discourse/lib/email/message_id_service.rb

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# frozen_string_literal: true
module Email
##
# Email Message-IDs are used in both our outbound and inbound email
# flow. For the outbound flow via Email::Sender, we assign a unique
# Message-ID for any emails sent out from the application.
# If we are sending an email related to a topic, such as through the
# PostAlerter class, then the Message-ID will contain references to
# the topic ID, and if it is for a specific post, the post ID,
# along with a random suffix to make the Message-ID truly unique.
# The host must also be included on the Message-IDs.
#
# For the inbound email flow via Email::Receiver, we use Message-IDs
# to discern which topic or post the inbound email reply should be
# in response to. In this case, the Message-ID is extracted from the
# References and/or In-Reply-To headers, and compared with either
# the IncomingEmail table, the Post table, or the IncomingEmail to
# determine where to send the reply.
#
# See https://datatracker.ietf.org/doc/html/rfc2822#section-3.6.4 for
# more specific information around Message-IDs in email.
#
# See https://tools.ietf.org/html/rfc850#section-2.1.7 for the
# Message-ID format specification.
class MessageIdService
class << self
def generate_default
"<#{SecureRandom.uuid}@#{host}>"
end
def generate_for_post(post, use_incoming_email_if_present: false)
if use_incoming_email_if_present && post.incoming_email&.message_id.present?
return "<#{post.incoming_email.message_id}>"
end
"<topic/#{post.topic_id}/#{post.id}.#{random_suffix}@#{host}>"
end
def generate_for_topic(topic, use_incoming_email_if_present: false, canonical: false)
first_post = topic.ordered_posts.first
incoming_email = first_post.incoming_email
# If the incoming email was created by handle_mail, then it was an
# inbound email sent to Discourse and handled by Email::Receiver,
# this is the only case where we want to use the original Message-ID
# because we want to maintain threading in the original mail client.
if use_incoming_email_if_present &&
incoming_email&.message_id.present? &&
incoming_email&.created_via == IncomingEmail.created_via_types[:handle_mail]
return "<#{first_post.incoming_email.message_id}>"
end
if canonical
"<topic/#{topic.id}@#{host}>"
else
"<topic/#{topic.id}.#{random_suffix}@#{host}>"
end
end
def find_post_from_message_ids(message_ids)
message_ids = message_ids.map { |message_id| message_id_clean(message_id) }
post_ids = message_ids.map { |message_id| message_id[message_id_post_id_regexp, 1] }.compact.map(&:to_i)
post_ids << Post.where(
topic_id: message_ids.map { |message_id| message_id[message_id_topic_id_regexp, 1] }.compact,
post_number: 1
).pluck(:id)
post_ids << EmailLog.where(message_id: message_ids).pluck(:post_id)
post_ids << IncomingEmail.where(message_id: message_ids).pluck(:post_id)
post_ids.flatten!
post_ids.compact!
post_ids.uniq!
return if post_ids.empty?
Post.where(id: post_ids).order(:created_at).last
end
def random_suffix
SecureRandom.hex(12)
end
def discourse_generated_message_id?(message_id)
!!(message_id =~ message_id_post_id_regexp) ||
!!(message_id =~ message_id_topic_id_regexp)
end
def message_id_post_id_regexp
Regexp.new "topic/\\d+/(\\d+|\\d+\.\\w+)@#{Regexp.escape(host)}"
end
def message_id_topic_id_regexp
Regexp.new "topic/(\\d+|\\d+\.\\w+)@#{Regexp.escape(host)}"
end
def message_id_rfc_format(message_id)
message_id.present? && !is_message_id_rfc?(message_id) ? "<#{message_id}>" : message_id
end
def message_id_clean(message_id)
message_id.present? && is_message_id_rfc?(message_id) ? message_id.gsub(/^<|>$/, "") : message_id
end
def is_message_id_rfc?(message_id)
message_id.start_with?('<') && message_id.include?('@') && message_id.end_with?('>')
end
def host
Email::Sender.host_for(Discourse.base_url)
end
end
end
end