DTLSServer Component

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The DTLSServer component provides server-side functionality for secure UDP communication utilizing the Datagram Transport Layer Security (DTLS) protocol.

Syntax

TipdDTLSServer

Remarks

The DTLSServer component functions as a server that facilitates incoming DTLS connections and offers a convenient means of transmitting and receiving datagrams over the established, secure connections.

Getting Started

First, a valid certificate must be selected before the server can start listening for incoming connections. The certificate can be specified via the SSLCert. Note the certificate must contain a private key.

After doing so, calling StartListening will cause the component to start listening for incoming connections. The component will listen on the interface defined by LocalHost and LocalPort, if specified. Otherwise, these values will be set by the component. If applicable, these values must be set before calling StartListening. For example:

//dtlsserver.LocalHost = "some_ip_address"; //dtlsserver.LocalPort = 1234; dtlsserver.SSLCert = new Certificate("/path/to/cert.pfx", CertStoreTypes.cstPFXFile, "cert_password", "cert_subject"); dtlsserver.StartListening(); Console.WriteLine("Listening on: " + dtlsserver.LocalHost + ":" + dtlsserver.LocalPort); while (dtlsserver.Listening) { dtlsserver.DoEvents(); }

Handling Incoming Connections

Once successfully listening, the component can now accept (or reject) incoming connections. The first indicator of an incoming connection will be through the ConnectionRequest event. Here, the connection's originating address and port can be queried. By default, the component will accept all incoming connections, but this behavior can be overridden within this event.

Assuming the connection is accepted, the DTLS handshake will proceed. Relevant handshake details will be reported by the SSLStatus event. By default, the client is not required to present a certificate to the server. To force this, the SSLAuthenticateClients property can be enabled. When enabled, the client's presented certificate will be available within the SSLClientAuthentication event, where the server can again choose to accept (or reject) incoming connections.

Once the connection is complete (or fails), the Connected event will fire. Note that this event will fire if a connection succeeds or fails. If successful, the event will fire with a StatusCode of 0. If this value is non-zero, it indicates the connection was unsuccessful. The Description parameter will contain relevant details.

After a successful connection, relevant connection-specific details will be available within the Connections collection. Each connection will be assigned a unique ConnectionId, which can be acquired for a given connection within the Connected event. For example:

dtlsserver.OnConnected += (o, e) => { if (e.StatusCode == 0) { Console.WriteLine("Successful connection from " + e.SourceAddr + ":" + e.SourcePort); Console.WriteLine("ConnectionId: " + e.ConnectionId); } else { Console.WriteLine("Connection failed from " + e.SourceAddr + ":" + e.SourcePort); Console.WriteLine("Error code: " + e.StatusCode); Console.WriteLine("Error description: " + e.Description); } }; dtlsserver.OnSSLClientAuthentication += (o, e) => { if (e.Accept) return; Console.Write("Client provided the following certificate:\nIssuer: " + e.CertIssuer + "\nSubject: " + e.CertSubject + "\n"); Console.Write("The following problems have been determined for this certificate: " + e.Status + "\n"); Console.Write("Would you like to accept anyways? [y/n] "); if (Console.Read() == 'y') e.Accept = true; }; dtlsserver.SSLCert = new Certificate("/path/to/cert.pfx", CertStoreTypes.cstPFXFile, "cert_password", "cert_subject"); dtlsserver.AuthenticateClients = true; dtlsserver.StartListening(); Console.WriteLine("Listening on: " + dtlsserver.LocalHost + ":" + dtlsserver.LocalPort); while (dtlsserver.Listening) { dtlsserver.DoEvents(); }

Sending and Receiving Data

The component can send data to individual connections, specified by the ConnectionId parameter, via the SendBytes and SendText methods.

While a connection is active, incoming data from a connection will be available within the DataIn event. Note that this event is non-reentrant, and it is recommended to offload time-consuming operations to ensure the best performance.

If required, the PauseData method can be called, disabling the reception of incoming data from a particular connection. Data reception can later be enabled via the ProcessData method. Note that if this reception is disabled for a connection, the connection may continue sending data, which will remain unprocessed by the component. In this case, the underlying socket buffer may be filled. This can result in possible data loss originating from this connection. Please use these methods with caution.

