Just some concept about TCP Socket, let's say there are 100 clients simultaneously communicating with a traditional HTTP/TCP web server. How many sockets are respectively at the server and at each client? Do all of the sockets at the server
have the same server-side port number?
The question is generic, so the answer is going to be as well.
For traditional TCP-based HTTP server, there will be 100 sockets on the server (one for each client), and one socket on every client. All server sockets will be bound to the same server port.
This answer doesn't take into account the fact that in modern HTTP model a client usually opens more than one socket to serve a single request.
Related
Hello I have a http server running on port 80. Now as I am new to sockets, I got to know that we can upgrade the connection on the same port and make both work on the same port.
Now I am confused what will happen to the other client.
Consider this:
I send a get request to the server that please upgrade my connection from http to websocket using the same TCP/IP. The server responded with 101. It upgraded the connection. So far so good.
Now the port 80 is a websocket port rather than http. So now, socket.io would be maintaining the connection and request and not the app in express();
So when the next client comes to the same port 80 to do something non-socket related or anything, how the http mechanism would work because the connected is already a socket one now.
How it is doing what it is doing here.
Now the port 80 is a websocket port rather than http.
A TCP listener socket is agnostic to the application protocol. It is only about establishing a new TCP connection. There are not even application data transferred on the listener socket.
Using a specific application protocol like HTTP or switching between application protocols like switching from HTTP to WebSocket, only effects the newly established (accepted) connection but not the listener socket. This also means that it is possible to use different application protocols on different TCP connections, even if all of these connections originated on a single TCP listener socket.
Here is my understanding of how a client-server HTTP server works.
The client creates a TCP socket connection to connect to the server and sends data.
The server creates a TCP socket connection to listen for incoming requests.
So it looks like both the client and the server need to agree on the use of the Transport protocol to use (in this case TCP). But if we want a website to work over UDP/QUIC protocol then we need both the client and the server to create a UDP socket connection. But some websites use TCP and others use UDP...
So does it mean it would need to look like this? To know beforehand which protocol a website uses?
if (URI == 'https://www.google.com') {
// Website that works over UDP
client.create.UDP.socket
client.sendData
server.create.UDP.socket
server.receive.data
} else {
// Website that works over TCP
client.create.TCP.socket
client.sendData
server.create.TCP.socket
server.receive.data
}
So the client needs to keep a record of which website uses TCP and which websites use UDP/QUIC and create that kind of socket to communicate with it?
If a protocol supports both TCP and UDP, the server listens both on the TCP port and the UDP port. The port number is generally the same, e.g. DNS uses TCP port 53 and UDP port 53.
Usually the client has a preference. Let's say it prefers TCP. The client will first try to connect with TCP. If the server does not respond, the client will retry with UDP. Alternatively, the server can respond over TCP but ask the client to switch to UDP. The client can then decide to continue with TCP or switch to UDP.
For QUIC 1 2, the browser will first connect using HTTP over TCP. The server will respond with a message stating that it also supports QUIC. If the browser also supports this protocol, the browser will reconnect to the server using QUIC.
My understanding is that a socket corresponds to a network identifier, port and TCP identifier. [1]
Operating systems enable a process to be associated with a port (which IIUC is a way of making the process addressable on the network for inbound data).
So a WebSocket server will typically be associated with a port well-known for accepting and understanding HTTP for the upgrade request (like 443) and then use TCP identifiers to enable multiple network sockets to be open concurrently for a single server process and a single port.
Please can someone confirm or correct my understanding?
[1] "To provide for unique names at
each TCP, we concatenate a NETWORK identifier, and a TCP identifier
with a port name to create a SOCKET name which will be unique
throughout all networks connected together." https://www.rfc-editor.org/rfc/rfc675
When a client connects to your server on a given port, the client connection is coming from an IP address and a client-side port number. The client-side port number is automatically generated by the client and will be unique for that client. So, you end up with four items that make a connection.
