[__haproxy_dualstack] Improve manpage

This is backwards compatible with what is already used internally @ungleich, but
adds on top of that the ability to customise ports and, most importantly, it
adds PROXY protocol support.

type/__haproxy_dualstack/files/http

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+frontend http
+	bind	BIND@:80
+	mode	http
+	option	httplog
+	default_backend	http
+
+backend http
+	mode	http

type/__haproxy_dualstack/files/https

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+frontend https
+	bind	BIND@:443
+	mode	tcp
+	option	tcplog
+	tcp-request	inspect-delay 5s
+	tcp-request	content accept if { req_ssl_hello_type 1 }
+	default_backend	https
+
+backend https
+	mode	tcp

type/__haproxy_dualstack/files/imaps

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+frontend imaps
+	bind	BIND@:143
+	bind	BIND@:993
+
+	mode	tcp
+	option	tcplog
+	tcp-request	inspect-delay 5s
+	tcp-request	content accept if { req_ssl_hello_type 1 }
+	default_backend	imaps
+
+backend imaps
+	mode	tcp

type/__haproxy_dualstack/files/smtps

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+frontend smtps
+	bind	BIND@:25
+	bind	BIND@:465
+
+	mode	tcp
+	option	tcplog
+	tcp-request	inspect-delay 5s
+	tcp-request	content accept if { req_ssl_hello_type 1 }
+	default_backend	smtps
+
+backend smtps
+	mode	tcp

