daemon: look up client-supplied hostname lazily

index 54a03bd..ef41943 100644
@@ -61,6 +61,22 @@ static char *canon_hostname;
 static char *ip_address;
 static char *tcp_port;
 
+static int hostname_lookup_done;
+
+static void lookup_hostname(void);
+
+static const char *get_canon_hostname(void)
+{
+	lookup_hostname();
+	return canon_hostname;
+}
+
+static const char *get_ip_address(void)
+{
+	lookup_hostname();
+	return ip_address;
+}
+
 static void logreport(int priority, const char *err, va_list params)
 {
 	if (log_syslog) {

@@ -147,8 +163,8 @@ static const char *path_ok(const char *directory)
 		struct strbuf_expand_dict_entry dict[6];
 
 		dict[0].placeholder = "H"; dict[0].value = hostname;
-		dict[1].placeholder = "CH"; dict[1].value = canon_hostname;
-		dict[2].placeholder = "IP"; dict[2].value = ip_address;
+		dict[1].placeholder = "CH"; dict[1].value = get_canon_hostname();
+		dict[2].placeholder = "IP"; dict[2].value = get_ip_address();
 		dict[3].placeholder = "P"; dict[3].value = tcp_port;
 		dict[4].placeholder = "D"; dict[4].value = directory;
 		dict[5].placeholder = NULL; dict[5].value = NULL;

@@ -254,8 +270,8 @@ static int run_access_hook(struct daemon_service *service, const char *dir, cons
 	*arg++ = service->name;
 	*arg++ = path;
 	*arg++ = STRARG(hostname);
-	*arg++ = STRARG(canon_hostname);
-	*arg++ = STRARG(ip_address);
+	*arg++ = STRARG(get_canon_hostname());
+	*arg++ = STRARG(get_ip_address());
 	*arg++ = STRARG(tcp_port);
 	*arg = NULL;
 #undef STRARG

@@ -509,6 +525,7 @@ static void parse_host_arg(char *extra_args, int buflen)
 				}
 				free(hostname);
 				hostname = xstrdup_tolower(host);
+				hostname_lookup_done = 0;
 			}
 
 			/* On to the next one */

@@ -517,11 +534,14 @@ static void parse_host_arg(char *extra_args, int buflen)
 		if (extra_args < end && *extra_args)
 			die("Invalid request");
 	}
+}
 
-	/*
-	 * Locate canonical hostname and its IP address.
-	 */
-	if (hostname) {
+/*
+ * Locate canonical hostname and its IP address.
+ */
+static void lookup_hostname(void)
+{
+	if (!hostname_lookup_done && hostname) {
 #ifndef NO_IPV6
 		struct addrinfo hints;
 		struct addrinfo *ai;

@@ -569,6 +589,7 @@ static void parse_host_arg(char *extra_args, int buflen)
 			ip_address = xstrdup(addrbuf);
 		}
 #endif
+		hostname_lookup_done = 1;
 	}
 }
 

index ef41943..09fa652 100644
@@ -122,6 +122,46 @@ static void NORETURN daemon_die(const char *err, va_list params)
 	exit(1);
 }
 
+static void strbuf_addstr_or_null(struct strbuf *sb, const char *s)
+{
+	if (s)
+		strbuf_addstr(sb, s);
+}
+
+struct expand_path_context {
+	const char *directory;
+};
+
+static size_t expand_path(struct strbuf *sb, const char *placeholder, void *ctx)
+{
+	struct expand_path_context *context = ctx;
+
+	switch (placeholder[0]) {
+	case 'H':
+		strbuf_addstr_or_null(sb, hostname);
+		return 1;
+	case 'C':
+		if (placeholder[1] == 'H') {
+			strbuf_addstr_or_null(sb, get_canon_hostname());
+			return 2;
+		}
+		break;
+	case 'I':
+		if (placeholder[1] == 'P') {
+			strbuf_addstr_or_null(sb, get_ip_address());
+			return 2;
+		}
+		break;
+	case 'P':
+		strbuf_addstr_or_null(sb, tcp_port);
+		return 1;
+	case 'D':
+		strbuf_addstr(sb, context->directory);
+		return 1;
+	}
+	return 0;
+}
+
 static const char *path_ok(const char *directory)
 {
 	static char rpath[PATH_MAX];

@@ -160,14 +200,10 @@ static const char *path_ok(const char *directory)
 	}
 	else if (interpolated_path && saw_extended_args) {
 		struct strbuf expanded_path = STRBUF_INIT;
-		struct strbuf_expand_dict_entry dict[6];
-
-		dict[0].placeholder = "H"; dict[0].value = hostname;
-		dict[1].placeholder = "CH"; dict[1].value = get_canon_hostname();
-		dict[2].placeholder = "IP"; dict[2].value = get_ip_address();
-		dict[3].placeholder = "P"; dict[3].value = tcp_port;
-		dict[4].placeholder = "D"; dict[4].value = directory;
-		dict[5].placeholder = NULL; dict[5].value = NULL;
+		struct expand_path_context context;
+
+		context.directory = directory;
+
 		if (*dir != '/') {
 			/* Allow only absolute */
 			logerror("'%s': Non-absolute path denied (interpolated-path active)", dir);

@@ -175,7 +211,7 @@ static const char *path_ok(const char *directory)
 		}
 
 		strbuf_expand(&expanded_path, interpolated_path,
-				strbuf_expand_dict_cb, &dict);
+			      expand_path, &context);
 		strlcpy(interp_path, expanded_path.buf, PATH_MAX);
 		strbuf_release(&expanded_path);
 		loginfo("Interpolated dir '%s'", interp_path);