SAMP Web Profile

[Mark Taylor]

Pierre,

On Thu, 9 Dec 2010, Pierre Fernique wrote:

> About Web SAMP  I have a question about multi-user machines. How it will works
> with only one local port (21012). How can I restrict the communications only
> between my applications ?

This is an excellent point, which had occurred to me, but I had forgotten 
to note it in my presentation or the draft spec.  The Web Profile is
not going to work where more than one user wants to use it on the 
same machine at the same time.  These days that's not a very common
usage scenario, but neither is it negligable.

In practice if user A attempts to start a Web Profile hub when
user B is already running one on a given machine, the attempt will 
fail since the socket is already in use.  If user A's web client 
attempts to register with a Web Profile hub owned by user B, 
user B will get a message from the hub asking for
permission to register, which B will hopefully recognise as an 
impostor (not corresponding to an action of user B) and reject.
In this context hub "ownership" is determined by whose
visual display the hub is associated with, which is presumably the
display the user who started the hub in the first place is 
sitting in front of (if the RECOMMENDATION to seek explicit 
confirmation from the user at registration time is disregarded however,
ownership may be undefined).  It is possible, but unlikely, that
user A and user B are visiting the same SAMP-enabled web page at the same
time.  In such a case, B could end up erroneously approving registration
for the wrong web client.  I can't think of any way round this,
since the HTTP (XML-RPC) registration request is unlikely to be
labelled by user.

I will make this issue explicit in the draft spec.  Since it will
only apply in a small minority of cases I don't think it's 
a serious enough deficiency to derail the proposal, but feel free 
to argue otherwise ...

Mark

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/