Class

AutoDiscovery

Description

AutoDiscovery uses the EasyUDPSocket class to automatically discover other Xojo applications on the network.

Methods

Name

Parameters

Returns

Shared

Bind

Port As Integer

Close

Connect

GetMemberList

String()

JoinMulticastGroup

Group As String

Boolean

LeaveMulticastGroup

Group As String

Poll

Purge

Read

[Encoding As TextEncoding]

Datagram

Register

GroupName As String

SendMessageToGroup

Command As Int32, Data As String

SendMessageToIndividual

IPAddress As String, Command As Int32, Data As String

Unregister

GroupName As String

UpdateMemberList

Write

Address As String, Data As String

Events

Name

Parameters

Returns

DataAvailable

Error

e As RuntimeException

MemberJoined

IPAddress As String

MemberLeft

IPAddress As String

ReceivedMessage

FromIP As String, Command As Integer, Data As String

SendComplete

UserAborted As Boolean

Property descriptions

AutoDiscovery.BroadcastAddress

BroadcastAddress As String

The machine's broadcast address.

This property is read-only.

You can specify this address when you call the Write method and the data will be broadcast across the network, but you will not receive the data you sent back.

This example uses the BroadcastAddress to get the address of the group.

EasyUDPSocket1.Write(EasyUDPSocket1.BroadcastAddress, "Hello World")

AutoDiscovery.Handle

Handle As Integer

This is the socket's internal descriptor and it can be used with Declare statements.

This property is read-only.

  • On Windows, Handle is a Socket, suitable for use in Declares on Windows.

  • On macOS and Linux, Handle is a UNIX socket descriptor.

The descriptor is platform-specific. If Handle is less than zero, the descriptor is not available.

AutoDiscovery.IsConnected

IsConnected As Boolean

Indicates whether the socket is currently connected.

This property is read-only.

For TCPSockets, a connection means you can send and receive data and are connected to a remote machine. For UDPSockets, this means that you are bound to the port and are able to send, receive, join or leave multicast groups, or set socket options.

If EasyUDPSocket1.IsConnected Then
  // proceed using the connection
Else
  MessageBox("Connection failed!")
End If

AutoDiscovery.LocalAddress

LocalAddress As String

The local IP address of the computer.

This property is read-only.

Var localIP As String = Socket1.LocalAddress

AutoDiscovery.NetworkInterface

NetworkInterface As NetworkInterface

Specifies which network interface the socket should use when binding.

You can get the network interface(s) of the user's computer by calling the GetNetworkInterface method of the System module.

Leaving this property set to Nil will use the currently selected interface. In the case of UDPSockets, if you assign a non-Nil value, the socket may not be able to receive broadcast messages. The behavior is OS-dependent; it appears to work on Windows but not on other supported operating systems. If you wish to send broadcast packets out, then you should not bind to a specific interface because the behavior is undefined.

This example specifies that the TCPSocket will use the first Network Interface on the user's computer.

TCPSocket1.NetworkInterface = System.NetworkInterface(0)

AutoDiscovery.PacketsAvailable

PacketsAvailable As Integer

The number of packets available in the internal receive buffer.

This property is read-only.

AutoDiscovery.PacketsLeftToSend

PacketsLeftToSend As Integer

The number of packets left in the queue to send.

This property is read-only.

This enables you to create a synchronous socket without needing to subclass the UDPSocket.

AutoDiscovery.Port

Port As Integer

The port to bind on or connect to.

On most operating systems, attempting to bind to a port less than 1024 causes a Error event to fire with an error number 107 unless the application is running with administrative permissions. This is due to security features built into the underlying OS.

You need to set the port property explicitly before any call to Listen or Connect as the Port property will be modified to reflect what the actual bound port is during the various stages of operation.

For instance, if you listen on port 8080 and a connection comes in, you can check the Port property to ensure that you're still listening on port 8080 (that the port hasn't been hijacked). Or, if you connect to a socket on port 8080, once the connection occurs, you can check to see what port the OS has bound you to. This will be a random-seeming port number.

This trick can be very useful when you do things like Listen on port 0. In that case, the OS will pick a port for you and listen on it. Then you can check the Port property to see which port the OS picked. This functionality is used for various protocols, such as FTP.

This example sets the Port to 8080.

TCPSocket1.Port = 8080

AutoDiscovery.RouterHops

RouterHops As Integer

Specifies how many router hops the data sent out can make.

Multicasting has some extra features that make it an even more powerful utility for network applications. If you wish to receive the data you sent out with a multicast send, you can set the SendToSelf property (also known as loopback) of the UDPSocket. If it is set to True, then when you do a send (to a multicast group) you will get that data back. You can also set the number of router hops a multicast datagram will take (This is also known as the Time To Live (or TTL). When your Datagram gets sent out, it runs through a series of routers on the way to its destinations. Every time the Datagram hits a router, its RouterHops property gets decremented. When that number reaches zero, the Datagram is destroyed. This means you can control who gets your datagrams with a lot more precision. There are some “best guesses” as to what the value of RouterHops should be.

