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96 lines
4.4 KiB
Plaintext
96 lines
4.4 KiB
Plaintext
T2hproxy
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This is a TFTP to HTTP proxy. To the TFTP client it looks like a TFTP
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server. To the HTTP server it looks like a HTTP client. So you can store
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your boot files on the HTTP server. Or even create them with a CGI
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program. E.g. if you can get dhcpd to send a filename which has strings
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representing attributes of the client, as determined from the DHCP
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request, then you can get the CGI program to parse this and send the
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appropriate image, which might even be synthesised.
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There are two versions of the proxy, in Perl and in Java.
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1. The Perl version.
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This is the original quick Perl hack conceived in a moment of madness.
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:-) Perl is great for prototyping.
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To run it, you need Perl 5.8.0 or later and all the Perl modules listed
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at the top of the program installed. Edit and install the xinetd config
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file as /etc/xinetd.d/t2hproxy and restart xinetd. The prefix is the
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string that is prepended to all filenames to form the URL requested from
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the HTTP server. Remember you need the trailing / if the filenames don't
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start with /.
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This is only a proof-of concept. It has these drawbacks at the moment:
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+ (I don't consider this a draback, but some may.) It's started from
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xinetd because xinetd handles all the socket listening, IP address
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checking, rate limiting, etc.
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+ It has no cache. Use a proxy to do the caching (there's a --proxy
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option). This also takes care of fetching from outside a firewall.
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+ It reads the entire HTTP content into memory before serving. Ideally
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it should stream it from the HTTP server to minimise memory usage. This
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is a serious drawback for booting lots of clients. Each instance of the
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server will consume an amount of memory equal to the size of image
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loaded.
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+ If the HTTP server is at the end of a slow link there is a delay
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before the first data block is sent. The client may timeout before
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then. Another reason for streaming, as this allows the first block to
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be sent sooner. A local cache primed with the images in advance may
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help. Using the blocksize option helps here because this causes the
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server to send the OACK to the client immediately before the data is
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fetched and this prevents it from starting up another connection.
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+ The transfer size may not be obtainable from the HTTP headers in all
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cases, e.g. a CGI constructed image. This matters for clients that need
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the tsize extension, which is not supported at the moment.
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If I'm feeling masochistic I may write a Java version, which should take
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care of the multi-threading and streaming.
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2. The Java version
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The main problem with the Perl version is that it does not stream the
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HTTP input but sucks it all in at once. As mentioned, this causes a
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delay as well as requiring memory to hold the image. I could fix this by
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doing the polling on the HTTP socket myself instead of letting LWP do
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it, but that's for later. Java has streaming facilities as well as
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threading and is also somewhat portable. So I decided to be masochistic
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and give it a go. But boy is Java bureaucratic.
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You will need a Java 1.4 JRE, because I use the java.nio classes; and
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the commons-httpclient and commons-logging jars from the
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jakarta.apache.org project. As I understand it, there are several ways
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to get those jars on your classpath. One is to put it in the directory
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where your java extensions jars are kept, normally
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$JAVA_HOME/jre/lib/ext. But it may not be writable to you. Another is to
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set your $CLASSPATH variable to have those jars in the path. A third is
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to use the -cp option of the java interpreter, see the shell script
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runT2hproxy for details.
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All the source is in one Java file. build.xml is a "Makefile" for ant to
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compile and jar it. You should then edit runT2proxy.sh as required, then
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start it. As with the Perl version, the prefix is what's prepended to
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the filenames requested by the TFTP client, and the proxy is the
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host:port string for the proxy if you are using one. On *ix you will
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need root permission to listen on ports below 1024 (TFTP is at 69 UDP by
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default).
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Currently it logs to stderr, but you can change this by downloading and
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installing the log4j jar from jakarta.apache.org and instructing
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commons-logging to use that, with a command line property setting and a
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property file. Destinations could be syslog, or a file, or an event
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logger, or...; it's supposedly very flexible.
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3. Licensing
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All this code is GPLed. For details read the file COPYING found in the
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Etherboot top directory since it currently bundled with Etherboot. I
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don't see the point of including COPYING in every directory.
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Ken Yap, October 2003
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