lib/json: Faster `parse_json_string` implementation

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>

diff --git a/lib/json/string_parser.nit b/lib/json/string_parser.nit
index d429697..51d302e 100644 (file)
--- a/lib/json/string_parser.nit
+++ b/lib/json/string_parser.nit
@@ -231,32 +231,103 @@ class JSONStringParser
                return val
        end
 
+       private var parse_str_buf = new FlatBuffer
+
        # Parses and returns a Nit string from a JSON String
        fun parse_json_string: Jsonable do
+               var src = src
                var ln = src.length
                var p = pos
                p += 1
                if p > ln then return make_parse_error("Malformed JSON String")
                var c = src[p]
-               var st = p
+               var ret = parse_str_buf
+               var chunk_st = p
                while c != '"' do
-                       if c == '\\' then
-                               if p + 1 >= ln then return make_parse_error("Malformed Escape sequence in JSON string")
+                       if c != '\\' then
                                p += 1
+                               if p >= ln then return make_parse_error("Malformed JSON string")
                                c = src[p]
-                               if c == 'u' then
+                               continue
+                       end
+                       ret.append_substring_impl(src, chunk_st, p - chunk_st)
+                       p += 1
+                       if p >= ln then return make_parse_error("Malformed Escape sequence in JSON string")
+                       c = src[p]
+                       if c == 'r' then
+                               ret.add '\r'
+                               p += 1
+                       else if c == 'n' then
+                               ret.add '\n'
+                               p += 1
+                       else if c == 't' then
+                               ret.add '\t'
+                               p += 1
+                       else if c == 'u' then
+                               var cp = 0
+                               p += 1
+                               for i in [0 .. 4[ do
+                                       cp <<= 4
+                                       if p >= ln then make_parse_error("Malformed \uXXXX Escape sequence in JSON string")
+                                       c = src[p]
+                                       if c >= '0' and c <= '9' then
+                                               cp += c.code_point - '0'.code_point
+                                       else if c >= 'a' and c <= 'f' then
+                                               cp += c.code_point - 'a'.code_point + 10
+                                       else if c >= 'A' and c <= 'F' then
+                                               cp += c.code_point - 'A'.code_point + 10
+                                       else
+                                               make_parse_error("Malformed \uXXXX Escape sequence in JSON string")
+                                       end
                                        p += 1
-                                       if p + 3 >= ln then return make_parse_error("Bad Unicode escape sequence in string")
-                                       for i in [0 .. 4[ do if not src[p + i].is_hexdigit then return make_parse_error("Bad Unicode escape sequence in string")
-                                       p += 3
                                end
+                               c = cp.code_point
+                               if cp >= 0xD800 and cp <= 0xDBFF then
+                                       if p >= ln then make_parse_error("Malformed \uXXXX Escape sequence in JSON string")
+                                       c = src[p]
+                                       if c != '\\' then make_parse_error("Malformed \uXXXX Escape sequence in JSON string")
+                                       p += 1
+                                       c = src[p]
+                                       if c != 'u' then make_parse_error("Malformed \uXXXX Escape sequence in JSON string")
+                                       var locp = 0
+                                       p += 1
+                                       for i in [0 .. 4[ do
+                                               locp <<= 4
+                                               if p > ln then make_parse_error("Malformed \uXXXX Escape sequence in JSON string")
+                                               c = src[p]
+                                               if c >= '0' and c <= '9' then
+                                                       locp += c.code_point - '0'.code_point
+                                               else if c >= 'a' and c <= 'f' then
+                                                       locp += c.code_point - 'a'.code_point + 10
+                                               else if c >= 'A' and c <= 'F' then
+                                                       locp += c.code_point - 'A'.code_point + 10
+                                               else
+                                                       make_parse_error("Malformed \uXXXX Escape sequence in JSON string")
+                                               end
+                                               p += 1
+                                       end
+                                       c = (((locp & 0x3FF) | ((cp & 0x3FF) << 10)) + 0x10000).code_point
+                               end
+                               ret.add c
+                       else if c == 'b' then
+                               ret.add 8.code_point
+                               p += 1
+                       else if c == 'f' then
+                               ret.add '\f'
+                               p += 1
+                       else
+                               p += 1
+                               ret.add c
                        end
-                       p += 1
-                       if p >= ln then return make_parse_error("Malformed JSON String")
+                       chunk_st = p
                        c = src[p]
                end
                pos = p + 1
-               return src.substring(st, p - st).unescape_json
+               if ret.is_empty then return src.substring(chunk_st, p - chunk_st)
+               ret.append_substring_impl(src, chunk_st, p - chunk_st)
+               var rets = ret.to_s
+               ret.clear
+               return rets
        end
 
        # Ignores any character until a JSON separator is encountered