Custom logic with Lua

When template functions are not enough - parsing a complex field, a checksum, a lookup table - write the logic in Lua and call it from the template.

1. Write the function

bafi loads ./lua/functions.lua from the current directory the first time a template calls lua. Every function receives its arguments as one JSON-encoded array and must return a string. The json.lua helper that ships with bafi decodes the arguments:

json = require './lua/json'

-- IBAN check: move the first 4 characters to the end, letters to numbers, mod 97 must be 1
function ibanValid(incomingData)
    local iban = string.upper(string.gsub(json.decode(incomingData)[1], "%s", ""))
    local moved = string.sub(iban, 5) .. string.sub(iban, 1, 4)
    local digits = string.gsub(moved, "%a", function(c) return tostring(string.byte(c) - 55) end)
    local remainder = 0
    for i = 1, #digits do
        remainder = (remainder * 10 + tonumber(string.sub(digits, i, i))) % 97
    end
    return tostring(remainder == 1)
end

lua/json.lua must sit next to it (it is included in every release archive).

2. Call it from a template

owner,iban
Alice,CZ65 0800 0000 1920 0014 5399
Bob,CZ65 0800 0000 1920 0014 5398

bafi -i accounts.csv -t '?{{range .}}{{.owner}}: {{lua "ibanValid" .iban}}{{"\n"}}{{end}}'

Alice: true
Bob: false

Arguments are passed as {{lua "functionName" arg1 arg2 ...}}; in Lua, json.decode(incomingData)[1] is the first one (Lua lists start at 1).

Errors

Problems inside Lua do not stop the template; the function's place in the output shows the message instead, for example luaError: ... attempt to call a non-function object for a misspelled function name. Search the output for luaError when something looks wrong.

Security

./lua/functions.lua is code, and it runs with your permissions. Only use a lua/ directory you trust. bafi removes the functions that start programs or delete files (os.execute, io.popen, os.remove, ...); the rest of the Lua standard library works. More in Security notes.

The shipped example defines sum and mul: {{lua "sum" .val1 .val2}}.

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