[openwrt/openwrt] procd: make mDNS TXT record parsing more solid

[LEDE Commits]

ansuel pushed a commit to openwrt/openwrt.git, branch main:
https://git.openwrt.org/4b043047132de0b3d90619d538f103af6153fa5a

commit 4b043047132de0b3d90619d538f103af6153fa5a
Author: Christian Marangi <ansuelsmth at gmail.com>
AuthorDate: Mon Apr 29 21:17:31 2024 +0200

    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 at gmail.com>
    Link: https://github.com/openwrt/openwrt/pull/15331
    Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
---
 package/system/procd/files/procd.sh | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/package/system/procd/files/procd.sh b/package/system/procd/files/procd.sh
index 8ee25f4f08..5dc8ec42b7 100644
--- a/package/system/procd/files/procd.sh
+++ b/package/system/procd/files/procd.sh
@@ -592,18 +592,21 @@ _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 ..
 }