lua filter with http request seg faults

[titibandit]

Hello,

I would like to use a lua filter that replaces links with the result of an https request.
So I wrote a lua script that fetches the data over the internet. As a standalone Lua script, this works well. However, when passed as a lua filter, the pandoc executable segfaults.
This is the (redacted) script:

local https = require "ssl.https"
local http = require "socket.http"
local ltn12 = require "ltn12"
local json = require "dkjson"

http.TIMEOUT=50
https.TIMEOUT=50

function api_call (query)
   local response_body = {}
   local r, c, h, s = https.request {
      url = 'https://gitlab.org/api/graphql',
      method = 'GET',
      headers = {
	 ["Content-Type"] = "application/json",
	 ["Content-Length"] = query:len(),
	 ["Authorization"] = "Bearer xxxxxxxxxxxxxxxxxxxxxxxxxxx"
      },
      source = ltn12.source.string(query),
      sink = ltn12.sink.table(response_body)
   }

   local obj, pos, err = json.decode(response_body[1], 1, nil)
   return obj
end

function get_issue_title (iid)
   local result = api_call('{"query": "query {project(fullPath: \\"some-project\\") {name issue(iid: \\"'.. iid ..'\\"){title}}}"}')
   return result.data.project.issue.title
end


function Link(el)
    el.content = get_issue_title(143)
   return el
end

Debugging pandoc using gdb, I gather that the tm object in not initialized (address of 0x0) in timeout.c line 81 of the luasocket module.
https://github.com/lunarmodules/luasocket/blob/e13de2013749961edaa126697f3290d3dca91823/src/timeout.c#L81

I have no clue why that would work in lua as is and not as a filter.
Thanks for any insight.

[tarleb]

What happens if you run the script with pandoc lua YOUR-SCRIPT.lua?

My first guess would be a version problem, maybe luasocket was compiled against a different Lua version. What does lua -v return?

[tarleb]

More ideas: the pandoc.mediabag.fetch function can be shoehorned into making GET requests. The Authorization header would have to be set via the request-header options, e.g., pandoc --request-header 'Authorization: Bearer xxxxxxx' …. This may allow to work around the issue, but it's not a full http library.

[titibandit]

Hello Tarleb,

What happens if you run the script with pandoc lua YOUR-SCRIPT.lua?

This produces no output and returns successfully (exit code 0).

My first guess would be a version problem, maybe luasocket was compiled against a different Lua version. What does lua -v return?

Lua 5.4.7  Copyright (C) 1994-2024 Lua.org, PUC-Rio

Does this suggest a version problem?

[tarleb]

This looks ok, version wise.

Since you're sending content, you'll probably want to use a POST request. Also, make sure to check the https.request results for errors.

[kainctl]

Hey, i haven't tested your code but instead of using gdb I prefer to use https://github.com/slembcke/debugger.lua
Then you can set a breakpoint and inspect all the different values.

[titibandit]

Since you're sending content, you'll probably want to use a POST request.

Oh you're right, POST is right-er. Using lua standalone, my script works (both with GET or POST requests), but as a pandoc filter, it still segfaults (both GET and POST)...

Also, make sure to check the https.request results for errors.

I'm not sure how to do that since the program crashes? It is the call to https.request that segfaults the script.