mcs/class/System.ServiceModel.Web/System.Runtime.Serialization.Json/JsonReader.cs

   1 //
   2 // JsonWriter.cs
   3 //
   4 // Author:
   5 //      Atsushi Enomoto  <atsushi@ximian.com>
   6 //
   7 // Copyright (C) 2007 Novell, Inc (http://www.novell.com)
   8 //
   9 // Permission is hereby granted, free of charge, to any person obtaining
  10 // a copy of this software and associated documentation files (the
  11 // "Software"), to deal in the Software without restriction, including
  12 // without limitation the rights to use, copy, modify, merge, publish,
  13 // distribute, sublicense, and/or sell copies of the Software, and to
  14 // permit persons to whom the Software is furnished to do so, subject to
  15 // the following conditions:
  16 //
  17 // The above copyright notice and this permission notice shall be
  18 // included in all copies or substantial portions of the Software.
  19 //
  20 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  21 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  22 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  23 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  24 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  25 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  26 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  27 //
  28 using System;
  29 using System.Collections.Generic;
  30 using System.Globalization;
  31 using System.IO;
  32 using System.Text;
  33 using System.Xml;
  34
  35 namespace System.Runtime.Serialization.Json
  36 {
  37         class PushbackReader : StreamReader
  38         {
  39                 Stack<int> pushback;
  40
  41                 public PushbackReader (Stream stream, Encoding encoding) : base (stream, encoding)
  42                 {
  43                         pushback = new Stack<int>();
  44                 }
  45
  46                 public PushbackReader (Stream stream) : base (stream, true)
  47                 {
  48                         pushback = new Stack<int>();
  49                 }
  50
  51                 public override void Close ()
  52                 {
  53                         pushback.Clear ();
  54                 }
  55
  56                 public override int Peek ()
  57                 {
  58                         if (pushback.Count > 0) {
  59                                 return pushback.Peek ();
  60                         }
  61                         else {
  62                                 return base.Peek ();
  63                         }
  64                 }
  65
  66                 public override int Read ()
  67                 {
  68                         if (pushback.Count > 0) {
  69                                 return pushback.Pop ();
  70                         }
  71                         else {
  72                                 return base.Read ();
  73                         }
  74                 }
  75
  76                 public void Pushback (int ch)
  77                 {
  78                         pushback.Push (ch);
  79                 }
  80         }
  81
  82         // FIXME: quotas check
  83         class JsonReader : XmlDictionaryReader, IXmlJsonReaderInitializer, IXmlLineInfo
  84         {
  85                 class ElementInfo
  86                 {
  87                         public readonly string Name;
  88                         public readonly string Type;
  89                         public bool HasContent;
  90
  91                         public ElementInfo (string name, string type)
  92                         {
  93                                 this.Name = name;
  94                                 this.Type = type;
  95                         }
  96                 }
  97
  98                 enum AttributeState
  99                 {
 100                         None,
 101                         Type,
 102                         TypeValue,
 103                         RuntimeType,
 104                         RuntimeTypeValue
 105                 }
 106
 107                 PushbackReader reader;
 108                 XmlDictionaryReaderQuotas quotas;
 109                 OnXmlDictionaryReaderClose on_close;
 110                 XmlNameTable name_table = new NameTable ();
 111
 112                 XmlNodeType current_node;
 113                 AttributeState attr_state;
 114                 string simple_value;
 115                 string next_element;
 116                 string current_runtime_type, next_object_content_name;
 117                 ReadState read_state = ReadState.Initial;
 118                 bool content_stored;
 119                 bool finished;
 120                 Stack<ElementInfo> elements = new Stack<ElementInfo> ();
 121
 122                 int line = 1, column = 0;
 123
 124                 // Constructors
 125
 126                 public JsonReader (byte [] buffer, int offset, int count, Encoding encoding, XmlDictionaryReaderQuotas quotas, OnXmlDictionaryReaderClose onClose)
 127                 {
 128                         SetInput (buffer, offset, count, encoding, quotas, onClose);
 129                 }
 130
 131                 public JsonReader (Stream stream, Encoding encoding, XmlDictionaryReaderQuotas quotas, OnXmlDictionaryReaderClose onClose)
 132                 {
 133                         SetInput (stream, encoding, quotas, onClose);
 134                 }
 135
 136                 internal bool LameSilverlightLiteralParser { get; set; }
 137
 138                 // IXmlLineInfo
 139
 140                 public bool HasLineInfo ()
 141                 {
 142                         return true;
 143                 }
 144
 145                 public int LineNumber {
 146                         get { return line; }
 147                 }
 148
 149                 public int LinePosition {
