My VBA code as below has been working fine for long time, but recently it always get response = "". But I still can get authentication token as before. 

Dim objRequest As Object
    Dim fullUrl As String
    Dim blnAsync As Boolean
    Dim strResponse As String
    
    Set objRequest = CreateObject("MSXML2.XMLHTTP")
    fullUrl = Query_Data_Url_Production & query
        
    blnAsync = True
    With objRequest
        .Open "GET", fullUrl, blnAsync
        .SetRequestHeader "Authorization", "Bearer " & token
        .Send
        'spin wheels whilst waiting for response
        While objRequest.readyState <> 4
            DoEvents
        Wend
        strResponse = .ResponseText
    End With

I also tried with curl and the token I obtain from salesforce api. 
and response is empty, too.
Please do me a favour.
 

Hi all,

We need to implement the following pattern at my org:

• callout to external data source
• if that callout takes too long (according to some configurable threshold), log an error (ie do some DML)
• if that callout timed out on the remote server, try it again

Recognizing the potential for the dreaded "You have uncommitted work pending. Please commit or rollback before calling out." error, I put the error logging code in a future method, thus isolating the DML from the callouts. However, the error is still being thrown. I reduced the issue down to this pattern:

public static void foo() {
    Http http = new Http();
    HttpRequest req = new Httprequest();
    req.setEndpoint('https://test.salesforce.com'); //whatever endpoint
    req.setMethod('GET');
    http.send(req); //works fine
    bar();
    http.send(req); //throws calloutexception
}

@future public static void bar() {

}

Am I correct to assume that calling a future method counts as a DML operation? Is there any documentation I'm missing somewhere?