Zig

Get a Header Attribute of a Related Item

Demonstrates the Chilkat Email.GetRelatedAttr method, which returns a header-field attribute value from a header field of the Nth related item. The first argument is the zero-based related-item index, the second names a header field, and the third names an attribute within it. This example loads an image from a file into a BinData object, adds it as a related item with AddRelatedBd (capturing the generated Content-ID and referencing it from the HTML), then reads the name attribute of the related item's Content-Type header.

Background: Related items (inline images, style sheets) are MIME parts whose headers may carry named parameters — for instance Content-Type: image/png; name="logo.png". Because an image is binary, it is loaded into a BinData object (here from a file) and added with AddRelatedBd, rather than being treated as text. GetRelatedAttr then extracts one named attribute from a chosen header of a specific related part, the related-item analogue of GetAttachmentAttr, so you don't have to parse the raw header yourself.

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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 GetRelatedAttr method, which returns a header-field attribute value
    // from a header field of the Nth related item.  The first argument is the zero-based related-item
    // index, the second is the header field name, and the third is the attribute name.

    const email = try chilkat.Email.init();
    defer email.deinit();
    email.setSubject("GetRelatedAttr example");

    // Load the image data from a file into a BinData object.
    const bd_image = try chilkat.BinData.init();
    defer bd_image.deinit();
    bd_image.loadFile("qa_data/images/logo.png") catch {
        std.debug.print("{s}\n", .{try bd_image.getLastErrorText(alloc)});
        return;
    };

    // Add the image as a related item from the BinData; capture its generated Content-ID.
    const cid = email.addRelatedBd(alloc, "logo.png", bd_image) catch {
        std.debug.print("{s}\n", .{try email.getLastErrorText(alloc)});
        return;
    };

    // Reference the related item in the HTML body by its Content-ID.
    const sb_html = try chilkat.StringBuilder.init();
    defer sb_html.deinit();
    sb_html.append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>") catch {};
    _ = sb_html.replace("PLACEHOLDER_CID", cid);
    email.setHtmlBody(try sb_html.getAsString(alloc));

    // Get the "name" attribute of the related item's Content-Type header (index 0).
    const val = try email.getRelatedAttr(alloc, 0, "Content-Type", "name");
    std.debug.print("Related item Content-Type name attribute: {s}\n", .{val});

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