关于iPhone：是否可以在Apple iOS设备上激活TCP Keepalive

Is it possible to activate TCP keepalive on Apple iOS devices

苹果设备===路由器=== WiFi模块

Apple设备(iPhone)正在通过TCP连接连接到WiFi模块端口2000。我想激活在Apple设备上发送的TCP keepalive数据包，以查找与WiFi模块的TCP连接丢失(模块关闭)。

我的流设置

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CFReadStreamRef readStream;
CFWriteStreamRef writeStream;

CFStreamCreatePairWithSocketToHost(NULL, (CFStringRef)CFBridgingRetain(moduleIPaddress), port2000, &readStream, &writeStream);

outputStream = (NSOutputStream *)CFBridgingRelease(writeStream);
inputStream = (NSInputStream *)CFBridgingRelease(readStream);

[outputStream setDelegate:(id)self];
[inputStream setDelegate:(id)self];
[outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[outputStream open];
[inputStream open];

我试图根据David H的帖子激活keepalive，使iOS中的套接字连接保持活动状态

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- (void) stream:(NSStream *)theStream handleEvent:(NSStreamEvent)streamEvent {
switch (streamEvent) {

case NSStreamEventOpenCompleted:

if (theStream == outputStream) {

/*
CFDataRef data = (CFDataRef)CFWriteStreamCopyProperty((__bridge CFWriteStreamRef)theStream, kCFStreamPropertySocketNativeHandle);
if(data) {
CFSocketNativeHandle socket_handle = *(CFSocketNativeHandle *)CFDataGetBytePtr(data);
CFRelease(data);

NSLog(@"SOCK HANDLE: %x", socket_handle);

//Enabling keep alive
int opt = 1;
if( setsockopt( socket_handle, SOL_SOCKET, SO_KEEPALIVE, &opt, sizeof( opt ) ) < 0 )
{
NSLog(@"Yikes 2: failed to set keepalive! ERRNO: %s", strerror(errno));
}
}
*/

NSData *data = (NSData *)[theStream propertyForKey:(__bridge NSString *)kCFStreamPropertySocketNativeHandle];
if(data) {
CFSocketNativeHandle socket_handle = *(CFSocketNativeHandle *)[data bytes];
NSLog(@"SOCK HANDLE: %x", socket_handle);

//Enabling keep alive
int opt = 1;
if( setsockopt( socket_handle, SOL_SOCKET, SO_KEEPALIVE, &opt, sizeof( opt ) ) < 0 )
{
NSLog(@"Yikes 2: failed to set keepalive! ERRNO: %s", strerror(errno));
}
}

}

这两个选项都打印出SOCK HANDLE：9，没有错误消息。当WiFi模块关闭时，当我不发送数据至outputstream时，连接仍保持打开状态30分钟或更长时间。如果我将数据发送到输出流，则会收到NSStreamEventErrorOccurred-错误域= NSPOSIXErrorDomain代码= 60大约60秒后，"操作无法完成。操作超时"。我在Apple设备上尝试过此操作。当我尝试使用iOS Simulator时，Wireshark没有看到keepalive数据包。

iOS中的NSStream tcp keepalive还介绍了keepalive设置。 Martin R示例代码为看似错误的输入流激活了保持活动状态。

是否可以在iPhone等Apple iOS设备上激活TCP keepalive(应根据David H)？如果有可能应该怎么做(我的代码中缺少什么)？

谢谢林太郎指导我正确的方向。

流设置与我的问题相同。
我测试了不同的设置，但没有发现问题中描述的套接字句柄检测示例之间的差异。

使用iPod设备和iOS 7.1激活keepalive的代码

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case NSStreamEventOpenCompleted:
@try {

if (theStream == outputStream)
{
NSData *data = (NSData *)[theStream propertyForKey:(__bridge NSString *)kCFStreamPropertySocketNativeHandle];

if(data)
{
CFSocketNativeHandle socket_handle = *(CFSocketNativeHandle *)[data bytes];
//NSLog(@"SOCK HANDLE: %x", socket_handle);

