[FEATURE] Binary blob support for OGR provider

Instead of converting binary fields to truncated strings, we instead
store their contents as QByteArray values, allowing the original binary
content to be retrieved.

This allows for plugins and scripts to utilise binary fields,
such as extracting their contents.

src/core/qgsfield.cpp

@@ -259,6 +259,10 @@ QString QgsField::displayString( const QVariant &v ) const
     QJsonDocument doc = QJsonDocument::fromVariant( v );
     return QString::fromUtf8( doc.toJson().data() );
   }
+  else if ( d->type == QVariant::ByteArray )
+  {
+    return QObject::tr( "BLOB" );
+  }
   // Fallback if special rules do not apply
   return v.toString();
 }

src/core/qgsogrutils.cpp

@@ -221,6 +221,17 @@ QVariant QgsOgrUtils::getOgrFeatureAttribute( OGRFeatureH ogrFet, const QgsField
           value = QDateTime( QDate( year, month, day ), QTime( hour, minute, second ) );
       }
       break;
+
+      case QVariant::ByteArray:
+      {
+        int size = 0;
+        const GByte *b = OGR_F_GetFieldAsBinary( ogrFet, attIndex, &size );
+        QByteArray ba = QByteArray::fromRawData( reinterpret_cast<const char *>( b ), size );
+        ba.detach();
+        value = ba;
+        break;
+      }
+
       default:
         Q_ASSERT_X( false, "QgsOgrUtils::getOgrFeatureAttribute", "unsupported field type" );
         if ( ok )

src/providers/ogr/qgsogrprovider.cpp

@@ -1028,6 +1028,11 @@ void QgsOgrProvider::loadFields()
       case OFTDateTime:
         varType = QVariant::DateTime;
         break;
+
+      case OFTBinary:
+        varType = QVariant::ByteArray;
+        break;
+
       case OFTString:
       default:
         varType = QVariant::String; // other unsupported, leave it as a string
@@ -1504,6 +1509,13 @@ bool QgsOgrProvider::addFeaturePrivate( QgsFeature &f, Flags flags )
           OGR_F_SetFieldString( feature.get(), ogrAttId, textEncoding()->fromUnicode( attrVal.toString() ).constData() );
           break;
 
+        case OFTBinary:
+        {
+          const QByteArray ba = attrVal.toByteArray();
+          OGR_F_SetFieldBinary( feature.get(), ogrAttId, ba.size(), const_cast< GByte * >( reinterpret_cast< const GByte * >( ba.data() ) ) );
+          break;
+        }
+
         default:
           QgsMessageLog::logMessage( tr( "type %1 for attribute %2 not found" ).arg( type ).arg( qgisAttId ), tr( "OGR" ) );
           break;
@@ -2059,6 +2071,14 @@ bool QgsOgrProvider::changeAttributeValues( const QgsChangedAttributesMap &attr_
           case OFTString:
             OGR_F_SetFieldString( of.get(), f, textEncoding()->fromUnicode( it2->toString() ).constData() );
             break;
+
+          case OFTBinary:
+          {
+            const QByteArray ba = it2->toByteArray();
+            OGR_F_SetFieldBinary( of.get(), f, ba.size(), const_cast< GByte * >( reinterpret_cast< const GByte * >( ba.data() ) ) );
+            break;
+          }
+
           default:
             pushError( tr( "Type %1 of attribute %2 of feature %3 unknown." ).arg( type ).arg( fid ).arg( f ) );
             break;

tests/src/core/testqgsfield.cpp

@@ -384,6 +384,11 @@ void TestQgsField::displayString()
   QCOMPARE( longField.displayString( 5 ), QString( "5" ) );
   QCOMPARE( longField.displayString( 599999898999LL ), QString( "599999898999" ) );
 
+  // binary field
+  QgsField binaryField( QStringLiteral( "binary" ), QVariant::ByteArray, QStringLiteral( "Binary" ) );
+  QString testBAString( QStringLiteral( "test string" ) );
+  QByteArray testBA( testBAString.toLocal8Bit() );
+  QCOMPARE( binaryField.displayString( testBA ), QStringLiteral( "BLOB" ) );
 }
 
 void TestQgsField::convertCompatible()

tests/src/python/test_provider_ogr.py

@@ -16,9 +16,10 @@ import os
 import shutil
 import sys
 import tempfile
+import hashlib
 
 from osgeo import gdal, ogr  # NOQA
-from qgis.PyQt.QtCore import QVariant
+from qgis.PyQt.QtCore import QVariant, QByteArray
 from qgis.core import (QgsApplication,
                        QgsRectangle,
                        QgsProviderRegistry,
@@ -489,6 +490,23 @@ class PyQgsOGRProvider(unittest.TestCase):
         self.assertEqual(f.id(), 8)
         del it
 
+    def testBinaryField(self):
+        source = os.path.join(TEST_DATA_DIR, 'attachments.gdb')
+        vl = QgsVectorLayer(source + "|layername=points__ATTACH")
+        self.assertTrue(vl.isValid())
+
+        fields = vl.fields()
+        data_field = fields[fields.lookupField('DATA')]
+        self.assertEqual(data_field.type(), QVariant.ByteArray)
+        self.assertEqual(data_field.typeName(), 'Binary')
+
+        features = {f['ATTACHMENTID']: f for f in vl.getFeatures()}
+        self.assertEqual(len(features), 2)
+        self.assertIsInstance(features[1]['DATA'], QByteArray)
+        self.assertEqual(hashlib.md5(features[1]['DATA'].data()).hexdigest(), 'ef3dbc530cc39a545832a6c82aac57b6')
+        self.assertIsInstance(features[2]['DATA'], QByteArray)
+        self.assertEqual(hashlib.md5(features[2]['DATA'].data()).hexdigest(), '4b952b80e4288ca5111be2f6dd5d6809')
+
 
 if __name__ == '__main__':
     unittest.main()