Source/DebuggerConnection.m

   1 /*
   2  * MacGDBp
   3  * Copyright (c) 2007 - 2010, Blue Static <http://www.bluestatic.org>
   4  *
   5  * This program is free software; you can redistribute it and/or modify it under the terms of the GNU
   6  * General Public License as published by the Free Software Foundation; either version 2 of the
   7  * License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
  10  * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along with this program; if not,
  14  * write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
  15  */
  16
  17 #import "DebuggerConnection.h"
  18
  19 #import <sys/socket.h>
  20 #import <netinet/in.h>
  21
  22 #import "AppDelegate.h"
  23 #import "LoggingController.h"
  24
  25 // DebuggerConnection (Private) ////////////////////////////////////////////////
  26
  27 @interface DebuggerConnection ()
  28
  29 @property (assign) CFSocketRef socket;
  30 @property (assign) CFReadStreamRef readStream;
  31 @property NSUInteger lastReadTransaction;
  32 @property (retain) NSMutableString* currentPacket;
  33 @property (assign) CFWriteStreamRef writeStream;
  34 @property NSUInteger lastWrittenTransaction;
  35 @property (retain) NSMutableArray* queuedWrites;
  36
  37 - (void)connectionThreadStart;
  38
  39 - (void)socketDidAccept;
  40 - (void)socketDisconnected;
  41 - (void)readStreamHasData;
  42
  43 - (void)performSend:(NSString*)command;
  44 - (void)sendQueuedWrites;
  45
  46 - (void)performQuitSignal;
  47
  48 - (void)handleResponse:(NSXMLDocument*)response;
  49 - (void)handlePacket:(NSString*)packet;
  50
  51 // Threadsafe wrappers for the delegate's methods.
  52 - (void)errorEncountered:(NSString*)error;
  53 - (LogEntry*)recordSend:(NSString*)command;
  54 - (LogEntry*)recordReceive:(NSString*)command;
  55
  56 @end
  57
  58 // CFNetwork Callbacks /////////////////////////////////////////////////////////
  59
  60 void ReadStreamCallback(CFReadStreamRef stream, CFStreamEventType eventType, void* connectionRaw)
  61 {
  62   DebuggerConnection* connection = (DebuggerConnection*)connectionRaw;
  63   switch (eventType)
  64   {
  65     case kCFStreamEventHasBytesAvailable:
  66       [connection readStreamHasData];
  67       break;
  68
  69     case kCFStreamEventErrorOccurred:
  70     {
  71       CFErrorRef error = CFReadStreamCopyError(stream);
  72       CFReadStreamUnscheduleFromRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
  73       CFReadStreamClose(stream);
  74       CFRelease(stream);
  75       [connection errorEncountered:[[(NSError*)error autorelease] description]];
  76       break;
  77     }
  78
  79     case kCFStreamEventEndEncountered:
  80       CFReadStreamUnscheduleFromRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
  81       CFReadStreamClose(stream);
  82       CFRelease(stream);
  83       [connection socketDisconnected];
  84       break;
  85   };
  86 }
  87
  88 void WriteStreamCallback(CFWriteStreamRef stream, CFStreamEventType eventType, void* connectionRaw)
  89 {
  90   DebuggerConnection* connection = (DebuggerConnection*)connectionRaw;
  91   switch (eventType)
  92   {
  93     case kCFStreamEventCanAcceptBytes:
  94       [connection sendQueuedWrites];
  95       break;
  96
  97     case kCFStreamEventErrorOccurred:
  98     {
  99       CFErrorRef error = CFWriteStreamCopyError(stream);
 100       CFWriteStreamUnscheduleFromRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
 101       CFWriteStreamClose(stream);
 102       CFRelease(stream);
 103       [connection errorEncountered:[[(NSError*)error autorelease] description]];
 104       break;
 105     }
 106
 107     case kCFStreamEventEndEncountered:
 108       CFWriteStreamUnscheduleFromRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
 109       CFWriteStreamClose(stream);
 110       CFRelease(stream);
 111       [connection socketDisconnected];
 112       break;
 113   }
 114 }
 115
 116 void SocketAcceptCallback(CFSocketRef socket,
 117                           CFSocketCallBackType callbackType,
 118                           CFDataRef address,
 119                           const void* data,
 120                           void* connectionRaw)
 121 {
 122   assert(callbackType == kCFSocketAcceptCallBack);
 123   NSLog(@"SocketAcceptCallback()");
 124
 125   DebuggerConnection* connection = (DebuggerConnection*)connectionRaw;
 126
 127   CFReadStreamRef readStream;
 128   CFWriteStreamRef writeStream;
 129
 130   // Create the streams on the socket.
