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