 150                         get { return column; }
 151                 }
 152
 153                 // IXmlJsonReaderInitializer
 154
 155                 public void SetInput (byte [] buffer, int offset, int count, Encoding encoding, XmlDictionaryReaderQuotas quotas, OnXmlDictionaryReaderClose onClose)
 156                 {
 157                         SetInput (new MemoryStream (buffer, offset, count), encoding, quotas, onClose);
 158                 }
 159
 160                 public void SetInput (Stream stream, Encoding encoding, XmlDictionaryReaderQuotas quotas, OnXmlDictionaryReaderClose onClose)
 161                 {
 162                         if (encoding != null)
 163                                 reader = new PushbackReader (stream, encoding);
 164                         else
 165                                 reader = new PushbackReader (stream);
 166                         if (quotas == null)
 167                                 throw new ArgumentNullException ("quotas");
 168                         this.quotas = quotas;
 169                         this.on_close = onClose;
 170                 }
 171
 172                 // XmlDictionaryReader
 173
 174                 public override int AttributeCount {
 175                         get { return current_node != XmlNodeType.Element ? 0 : current_runtime_type != null ? 2 : 1; }
 176                 }
 177
 178                 public override string BaseURI {
 179                         get { return String.Empty; }
 180                 }
 181
 182                 public override int Depth {
 183                         get {
 184                                 int mod = 0;
 185                                 switch (attr_state) {
 186                                 case AttributeState.Type:
 187                                 case AttributeState.RuntimeType:
 188                                         mod++;
 189                                         break;
 190                                 case AttributeState.TypeValue:
 191                                 case AttributeState.RuntimeTypeValue:
 192                                         mod += 2;
 193                                         break;
 194                                 case AttributeState.None:
 195                                         if (NodeType == XmlNodeType.Text)
 196                                                 mod++;
 197                                         break;
 198                                 }
 199                                 return read_state != ReadState.Interactive ? 0 : elements.Count - 1 + mod;
 200                         }
 201                 }
 202
 203                 public override bool EOF {
 204                         get {
 205                                 switch (read_state) {
 206                                 case ReadState.Closed:
 207                                 case ReadState.EndOfFile:
 208                                         return true;
 209                                 default:
 210                                         return false;
 211                                 }
 212                         }
 213                 }
 214
 215                 public override bool HasValue {
 216                         get {
 217                                 switch (NodeType) {
 218                                 case XmlNodeType.Attribute:
 219                                 case XmlNodeType.Text:
 220                                         return true;
 221                                 default:
 222                                         return false;
 223                                 }
 224                         }
 225                 }
 226
 227                 public override bool IsEmptyElement {
 228                         get { return false; }
 229                 }
 230
 231                 public override string LocalName {
 232                         get {
 233                                 switch (attr_state) {
 234                                 case AttributeState.Type:
 235                                         return "type";
 236                                 case AttributeState.RuntimeType:
 237                                         return "__type";
 238                                 }
 239                                 switch (NodeType) {
 240                                 case XmlNodeType.Element:
 241                                 case XmlNodeType.EndElement:
 242                                         return elements.Peek ().Name;
 243                                 default:
 244                                         return String.Empty;
 245                                 }
 246                         }
 247                 }
 248
 249                 public override string NamespaceURI {
 250                         get { return String.Empty; }
 251                 }
 252
 253                 public override XmlNameTable NameTable {
 254                         get { return name_table; }
 255                 }
 256
 257                 public override XmlNodeType NodeType {
 258                         get {
 259                                 switch (attr_state) {
 260                                 case AttributeState.Type:
 261                                 case AttributeState.RuntimeType:
 262                                         return XmlNodeType.Attribute;
 263                                 case AttributeState.TypeValue:
 264                                 case AttributeState.RuntimeTypeValue:
 265                                         return XmlNodeType.Text;
 266                                 default:
 267                                         return current_node;
 268                                 }
 269                         }
 270                 }
