Add a Custom Header to a Related Item

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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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#include <C_CkEmail.h>
#include <C_CkStringBuilder.h>

void ChilkatSample(void)
    {
    HCkEmail email;
    const char *cid;
    HCkStringBuilder sbHtml;
    int numReplaced;

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

    email = CkEmail_Create();
    CkEmail_putSubject(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 = CkEmail_addRelatedString(email,"styles.css","body { color: black; }","utf-8");
    if (CkEmail_getLastMethodSuccess(email) == FALSE) {
        printf("%s\n",CkEmail_lastErrorText(email));
        CkEmail_Dispose(email);
        return;
    }

    //  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 = CkStringBuilder_Create();
    CkStringBuilder_Append(sbHtml,"<html><head><link rel=\"stylesheet\" href=\"cid:PLACEHOLDER_CID\"/></head><body>Styled content.</body></html>");
    numReplaced = CkStringBuilder_Replace(sbHtml,"PLACEHOLDER_CID",cid);
    CkEmail_SetHtmlBody(email,CkStringBuilder_getAsString(sbHtml));

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

    //  The custom header now appears in the related item's MIME part.
    printf("%s\n",CkEmail_getMime(email));


    CkEmail_Dispose(email);
    CkStringBuilder_Dispose(sbHtml);

    }