I understand that http2 uses one tcp connection to serve multiple requests, for example, if I request index.html which contains a.css and a.js, these three requests will be done in one tcp connection.
What happens if user clicks index2.html? does this request still use the same previous tcp connection? If so, will the browser keep the connection open until user closes the browser? And on the server side, does the server keep many connections open all the time?
When using HTTP/2, browsers typically open only one connection per domain.
In your example, index2.html will be sent on the same TCP connection that was used for index.html, a.css and a.js.
In HTTP/2 requests are multiplexed on the same TCP connection, so that the browser can send them concurrently, without waiting for a previous request to be responded to.
Both browsers and servers have an idle timeout for TCP connections.
If the connection is idle for long enough, it will be closed by either party - the one that has the shorter idle timeout, to save resources.
For example, you may open a connection to a wikipedia.org, perform a few requests, and then leave that tab and work on something else.
After a while (typically 30 seconds) the browser will close the TCP connection to wikipedia.org.
On the server side, the server will keep the connections from various clients open, until they are either closed by the client or until the server-side idle timeout fires, at which point it's the server that initiated the close of the TCP connection.
With HTTP/2, the number of connections that a server has to maintain is vastly less than it was with HTTP/1.1.
With HTTP/2, a server has to maintain just 1 TCP connection per client; with HTTP/1.1, the server had to maintain typically 2-8 TCP connections per client.
What happens if user clicks index2.html? does this request still use the same previous tcp connection?
Yes. On top of that, multiple browser tabs/windows also share a single HTTP/2 connection.
If so, will the browser keep the connection open until user closes the browser?
Below from RFC - connection management
For best performance, it is expected that clients will not close
connections until it is determined that no further communication with
a server is necessary (for example, when a user navigates away from a
particular web page) or until the server closes the connection.
Clients SHOULD NOT open more than one HTTP/2 connection to a given
host and port pair.
And on the server side, does the server keep many connections open all the time?
Servers are encouraged to maintain open connections for as long as
possible but are permitted to terminate idle connections if necessary.
When either endpoint chooses to close the transport-layer TCP
connection, the terminating endpoint SHOULD first send a GOAWAY
(Section 6.8) frame so that both endpoints can reliably determine
whether previously sent frames have been processed and gracefully
complete or terminate any necessary remaining tasks.
More info on connection error below.
RFC connection-error-handling
A connection error is any error that prevents further processing of
the frame layer or corrupts any connection state. An endpoint that
encounters a connection error SHOULD first send a GOAWAY frame with
the stream identifier of the last stream that it successfully received
from its peer. The GOAWAY frame includes an error code that indicates
why the connection is terminating. After sending the GOAWAY frame for
an error condition, the endpoint MUST close the TCP connection. It is
possible that the GOAWAY will not be reliably received by the
receiving endpoint. In the event of a connection error, GOAWAY only
provides a best-effort attempt to communicate with the peer about why
the connection is being terminated.
An endpoint can end a connection at any time. In particular, an
endpoint MAY choose to treat a stream error as a connection error.
Endpoints SHOULD send a GOAWAY frame when ending a connection,
providing that circumstances permit it.
To explain my question I tried doodling the scenario. Keep in mind I've been digging into TCP on my own so the diagram might not be too reliable. Please let me know if this is so.
Question:
What happens if a client that has an open connection with a server over TCP does not ACK a FIN sent by the server (seen at #1)?
Possible Answers:
Does the server close the connection anyway?
Does the server wait for ACK until connections are cleaned up forcefully?
If the client wants to keep the connection open after the server sent FIN can the client do anything to tell the server to keep it open? ie Ask for some more data
The FIN will be sent again, exactly as for a data segment, subject to the same retry counters and timeouts.
If the client wants to keep the connection open after the server sent FIN can the client do anything to tell the server to keep it open? i.e. Ask for some more data.
No. Once a host has sent a FIN it cannot send any more data. However the peer can send in the other direction, unless the host has actually closed the socket.
HTTP is client - server communication where client always initiates the connection and server responds.
In the client server communication with HTTP 1.1 the following steps takes place:
1. Client sends the request to the server.
2. Server sends the response to the client with the response message and the status code.
My question is how is the data transfer handled in the protocol? I know HTTP is stateless and also it is either everything or nothing mechanism but how do you prove this? How is the handshake between server and client?
For example: When the server sends the response back to the client, what happens if 50% of the data is sent and then there is connection loss...then what will happen in this scenario? Will the client wait for remaining 50% of the message or it will start new transfer where server tries to send 100% of the message again? (In synchronous communication)
HTTP relies on a TCP connection, so in your example if 50% of the data is correctly sent but others packets (yes, you should think in terms of packets) are lost, the data will be sent again following the rules defined in TCP protocol
My understanding regarding network model communication:
Application layer:
1. HTTP(Not Persistent or stateless): For exchanging messages like get, post, put etc. Here connection is made to webserver and disconnected after sending response. So server will not keep track of the previous requests.
2. Websockets(Persistent or statefull): For creating a communication channel that will be open to exchange data. Here we can keep track of the previous requests. Like we can know how many users are currently connected to our server.
Transport layer:
TCP(Persistant and Statefull): Will let the server know to which application to connect using port number. Both HTTP and web sockets will work upon this layer.
Considering working with HTTP and TCP:
I make a HTTP request from browser(application layer):
Connects to web server sends all files requested and also makes a TCP connection with the application(transport layer).
After sending response it's disconnected.
My confusion:
I got totally confused when I heard, read that TCP is Statefull and Persistant connection.
Q1. Now after step three is browser still connected to webserver because of TCP?
Q2. Is the context object we get in server side in c# code is the complete request packet with HTTP info, TCP info, function to invoke or controller to invoke in MVC etc?
Q3. If client and server are still connected with TCP. Then on next HTTP request does it will use the available TCP connection or will create new TCP and HTTP connection? Why can't it use previous TCP to communicate? Or TCP will be destroyed after HTTP? Or what's happening?
I am using camel to build a tcp server. I am waiting for connections and responding to clients messages using the following route
<camel:route id="ServerListeningRoute">
<camel:from ref="tcpServerEndPoint" />
<camel:setBody>
<camel:simple>Server Received from you: ${body}</camel:simple>
</camel:setBody>
</camel:route>
It is working. I can connect to the server with telnet, sent a message and get back the response from the server.
Now i want to create a new route to send messages from my server to those connected clients but reusing the socket connection already established. I am not responding to a message previously sent by a client. These would be new Exchanges started from my server.
I have tried this
<camel:route id="ServerSendingRoute">
<camel:from uri="timer://foo?fixedRate=true&period=60s?amp;delay=25s" />
<camel:setBody>
<camel:simple>This is a message from the server</camel:simple>
</camel:setBody>
<camel:to ref="tcpServerEndPoint" />
</camel:route>
But it is not working. The server is receiving its own produced messages since the to endpoint is opening a client connection to the server.
Is it possible with Netty and Camel to reuse the established connection? Do i need to extent the netty component somehow? Any workaround you can think of?