diff --git a/python/core/mesh/qgsmeshlayer.sip.in b/python/core/mesh/qgsmeshlayer.sip.in
index 2560646250e..7e3519be066 100644
--- a/python/core/mesh/qgsmeshlayer.sip.in
+++ b/python/core/mesh/qgsmeshlayer.sip.in
@@ -100,6 +100,14 @@ QgsMeshLayer cannot be copied.
 
     virtual bool writeSymbology( QDomNode &node, QDomDocument &doc, QString &errorMessage, const QgsReadWriteContext &context ) const;
 
+    virtual QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const;
+
+    virtual QString decodedSource( const QString &source, const QString &provider, const QgsReadWriteContext &context ) const;
+
+    virtual bool readXml( const QDomNode &layer_node, QgsReadWriteContext &context );
+
+    virtual bool writeXml( QDomNode &layer_node, QDomDocument &doc, const QgsReadWriteContext &context ) const;
+
 
     QString providerType() const;
 %Docstring
diff --git a/python/core/qgsmaplayer.sip.in b/python/core/qgsmaplayer.sip.in
index ecd1fdde649..e3350ba64eb 100644
--- a/python/core/qgsmaplayer.sip.in
+++ b/python/core/qgsmaplayer.sip.in
@@ -1376,6 +1376,35 @@ project files.
 %Docstring
 Called by writeLayerXML(), used by children to write state specific to them to
 project files.
+%End
+
+    virtual QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const;
+%Docstring
+Called by writeLayerXML(), used by derived classes to encode provider's specific data
+source to project files. Typically resolving absolute or relative paths, usernames and
+passwords or drivers prefixes ("HDF5:")
+
+:param source: data source to encode, typically :py:func:`QgsMapLayer.source()`
+:param context: writing context (e.g. for conversion between relative and absolute paths)
+
+:return: encoded source, typically to be written in the dom element "datasource"
+
+.. versionadded:: 3.2
+%End
+
+    virtual QString decodedSource( const QString &source, const QString &dataProvider, const QgsReadWriteContext &context ) const;
+%Docstring
+Called by readLayerXML(), used by derived classes to decode provider's specific data
+source from project files. Typically resolving absolute or relative paths, usernames and
+passwords or drivers prefixes ("HDF5:")
+
+:param source: data source to decode, typically read from layer's dom element "datasource"
+:param dataProvider: string identification of data provider (e.g. "ogr"), typically read from layer's dom element
+:param context: reading context (e.g. for conversion between relative and absolute paths)
+
+:return: decoded source, typically to be used as the layer's datasource
+
+.. versionadded:: 3.2
 %End
 
     void readCustomProperties( const QDomNode &layerNode, const QString &keyStartsWith = QString() );
diff --git a/python/core/qgsvectorlayer.sip.in b/python/core/qgsvectorlayer.sip.in
index a4e7680918b..0159e43cad6 100644
--- a/python/core/qgsvectorlayer.sip.in
+++ b/python/core/qgsvectorlayer.sip.in
@@ -748,6 +748,11 @@ Write vector layer specific state to project file Dom node.
    Called by :py:func:`QgsMapLayer.writeXml()`
 %End
 
+    virtual QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const;
+
+    virtual QString decodedSource( const QString &source, const QString &provider, const QgsReadWriteContext &context ) const;
+
+
     virtual void resolveReferences( QgsProject *project );
 
 %Docstring
diff --git a/python/core/raster/qgsrasterlayer.sip.in b/python/core/raster/qgsrasterlayer.sip.in
index 456a2d90ab6..589bd5f3be2 100644
--- a/python/core/raster/qgsrasterlayer.sip.in
+++ b/python/core/raster/qgsrasterlayer.sip.in
@@ -347,6 +347,9 @@ In a world file, this is normally the first row (without the sign).
 
     virtual bool writeXml( QDomNode &layer_node, QDomDocument &doc, const QgsReadWriteContext &context ) const;
 
+    virtual QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const;
+
+    virtual QString decodedSource( const QString &source, const QString &provider,  const QgsReadWriteContext &context ) const;
 
 };
 
diff --git a/src/core/mesh/qgsmeshlayer.cpp b/src/core/mesh/qgsmeshlayer.cpp
index bbd382ac08d..d9f0f6c266a 100644
--- a/src/core/mesh/qgsmeshlayer.cpp
+++ b/src/core/mesh/qgsmeshlayer.cpp
@@ -25,6 +25,7 @@
 #include "qgsmeshlayer.h"
 #include "qgsmeshlayerrenderer.h"
 #include "qgsproviderregistry.h"
+#include "qgsreadwritecontext.h"
 #include "qgstriangularmesh.h"
 
 QgsMeshLayer::QgsMeshLayer( const QString &meshLayerPath,
@@ -180,9 +181,84 @@ bool QgsMeshLayer::writeSymbology( QDomNode &node, QDomDocument &doc, QString &e
   return true;
 }
 
