4,152 questions
How to Select Specific Network Interface for Socket Connections in MAUI iOS
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Tazzi
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Reputation points
I am trying to create a socket connection from Android/iOS that will connect to a ESP32 access point although MAUI keeps indicating "No Route to Host" when trying to open the connection. My understand of this is the host responded with that this request does not have a valid 'destination', which is expected if the requested IP address does not exist.
This access point (ESP) does not have an internet connection, it is purely used for connecting to a smartphone or PC to allow sending commands via a socket connection.
After connecting to the ES32 Wifi from the phone settings, I am able to use any free TCP applications on both Android and iOS to open a socket connection to 192.168.4.1 on port 23. Once the connection is opened, I am able to send and receive information happily.
I am able to use the code below on an android and the socket connection opens fine. When I use it on iOS, I get back a "No Route to Host" error. Considering I am able to connect using a different application on the same iphone, I know its not the ESP failing here.
CancellationToken CToken = new CancellationToken();
using Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
await socket.ConnectAsync(IPAddress.Parse("192.168.4.1"), 23, CToken);
When connected to the ESP32 and looking at the wifi settings off the iphone, we have:
IP Address: 192.168.4.2
Subnet Mask: 255.255.255.0
Router: 192.168.4.1
DNS (is on Automatic): 192.168.4.1
Now here comes the next confusing part. A work colleague is able to use his iphone using the exact same EP32 access point, and able to connect a socket with the exact three lines of code above using MAUI. Both phones are identical (iphone 12 pro) and running the exact same iOS firmware 16.1.2
The only thing I can kind of figure that may be a difference, is the iphone is selecting the incorrect network adapter. So instead of using the ESP32 wifi connection, its possibly trying to connect a socket from one of the other network interfaces? Such as cellular?
Does anyone know how to enforce using a specific network adaptor for iOS? Even if its iOS platform specific code that needs to be run to setup/enforce at the beginning? Or have any other suggestions?
Developer technologies .NET .NET MAUI
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Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,436 Reputation points Microsoft External Staff2023-01-17T09:22:26.6533333+00:00 You can bind to a specific network then connect through that endpoint, see the remarks at: Socket.Bind(EndPoint) Method (System.Net.Sockets) | Microsoft Learn
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Tazzi 0 Reputation points
2023-01-17T11:38:02.4733333+00:00 @Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.)
To confirm, I should be binding to "192.168.4.2" which is the IP address assigned to the iPhone so that the socket knows to use the Wifi adapter? Then I should be able to open up the socket on using the assigned router IP of 192.168.4.1 port 23.
Doing this still results in the same issue of "No route to host", the exact error is: "System.Net.Sockets.SocketException (65): No route to host"
Below is the code I am running. Just to confirm, I am able to use the ios application called TCP console and it is able to open the TCP connection using 192.168.4.1 on port 23, so its not the ESP server.CancellationToken CToken = new CancellationToken(); using Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); EndPoint localwifiEP = new IPEndPoint(new IPAddress(new byte[] { 192, 168, 4, 2 }), 23); socket.Bind(localwifiEP); await socket.ConnectAsync("192.168.4.1", 23, CToken); -
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,436 Reputation points Microsoft External Staff
2023-01-19T03:50:34.8+00:00 To investigate further, may I ask have you tried disabling your app from using cellular data on your iPhone? Go to Settings->Cellular->scroll down a little to find your app->go to details (and check if the settings are different from your work colleague's device)
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Tazzi 0 Reputation points
2023-01-20T02:18:20.04+00:00 @Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.)
The plot thickens. The application does not appear in the Cellular data section of the iphone. It does not use any internet and does not call to any website domains, so technically it would never use data.I have tried tuning off cellular but still fails with the same issue.
Maybe trying to use iOS specific code will produce more favorable results. I cannot find any examples demonstrating creating a socket connection using NSUrlSession which appears to be the recommend option.
I have tried the following option:
NSUrlSession session = NSUrlSession.SharedSession; NSUrlSessionStreamTask task = session.CreateBidirectionalStream("192.168.4.1", 23); task.StartSecureConnection(); task.WriteData(NSData.FromArray(new byte[] { 0x41, 0x54, 0x49, 0x0D }), 10000, new Action<NSError>( delegate (NSError d) { string Variable = "Never Reaches Here"; }));This does not appear to do anything, The ESP will light up an LED when data has been received, and the above does not reach it.
Another method I found to try is using CreatePairWithSocketToHost. I tried below but it errors out when opening the write stream:
CFReadStream readStream = null; CFWriteStream writeStream = null; CFNetwork.CFHTTPStream.CreatePairWithSocketToHost("192.168.4.1", 23, out readStream, out writeStream); readStream.Open(); writeStream.Open();The above method indicates it is obsolete and should use "Network.framework" although this does not exist.
And finally, tried using CFSocket with:
CFSocket mysocket = CFSocket.CreateConnectedToSocketSignature(System.Net.Sockets.AddressFamily.InterNetwork, System.Net.Sockets.SocketType.Stream, System.Net.Sockets.ProtocolType.Tcp, new IPEndPoint(new IPAddress(new byte[] { 192, 168, 4, 1 }), 23), 5000);And it simply throws a "CoreFoundation.CFSocketException", which I can't seem to get any finer details about?
I am genuinely trying my best to try every avenue first, but definitely needing some guidance.
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Tazzi 0 Reputation points
2023-01-24T02:20:11.7+00:00 Still searching for an answer for this.
@Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.)
Do you know of an example using apple platform code to setup a socket connection directly?
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