Helping nodecentral with multipart post

multipart.lua

-- see https://github.com/catwell/lua-multipart-post/issues/8#issuecomment-1307934583
-- fixed version (see diff)

local http = require("socket.http")
local ltn12 = require("ltn12")
local lfs = require "lfs"
http.TIMEOUT = 5

local function upload_file ( url, filename )
    local fileHandle = io.open( filename,"rb")
    local fileContent = fileHandle:read( "*a" )
    fileHandle:close()

    local boundary = 'abcd'

    local header_b = 'Content-Disposition: form-data; name="document"; filename="' .. filename .. '"\r\nContent-Type: application/pdf'
    local header_c = 'Content-Disposition: form-data; name="title"\r\n\r\nCompanies House File'
    local header_d = 'Content-Disposition: form-data; name="correspondent"\r\n\r\n12'

    local MP_b = '--'..boundary..'\r\n'..header_b..'\r\n\r\n'..fileContent..'\r\n'
    local MP_c = '--'..boundary..'\r\n'..header_c..'\r\n'
    local MP_d = '--'..boundary..'\r\n'..header_d..'\r\n'

    local MPCombined = MP_b..MP_c..MP_d..'--'..boundary..'--\r\n'

    local   response_body = { }
    local   _, code = http.request {
            url = url ,
            method = "POST",
            headers = {    ["Content-Length"] =  MPCombined:len(),
                           ['Content-Type'] = 'multipart/form-data; boundary=' .. boundary
                         },
            source = ltn12.source.string(MPCombined) ,
            sink = ltn12.sink.table(response_body),
                }
     return code, table.concat(response_body)
end

 local rc,content = upload_file ('http://httpbin.org/post', '/mnt/nas/10.pdf' )
 print(rc,content)