PureBasic

Prefetch a DKIM Public Key from DNS

Demonstrates the Chilkat Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and caches it for a specific selector and domain. The arguments are the selector and the domain. The TXT lookup is made at selector._domainkey.domain.

Background: DkimVerify already fetches the key from DNS on demand, so prefetching is about when the lookup happens: doing it up front lets you separate a potentially slow network step from the verification itself, warm the cache before a batch of messages from the same domain, or confirm the key is publishable before relying on it. After a successful prefetch, verification of a matching signature uses the cached key with no further DNS traffic.

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IncludeFile "CkDkim.pb"

Procedure ChilkatExample()

    success.i = 0

    ;  Demonstrates the Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and
    ;  caches it for a specific selector and domain.  The 1st argument is the selector and the 2nd is
    ;  the domain.

    dkim.i = CkDkim::ckCreate()
    If dkim.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ;  Retrieve the public key from the DNS TXT record at selector._domainkey.domain and cache it.
    ;  A later DkimVerify for the same selector and domain then uses the cached key.
    success = CkDkim::ckPrefetchPublicKey(dkim,"myselector","example.com")
    If success = 0
        Debug CkDkim::ckLastErrorText(dkim)
        CkDkim::ckDispose(dkim)
        ProcedureReturn
    EndIf

    Debug "Public key prefetched from DNS and cached."


    CkDkim::ckDispose(dkim)


    ProcedureReturn
EndProcedure