ios - 由于流中的优化，值暂时不可用

Question

我最近开始使用发布版本测试我的应用程序(管理方案并设置从调试到发布的运行)。我注意到的是，偶尔我会在流方法中弹出以下错误，但我似乎无法找到找到错误的方法。这在 Debug模式下完美运行，但在发布版本中，除了 SIGABRT 消息外，我没有收到任何通知。我也不知道如何检查模拟器上的崩溃日志以查看问题所在。下面我附上了崩溃的堆栈跟踪:

#0  0x918749c6 in __pthread_kill ()
#1  0x916c0f78 in pthread_kill ()
#2  0x916b1ce3 in __abort ()
#3  0x916ae64a in __stack_chk_fail ()
#4  0x00006d0d in -[MainViewController processMessage:len:] (_cmd=0x9ceb9, msg=0xdfd7004 "Login="User" Pass="Pass" Id="1234" PlayerId="345" Location="12,35" Color="Red" PlayerId="65" Location="180,0" Color="Blue" PlayerId="29" Location="0,200" Color="..., len=333295) at /Users/seb/Desktop/Tutorials/Networking/MainViewController.m:850
#5  0x000044b3 in -[MainViewController stream:handleEvent:] (_cmd=0x17a0410, stream=<value temporarily unavailable, due to optimizations>, eventCode=<value temporarily unavailable, due to optimizations>) at /Users/seb/Desktop/Tutorials/Networking/MainViewController.m:260
#6  0x01716501 in _inputStreamCallbackFunc ()
#7  0x016e606d in _signalEventSync ()
#8  0x016e67ca in _cfstream_solo_signalEventSync ()
#9  0x016e5e71 in _CFStreamSignalEvent ()
#10 0x016e6727 in CFReadStreamSignalEvent ()
#11 0x020083ad in SocketStream::dispatchSignalFromSocketCallbackUnlocked ()
#12 0x01f64191 in SocketStream::socketCallback ()
#13 0x01f640a1 in SocketStream::_SocketCallBack_stream ()
#14 0x016b3e44 in __CFSocketPerformV0 ()
#15 0x0171997f in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ ()
#16 0x0167cb73 in __CFRunLoopDoSources0 ()
#17 0x0167c454 in __CFRunLoopRun ()
#18 0x0167bdb4 in CFRunLoopRunSpecific ()
#19 0x0167bccb in CFRunLoopRunInMode ()
#20 0x0226f879 in GSEventRunModal ()
#21 0x0226f93e in GSEventRun ()
#22 0x0066aa9b in UIApplicationMain ()
#23 0x0000201b in main (argc=1, argv=0xbffff5e0) at /Users/seb/Desktop/Tutorials/Networking/main.m:14

stream:handleevent 中发生崩溃的案例语句:

case NSStreamEventHasBytesAvailable:
        {
            if (stream == inputStream)
            {
                NSLog(@"NSStreamEventHasBytesAvailable");

                uint8_t buffer[4096];
                unsigned int len = 0;
                NSInputStream* inputstream = (NSInputStream*)stream;
                len = [inputstream read:buffer maxLength:sizeof(buffer)];

                // Check if our stream is still valid
                if([inputstream streamError] != nil)
                {
                    //We lost our connection to the host
                    NSError *theError = [stream streamError];
                    [self setConnectError:[NSString stringWithFormat:@"Error %i: %@",
                                                            [theError code], [theError localizedDescription]]];

                    break;
                }

                [streamIncomingData appendBytes:buffer length:len];

                int processedBytes = 0;
                while (true)
                {
                    if ([streamIncomingData length] >= processedBytes + sizeof(uint32_t))
                    {
                        const char* bufferstart = ((const char*)[streamIncomingData mutableBytes]) + processedBytes;
                        uint32_t sz_n;
                        memcpy(&sz_n, bufferstart, sizeof(sz_n));
                        uint32_t sz_h = htonl(sz_n);

                        if ([streamIncomingData length] >= processedBytes + sz_h + sizeof(uint32_t))
                        {
                            [self processMessage:bufstart + sizeof(uint32_t) len:sz_h];
                            processedBytes += sz_h + sizeof(uint32_t);
                        }
                        else
                        {
                            break;
                        }
                    }
                    else
                    {
                        break;
                    }
                }
                if (processedBytes)
                {
                    if (processedBytes < [streamIncomingData length])
                    {
                        NSMutableData *newdata = [NSMutableData dataWithBytes:[streamIncomingData bytes] + processedBytes length:[streamIncomingData length] - processedBytes];
                        [streamIncomingData setData:newdata];
                    }
                    else
                    {
                        [streamIncomingData setLength:0];
                    }
                }
            }

            break;
        }

processMessage 方法:

- (void)processMessage:(const char*)msg len:(int)len
{
    NSLog(@"processMessage start (%d)", len);
    {
        char buffer[len + 1];
        memcpy(buffer, msg, len);
        buffer[len + 1] = '\0';
        NSLog(@"%s", buffer);
    }

    NSLog(@"processMessage end");
}

非常感谢任何建议。

Answer 1

您尝试在边界 len + 1 之外分配空终止符，导致 buffer 溢出，从而破坏了堆栈。正确的代码是:

    char buffer[len + 1];
    memcpy(buffer, msg, len);
    buffer[len] = '\0';
    NSLog(@"%s", buffer);

您所做的是未定义的行为，将未定义的行为与针对 Release模式所做的优化相结合很可能是您仅在 Release模式下看到此问题的原因。