type conversion

[Muthu Ram]

'BOOL HttpSendRequestEx(
' IN HINTERNET hRequest,
' IN LPINTERNET_BUFFERS lpBuffersIn,
' OUT LPINTERNET_BUFFERS lpBuffersOut,
' IN DWORD dwFlags,
' IN DWORD dwContext
');
'typedef struct _INTERNET_BUFFERS {
' DWORD dwStructSize;
' struct _INTERNET_BUFFERS% * next;
' LPCTSTR lpcszHeader;
' DWORD dwHeadersLength;
' DWORD dwHeadersTotal;
' LPVOID lpvBuffer;
' DWORD dwBufferLength;
' DWORD dwBufferTotal;
' DWORD dwOffsetLow;
' DWORD dwOffsetHigh;
'} INTERNET_BUFFERS, * LPINTERNET_BUFFERS;



anyone know how to convert those to vb types.. so i can call these functions?

[kbacheld]

NewString = StrConv(<string>,vbFromUnicode)

Try that...

Kurt

[Ravi Kiran]

Try this: Am not sure but...

The Structure goes as:
'typedef struct _INTERNET_BUFFERS {
' DWORD dwStructSize;
' struct _INTERNET_BUFFERS% * next;
' LPCTSTR lpcszHeader;
' DWORD dwHeadersLength;
' DWORD dwHeadersTotal;
' LPVOID lpvBuffer;
' DWORD dwBufferLength;
' DWORD dwBufferTotal;
' DWORD dwOffsetLow;
' DWORD dwOffsetHigh;
'}

type struct INTERNET_BUFFERS_VB
dwStructSize as long
next as long ' but actually lpINTERNET_BUFFERS ;
lpcszHeader as long
dwHeadersLength as long
dwHeadersTotal as long
lpvBuffer as long
dwBufferLength as long
dwBufferTotal as long
dwOffsetLow as long
dwOffsetHigh as long
end type




The function definition transforms like this:
'BOOL HttpSendRequestEx(
' IN HINTERNET hRequest,
' IN LPINTERNET_BUFFERS lpBuffersIn,
' OUT LPINTERNET_BUFFERS lpBuffersOut,
' IN DWORD dwFlags,
' IN DWORD dwContext
');

Declare Function HttpSendRequestEx Lib "???" (
byval hRequest as long, _
lpBuffersIn as Any, lpBuffersOut as Any , _
byval dwFlags as long, byval dwContext as long) as long



The definitions willl go thru. But care should be taken before and after calling the fn.
Like:
1. dim ttt as INTERNET_BUFFERS_VB, tmpbuf as string
dim ttt1 as INTERNET_BUFFERS_VB
2.
tmpbuf = space(256)
ttt.dwStructSize = Len(ttt)
ttt.lpcszHeader = StrPtr(tmpbuf) ''<<--****
ttt.dwHeadersLength = Len(tmpbuf)
ttt.Next = VarPtr(ttt1) ''<<--****

3. dim ttt2 as INTERNET_BUFFERS_VB, brtn as long
brtn = HttpSendRequestEx( ??, byval ttt, ttt2, ??,??)

This should be the typical kind of calling.

Ther are two types of APIs. Ones that fill in a structure, ones that pass a pointer to structure.
For those that fill in a structure, make sure that enough memory is available for all the items in the struct.
For those that pass a pointer to a structure, typically in VC, they typecase the pointer and use it directly. SInce VB has no typecast facility, people usually copy the structure to a local variable of same type. For this use this fn:
Public Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDest As Any, pSource As Any, ByVal dwLength As Long)
I dont know which is your case.


RK

[Muthu Ram]

perfect ravi. you said it right. now i am dealing with the copy memory function and i am not sure how to pass the 3rd argument, ie the number of bytes to copy.

do you know how to dereference the pointer back to my structure? basically as we do typecasting in c. i want to something like this in VB..

mytype A = *(pointerToA);


Here is the VB declarations for the API discussed here.

Declare Sub CopyMemory1 Lib "kernel32" Alias "RtlMoveMemory" ( _
hpvDest as Any, byval hpvSource as Long, byval cbCopy as Long)
Declare Sub CopyMemory2 Lib "kernel32" Alias "RtlMoveMemory" ( _
hpvDest as Long, hpvSource as Any, byval cbCopy as Long)
public Type INTERNET_BUFFERS
dwStructSize as Long ' used for API versioning. set to sizeof(INTERNET_BUFFERS)
next as Long ' INTERNET_BUFFERS chain of buffers
lpcszHeader as Long ' pointer to headers (may be null)
dwHeadersLength as Long ' length of headers if not null
dwHeadersTotal as Long ' size of headers if not enough buffer
lpvBuffer as Long ' pointer to data buffer (may be null)
dwBufferLength as Long ' length of data buffer if not null
dwBufferTotal as Long ' total size of chunk, or content-length if not chunked
dwOffsetLow as Long ' used for read-ranges (only used in HttpSendRequest2)
dwOffsetHigh as Long
End Type

public Declare Function HttpSendRequestEx Lib "wininet.dll" Alias "HttpSendRequestExA" _
(byval hHttpRequest as Long, lpBuffersIn as INTERNET_BUFFERS, byval lpBuffersOut as Long, _
byval dwFlags as Long, byval dwContext as Long) as Long

[Ravi Kiran]

Taking your example of HttpSendRequestEx, I dont know if this fn fills in the value of *Next field. Atleast the name suggests that you need to pass the pointer to a structure. So, first check that out]

Also my definition of CopyMemory (RtlMoveMemory) is defined with both memory pointers as Any
Though it is possible to play around with fn defitions, it is dangerous, unless you really know what VB thinks of your fn is same as what you want VB to think!!.

In yours, in both definitions either one of them is defined 'Long'. So i will go with that (both 'any') definitaion i sent in the first post.

Dim Ibuf1 as Internet_Buffers, Ibuf2 as Internet_Buffers

if you want the Ibuf2 = lBuf1.Next in VB, do it like this:


copymemory Ibuf2, byval Ibuf1.next, len(Ibuf2)




Byval identifier at calling line, like above, indicates that, the value passed is to be copied (value), but the difinition says, it is actually the address (pointer), which is correct in our case, because what we are passing is a pointer.

For this sturcture things are not finished yet. There are other memory pointers too in that.
To copy the lpcszHeader, if not null, define a byte array of appropriate size and copy into it:

dim tmpbuf() as byte
' after copying the info into IBuf2 structure as above
if IBuf2.lpcszHeader <> &H0& then
redim tmpbuf(Ibuf2.dwHeadersLength)
copymemory tmpbuf,byval IBuf2.lpczHeader, Ibuf2.dwHeadersLength
end if




IDK, how much this helps you!:-)

RK

[Muthu Ram]

I am having a tough time populating the INTERNET_BUFFERS structure used by the HttpSendRequestEx function. No documentation is available for this method. I know microsoft did not want us to use this method in VB but why cant they give us some documentation on this?

I guess this is the pain working with microsoft technologies.

anyone have any example of using HttpSendRequestEx and HttpEndRequest?