Catch back trace information without exit - lua

I'm trying to run a series of tests and collect some meta data on each test. If there is an error during one of the tests, I would like to save the back trace information but not to exit the script. For example:
-- Example program
for _, v in ipairs(tests) do
--check some results of function calls
if v == nil then
--error("function X failed") no exit
--save back trace to variable/file
-- continue with program
end
end
I'm not currently aware if it is possible in lua to tell the function error()
not to stop after creating the back trace. Any thoughts on how to do this?

debug.traceback ([thread,] [message [, level]]) (source) is what you're looking for. You can write a function that 1. gets a traceback 2. opens a file 3. writes the traceback to the file 4. closes the file.
In that case you'd have to use a level of 2, since 0 would be the debug.traceback function, 1 would be the function calling it (i.e. your function) and 2 the funcion calling that one. message could be your error code. Then you just override the error function locally in your script and you're done; calling error will just log the error and not exit the program.
EDIT: You can also override error globally, if you want, but that might lead to unexpected results if something goes terribly wrong somewhere else (code that you didn't write yourself) and the program continues nonetheless.
You'd be better off with a construct like this:
if os.getenv 'DEBUG' then
my_error = function()
-- what I explained above
end
else
my_error = error
end
and just use my_error in all the places where you'd usually use error.

Related

Lua io.popen freezing after a while of reading a log file

I'm attempting to constantly read and parse a log file (Minecraft log file) by using io.popen in tandem with Ubuntu's tail command so that I can send some messages upon certain events.
Now, I have mostly everything working here, except one small issue. After a while of reading, the entire program just freezes.
Here is the relevant code:
-- Open the tail command, return a file handle for it.
local pop = io.popen(config.listen_command)
-- Simply read a single line, I've pulled this into its own
-- function so that if this ever needs changing I can do so
-- easily.
local function get_line()
logger:log(4, "READ LINE")
return pop:read("*l")
end
-- For each line in the log file, check if it matches any
-- of a list of patterns, return the matches and the
-- pattern information if so.
local function match_line()
local line = get_line()
logger:log(4, "Line: %s", line)
-- This all works, and I've tested that it's not freezing
-- here. I've just included it for completion of the call
-- -stack.
for event_type, data in pairs(config.message_patterns) do
for event_name, pattern in pairs(data) do
local matches = {line:match(pattern)}
if matches[1] then
return event_type, event_name, matches
end
end
end
end
-- The main loop, simply read a line and send a message
-- if there was a match.
logger:log(4, "Main loop begin.")
while true do
local event_type, event_name, matches = match_line()
-- ...
-- The rest of the code here is not relevant.
config.listen_command = "tail -F --lines=1 latest.log"
The issue is in the get_line function. After a while of reading the log file, it completely freezes on the pop:read("*l"). It prints the READ LINE message, but never prints the Line: <whatever data here> line.
This is a really strange issue that I've been getting really confused about. I've tried swapping to different distributions of Lua (Luvit, LuaJIT, Lua) and a very large amount of debugging, changing small things, rerunning, ... But I cannot think of anything that'd be causing this.
Perhaps there's something small I've missed.
So my question here is this: Why is pop:read("*l") freezing, even though more data is being outputted to the logfile? Is there a way to fix this? Perhaps to detect if the next read will freeze indefinitely, so I can try closing the popen'ed file and re-open it (or to preferably stop it happening altogether?)

Basic LUA problems

I'm using ComputerCraft, a Minecraft mod that adds computers, monitors, modems and so on, which can be programmed using Lua scripts.
http://www.computercraft.info/wiki/Main_Page
While running my script I get this error: "bios:171: bad argument: string expected, got nil".
I dont understand because it says line 171 even though my code doesn't exceed 30 lines.. Can somebody explain?
monitor = peripheral.wrap("right")
monitor.clear()
monitor.setCursorPos(1, 1)
monitor.setTextScale(1)
monitor.write("Current mode:")
monitor.setCursorPos(1, 3)
monitor.write("furnace")
redstone.setOutput("back", false)
print("blablabla")
write()
if input == ja then
print("k")
redstone.setOutput("back", true)
monitor.clear()
monitor.setCursorPos(1, 1)
monitor.write("blabla")
else
print("u sux")
end
help would be highly appreciated.
You invoked an error in bios.lua which implements functions you can use in your script. Like write.
If we take a look into bios.lua we see that line 171 is actually part of the implementation of write.
It says: while string.len(sText) > 0 do, where sText
is the input argument to function write( sText ) in line 154.
There is no proper error handling or default value for the case that sText is nil. The programmer did a sloppy job here.
In that case string.len(sText) in line 171 will causes the error you received.
In order to fix that you have to either remove the empty call to write, which is equivalent to write(nil) or you have to provide some input string.
write("something") will not cause any error. If you want to print an empty string just call write("").

Run script instructions from external source in Lua

Ok, I'm wanting to know if there's a way of running scripts from an external source with Lua. Be it another file in .txt format or from pastebin, what have you, and run the code and wait for said code to finish, and then continue on with the rest of the function. I'm not quite sure at all about how it'd work, but this is basically the idea I'm going by and isn't actual code.
function runStuff()
print("checking for stuff")
run.script(derp.txt)
wait for script
if run.script == finished
continue program
elseif nil
print("looks like this script sucks.")
end
end
runStuff()
And for example what "derp.txt" contains is:
function lookFile()
if herp.txt exists then
rename herp.txt to herp.lua
else
nil
end
end
lookFile()
I'm still new to Lua so I'm coding like a moron here, but you get my picture hopefully. I'm working on a project that'll act like an installer package for repositories based from pastebin or anywhere else that'll supply raw format outputs of lua scripts and I'm going to use that idea for it to call on scripts to run externally. So when I supply a "First Time Run" version of the program, it'll call out to a lua script that'll call to another lua script and install that script, then close.
This is for minecraft, mind you. ComputerCraft made me take interest in Lua, but anyway, hopefully you got the gist of what I'm trying to figure out. Hopefully that's doable and if not, I'll just have to figure something else out.
To load and execute a Lua code fragment you can use something like this:
local http = require("socket.http")
local response, err = http.request("url to some Lua code")
if not response then error(err) end
local f, err = (loadstring or load)(response)
if not f then error(err) end
print("done with "..response)
-- make sure you read on (in)security implications of running remote code
-- f() -- call the function based on the remote code
You probably need to use sandboxing.

