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luaJIT error handling with FFI calls a non-existent method – Nginx

What I want to avoid is to capture/ignore the exception when FFI calls a non-existent method.

For example, the following code calls the non_existent_method. However, pcall cannot handle the error.

local ffi = require "ffi"
local C = ffi.C

ffi.cdef [[
    int non_existent_method(int num);
]]

local ok, ret = pcall(C.non_existent_method, 1)

if not ok then
    return
end

I got the following error with OpenResty/lua-nginx-module.

lua entry thread aborted: runtime error: dlsym(RTLD_DEFAULT, awd): symbol not found
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2

Answers


  1. Chosen as BEST ANSWER
    0

    One possible solution would be wrapping the C.non_existent_method call with a lua function.

    For example

    
local ok, ret = pcall(function()
    return C.non_existent_method(len)
end)

if not ok then
    ......
end

  2. 0

    One more apporach would be to call the index metamethod directly:
    You might want to wrap that into a function:

    
local ffi_mt = getmetatable(ffi.C)
function is_valid_ffi_call(sym)
  return pcall(ffi_mt.__index, ffi.C, sym) 
end

    example:

    
ffi.cdef[[void (*foo)();]]
ffi.cdef[[int puts(const char *);]]

a,func = is_valid_ffi_call("foo")
-- false, "error message: symbol not found or missing declaration, whatever it is"

a,func = is_valid_ffi_call("puts")
-- true, cdata<int ()>: 0x7ff93ad307f0
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