+QString QgsMeshLayer::decodedSource( const QString &source, const QString &provider, const QgsReadWriteContext &context ) const
+{
+  QString src( source );
+  if ( provider == QLatin1String( "mdal" ) )
+  {
+    src = context.pathResolver().readPath( src );
+  }
+  return src;
+}
+
+QString QgsMeshLayer::encodedSource( const QString &source, const QgsReadWriteContext &context ) const
+{
+  QString src( source );
+  if ( providerType() == QLatin1String( "mdal" ) )
+  {
+    src = context.pathResolver().writePath( src );
+  }
+  return src;
+}
+
+bool QgsMeshLayer::readXml( const QDomNode &layer_node, QgsReadWriteContext &context )
+{
+  Q_UNUSED( context );
+
+  QgsDebugMsgLevel( QStringLiteral( "Datasource in QgsMeshLayer::readXml: %1" ).arg( mDataSource.toLocal8Bit().data() ), 3 );
+
+  //process provider key
+  QDomNode pkeyNode = layer_node.namedItem( QStringLiteral( "provider" ) );
+
+  if ( pkeyNode.isNull() )
+  {
+    mProviderKey.clear();
+  }
+  else
+  {
+    QDomElement pkeyElt = pkeyNode.toElement();
+    mProviderKey = pkeyElt.text();
+  }
+
+  if ( !setDataProvider( mProviderKey ) )
+  {
+    return false;
+  }
+
+  return mValid; // should be true if read successfully
+}
+
+bool QgsMeshLayer::writeXml( QDomNode &layer_node, QDomDocument &document, const QgsReadWriteContext &context ) const
+{
+  // first get the layer element so that we can append the type attribute
+  QDomElement mapLayerNode = layer_node.toElement();
+
+  if ( mapLayerNode.isNull() || ( "maplayer" != mapLayerNode.nodeName() ) )
+  {
+    QgsDebugMsgLevel( QStringLiteral( "can't find <maplayer>" ), 2 );
+    return false;
+  }
+
+  mapLayerNode.setAttribute( QStringLiteral( "type" ), QStringLiteral( "mesh" ) );
+
+  // add provider node
+  if ( mDataProvider )
+  {
+    QDomElement provider  = document.createElement( QStringLiteral( "provider" ) );
+    QDomText providerText = document.createTextNode( providerType() );
+    provider.appendChild( providerText );
+    layer_node.appendChild( provider );
+  }
+
+  // renderer specific settings
+  QString errorMsg;
+  return writeSymbology( layer_node, document, errorMsg, context );
+}
+
 bool QgsMeshLayer::setDataProvider( QString const &provider )
 {
-  Q_ASSERT( !mDataProvider ); //called from ctor
+  if ( mDataProvider )
+    delete mDataProvider;
 
   mProviderKey = provider;
   QString dataSource = mDataSource;
diff --git a/src/core/mesh/qgsmeshlayer.h b/src/core/mesh/qgsmeshlayer.h
index 1359ce2380e..aea269b7c17 100644
--- a/src/core/mesh/qgsmeshlayer.h
+++ b/src/core/mesh/qgsmeshlayer.h
@@ -114,6 +114,10 @@ class CORE_EXPORT QgsMeshLayer : public QgsMapLayer
     virtual QgsMapLayerRenderer *createMapRenderer( QgsRenderContext &rendererContext ) override SIP_FACTORY;
     bool readSymbology( const QDomNode &node, QString &errorMessage, QgsReadWriteContext &context ) override;
     bool writeSymbology( QDomNode &node, QDomDocument &doc, QString &errorMessage, const QgsReadWriteContext &context ) const override;
+    QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const override;
+    QString decodedSource( const QString &source, const QString &provider, const QgsReadWriteContext &context ) const override;
+    bool readXml( const QDomNode &layer_node, QgsReadWriteContext &context ) override;
+    bool writeXml( QDomNode &layer_node, QDomDocument &doc, const QgsReadWriteContext &context ) const override;
 
     //! Return the provider type for this layer
     QString providerType() const;
diff --git a/src/core/qgsmaplayer.cpp b/src/core/qgsmaplayer.cpp
index 402dff6a726..9c7ecfb8fc6 100644
--- a/src/core/qgsmaplayer.cpp
+++ b/src/core/qgsmaplayer.cpp
@@ -41,6 +41,7 @@
 #include "qgsmaplayer.h"
 #include "qgsmaplayerlegend.h"
 #include "qgsmaplayerstylemanager.h"
+#include "qgsmeshlayer.h"
 #include "qgspathresolver.h"
 #include "qgsprojectfiletransform.h"
 #include "qgsproject.h"
@@ -228,182 +229,7 @@ bool QgsMapLayer::readLayerXml( const QDomElement &layerElement,  QgsReadWriteCo
     return false;
   }
 
