I'm having some trouble with this, and have a hard time explaining the problem in words, but I will do the best I can.
I would like to send a simple message to a computer from a different computer. Nothing fancy. I have done some research, and a lot of sources say to create a script that accesses the built-in MSG.EXE function in Windows (I am currently on Windows 10) however, this only seems to work on machines connected to LAN.
From what I have gathered, I would need to create a website that handles the requests: get message from Computer A and send it to Computer B. Could I do this (In Powershell or VBS) without having to make a site specifically for it?
What I want:
I want Computer A to send a plain-text message to Computer B. Preferably, when the message is successfully sent a message box will appear that says "From: (whomever) and the message. Using MSG.EXE did what I wanted it to do, however it only worked with LAN-connected devices. Could I make this work with static IP? If so, how?
Additional Information:
The two computers are not on a LAN, but are connected to the Internet.
Computer A (the sender) and Computer B (the receiver) each have a static IP address, however that can obviously change.
Ports are available in each computer.
I have a Raspberry Pi that could act as a server "middle man" should that be required.
To be very clear: There are a lot of posts that talk about sending messages over LAN. I am NOT trying to send a message over LAN. Any help would be appreciated.
You're being quite vague in why you want it and what you want it to do; the main problem is that home internet connections are built for things to connect out, and nothing to connect in.
Fixes:
Port forwarding where you say "incoming connections go to this or that computer.
Building a service where both sides "connect out", i.e. you have a website hosted somewhere out on the internet. One computer connects out to send the message, the other connects out to check for messages.
Outside that, the next problem is knowing where on the internet to connect to.
Fixes:
Hard code the end points. Static IPs are good for this because the definition of a static IP is that it's an address which doesn't change. Mysteriously, you have static IPs which can change and you consider that 'obvious'. (??)
DNS where you register a domain, and the computers look at a domain name for where to connect. You update DNS with the current IP.
DNS where you use a free DNS service on someone else's name and your service listener updates that as its IP changes.
And after that, most people's computers/laptops/phones are switched off or in low power sleep mode most of the time, and their internet connections are comparatively unreliable, so any random message probably won't be answered.
Fixes:
Use a serious website service
Run an always-on computer to be that service
Deal with it being offline and messages being flakey
Use a store-and-forward system like email, which queues and retries, like e-mail and instant messengers do
get message from Computer A and send it to Computer B. Could I do this (In Powershell or VBS) without having to make a site specifically for it?
Yes. Quick answer: pick a port, configure site B's modem/router to forward the port to computer B. Open the port on computer B's firewall. Write some kind of TCP socket listener on Computer B, and the sender on Computer A, connecting to the public IP address of site B.
Long answer: then enjoy writing your own messaging protocol, error handling, message authentication, etc.
Alternative: do the same but going to your rPi. Have it listening. Not in powershell (sadly) or vbscript (luckily), and have it serve the messages up by HTTP/JSON, both computers invoke-webrequest or invoke-restmethod and post/get them with regular polling.
Related
First I want to define my question:
1, I am talking about computer program doing the IM, not mobile app. The program should be working in every home, or office environment.
2, Right now all (or most) home computers are behind a router, protected by ISP's security policy. It is not like 20 years ago, when a computer connects to an adapter, it gets a universal IP, as good as Microsoft.com and whitehouse.gov. 10 years ago, you can advise user to do port forwarding, or use UPnP to stealthily perform the port forwarding task. But now in the name of security, ISP is taking port forwarding out from the ISP-managed router (xfinity is doing that, as far as I know).
I know how to do IM in LAN setting, or the universal IP setting, that you get the IP of the friend, establish connection using TCP or UDP, then transfer information. Now when all computers are behind the routers, what is the feasible way / popular way / right way to do IM again? Using a central server to transfer information, by establishing connections of UserA-Server and UserB-Server? I know it would work, but not very "instant", in my humble opinion.
Please advise, thanks.
Upnp and NAT-PMP can still work, it will map a external port like punchhole. The problem is that our external IP may not be sure. So if you want to send IM, there are two choices, DHT or Central Controller.
I suggest you to use DHT and a central server using ICE structure, if DHT can work then it is ok, or we can use the central server to do the UDP/TCP traversal. In some circumstances like symmetric NAT, the server need to do relay, but in others, it just start the connection and then it is a p2p connection without server.
I'm working on an Enterprise app that communicates with our company servers. I have full two-way communication between the phone and the server through 3G/4G, and it works from my home wifi, but using the wifi at the office where it is connected to the company network the app doesn't see the server that way.
