Subject:
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Re: rcxhttpd?
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Mon, 19 Jul 1999 17:47:22 GMT
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Viewed:
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1976 times
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In lugnet.robotics.rcx, Todd Lehman writes:
> [...] a scaled-down version of httpd actually running on the RCX brick
> itself. Obviously, it couldn't hold very many static pages, and it
> would need a dedicated IR link to a host machine, but I wonder what
> sorts of things could be done? Anything useful? [...]
Since the RCX has essentially a serial interface to the outside world, you
would need to encode and decode the HTTP requests and responses into a
serial-based protocol. If you actually wanted the RCX to be plug-and-play
compatible with existing TCP/IP communications devices (like your PC acting as
a firewall) then you would have to use an existing protocol for IP over serial
line, like SLIP or PPP. That means you're implementing four layers of protocol:
SLIP or PPP, IP, TCP and HTTP. Even a minimal subset of each of these protocols
adds up to a fair amount of code. I don't know how much memory the code would
take but it's probably pushing the 32K limit.
However, the minimal implementation of HTTP [1] is designed to operate over any
type of connection, not just a TCP connection. In other words, you can forego
the SLIP/PPP, IP, and TCP layers of the protocol and run HTTP directly over a
serial line. If you do this, HTTP is extremely simple. A request consists of
sending "GET " followed by the desired URL and a CRLF; and the response
consists of the ASCII text being sent back followed by "closing of the
connection". To signal "closing the connection" you would probably send a null
character (ASCII 0) or a control-D (ASCII 4).
This approach, of course, has side effects:
- The computer on the "other end" of the serial line has to know that it's
doing HTTP directly over serial. You'd probably have to write special software
to do this.
- No error checking or retry to handle noise in the line (which would come
mainly from the infrared link, not from the serial cable itself)
- No ability to run other protocols over the same link (like FINGER as
someone else suggested)
- Robert Munafo
1. http://www.w3.org/Protocols/HTTP/AsImplemented.html
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Message has 2 Replies:
 | | Re: rcxhttpd?
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| I don't think my first post succeeded, so here it is again. Sorry if you've already seen this. (...) wander around the house until it finds another 'bot. Then it would relay the message to that 'bot. This second 'bot could wander around until (...) (25 years ago, 21-Jul-99, to lugnet.robotics.rcx)
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Message is in Reply To:
| | rcxhttpd?
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| (OK, I know this sounds perverse, but heck, some high-end printers these days are coming with built-in webservers for configuration, so it's not that perverse.) Has anyone written an HTTP daemon for the RCX? I mean a scaled-down version of httpd (...) (25 years ago, 17-Jul-99, to lugnet.robotics.rcx)
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