Add a "nocc + mdns" distributed compile mode

nocc gained mDNS discovery, so it can now match what "distcc + zeroconf" does:
pick a mode in Settings -> Developer and the board finds its compile helpers on
the LAN instead of being handed a host list.

setup_nocc_host.sh turns advertising on when it sets a box up as a helper. The
nocc package ships with it off -- a server that answers anything on the network
should be a decision rather than a default -- and running that script IS the
decision, since it is what makes the box a helper in the first place. NOCC_MDNS=0
opts out, and re-running with it takes advertising back off.

That script now always restarts nocc-server rather than using "enable --now".
On a host where the helper was already running, --now is a no-op, so the options
it had just edited (the port, and now the mDNS flag) would sit in the env file
while the running server kept serving with its old ones. The nocc package has
the same trap on upgrade, which is why an upgraded helper needs an explicit
restart to actually be running the new binary.

DiscoverNoccHosts asks nocc itself ("nocc-daemon -print-discovered-servers")
instead of browsing with avahi-browse the way the distcc path does. A helper
with more than one interface announces more than one address: a raw browse lists
it twice, which hands that machine a double share of the build (nocc shards
files across the server list by index), and it may pick the address on a subnet
the board cannot reach. Both helpers here announce on two subnets, so that is
the normal case. nocc already resolves each helper to one routable address.

Verified on real boards: a 32-bit client discovered both helpers, sized -j from
them, and compiled through them, producing a correct 32-bit object with no local
fallback. A client whose nocc predates the flag falls back to a local build with
a clear message rather than misparsing anything.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: dkulp

scripts/functions

@@ -315,8 +315,33 @@ function DiscoverDistccHosts() {
     echo "${out# }"
 }
 
+# Discover nocc helpers advertised on the LAN via mDNS and emit a list of
+# "host:port" (space separated; SetupBuildEnv joins them with ';'). Helpers
+# advertise _nocc._tcp when set up with setup_nocc_host.sh.
+#
+# We ask nocc itself rather than browsing with avahi-browse as the distcc path
+# does. A helper with more than one interface announces more than one address,
+# and nocc resolves each helper to ONE address that is routable from here --
+# a raw browse would list that helper twice (handing it a double share of the
+# build, since nocc shards files across the server list by index) and might
+# pick the address on a subnet this board cannot reach. Empty if nocc is too
+# old to know the flag, or if no helper answers.
+function DiscoverNoccHosts() {
+    command -v nocc-daemon >/dev/null 2>&1 || return 0
+    local out="" line
+    while read -r line; do
+        # Accept only bare "host:port". An older nocc-daemon does not know the flag
+        # and prints its whole usage text instead, which must not be parsed as hosts.
+        case "${line}" in
+            *[[:space:]]*) continue ;;
+            *:[0-9]*)      out="${out} ${line}" ;;
+        esac
+    done < <(timeout 10 nocc-daemon -print-discovered-servers 2>/dev/null)
+    echo "${out# }"
+}
+
 # Prepare the environment for a source rebuild based on the "Distributed Compile"
-# developer setting (off | distcc | distcc-zeroconf | nocc). MUST be called
+# developer setting (off | distcc | distcc-zeroconf | nocc | nocc-zeroconf). MUST be called
 # directly (not in a $(...) subshell) so the exports survive into the make that
 # follows. Sets these globals:
 #   DISTCC_HOSTS / NOCC_SERVERS / NOCC_GO_EXECUTABLE / NOCC_LOG_FILENAME
@@ -369,8 +394,14 @@ function SetupBuildEnv() {
                 BUILD_CPUS=$(ComputeMakeParallelism)
             fi
             ;;
-        nocc)
-            hosts=$(getSetting DistccHosts)
+        nocc|nocc-zeroconf)
+            if [ "${mode}" = "nocc-zeroconf" ]; then
+                # Ask nocc what is advertising itself on the LAN (see DiscoverNoccHosts).
+                hosts=$(DiscoverNoccHosts)
+                [ -z "${hosts}" ] && echo "nocc: mDNS enabled but no helpers were discovered on the network"
+            else
+                hosts=$(getSetting DistccHosts)
+            fi
             if [ -n "${hosts}" ]; then
                 # nocc wants a ';'-delimited list of host:port and REQUIRES the
                 # port (unlike distcc's space-delimited host[:port][/jobs,opts]).
@@ -398,7 +429,11 @@ function SetupBuildEnv() {
                 BUILD_CPUS=$(ComputeDistccParallelism "${hosts}" nocc)
                 echo "Building with nocc: NOCC_SERVERS='${NOCC_SERVERS}', -j ${BUILD_CPUS} (PCH disabled; makefile selects the triplet compiler)"
             else
-                echo "nocc selected but no Compile Hosts configured -- building locally"
+                if [ "${mode}" = "nocc-zeroconf" ]; then
+                    echo "nocc + mdns selected but no helpers were discovered -- building locally"
+                else
+                    echo "nocc selected but no Compile Hosts configured -- building locally"
+                fi
                 BUILD_CPUS=$(ComputeMakeParallelism)
             fi
             ;;