 131   CFStreamCreatePairWithSocket(kCFAllocatorDefault,
 132                                *(CFSocketNativeHandle*)data,  // Socket handle.
 133                                &readStream,  // Read stream in-pointer.
 134                                &writeStream);  // Write stream in-pointer.
 135
 136   // Create struct to register callbacks for the stream.
 137   CFStreamClientContext context;
 138   context.version = 0;
 139   context.info = connection;
 140   context.retain = NULL;
 141   context.release = NULL;
 142   context.copyDescription = NULL;
 143
 144   // Set the client of the read stream.
 145   CFOptionFlags readFlags =
 146       kCFStreamEventOpenCompleted |
 147       kCFStreamEventHasBytesAvailable |
 148       kCFStreamEventErrorOccurred |
 149       kCFStreamEventEndEncountered;
 150   if (CFReadStreamSetClient(readStream, readFlags, ReadStreamCallback, &context))
 151     // Schedule in run loop to do asynchronous communication with the engine.
 152     CFReadStreamScheduleWithRunLoop(readStream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
 153   else
 154     return;
 155
 156   // Open the stream now that it's scheduled on the run loop.
 157   if (!CFReadStreamOpen(readStream))
 158   {
 159     CFStreamError error = CFReadStreamGetError(readStream);
 160     NSLog(@"error! %@", error);
 161     return;
 162   }
 163
 164   // Set the client of the write stream.
 165   CFOptionFlags writeFlags =
 166       kCFStreamEventOpenCompleted |
 167       kCFStreamEventCanAcceptBytes |
 168       kCFStreamEventErrorOccurred |
 169       kCFStreamEventEndEncountered;
 170   if (CFWriteStreamSetClient(writeStream, writeFlags, WriteStreamCallback, &context))
 171     // Schedule it in the run loop to receive error information.
 172     CFWriteStreamScheduleWithRunLoop(writeStream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
 173   else
 174     return;
 175
 176   // Open the write stream.
 177   if (!CFWriteStreamOpen(writeStream))
 178   {
 179     CFStreamError error = CFWriteStreamGetError(writeStream);
 180     NSLog(@"error! %@", error);
 181     return;
 182   }
 183
 184   connection.readStream = readStream;
 185   connection.writeStream = writeStream;
 186   [connection socketDidAccept];
 187 }
 188
 189 // Other Run Loop Callbacks ////////////////////////////////////////////////////
 190
 191 void PerformQuitSignal(void* info)
 192 {
 193   DebuggerConnection* obj = (DebuggerConnection*)info;
 194   [obj performQuitSignal];
 195 }
 196
 197 ////////////////////////////////////////////////////////////////////////////////
 198
 199 @implementation DebuggerConnection
 200
 201 @synthesize port = port_;
 202 @synthesize connected = connected_;
 203 @synthesize delegate = delegate_;
 204
 205 @synthesize socket = socket_;
 206 @synthesize readStream = readStream_;
 207 @synthesize lastReadTransaction = lastReadTransaction_;
 208 @synthesize currentPacket = currentPacket_;
 209 @synthesize writeStream = writeStream_;
 210 @synthesize lastWrittenTransaction = lastWrittenTransaction_;
 211 @synthesize queuedWrites = queuedWrites_;
 212
 213 - (id)initWithPort:(NSUInteger)aPort
 214 {
 215   if (self = [super init])
 216   {
 217     port_ = aPort;
 218   }
 219   return self;
 220 }
 221
 222 - (void)dealloc
 223 {
 224   self.currentPacket = nil;
 225   [super dealloc];
 226 }
 227
 228 /**
 229  * Kicks off the socket on another thread.
