[ naviserver-Feature Requests-1151137 ] New driver API and Udp module

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Feature Requests item #1151137, was opened at 2005-02-24 16:01
Message generated for change (Comment added) made by seryakov
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=719009&aid=1151137&group_id=130646

Category: C-API
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Vlad Seryakov (seryakov)
Assigned to: Vlad Seryakov (seryakov)
Summary: New driver API and Udp module

Initial Comment:
Hi guys,

Attached is minor driver extensions which do not change
existing drivers  but add new functionality. There are
some cosmetic changes, like moving some fields in the
Ns_Sock/Ns_Driver structres so they can be accessed
publically and made some private functions public but
functionality preserved as before.

I included udp driver as an example of new API, and
also added ns_sha1 command in the tclmisc.c, it is just
one command and it is uses practically everywhere.

-------------------------------------------------------------------------
To test udp driver i use new ns_udp command:

ossweb:nscp 8> ns_udp send 127.0.0.1 5060 "GET /
HTTP/1.0\n\n"

HTTP/1.0 200 OK
MIME-Version: 1.0
Date: Thu, 24 Feb 2005 05:39:50 GMT
Server: NaviServer/4.0.10
Content-Type: text/html; charset=iso-8859-1
Content-Length: 661
Connection: close

<HEAD><TITLE>Seryakov's Family Intranet</TITLE></HEAD>
.....

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>Comment By: Vlad Seryakov (seryakov)
Date: 2005-02-25 15:23

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I am not arguing with you about your ParseProc driver
extension, it is very usefull and makes driver more flexible.

I just want to add couple of new API functions that will allow
developer to queue connections from any place, that's it.
How drivers will be written and how developer will decide to
handle it is up to each particular developer. But nobody
will be locked up in only one way of doing it.

Each way has its own drawbacks so we have multiple choices
and developer will decide for itself how it should be.

Both our ways do not mutually exclusive.

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Comment By: Stephen Deasey (sdeasey)
Date: 2005-02-25 08:28

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Ah I see you're right, an extra thread is not created for
each incoming request.  'udpThread' is perhaps not the best
name for the socket callback though... :-)

I still don't see the advantage of using Ns_SockCalback.  A
single thread is created by the server to handle all
registered callbacks, including those from ns_sockcallback.
 At runtime, while this single thread is running tcl code to
handle one callback, your dirver callback cannot run, no new
connections will be accepted, etc.  Why is it better to use
the Ns_SockCallback thread rather than a driver thread?

Maybe I'm reading this wrong, but how do you handle the case
where the request arrives as more than one packet? 
Ns_DriverSockRead() is called from the 'udpThread' socket
callback.  The only return value checked is NS_OK, but
couldn't this also be SOCK_MORE?

How would you handle things like keepalive?  I think you'd
have to reimplement that in the Ns_SockCallback thread.

Re the proxy stuff, Ns_RegisterRequest() and
Ns_RegisterProxyRequest() seem very simillar.  With
Ns_RegisterRequest(), filters are run and you get the choice
of using C or Tcl.  Ns_RegisterProxyRequest() offers no
advantage that I can see -- you still need a complete
Request structure, even if you just ignore it.

The comm driver initialization should probably be changed to
automatically handle unix domain sockets.  You add /foo
rather that 127.0.0.1 in the config file and it knows to
create the correct type of socket.  nssock and nsopenssl
wouldn't have to be modified at all.

UDP is different.  There are two types of protocols: single
packet, such as DNS or RADIUS; multi packet, as used in some
streaming media and p2p protocols.

I think for the single packet case we again might want to
modify the driver code to automatically handle it.  No
read-ahead is necessary, there's only one packet per
request, so it's placed in the request buffer and passed on
to the next stage, which is parsing.  Here, a return code of
SOCK_MORE would be illegal.

Every multi-packet UDP protocol will require custom
framing/sequencing and the developer will have to create a
new socket driver.

Taking RADIUS as an example, which is a single packet UDP
protocol, you'd create a very simple Ns_ParseProc who's only
job is to check that the number of bytes specified in the
header actually arrived, and return SOCK_READY.  A default
request structure is created for you so the only other thing
you have to do is Ns_RegisterRequest() for the '/' URL. 
Within your request proc, call Ns_ConnContent() and parse
the buffer.

Now, you do have a number of other options to make this more
flexible.  You could parse the request in your Ns_ParseProc
and then fill out the request structure.  e.g. the different
RADIUS message types could be expressed as HTTP verbs.  This
buys you flexibility.  Now you can Ns_RegisterRequest() a
different routine for each RADIUS message type, and someone
reusing your code can override your default implementation.
 You can also handle some message types in C, and others in Tcl.

You might decide to put some useful information about the
RADIUS request in the URL line.  Now you get logging for free.

You might decide to parse the key/value pairs from the
RADIUS request into query vars or headers.  Now you don't
have to write a bunch of RADIUS specific Tcl commands to
access the data, should you want to handle that from Tcl. 
ns_queryget or ns_conn headers  will work.

How far you want to go is up to you, the writer of the
protocol module.  But at the low end all you need is an
Ns_ParseProc and usually a single registered request proc,
which is a lot less code to write than the Ns_Driver* stuff,
I think.

I'm sure it's not perfect!  So what's wrong with it? Why
would it suck to write a RADIUS protocol module as I've just
described, to take one example?

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Comment By: Vlad Seryakov (seryakov)
Date: 2005-02-25 05:51

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I think we need to collect all solutions and then see where
are going, i am holding to port all my old/running modules
because i do not know how naviserver will handle foreign
protocols.