 271
 272                 public override string Prefix {
 273                         get { return String.Empty; }
 274                 }
 275
 276                 public override ReadState ReadState {
 277                         get { return read_state; }
 278                 }
 279
 280                 public override string Value {
 281                         get {
 282                                 switch (attr_state) {
 283                                 case AttributeState.Type:
 284                                 case AttributeState.TypeValue:
 285                                         return elements.Peek ().Type;
 286                                 case AttributeState.RuntimeType:
 287                                 case AttributeState.RuntimeTypeValue:
 288                                         return current_runtime_type;
 289                                 default:
 290                                         return current_node == XmlNodeType.Text ? simple_value : String.Empty;
 291                                 }
 292                         }
 293                 }
 294
 295                 public override void Close ()
 296                 {
 297                         if (on_close != null) {
 298                                 on_close (this);
 299                                 on_close = null;
 300                         }
 301                         read_state = ReadState.Closed;
 302                 }
 303
 304                 public override string GetAttribute (int index)
 305                 {
 306                         if (index == 0 && current_node == XmlNodeType.Element)
 307                                 return elements.Peek ().Type;
 308                         else if (index == 1 && current_runtime_type != null)
 309                                 return current_runtime_type;
 310                         throw new ArgumentOutOfRangeException ("index", "Index is must be either 0 or 1 when there is an explicit __type in the object, and only valid on an element on this XmlDictionaryReader");
 311                 }
 312
 313                 public override string GetAttribute (string name)
 314                 {
 315                         if (current_node != XmlNodeType.Element)
 316                                 return null;
 317                         switch (name) {
 318                         case "type":
 319                                 return elements.Peek ().Type;
 320                         case "__type":
 321                                 return current_runtime_type;
 322                         default:
 323                                 return null;
 324                         }
 325                 }
 326
 327                 public override string GetAttribute (string localName, string ns)
 328                 {
 329                         if (ns == String.Empty)
 330                                 return GetAttribute (localName);
 331                         else
 332                                 return null;
 333                 }
 334
 335                 public override string LookupNamespace (string prefix)
 336                 {
 337                         if (prefix == null)
 338                                 throw new ArgumentNullException ("prefix");
 339                         else if (prefix.Length == 0)
 340                                 return String.Empty;
 341                         return null;
 342                 }
 343
 344                 public override bool MoveToAttribute (string name)
 345                 {
 346                         if (current_node != XmlNodeType.Element)
 347                                 return false;
 348                         switch (name) {
 349                         case "type":
 350                                 attr_state = AttributeState.Type;
 351                                 return true;
 352                         case "__type":
 353                                 if (current_runtime_type == null)
 354                                         return false;
 355                                 attr_state = AttributeState.RuntimeType;
 356                                 return true;
 357                         default:
 358                                 return false;
 359                         }
 360                 }
 361
 362                 public override bool MoveToAttribute (string localName, string ns)
 363                 {
 364                         if (ns != String.Empty)
 365                                 return false;
 366                         return MoveToAttribute (localName);
 367                 }
 368
 369                 public override bool MoveToElement ()
 370                 {
 371                         if (attr_state == AttributeState.None)
 372                                 return false;
 373                         attr_state = AttributeState.None;
 374                         return true;
 375                 }
 376
 377                 public override bool MoveToFirstAttribute ()
 378                 {
 379                         if (current_node != XmlNodeType.Element)
 380                                 return false;
 381                         attr_state = AttributeState.Type;
 382                         return true;
 383                 }
 384
 385                 public override bool MoveToNextAttribute ()
 386                 {
 387                         if (attr_state == AttributeState.None)
 388                                 return MoveToFirstAttribute ();
 389                         else
 390                                 return MoveToAttribute ("__type");
 391                 }
 392
 393                 public override bool ReadAttributeValue ()
 394                 {
 395                         switch (attr_state) {