 230  */
 231 - (void)connect
 232 {
 233   if (thread_ && !connected_) {
 234     // A thread has been detached but the socket has yet to connect. Do not
 235     // spawn a new thread otherwise multiple threads will be blocked on the same
 236     // socket.
 237     return;
 238   }
 239   [NSThread detachNewThreadSelector:@selector(connectionThreadStart) toTarget:self withObject:nil];
 240 }
 241
 242 /**
 243  * Creates, connects to, and schedules a CFSocket.
 244  */
 245 - (void)connectionThreadStart
 246 {
 247   NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
 248
 249   thread_ = [NSThread currentThread];
 250   runLoop_ = [NSRunLoop currentRunLoop];
 251
 252   // Pass ourselves to the callback so we don't have to use ugly globals.
 253   CFSocketContext context;
 254   context.version = 0;
 255   context.info = self;
 256   context.retain = NULL;
 257   context.release = NULL;
 258   context.copyDescription = NULL;
 259
 260   // Create the address structure.
 261   struct sockaddr_in address;
 262   memset(&address, 0, sizeof(address));
 263   address.sin_len = sizeof(address);
 264   address.sin_family = AF_INET;
 265   address.sin_port = htons(port_);
 266   address.sin_addr.s_addr = htonl(INADDR_ANY);
 267
 268   // Create the socket signature.
 269   CFSocketSignature signature;
 270   signature.protocolFamily = PF_INET;
 271   signature.socketType = SOCK_STREAM;
 272   signature.protocol = IPPROTO_TCP;
 273   signature.address = (CFDataRef)[NSData dataWithBytes:&address length:sizeof(address)];
 274
 275   socket_ = CFSocketCreateWithSocketSignature(kCFAllocatorDefault,
 276                                               &signature,  // Socket signature.
 277                                               kCFSocketAcceptCallBack,  // Callback types.
 278                                               SocketAcceptCallback,  // Callout function pointer.
 279                                               &context);  // Context to pass to callout.
 280   if (!socket_)
 281   {
 282     [self errorEncountered:@"Could not open socket."];
 283     return;
 284   }
 285
 286   // Allow old, yet-to-be recycled sockets to be reused.
 287   BOOL yes = YES;
 288   setsockopt(CFSocketGetNative(socket_), SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(BOOL));
 289
 290   // Schedule the socket on the run loop.
 291   CFRunLoopSourceRef source = CFSocketCreateRunLoopSource(kCFAllocatorDefault, socket_, 0);
 292   CFRunLoopAddSource([runLoop_ getCFRunLoop], source, kCFRunLoopCommonModes);
 293   CFRelease(source);
 294
 295   // Create a source that is used to quit.
 296   CFRunLoopSourceContext quitContext = { 0 };
 297   quitContext.version = 0;
 298   quitContext.info = self;
 299   quitContext.perform = PerformQuitSignal;
 300   quitSource_ = CFRunLoopSourceCreate(kCFAllocatorDefault, 0, &quitContext);
 301   CFRunLoopAddSource([runLoop_ getCFRunLoop], quitSource_, kCFRunLoopCommonModes);
 302
 303   CFRunLoopRun();
 304
 305   thread_ = nil;
 306   runLoop_ = nil;
 307
 308   CFRunLoopSourceInvalidate(quitSource_);
 309   CFRelease(quitSource_);
 310   quitSource_ = NULL;
 311
 312   [pool release];
 313 }
 314
 315 /**
 316  * Called by SocketWrapper after the connection is successful. This immediately calls
 317  * -[SocketWrapper receive] to clear the way for communication, though the information
 318  * could be useful server information that we don't use right now.
 319  */
 320 - (void)socketDidAccept
 321 {
 322   connected_ = YES;
 323   transactionID = 1;
 324   self.queuedWrites = [NSMutableArray array];
 325   writeQueueLock_ = [NSRecursiveLock new];
 326 }
 327
 328 /**
 329  * Closes a socket and releases the ref.
