/// <summary>
        /// Save a single segment's info. </summary>
        public override void Write(Directory dir, SegmentInfo si, FieldInfos fis, IOContext ioContext)
        {
            string fileName = IndexFileNames.SegmentFileName(si.Name, "", Lucene40SegmentInfoFormat.SI_EXTENSION);

            si.AddFile(fileName);

            IndexOutput output = dir.CreateOutput(fileName, ioContext);

            bool success = false;

            try
            {
                CodecUtil.WriteHeader(output, Lucene40SegmentInfoFormat.CODEC_NAME, Lucene40SegmentInfoFormat.VERSION_CURRENT);
                // Write the Lucene version that created this segment, since 3.1
                output.WriteString(si.Version);
                output.WriteInt(si.DocCount);

                output.WriteByte((byte)(sbyte)(si.UseCompoundFile ? SegmentInfo.YES : SegmentInfo.NO));
                output.WriteStringStringMap(si.Diagnostics);
                output.WriteStringStringMap(CollectionsHelper.EmptyMap <string, string>());
                output.WriteStringSet(si.Files);

                success = true;
            }
            finally
            {
                if (!success)
                {
                    IOUtils.CloseWhileHandlingException(output);
                    si.Dir.DeleteFile(fileName);
                }
                else
                {
                    output.Dispose();
                }
            }
        }
        public override FieldInfos Read(Directory directory, string segmentName, string segmentSuffix, IOContext iocontext)
        {
            string     fileName = IndexFileNames.SegmentFileName(segmentName, "", FIELD_INFOS_EXTENSION);
            IndexInput input    = directory.OpenInput(fileName, iocontext);

            bool success = false;

            try
            {
                int format = input.ReadVInt();

                if (format > FORMAT_MINIMUM)
                {
                    throw new IndexFormatTooOldException(input, format, FORMAT_MINIMUM, FORMAT_CURRENT);
                }
                if (format < FORMAT_CURRENT)
                {
                    throw new IndexFormatTooNewException(input, format, FORMAT_MINIMUM, FORMAT_CURRENT);
                }

                int         size  = input.ReadVInt(); //read in the size
                FieldInfo[] infos = new FieldInfo[size];

                for (int i = 0; i < size; i++)
                {
                    string name            = input.ReadString();
                    int    fieldNumber     = i;
                    byte   bits            = input.ReadByte();
                    bool   isIndexed       = (bits & IS_INDEXED) != 0;
                    bool   storeTermVector = (bits & STORE_TERMVECTOR) != 0;
                    bool   omitNorms       = (bits & OMIT_NORMS) != 0;
                    bool   storePayloads   = (bits & STORE_PAYLOADS) != 0;
                    FieldInfo.IndexOptions indexOptions;
                    if (!isIndexed)
                    {
                        indexOptions = default(FieldInfo.IndexOptions);
                    }
                    else if ((bits & OMIT_TERM_FREQ_AND_POSITIONS) != 0)
                    {
                        indexOptions = FieldInfo.IndexOptions.DOCS_ONLY;
                    }
                    else if ((bits & OMIT_POSITIONS) != 0)
                    {
                        if (format <= FORMAT_OMIT_POSITIONS)
                        {
                            indexOptions = FieldInfo.IndexOptions.DOCS_AND_FREQS;
                        }
                        else
                        {
                            throw new CorruptIndexException("Corrupt fieldinfos, OMIT_POSITIONS set but format=" + format + " (resource: " + input + ")");
                        }
                    }
                    else
                    {
                        indexOptions = FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS;
                    }

                    // LUCENE-3027: past indices were able to write
                    // storePayloads=true when omitTFAP is also true,
                    // which is invalid.  We correct that, here:
                    if (indexOptions != FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS)
                    {
                        storePayloads = false;
                    }
                    // LUCENE TO-DO
                    infos[i] = new FieldInfo(name, isIndexed, fieldNumber, storeTermVector, omitNorms, storePayloads, indexOptions, null, isIndexed && !omitNorms ? FieldInfo.DocValuesType_e.NUMERIC : default(FieldInfo.DocValuesType_e), CollectionsHelper.EmptyMap <string, string>());
                }

                if (input.FilePointer != input.Length())
                {
                    throw new CorruptIndexException("did not read all bytes from file \"" + fileName + "\": read " + input.FilePointer + " vs size " + input.Length() + " (resource: " + input + ")");
                }
                FieldInfos fieldInfos = new FieldInfos(infos);
                success = true;
                return(fieldInfos);
            }
            finally
            {
                if (success)
                {
                    input.Dispose();
                }
                else
                {
                    IOUtils.CloseWhileHandlingException(input);
                }
            }
        }