The complete process may look like the following:

dtlsserver.OnDataIn += (o, e) => { Console.WriteLine("Packet received from: " + e.ConnectionId); Console.WriteLine("Packet: " + e.Datagram); }; dtlsserver.SSLCert = new Certificate("/path/to/cert.pfx", CertStoreTypes.cstPFXFile, "cert_password", "cert_subject"); dtlsserver.StartListening(); Console.WriteLine("Listening on: " + dtlsserver.LocalHost + ":" + dtlsserver.LocalPort); ... ... ... // Broadcast data foreach (DTLSConnection c in dtlsserver.Connections.Values) { dtlsserver.SendText(c.ConnectionId, "Hello world!"); }

Removing Connections

To remove a connection, Disconnect must be called with the corresponding ConnectionId. In order to remove inactive connections, the DefaultIdleTimeout property can be set accordingly. By default, this property is set to 0, and idle connections are not removed automatically. When this property is set to a positive value, this will automatically remove connections that are idle for a specified amount of time.

Note: For DefaultIdleTimeout to work as intended, DoEvents must be called frequently in both console and form-based applications (e.g., using a loop or timer).

Finally, once a connection ends, Disconnected will fire. In the case a connection ends and an error is encountered, the StatusCode and Description parameters will contain relevant details regarding the error. The connection will be removed from the Connections collection. For example:

dtlsserver.OnDisconnected += (o, e) => { if (e.StatusCode == 0) { Console.WriteLine("Connection removed: " + e.ConnectionId); } else { Console.WriteLine("Connection removed: " + e.ConnectionId); Console.WriteLine("Error code: " + e.StatusCode); Console.WriteLine("Error description: " + e.Description); } }; dtlsserver.DefaultIdleTimeout = 60; // Remove connections inactive for 60 seconds dtlsserver.StartListening(); Console.WriteLine("Listening on: " + dtlsserver.LocalHost + ":" + dtlsserver.LocalPort); while (dtlsserver.Listening) { dtlsserver.DoEvents(); }

Additional Information

To support DefaultIdleTimeout and KeepAlive functionality, it is important to note that DoEvents must be called regularly in both console and form-based applications.

For DefaultIdleTimeout, DoEvents must be called frequently to ensure that idle connections are handled and removed in a timely manner. For KeepAlive, DoEvents must be called frequently to ensure the component sends keep-alive (or Heartbeat) packets to existing connections in a timely manner.

In form-based applications, this does not apply if DefaultIdleTimeout is set to 0 and KeepAlive is False.

Property List

The following is the full list of the properties of the component with short descriptions. Click on the links for further details.

Method List

The following is the full list of the methods of the component with short descriptions. Click on the links for further details.

Event List

The following is the full list of the events fired by the component with short descriptions. Click on the links for further details.

Config Settings

The following is a list of config settings for the component with short descriptions. Click on the links for further details.

Connections Property (DTLSServer Component)

This property includes a collection of currently connected clients.

Syntax

property Connections: TipdDTLSConnectionList read get_Connections write set_Connections;

Remarks

This property includes a collection of currently connected clients. All of the connections may be managed using this property. Each connection is described by different fields of the DTLSConnection type.

The collection is a hash-table type of collection, in which the ConnectionId string is used as the key to the desired connection. You may acquire the key for a given connection through the Connected event.

Example (Broadcasting Data)

foreach (DTLSConnection c in dtlsserver.Connections.Values) { dtlsserver.SendText(c.ConnectionId, "Hello world!"); }

This property is not available at design time.

DefaultIdleTimeout Property (DTLSServer Component)

This property includes the default idle timeout for inactive clients.

Syntax

property DefaultIdleTimeout: Integer read get_DefaultIdleTimeout write set_DefaultIdleTimeout;

Default Value

0

Remarks

This property specifies the idle timeout (in seconds) for clients. When set to a positive value, the component will disconnect idle clients after the specified timeout.

This applies only to clients that have not sent or received data within DefaultIdleTimeout seconds.

If set to 0 (default), no idle timeout is applied.

Note: DoEvents must be called for the component to check existing connections.

KeepAlive Property (DTLSServer Component)

When True, keep-alive functionality is enabled via the DTLS Heartbeat Extension.

Syntax

property KeepAlive: Boolean read get_KeepAlive write set_KeepAlive;

Default Value

false

Remarks

This property enables keep-alive functionality for established connections via the DTLS Heartbeat Extension (RFC 6520). Enabling this option can prevent long connections from timing out in case of inactivity.

Note: For this functionality to work as intended, DoEvents must be called frequently in both console and form-based applications (e.g., using a loop or timer).

Additionally, DTLS server implementations are not required to support Heartbeats.

Listening Property (DTLSServer Component)

This property indicates whether the component is listening for incoming connections on LocalPort.

Syntax

property Listening: Boolean read get_Listening;

Default Value

false

Remarks

This property indicates whether the component is listening for connections on the port specified by the LocalPort property. Use the StartListening and StopListening methods to control whether the component is listening.

