PureBasic

Add a Custom Header to a Related Item

Demonstrates the Chilkat Email.AddRelatedHeader method, which adds a custom MIME header field to an existing related item identified by its zero-based index. This example first adds a related style sheet (which becomes index 0) and captures its generated Content-ID, builds an HTML body that references the style sheet by that cid:, then attaches an extra header field to the related item and prints the resulting MIME.

Background: Like attachments, each related item (an inline image, style sheet, etc.) is a MIME part with its own small header block describing that part — Content-Type, Content-ID, Content-Location, and so on. AddRelatedHeader lets you insert additional fields into that per-part block, which is occasionally required for interoperability with clients that look for specific custom headers on embedded resources.

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IncludeFile "CkStringBuilder.pb"
IncludeFile "CkEmail.pb"

Procedure ChilkatExample()

    ;  Demonstrates the AddRelatedHeader method, which adds a custom MIME header field to an
    ;  existing related item, identified by its zero-based index.

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

    CkEmail::setCkSubject(email, "Related item with a custom header")

    ;  Add a related item first (a style sheet); capture its generated Content-ID.  It becomes
    ;  related-item index 0.
    cid.s = CkEmail::ckAddRelatedString(email,"styles.css","body { color: black; }","utf-8")
    If CkEmail::ckLastMethodSuccess(email) = 0
        Debug CkEmail::ckLastErrorText(email)
        CkEmail::ckDispose(email)
        ProcedureReturn
    EndIf

    ;  Build the HTML body, referencing the related style sheet by its Content-ID.  A
    ;  placeholder is used and then replaced with the actual Content-ID.
    sbHtml.i = CkStringBuilder::ckCreate()
    If sbHtml.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkStringBuilder::ckAppend(sbHtml,"<html><head><link rel=" + Chr(34) + "stylesheet" + Chr(34) + " href=" + Chr(34) + "cid:PLACEHOLDER_CID" + Chr(34) + "/></head><body>Styled content.</body></html>")
    numReplaced.i = CkStringBuilder::ckReplace(sbHtml,"PLACEHOLDER_CID",cid)
    CkEmail::ckSetHtmlBody(email,CkStringBuilder::ckGetAsString(sbHtml))

    ;  Add a custom header field to the first related item (index 0).
    CkEmail::ckAddRelatedHeader(email,0,"X-Custom-Related-Header","some value")

    ;  The custom header now appears in the related item's MIME part.
    Debug CkEmail::ckGetMime(email)


    CkEmail::ckDispose(email)
    CkStringBuilder::ckDispose(sbHtml)


    ProcedureReturn
EndProcedure