 396                         case AttributeState.Type:
 397                                 attr_state = AttributeState.TypeValue;
 398                                 return true;
 399                         case AttributeState.RuntimeType:
 400                                 attr_state = AttributeState.RuntimeTypeValue;
 401                                 return true;
 402                         }
 403                         return false;
 404                 }
 405
 406                 public override void ResolveEntity ()
 407                 {
 408                         throw new NotSupportedException ();
 409                 }
 410
 411                 public override bool Read ()
 412                 {
 413                         switch (read_state) {
 414                         case ReadState.EndOfFile:
 415                         case ReadState.Closed:
 416                         case ReadState.Error:
 417                                 return false;
 418                         case ReadState.Initial:
 419                                 read_state = ReadState.Interactive;
 420                                 next_element = "root";
 421                                 current_node = XmlNodeType.Element;
 422                                 break;
 423                         }
 424
 425                         MoveToElement ();
 426
 427                         if (content_stored) {
 428                                 if (current_node == XmlNodeType.Element) {
 429                                         if (elements.Peek ().Type == "null") {
 430                                                 // since null is not consumed as text content, it skips Text state.
 431                                                 current_node = XmlNodeType.EndElement;
 432                                                 content_stored = false;
 433                                         }
 434                                         else
 435                                                 current_node = XmlNodeType.Text;
 436                                         return true;
 437                                 } else if (current_node == XmlNodeType.Text) {
 438                                         current_node = XmlNodeType.EndElement;
 439                                         content_stored = false;
 440                                         return true;
 441                                 }
 442                         }
 443                         else if (current_node == XmlNodeType.EndElement) {
 444                                 // clear EndElement state
 445                                 elements.Pop ();
 446                                 if (elements.Count > 0)
 447                                         elements.Peek ().HasContent = true;
 448                                 else
 449                                         finished = true;
 450                         }
 451
 452                         SkipWhitespaces ();
 453
 454                         attr_state = AttributeState.None;
 455                         // Default. May be overriden only as EndElement or None.
 456                         current_node = XmlNodeType.Element;
 457
 458                         if (!ReadContent (false))
 459                                 return false;
 460                         if (finished)
 461                                 throw XmlError ("Multiple top-level content is not allowed");
 462                         return true;
 463                 }
 464
 465                 bool TryReadString (string str)
 466                 {
 467                         for (int i = 0; i < str.Length; i ++) {
 468                                 int ch = ReadChar ();
 469                                 if (ch != str[i]) {
 470                                         for (int j = i; j >= 0; j--)
 471                                                 PushbackChar (j);
 472                                         return false;
 473                                 }
 474                         }
 475
 476                         return true;
 477                 }
 478
 479                 bool ReadContent (bool objectValue)
 480                 {
 481                         int ch = ReadChar ();
 482                         if (ch < 0) {
 483                                 ReadEndOfStream ();
 484                                 return false;
 485                         }
 486
 487                         bool itemMustFollow = false;
 488
 489                         if (!objectValue && elements.Count > 0 && elements.Peek ().HasContent) {
 490                                 if (ch == ',') {
 491                                         switch (elements.Peek ().Type) {
 492                                         case "object":
 493                                         case "array":
 494                                                 SkipWhitespaces ();
 495                                                 ch = ReadChar ();
 496                                                 itemMustFollow = true;
 497                                                 break;
 498                                         }
 499                                 }
 500                                 else if (ch != '}' && ch != ']')
 501                                         throw XmlError ("Comma is required unless an array or object is at the end");
 502                         }
 503
 504                         if (elements.Count > 0 && elements.Peek ().Type == "array")
 505                                 next_element = "item";
 506                         else if (next_object_content_name != null) {
 507                                 next_element = next_object_content_name;
 508                                 next_object_content_name = null;
