BBC URI Fetcher Dispatch Mechanism
==================================

Osword 191 (&BF) - Fetch URI
An application can request a URI be dealt with by issuing Osword 191 with
the following control block:

On entry:	A=191, XY point to control block:
Control block: XY+0  string length + 5 - Length of entry control block
		XY+1  &04               - Length of exit control block
		XY+2  URI Command
		XY+3  Flags or handle
		XY+4... Text string of URI
		 :     terminated by a CR (value 13).		

On exit:	A,X,Y may be corrupted.
Control block: XY+0  undefined
		XY+1  undefined
		XY+2  Returned status byte
		XY+3  Returned URI handle
		XY+4... Text string may be overwritten

The following URI commands are available, passed in XY+2:

0: Version
On exit, the status byte is returned as version*100 and the URI handle is
returned as zero.  This call can be used to check for the presence of the
URI Handler.

1: Dispatch
This call is used by an application to pass a URI string to the handler
for dispatch.  The handler will pass the call around relavent programs and
return a handle to the opened URI.
On exit, the status byte:
	0 = URI found, handle in XY+3
	1 = URI not found, handle returned as zero.

If a URI is found, the returned handle should be examined.  If the handle
is zero, then the URI has been handled and completed.  This could be the
result of a mailto: URI where a mail handler has processed the URI
completely.  If the handle is nonzero, then it references a file that can
be accessed with OSBGet and OSGBPB for fetching.  This may be a temporary
file that is valid until the URI handle is closed.

2: Close
Closes the URI with handle in XY+3, possibly deleting any temporary files.
After this call the application must assume that the handle it passed is
invalid.

Notes
On calling, the flags/handle field at XY+3 should be set to zero if it is
not used on the call.  Currently, the passed URI string should not be more
than 59 characters long.

A simple URI client could be written as follows:

DIM X% 128:Y%=X%DIV256
OSWORD=&FFF1
REPEAT
CLS:INPUT "URI: "uri$
!X%=&00010405+LENuri$:$(X%+4)=uri$
A%=191:CALL OSWORD:status%=X%?2:handle%=X%?3
IFstatus%=0 AND handle%<>0 THEN REPEAT VDU BGET#handle%:UNTIL EOF#handle%
!X%=&00020404:X%?3=handle%:A%=191:CALL OSWORD
UNTIL FALSE