type/__haproxy_dualstack/man.rst

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+cdist-type__haproxy_dualstack(7)
+================================
+
+
+NAME
+----
+cdist-type__haproxy_dualstack - Proxy services from a dual-stack server
+
+
+DESCRIPTION
+-----------
+This (singleton) type installs and configures haproxy to act as a dual-stack
+proxy for single-stack services.
+
+This can be useful to add IPv4 support to IPv6-only services while only using
+one IPv4 for many such services.
+
+By default this type uses the plain TCP proxy mode, which means that there is no
+need for TLS termination on this host when SNI is supported.
+This also means that proxied services will not receive the client's IP address,
+but will see the proxy's IP address instead (that of `$__target_host`).
+
+This can be solved by using the PROXY protocol, but do take into account that,
+e.g. nginx cannot serve both regular HTTP(S) and PROXY protocols on the same
+port, so you will need to use other ports for that.
+
+As a recommendation in this type: use TCP ports 8080 and 591 respectively to
+serve HTTP and HTTPS using the PROXY protocol.
+
+See the EXAMPLES for more details.
+
+
+OPTIONAL PARAMETERS
+-------------------
+v4proxy
+    Proxy incoming IPv4 connections to the equivalent IPv6 endpoint.
+    In its simplest use, it must be a NAME with an `AAAA` DNS entry, which is
+    the IP address actually providing the proxied services.
+    The full format of this argument is:
+    `[proxy:]NAME[[:PROTOCOL_1=PORT_1]...[:PROTOCOL_N=PORT_N]]`
+    Where starting with `proxy:` determines that the PROXY protocol must be
+    used and each `:PROTOCOL=PORT` (e.g. `:http=8080` or `:https=591`) is a PORT
+    override for the given PROTOCOL (see `--protocol`), if not present the
+    PROTOCOL's default port will be used.
+
+
+v6proxy
+    Proxy incoming IPv6 connections to the equivalent IPv4 endpoint.
+    In its simplest use, it must be a NAME with an `A` DNS entry, which is
+    the IP address actually providing the proxied services.
+    See `--v4proxy` for more options and details.
+
+protocol
+    Can be passed multiple times or as a space-separated list of protocols.
+    Currently supported protocols are: `http`, `https`, `imaps`, `smtps`.
+    This defaults to: `http https imaps smtps`.
+
+
+EXAMPLES
+--------
+
+.. code-block:: sh
+
+    # Proxy the IPv6-only services so IPv4-only clients can access them
+    # This uses HAProxy's TCP mode for http, https, imaps and smtps
+    __haproxy_dualstack \
+        --v4proxy ipv6.chat \
+        --v4proxy matrix.ungleich.ch
+
+    # Proxy the IPv6-only HTTP(S) services so IPv4-only clients can access them
+    # Note this means that the backend IPv6-only server will only see
+    # the IPv6 address of the haproxy host managed by cdist, which can be
+    # troublesome if this information is relevant for analytics/security/...
+    # See the PROXY example below
+    __haproxy_dualstack \
+        --protocol http --protocol https \
+        --v4proxy ipv6.chat \
+        --v4proxy matrix.ungleich.ch
+
+    # Use the PROXY protocol to proxy the IPv6-only HTTP(S) services enabling
+    # IPv4-only clients to access them while maintaining the client's IP address
+    __haproxy_dualstack \
+        --protocol http --protocol https \
+        --v4proxy proxy:ipv6.chat:http=8080:https=591 \
+        --v4proxy proxy:matrix.ungleich.ch:http=8080:https=591
+    # Note however that the PROXY protocol is not compatible with regular
+    # HTTP(S) protocols, so your nginx will have to listen on different ports
+    # with the PROXY settings.
+    # Note that you will need to restrict access to the 8080 port to prevent
+    # Client IP spoofing.
+    # This can be something like:
+    # server {
+    #     # listen for regular HTTP connections
+    #     listen [::]:80 default_server;
+    #     listen 80 default_server;
+    #     # listen for PROXY HTTP connections
+    #     listen [::]:8080 proxy_protocol;
+    #     # Accept the Client's IP from the PROXY protocol
+    #     real_ip_header proxy_protocol;
+    # }
+
+
+SEE ALSO
+--------
+- https://www.haproxy.com/blog/enhanced-ssl-load-balancing-with-server-name-indication-sni-tls-extension/
+- https://www.haproxy.com/blog/haproxy/proxy-protocol/
+- https://docs.nginx.com/nginx/admin-guide/load-balancer/using-proxy-protocol/
+
+
+AUTHORS
+-------
+ungleich <foss--@--ungleich.ch>
+Evilham <cvs--@--evilham.com>
+
+
+COPYING
+-------
+Copyright \(C) 2021 ungleich glarus ag. You can redistribute it
+and/or modify it under the terms of the GNU General Public License as
+published by the Free Software Foundation, either version 3 of the
+License, or (at your option) any later version.