 330  */
 331 - (void)close
 332 {
 333   if (thread_) {
 334     [thread_ cancel];
 335   }
 336   if (runLoop_ && quitSource_) {
 337     CFRunLoopSourceSignal(quitSource_);
 338     CFRunLoopWakeUp([runLoop_ getCFRunLoop]);
 339   }
 340 }
 341
 342 /**
 343  * Quits the run loop and stops the thread.
 344  */
 345 - (void)performQuitSignal
 346 {
 347   self.queuedWrites = nil;
 348   connected_ = NO;
 349   [writeQueueLock_ release];
 350
 351   if (runLoop_) {
 352     CFRunLoopStop([runLoop_ getCFRunLoop]);
 353   }
 354
 355   // The socket goes down, so do the streams, which clean themselves up.
 356   if (socket_) {
 357     CFSocketInvalidate(socket_);
 358     CFRelease(socket_);
 359     socket_ = NULL;
 360   }
 361 }
 362
 363 /**
 364  * Notification that the socket disconnected.
 365  */
 366 - (void)socketDisconnected
 367 {
 368   if (connected_) {
 369     // The state still is connected, which means that we did not get here
 370     // through normal disconnected procedure (a call to |-close|, followed by
 371     // the downing of the socket and the stream, which also produces this
 372     // messsage). Instead, the stream callbacks encountered EOF unexpectedly.
 373     [self close];
 374   }
 375   if ([delegate_ respondsToSelector:@selector(connectionDidClose:)])
 376     [delegate_ connectionDidClose:self];
 377 }
 378
 379 /**
 380  * Writes a command into the write stream. If the stream is ready for writing,
 381  * we do so immediately. If not, the command is queued and will be written
 382  * when the stream is ready.
 383  */
 384 - (void)send:(NSString*)command
 385 {
 386   if (lastReadTransaction_ >= lastWrittenTransaction_ && CFWriteStreamCanAcceptBytes(writeStream_)) {
 387     [self performSend:command];
 388   } else {
 389     [writeQueueLock_ lock];
 390     [queuedWrites_ addObject:command];
 391     [writeQueueLock_ unlock];
 392   }
 393   [self sendQueuedWrites];
 394 }
 395
 396 /**
 397  * This will send a command to the debugger engine. It will append the
 398  * transaction ID automatically. It accepts a NSString command along with a
 399  * a variable number of arguments to substitute into the command, a la
 400  * +[NSString stringWithFormat:]. Returns the transaction ID as a NSNumber.
 401  */
 402 - (NSNumber*)sendCommandWithFormat:(NSString*)format, ...
 403 {
 404   // Collect varargs and format command.
 405   va_list args;
 406   va_start(args, format);
 407   NSString* command = [[NSString alloc] initWithFormat:format arguments:args];
 408   va_end(args);
 409
 410   NSNumber* callbackKey = [NSNumber numberWithInt:transactionID++];
 411   NSString* taggedCommand = [NSString stringWithFormat:@"%@ -i %@", [command autorelease], callbackKey];
 412   [self performSelector:@selector(send:)
 413                onThread:thread_
 414              withObject:taggedCommand
 415           waitUntilDone:YES];
 416
 417   return callbackKey;
 418 }
 419
 420 /**
 421  * Given a file path, this returns a file:// URI and escapes any spaces for the
 422  * debugger engine.
 423  */
 424 - (NSString*)escapedURIPath:(NSString*)path
 425 {
 426   // Custon GDBp paths are fine.
 427   if ([[path substringToIndex:4] isEqualToString:@"gdbp"])
 428     return path;
 429
 430   // Create a temporary URL that will escape all the nasty characters.
 431   NSURL* url = [NSURL fileURLWithPath:path];
 432   NSString* urlString = [url absoluteString];
 433
 434   // Remove the host because this is a file:// URL;
 435   urlString = [urlString stringByReplacingOccurrencesOfString:[url host] withString:@""];
 436
 437   // Escape % for use in printf-style NSString formatters.
