How to read a custom binary file made with Adobe air into Unity 3D & C#

I have a custom data file from a project that was authored in actionscript some years ago by another developer. I am porting parts of the project over to Unity 3D. I don't have any documentation for the original project (I hope to speak to the original developers at some point but I cannot wait for that).

The file is a special bitmap that represents the positions of objects on a grid. The custom file is created using an editor created in Adobe air. I believe (not knowing any better) that the source code I have for the file decoder is the same source from the editor. I don't have the editor source code.

Where I am getting into trouble is the binary file. From what I can tell at the moment, the file is a compressed byte array on the Adobe air side of things. I don't believe I can just load the compressed file with Unity3D as a resource object. I would like to decompress the file and use it as an asset in Unity.

I am trying to figure how to decompress the binary file. I have tried viewing the file contents in a hex editor to establish what the compression format is with no joy; I have not done anything specifically like this before 😊. I have tried to use gzip and a few other apps to decompress the file.

Form what I have read in the action script documentation that the default compression should be zlib.

Here is some edited code from the original project for decoding the bitmap:

import flash.utils.ByteArray;

public function decode(byteArray:ByteArray):Boolean
    {
        var i:uint;
        var j:uint;

        if(colourMap!=null)
        {
            colourMap.dispose();
            depthMap.dispose();
        }

        byteArray.uncompress();
        byteArray.position=0;

        var fileVersion:String=byteArray.readUTFBytes(FILE_VERSION.length);

        if(fileVersion==FILE_VERSION)
        {
            numWidth=byteArray.readUnsignedInt();
            numHeight=byteArray.readUnsignedInt();

            if(numWidth==0)
            {
                numWidth=30;
                trace("WARNING FOR SOME REASON WIDTH WAS 0 FROM FILE");
            }

            if(numHeight==0)
            {
                numHeight=30;
                trace("WARNING FOR SOME REASON HEIGHT WAS 0 FROM FILE");
            }

Here is a hex dump of the initial part of the binary data file:

78 da ec bd 55 cf 6c 5d 76 a5 79 7c 53 2a ff 8c