Why do many people say I/O completion port is a fast and nice model?  
What are the I/O completion port&#39;s advantages and disadvantages?  

I want to know some points which make the I/O completion port faster than other approaches.  

If you can explain it comparing to other models (select, epoll, traditional multithread/multiprocess), it would be better.

I/O completion port&#39;s advantages and disadvantages

I have discovered a running process with PID 26376 listening on port 9001 and 9002 as when I try to run my program(as a service) which binds to that port it fails.

But when I try to kill it using taskkill /PID it says that the process 26376 is not found. Similarly when I try to find the process in task manager with &quot;Show processes from all users&quot; selected, I couldn&#39;t find it anywhere.

Can anyone explain this? Is it a defunct zombie process? I suspect that the process listening on that port is a previous instance of my program running but what could have caused this?

EDIT:
Sysinternals TCPView shows the process as non-existent.
Sysinternals Process Explorer does not show the process.
Tasklist does not show the process.

![][1]


  [1]: http://i.stack.imgur.com/hJGeC.png

PID exists in netstat but does not exist in task manager

I have a simple program to check if a port is open, but I want to shorten the timeout length on the socket connection because the default is far too long. I&#39;m not sure how to do this though. Here&#39;s the code:

    #include &lt;sys/socket.h&gt;
    #include &lt;sys/time.h&gt;
    #include &lt;sys/types.h&gt;
    #include &lt;arpa/inet.h&gt;
    #include &lt;netinet/in.h&gt;
    #include &lt;errno.h&gt;
    #include &lt;fcntl.h&gt;
    #include &lt;stdio.h&gt;
    #include &lt;netdb.h&gt;
    #include &lt;stdlib.h&gt;
    #include &lt;string.h&gt;
    #include &lt;unistd.h&gt;
    
    int main(int argc, char **argv) {
    	u_short port;                /* user specified port number */
    	char addr[1023];             /* will be a copy of the address entered by u */
    	struct sockaddr_in address;  /* the libc network address data structure */
    	short int sock = -1;         /* file descriptor for the network socket */
    
    	if (argc != 3) {
    		fprintf(stderr, &quot;Usage %s &lt;port_num&gt; &lt;address&gt;&quot;, argv[0]);
    		return EXIT_FAILURE;
    	}
    
    	address.sin_addr.s_addr = inet_addr(argv[2]); /* assign the address */
    	address.sin_port = htons(atoi(argv[2]));            /* translate int2port num */
    
    	sock = socket(AF_INET, SOCK_STREAM, 0);
    	if (connect(sock,(struct sockaddr *)&amp;address,sizeof(address)) == 0) {
    		printf(&quot;%i is open\n&quot;, port);
    	}  
    	close(sock);
    	return 0;
    }

C: socket connection timeout

I open a TCP socket and connect it to another socket somewhere else on the network. I can then successfully send and receive data. I have a timer that sends something to the socket every second.

I then rudely interrupt the connection by forcibly losing the connection (pulling out the Ethernet cable in this case). My socket is still reporting that it is successfully writing data out every second. This continues for approximately 1hour and 30 minutes, where a write error is eventually given.

What specifies this time-out where a socket finally accepts the other end has disappeared? Is it the OS (Ubuntu 11.04), is it from the TCP/IP specification, or is it a socket configuration option?

TCP Socket no connection timeout

I know that sockaddr_in is for IPv4, and sockaddr_in6 for IPv6. The confusion to me is the difference between sockaddr and sockaddr_in[6]. 

Some functions accept `sockaddr` and some functions accept `sockaddr_in` or `sockaddr_in6`, so:

 - what&#39;s the rule?  
 - And why is there a need for two different structures?

And because the `sizeof(sockaddr_in6) &gt; sizeof(sockaddr) == sizeof(sockaddr_in)`.

 - Does that mean we should always use sockaddr_in6 to allocate memory in stack and cast to sockaddr and sockaddr_in if we need to support ipv4 and ipv6?

One example is: we have a socket, and we want to get the string ip address of it (it can be ipv4 or ipv6).

We first call `getsockname` to get an `addr` and then call `inet_ntop` based on the `addr.sa_family`.

