#!/bin/bash
#
# Purpose : Find what's on the local network over mDNS (Avahi), for the
#           configure.d items that set up servers, printers and storage on it.
#           Source this file.

# Every service Avahi can see, or only those of type $1 (e.g. _ipp._tcp), one
# per line after waiting a few seconds for answers:
# "name|type|host|address|port|txt". IPv4 only, so a machine isn't listed once
# per address family. The name has Avahi's escapes decoded.
mdns_services() {
  local name type host address port txt
  timeout 15 avahi-browse "${1:---all}" --resolve --terminate --parsable --no-db-lookup 2> /dev/null \
    | awk -F';' '$1 == "=" && $3 == "IPv4"' \
    | while IFS=';' read -r _ _ _ name type _ host address port txt; do
        printf '%s|%s|%s|%s|%s|%s\n' "$(mdns_unescape "$name")" "$type" "$host" "$address" "$port" "$txt"
      done | sort -u
}

# Avahi writes a space as \032 and a dot in a name as \. (decimal escapes)
mdns_unescape() {
  local s="$1" out="" ch code escape='^([^\\]*)\\([0-9][0-9][0-9]|.)(.*)$'
  while [[ "$s" =~ $escape ]]; do
    out+="${BASH_REMATCH[1]}"
    code="${BASH_REMATCH[2]}"
    s="${BASH_REMATCH[3]}"
    if [[ "$code" == [0-9][0-9][0-9] ]]; then
      # shellcheck disable=SC2059
      printf -v ch "\\$(printf %03o "$((10#$code))")"
      out+="$ch"
    else
      out+="$code"
    fi
  done
  echo "$out$s"
}

# This machine's own .local name, which mdns_hosts leaves out
mdns_own_host() {
  echo "$(hostnamectl hostname 2> /dev/null || cat /etc/hostname).local"
}

# The other machines on the network: one .local name per line
mdns_hosts() {
  local own
  own="$(mdns_own_host)"
  mdns_services | cut -d'|' -f3 | grep -vixF "$own" | sort -u
}