Description
Hi,
first of all thanks for your work on keeping VBA Web up-to-date, you are doing a great job. I'd like to follow up on an old item (#61) on gzip encoding. I have integrated the decoding for large JSON files in my application as I needed it, and thought I share what I did and give some input for further improving VBA-Web
First of all I found a module that can decode GZIP on Stack Overflow, that does the real work (see here: https://stackoverflow.com/questions/58026702/how-to-decompress-http-responses-in-vba-excel). The function "inflate" takes a GZIP byte array and transforms it unicode. Unfortunately it can only decode gzip, but not encode.
To integrate it with VBA Web, this is how I created the request:
Dim Request As New WebRequest
Dim Response As New WebResponse
Request.Resource = "/function"
Request.AddHeader "Accept-Encoding", "gzip"
Request.RequestFormat = Custom
Request.CustomResponseFormat = "gzip"
WebHelpers.RegisterConverter "gzip", "application/json", "GzipConverter.ConvertToGzip", "GzipConverter.ParseGzip", , "Binary"
Set Response = Client.Execute(Request)
I've then created a function "ParseGzip" in one the module GzipConverter that will receive the binary (that's important!) body from the requst and decode it.
Public Function ParseGzip(Bytes As Variant) As Object
Dim byteArray() As Byte
Dim strResponse As String
byteArray = Bytes ' convert variant array to byte array
Call Inflate(byteArray) 'decode the GZIP byte array
strResponse = StrConv(byteArray, vbUnicode) 'create a string from the encoded byte array
Set ParseGzip= ParseJson(strResponse) 'parse string to json
End Function
This functions returns the parsed JSON to the VBA web for further processing. This works, but it is a all bit hacky. Although proposed as a solution in #61, the RegisterConverter function is not really optimal here, because gzip is not an content type (in my case I am working with JSON). If the server does not return gzip (which is visibile in the encoding header of the response), it would still try to parse it as gzip and would through an error.
I think it would make sense to allow an additional hook for an encoding function, which is triggered by
content-encoding: gzip
in the header. Would love to see a more proper intergration into VBA Web...