Calling FindMimeFromData from VB6 - vb6

Question

Public Declare Function FindMimeFromData Lib "urlmon.dll" ( _
ByVal pbc As Long, _
ByVal pwzUrl As String, _
pBuffer As Any, _
cbSize As Long, _
ByVal pwzMimeProposed As String, _
dwMimeFlags As Long, _
ppwzMimeOut As Long, _
dwReserved As Long) As Long
In VB6, I can't seem to figure out how to pass the pBuffer parameter of the first 256 characters of a file. When I try to use a Dim buffer() As Byte and populate that, and pass it as the parameter, it throws the error of wrong param even those of the definition is Any.
I've tried to use this example, but passing the entire file name from a file system doesn't seem to work. so I have to try sending it like the C# example with the first 256 bytes of the file.
Can anyone help?

Answer 1

I played around with the following Declare, and built up some code around it. There are two wrappers, GetMimeTypeFromUrl() and GetMimeTypeFromData(). I found the former only worked when you used simple URLs such as http://host.com/file.xtn. You may have to play around with the other flags.
However, the other wrapper function sounds like what you need.
Note that all the string pointers are declared As Long, and I pass the underlying UTF-16 VB string as a pointer using StrPtr().
Also note that you have to use CoTaskMemFree() to free the output ppwzMimeOut string pointer, otherwise you will leak memory.
Option Explicit
Private Declare Function FindMimeFromData Lib "Urlmon.dll" ( _
ByVal pBC As Long, _
ByVal pwzUrl As Long, _
ByVal pBuffer As Long, _
ByVal cbSize As Long, _
ByVal pwzMimeProposed As Long, _
ByVal dwMimeFlags As Long, _
ByRef ppwzMimeOut As Long, _
ByVal dwReserved As Long _
) As Long
'
' Flags:
'
' Default
Private Const FMFD_DEFAULT As Long = &H0
' Treat the specified pwzUrl as a file name.
Private Const FMFD_URLASFILENAME As Long = &H1
' Internet Explorer 6 for Windows XP SP2 and later. Use MIME-type detection even if FEATURE_MIME_SNIFFING is detected. Usually, this feature control key would disable MIME-type detection.
Private Const FMFD_ENABLEMIMESNIFFING As Long = &H2
' Internet Explorer 6 for Windows XP SP2 and later. Perform MIME-type detection if "text/plain" is proposed, even if data sniffing is otherwise disabled. Plain text may be converted to text/html if HTML tags are detected.
Private Const FMFD_IGNOREMIMETEXTPLAIN As Long = &H4
' Internet Explorer 8. Use the authoritative MIME type specified in pwzMimeProposed. Unless FMFD_IGNOREMIMETEXTPLAIN is specified, no data sniffing is performed.
Private Const FMFD_SERVERMIME As Long = &H8
' Internet Explorer 9. Do not perform detection if "text/plain" is specified in pwzMimeProposed.
Private Const FMFD_RESPECTTEXTPLAIN As Long = &H10
' Internet Explorer 9. Returns image/png and image/jpeg instead of image/x-png and image/pjpeg.
Private Const FMFD_RETURNUPDATEDIMGMIMES As Long = &H20
'
' Return values:
'
' The operation completed successfully.
Private Const S_OK As Long = 0&
' The operation failed.
Private Const E_FAIL As Long = &H80000008
' One or more arguments are invalid.
Private Const E_INVALIDARG As Long = &H80000003
' There is insufficient memory to complete the operation.
Private Const E_OUTOFMEMORY As Long = &H80000002
'
' String routines
'
Private Declare Function lstrlen Lib "Kernel32.dll" Alias "lstrlenW" ( _
ByVal lpString As Long _
) As Long
Private Declare Sub CopyMemory Lib "Kernel32.dll" Alias "RtlMoveMemory" (ByVal pDest As Long, ByVal pSrc As Long, ByVal nCount As Long)
Private Declare Sub CoTaskMemFree Lib "Ole32.dll" ( _
ByVal pv As Long _
)
Private Function CopyPointerToString(ByVal in_pString As Long) As String
Dim nLen As Long
' Need to copy the data at the string pointer to a VB string buffer.
' Get the length of the string, allocate space, and copy to that buffer.
nLen = lstrlen(in_pString)
CopyPointerToString = Space$(nLen)
CopyMemory StrPtr(CopyPointerToString), in_pString, nLen * 2
End Function
Private Function GetMimeTypeFromUrl(ByRef in_sUrl As String, ByRef in_sProposedMimeType As String) As String
Dim pMimeTypeOut As Long
Dim nRet As Long
nRet = FindMimeFromData(0&, StrPtr(in_sUrl), 0&, 0&, StrPtr(in_sProposedMimeType), FMFD_DEFAULT, pMimeTypeOut, 0&)
If nRet = S_OK Then
GetMimeTypeFromUrl = CopyPointerToString(pMimeTypeOut)
CoTaskMemFree pMimeTypeOut
Else
Err.Raise nRet
End If
End Function
Private Function GetMimeTypeFromData(ByRef in_abytData() As Byte, ByRef in_sProposedMimeType As String) As String
Dim nLBound As Long
Dim nUBound As Long
Dim pMimeTypeOut As Long
Dim nRet As Long
nLBound = LBound(in_abytData)
nUBound = UBound(in_abytData)
nRet = FindMimeFromData(0&, 0&, VarPtr(in_abytData(nLBound)), nUBound - nLBound + 1, StrPtr(in_sProposedMimeType), FMFD_DEFAULT, pMimeTypeOut, 0&)
If nRet = S_OK Then
GetMimeTypeFromData = CopyPointerToString(pMimeTypeOut)
CoTaskMemFree pMimeTypeOut
Else
Err.Raise nRet
End If
End Function
Private Sub Command1_Click()
Dim sRet As String
Dim abytData() As Byte
sRet = GetMimeTypeFromUrl("http://msdn.microsoft.com/en-us/library/ms775107%28v=vs.85%29.aspx", vbNullString)
Debug.Print sRet
abytData() = StrConv("<HTML><HEAD><TITLE>Stuff</TITLE></HEAD><BODY>Test me</BODY></HTML>", vbFromUnicode)
sRet = GetMimeTypeFromData(abytData(), vbNullString)
Debug.Print sRet
End Sub