Fix errors in the JSON parser.

lib/json/json.dart

Index: lib/json/json.dart
diff --git a/lib/json/json.dart b/lib/json/json.dart
index a3542c5cf0aca1258bb40b883277f838b3d237c1..0c52517c3a08e6c1f56e9877742300d97f9759ff 100644
--- a/lib/json/json.dart
+++ b/lib/json/json.dart
@@ -96,7 +96,9 @@ class _JsonParser {
     return new _JsonParser._internal(json)._parseToplevel();
   }
 
-  _JsonParser._internal(String json) : this.json = '${json} ' {
+  _JsonParser._internal(String json)

[Anton Muhin, 2012/04/28 09:09:24]

nit: ._internal(this.json) ?

[Anders Johnsen, 2012/04/28 09:28:26]

Not possible when extracting length in initializer list. :(

+      : json = json,
+        length = json.length {
     if (tokens !== null) return;
 
     // Use a list as jump-table, faster then switch and if.
@@ -221,7 +223,7 @@ class _JsonParser {
       }
       if (c == BACKSLASH) {
         position++;
-        if (position == json.length) {
+        if (position == length) {
           _error('\\ at the end of input');
         }
 
@@ -251,7 +253,7 @@ class _JsonParser {
             c = TAB;
             break;
           case CHAR_U:
-            if (position + 5 > json.length) {
+            if (position + 5 > length) {
               _error('Invalid unicode esacape sequence');
             }
             final codeString = json.substring(position + 1, position + 5);
@@ -291,15 +293,15 @@ class _JsonParser {
     if (_isChar(DOT)) {
       position++;
       if (_isDigit()) {
+        position++;
         isInt = false;
         while (_isDigit()) position++;
       } else {
-        position--;  // No digit, backtrack.
+        _error("Expected digit following comma");

[Anton Muhin, 2012/04/28 09:09:24]

nit: single quotes

[Anton Muhin, 2012/04/28 09:09:24]

is it a correct thing, may we double check with JS if indeed 1. shouldn't be
parsable.  I just asking.  And if not, please, add a test (if absent)

[Anders Johnsen, 2012/04/28 09:28:26]

Done.

[Anders Johnsen, 2012/04/28 09:28:26]

There is not token in JSON that can follow a number and start with a '.', so I
think saying expected digit after '.' is better then saying invalid token to
'.'.

I test for the case of '3.a'.

       }
     }
 
     if (_isChar(CHAR_E) || _isChar(CHAR_CAPITAL_E)) {

[Anton Muhin, 2012/04/28 09:09:24]

ditto here: fetch char once and then do both checks.

[Anders Johnsen, 2012/04/28 09:28:26]

Done.

-      int backtrackTo = position;
       position++;
       if (_isChar(MINUS) || _isChar(PLUS)) position++;

[Anton Muhin, 2012/04/28 09:09:24]

ditto

[Anders Johnsen, 2012/04/28 09:28:26]

Done.

       if (_isDigit()) {
@@ -307,7 +309,7 @@ class _JsonParser {
         isInt = false;
         while (_isDigit()) position++;
       } else {
-        position = backtrackTo;  // No digit, backtrack.
+        _error("Expected digit following 'e' or 'E'");

[Anton Muhin, 2012/04/28 09:09:24]

ditto nit for ''

[Anders Johnsen, 2012/04/28 09:28:26]

Done.

       }
     }
 
@@ -319,17 +321,21 @@ class _JsonParser {
     }
   }
 
-  bool _isChar(int char) => _char() == char;
+  bool _isChar(int char) {
+    if (position >= length) return false;
+    return json.charCodeAt(position) == char;
+  }
 
   bool _isDigit() {
-    int char = _char();
+    if (position >= length) return false;
+    int char = json.charCodeAt(position);
     return char >= CHAR_0 && char <= CHAR_9;
   }
 
   bool _isToken(int tokenKind) => _token() == tokenKind;
 
   int _char() {
-    if (position >= json.length) {
+    if (position >= length) {
       _error("Unexpected end of JSON stream");
     }
     return json.charCodeAt(position);
@@ -337,14 +343,14 @@ class _JsonParser {
 
   int _token() {
     while (true) {
-      if (position >= json.length) return null;
+      if (position >= length) return null;
       int char = json.charCodeAt(position);
       int token = tokens[char];
       if (token === WHITESPACE) {
         position++;
         continue;
       }
-      if (token === null) _error("Invalid JSON token");
+      if (token === null) return 0;
       return token;
     }
   }
@@ -354,6 +360,7 @@ class _JsonParser {
   }
 
   final String json;
+  final int length;
   int position = 0;
   static List<int> tokens;
 }