 509                                 if (ch != ':')
 510                                         throw XmlError ("':' is expected after a name of an object content");
 511                                 SkipWhitespaces ();
 512                                 ReadContent (true);
 513                                 return true;
 514                         }
 515
 516                         switch (ch) {
 517                         case '{':
 518                                 ReadStartObject ();
 519                                 return true;
 520                         case '[':
 521                                 ReadStartArray ();
 522                                 return true;
 523                         case '}':
 524                                 if (itemMustFollow)
 525                                         throw XmlError ("Invalid comma before an end of object");
 526                                 if (objectValue)
 527                                         throw XmlError ("Invalid end of object as an object content");
 528                                 ReadEndObject ();
 529                                 return true;
 530                         case ']':
 531                                 if (itemMustFollow)
 532                                         throw XmlError ("Invalid comma before an end of array");
 533                                 if (objectValue)
 534                                         throw XmlError ("Invalid end of array as an object content");
 535                                 ReadEndArray ();
 536                                 return true;
 537                         case '"':
 538                                 bool lame = LameSilverlightLiteralParser && ch != '"';
 539                                 string s = ReadStringLiteral (lame);
 540                                 if (!objectValue && elements.Count > 0 && elements.Peek ().Type == "object") {
 541                                         next_element = s;
 542                                         SkipWhitespaces ();
 543                                         if (!lame)
 544                                                 Expect (':');
 545                                         SkipWhitespaces ();
 546                                         ReadContent (true);
 547                                 }
 548                                 else
 549                                         ReadAsSimpleContent ("string", s);
 550                                 return true;
 551                         case '-':
 552                                 ReadNumber (ch);
 553                                 return true;
 554                         case 'n':
 555                                 if (TryReadString("ull")) {
 556                                         ReadAsSimpleContent ("null", "null");
 557                                         return true;
 558                                 }
 559                                 else {
 560                                         // the pushback for 'n' is taken care of by the
 561                                         // default case if we're in lame silverlight literal
 562                                         // mode
 563                                         goto default;
 564                                 }
 565                         case 't':
 566                                 if (TryReadString ("rue")) {
 567                                         ReadAsSimpleContent ("boolean", "true");
 568                                         return true;
 569                                 }
 570                                 else {
 571                                         // the pushback for 't' is taken care of by the
 572                                         // default case if we're in lame silverlight literal
 573                                         // mode
 574                                         goto default;
 575                                 }
 576                         case 'f':
 577                                 if (TryReadString ("alse")) {
 578                                         ReadAsSimpleContent ("boolean", "false");
 579                                         return true;
 580                                 }
 581                                 else {
 582                                         // the pushback for 'f' is taken care of by the
 583                                         // default case if we're in lame silverlight literal
 584                                         // mode
 585                                         goto default;
 586                                 }
 587                         default:
 588                                 if ('0' <= ch && ch <= '9') {
 589                                         ReadNumber (ch);
 590                                         return true;
 591                                 }
 592                                 if (LameSilverlightLiteralParser) {
 593                                         PushbackChar (ch);
 594                                         goto case '"';
 595                                 }
 596                                 throw XmlError (String.Format ("Unexpected token: '{0}' ({1:X04})", (char) ch, (int) ch));
 597                         }
 598                 }
 599
 600                 void ReadStartObject ()
 601                 {
 602                         ElementInfo ei = new ElementInfo (next_element, "object");
 603                         elements.Push (ei);
 604
 605                         SkipWhitespaces ();
 606                         if (PeekChar () == '"') { // it isn't premise: the object might be empty
 607                                 ReadChar ();
 608                                 string s = ReadStringLiteral ();
