MINOR: lua: Add date functions

This patch add date parsing function in Lua API. These function
are usefull for parsing standard HTTP date provided in headers.

src/hlua_fcn.c

@@ -22,6 +22,56 @@ int hlua_now(lua_State *L)
 	return 1;
 }
 
+/* This functions expects a Lua string as HTTP date, parse it and
+ * returns an integer containing the epoch format of the date, or
+ * nil if the parsing fails.
+ */
+static int hlua_parse_date(lua_State *L, int (*fcn)(const char *, int, struct tm*))
+{
+	const char *str;
+	size_t len;
+	struct tm tm;
+	time_t time;
+
+	str = luaL_checklstring(L, 1, &len);
+
+	if (!fcn(str, len, &tm)) {
+		lua_pushnil(L);
+		return 1;
+	}
+
+	/* This function considers the content of the broken-down time
+	 * is exprimed in the UTC timezone. timegm don't care about
+	 * the gnu variable tm_gmtoff. If gmtoff is set, or if you know
+	 * the timezone from the broken-down time, it must be fixed
+	 * after the conversion.
+	 */
+	time = timegm(&tm);
+	if (time == -1) {
+		lua_pushnil(L);
+		return 1;
+	}
+
+	lua_pushinteger(L, (int)time);
+	return 1;
+}
+static int hlua_http_date(lua_State *L)
+{
+	return hlua_parse_date(L, parse_http_date);
+}
+static int hlua_imf_date(lua_State *L)
+{
+	return hlua_parse_date(L, parse_imf_date);
+}
+static int hlua_rfc850_date(lua_State *L)
+{
+	return hlua_parse_date(L, parse_rfc850_date);
+}
+static int hlua_asctime_date(lua_State *L)
+{
+	return hlua_parse_date(L, parse_asctime_date);
+}
+
 static void hlua_array_add_fcn(lua_State *L, const char *name,
                                int (*function)(lua_State *L))
 {
@@ -33,5 +83,9 @@ static void hlua_array_add_fcn(lua_State *L, const char *name,
 int hlua_fcn_reg_core_fcn(lua_State *L)
 {
 	hlua_array_add_fcn(L, "now", hlua_now);
-	return 1;
+	hlua_array_add_fcn(L, "http_date", hlua_http_date);
+	hlua_array_add_fcn(L, "imf_date", hlua_imf_date);
+	hlua_array_add_fcn(L, "rfc850_date", hlua_rfc850_date);
+	hlua_array_add_fcn(L, "asctime_date", hlua_asctime_date);
+	return 5;
 }