Power Query M Formula Language - DecompressZip - function (ZIPFile as any) as any

DecompressZip.pqm

= (ZIPFile) =>
// expects full path to the ZIP file, only extracts the first data file after getting its size from the central directory
// https://en.wikipedia.org/wiki/Zip_(file_format)#Structure

let
    //read the entire ZIP file into memory - we'll use it often so this is worth it
    Source = Binary.Buffer(File.Contents(ZIPFile)),
    // get the full size of the ZIP file
    Size = Binary.Length(Source),
    //Find the start of the central directory at the sixth to last byte
    Directory = BinaryFormat.Record([ 
                    MiscHeader=BinaryFormat.Binary(Size-6), 
                    Start=BinaryFormat.ByteOrder(BinaryFormat.UnsignedInteger32, ByteOrder.LittleEndian)
            ]) ,
    Start = Directory(Source)[Start],
    //find the first entry in the directory and get the compressed file size
    FirstDirectoryEntry = BinaryFormat.Record([ 
                    MiscHeader=BinaryFormat.Binary(Start+20), 
                    FileSize=BinaryFormat.ByteOrder(BinaryFormat.UnsignedInteger32, ByteOrder.LittleEndian),
                    UnCompressedFileSize=BinaryFormat.Binary(4),
                    FileNameLen=BinaryFormat.ByteOrder(BinaryFormat.UnsignedInteger16, ByteOrder.LittleEndian),
                    ExtrasLen=BinaryFormat.ByteOrder(BinaryFormat.UnsignedInteger16, ByteOrder.LittleEndian)
            ]) ,
    //figure out where the raw data starts            
    Offset = 30+FirstDirectoryEntry(Source)[FileNameLen]+FirstDirectoryEntry(Source)[ExtrasLen],
    Compressed = FirstDirectoryEntry(Source)[FileSize]+1,
    //get the raw data of the compressed file
    Raw = BinaryFormat.Record([
                    Header=BinaryFormat.Binary(Offset), 
                    Data=BinaryFormat.Binary(Compressed)
            ]) 
    // unzip it
in 
    Binary.Decompress(Raw(Source)[Data], Compression.Deflate)