 609                                 if (s == "__type") {
 610                                         SkipWhitespaces ();
 611                                         Expect (':');
 612                                         SkipWhitespaces ();
 613                                         Expect ('"');
 614                                         current_runtime_type = ReadStringLiteral ();
 615                                         SkipWhitespaces ();
 616                                         ei.HasContent = true;
 617                                 }
 618                                 else
 619                                         next_object_content_name = s;
 620                         }
 621                 }
 622
 623                 void ReadStartArray ()
 624                 {
 625                         elements.Push (new ElementInfo (next_element, "array"));
 626                 }
 627
 628                 void ReadEndObject ()
 629                 {
 630                         if (elements.Count == 0 || elements.Peek ().Type != "object")
 631                                 throw XmlError ("Unexpected end of object");
 632                         current_node = XmlNodeType.EndElement;
 633                 }
 634
 635                 void ReadEndArray ()
 636                 {
 637                         if (elements.Count == 0 || elements.Peek ().Type != "array")
 638                                 throw XmlError ("Unexpected end of array");
 639                         current_node = XmlNodeType.EndElement;
 640                 }
 641
 642                 void ReadEndOfStream ()
 643                 {
 644                         if (elements.Count > 0)
 645                                 throw XmlError (String.Format ("{0} missing end of arrays or objects", elements.Count));
 646                         read_state = ReadState.EndOfFile;
 647                         current_node = XmlNodeType.None;
 648                 }
 649
 650                 void ReadAsSimpleContent (string type, string value)
 651                 {
 652                         elements.Push (new ElementInfo (next_element, type));
 653                         simple_value = value;
 654                         content_stored = true;
 655                 }
 656
 657                 void ReadNumber (int ch)
 658                 {
 659                         elements.Push (new ElementInfo (next_element, "number"));
 660                         content_stored = true;
 661
 662                         int init = ch;
 663                         int prev;
 664                         bool floating = false, exp = false;
 665
 666                         StringBuilder sb = new StringBuilder ();
 667                         bool cont = true;
 668                         do {
 669                                 sb.Append ((char) ch);
 670                                 prev = ch;
 671                                 ch = ReadChar ();
 672
 673                                 if (prev == '-' && !IsNumber (ch)) // neither '.', '-' or '+' nor anything else is valid
 674                                         throw XmlError ("Invalid JSON number");
 675
 676                                 switch (ch) {
 677                                 case 'e':
 678                                 case 'E':
 679                                         if (exp)
 680                                                 throw XmlError ("Invalid JSON number token. Either 'E' or 'e' must not occur more than once");
 681                                         if (!IsNumber (prev))
 682                                                 throw XmlError ("Invalid JSON number token. only a number is valid before 'E' or 'e'");
 683                                         exp = true;
 684                                         break;
 685                                 case '.':
 686                                         if (floating)
 687                                                 throw XmlError ("Invalid JSON number token. '.' must not occur twice");
 688                                         if (exp)
 689                                                 throw XmlError ("Invalid JSON number token. '.' must not occur after 'E' or 'e'");
 690                                         floating = true;
 691                                         break;
 692                                 case '+':
 693                                 case '-':
 694                                         if (prev == 'E' || prev == 'e')
 695                                                 break;
 696                                         goto default;
 697                                 default:
 698                                         if (!IsNumber (ch)) {
 699                                                 PushbackChar (ch);
 700                                                 cont = false;
 701                                         }
 702                                         break;
 703                                 }
 704                         } while (cont);
 705
 706                         if (!IsNumber (prev)) // only number is valid at the end
 707                                 throw XmlError ("Invalid JSON number");
 708
 709                         simple_value = sb.ToString ();
 710
 711                         if (init == '0' && !floating && !exp && simple_value != "0")
 712                                 throw XmlError ("Invalid JSON number");
 713                 }
 714
 715                 bool IsNumber (int c)
 716                 {
 717                         return '0' <= c && c <= '9';
 718                 }
 719
 720                 StringBuilder vb = new StringBuilder ();
 721
 722                 string ReadStringLiteral ()
 723                 {
