question: private Map < String , FileEntry > readEntries ( byte [ ] segmentID , Directory dir , String entriesFileName ) throws IOException { Map < String , FileEntry > mapping = null ; try ( ChecksumIndexInput entriesStream = dir . openChecksumInput ( entriesFileName , IOContext . READONCE ) ) { Throwable priorE = null ; try { version = CodecUtil . checkIndexHeader ( entriesStream , Lucene50CompoundFormat . ENTRY_CODEC , Lucene50CompoundFormat . VERSION_START , Lucene50CompoundFormat . VERSION_CURRENT , segmentID , "" ) ; final int numEntries = entriesStream . readVInt ( ) ; mapping = new HashMap < > ( numEntries ) ; for ( int i = 0 ; i < numEntries ; i ++ ) { final FileEntry fileEntry = new FileEntry ( ) ; final String id = entriesStream . readString ( ) ; FileEntry previous = mapping . put ( id , fileEntry ) ; if ( previous != null ) { throw new CorruptIndexException ( "Duplicate cfs entry id=" + id + " in CFS " , entriesStream ) ; } fileEntry . offset = entriesStream . readLong ( ) ; fileEntry . length = entriesStream . readLong ( ) ; } } catch ( Throwable exception ) { priorE = exception ; } finally { CodecUtil . checkFooter ( entriesStream , priorE ) ; } } return Collections . unmodifiableMap ( mapping ) ; }
target:  Helper method that reads CFS entries from an input stream 