This property is read-only and not available at design time.

LocalHost Property (DTLSServer Component)

The name of the local host or user-assigned IP interface through which connections are initiated or accepted.

Syntax

property LocalHost: String read get_LocalHost write set_LocalHost;

Default Value

''

Remarks

This property contains the name of the local host as obtained by the gethostname() system call, or if the user has assigned an IP address, the value of that address.

In multihomed hosts (machines with more than one IP interface) setting LocalHost to the IP address of an interface will make the component initiate connections (or accept in the case of server components) only through that interface. It is recommended to provide an IP address rather than a hostname when setting this property to ensure the desired interface is used.

If the component is connected, the LocalHost property shows the IP address of the interface through which the connection is made in internet dotted format (aaa.bbb.ccc.ddd). In most cases, this is the address of the local host, except for multihomed hosts (machines with more than one IP interface).

Note: LocalHost is not persistent. You must always set it in code, and never in the property window.

LocalPort Property (DTLSServer Component)

This property includes the Transmission Control Protocol (TCP) port in the local host where the component listens.

Syntax

property LocalPort: Integer read get_LocalPort write set_LocalPort;

Default Value

0

Remarks

This property must be set before the component can start listening. If its value is 0, then the TCP/IP subsystem picks a port number at random. The port number can be found by checking the value of this property after the component is listening (i.e., after successfully assigning True to the Listening property).

The service port is not shared among servers so two components cannot be listening on the same port at the same time.

SSLAuthenticateClients Property (DTLSServer Component)

If set to True, the server asks the client(s) for a certificate.

Syntax

property SSLAuthenticateClients: Boolean read get_SSLAuthenticateClients write set_SSLAuthenticateClients;

Default Value

false

Remarks

This property is used in conjunction with the SSLClientAuthentication event. Please refer to the documentation of the SSLClientAuthentication event for details.

SSLCert Property (DTLSServer Component)

The certificate to be used during Secure Sockets Layer (SSL) negotiation.

Syntax

property SSLCert: TipdCertificate read get_SSLCert write set_SSLCert;

Remarks

This property includes the digital certificate that the component will use during SSL negotiation. Set this property to a valid certificate before starting SSL negotiation. To set a certificate, you may set the Encoded field to the encoded certificate. To select a certificate, use the store and subject fields.

Config Method (DTLSServer Component)

Sets or retrieves a configuration setting.

Syntax

function Config(ConfigurationString: String): String;

Remarks

Config is a generic method available in every component. It is used to set and retrieve configuration settings for the component.

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the component, access to these internal properties is provided through the Config method.

To set a configuration setting named PROPERTY, you must call Config("PROPERTY=VALUE"), where VALUE is the value of the setting expressed as a string. For boolean values, use the strings "True", "False", "0", "1", "Yes", or "No" (case does not matter).

To read (query) the value of a configuration setting, you must call Config("PROPERTY"). The value will be returned as a string.

Disconnect Method (DTLSServer Component)

This method disconnects the specified client.

Syntax

procedure Disconnect(ConnectionId: Integer);

Remarks

Calling this method will disconnect the client specified by the ConnectionId parameter.

DoEvents Method (DTLSServer Component)

This method processes events from the internal message queue.

Syntax

procedure DoEvents();

Remarks

When DoEvents is called, the component processes any available events. If no events are available, it waits for a preset period of time, and then returns.

PauseData Method (DTLSServer Component)

This method pauses data reception.

Syntax

procedure PauseData(ConnectionId: Integer);

Remarks

This method pauses data reception for the connection identified by ConnectionId when called. While data reception is paused, the DataIn event will not fire for the specified connection. Call ProcessData to reenable data reception.

ProcessData Method (DTLSServer Component)

This method reenables data reception after a call to PauseData .

Syntax

procedure ProcessData(ConnectionId: Integer);

Remarks

This method reenables data reception for the connection identified by ConnectionId after a previous call to PauseData. When PauseData is called, the DataIn event will not fire for the specified connection. To reenable data reception and allow DataIn to fire, call this method.

Note: This method is used only after previously calling PauseData. It does not need to be called to process incoming data by default.

Reset Method (DTLSServer Component)

This method will reset the component.

Syntax

procedure Reset();

Remarks

This method will reset the component's properties to their default values.

SendBytes Method (DTLSServer Component)

This method sends binary data to the specified client.