Calling back to a main file from a dofile in lua

Say i have two files:
One is called mainFile.lua:
function altDoFile(name)
dofile(debug.getinfo(1).source:sub(debug.getinfo(1).source:find(".*\\")):sub(2)..name)
end
altDoFile("libs/caller.lua")
function callBack()
print "called back"
end
doCallback()
The other called caller.lua, located in a libs folder:
function doCallback()
print "performing call back"
_G["callBack"]()
end
The output of running the first file is then:
"performing call back"
Then nothing more, i'm missing a line!
Why is callBack never getting executed? is this intended behavior, and how do i get around it?
The fact that the function is getting called from string is important, so that can't be changed.
UPDATE:
I have tested it further, and the _G["callBack"] does resolve to a function (type()) but it still does not get called
Why not just use dofile?
It seems that the purpose of altDoFile is to replace the running script's filename with the script you want to call thereby creating an absolute path. In this case the path for caller.lua is a relative path so you shouldn't need to change anything for Lua to load the file.
Refactoring your code to this:
dofile("libs/caller.lua")
function callBack()
print "called back"
end
doCallback()
Seems to give the result you are looking for:
$ lua mainFile.lua
performing call back
called back
Just as a side note, altDoFile throws an error if the path does not contain a \ character. Windows uses the backslash for path names, but other operating systems like Linux and MacOS do not.
In my case running your script on Linux throws an error because string.find returns nill instead of an index.
lua: mainFile.lua:2: bad argument #1 to 'sub' (number expected, got nil)
If you need to know the working path of the main script, why not pass it as a command line argument:
C:\LuaFiles> lua mainFile.lua C:/LuaFiles
Then in Lua:
local working_path = arg[1] or '.'
dofile(working_path..'/libs/caller.lua')
If you just want to be able to walk back up one directory, you can also modify the loader
package.path = ";../?.lua" .. package.path;
So then you could run your file by doing:
require("caller")
dofile "../Untitled/SensorLib.lua" --use backpath librarys
Best Regards
K.

Getting return status AND program output

I need to use Lua to run a binary program that may write something in its stdout and also returns a status code (also known as "exit status").
I searched the web and couldn't find something that does what I need. However I found out that in Lua:
os.execute() returns the status code
io.popen() returns a file handler that can be used to read process output
However I need both. Writing a wrapper function that runs both functions behind the scene is not an option because of process overhead and possibly changes in result on consecutive runs. I need to write a function like this:
function run(binpath)
...
return output,exitcode
end
Does anyone has an idea how this problem can be solved?
PS. the target system rung Linux.
With Lua 5.2 I can do the following and it works
-- This will open the file
local file = io.popen('dmesg')
-- This will read all of the output, as always
local output = file:read('*all')
-- This will get a table with some return stuff
-- rc[1] will be true, false or nil
-- rc[3] will be the signal
local rc = {file:close()}
I hope this helps!
I can't use Lua 5.2, I use this helper function.
function execute_command(command)
local tmpfile = '/tmp/lua_execute_tmp_file'
local exit = os.execute(command .. ' > ' .. tmpfile .. ' 2> ' .. tmpfile .. '.err')
local stdout_file = io.open(tmpfile)
local stdout = stdout_file:read("*all")
local stderr_file = io.open(tmpfile .. '.err')
local stderr = stderr_file:read("*all")
stdout_file:close()
stderr_file:close()
return exit, stdout, stderr
end
This is how I do it.
local process = io.popen('command; echo $?') -- echo return code of last run command
local lastline
for line in process:lines() do
lastline = line
end
print(lastline) -- the return code is the last line of output
If the last line has fixed length you can read it directly using file:seek("end", -offset), offset should be the length of the last line in bytes.
This functionality is provided in C by pclose.
Upon successful return, pclose() shall return the termination status
of the command language interpreter.
The interpreter returns the termination status of its child.
But Lua doesn't do this right (io.close always returns true). I haven't dug into these threads but some people are complaining about this brain damage.
http://lua-users.org/lists/lua-l/2004-05/msg00005.html
http://lua-users.org/lists/lua-l/2011-02/msg00387.html
If you're running this code on Win32 or in a POSIX environment, you could try this Lua extension: http://code.google.com/p/lua-ex-api/
Alternatively, you could write a small shell script (assuming bash or similar is available) that:
executes the correct executable, capturing the exit code into a shell variable,
prints a newline and terminal character/string onto standard out
prints the shell variables value (the exit code) onto standard out
Then, capture all the output of io.popen and parse backward.
Full disclosure: I'm not a Lua developer.
yes , your are right that os.execute() has returns and it's very simple if you understand how to run your command with and with out lua
you also may want to know how many variables it returns , and it might take a while , but i think you can try
local a, b, c, d, e=os.execute(-what ever your command is-)
for my example a is an first returned argument , b is the second returned argument , and etc.. i think i answered your question right, based off of what you are asking.

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