type/__haproxy_dualstack/manifest

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+#!/bin/sh -eu
+
+__package haproxy
+require="__package/haproxy" __start_on_boot haproxy
+
+tmpdir="$__object/files"
+mkdir "$tmpdir"
+configtmp="$__object/files/haproxy.cfg"
+
+os=$(cat "$__global/explorer/os")
+case $os in
+	freebsd)
+		CONFIG_FILE="/usr/local/etc/haproxy.conf"
+		cat <<EOF > "$configtmp"
+global
+	maxconn	4000
+	user	nobody
+	group	nogroup
+	daemon
+
+EOF
+
+		;;
+	*)
+		CONFIG_FILE="/etc/haproxy/haproxy.cfg"
+		cat <<EOF > "$configtmp"
+global
+	log	[::1] local2
+	chroot	/var/lib/haproxy
+	pidfile	/var/run/haproxy.pid
+	maxconn	4000
+	user	haproxy
+	group	haproxy
+	daemon
+
+	# turn on stats unix socket
+	stats socket	/var/lib/haproxy/stats
+
+EOF
+		;;
+esac
+
+cat <<EOF >> "$configtmp"
+defaults
+	retries	3
+	log	global
+	timeout http-request	10s
+	timeout queue		1m
+	timeout connect		10s
+	timeout client		1m
+	timeout server		1m
+	timeout http-keep-alive	10s
+	timeout check		10s
+EOF
+
+dig_cmd="$(command -v dig || true)"
+get_ip() {
+	# Usage: get_ip (ipv4|ipv6) NAME
+	# uses "dig" if available, else fallback to "host"
+	case $1 in
+		ipv4)
+			if [ -n "${dig_cmd}" ]; then
+				${dig_cmd} +short A "$2"
+			else
+				host -t A "$2" | cut -d ' ' -f 4 | grep -v 'found:'
+			fi
+			;;
+		ipv6)
+			if [ -n "${dig_cmd}" ]; then
+				${dig_cmd} +short AAAA "$2"
+			else
+				host -t AAAA "$2" | cut -d ' ' -f 5 | grep -v 'NXDOMAIN'
+			fi
+			;;
+	esac
+}
+
+PROTOCOLS="$(cat "$__object/parameter/protocol")"
+
+for proxy in v4proxy v6proxy; do
+	param=$__object/parameter/$proxy
+	# no backend? skip generating code
+	if [ ! -f "$param" ]; then
+		continue
+	fi
+
+	# turn backend name into bind parameter: v4backend -> ipv4@
+	bind=$(echo $proxy | sed -e 's/^/ip/' -e 's/proxy//')
+
+	case $bind in
+		ipv4)
+			backendproto=ipv6
+			;;
+		ipv6)
+			backendproto=ipv4
+			;;
+	esac
+
+	for proto in ${PROTOCOLS}; do
+		# Add protocol "header"
+		printf "\n# %s %s \n" "${bind}" "${proto}" >> "$configtmp"
+
+		sed -e "s/BIND/$bind/" \
+			-e "s/\(frontend[[:space:]].*\)/\1$bind/" \
+			-e "s/\(backend[[:space:]].*\)/\\1$bind/" \
+			"$__type/files/$proto" >> "$configtmp"
+
+		while read -r hostdefinition; do
+			if echo "$hostdefinition" | grep -qE '^proxy:'; then
+				# Proxy protocol was requested
+				host="$(echo "$hostdefinition" | sed -E 's/^proxy:([^:]+).*$/\1/')"
+				send_proxy=" send-proxy"
+			else
+				# Just use tcp proxy mode
+				host="$hostdefinition"
+				send_proxy=""
+			fi
+			if echo "$hostdefinition" | grep -qE ":${proto}="; then
+				# Use custom port definition if requested
+				port="$(echo "$hostdefinition" | sed -E "s/^(.*:)?${proto}=([0-9]+).*$/:\2/")"
+			else
+				# Else use the default
+				port=""
+			fi
+			servername=$host
+
+			res=$(get_ip "$bind" "$servername")
+
+			if [ -z "$res" ]; then
+				echo "$servername does not resolve - aborting config" >&2
+				exit 1
+			fi
+
+			# Treat protocols without TLS+SNI specially
+			if [ "$proto" = http ]; then
+				echo "	use-server $servername if { hdr(host) -i $host }" >> "$configtmp"
+			else
+				echo "	use-server $servername if { req_ssl_sni -i $host }" >> "$configtmp"
+			fi
+
+			# Create the "server" itself.
+			# Note that port and send_proxy will be empty unless
+			# they were requested by the type user
+			echo "	server $servername ${backendproto}@${host}${port}${send_proxy}" >> "$configtmp"
+
+		done < "$param"
+	done
+done
+
+# Create config file
+require="__package/haproxy" __file ${CONFIG_FILE} --source "$configtmp" --mode 0644
+
+require="__file${CONFIG_FILE}" __check_messages "haproxy_reload" \
+	--pattern "^__file${CONFIG_FILE}" \
+	--execute "service haproxy reload || service haproxy restart"

type/__haproxy_dualstack/parameter/default/protocol

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+http https imaps smtps

type/__haproxy_dualstack/parameter/optional_multiple

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+protocol
+v4proxy
+v6proxy