-  // TODO: this should go to providers
-  if ( provider == QLatin1String( "spatialite" ) )
-  {
-    QgsDataSourceUri uri( mDataSource );
-    uri.setDatabase( context.pathResolver().readPath( uri.database() ) );
-    mDataSource = uri.uri();
-  }
-  else if ( provider == QLatin1String( "ogr" ) )
-  {
-    QStringList theURIParts = mDataSource.split( '|' );
-    theURIParts[0] = context.pathResolver().readPath( theURIParts[0] );
-    mDataSource = theURIParts.join( QStringLiteral( "|" ) );
-  }
-  else if ( provider == QLatin1String( "gpx" ) )
-  {
-    QStringList theURIParts = mDataSource.split( '?' );
-    theURIParts[0] = context.pathResolver().readPath( theURIParts[0] );
-    mDataSource = theURIParts.join( QStringLiteral( "?" ) );
-  }
-  else if ( provider == QLatin1String( "delimitedtext" ) )
-  {
-    QUrl urlSource = QUrl::fromEncoded( mDataSource.toLatin1() );
-
-    if ( !mDataSource.startsWith( QLatin1String( "file:" ) ) )
-    {
-      QUrl file = QUrl::fromLocalFile( mDataSource.left( mDataSource.indexOf( '?' ) ) );
-      urlSource.setScheme( QStringLiteral( "file" ) );
-      urlSource.setPath( file.path() );
-    }
-
-    QUrl urlDest = QUrl::fromLocalFile( context.pathResolver().readPath( urlSource.toLocalFile() ) );
-    urlDest.setQueryItems( urlSource.queryItems() );
-    mDataSource = QString::fromLatin1( urlDest.toEncoded() );
-  }
-  else if ( provider == QLatin1String( "wms" ) )
-  {
-    // >>> BACKWARD COMPATIBILITY < 1.9
-    // For project file backward compatibility we must support old format:
-    // 1. mode: <url>
-    //    example: http://example.org/wms?
-    // 2. mode: tiled=<width>;<height>;<resolution>;<resolution>...,ignoreUrl=GetMap;GetFeatureInfo,featureCount=<count>,username=<name>,password=<password>,url=<url>
-    //    example: tiled=256;256;0.703;0.351,url=http://example.org/tilecache?
-    //    example: featureCount=10,http://example.org/wms?
-    //    example: ignoreUrl=GetMap;GetFeatureInfo,username=cimrman,password=jara,url=http://example.org/wms?
-    // This is modified version of old QgsWmsProvider::parseUri
-    // The new format has always params crs,format,layers,styles and that params
-    // should not appear in old format url -> use them to identify version
-    // XYZ tile layers do not need to contain crs,format params, but they have type=xyz
-    if ( !mDataSource.contains( QLatin1String( "type=" ) ) &&
-         !mDataSource.contains( QLatin1String( "crs=" ) ) && !mDataSource.contains( QLatin1String( "format=" ) ) )
-    {
-      QgsDebugMsg( "Old WMS URI format detected -> converting to new format" );
-      QgsDataSourceUri uri;
-      if ( !mDataSource.startsWith( QLatin1String( "http:" ) ) )
-      {
-        QStringList parts = mDataSource.split( ',' );
-        QStringListIterator iter( parts );
-        while ( iter.hasNext() )
-        {
-          QString item = iter.next();
-          if ( item.startsWith( QLatin1String( "username=" ) ) )
-          {
-            uri.setParam( QStringLiteral( "username" ), item.mid( 9 ) );
-          }
-          else if ( item.startsWith( QLatin1String( "password=" ) ) )
-          {
-            uri.setParam( QStringLiteral( "password" ), item.mid( 9 ) );
-          }
-          else if ( item.startsWith( QLatin1String( "tiled=" ) ) )
-          {
-            // in < 1.9 tiled= may apper in to variants:
-            // tiled=width;height - non tiled mode, specifies max width and max height
-            // tiled=width;height;resolutions-1;resolution2;... - tile mode
-
-            QStringList params = item.mid( 6 ).split( ';' );
-
-            if ( params.size() == 2 ) // non tiled mode
-            {
-              uri.setParam( QStringLiteral( "maxWidth" ), params.takeFirst() );
-              uri.setParam( QStringLiteral( "maxHeight" ), params.takeFirst() );
-            }
-            else if ( params.size() > 2 ) // tiled mode
-            {
-              // resolutions are no more needed and size limit is not used for tiles
-              // we have to tell to the provider however that it is tiled
-              uri.setParam( QStringLiteral( "tileMatrixSet" ), QLatin1String( "" ) );
-            }
-          }
-          else if ( item.startsWith( QLatin1String( "featureCount=" ) ) )
-          {
-            uri.setParam( QStringLiteral( "featureCount" ), item.mid( 13 ) );
-          }
-          else if ( item.startsWith( QLatin1String( "url=" ) ) )
-          {
-            uri.setParam( QStringLiteral( "url" ), item.mid( 4 ) );
-          }
-          else if ( item.startsWith( QLatin1String( "ignoreUrl=" ) ) )
-          {
-            uri.setParam( QStringLiteral( "ignoreUrl" ), item.mid( 10 ).split( ';' ) );
-          }
-        }
-      }
-      else
-      {
-        uri.setParam( QStringLiteral( "url" ), mDataSource );
-      }
-      mDataSource = uri.encodedUri();
-      // At this point, the URI is obviously incomplete, we add additional params
-      // in QgsRasterLayer::readXml
-    }
-    // <<< BACKWARD COMPATIBILITY < 1.9
-  }
-  else
-  {
-    bool handled = false;
-
-    if ( provider == QLatin1String( "gdal" ) )
-    {
-      if ( mDataSource.startsWith( QLatin1String( "NETCDF:" ) ) )
-      {
-        // NETCDF:filename:variable
-        // filename can be quoted with " as it can contain colons
-        QRegExp r( "NETCDF:(.+):([^:]+)" );
-        if ( r.exactMatch( mDataSource ) )
-        {
-          QString filename = r.cap( 1 );
-          if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
-            filename = filename.mid( 1, filename.length() - 2 );
-          mDataSource = "NETCDF:\"" + context.pathResolver().readPath( filename ) + "\":" + r.cap( 2 );
-          handled = true;
-        }
-      }
-      else if ( mDataSource.startsWith( QLatin1String( "HDF4_SDS:" ) ) )
-      {
-        // HDF4_SDS:subdataset_type:file_name:subdataset_index
-        // filename can be quoted with " as it can contain colons
-        QRegExp r( "HDF4_SDS:([^:]+):(.+):([^:]+)" );
-        if ( r.exactMatch( mDataSource ) )
-        {
-          QString filename = r.cap( 2 );
-          if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
-            filename = filename.mid( 1, filename.length() - 2 );
-          mDataSource = "HDF4_SDS:" + r.cap( 1 ) + ":\"" + context.pathResolver().readPath( filename ) + "\":" + r.cap( 3 );
-          handled = true;
-        }
-      }
-      else if ( mDataSource.startsWith( QLatin1String( "HDF5:" ) ) )
-      {
-        // HDF5:file_name:subdataset
-        // filename can be quoted with " as it can contain colons
-        QRegExp r( "HDF5:(.+):([^:]+)" );
-        if ( r.exactMatch( mDataSource ) )
-        {
-          QString filename = r.cap( 1 );
-          if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
-            filename = filename.mid( 1, filename.length() - 2 );
-          mDataSource = "HDF5:\"" + context.pathResolver().readPath( filename ) + "\":" + r.cap( 2 );
-          handled = true;
-        }
-      }
-      else if ( mDataSource.contains( QRegExp( "^(NITF_IM|RADARSAT_2_CALIB):" ) ) )
-      {
-        // NITF_IM:0:filename
-        // RADARSAT_2_CALIB:?:filename
-        QRegExp r( "([^:]+):([^:]+):(.+)" );
-        if ( r.exactMatch( mDataSource ) )
-        {
-          mDataSource = r.cap( 1 ) + ':' + r.cap( 2 ) + ':' + context.pathResolver().readPath( r.cap( 3 ) );
-          handled = true;
-        }
-      }
-    }
-
-    if ( !handled )
-      mDataSource = context.pathResolver().readPath( mDataSource );
-  }
+  mDataSource = decodedSource( mDataSource, provider, context );
 
