GET request data doesn't update

Question

I\'m trying to retrieve data from an API but my variable doesn\'t update even if I set it as nothing before the GET request.

The data of the variable update only if

Answer 1

This is for diagnostic purposes.

On Error Resume Next
Set File = WScript.CreateObject("Msxml2.XMLHTTP.6.0")
File.Open "GET", "https://www.google.com.au/search?q=cat", False
File.setRequestHeader "User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 1.1.4322; .NET CLR 3.5.30729; .NET CLR 3.0.30618; .NET4.0C; .NET4.0E; BCD2000; BCD2000)"
File.Send

wscript.echo "==================" 
    wscript.echo "" 
    wscript.echo "Error " & err.number & "(0x" & hex(err.number) & ") " & err.description 
    wscript.echo "Source " & err.source 
    wscript.echo "" 
    wscript.echo "Server Response " & File.Status & " " & File.StatusText
    wscript.echo    File.getAllResponseHeaders
    wscript.echo    File.ResponseBody

Answer 2

You can add an instruction to avoid being served cached results (server can ignore this but I have had good success with this in the past). Make sure your async argument is always False and leave more time between tests. I notice that sometimes the prices are slow to change so you may miss the change due to too small an interval/not enough attempts. You will notice the size change though. You should add a max timeout to the loop in the bottom script.

Also removed the hungarian notation.

Option Explicit

Public Sub getJsonResult()
    Dim http As Object
    Dim urlXBTUSD As String
    Dim response As String
    Dim j As Long
    Const ASYNC_ARG As Boolean = False

    Set http  = CreateObject("MSXML2.XMLHTTP")
    For j = 1 To 10
        response = vbNullString
        urlXBTUSD = "https://www.bitmex.com/api/v1/orderBook/L2?symbol=XBTUSD&depth=3"

        With http 
            .Open "GET", urlXBTUSD,  ASYNC_ARG
            .setRequestHeader "Content-Type", "application/json"
            .setRequestHeader "If-Modified-Since", "Sat, 1 Jan 2000 00:00:00 GMT"
            .send
            response = .responseText
            Debug.Print response
        End With
        Application.Wait Now + TimeSerial(0, 0, 15)
    Next
End Sub

---

Here is a long and tedious way of proving it by looping until price of first item in return collection changes. I use jsonconverter.bas added to project and VBE > Tools > References > Microsoft Scripting Runtime reference.

Option Explicit

Public Sub getJsonResult()
    Dim http  As Object
    Dim urlXBTUSD As String
    Dim response As String
    Dim j As Long
    Const ASYNC_ARG As Boolean = False
    Dim price As String, firstValue As String

    Set http  = CreateObject("MSXML2.XMLHTTP")
    urlXBTUSD = "https://www.bitmex.com/api/v1/orderBook/L2?symbol=XBTUSD&depth=3"

    With http 
        .Open "GET", urlXBTUSD,  ASYNC_ARG
        .setRequestHeader "Content-Type", "application/json"
        .setRequestHeader "If-Modified-Since", "Sat, 1 Jan 2000 00:00:00 GMT"
        .send
         firstValue = JsonConverter.ParseJson(.responseText)(1)("price")
        Debug.Print  firstValue
        Do
            .Open "GET", urlXBTUSD, blnAsync
            .setRequestHeader "Content-Type", "application/json"
            .setRequestHeader "If-Modified-Since", "Sat, 1 Jan 2000 00:00:00 GMT"
            .send
            price = JsonConverter.ParseJson(.responseText)(1)("price")
            Application.Wait Now + TimeSerial(0, 0, 5)
        Loop While price = firstValue
        Debug.Print price
    End With
End Sub