Rewrite the json_tokener_state_inf handling in json_tokener to be simpler, and avoid needless copying of the input into a temporary buffer.

json_tokener.c

@@ -57,7 +57,8 @@
 static const char json_null_str[] = "null";
 static const int json_null_str_len = sizeof(json_null_str) - 1;
 static const char json_inf_str[] = "Infinity";
-static const int json_inf_str_len = sizeof(json_inf_str) - 1;
+static const char json_inf_str_lower[] = "infinity";
+static const unsigned int json_inf_str_len = sizeof(json_inf_str) - 1;
 static const char json_nan_str[] = "NaN";
 static const int json_nan_str_len = sizeof(json_nan_str) - 1;
 static const char json_true_str[] = "true";
@@ -383,40 +384,55 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
       tok->depth--;
       goto redo_char;
 
-    case json_tokener_state_inf: /* aka starts with 'i' */
+    case json_tokener_state_inf: /* aka starts with 'i' (or 'I', or "-i", or "-I") */
       {
-	size_t size_inf;
+	/* If we were guaranteed to have len set, then we could (usually) handle
+	 * the entire "Infinity" check in a single strncmp (strncasecmp), but
+	 * since len might be -1 (i.e. "read until \0"), we need to check it
+	 * a character at a time.
+	 * Trying to handle it both ways would make this code considerably more
+	 * complicated with likely little performance benefit.
+	 */
 	int is_negative = 0;
-	char *infbuf;
+	const char *_json_inf_str = json_inf_str;
+	if (!(tok->flags & JSON_TOKENER_STRICT))
+		_json_inf_str = json_inf_str_lower;
 
-	printbuf_memappend_fast(tok->pb, &c, 1);
-	size_inf = json_min(tok->st_pos+1, json_inf_str_len);
-	infbuf = tok->pb->buf;
-	if (*infbuf == '-')
-	{
-		infbuf++;
-		is_negative = 1;
-	}
-	if ((!(tok->flags & JSON_TOKENER_STRICT) &&
-	          strncasecmp(json_inf_str, infbuf, size_inf) == 0) ||
-	         (strncmp(json_inf_str, infbuf, size_inf) == 0)
-	        )
+	/* Note: tok->st_pos must be 0 when state is set to json_tokener_state_inf */
+	while (tok->st_pos < (int)json_inf_str_len)
 	{
-		if (tok->st_pos == json_inf_str_len)
+		char inf_char = *str;
+		if (!(tok->flags & JSON_TOKENER_STRICT))
+			inf_char = tolower(*str);
+		if (inf_char != _json_inf_str[tok->st_pos])
 		{
-			current = json_object_new_double(is_negative
-							 ? -INFINITY : INFINITY);
-			if(current == NULL)
-			    goto out;
-			saved_state = json_tokener_state_finish;
-			state = json_tokener_state_eatws;
-			goto redo_char;
+			tok->err = json_tokener_error_parse_unexpected;
+			goto out;
+		}
+		tok->st_pos++;
+		(void)ADVANCE_CHAR(str, tok);
+		if (!PEEK_CHAR(c, tok))
+		{
+			/* out of input chars, for now at least */
+			goto out;
 		}
-	} else {
-		tok->err = json_tokener_error_parse_unexpected;
-		goto out;
 	}
-	tok->st_pos++;
+	/* We checked the full length of "Infinity", so create the object.
+	 * When handling -Infinity, the number parsing code will have dropped
+	 * the "-" into tok->pb for us, so check it now.
+	 */
+	if (printbuf_length(tok->pb) > 0 && *(tok->pb->buf) == '-')
+	{
+		is_negative = 1;
+	}
+	current = json_object_new_double(is_negative
+					 ? -INFINITY : INFINITY);
+	if (current == NULL)
+		goto out;
+	saved_state = json_tokener_state_finish;
+	state = json_tokener_state_eatws;
+	goto redo_char;
+	 
       }
       break;
     case json_tokener_state_null: /* aka starts with 'n' */
@@ -934,7 +950,7 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
     }
     if (!ADVANCE_CHAR(str, tok))
       goto out;
-  } /* while(POP_CHAR) */
+  } /* while(PEEK_CHAR) */
 
  out:
   if (c &&