Lua

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.

Chilkat Lua Downloads

Download Chilkat for Lua

Lua

local chilkat = require("chilkat")

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

local email = chilkat.Email.new()
email.subject = "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.
local cid = email:add_related_string("styles.css", "body { color: black; }", "utf-8")
if not email.last_method_success then
    print(email.last_error_text)
    return
end

-- 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.
local sbHtml = chilkat.StringBuilder.new()
sbHtml:append("<html><head><link rel=\"stylesheet\" href=\"cid:PLACEHOLDER_CID\"/></head><body>Styled content.</body></html>")
local numReplaced = sbHtml:replace("PLACEHOLDER_CID", cid)
email:set_html_body(sbHtml:get_as_string())

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

-- The custom header now appears in the related item's MIME part.
print(email:get_mime())