Is there anything wrong with this code snippet?

    char ipStr[256];
    sockaddr_in6 addr_inv6;
    sockaddr* addr = (sockaddr*)&amp;addr_inv6;
    sockaddr_in* addr_in = (sockaddr_in*)&amp;addr_inv6;
    
    socklen_t len = sizeof(addr_inv6);
    getsockname(_socket, addr, &amp;len);

    if (addr-&gt;sa_family == AF_INET6) {
        inet_ntop(addr_inv6.sin6_family, &amp;addr_inv6.sin6_addr, ipStr, sizeof(ipStr)); 
        // &lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;IS THIS LINE VALID, getsockname expected a sockaddr, but we use 
        // it output parameter as sockaddr_in6.
    } else {
        inet_ntop(addr_in-&gt;sin_family, &amp;addr_in-&gt;sin_addr, ipStr, sizeof(ipStr));
    }


What&#39;s the difference between sockaddr, sockaddr_in, and sockaddr_in6?

When I send a normal HTTP request via a socket, the server does not respond with an OK response. I copied the HTTP header from Firefox. Here is the code:

    Socket s = new Socket(InetAddress.getByName(&quot;stackoverflow.com&quot;), 80);
    PrintWriter pw = new PrintWriter(s.getOutputStream());
    pw.print(&quot;GET / HTTP/1.1&quot;);
    pw.print(&quot;Host: stackoverflow.com&quot;);
    pw.flush();
    BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
    String t;
    while((t = br.readLine()) != null) System.out.println(t);
    br.close();

However, here is the response I received:

    HTTP/1.0 408 Request Time-out
    Cache-Control: no-cache
    Connection: close
    Content-Type: text/html
    
    &lt;html&gt;&lt;body&gt;&lt;h1&gt;408 Request Time-out&lt;/h1&gt;
    Your browser didn&#39;t send a complete request in time.
    &lt;/body&gt;&lt;/html&gt;

I know that I can do this by using `URL.openStream()`, but why doesn&#39;t the server identify the HTTP request when I send it manually?


Send HTTP request manually via socket

How to simulating two client-controlled vehicles colliding (sensibly) in a typical client/server setup for a network game? I did read [this eminent blog post][1] on how to do distributed network physics in general (without traditional client prediction), but this question is specifically on how to handle collisions of owned objects.

&lt;h3&gt;Example&lt;/h3&gt;
Say client A is 20 ms ahead of server, client B 300 ms ahead of server (counting both latency and maximum jitter). This means that when the two vehicles collide, both clients will see the other as 320 ms behind - in the opposite direction of the velocity of the other vehicle. Head-to-head on a Swedish highway means a difference of 16 meters/17.5 yards!

&lt;h3&gt;What not to try&lt;/h3&gt;
It is virtually impossible to extrapolate the positions, since I also have very complex vehicles with joints and bodies all over, which in turn have linear and angular positions, velocities and accelerations, not to mention states from user input.


  [1]: https://web.archive.org/web/20181107181430/https://gafferongames.com/post/networked_physics_2004/

Game network physics collision

I&#39;m in the process of rethinking my approach to the request architecture of a large app I&#39;m developing. I&#39;m currently using ASIHTTPRequest to actually make requests, but since I need many different types of requests as a result of many different actions taken in different view controllers, I&#39;m trying to work out the best system of organizing these requests.

I&#39;m currently building singleton &quot;requesters&quot; that are retained by the app delegate and sit around listening for NSNotifications that signal a request needs to be made; they make the request, listen for the response, and send out a new NSNotification with the response data. This solves most of my problems, but doesn&#39;t elegantly handle failed requests or simultaneous requests to the same singleton requester.

Anyone have any success devising a clear, OO architecture for making many different types of requests in an iOS app?

Best architecture for an iOS application that makes many network requests?

I am going to develop an instant messaging application that runs in the browser.

What browsers support the [WebSocket API][1]?

[1]: http://en.wikipedia.org/wiki/WebSocket

What browsers support HTML5 WebSocket API?

What is the difference between `read()` and `recv()`, and between `send()` and `write()` in socket programming in terms of performances, speed and other behaviors?

What is the Difference Between read() and recv() , and Between send() and write()?

I get the following warning when using `java.net.URLEncoder.encode`:

&lt;pre&gt;warning: [deprecation] encode(java.lang.String)
         in java.net.URLEncoder has been deprecated&lt;/pre&gt;

What should I be using instead?



java.net.URLEncoder.encode(String) is deprecated, what should I use instead?

