{standard} A compressed vector with 0 records must still write a data…

… packet

Part of #262

src/CompressedVectorWriterImpl.cpp

@@ -290,6 +290,12 @@ namespace e57
       checkImageFileOpen( __FILE__, __LINE__, static_cast<const char *>( __FUNCTION__ ) );
       checkWriterOpen( __FILE__, __LINE__, static_cast<const char *>( __FUNCTION__ ) );
 
+      if ( requestedRecordCount == 0 )
+      {
+         packetWriteZeroRecords();
+         return;
+      }
+
       // Check that requestedRecordCount is not larger than the sbufs
       if ( requestedRecordCount > sbufs_.at( 0 ).impl()->capacity() )
       {
@@ -610,6 +616,51 @@ namespace e57
       return ( packetPhysicalOffset ); //??? needed
    }
 
+   // If we don't have any records, write a packet which is only the header + zero padding.
+   // Code is a simplified version of packetWrite().
+   void CompressedVectorWriterImpl::packetWriteZeroRecords()
+   {
+      ImageFileImplSharedPtr imf( cVector_->destImageFile_ );
+
+      dataPacket_.header.reset();
+
+      // Use temp buf in object (is 64KBytes long) instead of allocating each time here
+      char *packet = reinterpret_cast<char *>( &dataPacket_ );
+
+      auto packetLength = sizeof( DataPacketHeader );
+
+      // packetLength must be multiple of 4, add zero padding
+      auto data = reinterpret_cast<char *>( &packet[sizeof( DataPacketHeader )] );
+      while ( packetLength % 4 )
+      {
+         *data++ = 0;
+
+         packetLength++;
+      }
+
+      // Prepare header in dataPacket_, now that we are sure of packetLength
+      dataPacket_.header.packetLogicalLengthMinus1 = static_cast<uint16_t>( packetLength - 1 );
+
+      // Double check that data packet is well formed
+      dataPacket_.verify( packetLength );
+
+      // Write packet at beginning of free space in file
+      uint64_t packetLogicalOffset = imf->allocateSpace( packetLength, false );
+      uint64_t packetPhysicalOffset = imf->file_->logicalToPhysical( packetLogicalOffset );
+
+      imf->file_->seek( packetLogicalOffset );
+      imf->file_->write( packet, packetLength );
+
+      // If first data packet written for this CompressedVector binary section,
+      // save address to put in section header
+      if ( dataPacketsCount_ == 0 )
+      {
+         dataPhysicalOffset_ = packetPhysicalOffset;
+      }
+
+      dataPacketsCount_++;
+   }
+
    void CompressedVectorWriterImpl::flush()
    {
       for ( auto &bytestream : bytestreams_ )

src/CompressedVectorWriterImpl.h

@@ -57,6 +57,8 @@ namespace e57
       size_t totalOutputAvailable() const;
       size_t currentPacketSize() const;
       uint64_t packetWrite();
+      void packetWriteZeroRecords();
+
       void flush();
 
       std::vector<SourceDestBuffer> sbufs_;

src/Packet.cpp

@@ -354,6 +354,8 @@ void DataPacketHeader::reset()
 void DataPacketHeader::verify( unsigned bufferLength ) const
 {
    // Verify that packet is correct type
+   // cppcheck-suppress knownConditionTrueFalse; (data is read as a blob, so the const might not
+   // be valid)
    if ( packetType != DATA_PACKET )
    {
       throw E57_EXCEPTION2( ErrorBadCVPacket,
@@ -382,9 +384,8 @@ void DataPacketHeader::verify( unsigned bufferLength ) const
                                                  " bufferLength=" + toString( bufferLength ) );
    }
 
-   // Make sure there is at least one entry in packet  ??? 0 record cvect
-   // allowed?
-   if ( bytestreamCount == 0 )
+   // Make sure there is at least one entry in packet
+   if ( hasRecords() && ( bytestreamCount == 0 ) )
    {
       throw E57_EXCEPTION2( ErrorBadCVPacket,
                             "DATA; bytestreamCount=" + toString( bytestreamCount ) );
@@ -482,7 +483,7 @@ char *DataPacket::getBytestream( unsigned bytestreamNumber, unsigned &byteCount
    {
       throw E57_EXCEPTION2( ErrorInternal,
                             "bytestreamNumber=" + toString( bytestreamNumber ) +
-                               "bytestreamCount=" + toString( header.bytestreamCount ) );
+                               " bytestreamCount=" + toString( header.bytestreamCount ) );
    }
 
    // Calc positions in packet

src/Packet.h

@@ -107,7 +107,15 @@ namespace e57
 
       void reset();
 
-      void verify( unsigned bufferLength = 0 ) const; //???use
+      void verify( unsigned bufferLength = 0 ) const;
+
+      // Does this packet have any records?
+      bool hasRecords() const
+      {
+         // If the packet does not have records, the logical length will be 8 bytes (the length of
+         // the header padded to 8-byte boundary).
+         return packetLogicalLengthMinus1 > 7;
+      }
 
 #ifdef E57_ENABLE_DIAGNOSTIC_OUTPUT
       void dump( int indent = 0, std::ostream &os = std::cout ) const;

test/src/test_SimpleWriter.cpp

@@ -148,6 +148,34 @@ TEST( SimpleWriter, Empty )
    E57_ASSERT_NO_THROW( e57::Writer writer( "./empty.e57", options ) );
 }
 
+TEST( SimpleWriter, ZeroPoints )
+{
+   e57::WriterOptions options;
+   options.guid = "Zero Points GUID";
+
+   e57::Writer *writer = nullptr;
+
+   E57_ASSERT_NO_THROW( writer = new e57::Writer( "./ZeroPoints.e57", options ) );
+
+   constexpr uint16_t cNumPoints = 0;
+
+   e57::Data3D header;
+   header.guid = "Zero Points Header GUID";
+   header.pointCount = cNumPoints;
+
+   // For a valid file, we need to specify cartesian or spherical.
+   header.pointFields.cartesianXField = true;
+   header.pointFields.cartesianYField = true;
+   header.pointFields.cartesianZField = true;
+   header.cartesianBounds.xMinimum = 0.0;
+
+   e57::Data3DPointsDouble pointsData( header );
+
+   E57_ASSERT_NO_THROW( writer->WriteData3DData( header, pointsData ) );
+
+   delete writer;
+}
+
 TEST( SimpleWriter, InvalidData3DValueCartesian )
 {
    e57::WriterOptions options;