lua: ./9p.lua:138: attempt to get length of local 'from' (a nil value)

[metacoma]

There are two public 9p fileservers (without any authentication) and hosted by different OS/Platforms

• tcp!9p.io!564 (9front OS)
• tcp!registry.demo.metacoma.io!30099 (Inferno OS)

1. If we connect to tcp!9p.io!564 and call Twalk ./ - everything is fine
2. If we connect to tcp!9p.io!564 and call Twalk / then get error lua: ./9p.lua:138: attempt to get length of local 'from' (a nil value)
3. If we connect to tcp!registry.demo!metacoma.io!30099 and call Twalk ./ then get error lua: ./9p.lua:118: file does not exist
4. If we connect to tcp!registry.demo!metacoma.io!30099 and call Twalk / then get error lua: ./9p.lua:138: attempt to get length of local 'from' (a nil value)
5. If we connect to tcp!registry.demo.metacoma.io!30099 and call Twalk ../ - everything is fine
6. If we connect to tcp!9p.io!564 and call Twalk ../ - everything is fine, but the result is different from Twalk ./

How to call properly Twalk against root(/) path of these fileservers in the same way?

Steps to reproduce:

$ git clone -b 9p_walk_bug github.com/metacoma/lua9p
$ cd lua9p
#
# 1 case
#
$ lua ./tcp_testclient.lua 'tcp!9p.io!564' './'                 
Connecting to tcp!9p.io!564
Walking on ./
#
# 2 case
# 
$ lua ./tcp_testclient.lua 'tcp!9p.io!564' '/'
Connecting to tcp!9p.io!564
Walking on /
lua: ./9p.lua:138: attempt to get length of local 'from' (a nil value)
#
# 3 case
# 
$ lua ./tcp_testclient.lua 'tcp!registry.demo.metacoma.io!30099' '/'  
$ Connecting to tcp!registry.demo.metacoma.io!30099
Walking on /
lua: ./9p.lua:118: file does not exist
#
# 4 case
# 
$ lua ./tcp_testclient.lua 'tcp!registry.demo.metacoma.io!30099' './'  
$ Connecting to tcp!registry.demo.metacoma.io!30099
Walking on ./
lua: ./9p.lua:138: attempt to get length of local 'from' (a nil value)
#
# 5 case
# 
$ lua ./tcp_testclient.lua 'tcp!registry.demo.metacoma.io!30099' '../'
Connecting to tcp!registry.demo.metacoma.io!30099
Walking on ../
Ok
#
# 6 case
# 
$ lua ./tcp_testclient.lua 'tcp!9p.io!564' '../'                 
Connecting to tcp!9p.io!564
Walking on ../
Ok

[iru-]

Good catch, @metacoma!

I couldn't clone your 9p_walk_bug branch, but I wrote two scripts to reproduce the issue (https://gist.github.com/iru-/717ab72326d2f9889a5ab2aae94aa51e). See their output below:

% ./test_walk_bug.sh
case 1
connected to tcp!9p.io!564
walking on "./"
ok! "./" on fid 1

case 2
connected to tcp!9p.io!564
walking on "/"
./9p.lua:138: attempt to get length of a nil value (local 'from')

case 3
connected to tcp!registry.demo.metacoma.io!30099
walking on "/"
./9p.lua:138: attempt to get length of a nil value (local 'from')

case 4
connected to tcp!registry.demo.metacoma.io!30099
walking on "./"
./9p.lua:118: file does not exist

case 5
connected to tcp!registry.demo.metacoma.io!30099
walking on "../"
ok! "../" on fid 1

case 6
connected to tcp!9p.io!564
walking on "../"
ok! "../" on fid 1

The bug stems from incorrectly breaking paths into path elements for Twalk (see

lua9p/9p.lua

Line 307 in 07c4af2

local function breakpath(path)

).

The fix is available at https://github.com/iru-/lua9p/pull/4. The new test output is:

% ./test_walk_bug.sh
case 1
connected to tcp!9p.io!564
walking on "./"
ok! "./" on fid 1

case 2
connected to tcp!9p.io!564
walking on "/"
./9p.lua:118: file does not exist

case 3
connected to tcp!registry.demo.metacoma.io!30099
walking on "/"
./9p.lua:118: file does not exist

case 4
connected to tcp!registry.demo.metacoma.io!30099
walking on "./"
./9p.lua:118: file does not exist

case 5
connected to tcp!registry.demo.metacoma.io!30099
walking on "../"
ok! "../" on fid 1

case 6
connected to tcp!9p.io!564
walking on "../"
ok! "../" on fid 1

Do you confirm the fix works on your side?

[metacoma]

hey @iru- thank you for your rapid answer!

Sorry about the tcp_testclient.lua, I pushed it in the wrong place :( https://github.com/metacoma/lua9p/blob/a67faf06e616397339bd24285f87b26dea856e78/tcp_testclient.lua

Your fix helps, the problem attempt to get length of local 'from' (a nil value) is gone.

but I still don't understand, how to properly "generate" Twalk packet for walking "root(/)" on tcp!9p.io!564 and tcp!registry.demo.metacoma.io!30099 in the same way

[iru-]

What you want is most easily achieved by conn:clone(conn.rootfid, newfid), where newfid has already been allocated.

Even though not explicitly defined, in 9P parlance a "clone" is a walk with no paths to be walked to. The effect of this is to clone/duplicate the old fid into the new fid in the server and the client. You can think of it as the 9P analogous to the dup2 system call.

Let me know if that works for you. It worked here for both 9p.io and registry.demo.metacoma.io

[metacoma]

Thank you @iru- it works!

Also thanks to @dievri 9mine/9mine@a0d76fd...3346ddf

[iru-]

Awesome! Thanks again, @metacoma!

Since the bug has been fixed in 3af266d and your question has been answered, I'm closing the issue.