Value

Description

0

Same host

1

Same subnet

32

Same site

64

Same region

128

Same continent

255

Unrestricted

Note that if your Datagram runs through a router that does not support multicasting, it is killed immediately.

EasyUDPSocket1.RouterHops = 32

AutoDiscovery.SendToSelf

SendToSelf As Boolean

Specifies whether the data you send out will be sent to yourself as well.

This is also known as loopback. This property applies only to multicast sends.

Setting the SendToSelf property to True may not work on all versions of Windows. MSDN states that the SendToSelf property on NT 4 cannot be turned off. A multicasting socket will always receive the data it sends out.

EasyUDPSocket1.SendToSelf = True

Method descriptions

AutoDiscovery.Bind

Bind(Port As Integer)

Binds the socket to the specified port.

This example binds the socket to any available port between 8192 and 65535 (Note: the other member of the group must then use the same port, so you need to find a way to communicate this port to the others):

Var success As Boolean
Do
  success = True
  Try
    Me.Bind (Rnd * (65536 - 8192) + 8192)
  Catch error As RuntimeException
    success = False
  End Try
Loop Until success

AutoDiscovery.Close

Close

Closes the socket's connection, closes any connections the socket may have, and resets the socket.

The only information that is retained after calling Close is the socket's port, address (in the case of TCPSockets), LastErrorCode properties, and data left in the socket's receive buffer. All other information is discarded.

This example closes the EasyTCPSockets that were open. The sockets were added to the main window.

Connector.Close
Listener.Close

AutoDiscovery.Connect

Connect

Attempts to connect.

For TCPSockets, the address and port properties must be set. For UDPSockets, the port property must be set. The Connect method binds a socket to a port. After calling Connect, the Port property will report the actual port you are bound to.

AutoDiscovery.GetMemberList

GetMemberList As String()

Returns a String array of IP addresses belonging to the list of machines on the network who are in the group.

AutoDiscovery.JoinMulticastGroup

JoinMulticastGroup(Group As String) As Boolean

Joins the specified multicast group. Returns True if the group was successfully joined, False if not.

If EasyUDPSocket1.JoinMulticastGroup(TextField5.Value) Then
  MessageBox("Joined!")
End If

AutoDiscovery.LeaveMulticastGroup

LeaveMulticastGroup(Group As String)

Leaves the specified multicast group. The TextField contains the name of the group.

EasyUDPSocket1.LeaveMulticastGroup(TextField5.Text)

AutoDiscovery.Poll

Poll

Polls the socket manually, which allows a socket to be used synchronously.

The EasyTCPSocket "Listener" has been added to the window.

Listener.Poll

AutoDiscovery.Purge

Purge

Removes all data from the socket's internal receive buffer. It does not affect the socket's internal send buffer.

Listener.Purge

AutoDiscovery.Read

Read([Encoding As TextEncoding]) As Datagram

Returns a Datagram from the internal receive buffer.

The address property of the Datagram is the remote address from which the data was sent. The optional Encoding parameter enables you to specify the text encoding of the data to be returned. Use the Encodings module to specify a text encoding.

AutoDiscovery.Register

Register(GroupName As String)

Registers GroupName as an identifier for messages sent by SendMessageToGroup.

GroupName can be any string, which will be mapped it to a valid Class D IP address. Class D IP addresses are in the range: [224.0.0.0 to 239.255.255.255]. For example, you can call Register("My Cool App"), and it will be hashed to a valid Class D IP address. However, if you use a valid Class D IP address, it will use that without modifications.

Before calling Register, please set the port and call Connect.

This example registers the user as a group member and updates the list. Everyone on the network who wants to join the group needs to use the same group name:

AutoDiscovery1.Register("MyGroup")
AutoDiscovery1.UpdateMemberList

AutoDiscovery.SendMessageToGroup

SendMessageToGroup(Command As Int32, Data As String)

Sends the message consisting of command and data to the group.

Effective with 2017r3, the command parameter is Int32 instead of Integer to prevent incorrect behavior in 64-bit apps.

In order for this method to work you must have first registered a group (using the Register method).

AutoDiscovery.SendMessageToIndividual

SendMessageToIndividual(IPAddress As String, Command As Int32, Data As String)

Sends a message consisting of command and data to the machine having the IP address specified by IPAddress.

Effective with 2017r3, the command parameter is Int32 instead of Integer to prevent incorrect behavior in 64-bit apps.

The text encoding is not sent to the other application. So if you want to preserve text encoding, you should use ConvertEncoding to e.g. UTF-8 before sending the string and use DefineEncoding when you receive a message to restore the text encoding.

AutoDiscovery.Unregister

Unregister(GroupName As String)

Unregisters the GroupName passed.

