POSTing data

Hi everyone. I'm slowly figuring out the ins and outs of C... at the moment I'm trying to create a small program that connects to a device via HTTP and sends some data via POST. I've managed to convert the MSDN existing code for my own use; at the moment I can request a file from the device.

From using Intel's UPnP tools, this is the entire data that I need to send to the device:

Code:

POST /AudioIn/Control HTTP/1.1
HOST: 10.0.1.136:1400
SOAPACTION: "urn:schemas-upnp-org:service:AudioIn:1#GetAudioInputName"
CONTENT-TYPE: text/xml ; charset="utf-8"
Content-Length: 286

<?xml version="1.0" encoding="utf-8"?>
<s:Envelope s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
   <s:Body>
      <u:GetAudioInputName xmlns:u="urn:schemas-upnp-org:service:AudioIn:1" />
   </s:Body>
</s:Envelope>

I assume I have to put that code in the "WINHTTP_NO_ADDITIONAL_HEADERS" area of the following statement:

Code:

  if( hRequest )
    bResults = WinHttpSendRequest( hRequest,
                                   WINHTTP_NO_ADDITIONAL_HEADERS, 0,
                                   "sweet", 0,
                                   0, 0 );

Is that right? I can post my whole code if requested, its only about 100 lines. It's very similar to the sample on MSDN

So... I guess my question is, is this the right way of going about a POST? Later on I'll have to recieve a response from the device but I'd like to get this down first.

No, you have to send the POST length as well.

Code:

if( hRequest )
    bResults = WinHttpSendRequest( hRequest,
                                   WINHTTP_NO_ADDITIONAL_HEADERS, 0,
                                   "sweet", 5,
                                   5, 0 );

OK, I've moved on a bit now. Managed to iron out most of the POST I think. Here's the code I've added at the start:

Code:

	// UPnP request to be sent via POST in XML format
	char *PostData =
	"<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"
	"	<s:Envelope s:encodingStyle=\"http://schemas.xmlsoap.org/soap/encoding/\" xmlns:s=\"http://schemas.xmlsoap.org/soap/envelope/\">\n"
	"	<s:Body>\n"
	"		<u:GetAudioInputName xmlns:u=\"urn:schemas-upnp-org:service:AudioIn:1\" />\n"
	"	</s:Body>\n"
	"</s:Envelope>";

	// SOAP header required for UPnP request
	unsigned char *ExtraHeader = "SOAPACTION: \"urn:schemas-upnp-org:service:AudioIn:1#GetAudioInputName\"";


	// Length of UPnP request
	char PostLength = lstrlen(PostData)*sizeof(TCHAR);
	// Length of SOAP header
	char HeaderLength = lstrlen(ExtraHeader)*sizeof(TCHAR);
	// Total length
	char TotalLength = PostLength + HeaderLength;

	// FYI
	printf("postlength is %d\n", PostLength);
	printf("headerlength is %d\n", HeaderLength);
	printf("totallength is %d\n", TotalLength);

(By the way - the SOAP header gave a huge horrible error - assignment of pointer to const unsigned short to pointer to char - until I added the word "unsigned" in front of it. I hope this was the right fix, all I know is that it works.)

Anyway, here's my new HTTP request code:

Code:

  // Send a request.
  if( hRequest )
    bResults = WinHttpSendRequest( hRequest,
                                   ExtraHeader,
								   HeaderLength,
                                   PostData, PostLength,
                                   PostLength, 0 );

This now returns an error 87, which I beleive may be due to incorrect values of HeaderLength, PostLength and/or TotalLength.

Interestingly enough, when I run my program, with my "FYI" information that prints out the lengths of the header and POST data, this is what I get:

Code:

postlength is 18
headerlength is 70
totallength is 88

Now the 70 value looks about right, and totallength is calculating OK, but I know for a fact that the XML code I'm sending is a lot longer than 18 characters! What am i doing wrong here?

One more question - why do I use "*sizeof(TCHAR)" when figuring out length? I got that code from another sample somewhere.

I'm not sure. I copied/pasted your code into my compiler, and it gave me 274, not 18.

Fuh. I blame LCC or something.

Anyway, made a bit of progress.

New code that gives correct lengths:

Code:

	// Length of UPnP request
	int PostLength = strlen(PostData);
	// Length of SOAP header
	int HeaderLength = strlen(ExtraHeader);
	// Total length
	int TotalLength = PostLength + HeaderLength;

and

Code:

  // Send a request.
  if( hRequest )
    bResults = WinHttpSendRequest( hRequest,
                                   ExtraHeader, HeaderLength, // extra header data and length
                                   PostData, PostLength, //data to post and length
                                   TotalLength, 0 ); // length of extra header plus post data

Still getting Error 87. What's the deal? Should I post all my code?

OK, I think I've broken it down some more.

Here's what I need to have in my WinHttpSendRequest statement (from the MSDN article ):
pwszHeaders
[in] A pointer to a string that contains the additional headers to append to the request. This parameter can be WINHTTP_NO_ADDITIONAL_HEADERS if there are no additional headers to append.

It seems the POST data is a "pointer to a buffer" (char *postdata = "post data"; works) but the headers are a "pointer to a string". I don't know how to make a pointer to a string. God only knows why they aren't BOTH a "pointer to a buffer". I guess I'll start googling...

char *postdata = "post data"; is not a pointer to a buffer. It's a pointer to a string. If you want to pass a pointer to a buffer then just pass the name of the buffer. Example:

Code:

{
  char buffer[512];

  SomeFuncThatWantsABuffer(buffer);
}

Thats what I suspected... but... well... it works. I mean that part of my code does. WinHttpSendRequest accepts the code fine.

:/