Lua

Set a MIME Header Field

Demonstrates the Chilkat Mime.SetHeaderField method, which sets a single header field. The first argument is the field name and the second is the value. All existing occurrences are removed and one replacement is inserted, or a new field is added if none exists.

Background: For headers that should appear exactly once — Subject, From, Content-Type — this is the method to use, because it guarantees a single occurrence no matter how many times you call it. That idempotence is the key difference from AddHeaderField, which would leave duplicates behind. Setting an empty value removes the field.

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Lua

local chilkat = require("chilkat")

-- Demonstrates the Mime.SetHeaderField method, which sets a single header field.  The 1st argument
-- is the field name and the 2nd is the value.  All existing occurrences are removed and one
-- replacement is inserted (or a new field is added if none exists).

local mime = chilkat.Mime.new()

local success = mime:set_body_from_plain_text("Hello.")
if not success then
    print(mime.last_error_text)
    return
end

-- Unlike AddHeaderField, SetHeaderField ensures exactly one field with this name.
success = mime:set_header_field("Subject", "Weekly Report")
if not success then
    print(mime.last_error_text)
    return
end

-- Setting it again replaces the previous value rather than adding a duplicate.
success = mime:set_header_field("Subject", "Weekly Report (revised)")
if not success then
    print(mime.last_error_text)
    return
end

local subject = mime:get_header_field("Subject")
if not mime.last_method_success then
    print(mime.last_error_text)
    return
end

print("Subject: " .. subject)