 438   urlString = [urlString stringByReplacingOccurrencesOfString:@"%" withString:@"%%"];
 439   return urlString;
 440 }
 441
 442 /**
 443  * Returns the transaction_id from an NSXMLDocument.
 444  */
 445 - (NSInteger)transactionIDFromResponse:(NSXMLDocument*)response
 446 {
 447   return [[[[response rootElement] attributeForName:@"transaction_id"] stringValue] intValue];
 448 }
 449
 450 /**
 451  * Scans a command string for the transaction ID component. If it is not found,
 452  * returns NSNotFound.
 453  */
 454 - (NSInteger)transactionIDFromCommand:(NSString*)command
 455 {
 456   NSRange occurrence = [command rangeOfString:@"-i "];
 457   if (occurrence.location == NSNotFound)
 458     return NSNotFound;
 459   NSString* transaction = [command substringFromIndex:occurrence.location + occurrence.length];
 460   return [transaction intValue];
 461 }
 462
 463 // Private /////////////////////////////////////////////////////////////////////
 464 #pragma mark Private
 465
 466 // Delegate Thread-Safe Wrappers ///////////////////////////////////////////////
 467
 468 /**
 469  * Receives errors from the SocketWrapper and updates the display
 470  */
 471 - (void)errorEncountered:(NSString*)error
 472 {
 473   if (![delegate_ respondsToSelector:@selector(errorEncountered:)])
 474     return;
 475   [delegate_ performSelectorOnMainThread:@selector(errorEncountered:)
 476                               withObject:error
 477                            waitUntilDone:NO];
 478 }
 479
 480 - (LogEntry*)recordSend:(NSString*)command
 481 {
 482   LoggingController* logger = [[AppDelegate instance] loggingController];
 483   LogEntry* entry = [LogEntry newSendEntry:command];
 484   entry.lastReadTransactionID = lastReadTransaction_;
 485   entry.lastWrittenTransactionID = lastWrittenTransaction_;
 486   [logger performSelectorOnMainThread:@selector(recordEntry:)
 487                            withObject:entry
 488                         waitUntilDone:NO];
 489   return [entry autorelease];
 490 }
 491
 492 - (LogEntry*)recordReceive:(NSString*)command
 493 {
 494   LoggingController* logger = [[AppDelegate instance] loggingController];
 495   LogEntry* entry = [LogEntry newReceiveEntry:command];
 496   entry.lastReadTransactionID = lastReadTransaction_;
 497   entry.lastWrittenTransactionID = lastWrittenTransaction_;
 498   [logger performSelectorOnMainThread:@selector(recordEntry:)
 499                            withObject:entry
 500                         waitUntilDone:NO];
 501   return [entry autorelease];
 502 }
 503
 504 // Stream Managers /////////////////////////////////////////////////////////////
 505
 506 /**
 507  * Callback from the CFReadStream that there is data waiting to be read.
 508  */
 509 - (void)readStreamHasData
 510 {
 511   const NSUInteger kBufferSize = 1024;
 512   UInt8 buffer[kBufferSize];
 513   CFIndex bufferOffset = 0;  // Starting point in |buffer| to work with.
 514   CFIndex bytesRead = CFReadStreamRead(readStream_, buffer, kBufferSize);
 515   const char* charBuffer = (const char*)buffer;
 516
 517   // The read loop works by going through the buffer until all the bytes have
 518   // been processed.
 519   while (bufferOffset < bytesRead)
 520   {
 521     // Find the NULL separator, or the end of the string.
 522     NSUInteger partLength = 0;
 523     for (NSUInteger i = bufferOffset; i < bytesRead && charBuffer[i] != '\0'; ++i, ++partLength) ;
 524
 525     // If there is not a current packet, set some state.
 526     if (!self.currentPacket)
 527     {
 528       // Read the message header: the size.  This will be |partLength| bytes.
