OPC UA Pub Sub Discovery Request Header Parsing|OPC UA Standard|Forum|OPC Foundation

In the OPC UA Part 14 – PubSub Release 1.04 specification, page number 75, it says about how to parse the Discovery Request Header. Assuming that the RequestType is Publisher information request message, I then look in the Table 86 where it is described about how to parse the “Publisher Information Request Message Type”. In that table, after parsing the InformationType which is 1 Byte long, I need to parse the DataSetWriterIds. So the question is, how do I know how many DataSetWriterIds I should be parsing? Is there a count or size information that I can use to parse those many DataSetWriterId? 

Can someone please help me with this?