scripts/setup_nocc_host.sh

@@ -13,9 +13,11 @@
 # actually gets fed. Measured ~3x faster full builds on a BBB.
 #
 # This is OPT-IN. A client only uses the helper when its build env points at it
-# (NOCC_SERVERS=thishost:43210; FPP's makefiles then run nocc as the compiler
-# launcher directly). The nocc binaries and the (disabled) nocc-server unit come
-# from the FPP apt repo:  apt-get install nocc
+# -- either explicitly (NOCC_SERVERS=thishost:43210) or by finding it on the LAN,
+# since this script makes the helper advertise itself over mDNS as _nocc._tcp
+# (clients pick "nocc + mdns" under Settings -> Developer). FPP's makefiles then
+# run nocc as the compiler launcher directly. The nocc binaries and the
+# (disabled) nocc-server unit come from the FPP apt repo:  apt-get install nocc
 #
 # ---------------------------------------------------------------------------
 # Serving both 32-bit and 64-bit clients: YES, one host.
@@ -39,6 +41,7 @@
 #   sudo PORT=43210 ./setup_nocc_host.sh         # override port
 #   sudo NOCC_FIREWALL=1 ./setup_nocc_host.sh    # + LAN-only nftables rule
 #   sudo NOCC_FIREWALL=1 ./setup_nocc_host.sh 192.168.7.0/24   # force LAN CIDR(s)
+#   sudo NOCC_MDNS=0 ./setup_nocc_host.sh        # do not advertise over mDNS
 #   sudo ./setup_nocc_host.sh disable            # stop & disable the helper
 #####################################
 
@@ -94,6 +97,30 @@ if [ "$PORT" != "43210" ] && [ -f "$ENVF" ]; then
     sed -i -E "s/-port [0-9]+/-port ${PORT}/" "$ENVF"
 fi
 
+# ---- advertise over mDNS so clients can find this helper --------------------
+# The nocc package ships with advertising OFF, because a server answering
+# anything on the LAN should be a decision, not a default. Running THIS script
+# is that decision: it is what turns a box into a helper. NOCC_MDNS=0 opts out.
+if [ -f "$ENVF" ]; then
+    if [ "${NOCC_MDNS:-1}" = "1" ]; then
+        if grep -q -- "-advertise-mdns" "$ENVF"; then
+            echo "==> Already advertising over mDNS (_nocc._tcp)"
+        elif nocc-server -help 2>&1 | grep -q -- "-advertise-mdns"; then
+            echo "==> Enabling mDNS advertisement (_nocc._tcp) in ${ENVF}"
+            sed -i -E 's/^(NOCC_SERVER_OPTS=")/\1-advertise-mdns /' "$ENVF"
+        else
+            echo "NOTE: this nocc-server predates -advertise-mdns; upgrade the nocc package"
+            echo "      to let clients discover this helper automatically."
+        fi
+    else
+        # NOCC_MDNS=0 on a host that was advertising: take it back off
+        if grep -q -- "-advertise-mdns" "$ENVF"; then
+            echo "==> Disabling mDNS advertisement in ${ENVF}"
+            sed -i -E 's/ ?-advertise-mdns//' "$ENVF"
+        fi
+    fi
+fi
+
 # ---- optional LAN-only firewall (nocc-server has no ACL of its own) ----------
 if [ "${NOCC_FIREWALL:-0}" = "1" ]; then
     if command -v nft >/dev/null 2>&1; then
@@ -120,9 +147,13 @@ else
 fi
 