 724                         return ReadStringLiteral (false);
 725                 }
 726
 727                 string ReadStringLiteral (bool endWithColon)
 728                 {
 729                         vb.Length = 0;
 730                         while (true) {
 731                                 int c = ReadChar ();
 732                                 if (c < 0)
 733                                         throw XmlError ("JSON string is not closed");
 734                                 if (c == '"' && !endWithColon)
 735                                         return vb.ToString ();
 736                                 else if (c == ':' && endWithColon)
 737                                         return vb.ToString ();
 738                                 else if (c != '\\') {
 739                                         vb.Append ((char) c);
 740                                         continue;
 741                                 }
 742
 743                                 // escaped expression
 744                                 c = ReadChar ();
 745                                 if (c < 0)
 746                                         throw XmlError ("Invalid JSON string literal; incomplete escape sequence");
 747                                 switch (c) {
 748                                 case '"':
 749                                 case '\\':
 750                                 case '/':
 751                                         vb.Append ((char) c);
 752                                         break;
 753                                 case 'b':
 754                                         vb.Append ('\x8');
 755                                         break;
 756                                 case 'f':
 757                                         vb.Append ('\f');
 758                                         break;
 759                                 case 'n':
 760                                         vb.Append ('\n');
 761                                         break;
 762                                 case 'r':
 763                                         vb.Append ('\r');
 764                                         break;
 765                                 case 't':
 766                                         vb.Append ('\t');
 767                                         break;
 768                                 case 'u':
 769                                         ushort cp = 0;
 770                                         for (int i = 0; i < 4; i++) {
 771                                                 if ((c = ReadChar ()) < 0)
 772                                                         throw XmlError ("Incomplete unicode character escape literal");
 773                                                 cp *= 16;
 774                                                 if ('0' <= c && c <= '9')
 775                                                         cp += (ushort) (c - '0');
 776                                                 if ('A' <= c && c <= 'F')
 777                                                         cp += (ushort) (c - 'A' + 10);
 778                                                 if ('a' <= c && c <= 'f')
 779                                                         cp += (ushort) (c - 'a' + 10);
 780                                         }
 781                                         vb.Append ((char) cp);
 782                                         break;
 783                                 default:
 784                                         throw XmlError ("Invalid JSON string literal; unexpected escape character");
 785                                 }
 786                         }
 787                 }
 788
 789                 int PeekChar ()
 790                 {
 791                         return reader.Peek ();
 792                 }
 793
 794                 int ReadChar ()
 795                 {
 796                         int v = reader.Read ();
 797                         if (v == '\n') {
 798                                 line++;
 799                                 column = 0;
 800                         }
 801                         else
 802                                 column++;
 803                         return v;
 804                 }
 805
 806                 void PushbackChar (int ch)
 807                 {
 808                         // FIXME handle lines (and columns?  ugh, how?)
 809                         reader.Pushback (ch);
 810                 }
 811
 812                 void SkipWhitespaces ()
 813                 {
 814                         do {
 815                                 switch (PeekChar ()) {
 816                                 case ' ':
 817                                 case '\t':
 818                                 case '\r':
 819                                 case '\n':
 820                                         ReadChar ();
 821                                         continue;
 822                                 default:
 823                                         return;
 824                                 }
 825                         } while (true);
 826                 }
 827
 828                 void Expect (char c)
 829                 {
 830                         int v = ReadChar ();
 831                         if (v < 0)
 832                                 throw XmlError (String.Format ("Expected '{0}' but got EOF", c));
 833                         if (v != c)
 834                                 throw XmlError (String.Format ("Expected '{0}' but got '{1}'", c, (char) v));
 835                 }
 836
 837                 Exception XmlError (string s)
 838                 {
 839                         return new XmlException (String.Format ("{0} ({1},{2})", s, line, column));
 840                 }
 841         }
 842 }