+     * \param uri decoded layer uri
+     * \returns TRUE if \a string was successfully decoded
+     *
+     * \since QGIS 3.14
+     */
+    static bool decodeProviderKeyAndUri( const QString &string, QString &providerKey SIP_OUT, QString &uri SIP_OUT );
+
     /**
      * Layer type hints.
      * \since QGIS 3.4

tests/src/analysis/testqgsprocessing.cpp

@@ -518,6 +518,7 @@ class TestQgsProcessing: public QObject
     void providerById();
     void removeProvider();
     void compatibleLayers();
+    void encodeDecodeUriProvider();
     void normalizeLayerSource();
     void context();
     void mapLayers();
@@ -860,6 +861,28 @@ void TestQgsProcessing::compatibleLayers()
   QCOMPARE( lIds, QStringList() << "R1" << "ar2" << "zz"  << "V4" << "v1" << "v3" << "vvvv4" << "MX" << "mA" );
 }
 
+void TestQgsProcessing::encodeDecodeUriProvider()
+{
+  QString provider;
+  QString uri;
+  QCOMPARE( QgsProcessingUtils::encodeProviderKeyAndUri( QStringLiteral( "ogr" ), QStringLiteral( "/home/me/test.shp" ) ), QStringLiteral( "ogr:///home/me/test.shp" ) );
+  QVERIFY( QgsProcessingUtils::decodeProviderKeyAndUri( QStringLiteral( "ogr:///home/me/test.shp" ), provider, uri ) );
+  QCOMPARE( provider, QStringLiteral( "ogr" ) );
+  QCOMPARE( uri, QStringLiteral( "/home/me/test.shp" ) );
+  QCOMPARE( QgsProcessingUtils::encodeProviderKeyAndUri( QStringLiteral( "ogr" ), QStringLiteral( "http://mysourcem/a.json" ) ), QStringLiteral( "ogr://http://mysourcem/a.json" ) );
+  QVERIFY( QgsProcessingUtils::decodeProviderKeyAndUri( QStringLiteral( "ogr://http://mysourcem/a.json" ), provider, uri ) );
+  QCOMPARE( provider, QStringLiteral( "ogr" ) );
+  QCOMPARE( uri, QStringLiteral( "http://mysourcem/a.json" ) );
+  QCOMPARE( QgsProcessingUtils::encodeProviderKeyAndUri( QStringLiteral( "postgres" ), QStringLiteral( "host=blah blah etc" ) ), QStringLiteral( "postgres://host=blah blah etc" ) );
+  QVERIFY( QgsProcessingUtils::decodeProviderKeyAndUri( QStringLiteral( "postgres://host=blah blah etc" ), provider, uri ) );
+  QCOMPARE( provider, QStringLiteral( "postgres" ) );
+  QCOMPARE( uri, QStringLiteral( "host=blah blah etc" ) );
+
+  // should reject non valid providers
+  QVERIFY( !QgsProcessingUtils::decodeProviderKeyAndUri( QStringLiteral( "asdasda://host=blah blah etc" ), provider, uri ) );
+  QVERIFY( !QgsProcessingUtils::decodeProviderKeyAndUri( QStringLiteral( "http://mysourcem/a.json" ), provider, uri ) );
+}
+
 void TestQgsProcessing::normalizeLayerSource()
 {
   QCOMPARE( QgsProcessingUtils::normalizeLayerSource( "data\\layers\\test.shp" ), QString( "data/layers/test.shp" ) );