This might be a very basic question but it confuses me.  

Can two different connected sockets share a port? I&#39;m writing an application server that should be able to handle more than 100k concurrent connections, and we know that the number of ports available on a system is around 60k (16bit). A connected socket is assigned to a new (dedicated) port, so it means that the number of concurrent connections is limited by the number of ports, unless multiple sockets can share the same port. So the question.

TCP: can two different sockets share a port?

Sorry about the length, it&#39;s kinda necessary.

**Introduction**


I&#39;m developing a remote desktop software (just for fun) in C# 4.0 for Windows Vista/7. I&#39;ve gotten through basic obstacles: I have a robust UDP messaging system, relatively clean program design, I&#39;ve got a mirror driver (the free DFMirage mirror driver from DemoForge) up and running, and I&#39;ve implemented NAT traversal for all NAT types except Symmetric NATs (present in corporate firewall situations).

Regarding screen transfer/sharing, thanks to the mirror driver, I&#39;m automatically notified of changed screen regions and I can simply marshal the mirror driver&#39;s ever-changing screen bitmap to my own bitmap. Then I compress the screen region as a PNG and send it off from the server to my client. Things are looking pretty good, but it&#39;s not fast enough. It&#39;s just as slow as VNC (btw, I don&#39;t use the VNC protocol, just a custom amateur protocol).

From the slowest remote desktop software to the fastest, the list usually begins at all VNC-like implementations, then climbs up to Microsoft Windows Remote Desktop...and then...TeamViewer. Not quite sure about CrossLoop, LogMeIn - I haven&#39;t used them, but TeamViewer is *insanely* fast. It&#39;s quite literally live. I ran a `tree` command on Command Prompt and it updated with 20 ms delay. I can browse the web just a few milliseconds slower than on my laptop. Scrolling code vertically in Visual Studio has 50 ms lag time. Think about how robust TeamViewer&#39;s screen-transfer solution must be to accomplish all this.

VNCs use poll-based hooks for detecting screen change and brute force screen capturing/comparing at their worst. At their best, they use a mirror driver like DFMirage. I&#39;m at this level. And they use something called the RFB protocol.

Microsoft Windows Remote Desktop apparently goes one step higher than VNC. I heard, from somewhere on StackOverflow, that Windows Remote Desktop doesn&#39;t send screen bitmaps, but actual drawing commands. That&#39;s quite brilliant, because it can just send simple text (draw this rectangle at this coordinate and color it with this gradient)! Remote Desktop really is pretty fast - and it&#39;s the standard way of working from home. And it uses something called the RDP protocol.

Now TeamViewer is a complete mystery to me. Apparently, they released their source code for Version 2 (TeamViewer is Version 7 as of February 2012). People have read it and said that Version 2 is useless - that it&#39;s just a few improvements over VNC with automatic NAT traversal. 

But Version 7...it&#39;s ridiculously fast now. I mean, it&#39;s actually faster than Windows Remote Desktop. I&#39;ve streamed DirectX 3D games with TeamViewer (at 1 fps, but Windows Remote Desktop doesn&#39;t even allow DirectX to run).

By the way, TeamViewer does all this *without* a mirror driver. There is an option to install one, and it gets just a bit faster.

**The Question**

**My question is, how is TeamViewer so fast?** It must not be possible. If you&#39;ve got 1920 by 1080 resolution at even 24 bit depth (16 bit depth would be noticeably ugly), thats still 6,220,800 bytes raw. Even using libjpeg-turbo (one of the fastest JPG compression libraries used by large corporations), compressing it down to 30KB (let&#39;s be extremely generous), would take time to route through TeamViewer&#39;s servers (TeamViewer bypasses corporate Symmetric NATs by simply proxying traffic through their servers). And that libjpeg-turbo compression would take time to compress. High-quality JPG compression takes 175 milliseconds for a full 1920 by 1080 screenshot for me. And that number goes up if the host&#39;s computer runs an Atom processor. I simply don&#39;t understand how TeamViewer has optimized their screen transfer so well. Again, small-size images might be highly compressed, but take at least tens of milliseconds to compress. Large-size images take no time to compress, but take a long time to get through. Somehow, TeamViewer completes this entire process to get roughly 20-25 frames per second. I&#39;ve used a network monitor, and TeamViewer is still lagless at speeds of 500 Kbps and 1 Mbps (VNC software lag for a few seconds at that transfer rate). During my `tree` Command Prompt test, TeamViewer was receiving inbound data at a rate of 1 Mbps and still running 5-6 fps. VNC and remote desktop don&#39;t do that. So, how?