The app is set to look for our external IP address, and the port is open to the server. But I guess the external IP address is not 'visible' from within the network. When I plug in the internal IP address of the server, it goes through just fine.
For the vast number of our users, that would not be a problem. Most of our users (employees) work in the field or in other offices. But for users inside our network, this arrangement is useless unless the user turned off his wifi. But that's not a professional way to do it.
I need to know if there's a way for my app to either use 3G/4G exclusively, or to discover the SSID of the wifi and decide which IP address to use. I'm guessing that the answers to both of these will be, "you can't do that," But I thought I'd ask anyway.
Thanks!
You could have it attempt the internal IP, and fall back to the external IP if it can't connect. A better solution might be to have an internal DNS server that serves the internal IP to in-network devices, though.
Well, I discovered this code is exactly what I need. It gives me the SSID in string form, and I can compare the SSID string with a string of our wifi's SSID, and if it matches then the app uses the internal IP address. And if it doesn't match, it will connect to the external IP address. So far it works perfectly!
Followup: ceejayoz, I don't know if your second suggestion is the same as what our IT guy did, but he created a domain name that will resolve to the server whether it's internal or external. That seems to be the best way to go. So even though I had a workable answer, the URL works better with less code.
I've read tons of questions about this all over the web, and can't seem to find a solid answer. If I have an iPhone that's running on cellular data and another iOS device on wifi (in two separate locations), is it possible for them to send data to each other directly without sending it first to a web server, then retrieving it? Are the only options sending and receiving from a server/Apple's iCloud? What if I knew the devices' ip addresses? Note that the iPhone has WiFi disabled.
I'm not looking to put this in the app store, it is for personal use. I know NSNotificationCenter isn't an option.
Using the gamekit framework you can send data between two iOS devices. It is easy to implement. Other than that I don't think there is any other way to send data between two iOS devices.
Actually, it IS possible. You may want to google for something called "UDP hole punching" or "TCP hole punching".
The main approach in short: Assuming you got something like a relay server, that is some server in the internet that is publicly addressable from every private LAN that is connected to the www. No you have your two clients A and B in (different) private LANs, with some Network address translation (NAT) going on, that want to establish a peer to peer connection.
First of all both will tell the server their IP address and the port they have in their own LAN. In the UDP or TCP packet, the server will find the public address and port of the device (or the NAT (router)). So the server knows the private and the public IP address as well as the ports.
If now A wants to communicate with B, it asks the server for help. The server will send a message to B that A wants to communicate with her telling her A's public and private IP and port. A gets back B's public and private information and port.
Now here is where the magic happens. Both clients now send packets out to establish a connection simultaneously to the private and public addresses of the other party and thus punching a whole in their NATs such that incoming connections will not be blocked. Even if one party's connection establishing packets will arrive before this whole is created, the other's packets will get through to such that a connection can be created.
Beware of some NATs that scan the data for IP addresses and translate them as well, but if you encrypt your data or change the appearance of the address (complement, ...) you will be fine.
Now the master question, how can the server communicate with one of the clients without an active connection. Well in this case you can use "connection reversal" and apple's "push notifications". Use the "push notifications" (pn) to tell a client behind a NAT that there is something of interest going on and that it should contact the server. Once it has done that the connection is active and can be used in the previous described fashion.
I hope this helps some people that get to this problem although the post is quite old!
You can only use direct IP address communications if the IP address are publicly reachable IP addresses accessible over the internet, and they are static (enough) so that they are not changing on you regularly as devices get assigned to addresses dynamically. In many (most) cases, that won't be true because your devices will be assigned their IP address dynamically and those addresses are frequently going to be self-assigned IP addresses that aren't publicly addressable.
As others have commented, using Apple-provided mechanisms like iCloud are probably the easiest options. If that's not something you'd like to entertain, there are probably ways to make use of a dynamic DNS service like DynDNS to manage the actual IP addresses of your devices. With something like that you might be able to use a direct IP connection between devices based on a named DNS lookup. You'd probably have to jump through some hoops to make that happen though and I'm not sure you'd want to go to that extent.
I think that Bluetooth would be a good option for you
I am building an app that uses a async socket connection with a web server.
For sending large amounts of data I would like to connect two iPhones into a Peer to Peer connection using an async socket. I am more familiar with GCDAsyncSocket than to the iOS SDK socket API.
I have done something similar, but only within a local network were I would user NSNetService to publish a presence and get the addresses needed from the p2p connection.
Can you give me a hint on how to connect two iPhone over the internet using a p2p socket connection?