   // Set the CRS from project file, asking the user if necessary.
   // Make it the saved CRS to have WMS layer projected correctly.
@@ -599,118 +425,11 @@ bool QgsMapLayer::writeLayerXml( QDomElement &layerElement, QDomDocument &docume
 
   // data source
   QDomElement dataSource = document.createElement( QStringLiteral( "datasource" ) );
-
-  QString src = source();
-
-  const QgsVectorLayer *vlayer = qobject_cast<const QgsVectorLayer *>( this );
-  // TODO: what about postgres, mysql and others, they should not go through writePath()
-  if ( vlayer && vlayer->providerType() == QLatin1String( "spatialite" ) )
-  {
-    QgsDataSourceUri uri( src );
-    QString database = context.pathResolver().writePath( uri.database() );
-    uri.setConnection( uri.host(), uri.port(), database, uri.username(), uri.password() );
-    src = uri.uri();
-  }
-  else if ( vlayer && vlayer->providerType() == QLatin1String( "ogr" ) )
-  {
-    QStringList theURIParts = src.split( '|' );
-    theURIParts[0] = context.pathResolver().writePath( theURIParts[0] );
-    src = theURIParts.join( QStringLiteral( "|" ) );
-  }
-  else if ( vlayer && vlayer->providerType() == QLatin1String( "gpx" ) )
-  {
-    QStringList theURIParts = src.split( '?' );
-    theURIParts[0] = context.pathResolver().writePath( theURIParts[0] );
-    src = theURIParts.join( QStringLiteral( "?" ) );
-  }
-  else if ( vlayer && vlayer->providerType() == QLatin1String( "delimitedtext" ) )
-  {
-    QUrl urlSource = QUrl::fromEncoded( src.toLatin1() );
-    QUrl urlDest = QUrl::fromLocalFile( context.pathResolver().writePath( urlSource.toLocalFile() ) );
-    urlDest.setQueryItems( urlSource.queryItems() );
-    src = QString::fromLatin1( urlDest.toEncoded() );
-  }
-  else if ( vlayer && vlayer->providerType() == QLatin1String( "memory" ) )
-  {
-    // Refetch the source from the provider, because adding fields actually changes the source for this provider.
-    src = vlayer->dataProvider()->dataSourceUri();
-  }
-  else
-  {
-    bool handled = false;
-
-    if ( !vlayer )
-    {
-      const QgsRasterLayer *rlayer = qobject_cast<const QgsRasterLayer *>( this );
-      // Update path for subdataset
-      if ( rlayer && rlayer->providerType() == QLatin1String( "gdal" ) )
-      {
-        if ( src.startsWith( QLatin1String( "NETCDF:" ) ) )
-        {
-          // NETCDF:filename:variable
-          // filename can be quoted with " as it can contain colons
-          QRegExp r( "NETCDF:(.+):([^:]+)" );
-          if ( r.exactMatch( src ) )
-          {
-            QString filename = r.cap( 1 );
-            if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
-              filename = filename.mid( 1, filename.length() - 2 );
-            src = "NETCDF:\"" + context.pathResolver().writePath( filename ) + "\":" + r.cap( 2 );
-            handled = true;
-          }
-        }
-        else if ( src.startsWith( QLatin1String( "HDF4_SDS:" ) ) )
-        {
-          // HDF4_SDS:subdataset_type:file_name:subdataset_index
-          // filename can be quoted with " as it can contain colons
-          QRegExp r( "HDF4_SDS:([^:]+):(.+):([^:]+)" );
-          if ( r.exactMatch( src ) )
-          {
-            QString filename = r.cap( 2 );
-            if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
-              filename = filename.mid( 1, filename.length() - 2 );
-            src = "HDF4_SDS:" + r.cap( 1 ) + ":\"" + context.pathResolver().writePath( filename ) + "\":" + r.cap( 3 );
-            handled = true;
-          }
-        }
-        else if ( src.startsWith( QLatin1String( "HDF5:" ) ) )
-        {
-          // HDF5:file_name:subdataset
-          // filename can be quoted with " as it can contain colons
-          QRegExp r( "HDF5:(.+):([^:]+)" );
-          if ( r.exactMatch( src ) )
-          {
-            QString filename = r.cap( 1 );
-            if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
-              filename = filename.mid( 1, filename.length() - 2 );
-            src = "HDF5:\"" + context.pathResolver().writePath( filename ) + "\":" + r.cap( 2 );
-            handled = true;
-          }
-        }
-        else if ( src.contains( QRegExp( "^(NITF_IM|RADARSAT_2_CALIB):" ) ) )
-        {
-          // NITF_IM:0:filename
-          // RADARSAT_2_CALIB:?:filename
-          QRegExp r( "([^:]+):([^:]+):(.+)" );
-          if ( r.exactMatch( src ) )
-          {
-            src = r.cap( 1 ) + ':' + r.cap( 2 ) + ':' + context.pathResolver().writePath( r.cap( 3 ) );
-            handled = true;
-          }
-        }
-      }
-    }
-
-    if ( !handled )
-      src = context.pathResolver().writePath( src );
-  }
-
+  QString src = encodedSource( source(), context );
   QDomText dataSourceText = document.createTextNode( src );
   dataSource.appendChild( dataSourceText );
-
   layerElement.appendChild( dataSource );
 
