procd: make mDNS TXT record parsing more solid

mDNS broadcast can't accept empty TXT record and would fail
registration.

Current procd_add_mdns_service checks only if the first passed arg is
empty but don't make any verification on the other args permittins
insertion of empty values in TXT record.

Example:

	procd_add_mdns "blah" \
				"tcp" "50" \
				"1" \
				"" \
				"3"

Produce:

{ "blah_50": { "service": "_blah._tcp.local", "port": 50, "txt": [ "1", "", "3" ] } }

The middle empty TXT record should never be included as it's empty.

This can happen with scripts that make fragile parsing and include
variables even if they are empty.

Prevent this and make the TXT record more solid by checking every
provided TXT record and include only the non-empty ones.

The fixed JSON is the following:

{ "blah_50": { "service": "_blah._tcp.local", "port": 50, "txt": [ "1", "3" ] } }

Fixes: b0d9dcf84dd0 ("procd: update to latest git HEAD")
Reported-by: Paul Donald <newtwen@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/15331
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
(cherry picked from commit 4b043047132de0b3d90619d538f103af6153fa5a)

diff --git a/package/system/procd/files/procd.sh b/package/system/procd/files/procd.sh
index 5148b2f03c3511ee5c3de1d5d631ecd5a26c730a..d834fa601a0cc22c3c085551f60d942b2070a1de 100644 (file)
--- a/package/system/procd/files/procd.sh
+++ b/package/system/procd/files/procd.sh
@@ -570,18 +570,21 @@ _procd_set_config_changed() {
 }
 
 procd_add_mdns_service() {
-       local service proto port
+       local service proto port txt_count=0
        service=$1; shift
        proto=$1; shift
        port=$1; shift
        json_add_object "${service}_$port"
        json_add_string "service" "_$service._$proto.local"
        json_add_int port "$port"
-       [ -n "$1" ] && {
-               json_add_array txt
-               for txt in "$@"; do json_add_string "" "$txt"; done
-               json_select ..
-       }
+       for txt in "$@"; do
+               [ -z "$txt" ] && continue
+               txt_count=$((txt_count+1))
+               [ $txt_count -eq 1 ] && json_add_array txt
+               json_add_string "" "$txt"
+       done
+       [ $txt_count -gt 0 ] && json_select ..
+
        json_select ..
 }