AutoDiscovery.UpdateMemberList

UpdateMemberList

Clears the internal list of connected members and queries the network for all members of the current group.

This code registers as a group member and updates the list. Everyone on the network who wants to join the group needs to use the same group name:

AutoDiscovery1.Register("MyGroup")
AutoDiscovery1.UpdateMemberList

AutoDiscovery.Write

Write(Address As String, Data As String)

Constructs a Datagram and sends the data to the specified address.

This example uses BroadcastAddress to get the address of the group.

UDPSocket1.Write(UDPSocket1.BroadcastAddress, "Hello World")

Event descriptions

AutoDiscovery.DataAvailable

DataAvailable

Occurs when additional data has come into the internal receive buffer.

AutoDiscovery.Error

Error(e As RuntimeException)

Occurs when an error occurs with the socket.

These error codes provide you with key information about your socket, and it is not advisable to ignore them.

When an error occurs, the RuntimeException.ErrorNumber property will likely contain one of the following error codes:

Error Code

Description

0

No error occurred.

100

There was an error opening and initializing the drivers.

101

This error code is no longer used.

102

This code means that you lost your connection.

103

The socket was unable to resolve the address that was specified.

104

This error code is no longer used.

105

The address is currently in use.

106

This is an invalid state error, which means that the socket is not in the proper state to be doing a certain operation.

107

This error means that the port you specified is invalid.

108

This error indicates that your application has run out of memory.

These are not the only errors that are returned. For Windows, additional error codes are usually positive numbers in the range [10004, 11004]. For Windows error codes, see WinSock.h. MacOS and Linux use POSIX error codes. For a description of macOS and Linux error codes, see http://www.ioplex.com/~miallen/errcmp.html.

e.g. error 64 is for "host is down".

The following example in the Error event handler displays the error code.

MessageBox(Me.e.ErrorNumber.ToString)

AutoDiscovery.MemberJoined

MemberJoined(IPAddress As String)

A machine identified as IPAddress has joined.

AutoDiscovery.MemberLeft

MemberLeft(IPAddress As String)

A machine identified as IPAddress has left.

AutoDiscovery.ReceivedMessage

ReceivedMessage(FromIP As String, Command As Integer, Data As String)

A new complete message, consisting of an identifying integer, command, and the text data, has been received from the computer with FromIP IP address.

Effective with 2017r3, the command parameter is Int32 instead of Integer to prevent incorrect behavior in 64-bit apps.

Both fromIP and data strings both have no encoding set. If you know the encoding, you should use DefineEncoding to set it.

AutoDiscovery.SendComplete

SendComplete(UserAborted As Boolean)

Occurs when a send has completed.

Use this to determine when all your data has been sent. UserAborted will be True if the user aborted the send by returning True from the SendProgress event. You can use this information to update different status variables or to inform user about the success or failure of the transfer. If the send was completed, this value is False. UserAborted will always be False for UDP sockets.

Notes

The AutoDiscovery class lets you automatically discover other machines on the local network that are communicating using the EasyUDPSocket class. It does so by checking to see which other applications are using the same group name that you pass to the Register function of the EasyUDPSocket class. When a member joins (this includes your application when you first call the Register method), you will get a MemberJoined event with the IP address of the member that joined. When a member leaves, then you get a MemberLeft event with their IP as well. If you would like a list of the currently connected members, you can get an array of their IPs by calling the GetMemberList method. You can refresh the list by calling the UpdateMemberList method. It clears the internal list of connected members and re-queries the network for members.

The AutoDiscovery class is intended to make communication among network users as easy as possible. To do so, it uses of a proprietary protocol. Because of this, it is unable to discover other communications protocols that may also be running on the network, such as iChat. Use the generic classes such as TCPSocket, UDPSocket, URLConnection, and so forth.

Sample code

Binding to any available port between 8192 and 65535 (Note: the other member of the group must then use the same port, so you need to find a way to communicate this port to the others):

Do
  AutoDiscovery1.Bind(Rnd * (65536 - 8192) + 8192)
Loop Until AutoDiscovery1.IsConnected

Registering as a group member. Everyone on the network who wants to join the group needs to use the same group name:

AutoDiscovery1.Register("MyGroup")
AutoDiscovery1.UpdateMemberList

Getting the member list and displaying it in a ListBox:

For Each member As String In AutoDiscovery1.GetMemberList
  ListBox1.AddRow(member)
Next

Leaving the group:

AutoDiscovery1.Unregister("MyGroup")

Sending a message to the group:

AutoDiscovery1.SendMessageToGroup(100, "Hello world")

Receiving a message using the ReceivedMessage event:

Sub ReceivedMessage (fromIP As String, command As Integer, data As String)
  MessageBox(fromIP + " sent us " + command.ToString + ": " + Data)
End Sub

Compatibility

All project types on all supported operating systems.

See also

EasyUDPSocket parent class; EasyUDPSocket, UDPSocket classes.