fix(macos): preserve DNS and proxy state across network changes

scripts/set_dns.sh

@@ -32,7 +32,9 @@ function is_valid_ip() {
 
 # Prints one value of a SystemConfiguration dictionary, or nothing when the key is absent.
 function sc_value() {
-    printf 'show %s\nquit\n' "$1" | scutil | sed -n "s/^ *$2 : //p"
+    local dictionary
+    dictionary=$(printf 'show %s\nquit\n' "$1" | scutil) || return 1
+    sed -n "s/^ *$2 : //p" <<<"$dictionary"
 }
 
 # Prints the service's DNS servers, or "empty" when none is set; fails on any other answer.
@@ -50,31 +52,62 @@ function dns_of() {
     echo "$dns"
 }
 
-[ $# -lt 1 ] && echo "Usage: $0 <IP address>" && exit 1
-! is_valid_ip "$1" && echo "$1 is not a valid IP address." && exit 1
+[ $# -lt 1 ] && echo "Usage: $0 <newline-separated DNS servers> [legacy state directory]" >&2 && exit 1
+dns_servers=()
+while read -r server; do
+    ! is_valid_ip "$server" && echo "$server is not a valid IP address." >&2 && exit 1
+    dns_servers+=("$server")
+done <<<"$1"
 
 # Backups are keyed by service ID, which survives renaming the service and renumbering its interface.
-service_id=$(sc_value State:/Network/Global/IPv4 PrimaryService)
-hardware_port=$(sc_value "Setup:/Network/Service/$service_id" UserDefinedName)
-[ -z "$hardware_port" ] && echo "No primary network service." && exit 1
+service_id=$(sc_value State:/Network/Global/IPv4 PrimaryService) || exit 1
+hardware_port=$(sc_value "Setup:/Network/Service/$service_id" UserDefinedName) || exit 1
+[ -z "$hardware_port" ] && echo "No primary network service; waiting for the network." >&2 && exit 75
 
 original_dns=$(dns_of "$hardware_port") || { echo "Cannot read DNS servers of $hardware_port." >&2; exit 1; }
 
 backup=".original_dns/$service_id"
 mkdir -p .original_dns || exit 1
-# Older releases kept a single backup for whichever service was primary.
-if [ -f .original_dns.txt ]; then
-    if [ -f "$backup" ]; then
-        rm -f .original_dns.txt || exit 1
-    else
-        mv .original_dns.txt "$backup" || exit 1
+# Key old single-slot backups before import so a later network switch cannot reassign them.
+for state_dir in "$PWD" "${2:-$PWD}"; do
+    if [ -f "$state_dir/.original_dns.txt" ]; then
+        mkdir -p "$state_dir/.original_dns" || exit 1
+        if [ -f "$state_dir/.original_dns/$service_id" ]; then
+            rm -f "$state_dir/.original_dns.txt" || exit 1
+        else
+            mv "$state_dir/.original_dns.txt" "$state_dir/.original_dns/$service_id" || exit 1
+        fi
     fi
+done
+if [ ! -f "$backup" ] && [ -n "$2" ] && [ -f "$2/$backup" ]; then
+    cp "$2/$backup" ".original_dns/.$service_id" || exit 1
+    mv ".original_dns/.$service_id" "$backup" || exit 1
+fi
+backup_header='# clash-verge-dns-managed'
+function save_backup() {
+    printf '%s\n%s\n' "$backup_header" "$1" >".original_dns/.$service_id" &&
+        mv ".original_dns/.$service_id" "$backup"
+}
+
+saved_dns=
+legacy_backup=false
+if [ -f "$backup" ]; then
+    saved_dns=$(cat "$backup") || exit 1
+    case "$saved_dns" in
+        "$backup_header"$'\n'*) saved_dns=${saved_dns#*$'\n'} ;;
+        *) legacy_backup=true ;;
+    esac
 fi
-# The placeholder is ours, not the user's: keep the backup taken before it was applied.
 if [ "$original_dns" != "$1" ]; then
-    echo "$original_dns" >"$backup" || exit 1
-    networksetup -setdnsservers "$hardware_port" "$1"
+    # Only an unmarked historical backup owns the old single-address placeholder.
+    if [ "$original_dns" != "114.114.114.114" ] || [ "$legacy_backup" != true ]; then
+        save_backup "$original_dns" || exit 1
+        legacy_backup=false
+    fi
+    networksetup -setdnsservers "$hardware_port" "${dns_servers[@]}"
     [ "$(dns_of "$hardware_port")" = "$1" ] || { echo "Failed to set DNS for $hardware_port." >&2; exit 1; }
-elif [ ! -f "$backup" ]; then
-    echo "empty" >"$backup" || exit 1
+fi
+# Keep legacy ownership until the new list is verified, including a retry after a failed marker write.
+if [ "$legacy_backup" = true ]; then
+    save_backup "$saved_dns" || exit 1
 fi