Lua

Count the DKIM Signatures in a Message

Demonstrates the Chilkat Dkim.NumDkimSigs method, which returns the number of DKIM-Signature header fields in a MIME message. The only argument is a BinData holding the complete MIME.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: A message can legitimately carry several DKIM signatures — the original sender's plus ones added by forwarders or mailing lists — so a verifier needs to know how many there are before checking each. This count is what supplies the valid index range for DkimVerify. Note that it counts header fields by name only, without validating them, so a malformed DKIM-Signature field is still included in the total.

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Lua

local chilkat = require("chilkat")

-- Demonstrates the Dkim.NumDkimSigs method, which returns the number of DKIM-Signature header
-- fields in a MIME message.  The only argument is a BinData holding the complete MIME.

local dkim = chilkat.Dkim.new()

-- Load the complete MIME message.
local mimeData = chilkat.BinData.new()
local success = mimeData:load_file("qa_data/received.eml")
if not success then
    print(mimeData.last_error_text)
    return
end

-- Count the DKIM-Signature header fields.  The count includes malformed signatures, since the
-- fields are counted without validating their syntax.
local numSigs = dkim:num_dkim_sigs(mimeData)
print("The message has " .. numSigs .. " DKIM-Signature header(s).")