 # ---- enable + (re)start -----------------------------------------------------
+# Always restart, never just "enable --now": on a host where the helper is
+# already running, --now is a no-op, so the options edited above (port, mDNS)
+# would sit in the env file while the running server kept its old ones.
 echo "==> Enabling and starting nocc-server"
 systemctl daemon-reload
-systemctl enable --now nocc-server
+systemctl enable nocc-server
+systemctl restart nocc-server
 sleep 1
 
 echo
@@ -134,6 +165,9 @@ else
 fi
 ss -ltn 2>/dev/null | grep -q ":${PORT}" && echo "Listening on TCP ${PORT}." || \
     echo "NOTE: did not see a listener on ${PORT} yet."
+if grep -q -- "-advertise-mdns" "$ENVF" 2>/dev/null; then
+    echo "Advertising over mDNS as _nocc._tcp (clients can select 'nocc + mdns')."
+fi
 
 echo
 echo "Installed compilers on this host (clients MUST match the major version):"
@@ -160,8 +194,11 @@ CLIENT USAGE (on the SLOW board you want to speed up):
       cd /opt/fpp/src && make -j6 CXXCOMPILER=<triplet>-g++ ...
 
   <triplet> is arm-linux-gnueabihf (32-bit) or aarch64-linux-gnu (64-bit).
-  nocc has no host auto-discovery (unlike distcc's mDNS); list this helper
-  explicitly in NOCC_SERVERS.
+
+  Or skip the host list entirely: in the FPP UI, Settings -> Developer ->
+  Distributed Compile -> "nocc + mdns" finds this helper on the LAN by itself.
+  Outside FPP, that is NOCC_DISCOVER_MDNS=1 (and 'nocc -print-discovered-servers'
+  prints what is out there).
 
 To turn the helper back off:  sudo $0 disable
 ============================================================

www/settings.json

@@ -1714,7 +1714,7 @@
 		"DistributedCompile": {
 			"name": "DistributedCompile",
 			"description": "Distributed Compile",
-			"tip": "Distribute FPP source compiles to a helper host to speed up full rebuilds (e.g. after a branch switch or a header change that invalidates ccache). Set up the helper with scripts/setup_distcc_host.sh (distcc) or scripts/setup_nocc_host.sh (nocc), running the same compiler major version. Any distributed mode disables the precompiled header. 'nocc' does NOT preprocess locally, so it is far faster on slow single-core boards (BeagleBone Black, Pi Zero); 'distcc' preprocesses locally then compiles on the helper; 'distcc + zeroconf' auto-discovers distcc helpers on the LAN via mDNS.",
+			"tip": "Distribute FPP source compiles to a helper host to speed up full rebuilds (e.g. after a branch switch or a header change that invalidates ccache). Set up the helper with scripts/setup_distcc_host.sh (distcc) or scripts/setup_nocc_host.sh (nocc), running the same compiler major version. Any distributed mode disables the precompiled header. 'nocc' does NOT preprocess locally, so it is far faster on slow single-core boards (BeagleBone Black, Pi Zero); 'distcc' preprocesses locally then compiles on the helper; 'distcc + zeroconf' auto-discovers distcc helpers on the LAN via mDNS, and 'nocc + mdns' does the same for nocc helpers (set one up with 'sudo scripts/setup_nocc_host.sh', which makes it advertise itself).",
 			"level": 3,
 			"restart": 0,
 			"reboot": 0,
@@ -1724,7 +1724,8 @@
 				"Off": "off",
 				"distcc": "distcc",
 				"distcc + zeroconf": "distcc-zeroconf",
-				"nocc": "nocc"
+				"nocc": "nocc",
+				"nocc + mdns": "nocc-zeroconf"
 			},
 			"children": {
 				"distcc": [
@@ -1738,7 +1739,7 @@
 		"DistccHosts": {
 			"name": "DistccHosts",
 			"description": "Compile Hosts",
-			"tip": "Space separated list of helper hosts. distcc: host[:port][/jobs][,options], e.g. 'fpppi5:3632/6,lzo'. nocc: host[:port] (default port 43210), e.g. 'fpppi5'. Not used for 'distcc + zeroconf' (helpers are discovered via mDNS).",
+			"tip": "Space separated list of helper hosts. distcc: host[:port][/jobs][,options], e.g. 'fpppi5:3632/6,lzo'. nocc: host[:port] (default port 43210), e.g. 'fpppi5'. Not used for 'distcc + zeroconf' or 'nocc + mdns' (helpers are discovered via mDNS).",
 			"level": 3,
 			"restart": 0,
 			"reboot": 0,