Unholy bash e-mail generation library

libmail.sh

#!/bin/bash

MAIL_WIDTH=76

function mail_example() {
	From alice@example.com
	To bob@example.com
	Subject "Look at my test email!"
	header_message_id
	header_date_now
	header_mime_version
	multipart_begin alternative
		Content-Type text/plain 'charset="UTF-8"'
		Content-Transfer-Encoding quoted-printable
		body_begin
		echo "This is a sweet test email isn’t it?" | transfer_encoding_quoted_printable
	multipart_next
		Content-Type text/html 'charset="UTF-8"'
		Content-Transfer-Encoding quoted-printable
		body_begin
		echo "<p>This is a <em>sweet</em> test email isn’t it?</p>" | transfer_encoding_quoted_printable
	multipart_end
}

transfer_encoding_base64() {
	base64 --wrap=$MAIL_WIDTH
}

transfer_encoding_quoted_printable() {
	perl -MMIME::QuotedPrint -pe '$_=MIME::QuotedPrint::encode($_)'
}

function generate_boundary() {
	head -c12 /dev/urandom | xxd -p
}

function header() {
	headerindent='    '
	{
		printf "%s: " "$1"
		shift
		printf "%s" "$1"
		shift
		while [[ $# -gt 0 ]]
		do
			printf "; %s" "$1"
			shift
		done
		echo
	} \
	| fold \
		--spaces \
		--width=$((MAIL_WIDTH - ${#headerindent})) \
	| sed "2,\$s/^/${headerindent}/"
}

function From() {
	header From "$@"
}

function To() {
	header To "$@"
}

function Subject() {
	header Subject "$@"
}

function Date() {
	header Date "$@"
}

function Content-Transfer-Encoding() {
	header Content-Transfer-Encoding "$@"
}

function Content-Type() {
	header Content-Type "$@"
}

function Content-Disposition() {
	header Content-Disposition "$@"
}

function header_message_id() {
	header Message-ID "<$(generate_boundary)@$(hostname)>"
}

function header_date_now() {
	Date "$(date --rfc-email)"
}

function header_mime_version() {
	header MIME-Version 1.0
}

function body_begin() {
	echo
}

boundary=
function multipart_begin() {
	local content_type="multipart/$1"
	shift
	boundary=$(generate_boundary)
	header Content-Type "$content_type" "boundary=$boundary" "$@"
	body_begin
	echo "--$boundary"
}

function multipart_next() {
	echo
	echo "--$boundary"
}

function multipart_end() {
	echo
	echo "--$boundary--"
}

function transform_pgp_signed() {
	local tmp=$(mktemp)
	cat > "$tmp"

	header Content-Transfer-Encoding 7bit
	header Content-Disposition inline
	multipart_begin signed 'protocol="application/pgp-signature"' micalg="pgp-sha256"
		sed -e '${/^$/d}' "$tmp" 
	multipart_next
		header Content-type application/pgp-signature 'name="signature.asc"'
		body_begin
		gpg2 --armor --detach-sign --textmode < "$tmp"
	multipart_end
}

function transform_pgp_encrypted() {
	header Content-Transfer-Encoding 7bit
	header Content-Disposition inline
	multipart_begin encrypted 'protocol="application/pgp-encrypted"'
		header Content-Type application/pgp-encrypted
		body_begin
		echo 'Version: 1'
	multipart_next
		header Content-Type application/octet-stream
		body_begin
		gpg2 --armor --encrypt --textmode "$@"
	multipart_end
}

function transform_pgp_signed_encrypted() {
	header Content-Transfer-Encoding 7bit
	header Content-Disposition inline
	multipart_begin encrypted 'protocol="application/pgp-encrypted"'
		Content-Type application/pgp-encrypted
		body_begin
		echo 'Version: 1'
	multipart_next
		Content-Type application/octet-stream 'name="signature.asc"'
		body_begin
		gpg2 --armor --sign --encrypt --textmode "$@"
	multipart_end
}

function transform_asciidoc_html_content() {
	asciidoc --backend xhtml11 -
}

function transform_asciidoc_html() {
	header Content-Transfer-Encoding quoted-printable
	header Content-Disposition inline
	header Content-Type text/html 'charset="UTF-8"'
	body_begin
	transform_asciidoc_html_content | transfer_encoding_quoted_printable
}

function transform_asciidoc_plain() {
	header Content-Transfer-Encoding quoted-printable
	header Content-Disposition inline
	header Content-Type text/plain 'charset="UTF-8"' 'format=flowed'
	body_begin
	sed -n '/^$/,${/./,$p}' | transfer_encoding_quoted_printable
}

function mail_send() {
	nslookup smtp.gmail.com >/dev/null
	msmtp -- "$@"
}