Swift vs. The Compound File Binary File Format (aka OLE/COM): Part Ten — Records, Records And More Records

The result of decompressing the contents of the dir stream object is almost as incomprehensible as the compressed data.

It consists of a large number of records of which we want a grand total of two per module.

The records we are interested in are preceded by a large number of records we are not interested in. Most of these records have a length field so it is possible to ‘skip’ them, but some of them do not, so there is nothing for it but to brute force our way through to the ones we want.

The top-level method

    func parse() -> [VBAModule]?
    {
        informationRecord()
        projectReferences()
        return modules()
    }

is reasonably tidy, the others just consist of a lot of calls to a variety of methods for reading the different types of record, for example

    private func informationRecord()
    {
        readRecord(0x01)
        readRecord(0x02)
        readRecord(0x14)
        readRecord(0x03)
        readRecord(0x04)
        readRecordTwo(0x05)
        readRecordTwo(0x06)
        readRecord(0x07)
        readRecord(0x08)
        readRecordThree(0x09)
        readRecordTwo(0x0c)
    }

The end result should be an array of containing one or more instances of VBAModule.

    struct VBAModule
    {
        let streamName  : String
        let offset      : UInt32
    }

A VBAModule is simply two pieces of information

• the name of the stream object that contains the module’s compressed source, and

• the offset within the stream object at which the compressed data starts.

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