The answers will be somewhat complicated and intricate, so *please don&#39;t post your $0.02 if you&#39;re only going to say it&#39;s because they use UDP instead of TCP* (would you believe they actually do use TCP just as successfully though).

I&#39;m hoping there&#39;s a TeamViewer developer somewhere here on StackOverflow.

**Potential Answers**

Will update this once people reply.

1. My thoughts are, first of all, that TeamViewer has very fine network control. For example, they split large packets to just under the MTU size and never waste a trip. They probably have all sorts of fancy hooks to detect screen changes along with extremely fast XOR image comparisons.

How is TeamViewer so fast?

In my main thread I have a `while(listening)` loop which calls `accept()` on my `ServerSocket` object, then starts a new client thread and adds it to a Collection when a new client is accepted.

I also have an Admin thread which I want to use to issue commands, like `&#39;exit&#39;`, which will cause all the client threads to be shut down, shut itself down, and shut down the main thread, by turning listening to false.

However, the `accept()` call in the `while(listening)` loop blocks, and there doesn&#39;t seem to be any way to interrupt it, so the while condition cannot be checked again and the program cannot exit!

Is there a better way to do this? Or some way to interrupt the blocking method?

How can I interrupt a ServerSocket accept() method?

What is the difference between TCP and UDP? 

I know that TCP is used in the case of non-time critical applications, and UDP is used for games or applications that require fast transmission of data. I know that TCP is used for HTTP, HTTPs, FTP, SMTP, and Telnet. I know that UDP is used for DNS and DHCP.

But why? What characteristics of TCP and UDP make it useful for their respective use cases? 

Difference between TCP and UDP?

Say if I was to get shared, virtual or dedicated hosting, I read somewhere a server/machine can only handle 64,000 TCP connections at one time, is this true? How many could any type of hosting handle regardless of bandwidth? I&#39;m assuming HTTP works over TCP.

Would this mean only 64,000 users could connect to the website, and if I wanted to serve more I&#39;d have to move to a web farm?

How many socket connections can a web server handle?

Both `connect()` and `bind()` system calls &#39;associate&#39; the socket file descriptor to an address (typically an ip/port combination). Their prototypes are like:-

    int connect(int sockfd, const struct sockaddr *addr,
                   socklen_t addrlen);
and 

    int bind(int sockfd, const struct sockaddr *addr,
                socklen_t addrlen);

What is the exact difference between 2 calls? When should one use `connect()` and when `bind()`?

Specifically, in some sample server client codes, found that client is using `connect()` and server is using the `bind()` call. Reason was not fully clear to me.

socket connect() vs bind()

They both provide roughly the same functionality. Which one should I choose to develop my high-performance TCP server? What are the pros &amp; cons?

Reference links:

[Apache MINA][1] ([source][2])

[Netty][3] ([source][4])


  [1]: https://mina.apache.org/
  [2]: https://github.com/apache/mina
  [3]: http://netty.io/
  [4]: https://github.com/netty/netty

Netty vs Apache MINA

What&#39;s the difference between sockets (stream) vs sockets (datagrams)? Why use one over the other? 

What&#39;s the difference between streams and datagrams in network programming?

What are the advantages (or limitations) of one over the other for transferring files over the Internet?

(I am aware of secure forms of both protocols. I&#39;d like to hear comparisons through personal experiences in terms of performance, reliability, file size limitations etc.)

Comparing HTTP and FTP for transferring files

What is the difference between socket programming and Http programming? can anyone help please?

difference between socket programming and Http programming

I&#39;m a bit confused about how and when to use `beginBackgroundTaskWithExpirationHandler`.

Apple shows in their examples to use it in `applicationDidEnterBackground` delegate, to get more time to complete some important task, usually a network transaction.

When looking on my app, it seems like most of my network stuff is important, and when one is started I would like to complete it if the user pressed the home button.

