Hi
let me make my question clear. Two people using my app are connected to the internet. Both have each other's IP and they want to chat (like Y!messanger) with each other.
I think I need to use Indy components; right? Which component should I use?
Thanks in advance
Have you looked at any of the demos on Indy's website yet?
In general, you are looking to create a "Client/Server" type application. A quick Google search for "indy client server example" pulls up lots of results, including this one: http://www.devarticles.com/c/a/Delphi-Kylix/A-Real-World-Client-Server-Application-in-Delphi/
In reality, this gets a lot more complicated when you have firewalls and NATs with private IP addresses. You will have to consider how your application will either get around or through these types of technologies.
Similar to what Scott said, I think that your biggest problem is getting them talking to each other. My computers at home go through a router, which blocks all incoming connection requests (i.e. requests to start a conversation between two computers) from the Internet. My computers can send connection requests OUT, and start a conversation that way, but unless you modify the router (port forwarding) my computers can not receive connection requests.
You need a server somewhere to which both people will connect, that can then relay messages back and forth. To get really tricky, once the connection is made to the server the two computers can then be put into direct contact, but that involves UDP packets and some clever magic.
You don't have to use Indy components, you just need anything that will handle communications over the network. Any HTTP or sockets network stack will do. Indy is the defacto standard for Delphi Win32.
To do network communications, you will need to create a listener object or service on machine A and a sender object on machine B to send a network message from A to B. To send a message from B to A, you will need a reverse path as well - 4 objects total to perform bidirectional comms. Some object wrappers hide this detail internally. I don't recall offhand whether Indy hides this or not.
It would probably be easiest if you use a common TCP/IP protocol for your machine to machine communications, such as HTTP. This will make it easier to get your connections through firewalls and proxies that frequently exist between arbitrary users. To avoid conflicting with any HTTP web services that might be running on either machine, you should use a custom port number with the IP address: 192.168.1.10:12345, not the standard HTTP web server port 80. This is what most of the IM clients do.
Related
I would like to understand networking services with a large user base a bit better so that I know how to approach a project I am busy with.
The following statements that I make may be incorrect but they still lead to the question that I want to ask...
Please consider Skype and TeamViewer clients. It seems that both keep persistent network connections open to their respective servers. They use these persistent connections to initiate additional connections. Some of these connections are created by means of Hole Punching if the clients are behind NATs. They are then used for direct Peer-to-Peer communications.
Now according to http://expandedramblings.com/index.php/skype-statistics/ there are 300 million users using Skype and 4.9 million daily active users. I would assume that most of that 4.9 million users will most probably have their client apps running most of the day. That is a lot of connections to the Skype servers that are open at any given time.
So to my question; Is this feasible or at least acceptable? I mean, wouldn't it be better to not have a network connection open while idle and aspecially when there are so many connections open to the servers at once? The only reason I can think is that it would be the only way to properly do Hole Punching. Techically, how is this achieved on the server side?
Is this feasible or at least acceptable?
Feasible it certainly is, you mention already two popular apps that do it, so it is very doable in practice.
As for acceptable, to start no internet authority (e.g. IETF) has ever said it is unacceptable to have long-lived connections even with low traffic.
Furthermore, the only components for which this matters are network elements that keep connection/flow state. These are for sure the endpoints and so-called middleboxes like NAT and firewalls. For the client this is only one connection, the server is usually fine tuned by the application developers (who made this choice) themselves, so for these it is acceptable. For middleboxes it's simple: they have no choice, they're designed to just work with all kind of flows, including long-lived persistent connections.
I mean, wouldn't it be better to not have a network connection open while idle and aspecially when there are so many connections open to the servers at once?
Not at all. First of all, that could be 'much' slower as you'd need to set up a full connection before each control-plane call. This is especially noticeable if your RTT is big or if the servers do some complicated connection proxying/redirection for load-balancing/localization purposes.
