iOS：使用CFStreamCreatePairWithSocketToHost的套接字网络基础

用例

我正在使用套接字使用CFStreamCreatePairWithSocketToHost()发送和接收数据,并试图在发送多组数据(即不仅仅是1个请求)时如何完成此操作.

问题

目前我可以发送数据并接收响应(即1次往返).但是,在我发送outputStream中的所有数据后,流被关闭(即接收NSStreamEventEndEncountered).

题

所以问题是,当我想发送多个数据请求时会发生什么？

>每次要发送新数据对象时,是否设置了新套接字？
>我是否必须重置outputStream并发送更多数据.

码

大部分代码来自Cocoa Streams Documentation：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view,typically from a nib.

    _data = [[NSMutableData alloc] init];
    [self initNetworkCommunication];

    [self sendString:@"Hello World!"];
}

- (void)initNetworkCommunication {
    CFReadStreamRef readStream;
    CFWriteStreamRef writeStream;

    CFStreamCreatePairWithSocketToHost(NULL,(CFStringRef)@"123.456.0.0",1234,&readStream,&writeStream);

    inputStream = (NSInputStream *)readStream; // ivar
    [inputStream setDelegate:self];
    [inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [inputStream open];

    outputStream = (NSOutputStream *)writeStream; // ivar
    [outputStream setDelegate:self];
    [outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [outputStream open];
}

- (void)sendString:(NSString *)string {
    NSData *data = [[NSData alloc] initWithData:[string dataUsingEncoding:NSASCIIStringEncoding]];
    [_data appendData:data];
    [data release];
}

- (void)stream:(NSStream *)theStream handleEvent:(NSStreamEvent)streamEvent {
    NSLog(@"stream event %u",streamEvent);

    switch (streamEvent) {
        case NSStreamEventOpenCompleted:
            NSLog(@"Stream opened");
            break;
        case NSStreamEventHasSpaceAvailable: {
            uint8_t *readBytes = (uint8_t *)[_data mutableBytes];
            readBytes += byteIndex; // ivar
            int data_len = [_data length];
            unsigned int len = ((data_len - byteIndex >= 1024) ? 1024 : (data_len - byteIndex));
            uint8_t buf[len];
            (void)memcpy(buf,readBytes,len);
            len = [(NSOutputStream *)theStream write:(const uint8_t *)buf maxLength:len];
            NSLog(@"Sending buffer of len: %d",len);
            byteIndex += len;
            break;
        }
        case NSStreamEventHasBytesAvailable:
            if (theStream == inputStream) {
                uint8_t buffer[1024];
                int len;

                while ([inputStream hasBytesAvailable]) {
                    len = [inputStream read:buffer maxLength:sizeof(buffer)];
                    if (len > 0) {
                        NSString *output = [[NSString alloc] initWithBytes:buffer length:len encoding:NSASCIIStringEncoding];

                        if (nil != output) {
                            NSLog(@"server said: %@",output);
                        }
                    }
                }

                [self sendString:@"Another Test"];
            }
            break;
        case NSStreamEventErrorOccurred:
            NSLog(@"Can not connect to the host!");
            break;
        case NSStreamEventEndEncountered:
            NSLog(@"Closing stream...");
            [theStream close];
            [theStream removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
            [theStream release];
            theStream = nil;
            break;
        default:
            NSLog(@"Unknown event");
    }
}

响应：

2012-08-15 08:16:30.896 Sockets[34836:f803] Opened input stream.
2012-08-15 08:16:30.898 Sockets[34836:f803] Opened output stream.
2012-08-15 08:16:30.899 Sockets[34836:f803] Sending buffer of len: 12
2012-08-15 08:16:30.900 Sockets[34836:f803] Sending buffer of len: 0
2012-08-15 08:16:30.901 Sockets[34836:f803] Closing output stream.
2012-08-15 08:16:30.939 Sockets[34836:f803] server said: Hello World!

请注意,在发送数据后,outputStream流将关闭.我尝试在[self sendString：@“Another Test”]之前重新启动outputStream.我也试过了idz的回答.

根据文档,我相信len：0的发送缓冲区是我的问题.

If the delegate receives an NSStreamEventHasSpaceAvailable event and
does not write anything to the stream,it does not receive further
space-available events from the run loop until the NSOutputStream
object receives more bytes. When this happens,the run loop is
restarted for space-available events.

但是,文档没有说明在到达流末尾时关闭流.所以我很困惑……

解决方法

套接字是连接两个程序的双向流,可能在两台不同的计算机上.它只是将您在一端写入的数据传输到另一端进行读取.它在数据中不强制执行任何结构,并且不了解有关请求或响应的任何信息.

CFStreamCreatePairWithSocketToHost API将单个连接拆分为两个独立的流 – 一个可以读取,另一个可以写入.这是一个很好的接触,底层套接字API只使用一个文件描述符进行读取和写入,这可能会让人非常困惑.

连接保持打开,直到一侧关闭插座.还有可能仅在一个方向上关闭插座.也可以仅在一个方向上关闭连接.如果遥控器关闭它的读取流,您的写入流将被关闭,反之亦然.

Do I setup a new socket every time I have a new data object to send?

你应该避免这样做.建立新连接需要一些时间,并且在连接达到全速之前需要更多时间.因此,您应该尽可能多地重用相同的连接.

Do I have to reset outputStream and send more data.

不,这不是必需的,只需发送更多数据.

Per the documentation,I believe the Sending buffer of len: 0 is my
problem.

什么都不写(这是一个长度为0的缓冲区)应该不是问题.文档没有说明会发生什么.所以我今天写了一个测试程序,看看会发生什么,什么也不期待.事实证明,写入长度为0的缓冲区会关闭输出流.所以这真的是你的问题.我将在Apple Bug Reporter上提出有关该文档问题的错误,您也应如此.

您引用的文档部分是关于不同的东西.如果您在获得可用空间通知后没有写信,那么在您写完文章之前,您将无法获得另一个通知.这很有用,因为系统不会浪费CPU周期来反复告诉您的代码,如果您没有任何要编写的内容,您可以写一些东西.

iOS：使用CFStreamCreatePairWithSocketToHost的套接字网络基础

解决方法

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