So is it accepted/good practice to wrap every network transaction (and I&#39;m not talking about downloading big chunk of data, it mostly some short xml) with  `beginBackgroundTaskWithExpirationHandler` to be on the safe side? 



Proper use of beginBackgroundTaskWithExpirationHandler

If you have a situation where a TCP connection is potentially too slow and a UDP &#39;connection&#39; is potentially too unreliable what do you use? There are various standard reliable UDP protocols out there, what experiences do you have with them?

Please discuss one protocol per reply and if someone else has already mentioned the one you use then consider voting them up and using a comment to elaborate if required.

**I&#39;m interested in the various options here, of which TCP is at one end of the scale and UDP is at the other. Various reliable UDP options are available and each brings some elements of TCP to UDP.**

I know that often TCP is the correct choice but having a list of the alternatives is often useful in helping one come to that conclusion. Things like Enet, RUDP, etc that are built on UDP have various pros and cons, have you used them, what are your experiences?

For the avoidance of doubt there is no more information, this is a hypothetical question and one that I hoped would elicit a list of responses that detailed the various options and alternatives available to someone who needs to make a decision.

What do you use when you need reliable UDP?

I am working on an a PHP web application and i need to perform some network operations in the request like fetching someone from remote server based on user&#39;s request.

Is it possible to simulate asynchronous behavior in PHP given that i have to pass some data to a function and also need output from it.

My code is like:

    &lt;?php
    
         $data1 = processGETandPOST();
         $data2 = processGETandPOST();
         $data3 = processGETandPOST();
    
         $response1 = makeNetworkCall($data1);
         $response2 = makeNetworkCall($data2);
         $response3 = makeNetworkCall($data3);

         processNetworkResponse($response1);
         processNetworkResponse($response2);
         processNetworkResponse($response3);
    
         /*HTML and OTHER UI STUFF HERE*/
    
         exit;
    ?&gt;


Each network operation takes around 5 seconds to complete adding a total of 15 seconds to the response time of my application given i make 3 requests.

The  makeNetworkCall() function just do a HTTP POST request.

The remote server is an 3rd party API so i don&#39;t have any control over there.


PS: Please do not answer giving suggestions about AJAX or Other things. I am currently looking if i can do this through PHP may be with an C++ extension or something like that.

Asynchronous Function Call in PHP

As a follow up to a [recent question][1], I wonder why it is impossible in Java, without attempting reading/writing on a TCP socket, to detect that the socket has been gracefully closed by the peer? This seems to be the case regardless of whether one uses the pre-NIO &lt;code&gt;Socket&lt;/code&gt; or the NIO &lt;code&gt;SocketChannel&lt;/code&gt;.

When a peer gracefully closes a TCP connection, the TCP stacks on both sides of the connection know about the fact. The server-side (the one that initiates the shutdown) ends up in state &lt;code&gt;FIN\_WAIT2&lt;/code&gt;, whereas the client-side (the one that does not explicitly respond to the shutdown) ends up in state &lt;code&gt;CLOSE\_WAIT&lt;/code&gt;. Why isn&#39;t there a method in &lt;code&gt;Socket&lt;/code&gt; or &lt;code&gt;SocketChannel&lt;/code&gt; that can query the TCP stack to see whether the underlying TCP connection has been terminated? Is it that the TCP stack doesn&#39;t provide such status information? Or is it a design decision to avoid a costly call into the kernel?

With the help of the users who have already posted some answers to this question, I think I see where the issue might be coming from. The side that doesn&#39;t explicitly close the connection ends up in TCP state &lt;code&gt;CLOSE\_WAIT&lt;/code&gt; meaning that the connection is in the process of shutting down and waits for the side to issue its own &lt;code&gt;CLOSE&lt;/code&gt; operation. I suppose it&#39;s fair enough that &lt;code&gt;isConnected&lt;/code&gt; returns &lt;code&gt;true&lt;/code&gt; and &lt;code&gt;isClosed&lt;/code&gt; returns &lt;code&gt;false&lt;/code&gt;, but why isn&#39;t there something like &lt;code&gt;isClosing&lt;/code&gt;?

