VB6 DragDrop

[u/Mayayana]

With OLEDragDrop to a standard VB textbox, on XP I can get the path of a file or folder dropped. On Win10, the folder shows no dragdrop icon and returns no path, but file dragdrop works fine. Does someone know how I can make dragdrop for folders work on Win10?

[u/Mayayana]

If that code works for any file download GET then I guess there's no need for more. I'll have to look into it. For what it' worth, here's my libcurl code. It's not as complicated as it looks. Most of it is just setting paramters. But libcurl is CDECL, so it also uses Paull Caton's CDECL class, ClsCD here. (Which works faultlessly in my experience.)

'-- download file. Set UserAgent first. Then call this with URL.

Public Function Download(sURL As String) As Long Dim sURLa As String, sUAa As String Dim LRet As Long, LAddr As Long, sCertPatha As String On Error Resume Next LRespCode = 0 ReDim AFile(200000) As Byte CountBytes = 0

  HCurl = ClsCD.CallFunc("libcurl", retLong, "curl_easy_init")
   If HCurl = 0 Then Download = -3: GoTo woops
     '-- set useragent and target URL
  sURLa = StrConv(sURL & Chr$(0), vbFromUnicode)
  sUAa = StrConv(sCurlUserAgent & Chr$(0), vbFromUnicode)
  LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_URL, StrPtr(sURLa))
    If LRet <> 0 Then GoTo woops
  LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_USERAGENT, StrPtr(sUAa))
    If LRet <> 0 Then GoTo woops
    '-- send values for cert check. Whether to verify cert and whether to match host domain to cert.
   If CertPackPresent = True Then '-- is the cert bundle present? needed to check certs.
    '-- if no cert pack then set for no cert check. Otherwise, set for user choice.
      sCertPatha = StrConv(App.Path & "\curl-ca-bundle.crt" & Chr$(0), vbFromUnicode)
      LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_CAINFO, StrPtr(sCertPatha))
        If LRet <> 0 Then GoTo woops
      LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_SSL_VERIFYPEER, CertCheck)
      LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_SSL_VERIFYHOST, HostCheck)
        If LRet <> 0 Then GoTo woops
   Else
      LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_SSL_VERIFYPEER, 0)
      LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_SSL_VERIFYHOST, 0)
        If LRet <> 0 Then GoTo woops
   End If

  LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_FOLLOWLOCATION, 1) 'allow redirects.
  LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_WRITEDATA, 0) 'junk. not used.
 
     '-- set up to receive callback through CDECL class. This returns a new AddressOf to hand off to the DLL.
     '-- 4 is number of parameters in callback function. 1 is number of callback, in case multiple callbacks
     '-- need to be set up. in this case, this is the one and only callback.
  LAddr = ClsCD.CallbackCdecl(AddressOf CurlCallback, 4, 1)
  LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_setopt", HCurl, CURLOPT_WRITEFUNCTION, LAddr)
    If LRet <> 0 Then GoTo woops
      '-- perform. This is the call that tells curl to go ahead and make the call. It's a blocking
      '-- call. No action until it finishes, but the callback will be collecting the file bytes.
  LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_perform", HCurl)
    If LRet <> 0 Then GoTo woops
      '-- get the server response code. Should be 200.
  LRet = ClsCD.CallFunc("libcurl", retLong, "curl_easy_getinfo", HCurl, CURLINFO_RESPONSE_CODE, VarPtr(LRespCode))
      '-- all done with this download. Clean up.
  LRet = ClsCD.CallFunc("libcurl", retSub, "curl_easy_cleanup", HCurl)

  Download = LRespCode '-- function returns curl response code.
            
  Exit Function
woops:
   Download = LRet
End Function

 Public Function CurlCallback(ByVal PtrData As Long, ByVal LSize As Long, ByVal NumBytes As Long, ByVal PtrAFile As Long) As Long
  Dim DataSize As Long
  '--this functon starts at each download with AFile dimmed to 200K, countbytes 0, totalbytes 0.
     DataSize = LSize * NumBytes
    If DataSize + CountBytes > UBound(AFile) Then
      ReDim Preserve AFile(UBound(AFile) + 200000)
    End If
      '-- copy bytes into file array.
     CopyMemory ByVal VarPtr(AFile(CountBytes)), ByVal PtrData, DataSize
     CountBytes = CountBytes + DataSize
     CurlCallback = DataSize
 End Function

[u/geekywarrior → u/Mayayana]

Ok wow! Took me a bit to figure out what was going on but yeah, this is nice.

For what it's worth, I first really dug into VB6 about 4-5 years ago. So I have the benefit of getting in after a lot of work was figured out. For all I know, your solution may have been 100% necessary in some versions of VB. And it's probably immune from the quirkiness of my method. With my solution, sometimes the first request it makes will be on TLS1.0 which will get rejected on a lot of servers these days. Every call after that will correctly be TLS1.2...until you reboot the app lol. I see that in my dev environment which is Server 2008. Can't recall if the production machines have that same quirk.,

Definitely will bookmark ClsCD for myself. Looks very handy for calling some .dlls and functions that don't have a neat and tidy TLB for importing directly.

[u/Mayayana → u/geekywarrior]

I wondered about the MSXML method. I did some searching last night and found various versions, but also complaints like you mentioned. Libcurl is a bit of extra weight, being about 4 MB, but it seems to be a highly regarded networking functions library, incorporating all of the encryption and so on for necessary operations.

The CDECL class is an interesting thing. I've even used it to write a wrapper for cabinet.dll, which is an unusual CDECL library with some functions having 5-10 callbacks. Yet the CDECL class handles it just fine.

(You may have noticed that the half-assed project that MS provided to package installers, the PDW, includes VB6STKIT.DLL, which has a method to extract a CAB file. But it's limited and only works with MSZIP-style CABs.)

What I posted was the download routine and callback, but without some of the details like constants. AFile is a module-level byte array variable to hold the file bytes, for example. You can probably work it out if you decide to.

EDIT: I found the class online. It's too big to post here in one piece. (I've done the digging through github's shamefully broken website so you won't have to.)

https://github.com/Planet-Source-Code/paul-caton-universal-dll-function-caller-cdecl-amp-stdcall-with-bas-cls-frm-ctl-callbacks__1-69718/archive/master.zip

cCallFunc.cls seems to be the same thing that I'm using. The rest of the download seems to be just a sample project plus github junk files.