Next to that this would historically make incoming calls difficult for a huge amount of users. Many ISP's block/blocked unknown incoming connections from the internet by means of a firewall. Similar, if you are behind a NAT device that does not support UPnP or PCP you can't open a port to listen on for your public IP address. So you need it even aside from hole-punching.
The only reason I can think is that it would be the only way to
properly do Hole Punching. Techically, how is this achieved on the
server side?
Technically you can't do proper hole-punching as soon as the NAT devices maintain a full <src-ip,src-port,dest-ip,dest-port,protocol> (classical 5-tuple) flow match. Then the best you can do with 'hole punching' is set up a proxy between peers.
What hole-punching relies on is that the NAT flow lookup is only looking at <src-ip,src-port,protocol> upstream and <dest-ip,dest-port,protocol> downstream to do the translation. In that case both clients just set up a connection to the server, their ip and port gets translated and the server passes this to the other client. The other client can now start sending packets to that translated <ip,port> combination which should work because NAT ignores the server's ip/port. But even if the particular NAT would work like this, some security device (e.g. stateful firewall) might detect session hi-jacking and drop this anyway.
Nowadays you rather use UPnP to open up a port to listen on your public IP which is much easier if supported.
I have a strange szenario:
Webserver / Appserver (Java) sends requests to many different satellite systems (on customers site). Only satellite systems can initiate connection due to firewall rules.
The model I think should be something like REQ/REP, but here the REQuester have to bind and the REPlyer would have to connect.
Is this possible and a stable architecture?
Are there better solutions? (We first had WebSockets in mind...)
Remark: we don't have to use Java on both ends. To be precise on customers site we have Delphi, but we could bridge it somehow.
The model I think should be something like REQ/REP, but here the
REQuester have to bind and the REPlyer would have to connect.
This will be problematic. When the server initiates the connection, it must be aware of all peers and their bind address. Not a big deal for a handful of peers, but for many peers changing constantly, it's a mess.
Only satellite systems can initiate connection due to firewall rules.
If that's the case, your mileage will vary with WebSockets; google around, lots of info on this.
Are there better solutions?
Well, with ZeroMq, one solution that comes to mind to support client request initiation is this:
Server binds with ROUTER
Clients connect with DEALER.
This approach offers bi-directional request/reply, does not block (asynchronous), and eliminates the client-side bind problem mentioned in your question. Here, the server binds, and either side can initiate the conversation.
I recommend reading this section in the guide, it covers extended async request/reply and message enveloping, important when using ROUTER/DEALER sockets.
I want to write a app which will run on different computers and need all of then to communicate with each other like "utorrent" (peer to peer). This app only will send text messages.
How can I do this? I mean sending one message to remote computer on the internet?
I have a website and every app at start can send some information to it and find information of other apps on other computers (with PHP) but I do not know how address one computer through internet and send the data directly to that. I can find the ip address with PHP but it is the ip address of router (ISP).
How a message reaches a computer? I'm wondering about addressing every computer?
My brain really stuck here, I really appreciate any help. Thanks.
In a peer-to-peer network there's no centralized server for transmitting the data from one client to another, in this case the clients must be able to act as both the server and client. This means that either you'll have to be using UPnP like most modern torrent clients, which handles port forwarding in the router, or you'll have to manually forward a port to the computer in the router.
A centralized server (like a torrent tracker) is usually used to make the clients aware of each other's existence and tell them where to connect. This is where your PHP script comes in, though PHP might not offer the most effective way of doing this, assuming you're using it in combination with a webserver to serve the data though the http protocol.
As for actual text communication, you could use the Indy socket library for that. I found this example, basically which shows how to do it: http://www.ciuly.com/delphi/indy/indy-10-client-server-basic-demo/
I have a custom pair of client/server sockets (TJDServerSocket and TJDClientSocket) which wrap the TServerSocket and TClientSocket in the ScktComp unit. I don't have any issues to fix, but would like to know something. I'd like to add a feature to the client side to automatically search the network for any instances of a server socket (specifically my server component).