 529       packetSize_ = atoi(charBuffer + bufferOffset);
 530       currentPacketIndex_ = 0;
 531       self.currentPacket = [NSMutableString stringWithCapacity:packetSize_];
 532       bufferOffset += partLength + 1;  // Pass over the NULL byte.
 533       continue;  // Spin the loop to begin reading actual data.
 534     }
 535
 536     // Substring the byte stream and append it to the packet string.
 537     CFStringRef bufferString = CFStringCreateWithBytes(kCFAllocatorDefault,
 538                                                        buffer + bufferOffset,  // Byte pointer, offset by start index.
 539                                                        partLength,  // Length.
 540                                                        kCFStringEncodingUTF8,
 541                                                        true);
 542     [self.currentPacket appendString:(NSString*)bufferString];
 543     CFRelease(bufferString);
 544
 545     // Advance counters.
 546     currentPacketIndex_ += partLength;
 547     bufferOffset += partLength + 1;
 548
 549     // If this read finished the packet, handle it and reset.
 550     if (currentPacketIndex_ >= packetSize_)
 551     {
 552       [self handlePacket:[[currentPacket_ retain] autorelease]];
 553       self.currentPacket = nil;
 554       packetSize_ = 0;
 555       currentPacketIndex_ = 0;
 556     }
 557   }
 558 }
 559
 560 /**
 561  * Performs the packet handling of a raw string XML packet. From this point on,
 562  * the packets are associated with a transaction and are then dispatched.
 563  */
 564 - (void)handlePacket:(NSString*)packet
 565 {
 566   // Test if we can convert it into an NSXMLDocument.
 567   NSError* error = nil;
 568   NSXMLDocument* xmlTest = [[NSXMLDocument alloc] initWithXMLString:currentPacket_ options:NSXMLDocumentTidyXML error:&error];
 569
 570   // Try to recover if we encountered an error.
 571   if (!xmlTest)
 572   {
 573     // We do not want to starve the write queue, so manually parse out the
 574     // transaction ID.
 575     NSRange location = [currentPacket_ rangeOfString:@"transaction_id"];
 576     if (location.location != NSNotFound)
 577     {
 578       NSUInteger start = location.location + location.length;
 579       NSUInteger end = start;
 580
 581       NSCharacterSet* numericSet = [NSCharacterSet decimalDigitCharacterSet];
 582
 583       // Loop over the characters after the attribute name to extract the ID.
 584       while (end < [currentPacket_ length])
 585       {
 586         unichar c = [currentPacket_ characterAtIndex:end];
 587         if ([numericSet characterIsMember:c])
 588         {
 589           // If this character is numeric, extend the range to substring.
 590           ++end;
 591         }
 592         else
 593         {
 594           if (start == end)
 595           {
 596             // If this character is nonnumeric and we have nothing in the
 597             // range, skip this character.
 598             ++start;
 599             ++end;
 600           }
 601           else
 602           {
 603             // We've moved past the numeric ID so we should stop searching.
 604             break;
 605           }
 606         }
 607       }
 608
 609       // If we were able to extract the transaction ID, update the last read.
 610       NSRange substringRange = NSMakeRange(start, end - start);
 611       NSString* transactionStr = [currentPacket_ substringWithRange:substringRange];
 612       if ([transactionStr length])
 613         lastReadTransaction_ = [transactionStr intValue];
 614     }
 615
 616     // Otherwise, assume +1 and hope it works.
 617     ++lastReadTransaction_;
 618   }
 619   else
 620   {
 621     // See if the transaction can be parsed out.
 622     NSInteger transaction = [self transactionIDFromResponse:xmlTest];
 623     if (transaction < lastReadTransaction_)
 624     {
 625       NSLog(@"tx = %d vs %d", transaction, lastReadTransaction_);
 626       NSLog(@"out of date transaction %@", packet);
 627       return;
 628     }
 629
 630     if (transaction != lastWrittenTransaction_)
 631       NSLog(@"txn %d <> %d last written, %d last read", transaction, lastWrittenTransaction_, lastReadTransaction_);
 632
 633     lastReadTransaction_ = transaction;
 634   }
 635
 636   // Log this receive event.
