Lua

Monitor and Cancel a Running DKIM Operation

Demonstrates the Chilkat Dkim.HeartbeatMs and Dkim.AbortCurrent properties, which monitor and cancel a long-running operation such as a DNS public-key lookup. HeartbeatMs sets how often an AbortCheck event fires, and AbortCurrent requests cancellation.

Background: Most Dkim work is instant, but anything touching DNS can stall on a slow or unresponsive server. HeartbeatMs makes the object emit a periodic AbortCheck callback during such calls so an application stays responsive and can show progress, and AbortCurrent — set from that callback or from another thread — breaks a blocked synchronous call out early. Together they turn an otherwise uninterruptible operation into a cancellable one.

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Lua

local chilkat = require("chilkat")

-- Demonstrates the Dkim properties HeartbeatMs and AbortCurrent, which monitor and cancel a
-- long-running operation such as a DNS public-key lookup.

local dkim = chilkat.Dkim.new()

-- Fire an AbortCheck event callback every 100 ms during method calls.  In programming languages
-- where Chilkat supports event callbacks, the callback can request cancellation.
dkim.heartbeat_ms = 100

-- AbortCurrent may be set to true to request cancellation of a running operation.  It is
-- typically set from another thread, or from within an AbortCheck callback.  Setting it false
-- here ensures the operation is not pre-emptively aborted.
dkim.abort_current = false

-- PrefetchPublicKey performs a synchronous DNS lookup, which HeartbeatMs monitors and
-- AbortCurrent can cancel.
local success = dkim:prefetch_public_key("myselector", "example.com")
if not success then
    print(dkim.last_error_text)
    return
end

print("Public key prefetched.")