I'm open to any suggestions, but has to be specific to the use of the ScktComp unit in Delphi 7.
Here's a link to the components of mine.
Never used the TServerSocket and TClientSocket myself, and I don't have the help files within reach, so I can't immediately see if this would work with those components.
For a project I did I needed something like that too. I ended up with using UDP to broadcast a discovery request (within the same subnet of course). The server, listening on a particular port for such a request, would reply its data back. When multiple servers would exist (a situation that though rare could occur) the client just picked the server with the required service(s) and the least load. That load was part of the data the server send back.
It worked out nice, wasn't all that difficult to write, and turned out reasonably efficient too.
The request protocol is completely up to you. The one I devised allowed clients to send a request detailing the services they need, and servers replying listing their services and the load (= connected clients in active use).
After selecting the server to talk to, a client would register itself for the services it needed, and could use them after that.
Hope this helps.
There are some standard protocols for service discovery. See for example: http://en.wikipedia.org/wiki/Zero_configuration_networking
Mailslots is a nice option here. It'll broadcast to every PC on your subnet. See Jeroen's answer to this question:
Suggestions on writing a TCP IP messaging system (Client/Server) using Delphi 2010
Searching is as easy as port scanning.
If you don't like the brute force approach, the server can register itself to a well known service application (could be a web server), and the client can connect to the service application to ask. It's quieter than broadcasting.
With more information, such as details about the network (who's it for?), I can suggest a more precise answer.
I would like to write a messaging system using TCP IP in Delphi 2010. I would like to hear what my best options are for using the standard delphi 2010 components/indy components for doing this.
I would like to write a server which does the listening and forwarding of messages to all machines on the network running a client.
1.) a.) clients can send a message to server to be forwarded to all other clients
b.) clients listen for messages from other senders (via server) and displays messages.
2.) a.) Server can send a message to all clients
b.) Server forwards any messages from clients to all other clients
thanks for any suggestions
NOTE: I am not writing a instant messaging or chat program. This is merely a system where users can send alerts/messages to other users - they can not reply to each other! NO commercial, shareware, etc links - please! I would like to hear about how you would go about writing this type of system and what approachs you would take, and possibly the TCP IP messaging architecture you would use. Whether it be straight Winows API, Indy components, etc, etc.
If this is Windows only, and you don't want to use 3rd party libraries, then you can skip TCP/IP and go for Mailslots.
Edit: if you want guaranteed delivery, than named pipes is a better solution. This SO question has a few nice answers with Delphi named pipe examples.
A mailslot is a mechanism for one-way
interprocess communications (IPC).
Applications can store messages in a
mailslot. The owner of the mailslot
can retrieve messages that are stored
there. These messages are typically
sent over a network to either a
specified computer or to all computers
in a specified domain. A domain is a
group of workstations and servers that
share a group name.
They don't need a Windows domain, they work over a LAN.
DelphiPages has a nice run-down on doing IPC in Delphi, including mailslots.
--jeroen
If you want save yourself some work and use ready solution:
0MQ
STOMP
AMQP
XMPP
in above order. Last two listed rather in informational purposes.
IMO 0MQ it's best bet - it's well-thought-out, lightweight, fast and reliable.
Looks like publish-subscribe messaging. kbmMW offers one.
There's an instant message client from Aid Aim:
http://www.aidaim.com/products/msgcommunicator/manual_instant-messaging-im-sdk/index.php
About using indy, such as in this demo: indy10clieservr.sourceforge.net OR using the TServerSocket and TClientSocket package
-> now with x64 demo sample from INDY
To get this working reliably is more work than you might think - about 5% effort to get it working, and 95% effort to ensure it works under all circumstances, including network dropouts, etc. If you go here (http://www.csinnovations.com/framework_delphi.htm) you can see how I implemented my inter-process communications framework. The TCP stuff comprises about 10,000 lines of code using the Indy components.