-
   // layer name
   QDomElement layerName = document.createElement( QStringLiteral( "layername" ) );
   QDomText layerNameText = document.createTextNode( name() );
@@ -846,7 +565,20 @@ bool QgsMapLayer::writeXml( QDomNode &layer_node, QDomDocument &document, const
   // NOP by default; children will over-ride with behavior specific to them
 
   return true;
-} // void QgsMapLayer::writeXml
+}
+
+QString QgsMapLayer::encodedSource( const QString &source, const QgsReadWriteContext &context ) const
+{
+  Q_UNUSED( context );
+  return source;
+}
+
+QString QgsMapLayer::decodedSource( const QString &source, const QString &dataProvider, const QgsReadWriteContext &context ) const
+{
+  Q_UNUSED( context );
+  Q_UNUSED( dataProvider );
+  return source;
+}
 
 void QgsMapLayer::resolveReferences( QgsProject *project )
 {
diff --git a/src/core/qgsmaplayer.h b/src/core/qgsmaplayer.h
index 3b381f30e64..31e97e89a32 100644
--- a/src/core/qgsmaplayer.h
+++ b/src/core/qgsmaplayer.h
@@ -1197,6 +1197,33 @@ class CORE_EXPORT QgsMapLayer : public QObject
      */
     virtual bool writeXml( QDomNode &layer_node, QDomDocument &document, const QgsReadWriteContext &context ) const;
 
+    /**
+     * Called by writeLayerXML(), used by derived classes to encode provider's specific data
+     * source to project files. Typically resolving absolute or relative paths, usernames and
+     * passwords or drivers prefixes ("HDF5:")
+     *
+     * \param source data source to encode, typically QgsMapLayer::source()
+     * \param context writing context (e.g. for conversion between relative and absolute paths)
+     * \return encoded source, typically to be written in the dom element "datasource"
+     *
+     * \since QGIS 3.2
+     */
+    virtual QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const;
+
+    /**
+     * Called by readLayerXML(), used by derived classes to decode provider's specific data
+     * source from project files. Typically resolving absolute or relative paths, usernames and
+     * passwords or drivers prefixes ("HDF5:")
+     *
+     * \param source data source to decode, typically read from layer's dom element "datasource"
+     * \param dataProvider string identification of data provider (e.g. "ogr"), typically read from layer's dom element
+     * \param context reading context (e.g. for conversion between relative and absolute paths)
+     * \return decoded source, typically to be used as the layer's datasource
+     *
+     * \since QGIS 3.2
+     */
+    virtual QString decodedSource( const QString &source, const QString &dataProvider, const QgsReadWriteContext &context ) const;
+
     /**
      * Read custom properties from project file.
       \param layerNode note to read from
diff --git a/src/core/qgsproject.cpp b/src/core/qgsproject.cpp
index f339e9025c9..070adcc7c4c 100644
--- a/src/core/qgsproject.cpp
+++ b/src/core/qgsproject.cpp
@@ -48,6 +48,7 @@
 #include "qgsprojectbadlayerhandler.h"
 #include "qgssettings.h"
 #include "qgsmaplayerlistutils.h"
+#include "qgsmeshlayer.h"
 #include "qgslayoutmanager.h"
 #include "qgsmaplayerstore.h"
 #include "qgsziputils.h"
@@ -820,6 +821,10 @@ bool QgsProject::addLayer( const QDomElement &layerElem, QList<QDomNode> &broken
   {
     mapLayer = new QgsRasterLayer;
   }
+  else if ( type == QLatin1String( "mesh" ) )
+  {
+    mapLayer = new QgsMeshLayer;
+  }
   else if ( type == QLatin1String( "plugin" ) )
   {
     QString typeName = layerElem.attribute( QStringLiteral( "name" ) );
diff --git a/src/core/qgsvectorlayer.cpp b/src/core/qgsvectorlayer.cpp
index 4ad78c235aa..00542c91159 100644
--- a/src/core/qgsvectorlayer.cpp
+++ b/src/core/qgsvectorlayer.cpp
@@ -1718,7 +1718,97 @@ bool QgsVectorLayer::writeXml( QDomNode &layer_node,
   // renderer specific settings
   QString errorMsg;
   return writeSymbology( layer_node, document, errorMsg, context );
-} // bool QgsVectorLayer::writeXml
+}
+
+QString QgsVectorLayer::encodedSource( const QString &source, const QgsReadWriteContext &context ) const
+{
+  QString src( source );
+
+  // TODO: what about postgres, mysql and others, they should not go through writePath()
+  if ( providerType() == QLatin1String( "spatialite" ) )
+  {
+    QgsDataSourceUri uri( src );
+    QString database = context.pathResolver().writePath( uri.database() );
+    uri.setConnection( uri.host(), uri.port(), database, uri.username(), uri.password() );
+    src = uri.uri();
+  }
+  else if ( providerType() == QLatin1String( "ogr" ) )
+  {
+    QStringList theURIParts = src.split( '|' );
+    theURIParts[0] = context.pathResolver().writePath( theURIParts[0] );
+    src = theURIParts.join( QStringLiteral( "|" ) );
+  }
+  else if ( providerType() == QLatin1String( "gpx" ) )
+  {
+    QStringList theURIParts = src.split( '?' );
+    theURIParts[0] = context.pathResolver().writePath( theURIParts[0] );
+    src = theURIParts.join( QStringLiteral( "?" ) );
+  }
+  else if ( providerType() == QLatin1String( "delimitedtext" ) )
+  {
+    QUrl urlSource = QUrl::fromEncoded( src.toLatin1() );
+    QUrl urlDest = QUrl::fromLocalFile( context.pathResolver().writePath( urlSource.toLocalFile() ) );
+    urlDest.setQueryItems( urlSource.queryItems() );
+    src = QString::fromLatin1( urlDest.toEncoded() );
+  }
+  else if ( providerType() == QLatin1String( "memory" ) )
+  {
+    // Refetch the source from the provider, because adding fields actually changes the source for this provider.
+    src = dataProvider()->dataSourceUri();
+  }
+  else
+  {
+    src = context.pathResolver().writePath( src );
+  }
+
+  return src;
+}
+
+QString QgsVectorLayer::decodedSource( const QString &source, const QString &provider, const QgsReadWriteContext &context ) const
+{
+  QString src( source );
+
+  if ( provider == QLatin1String( "spatialite" ) )
+  {
+    QgsDataSourceUri uri( src );
+    uri.setDatabase( context.pathResolver().readPath( uri.database() ) );
+    src = uri.uri();
+  }
+  else if ( provider == QLatin1String( "ogr" ) )
+  {
+    QStringList theURIParts = src.split( '|' );
+    theURIParts[0] = context.pathResolver().readPath( theURIParts[0] );
+    src = theURIParts.join( QStringLiteral( "|" ) );
+  }
+  else if ( provider == QLatin1String( "gpx" ) )
+  {
+    QStringList theURIParts = src.split( '?' );
+    theURIParts[0] = context.pathResolver().readPath( theURIParts[0] );
+    src = theURIParts.join( QStringLiteral( "?" ) );
+  }
+  else if ( provider == QLatin1String( "delimitedtext" ) )
+  {
+    QUrl urlSource = QUrl::fromEncoded( src.toLatin1() );
+
+    if ( !src.startsWith( QLatin1String( "file:" ) ) )
+    {
+      QUrl file = QUrl::fromLocalFile( src.left( src.indexOf( '?' ) ) );
+      urlSource.setScheme( QStringLiteral( "file" ) );
+      urlSource.setPath( file.path() );
+    }
+
+    QUrl urlDest = QUrl::fromLocalFile( context.pathResolver().readPath( urlSource.toLocalFile() ) );
+    urlDest.setQueryItems( urlSource.queryItems() );
+    src = QString::fromLatin1( urlDest.toEncoded() );
+  }
+  else
+  {
+    src = context.pathResolver().readPath( src );
+  }
+
+  return src;
+}
+
 
