Lua is a powerful light-weight programming language designed for extending applications. Lua is designed and implemented by a [http://www.lua.org/authors.html team] at [http://www.puc-rio.br/ PUC-Rio], the Pontifical Catholic University of Rio de Janeiro in Brazil. Lua was born and raised at [http://www.tecgraf.puc-rio.br/ Tecgraf], the Computer Graphics Technology Group of PUC-Rio, and is now housed at [http://www.lua.org Lua.org]. Both Tecgraf and Lua.org are laboratories of the [http://www.inf.puc-rio.br/ Department of Computer Science]. Lua's been added to ethereal as for prototyping and scripting.
For more information about Lua refer to [http://www.lua.org Lua's main site], there you can find its [http://www.lua.org/manual/5.0/manual.html Reference Manual] and a [http://www.lua.org/pilhttp://www.lua.org/pil book] that describes the language.
Lua in Ethereal
Lua can be used to write [:Lua/Dissectors: dissectors], post-dissectors and [:Lua/Taps: taps].
Although it's possible to write [:Lua/Dissectors: dissectors] in Lua, ethereal dissectors are written in C, as C is several times faster than Lua. Lua is ok for prototyping dissectors, during Reverse Engineering you can use your time for finding out how things work instead of compiling and debugging your C dissector.
Post-dissectors are dissectors meant to run after every other dissector has run. They can add items the dissection tree so they can be used to create your own extensions to the filtering mechanism.
[:Lua/Taps: Taps] are used to collect information after the packet has been dissected.
- [:Lua/Tap: Tap]
- [:Lua/Field: Field] a handy tool to get fileds from the tree
- [:Lua/Proto: Proto] represents a protocol
[:Lua/ProtoField: ProtoField] the fields of a protocol
- [:Lua/Dissector: Dissector] utility class to handle dissectors
[:Lua/Dissector: DissectorTable] utility class to handle dissectors
- [:Lua/Pinfo: Pinfo] current packet information
[:Lua/SubTree: SubTree] subtrees
- [:Lua/Tvb: Tvb] access to the packet's actual bytes
[:Lua/ByteArray: ByteArray] utility class to manage an array of bytes
Examples of generic Lua code can be found in [http://lua-users.org/wiki/SampleCode The Sample Code] page of Lua-Users wiki.
- [:Lua/Examples/Tap: tap example]
- [:Lua/Examples/Dissector: dissector example]
- [:Lua/Examples/PostDissector: post-dissector example]
This page is a good start. However, some things remain unclear:
- How to install/use lua?
- What's the difference between a post-dissector and a tap
That's what it is, a start... I think it's soon to complete as things are changing as I go ahead.
So far it works only on *NIX as I'm still bringing it up. If you want the lua plugin installed configure --with-lua=<lua_directory> to get it to work for windows I'll need help.
- I do not have yet a clear idea on how Lua will be invoked from ethereal. So far it either looks for ~/.ethereal/init.lua and loads that script or looks for the pointed by the environment variable ETHEREAL_LUA_INIT, but that's a temporary solution. It will change as soon as I (or someone else, proposals are welcome) come out with a good way to do it.
- -- Luis E. G. O.