Below are the test classes that use pre-NIO sockets. But identical results are obtained using NIO.


    import java.net.ServerSocket;
    import java.net.Socket;

    public class MyServer {
      public static void main(String[] args) throws Exception {
        final ServerSocket ss = new ServerSocket(12345);
        final Socket cs = ss.accept();
        System.out.println(&quot;Accepted connection&quot;);
        Thread.sleep(5000);
        cs.close();
        System.out.println(&quot;Closed connection&quot;);
        ss.close();
        Thread.sleep(100000);
      }
    }


    import java.net.Socket;

    public class MyClient {
      public static void main(String[] args) throws Exception {
        final Socket s = new Socket(&quot;localhost&quot;, 12345);
        for (int i = 0; i &lt; 10; i++) {
          System.out.println(&quot;connected: &quot; + s.isConnected() + 
            &quot;, closed: &quot; + s.isClosed());
          Thread.sleep(1000);
        }
        Thread.sleep(100000);
      }
    }

When the test client connects to the test server the output remains unchanged even after the server initiates the shutdown of the connection:

    connected: true, closed: false
    connected: true, closed: false
    ...


  [1]: https://stackoverflow.com/questions/151590/java-how-do-detect-a-remote-side-socket-close

Why is it impossible, without attempting I/O, to detect that TCP socket was gracefully closed by peer?

In every example and discussion I run across in the context of BSD socket programming, it seems that the recommended way to set a file descriptor to nonblocking I/O mode is using the `O_NONBLOCK` flag to `fcntl()`, e.g.

    int flags = fcntl(fd, F_GETFL, 0);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);

I&#39;ve been doing network programming in UNIX for over ten years, and have always used the `FIONBIO ioctl()` call to do this:

    int opt = 1;
    ioctl(fd, FIONBIO, &amp;opt);

Never really gave much thought to why.  Just learned it that way.  

Does anyone have any commentary on the possible respective merits of one or the other?  I imagine the portability locus differs somewhat, but do not know to what extent as `ioctl_list(2)` doesn&#39;t speak to that aspect of individual `ioctl` methods.  

UNIX nonblocking I/O: O_NONBLOCK vs. FIONBIO

Two words commonly used in networking world - Packets and frames.

Can anyone please give the detail difference between these two words?

Hope it might sounds silly but does it mean as below

A packet is the PDU(Protocol Data Unit) at layer 3 (network layer - ip packet) of the networking OSI model.

A frame is the PDU of layer 2 (data link) of the OSI model.

Difference between PACKETS and FRAMES

I&#39;m not too sure how to go about getting the external IP address of the machine as a computer outside of a network would see it.

My following IPAddress class only gets the local IP address of the machine.

    public class IPAddress {
    
        private InetAddress thisIp;
    
        private String thisIpAddress;
    
        private void setIpAdd() {
            try {
                InetAddress thisIp = InetAddress.getLocalHost();
                thisIpAddress = thisIp.getHostAddress().toString();
            } catch (Exception e) {
            }
        }
    
        protected String getIpAddress() {
            setIpAdd();
            return thisIpAddress;
        }
    }



Getting the &#39;external&#39; IP address in Java

How do I ping a website or IP address with Python?

Ping a site in Python?

I create `requests` POST-requests like this, where I specify timeout threshold:

`response = requests.post(url, data=post_fields, timeout=timeout)`

However, to determine a &quot;good&quot; threshold value, I would like to benchmark the server response time in advance.

How do I compute the minimum and maximum response times for the server?

How to measure server response time for Python requests POST-request

I need to get IP Address of iOS device in Swift. This is not a duplicate of other questions about this! I need to get only WiFi IP address, if there is no wifi ip address - I need to handle it. There are a few questions about it on Stack Overflow, but there are only functions that return ip addresses. For example (from https://stackoverflow.com/questions/25626117/how-to-get-ip-address-in-swift/25627545#25627545):


    func getIFAddresses() -&gt; [String] {
        var addresses = [String]()
        
        // Get list of all interfaces on the local machine:
        var ifaddr : UnsafeMutablePointer&lt;ifaddrs&gt; = nil
        if getifaddrs(&amp;ifaddr) == 0 {
            
            // For each interface ...
            for (var ptr = ifaddr; ptr != nil; ptr = ptr.memory.ifa_next) {
                let flags = Int32(ptr.memory.ifa_flags)
                var addr = ptr.memory.ifa_addr.memory
                