I do not know much about NSNetService but it seems that it only works in a local network. If you want to establish a p2p connection from an iphone to another you will always have the problem of several NATs (Network address translators) in your route. How to find the address and route to the peer? And how to get trough all the firewalls and NATs?
I am working on an app that needs to deal with the same problem and I have answered a similar question before which I will cite here:
Actually, it IS possible. You may want to google for something called
"UDP hole punching" or "TCP hole punching".
The main approach in short: Assuming you got something like a relay
server, that is some server in the internet that is publicly
addressable from every private LAN that is connected to the www. No
you have your two clients A and B in (different) private LANs, with
some Network address translation (NAT) going on, that want to
establish a peer to peer connection.
First of all both will tell the server their IP address and the port
they have in their own LAN. In the UDP or TCP packet, the server will
find the public address and port of the device (or the NAT (router)).
So the server knows the private and the public IP address as well as
the ports.
If now A wants to communicate with B, it asks the server for help. The
server will send a message to B that A wants to communicate with her
telling her A's public and private IP and port. A gets back B's public
and private information and port.
Now here is where the magic happens. Both clients now send packets out
to establish a connection simultaneously to the private and public
addresses of the other party and thus punching a whole in their NATs
such that incoming connections will not be blocked. Even if one
party's connection establishing packets will arrive before this whole
is created, the other's packets will get through to such that a
connection can be created.
Beware of some NATs that scan the data for IP addresses and translate
them as well, but if you encrypt your data or change the appearance of
the address (complement, ...) you will be fine.
Now the master question, how can the server communicate with one of
the clients without an active connection. Well in this case you can
use "connection reversal" and apple's "push notifications". Use the
"push notifications" (pn) to tell a client behind a NAT that there is
something of interest going on and that it should contact the server.
Once it has done that the connection is active and can be used in the
previous described fashion.
I hope this helps some people that get to this problem although the
post is quite old!
Now if you find this solution helpful and you try to implement it, please tell me if you are successful in getting the public ip and port of the server-client connection on the server side. You can also answer my question about this on stackoverflow.
Please be specific, u may use GCDAsyncSocket to connect 2 phones, u may use sample code from Github.
I have been working on a local LAN service which uses a multicast port to coordinate several machines. Each machine listens on the multicast port for instructions, and when a certain instruction is received, will send messages directly to other machines.
In other words the multicast port is used to coordinate peer-to-peer UDP messaging.
In practice this works quite well but there is a lingering issue related to correctly setting up these peer-to-peer transmissions. Basically, each machine needs to announce on the multicast port its own IP address, so that other machines know where to send messages when they wish to start a P2P transmission.
I realize that in general the idea of identifying the local IP is not necessarily sensible, but I don't see any other way-- the local receiving IP must be announced one way or another. At least I am not working on the internet, so in general I won't need to worry about NATs, just need to identify the local LAN IP. (No more than 1 hop for the multicast packets is allowed.)
I wanted to, if possible, determine the IP passively, i.e., without sending any messages.
I have been using code that calls getifaddrs(), which returns a linked list of NICs on the machine, and I scan this list for non-zero IP addresses and choose the first one.
In general this has worked okay, but we have had issues where for example a machine with both a wired and wifi connection are active, it will identify the wrong one, and the only work-around we found was to turn off the wifi.
Now, I imagine that a more reliable solution would be to send a message to the multicast telling other machines to report back with the source address of the message; that might allow to identify which IP is actually visible to the other machines on the net. Alternatively maybe even just looking at the multicast loopback message would work.
What do you think, are there any passive solutions to identify which address to use? If not, what's the best active solution?
I'm using POSIX socket API from C. Must work on Linux, OS X, Windows. (For Windows I have been using GetAdapterAddresses().)
Your question about how to get the address so you can advertise it right is looking at it from the wrong side. It's a losing proposition to try to guess what your address is. Better for the other side to detect it itself.
When a listening machine receives a message, it is probably doing do using recvfrom(2). The fifth argument is a buffer into which the kernel will store the address of the peer, if the underlying protocol offers it. Since you are using IP/UDP, the buffer should get filled in with a sockaddr_in showing the IP address of the sender.
I'd use the address on the interface I use to send the announcement multicast message -- on the wired interface announce the wired address and on the wireless interface announce the wireless address.
When all the receivers live on the wired side, they will never see the message on the wireless network.
When there is a bridge between the wired and the wireless network, add a second step in discovery for round-trip time estimation, and include a unique host ID in the announcement packet, so multiple routes to the same host can be detected and the best one chosen.
Also, it may be a good idea to add a configuration option to limit the service to certain interfaces.