 
 void QgsVectorLayer::resolveReferences( QgsProject *project )
diff --git a/src/core/qgsvectorlayer.h b/src/core/qgsvectorlayer.h
index dc8d4be71e5..8bcd113c3b4 100644
--- a/src/core/qgsvectorlayer.h
+++ b/src/core/qgsvectorlayer.h
@@ -764,6 +764,9 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
      */
     bool writeXml( QDomNode &layer_node, QDomDocument &doc, const QgsReadWriteContext &context ) const override;
 
+    QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const override;
+    QString decodedSource( const QString &source, const QString &provider, const QgsReadWriteContext &context ) const override;
+
     /**
      * Resolve references to other layers (kept as layer IDs after reading XML) into layer objects.
      * \since QGIS 3.0
diff --git a/src/core/raster/qgsrasterlayer.cpp b/src/core/raster/qgsrasterlayer.cpp
index f7b87e8762e..d553d5c3c81 100644
--- a/src/core/raster/qgsrasterlayer.cpp
+++ b/src/core/raster/qgsrasterlayer.cpp
@@ -29,6 +29,7 @@ email                : tim at linfiniti.com
 #include "qgsmultibandcolorrenderer.h"
 #include "qgspainting.h"
 #include "qgspalettedrasterrenderer.h"
+#include "qgspathresolver.h"
 #include "qgsprojectfiletransform.h"
 #include "qgsproviderregistry.h"
 #include "qgsrasterdataprovider.h"
@@ -41,6 +42,7 @@ email                : tim at linfiniti.com
 #include "qgsrasterrendererregistry.h"
 #include "qgsrasterresamplefilter.h"
 #include "qgsrastershader.h"
+#include "qgsreadwritecontext.h"
 #include "qgsrectangle.h"
 #include "qgsrendercontext.h"
 #include "qgssinglebandcolordatarenderer.h"
@@ -1621,6 +1623,225 @@ bool QgsRasterLayer::writeXml( QDomNode &layer_node,
   return writeSymbology( layer_node, document, errorMsg, context );
 }
 