                // Check for running IPv4, IPv6 interfaces. Skip the loopback interface.
                if (flags &amp; (IFF_UP|IFF_RUNNING|IFF_LOOPBACK)) == (IFF_UP|IFF_RUNNING) {
                    if addr.sa_family == UInt8(AF_INET) || addr.sa_family == UInt8(AF_INET6) {
                        
                        // Convert interface address to a human readable string:
                        var hostname = [CChar](count: Int(NI_MAXHOST), repeatedValue: 0)
                        if (getnameinfo(&amp;addr, socklen_t(addr.sa_len), &amp;hostname, socklen_t(hostname.count),
                            nil, socklen_t(0), NI_NUMERICHOST) == 0) {
                                if let address = String.fromCString(hostname) {
                                    addresses.append(address)
                                }
                        }
                    }
                }
            }
            freeifaddrs(ifaddr)
        }
        
        return addresses
    }

Here I get 2 values - address from mobile internet(I think) and WiFi address I need. Is there any other way to get ONLY WiFi IP Address?

Swift - Get device&#39;s WIFI IP Address

I found a couple of answers, but they seem to be specifically relating to Windows machines. 
So my question is what are the differences between pipes and sockets, and when/how should you choose one over the other? 

What&#39;s the difference between pipes and sockets?

We use the example.com often for domain name reference. I wonder if any IP address used as an example IP address to mention in references like tutorial or notes?. I knew the loop back interface 127.0.0.1 can be used but it has been known for local system always.

Can example.com IP Address used for this purpose legally?

example.com is OK for domain example, what is example IP Address?

Let&#39;s assume there is a client that makes a lot of short-living connections to a server.

If the client closes the connection, there will be many ports in `TIME_WAIT` state on the client side.  Since the client runs out of local ports, it becomes impossible to make a new connection attempt quickly.

If the server closes the connection, I will see many `TIME_WAIT`s on the server side.  However, does this do any harm?  The client (or other clients) can keep making connection attempts since it never runs out of local ports, and the number of `TIME_WAIT` state will increase on the server side.  What happens eventually?  Does something bad happen? (slowdown, crash, dropped connections, etc.)

Please note that my question is not &quot;What is the purpose of `TIME_WAIT`?&quot; but &quot;What happens if there are so many `TIME_WAIT` states on the server?&quot; I already know what happens when a connection is closed in TCP/IP and why `TIME_WAIT` state is required.  I&#39;m not trying to trouble-shoot it but just want to know what is the potential issue with it.

To put simply, let&#39;s say `netstat -nat | grep :8080 | grep TIME_WAIT | wc -l` prints `100000`.  What would happen?  Does the OS&#39;s network stack slow down?  &quot;Too many open files&quot; error? Or, just nothing to worry about?

What is the cost of many TIME_WAIT on the server side?

How does a web server handle multiple incoming requests at the same time on a single port(80)?

Example :
At the same time 300k users want to see an image from www.abcdef.com which is assigned IP 10.10.100.100 and port 80. So how can www.abcdef.com handle this incoming users&#39; load?

Can one server (which is assigned with IP 10.10.100.100) handle this vast amount of incoming users? If not, then how can one IP address be assigned to more than one server to handle this load? 
 

How can a web server handle multiple user&#39;s incoming requests at a time on a single port (80)?

I&#39;ve had a bug in our software that occurs when I receive a connection timeout. These errors are very rare (usually when my connection gets dropped by our internal network). How can I generate this kind of effect artificially so I can test our software? 

If it matters the app is written in C++/MFC using CAsyncSocket classes.

**Edit:**

I&#39;ve tried using a non-existent host, and I get the socket error:

&gt; WSAEINVAL (10022) Invalid argument

My next attempt was to use [Alexander][1]&#39;s suggestion of connecting to a different port, e.g. 81 (on my own server though). That worked great. Exactly the same as a dropped connection (60 second wait, then error). Thank you!


  [1]: https://stackoverflow.com/questions/100841?sort=oldest#100859

Artificially create a connection timeout error

Which of the following is the best and most portable way to get the hostname of the current computer in Java?

`Runtime.getRuntime().exec(&quot;hostname&quot;)` 

vs 

`InetAddress.getLocalHost().getHostName()`

Recommended way to get hostname in Java

These errors are getting more and more frequent on my Game Server. They are causing the server to keep closing and restarting...