 637   LogEntry* log = [self recordReceive:currentPacket_];
 638   log.error = error;
 639
 640   // Finally, dispatch the handler for this response.
 641   [self handleResponse:[xmlTest autorelease]];
 642 }
 643
 644 - (void)handleResponse:(NSXMLDocument*)response
 645 {
 646   // Check and see if there's an error.
 647   NSArray* error = [[response rootElement] elementsForName:@"error"];
 648   if ([error count] > 0)
 649   {
 650     NSLog(@"Xdebug error: %@", error);
 651     NSString* errorMessage = [[[[error objectAtIndex:0] children] objectAtIndex:0] stringValue];
 652     [self errorEncountered:errorMessage];
 653   }
 654
 655   if ([[[response rootElement] name] isEqualToString:@"init"])
 656   {
 657     [delegate_ performSelectorOnMainThread:@selector(handleInitialResponse:)
 658                                 withObject:response
 659                              waitUntilDone:NO];
 660     return;
 661   }
 662
 663   if ([delegate_ respondsToSelector:@selector(handleResponse:)])
 664     [delegate_ performSelectorOnMainThread:@selector(handleResponse:)
 665                                 withObject:response
 666                              waitUntilDone:NO];
 667
 668   [self sendQueuedWrites];
 669 }
 670
 671 /**
 672  * This performs a blocking send. This should ONLY be called when we know we
 673  * have write access to the stream. We will busy wait in case we don't do a full
 674  * send.
 675  */
 676 - (void)performSend:(NSString*)command
 677 {
 678   // If this is an out-of-date transaction, do not bother sending it.
 679   NSInteger transaction = [self transactionIDFromCommand:command];
 680   if (transaction != NSNotFound && transaction < lastWrittenTransaction_)
 681     return;
 682
 683   BOOL done = NO;
 684
 685   char* string = (char*)[command UTF8String];
 686   int stringLength = strlen(string);
 687
 688   // Busy wait while writing. BAADD. Should background this operation.
 689   while (!done)
 690   {
 691     if (CFWriteStreamCanAcceptBytes(writeStream_))
 692     {
 693       // Include the NULL byte in the string when we write.
 694       int bytesWritten = CFWriteStreamWrite(writeStream_, (UInt8*)string, stringLength + 1);
 695       if (bytesWritten < 0)
 696       {
 697         NSLog(@"write error");
 698       }
 699       // Incomplete write.
 700       else if (bytesWritten < strlen(string))
 701       {
 702         // Adjust the buffer and wait for another chance to write.
 703         stringLength -= bytesWritten;
 704         memmove(string, string + bytesWritten, stringLength);
 705       }
 706       else
 707       {
 708         done = YES;
 709
 710         // We need to scan the string to find the transactionID.
 711         if (transaction == NSNotFound)
 712         {
 713           NSLog(@"sent %@ without a transaction ID", command);
 714           continue;
 715         }
 716         lastWrittenTransaction_ = transaction;
 717       }
 718     }
 719   }
 720
 721   // Log this trancation.
 722   [self recordSend:command];
 723 }
 724
 725 /**
 726  * Checks if there are unsent commands in the |queuedWrites_| queue and sends
 727  * them if it's OK to do so. This will not block.
 728  */
 729 - (void)sendQueuedWrites
 730 {
 731   if (!connected_)
 732     return;
 733
 734   [writeQueueLock_ lock];
 735   if (lastReadTransaction_ >= lastWrittenTransaction_ && [queuedWrites_ count] > 0)
 736   {
 737     NSString* command = [queuedWrites_ objectAtIndex:0];
 738
 739     // We don't want to block because this is called from the main thread.
 740     // |-performSend:| busy waits when the stream is not ready. Bail out
 741     // before we do that becuase busy waiting is BAD.
 742     if (CFWriteStreamCanAcceptBytes(writeStream_))
 743     {
 744       [self performSend:command];
 745       [queuedWrites_ removeObjectAtIndex:0];
 746     }
 747   }
 748   [writeQueueLock_ unlock];
 749 }
 750
 751 @end