+QString QgsRasterLayer::encodedSource( const QString &source, const QgsReadWriteContext &context ) const
+{
+  QString src( source );
+  bool handled = false;
+
+  // Update path for subdataset
+  if ( providerType() == QLatin1String( "gdal" ) )
+  {
+    if ( src.startsWith( QLatin1String( "NETCDF:" ) ) )
+    {
+      // NETCDF:filename:variable
+      // filename can be quoted with " as it can contain colons
+      QRegExp r( "NETCDF:(.+):([^:]+)" );
+      if ( r.exactMatch( src ) )
+      {
+        QString filename = r.cap( 1 );
+        if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
+          filename = filename.mid( 1, filename.length() - 2 );
+        src = "NETCDF:\"" + context.pathResolver().writePath( filename ) + "\":" + r.cap( 2 );
+        handled = true;
+      }
+    }
+    else if ( src.startsWith( QLatin1String( "HDF4_SDS:" ) ) )
+    {
+      // HDF4_SDS:subdataset_type:file_name:subdataset_index
+      // filename can be quoted with " as it can contain colons
+      QRegExp r( "HDF4_SDS:([^:]+):(.+):([^:]+)" );
+      if ( r.exactMatch( src ) )
+      {
+        QString filename = r.cap( 2 );
+        if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
+          filename = filename.mid( 1, filename.length() - 2 );
+        src = "HDF4_SDS:" + r.cap( 1 ) + ":\"" + context.pathResolver().writePath( filename ) + "\":" + r.cap( 3 );
+        handled = true;
+      }
+    }
+    else if ( src.startsWith( QLatin1String( "HDF5:" ) ) )
+    {
+      // HDF5:file_name:subdataset
+      // filename can be quoted with " as it can contain colons
+      QRegExp r( "HDF5:(.+):([^:]+)" );
+      if ( r.exactMatch( src ) )
+      {
+        QString filename = r.cap( 1 );
+        if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
+          filename = filename.mid( 1, filename.length() - 2 );
+        src = "HDF5:\"" + context.pathResolver().writePath( filename ) + "\":" + r.cap( 2 );
+        handled = true;
+      }
+    }
+    else if ( src.contains( QRegExp( "^(NITF_IM|RADARSAT_2_CALIB):" ) ) )
+    {
+      // NITF_IM:0:filename
+      // RADARSAT_2_CALIB:?:filename
+      QRegExp r( "([^:]+):([^:]+):(.+)" );
+      if ( r.exactMatch( src ) )
+      {
+        src = r.cap( 1 ) + ':' + r.cap( 2 ) + ':' + context.pathResolver().writePath( r.cap( 3 ) );
+        handled = true;
+      }
+    }
+  }
+
+  if ( !handled )
+    src = context.pathResolver().writePath( src );
+
+  return src;
+}
+
+QString QgsRasterLayer::decodedSource( const QString &source, const QString &provider, const QgsReadWriteContext &context ) const
+{
+  QString src( source );
+
+  if ( provider == QLatin1String( "wms" ) )
+  {
+    // >>> BACKWARD COMPATIBILITY < 1.9
+    // For project file backward compatibility we must support old format:
+    // 1. mode: <url>
+    //    example: http://example.org/wms?
+    // 2. mode: tiled=<width>;<height>;<resolution>;<resolution>...,ignoreUrl=GetMap;GetFeatureInfo,featureCount=<count>,username=<name>,password=<password>,url=<url>
+    //    example: tiled=256;256;0.703;0.351,url=http://example.org/tilecache?
+    //    example: featureCount=10,http://example.org/wms?
+    //    example: ignoreUrl=GetMap;GetFeatureInfo,username=cimrman,password=jara,url=http://example.org/wms?
+    // This is modified version of old QgsWmsProvider::parseUri
+    // The new format has always params crs,format,layers,styles and that params
+    // should not appear in old format url -> use them to identify version
+    // XYZ tile layers do not need to contain crs,format params, but they have type=xyz
+    if ( !src.contains( QLatin1String( "type=" ) ) &&
+         !src.contains( QLatin1String( "crs=" ) ) && !src.contains( QLatin1String( "format=" ) ) )
+    {
+      QgsDebugMsg( "Old WMS URI format detected -> converting to new format" );
+      QgsDataSourceUri uri;
+      if ( !src.startsWith( QLatin1String( "http:" ) ) )
+      {
+        QStringList parts = src.split( ',' );
+        QStringListIterator iter( parts );
+        while ( iter.hasNext() )
+        {
+          QString item = iter.next();
+          if ( item.startsWith( QLatin1String( "username=" ) ) )
+          {
+            uri.setParam( QStringLiteral( "username" ), item.mid( 9 ) );
+          }
+          else if ( item.startsWith( QLatin1String( "password=" ) ) )
+          {
+            uri.setParam( QStringLiteral( "password" ), item.mid( 9 ) );
+          }
+          else if ( item.startsWith( QLatin1String( "tiled=" ) ) )
+          {
+            // in < 1.9 tiled= may apper in to variants:
+            // tiled=width;height - non tiled mode, specifies max width and max height
+            // tiled=width;height;resolutions-1;resolution2;... - tile mode
+
+            QStringList params = item.mid( 6 ).split( ';' );
+
+            if ( params.size() == 2 ) // non tiled mode
+            {
+              uri.setParam( QStringLiteral( "maxWidth" ), params.takeFirst() );
+              uri.setParam( QStringLiteral( "maxHeight" ), params.takeFirst() );
+            }
+            else if ( params.size() > 2 ) // tiled mode
+            {
+              // resolutions are no more needed and size limit is not used for tiles
+              // we have to tell to the provider however that it is tiled
+              uri.setParam( QStringLiteral( "tileMatrixSet" ), QLatin1String( "" ) );
+            }
+          }
+          else if ( item.startsWith( QLatin1String( "featureCount=" ) ) )
+          {
+            uri.setParam( QStringLiteral( "featureCount" ), item.mid( 13 ) );
+          }
+          else if ( item.startsWith( QLatin1String( "url=" ) ) )
+          {
+            uri.setParam( QStringLiteral( "url" ), item.mid( 4 ) );
+          }
+          else if ( item.startsWith( QLatin1String( "ignoreUrl=" ) ) )
+          {
+            uri.setParam( QStringLiteral( "ignoreUrl" ), item.mid( 10 ).split( ';' ) );
+          }
+        }
+      }
+      else
+      {
+        uri.setParam( QStringLiteral( "url" ), src );
+      }
+      src = uri.encodedUri();
+      // At this point, the URI is obviously incomplete, we add additional params
+      // in QgsRasterLayer::readXml
+    }
+    // <<< BACKWARD COMPATIBILITY < 1.9
+  }
+  else
+  {
+    bool handled = false;
+
+    if ( provider == QLatin1String( "gdal" ) )
+    {
+      if ( src.startsWith( QLatin1String( "NETCDF:" ) ) )
+      {
+        // NETCDF:filename:variable
+        // filename can be quoted with " as it can contain colons
+        QRegExp r( "NETCDF:(.+):([^:]+)" );
+        if ( r.exactMatch( src ) )
+        {
+          QString filename = r.cap( 1 );
+          if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
+            filename = filename.mid( 1, filename.length() - 2 );
+          src = "NETCDF:\"" + context.pathResolver().readPath( filename ) + "\":" + r.cap( 2 );
+          handled = true;
+        }
+      }
+      else if ( src.startsWith( QLatin1String( "HDF4_SDS:" ) ) )
+      {
+        // HDF4_SDS:subdataset_type:file_name:subdataset_index
+        // filename can be quoted with " as it can contain colons
+        QRegExp r( "HDF4_SDS:([^:]+):(.+):([^:]+)" );
+        if ( r.exactMatch( src ) )
+        {
+          QString filename = r.cap( 2 );
+          if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
+            filename = filename.mid( 1, filename.length() - 2 );
+          src = "HDF4_SDS:" + r.cap( 1 ) + ":\"" + context.pathResolver().readPath( filename ) + "\":" + r.cap( 3 );
+          handled = true;
+        }
+      }
+      else if ( src.startsWith( QLatin1String( "HDF5:" ) ) )
+      {
+        // HDF5:file_name:subdataset
+        // filename can be quoted with " as it can contain colons
+        QRegExp r( "HDF5:(.+):([^:]+)" );
+        if ( r.exactMatch( src ) )
+        {
+          QString filename = r.cap( 1 );
+          if ( filename.startsWith( '"' ) && filename.endsWith( '"' ) )
+            filename = filename.mid( 1, filename.length() - 2 );
+          src = "HDF5:\"" + context.pathResolver().readPath( filename ) + "\":" + r.cap( 2 );
+          handled = true;
+        }
+      }
+      else if ( src.contains( QRegExp( "^(NITF_IM|RADARSAT_2_CALIB):" ) ) )
+      {
+        // NITF_IM:0:filename
+        // RADARSAT_2_CALIB:?:filename
+        QRegExp r( "([^:]+):([^:]+):(.+)" );
+        if ( r.exactMatch( src ) )
+        {
+          src = r.cap( 1 ) + ':' + r.cap( 2 ) + ':' + context.pathResolver().readPath( r.cap( 3 ) );
+          handled = true;
+        }
+      }
+    }
+
+    if ( !handled )
+      src = context.pathResolver().readPath( src );
+  }
+
+  return src;
+}
+
 int QgsRasterLayer::width() const
 {
   if ( !mDataProvider ) return 0;
diff --git a/src/core/raster/qgsrasterlayer.h b/src/core/raster/qgsrasterlayer.h
index d4638b834a4..3ba0f65f5b3 100644
--- a/src/core/raster/qgsrasterlayer.h
+++ b/src/core/raster/qgsrasterlayer.h
@@ -388,7 +388,8 @@ class CORE_EXPORT QgsRasterLayer : public QgsMapLayer
     bool writeSymbology( QDomNode &, QDomDocument &doc, QString &errorMessage, const QgsReadWriteContext &context ) const override;
     bool writeStyle( QDomNode &node, QDomDocument &doc, QString &errorMessage, const QgsReadWriteContext &context ) const override;
     bool writeXml( QDomNode &layer_node, QDomDocument &doc, const QgsReadWriteContext &context ) const override;
-
+    QString encodedSource( const QString &source, const QgsReadWriteContext &context ) const override;
+    QString decodedSource( const QString &source, const QString &provider,  const QgsReadWriteContext &context ) const override;
   private:
     //! \brief Initialize default values
     void init();
diff --git a/src/providers/mdal/qgsmdalprovider.h b/src/providers/mdal/qgsmdalprovider.h
index db593dfc06f..4c838fdcf5f 100644
--- a/src/providers/mdal/qgsmdalprovider.h
+++ b/src/providers/mdal/qgsmdalprovider.h
@@ -60,4 +60,3 @@ class QgsMdalProvider : public QgsMeshDataProvider
 };
 