//SO_KEEPALIVE option to activate
int option = 1;
//TCP_NODELAY option to activate
int option2 = 1;
//Idle time used when SO_KEEPALIVE is enabled. Sets how long connection must be idle before keepalive is sent
int keepaliveIdle = 10;
//Interval between keepalives when there is no reply. Not same as idle time
int keepaliveIntvl = 2;
//Number of keepalives before close (including first keepalive packet)
int keepaliveCount = 4;
//Time after which tcp packet retransmissions will be stopped and the connection will be dropped.Stream is closed
int retransmissionTimeout = 5;

if (setsockopt(socket_handle, SOL_SOCKET, SO_KEEPALIVE, &option, sizeof (int)) == -1)
{
NSLog(@"setsockopt SO_KEEPALIVE failed: %s", strerror(errno));
}else
{
NSLog(@"setsockopt SO_KEEPALIVE ok");
}

if (setsockopt(socket_handle, IPPROTO_TCP, TCP_KEEPCNT, &keepaliveCount, sizeof(int)) == -1)
{
NSLog(@"setsockopt TCP_KEEPCNT failed: %s", strerror(errno));
}else
{
NSLog(@"setsockopt TCP_KEEPCNT ok");
}

if (setsockopt(socket_handle, IPPROTO_TCP, TCP_KEEPALIVE, &keepaliveIdle, sizeof(int)) == -1)
{
NSLog(@"setsockopt TCP_KEEPALIVE failed: %s", strerror(errno));
}else
{
NSLog(@"setsockopt TCP_KEEPALIVE ok");
}

if (setsockopt(socket_handle, IPPROTO_TCP, TCP_KEEPINTVL, &keepaliveIntvl, sizeof(int)) == -1)
{
NSLog(@"setsockopt TCP_KEEPINTVL failed: %s", strerror(errno));
}else
{
NSLog(@"setsockopt TCP_KEEPINTVL ok");
}

if (setsockopt(socket_handle, IPPROTO_TCP, TCP_RXT_CONNDROPTIME, &retransmissionTimeout, sizeof(int)) == -1)
{
NSLog(@"setsockopt TCP_RXT_CONNDROPTIME failed: %s", strerror(errno));
}else
{
NSLog(@"setsockopt TCP_RXT_CONNDROPTIME ok");
}

if (setsockopt(socket_handle, IPPROTO_TCP, TCP_NODELAY, &option2, sizeof(int)) == -1)
{
NSLog(@"setsockopt TCP_NODELAY failed: %s", strerror(errno));
}else
{
NSLog(@"setsockopt TCP_NODELAY ok");
}
}
}

TCP连接空闲时，应用程序将在10秒间隔后开始发送保持活动状态。如果没有答案，则应用会以2秒的间隔开始发送Keepalive数据包，并在有4个Keepalive数据包无应答时关闭流。这意味着，在成功进行Keepalive交换后关闭WiFi模块时，如果连接断开，空闲时最多需要18秒钟才能关闭流。

另一个参数是重传超时值。默认值似乎在6秒左右。当第一次有数据包重传时，此计时器启动。应用会尝试重传数据包，但如果5秒钟内数据包重传失败，则流将关闭。

注意！设备和模拟器的结果不同。

iPod设置激活日志

setsockopt SO_KEEPALIVE好的
setsockopt TCP_KEEPCNT确定
setsockopt TCP_KEEPALIVE好的
setsockopt TCP_KEEPINTVL好的
setsockopt TCP_RXT_CONNDROPTIME好的
setsockopt TCP_NODELAY确定

模拟器设置激活日志

setsockopt SO_KEEPALIVE好的
setsockopt TCP_KEEPCNT失败：协议不可用
setsockopt TCP_KEEPALIVE好的
setsockopt TCP_KEEPINTVL失败：协议不可用
setsockopt TCP_RXT_CONNDROPTIME好的
setsockopt TCP_NODELAY确定

这意味着无法使用iOS模拟器激活和跟踪。
我没有发现为什么模拟器中显示错误消息" Protocol not available"。