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Comment By: Vlad Seryakov (seryakov)
Date: 2005-02-25 05:48

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yes, using proxy can solve immediate requirements without
hacking NsConnProc by adding hooks to call driver specific C
functions.

If i need my smtp server and main loop is in C, i need
somehow call it
in the connection thread. Using registered proxy function i
can do it now, i do not need filter/traces. This is for
completely new modules.

I can implement main loop in the module as Tcl command and
then call it in the connection filter, it is possible, it
will just require many different parts to be in place and
still filter should be registered as Tcl proc which will
call another driver main loop.

sometimes low level stuff makes things easier and simpler:-)))

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Comment By: Vlad Seryakov (seryakov)
Date: 2005-02-25 05:45

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In all my installations i need sha module but it wasn't in
the distribution, so i need to download it or repackage
aolserver to include nssha1. That is my point, it is just
one simple function use more often than something like
ns_jpegsize or so.

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Comment By: Stephen Deasey (sdeasey)
Date: 2005-02-25 05:42

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Well I don't know about the wisdom of adding sha1 to the
core at this stage  :-)

I see your point though, encryption and hashing functions
are almost universally required for systems/server work. 
Maybe we need to consider adding a new encryption module to
the core distribution.  Like nsdb it would export a C API
via libnscypher.so (or whatever) as well as the Tcl module
nscypher.so.

Times have changed and things like the openssl libraries are
common on all platforms so it's not the big deal it used to
be to add such dependiencies.

Such a module should make implementing SSL in nsopenssl easier.

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Comment By: Vlad Seryakov (seryakov)
Date: 2005-02-25 05:41

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No, i do not spawn new thread, i use callback feature of the
server, when socket is ready, server calls provided callback
ad that callback just submits the socket to connection pool.
if pool is full, Ns_DriverSockQueue will return NS_TIMEOUT,
you can retry.
Yes, it is low-level, for high level, HTTP driver provides a
lot of functionality, it could be extended like you did, but
still it is HTTP driver hacked. If i want completely new
driver, like RADIUS server, http driver will not help me, i
need low level stuff, and it is there already.

To reuse resource limiting, i added Ns_DriverSockQueue
function, so
new conections can be queue instead of creating new threads.

I do not have anything against your patch for extending
current driver, it is very usefull. i am offering new API
for low level drivers.

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Comment By: Stephen Deasey (sdeasey)
Date: 2005-02-25 05:36

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The proxy stuff is too late in the cycle to do much.  The
request has to be fully parsed by then (for read-ahead).

If a proxy function is available, then all filters, the auth
phase, registered procs, cleanup procs etc. are bypassed.  A
lot of that stuff can be very useful for non-HTTP protocols.

I don't think handling stuff via a proxy function buys you much.

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Comment By: Stephen Deasey (sdeasey)
Date: 2005-02-25 05:32

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I don't understand what you're trying to acheive here (well,
apart from multi-protocol... :-).  The newly exposed
Ns_Driver* entry points are quite low level, and so the
implementor of the new protocol is left to do a lot of the
heavy lifting.

For example, the way I read it you have to create your own
listen socket and register a callback.  Every time a new
reaquest comes in a thread is spawned to handle it.  From
that thread you then submit the parsed request to one of the
conn threads.

Excessive thread creation and message passing between
threads is not going to perform well.  And it seems you have
to write more code than e.g. the example POP3 driver I
posted some time ago.

You're also not taking advantage of the other facilities
that the server offers.  What happens if 1000 connections
arrive, do you spawn 1000 threads?  You could of course code
up some limit checks, but this already exists.  What if a
client sends you a continuous stream of data, 2GB...  etc.

By using the driver hooks to provide the new protocol
parser, you deny yourself the opportunity to use something
like the nsopenssl module.  This should work just fine for
protocols like SMTP, IMAP, POP3 and probably others.

Anyway, I think one of the most carefully coded aspects of
the server is it's attention to resource usage.  That goes
for IO, context switching, memory, etc.  It's espescialy
nice that most of the time you're not even aware that all
this work is being done for you.  I'd like new protocol
drivers to be able to transparently take advantage of that.

Could you take a look at my old POP3 demo driver?  It's the
attachment nspopd-0.3.tar.bz2 over here:

http://sourceforge.net/tracker/index.php?func=detail&aid=973010&group_id=3152&atid=353152

It's not obvious that anything interesting is going on, so
it's not much to look at.  But actually, conn socket
read-ahead is happening eficiently in one thread with async
IO, the conn threads are treated as a precious resource
(heavy-weight Tcl interps) and are allocated at the last
minute, there's an easy API in C and Tcl to implement the
actual reading of data from the INBOX (could be from the
file system, db etc.).

You've got a lot of experience writing servers, what do you
think is wrong with this model?  What can it not do, or what
could it do better?

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Comment By: Vlad Seryakov (seryakov)
Date: 2005-02-24 21:29

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Another thing, once we can submit connections from any
place, no need to build any drivers, even in C, i can
register new proxy proc and set protocol field in my
request, so when submitted, connection will run registered
proxy proc.
for example: 
 in my smtp driver/module, i create driver, register proxy
for smtp: protocol, register callback for the socket. Once
connection accepted, in my module i submit that connection
to the queue with request-protocl set to smtp:.
queue.c will call my proxy handler, which is C function.

No need to add anything else. This way even standard
aolserver can be extended without touching precious http
driver thread. Sorry for sarcasm.

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[ naviserver-Feature Requests-1151137 ] New driver API and Udp module

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[ naviserver-Feature Requests-1151137 ] New driver API and Udp module