Lua

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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Lua

local chilkat = require("chilkat")

-- 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.

local email = chilkat.Email.new()
email.subject = "GetRelatedAttr example"

-- Load the image data from a file into a BinData object.
local bdImage = chilkat.BinData.new()
local success = bdImage:load_file("qa_data/images/logo.png")
if not success then
    print(bdImage.last_error_text)
    return
end

-- Add the image as a related item from the BinData; capture its generated Content-ID.
local cid = email:add_related_bd("logo.png", bdImage)
if not email.last_method_success then
    print(email.last_error_text)
    return
end

-- Reference the related item in the HTML body by its Content-ID.
local sbHtml = chilkat.StringBuilder.new()
sbHtml:append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>")
local numReplaced = sbHtml:replace("PLACEHOLDER_CID", cid)
email:set_html_body(sbHtml:get_as_string())

-- Get the "name" attribute of the related item's Content-Type header (index 0).
local val = email:get_related_attr(0, "Content-Type", "name")
print("Related item Content-Type name attribute: " .. 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.