HTTP Post/Upload From Visual Basic 6 - file-upload

Question

I'm using Visual Basic 6 and want to do an HTTP POST to a server (it runs Java code) by sending a custom input field along with a PDF file. the PDF file would have to be base 64 bit encoded or use the normal way that HTTP POST work over the Internet when uploading a file. Basically, I just want to upload a file from my Visual Basic 6 program.
How do I do this? Any example source code?

Answer 1

Assuming you know how to load the PDF in to a byte array you've got to get it Base64 encoded and then post that to server using MIME multipart encoding.
You can utilise the MSXML libraries ability to perform Base64 encoding. See this link for details.
Once you have the PDF as a Bas64 string you need to package that as MIME multipart. You can use XMLHTTP object from MSXML to perform that posting for you:-
sEntityBody = "----boundary" & vbCrLf
sEntityBody = sEntityBody & "Content-Disposition: form-data; name=fileInputElementName; filename=""" + sFileName + """" & vbCrLf
sEntityBody = sEntityBody & "Content-Transfer-Encoding: base64" & vbCrLf
sEntityBody = sEntityBody & "Content-Type: application/pdf" & vbCrLf & vbCrLf
sEntityBody = sEntityBody & sPDFBase64 & vbCrLf
sEntityBody = sEntityBody & "-----boundary--" & vbCrLf & vbCrLf
Set xhr = New MSXML2.XMLHTTP30
xhr.setRequestHeader("Content-Type", "multipart/form-data; boundary=-----boundary")
xhr.Open "POST", sUrl, False
xhr.send sEntityBody
Perhaps not elegant or efficient but it should it work.

Answer 2

Here's the code to handle base 64
Private Declare Function CryptBinaryToString Lib "Crypt32.dll" Alias "CryptBinaryToStringW" (ByRef pbBinary As Byte, ByVal cbBinary As Long, ByVal dwFlags As Long, ByVal pszString As Long, ByRef pcchString As Long) As Long
Private Declare Function CryptStringToBinary Lib "Crypt32.dll" Alias "CryptStringToBinaryW" (ByVal pszString As Long, ByVal cchString As Long, ByVal dwFlags As Long, ByVal pbBinary As Long, ByRef pcbBinary As Long, ByRef pdwSkip As Long, ByRef pdwFlags As Long) As Long
Public Function Base64Decode(sBase64Buf As String) As String
Const CRYPT_STRING_BASE64 As Long = 1
Dim bTmp() As Byte, lLen As Long, dwActualUsed As Long
If CryptStringToBinary(StrPtr(sBase64Buf), Len(sBase64Buf), CRYPT_STRING_BASE64, StrPtr(vbNullString), lLen, 0&, dwActualUsed) = 0 Then Exit Function 'Get output buffer length
ReDim bTmp(lLen - 1)
If CryptStringToBinary(StrPtr(sBase64Buf), Len(sBase64Buf), CRYPT_STRING_BASE64, VarPtr(bTmp(0)), lLen, 0&, dwActualUsed) = 0 Then Exit Function 'Convert Base64 to binary.
Base64Decode = StrConv(bTmp, vbUnicode)
End Function
Public Function Base64Encode(Text As String) As String
Const CRYPT_STRING_BASE64 As Long = 1
Dim lLen As Long, m_bData() As Byte, sBase64Buf As String
m_bData = StrConv(Text, vbFromUnicode)
If CryptBinaryToString(m_bData(0), UBound(m_bData) + 1, CRYPT_STRING_BASE64, StrPtr(vbNullString), lLen) = 0 Then Exit Function 'Determine Base64 output String length required.
sBase64Buf = String$(lLen - 1, Chr$(0)) 'Convert binary to Base64.
If CryptBinaryToString(m_bData(0), UBound(m_bData) + 1, CRYPT_STRING_BASE64, StrPtr(sBase64Buf), lLen) = 0 Then Exit Function
Base64Encode = sBase64Buf
End Function