Re: SOAP-over-UDP

Wed, 01 Jun 2005 02:58:53 -0700 

Great thread, guys!

Just my grain of salt :-)
With respect to the UDP vs. TCP question: UDP is not a reliable protocol. You cannot send a message and be sure it will reach the other side at all. And if the message is larger than the packet size, it can be received in an altered order. This makes UDP a hard choice for SOAP, because it would require a lot of code for implementing the packet reordering and retransmition.
Related to this, it is technically possible to have URLs larger than a single packet size, so I would advice you to send the UDDI request via TCP. 

Another place I do not agree:
Publishing equivalent services in more than one UDDI registries is not necessarily an error. If you are searching a service just by a key word, more than one service could be valid, even in the same registry. You can also have services that can be down at some hours in a day in some computers, so they are replicated among different servers.
You could complicate this schema just a little bit, and collect all matching services in your client as a List. I even would firstly collect all UDDI registries in a list and query all of them. This way, if you just need one, you can use any of the items in the list (the first, for example), and if it is down, you can try the next one in the list.
Later, you could extend the client and make it maintain a history of recently failed services, for faster execution; or let the user select one of the found services through a GUI, etc. 

Hope this helps you,
Rodrigo Ruiz


Francesco Munari wrote:
Mark, 
Yes, that's seems to be great idea, I would even say elegant.



...and it seems to work very very well!! ;)

It all works! It seems very efficient.
Saving the URLs send as a reply by the servers in a hash eliminates
also possible duplicates because the add(Object o), if it finds an
equal Object inside the hash, replace the old one with the new one.
So, if erroneously some service was published into more tha one UDDI
registry present in the LAN, the result hash, at the end of the
"request round", will have only one WSDL URL representing that
service.

Wow! It has been very cool solving my problem with you all! A parte of
my thesis is your merit!

But now the very last question (^_^): why (apart the difficult that I
had in implementing it) the use of SOAP or XML-RPC broadcast message
over UDP are so unsuitable?

Thank you very much!

Francesco
2005/5/31, mdonaghue <[EMAIL PROTECTED]>:

Francesco,



In this way the
proxy receives the message, ask its UDDI registry for that service and
reply with a byte[] containing the URL of the service's WSDL file. Uh?

Yes, that's seems to be great idea, I would even say elegant.

Regards,
Mark


-----Original Message-----
From: Francesco Munari [mailto:[EMAIL PROTECTED]
Sent: Tuesday, May 31, 2005 4:54 PM
To: [email protected]
Subject: Re: SOAP-over-UDP

Great Mark!

You have explained your point of view as well as you could.
So the point is to give a proxy to every server that has an UDDI
registry. This proxy, written in Java, waits for UDP datagrams. Maybe
the broadcast UDP message sent by the client could also contains the
key of the service that the client is searching for. In this way the
proxy receives the message, ask its UDDI registry for that service and
reply with a byte[] containing the URL of the service's WSDL file. Uh?

Should be a good idea instead of retreiving the IP address and having
also to ask the registry for the service?

Thank's again to you all!! You're help me more than you think! Thank's.

Cheers

Francesco

2005/5/31, mdonaghue <[EMAIL PROTECTED]>:

Hi Francesco,

My original suggestion was to use DNS to identify the URL of the UDDI

server

in the local subnet. The advantage to this is that no broadcast message is
needed and it's using a common solution. The disadvantage is it requires

an

entry in the DNS server database, some knowledge of how to administrate

it,

and isn't automated.

So, I tend to agree with Eric's solution (except for the last step which I
believe should be unicast, not broadcast).  The basic idea is to have the
client broadcast a "who has a UDDI Server" message when it comes online.

XML

will be ok, because since the broadcast only happens once, verbosity is

not

an issue. However, a simple text message would also do the trick and
eliminates the need to parse XML. In either case, a simple UDP server
process listening on over a known port on the UDDI server machine will
respond, identifying itself to the client. At that point the IP address of
the UDDI server is available to the client and the UDDI request can be
unicast to it.

This message sequence is identical the ARP protocol, which allows an
end-host to determine the MAC address of system with a known IP address.

The

end-host broadcasts a "who has this IP address?" message to the subnet. If

a

host with that IP address receives the message, it unicasts an "I have it"
message, enclosing its MAC address along with it. From then on, all
communication for that flow can be unicast.

The actual messaging discussed above should be handled outside of SOAP,
since SOAP is not intended for this kind of functionality. It could be
easily implemented as with Java using UDP datagram sockets.

This approach handles the potential problem of multiple servers on the

same

subnet, since the client can just choose one. It also solves the problem

of

the UDDI server not being architected around a possible broadcast

scenario,

typically running over TCP.  You won't need SOAP over UDP. It minimizes
network overhead since only a single broadcast is made, when the client
comes online.

