Subject: Re: Lisp-based protocols [was Re: OS wars and Lisp] From: Erik Naggum <email@example.com> Date: 1998/12/17 Newsgroups: comp.lang.lisp Message-ID: <firstname.lastname@example.org> * email@example.com (Paolo Amoroso) | If I get things right, you designed a--network?--protocol whose commands | can be parsed with READ. yes. for two reasons: Common Lisp already has a well-defined syntax for all the object types we need, and the syntax we use is fairly trivial to generate and parse for non-Lisp programs, too. | What are the possible strategies for executing or serving incoming | commands/requests with such a protocol? two points: I don't call READ on the stream itself. I implemented a stream with memory, so I set the stream's mark, eat characters until I see a newline, call READ-FROM-STRING on the STREAM-SUBSTRING, and if it barfs on end of file, I set up a timeout and eat characters until the next newline comes along. the timeout is cancelled and the mark is reset when READ-FROM-STRING succeeds. the timeout action is simply to emit an error message and reset the mark, effectively cancelling the input. (this simple setup makes it possible to handle all the clients' input streams in one Lisp process, dramatically reducing scheduler overhead.) | I can think of at least the following: | | 1) direct evaluation with EVAL | 2) interpretation | | Option 1) has potential security problems, but this may not be an issue for | systems running in a trusted environment. the list of functions that may be called is a property of the stream, and if the first element of a list passes this test, the arguments are checked to be symbols (which have values) or treated as constants, and then I do (apply #'funcall <list>). running with full safety in the functions that accept these arguments, errors are reported back to the client with a list (ERROR "<error message>"). the functions basically hand off the request to a running process or start up a new process if they cannot return immediately with a value. this has saved me a _lot_ of work that would otherwise have been spent on protocol syntax design and such silly details. people seem to have bought it, and I'm quite happy. (now, the annoying thing is that TCP connections are such unruly beasts -- back to work.) #:Erik -- Attention, Republican members of the House Judiciary Committee! We have intercepted a coded transmission from Bill Clinton to Saddam Hussein that puts your life in jeopardy. Clinton is prepared to cease fire if all of you are killed by Iraqi terrorists, whom he won't prosecute. Be warned!