 #endif //QGSMDALPROVIDER_H
-
diff --git a/tests/src/core/testqgsmeshlayer.cpp b/tests/src/core/testqgsmeshlayer.cpp
index 61c6b763967..5f7b62a259e 100644
--- a/tests/src/core/testqgsmeshlayer.cpp
+++ b/tests/src/core/testqgsmeshlayer.cpp
@@ -47,10 +47,12 @@ class TestQgsMeshLayer : public QObject
     void init() {} // will be called before each testfunction is executed.
     void cleanup() {} // will be called after every testfunction.
 
+    void test_write_read_project();
     void test_data_provider();
     void test_extent();
 };
 
+
 void TestQgsMeshLayer::initTestCase()
 {
   // init QGIS's paths - true means that all path will be inited from prefix
@@ -120,5 +122,24 @@ void TestQgsMeshLayer::test_extent()
   QCOMPARE( mMdalLayer->dataProvider()->extent(), mMdalLayer->extent() );
 }
 
+void TestQgsMeshLayer::test_write_read_project()
+{
+  QgsProject prj;
+  prj.addMapLayer( mMemoryLayer->clone() );
+  prj.addMapLayer( mMdalLayer->clone() );
+
+  QTemporaryFile f;
+  QVERIFY( f.open() );
+  f.close();
+  prj.setFileName( f.fileName() );
+  prj.write();
+
+  QgsProject prj2;
+  prj2.setFileName( f.fileName() );
+  QVERIFY( prj2.read() );
+  QVector<QgsMapLayer *> layers = prj2.layers<QgsMapLayer *>();
+  QVERIFY( layers.size() == 2 );
+}
+
 QGSTEST_MAIN( TestQgsMeshLayer )
 #include "testqgsmeshlayer.moc"