Regards,
Mark


-----Original Message-----
From: Eric VERGNAUD [mailto:[EMAIL PROTECTED]
Sent: Tuesday, May 31, 2005 7:58 AM
To: [email protected]
Subject: Re: SOAP-over-UDP

It depends on what you mean by continuous. a 16 bytes packet every 5
seconds certainly won't.

If you need a higher reactivity, you can do the following:
- have the client broadcast a message on a port
- have the server listen on that port
- when the server receives a connection, have it broadcast as
suggested in my previous email

Le 31 mai 05 � 13:17, Francesco Munari a �crit :


But there isn't the risk of flooding the LAN with these continuous
broadcast messages?

2005/5/31, Eric VERGNAUD <[EMAIL PROTECTED]>:


Have your server regularly broadcast its address on a port.
Have your client act as a server on startup and listen on the same
port.
When the real server broadcasts its address, the client will receive
a connection request.
One you have the server address, ask the server for the information
you need (what you call the context).

Le 31 mai 05 � 11:41, Francesco Munari a �crit :



Hi, Eric.

Ok, but how can I do this? I think I'm a newbie in this kind of
operation, sorry. How can I look to a port of servers in a LAN
without
knowing their IP? And in this way may I keep the context-
awareness of
the communication?

thank you for you reply

Cheers

francesco

2005/5/31, Eric VERGNAUD <[EMAIL PROTECTED]>:



I'm afraid that is a very verbose way of doing things. The typical
way to do this is determine a port, have your server broadcast
its IP
address on that port, and your clients look on that port to grab
the
address.

Once the address is found, you can safely interact with the server
using SOAP over HTTP.

Le 30 mai 05 � 22:19, Francesco Munari a �crit :




I'm alredy using UDDI4j. The idea is that I don't know where the
UDDI
registry can be in the LAN.
I assume that the client knows only two things:
1) the network (of course)
2) a "search key" for a particular tipe of service

and that's all.
The client should send a broadcast SOAP (or XML-RPC) request
containing the search method to call on the server with the "key"
passed as a parameter and somewhere into the LAN should be a
server
(or more) with its private UDDI registry that should reply with a
response containing the result of the invoking of the method
contained
in the sender's RPC request. The response should contain just the
URL
of the WSDL file related to the service found.

The need of the broadcast message is that the client don't know
where
(or if) there could be any UDDI registry in the network. With this
framework a client can change network configuration (for example,
going from a floor to another with a Palm in a wireless LAN) and,
after leaving the service provided in the first network, find
anothe
one similar on the other network only by pressing the button
"Refresh"
:)

Francesco

2005/5/30, Martin Gainty <[EMAIL PROTECTED]>:




The side effect of a broadcast without authentication is
flooding the
network with unwanted disovery packets
I guess this is OK if you're utilising a high datarate
transmission i guess

In your case your SOAP Request should look like

<?xml version="1.0"?>
<SOAP-ENV:Envelope
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"; >
<SOAP-ENV:Body>
  <getTest>
    <Test>Test</Test>
  </getTest>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

If you want to discover a "SOAP based" web-service based on some
characteristic such as Business Service Category why not use
UDDI4J?
Take a look at
http://sourceforge.net/projects/uddi4j

Martin-

----- Original Message -----
From: "Francesco Munari" <[EMAIL PROTECTED]>
To: "Martin Gainty" <[EMAIL PROTECTED]>
Cc: <[email protected]>
Sent: Monday, May 30, 2005 12:44 PM
Subject: Re: SOAP-over-UDP

Martins,

It is for this reason that I'd like to broadcast a SOAP request
instead of a simple XML-RPC message. The goal of my framework
is to
keep the "context awareness" offered by XML language.
If you are sure that there is no way to send a broadcast SOAP
request,
the last solution, I think, it could be XML-RPC.

So, two questions:

1) are you sure ther's no way to send a broadcast SOAP request?
2) In order to send a broadcast XML-RPC message I've to cerate a
StringWriter like this (for example)?

<?xml version="1.0" ?>
 <methodCall>
     <methodName>getTest</methodName>
     <params>
         <param>
             <value>
                <string>Test</string>
             </value>
         </param>
     </params>
</methodCall>

Thank's Martin.

