private int getLength ( ) throws IOException { int i = in . read ( ) ; if ( i == - 1 ) throw new IOException ( "Invalid DER: length missing" ) ; //$NON-NLS-1$ // A single byte short length if ( ( i & ~ 0x7F ) == 0 ) return i ; int num = i & 0x7F ; // We can't handle length longer than 4 bytes if ( i >= 0xFF || num > 4 ) throw new IOException ( "Invalid DER: length field too big (" //$NON-NLS-1$ + i + ")" ) ; //$NON-NLS-1$ byte [ ] bytes = new byte [ num ] ; int n = in . read ( bytes ) ; if ( n < num ) throw new IOException ( "Invalid DER: length too short" ) ; //$NON-NLS-1$ return new BigInteger ( 1 , bytes ) . intValue ( ) ; }
Decode the length of the field . Can only support length encoding up to 4 octets .