Zig

Add a Related File to an HTML Email

Demonstrates the Chilkat Email.AddRelatedFile method, which adds the contents of a local file as a related MIME resource and returns the generated Content-ID. The returned value is the bare Content-ID — no angle brackets and no cid: prefix — so if it returns CID-123@example, the HTML reference is cid:CID-123@example. Because the Content-ID is generated by the call, this example adds the image first, then builds the HTML body in a StringBuilder — using a placeholder in the <img> tag that is replaced with the returned Content-ID — and passes the result to SetHtmlBody.

Background: To embed an image so it displays inside an HTML email (rather than being downloaded from a web server), you add it as a "related" part and reference it from the HTML with a cid: URL that matches the part's Content-ID. Since Chilkat assigns that ID when you add the file, the natural order is: add the related file, capture the returned ID, then build the <img src="cid:..."> reference from it. A StringBuilder makes assembling and updating the HTML convenient.

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Zig

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

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

    // Demonstrates the AddRelatedFile method, which adds a local file as a related MIME
    // resource (such as an image displayed by an HTML body) and returns the generated
    // Content-ID.  The HTML references the item using cid:<Content-ID>.

    const email = try chilkat.Email.init();
    defer email.deinit();
    email.setSubject("Email with a related image");

    // Add the image file as a related item first.  The return value is the bare Content-ID
    // (no angle brackets and no "cid:" prefix).
    const cid = email.addRelatedFile(alloc, "qa_data/images/logo.png") catch {
        std.debug.print("{s}\n", .{try email.getLastErrorText(alloc)});
        return;
    };

    // Build the HTML body in a StringBuilder, using a placeholder where the image's
    // Content-ID will go.
    const sb_html = try chilkat.StringBuilder.init();
    defer sb_html.deinit();
    sb_html.append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>") catch {};

    // Replace the placeholder with the actual Content-ID returned by AddRelatedFile.
    _ = sb_html.replace("PLACEHOLDER_CID", cid);

    // Set the HTML body from the StringBuilder result.
    email.setHtmlBody(try sb_html.getAsString(alloc));

    std.debug.print("Related Content-ID = {s}\n", .{cid});
    std.debug.print("NumRelatedItems = {d}\n", .{email.getNumRelatedItems()});

    // Note: The path "qa_data/images/logo.png" is a relative local filesystem path,
    // relative to the current working directory of the running application.
}