Server IP address (well known to all clients)
Server port (well known to all clients)
Client IP address (unique for that client)
Client port (dynamically unique for that client and that socket)
So, it is the combination of these four items that make a unique TCP connection. If the same client makes a second connection to the same server and port, then that second connection will have a different client port number (each connection a client makes will be given a different client port number) and thus the combination of those four items above will be different for that second client connection, allowing it's traffic to be completely separate from the first connection that client made.
So, a TCP socket is a unique combination of the four items above. To see how that is used, let's look at how some traffic flows.
After a client connects to the server and a TCP socket is created to represent that connection, then the client sends a packet. The packet is sent from the client IP address and from the unique client port number that that particular socket is using. When the server receives that packet on its own port number, it can see that the packet is coming from the client IP address and from that particular client port number. It can use these items to look up in its table and see which TCP socket this traffic is associated with and trigger an event for that particular socket. This separates that client's traffic from all the other currently connected sockets (whether they are other connections from that same client or connections from other clients).
Now, the server wants to send a response to that client. The packet is sent to the client's IP address and client port number. The client TCP stack does the same thing. It receives the packet from the server IP/port and addressed to the specific client port number and can then associate that packet with the appropriate TCP socket on the client so it can trigger an event on the right socket.
All traffic can uniquely be associated with the appropriate client or server TCP socket in this way, even though many clients may connect to the same server IP and port. The uniqueness of the client IP/port allows both ends to tell which socket a given packet belongs to.
webSocket connections start out with an HTTP connection (which is a TCP socket running the HTTP protocol). That initial HTTP request contains an "upgrade" header requesting the server to upgrade the protocol from HTTP to webSocket. If the server agrees to the upgrade, then it returns a response that indicates that the protocol will be changed to the webSocket protocol. The TCP socket remains the same, but both sides agree that they will now speak the webSocket protocol instead of the HTTP protocol. So, once connected, you then have a TCP socket where both sides are speaking the webSocket protocol. This TCP connection uses the same logic described above to remain unique from other TCP connections to the same server.
In this manner, you can have a single server on a single port that works for both HTTP connections and webSocket connections. All connections to that server start out as HTTP connections, but some are converted to webSocket connections after both sides agree to change the protocol. The HTTP connections that remain HTTP connections will be typical request/response and then the socket will be closed. The HTTP connections that are "upgraded" to the webSocket protocol will remain open for the duration of the webSocket session (which can be long lived). You can have many concurrent open webSocket connections that are all distinct from one another while new HTTP connections are regularly serviced all by the same server. The TCP logic above is used to keep track of which packets to/from the same server/port belong to which connection.
FYI, you may have heard about NAT (Network Address Translation). This is commonly used to allow private networks (like a home or corporate network) to interface to a public network (like the internet). With NAT a server may see multiple clients as having the same client IP address even though they are physically different computers on a private network). With NAT, multiple computers are routed through a common IP address, but NAT still guarantees that the client IP address and client port number are still a unique combination so the above scheme still works. When using NAT an incoming packet destined for a particular client arrives at the shared IP address. The IP/port is then translated to the actual client IP address and port number on the private network and then packet is forwarded to that device. The server is generally unaware of this translation and packet forwarding. Because the NAT server still maintains the uniqueness of the client IP/client port combination, the server's logic still works just fine even though it appears that many clients are sharing a common IP address). Note, home network routes are usually configured to use NAT since all computers on the home network will "share" the one public IP address that your router has when accessing the internet.
You will not enable multiple sockets, there is no need for it. You will have multiple conections. It's a little different, but you undesrstand well. For UDP there's nothing to do, cause there is no connections.
In TCP, if two different machines connect to the same port on a third machine, there are two distinct connections because the source IPs differ. If the same machine (or two behind NAT or otherwise sharing the same IP address) connects twice to a single remote end, the connections are differentiated by source port, the same machine cannot open 2 connections on the same port.
Usually a web server is listening to any incoming connection through port 80. So, my question is that shouldn't it be that in general concept of socket programming is that port 80 is for listen for incoming connection. But then after the server accepted the connection, it will use another port e.g port 12345 to communicate with the client. But, when I look into the wireshark, the server is always using port 80 during the communication. I am confused here.
