util.json: Optimize long string parsing.

diff --git a/util/json.lua b/util/json.lua
index 9c2dd2c6127b6d9275ffba29639eab079ca82d52..6251af1a0ac5b05501e9e222aa4d468587e9d286 100644 (file)
--- a/util/json.lua
+++ b/util/json.lua
@@ -258,16 +258,16 @@ function json.decode(json)
                return val;
        end
        local function readstring()
-               local s = "";
+               local s = {};
                checkandskip("\"");
                while ch do
                        while ch and ch ~= "\\" and ch ~= "\"" do
-                               s = s..ch; next();
+                               t_insert(s, ch); next();
                        end
                        if ch == "\\" then
                                next();
                                if unescapes[ch] then
-                                       s = s..unescapes[ch];
+                                       t_insert(s, unescapes[ch]);
                                        next();
                                elseif ch == "u" then
                                        local seq = "";
@@ -277,13 +277,13 @@ function json.decode(json)
                                                if not ch:match("[0-9a-fA-F]") then error("invalid unicode escape sequence in string"); end
                                                seq = seq..ch;
                                        end
-                                       s = s..codepoint_to_utf8(tonumber(seq, 16));
+                                       t_insert(s, codepoint_to_utf8(tonumber(seq, 16)));
                                        next();
                                else error("invalid escape sequence in string"); end
                        end
                        if ch == "\"" then
                                next();
-                               return s;
+                               return t_concat(s);
                        end
                end
                error("eof while reading string");