attempt to index global index 'zmq' (a nil value)

[dustingooding]

I'm trying to use your Lua bindings for ZMQ, but am not having much luck.

I'm running Ubuntu 11.10 (up to date). I installed ZMQ from the Ubuntu package (sudo apt-get install libzmq-dev libzmq1). Then I used the instructions here to install lua-zmq using CMake (as I didn't have luarocks installed, yet). I didn't see any errors during the install.

I copy-pasted an example from zeromq.org (http://zguide.zeromq.org/lua:interrupt) but it fails to execute. The example, as written, gives the following output:

$ lua -i interruptTest.lua 
Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
lua: interruptTest.lua:7: module 'zhelpers' not found:
    no field package.preload['zhelpers']
    no file './zhelpers.lua'
    no file '/usr/local/share/lua/5.1/zhelpers.lua'
    no file '/usr/local/share/lua/5.1/zhelpers/init.lua'
    no file '/usr/local/lib/lua/5.1/zhelpers.lua'
    no file '/usr/local/lib/lua/5.1/zhelpers/init.lua'
    no file '/usr/share/lua/5.1/zhelpers.lua'
    no file '/usr/share/lua/5.1/zhelpers/init.lua'
    no file '/opt/ros/electric/stacks/orocos_toolchain/ocl/lua/modules/zhelpers.lua'
    no file './zhelpers.so'
    no file '/usr/local/lib/lua/5.1/zhelpers.so'
    no file '/usr/lib/x86_64-linux-gnu/lua/5.1/zhelpers.so'
    no file '/usr/lib/lua/5.1/zhelpers.so'
    no file '/usr/local/lib/lua/5.1/loadall.so'
stack traceback:
    [C]: in function 'require'
    interruptTest.lua:7: in main chunk
    [C]: ?

Sure enough, "zhelpers.h" is nowhere to be found on my machine. I don't blame lua-zmq for this. So, I comment out the require"zhelpers" line and run again.

$ lua -i interruptTest.lua 
Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
lua: interruptTest.lua:9: attempt to index global 'zmq' (a nil value)
stack traceback:
    interruptTest.lua:9: in main chunk
    [C]: ?

This, I believe is a problem. Lua had no problem with require"zmq", but it did when I attempt to use zmq functionality. What am I missing?

For completeness, I installed the Ubuntu package for Lua's Python bindings (sudo apt-get install python-zmq) and attempted running the companion example (http://zguide.zeromq.org/py:interrupt), and I had no trouble. So, this tells me ZMQ is installed correctly and bindings work.

I went to reinstall lua-zmq using Ubuntu's package for luarocks (sudo apt-get install luarocks). I used the first instruction (sudo luarocks install https://github.com/Neopallium/lua-zmq/raw/master/rockspecs/lua-zmq-scm-1.rockspec), but because I'm behind a firewall, I'm unable to use the git:// protocol to access github.com. So, I just downloaded the rockspec, changed the url line:

package = "lua-zmq"
version = "scm-1"
source = {
        url = "https://github.com/Neopallium/lua-zmq.git",
}
...

But, even that fails.

$ sudo luarocks install lua-zmq-scm-1.rockspec 

Error: Error fetching file: Failed downloading https://github.com/Neopallium/lua-zmq.git

I really would like to use your software, but I'm just having the worst luck. Any help?

[dustingooding]

Forgive me. I'm still new to Lua.

Apparently I was supposed to use zmq = require"zmq", not just require"zmq".

And apparently luarocks doesn't support the smart http protocol.

[Neopallium]

the zhelpers.lua file is located at:
https://github.com/imatix/zguide/blob/master/examples/Lua/zhelpers.lua

When running the Lua examples from the guide it is best to download all the *.lua files from this folder:
https://github.com/imatix/zguide/blob/master/examples/Lua/

Older releases of lua-zmq had registered the module as the global "zmq". But it seems the Lua community is recommending that module don't create globals and just return a value during initialization.

New code should do:
local zmq = require"zmq"

For now I have change lua-zmq to still create a global for the module, until I have time to update the examples in the zmq guide.

When using a "https://" url luarocks doesn't know that it is a git repository. Maybe report this issue to the luarocks mailing list:
http://luarocks.org/en/Mailing_list
since other people behind firewalls may have the same problem.

LuaRocks should add support for using an http proxy for accessing repositories from behind firewalls:
http://stackoverflow.com/questions/128035/how-do-i-pull-from-a-git-repository-through-an-http-proxy