So what if https://www.facebook.com:443, it has hundreds of thousands of connection to the it at a second. Is it possible for a single port to handle such a large amount of traffic?
A particular socket is uniquely identified by a 5-tuple (i.e. a list of 5 particular properties.) Those properties are:
Source IP Address
Destination IP Address
Source Port Number
Destination Port Number
Transport Protocol (usually TCP or UDP)
These parameters must be unique for sockets that are open at the same time. Where you're probably getting confused here is what happens on the client side vs. what happens on the server side in TCP. Regardless of the application protocol in question (HTTP, FTP, SMTP, whatever,) TCP behaves the same way.
When you open a socket on the client side, it will select a random high-number port for the new outgoing connection. This is required, otherwise you would be unable to open two separate sockets on the same computer to the same server. Since it's entirely reasonable to want to do that (and it's very common in the case of web servers, such as having stackoverflow.com open in two separate tabs) and the 5-tuple for each socket must be unique, a random high-number port is used as the source port. However, each of those sockets will connect to port 80 at stackoverflow.com's webserver.
On the server side of things, stackoverflow.com can already distinguish between those two different sockets from your client, again, because they already have different client-side port numbers. When it sees an incoming request packet from your browser, it knows which of the sockets it has open with you to respond to because of the different source port number. Similarly, when it wants to send a response packet to you, it can send it to the correct endpoint on your side by setting the destination port number to the client-side port number it got the request from.
The bottom line is that it's unnecessary for each client connection to have a separate port number on the server's side because the server can already uniquely identify each client connection by its client IP address and client-side port number. This is the way TCP (and UDP) sockets work regardless of application-layer protocol.
shouldn't it be that in general concept of socket programming is that port 80 is for listen for incoming connection. But then after the server accepted the connection, it will use another port e.g port 12345 to communicate with the client.
No.
But, when I look into the wireshark, the server is always using port 80 during the communication.
Yes.
I am confused here.
Only because your 'general concept' isn't correct. An accepted socket uses the same local port as the listening socket.
So what if https://www.facebook.com:443, it has hundreds of thousands of connection to the it at a second. Is it possible for a single port to handle such a large amount of traffic?
A port is only a number. It isn't a physical thing. It isn't handling anything. TCP is identifying connections based on the tuple {source IP, source port, target IP, target port}. There's no problem as long as the entire tuple is unique.
Ports are a virtual concept, not a hardware ressource, it's no harder to handle 10 000 connection on 1 port than 1 connection each on 10 000 port (it's probably much faster even)
Not all servers are web servers listening on port 80, nor do all servers maintain lasting connections. Web servers in particular are stateless.
Your suggestion to open a new port for further communication is exactly what happens when using the FTP protocol, but as you have seen this is not necessary.
Ports are not a physical concept, they exist in a standardised form to allow multiple servers to be reachable on the same host without specialised multiplexing software. Such software does still exist, but for entirely different reasons (see: sshttp). What you see as a response from the server on port 80, the server sees as a reply to you on a not-so-random port the OS assigned your connection.
When a server listening socket accepts a TCP request in the first time ,the function such as Socket java.net.ServerSocket.accept() will return a new communication socket whoes port number is the same as the port from java.net.ServerSocket.ServerSocket(int port).
Here are the screen shots.
Is it possible this Scenario without using webrtc?
Client A connects to Server
Client B connects to Server
Server send information to B and to A with each others information
A and B start talking directly using the same connection (by transforming their sockets info with the new port/ip address for example)
note: Client A and B doesn't have any socket server. They are only clients
Thank you very much.
It's definitely possible to set up a direct TCP connection, if at least one of the clients can accept an incoming TCP connection. In that case the server can just tell the other client what IP address and port to connect to, and then the two clients can communicate directly over the new TCP connection.
If both clients are behind firewalls or NAT, on the other hand, things get a lot more iffy -- in some cases you can use TCP hole punching techniques to get a direct TCP connection started; in other cases you're just out of luck.
In no case (AFAIK) can you modify an existing TCP connection to have new endpoints; a TCP connection's endpoints are fixed, and to get new endpoints you have to set up a new TCP connection.