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?
Related
I'm implementing HTTP over TLS proxy server (sni-proxy) that make two socket connection:
Client to ProxyServer
ProxyServer to TargetServer
and transfer data between Client and TargetServer(TargetServer detected using server_name extension in ClientHello)
The problem is that the client doesn't close the connection after the response has been received and the proxy server waits for data to transfer and uses resources when the request has been done.
What is the best practice for implementing this project?
The client behavior is perfectly normal - HTTP keep alive inside the TLS connection or maybe even a Websocket connection. Given that the proxy does transparent forwarding of the encrypted traffic it is not possible to look at the HTTP traffic in order to determine exactly when the connection can be closed. A good approach is therefore to keep the connection open as long as the resources allow this and on resource shortage close the connections which were idle (no traffic) the longest time.
I read that HTTP protocol uses the reliable TCP connections by default
,and one of the HTTP feature is connectionless.
Now I am confused how does it make sense ?
How does it use TCP and the same time it is connectionless and as I know TCP is connection-oriented
HTTP and TCP are different things. TCP is a transport layer protocol, whereas HTTP is an application layer protocol. HTTP uses TCP for data transmissions.
IMO this website has a nice explanation:
HTTP is connectionless: The HTTP client, i.e., a browser initiates an HTTP request and after a request is made, the client waits for the response. The server processes the request and sends a response back after which client disconnect the connection. So client and server knows about each other during current request and response only. Further requests are made on new connection like client and server are new to each other.
However, Wikipedia defines HTTP as stateless:
HTTP is a stateless protocol. A stateless protocol does not require the HTTP server to retain information or status about each user for the duration of multiple requests. However, some web applications implement states or server side sessions using for instance HTTP cookies or hidden variables within web forms.
Based on their explanations, the terms seems to be used interchangeably. However, these are not really true as the in-use HTTP versions allow you to identify the users through cookies etc. and create persistent connections.
I know that a http request first makes a 3 way handshake to establish connection. Followed by the request and response.
If a handshake is required for future requests then it is called non persistent connection.
The server can choose to keep the connection alive so that a handshake is not required untill a timeout value (persistent). This is called persistent connection. It saves time required by not requiring the 3 way handshake for each request.
My colleague mentions that http supports both persistent and non persistent. My understanding is that - tcp makes the connection. So persistence is controlled by tcp layer. Am I right?
May be not right. HTTP is higher layer than TCP and HTTP 1.0 will send close() when they finish tranportint some data streams. But in HTTP 1.1, the controller will not send close(), instead, it'll send keepalive/hearbeat to the other side for live. It is controlled by the application layer, in other words, by the HTTP itself.
One way HTTP can support a persistent connection is called Server-Sent-Events.
An alternative to HTTP for persistant connections is WebSocket. WebSocket is a computer communications protocol, providing full-duplex communication channels over a single TCP connection. WebSocket enables streams of messages on top of TCP. WebSocket is distinct from HTTP.
I've read some articles comparing the differences between WebSocket and the other push methods like Long polling. All the conclusions tend to be WebSocket is better then HTTP with low latency in the server and client bidirectional communication process.
But if server push is not a must, for example, a client game program just make a few queries to the server for some information, does it still better to use WebSocket then HTTP? More specially, I have two doubts here:
1. In a single Request-Response procedure, which is more efficency ? (I establish a WebSocket connection each time querying in the above case.)
2. Will the server capacity (The total number of clients that the server can serve) be affected by the unnecessary long-lived connection if I keep an WebSocket connection during the life cycle of the client?
Added Question:
3. Suppose there is only one TCP connection between the server and the client, will the stability of the connection go down and down as time flows?
The basic thing behind both the WebSocket and HTTP is the socket. In HTTP, it opens a connection on request and closes on response. For WebSocket, concept is a 2 way communication (full duplex) rather than request-response cycle.
Answers to your question:
Either you can use HTTP server or can create request-response design
using WebSocket
That's obvious. Each connection is a socket object. Server capacity
will be affected if we are not managing connections.
In WebSocket, it's using ping-pong mechanism to make sure that the client or
the server is alive. For every ping requests from one end, other end is
subjected to reply a pong response. This mechanism helps to detect failures and hence to maintain stability.
At the moment I have an existing application which basically consists of a desktop GUI and a TCP server. The client connects to the server, and the server notifies the client if something interesting happens.
Now I'm supposed to replace the desktop GUI by a web GUI, and I'm wondering if I have to rewrite the server to send http packets instead of tcp packets or if I can somehow use some sort of proxy to grab the tcp packets and forward them to the web client?
Do I need some sort of comet server?
If you can make your client ask something like "Whats new pal?" to your server from time to time you can start implementing HTTP server emulator over TCP - its fun and easy process. And you could have any web based GUI.
You can just add to your TCP responds Http headers - itll probably do=)
So I mean HTTP is just a TCP with some headers like shown in here.
You should probably install fiddler and monitor some http requests/ responses you normally do on the web and you'll get how to turn your TCP server into http emulator=)
If you want keep sockets based approche use flash (there is some socket api) or silverlight (there is socket API and you can go for NetTcpBinding or Duplexbinding something like that - it would provide you with ability to receive messages from server when server wants you to receive them (server pushes messages))
So probably you should tall us which back end you plan to use so we could recomend to you something more usefull.