docker: add script and awk program

docker/docker-healthcheck.sh

@@ -0,0 +1,55 @@
+#!/bin/sh
+
+# AdGuard Home Docker healthcheck script
+
+# Exit the script if a pipeline fails (-e), prevent accidental filename
+# expansion (-f), and consider undefined variables as errors (-u).
+set -e -f -u
+
+# Function log is an echo wrapper that writes to stderr if the caller requested
+# verbosity level greater than 0.  Otherwise, it does nothing.
+log() {
+	# if [ "$VERBOSE" -gt '0' ]
+	# then
+		echo "$1" 1>&2
+	# fi
+}
+
+# TODO(e.burkov):  Deal with custom configuration file name.
+filename='./AdGuardHome.yaml'
+readonly filename
+
+if ! [ -f "$filename" ]
+then
+    log "AdGuard Home is probably not set up yet"
+
+    exit 0
+fi
+
+hosts=$(awk -f './docker/get_bind_hosts.awk' "$filename")
+readonly hosts
+
+if [ "$hosts" == '' ]
+then
+    log "No hosts could be retrieved from $filename"
+
+    exit 1
+fi
+
+case "$hosts"
+in
+("0.0.0.0:"*|"[::]:"*)
+    # TODO(e.burkov):  Deal with unspecified addresses.
+    log "The unspecified address isn't supported by healthcheck"
+
+    exit 1
+    ;;
+(*)
+    # Go on.
+    ;;
+esac
+
+echo "$hosts" | while read -r host
+do
+    echo $host
+done

docker/get_bind_hosts.awk

@@ -0,0 +1,40 @@
+BEGIN {
+    naddrs = 0
+}
+bind_subsection  {
+    # Subsection of bind_hosts field lasts as long as there are array elements.
+    bind_subsection = /[[:space:]+]- /;
+    if (bind_subsection) {
+        addr = $2
+        if (addr == "0.0.0.0" || addr == "::") {
+            # Only return the unspecified address if it's set at least once.
+            addrs[0] = addr; naddrs = 1;
+            bind_subsection = 0;
+        } else {
+            addrs[naddrs++] = addr
+        }
+    }
+}
+dns_subsection && !bind_subsection {
+    bind_subsection = /[[:space:]+]bind_hosts:/;
+    if (/^[[:space:]]+port:/) {
+        port = $2;
+    };
+    next
+}
+/^[^[:space:]]/ {
+    dns_subsection = /^dns:/;
+    next
+}
+END {
+    for (i = 0; i < naddrs; i++) {
+        addr = addrs[i];
+        if (match(addr, ":")) {
+            # It's an IPv6.
+            print "[" addr "]:" port;
+        } else {
+            # It's an IPv4.
+            print addr ":" port;
+        }
+    }
+}