&lt;!-- language: lang-none --&gt;

    System.Net.Sockets.SocketException (0x80004005): An established connection was aborted by the software in your host machine 
       at System.Net.Sockets.Socket.BeginSend(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, AsyncCallback callback, Object state) 
       at iRP.Game.Sessions.Session.SendData(Byte[] Data)


This is the code from which these errors are generated:

&lt;!-- language: lang-cs --&gt;

    public void SendData(byte[] Data)
    {
        try
        {
            if (mSocket == null)
            {
                //Output.WriteLine(&quot;[SND] Socket has a null exception, which means it is now invalid. Remove this socket!&quot;, OutputLevel.CriticalError);
            }
            else
            {
                mSocket.BeginSend(Data, 0, Data.Length, SocketFlags.None, sendCallback, mSocket);
            }
        }
        catch (Exception e)
        {
            string WhatToWrite = &quot;Error handled (SESSION): &quot; + e.ToString() + &quot;\n\n&quot; + e.Message + &quot;\n\nStack: &quot; + e.StackTrace + Environment.NewLine + &quot;\n\n&quot;;
            File.AppendAllText(Environment.CurrentDirectory + &quot;\\data\\fatal.txt&quot;, WhatToWrite);
            Program.Stop();
        }
    }

The buffer sizes are correctly set, we are using KeepAlive on the socket and were using Send and Receive Timeouts.

People suggested that disabling the firewall would help, but whenever I do this our Game Server (Dedicated Server) restarts itself as if it&#39;s under attack, so the firewall must remain enabled.

Anyone else got any other solutions for this?

PS: We are behind DDoS Mitigation Services which may be limiting the number of connections...

C# An established connection was aborted by the software in your host machine

I don&#39;t see much use of `TCPClient`, yet there is a lot of `Socket`? What is the major difference between them and when would you use each?

I understand that .NET `Socket` is written on top of WINSOCK, and `TCPClient` is a wrapper over `Socket` class. Thus `TCPClient` is way up the chain, and possibly inefficient. Correct me if I am wrong. 


TCPClient vs Socket in C#

When using HttpURLConnection does the InputStream need to be closed if we do not &#39;get&#39; and use it?

i.e. is this safe?

    HttpURLConnection conn = (HttpURLConnection) uri.getURI().toURL().openConnection();
    conn.connect();
    // check for content type I don&#39;t care about
    if (conn.getContentType.equals(&quot;image/gif&quot;) return; 
    // get stream and read from it
    InputStream is = conn.getInputStream();
    try {
        // read from is
    } finally {
        is.close();
    }
				

Secondly, is it safe to close an InputStream ***before all of it&#39;s content has been fully read***?

Is there a risk of leaving the underlying socket in ESTABLISHED or even CLOSE_WAIT state?

Safe use of HttpURLConnection

I wanted to know the exact function of bind() in TCP. What does it mean by &#39;binding&#39; a local address to the socket? If it&#39;s assigning a port number to the socket, then why don&#39;t we use it in the client? I know that port is assigned by OS automatically in the client side, but I&#39;m not getting the big picture of how all of this works.

After bind(), we listen(). How is the bind related to listen()? Will the listen() know that bind() has been executed? If so, what changes does bind() make so that it is known? I mean, how does returning zero for successful execution help?

I&#39;ve gone through many definitions, but no where I could get all of this in detail. So if anyone can please explain this to me, I will be grateful.

Why is bind() used in TCP? Why is it used only on server side and not in client side?

Wikipedia says 

&gt; unlike the older system calls, which
&gt; operate at O(n), epoll operates in
&gt; O(1) [2]).

http://en.wikipedia.org/wiki/Epoll


However, the source code at fs/eventpoll.c on Linux-2.6.38,
seems it is implemented with an RB tree for searching, which has O(logN)

    /*
     * Search the file inside the eventpoll tree. The RB tree operations
     * are protected by the &quot;mtx&quot; mutex, and ep_find() must be called with
     * &quot;mtx&quot; held.
     */
    static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
    {


In fact, I couldn&#39;t see any man page saying the complexity of epoll() is O(1).
Why is it known as O(1)?




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