Zig

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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const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

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

    const email = try chilkat.Email.init();
    defer email.deinit();
    email.setSubject("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.
    const cid = email.addRelatedString(alloc, "styles.css", "body { color: black; }", "utf-8") catch {
        std.debug.print("{s}\n", .{try email.getLastErrorText(alloc)});
        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.
    const sb_html = try chilkat.StringBuilder.init();
    defer sb_html.deinit();
    sb_html.append("<html><head><link rel=\"stylesheet\" href=\"cid:PLACEHOLDER_CID\"/></head><body>Styled content.</body></html>") catch {};
    _ = sb_html.replace("PLACEHOLDER_CID", cid);
    email.setHtmlBody(try sb_html.getAsString(alloc));

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

    // The custom header now appears in the related item's MIME part.
    std.debug.print("{s}\n", .{try email.getMime(alloc)});
}