Francesco

2005/5/30, Martin Gainty <[EMAIL PROTECTED]>:




Francesco-
You can Broadcast XML-RPC assuming you dont mind flooding your
network
The question is can you confine your application to using the
more basic
datatypes supported by XML-RPC
vs implementing SOAP features (user-defined datatypes, namespace
URI)?
Anyone else?
Martin-
----- Original Message -----
From: "Francesco Munari" <[EMAIL PROTECTED]>
To: "Martin Gainty" <[EMAIL PROTECTED]>
Cc: <[email protected]>
Sent: Monday, May 30, 2005 6:45 AM
Subject: Re: SOAP-over-UDP

Grazie! :)

Could someone tell me if a simple XML-RPC message may be sent
to a
broadcast address? A simple message with the medthod to be
invoked. In
this way I should be able to send a broadcast XML-RPC request
with the
appropriate UDDI inquiry method; a server (containing a UDDI
registry)
should receive it, invoke that method and send a reply in XML
format
to the sender.

It could be a good idea?

thank you again!

Francesco

2005/5/29, Martin Gainty <[EMAIL PROTECTED]>:




benvenuto!
Martin-

----- Original Message -----
From: "Francesco Munari" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Saturday, May 28, 2005 5:41 PM
Subject: Re: SOAP-over-UDP

Thank you all for your very quick reply!

I've heard about this SOAP-over-UDP spec
(http://msdn.microsoft.com/library/default.asp?url=/library/en-
us/dnglobspec/html/soap-over-udp.asp).
So, Martin, you say that it could not be a solution? Perhaps it
should
be an idea using Mark's solution (with DNS).

I thought to resolve the problem putting a SOAP envelope into
a UDP
datagram, send the datagram to a broadcast ip and that's all
folks...but I don't know how and, as you, Martins, wrote, I
was not
able to find anybody who has implemented this yet.

Can you suggest me another solutions?

Thank you very much again!!

Cheers,

Francesco

2005/5/28, Martin Gainty <[EMAIL PROTECTED]>:




Mark/Francesco
I would caution on use of UDP as the SOAP Portocols (e.g.
HTTP)
is/are
decidely not UDP but instead a connection-oriented TCP
To date I have not seen UDP Ports used for SOAP transmission
although
since
there is no requirement for verifiable connection and or
handshakes
I would venture to guess UDP is available as the transmission
medium
but
I
have not seen any UDP Ports used for SOAP thus far
Anyone else ???
Ciao-
Martin-

----- Original Message -----
From: "mdonaghue" <[EMAIL PROTECTED]>
To: <[email protected]>; "'Francesco Munari'"
<[EMAIL PROTECTED]>
Sent: Saturday, May 28, 2005 3:14 PM
Subject: RE: SOAP-over-UDP





Hi Franceso,

I've worked briefly with the apache soap api, not that
familiar with
it.
Typically a soap message is sent to a single soap server
address,
which
is
specified by a url or an ip address, as well as a port. So
your
server
address on the LAN might be something like
192.168.100.2:8080.
(I'm
not
sure
what the port is for UDDI, so just using standard TomCat Web
Server
port).

IIRC, you there's a point at which you specify that
address in
the
setup
for
your soap call. One thing you could try is to change the
address to
the
subnet's broadcast address, 255.255.255.0:8080, assuming a
class c
network
where the first 3 quads specify the network portion of the
submask.

However, this may not a scalable solution, since the
broadcast
wouldn't
carry beyond the physical subnet on which you are located.
Using
UDDI
to
discover services is one thing, but dynamically discovering
UDDI
servers
is
obviously a different problem. It also doesn't address the
issue of
more
than one UDDI server running on the same subnet.

A more generalized solution might involve a distributed ip
lookup
service,
namely DNS. For example when DNS looks up the ip address of
Yahoo.com,
at
some point the actual ip address that serves the request is
dynamically
assigned to one of dozens (or hundreds) of servers based on a
scheduling
scheme.  You could locally enable DNS lookup, and create an
entry
based
on
some url like "myuddpsever.com", and give it your local UDDI
server's
ip
address, and the rest would be handled within the network.
The
advantage
to
this is your UDDP server could be anywhere and your message
would
still
reach it.

hth,
Mark





-----Original Message-----
From: Francesco Munari [mailto:[EMAIL PROTECTED]
Sent: Saturday, May 28, 2005 4:58 AM
To: [email protected]
Subject: SOAP-over-UDP

Hi, I'm desperate!
I'm trying to find out how to send a broadcast SOAP request
to a
UDDI
registry in a LAN, but I'm not able to do this. I've looked
for some
example but I've not found anithing.

Please...could anybody help me?
I'm making a thesis for the University of Florence (Italy)
and I
have
to discovery dinamically web service published in some UDDI
registry
somewhere in a LAN. I have to send a broadcast SOAP
request to
these
UDDI registry (as I wrote few lines above).
Of course I'm using Java language.

Thank you very much for your help...I'm in a great
hurry...thanks
very
very much to everyone could help me!

Best reguards,

Francesco

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