Syntax

procedure SendBytes(ConnectionId: Integer; Data: TBytes);

Remarks

This method sends binary data to the client identified by ConnectionId. For example:

byte[] dataToSend = new byte[] { 72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 33 }; foreach (DTLSConnection c in dtlsserver.Connections.Values) { dtlsserver.SendBytes(c.ConnectionId, dataToSend); }

To send text, use the SendText method instead.

SendText Method (DTLSServer Component)

This method sends text to the specified client.

Syntax

procedure SendText(ConnectionId: Integer; Text: String);

Remarks

This method sends text to the client identified by ConnectionId. For example:

string dataToSend = "Hello world!"; foreach (DTLSConnection c in dtlsserver.Connections.Values) { dtlsserver.SendText(c.ConnectionId, dataToSend); }

To send binary data, use the SendBytes method instead.

Shutdown Method (DTLSServer Component)

This method shuts down the server.

Syntax

procedure Shutdown();

Remarks

This method shuts down the server. Calling this method is equivalent to calling StopListening and then breaking every client connection by calling Disconnect.

StartListening Method (DTLSServer Component)

This method starts listening for incoming connections.

Syntax

procedure StartListening();

Remarks

This method begins listening for incoming connections on the port specified by LocalPort. Once listening, events will fire as new clients connect and data are transferred.

To stop listening for new connections, call StopListening. To stop listening for new connections and to disconnect all existing clients, call Shutdown.

StopListening Method (DTLSServer Component)

This method stops listening for new connections.

Syntax

procedure StopListening();

Remarks

This method stops listening for new connections. After being called, any new connection attempts will be rejected. Calling this method does not disconnect existing connections.

To stop listening and to disconnect all existing clients, call Shutdown instead.

Connected Event (DTLSServer Component)

This event is fired immediately after a connection completes (or fails).

Syntax

type TConnectedEvent = procedure (
  Sender: TObject;
  ConnectionId: Integer;
  const SourceAddr: String;
  SourcePort: Integer;
  StatusCode: Integer;
  const Description: String
) of Object;

property OnConnected: TConnectedEvent read FOnConnected write FOnConnected;

Remarks

This event is fired immediately after a connection completes (or fails). The ConnectionId parameter indicates the unique ID assigned to this connection.

SourceAddr contains the IP number (Internet address) of the remote party, and SourcePort contains the port from which the packet originated.

If the connection is made normally, StatusCode is 0 and Description is "OK".

If the connection fails, StatusCode has the error code returned by the system. Description contains a description of this code. The value of StatusCode is equal to the value of the system error.

Please refer to the Error Codes section for more information.

ConnectionRequest Event (DTLSServer Component)

This event is fired when a request for connection comes from a remote host.

Syntax

type TConnectionRequestEvent = procedure (
  Sender: TObject;
  const Address: String;
  Port: Integer;
  var Accept: Boolean
) of Object;

property OnConnectionRequest: TConnectionRequestEvent read FOnConnectionRequest write FOnConnectionRequest;

Remarks

This event indicates an incoming connection. The connection is accepted by default. Address and Port will contain information about the remote host requesting the inbound connection. If you want to refuse it, you can set the Accept parameter to False.

DataIn Event (DTLSServer Component)

This event is fired when data is received.

Syntax

type TDataInEvent = procedure (
  Sender: TObject;
  ConnectionId: Integer;
  const Datagram: String;
  const DatagramB: TBytes
) of Object;

property OnDataIn: TDataInEvent read FOnDataIn write FOnDataIn;

Remarks

The DataIn event is fired every time a new datagram is received.

ConnectionId indicates the unique Id of the DTLSConnection from which the packet originated.

Datagram contains the packet as sent by the remote host.

Note: Events are not re-entrant. Performing time-consuming operations within this event will prevent it from firing again in a timely manner and may affect overall performance.

Disconnected Event (DTLSServer Component)

This event is fired when a connection is closed.

Syntax

type TDisconnectedEvent = procedure (
  Sender: TObject;
  ConnectionId: Integer;
  StatusCode: Integer;
  const Description: String
) of Object;

property OnDisconnected: TDisconnectedEvent read FOnDisconnected write FOnDisconnected;

Remarks

If the connection is broken normally, StatusCode is 0, and Description is 'OK'.

If the connection is broken for any other reason, StatusCode has the error code returned by the system. Description contains a description of this code. The value of StatusCode is equal to the value of the system error.

Please refer to the Error Codes section for more information.

Error Event (DTLSServer Component)

This event fires information about errors during data delivery.

Syntax

type TErrorEvent = procedure (
  Sender: TObject;
  ConnectionId: Integer;
  ErrorCode: Integer;
  const Description: String
) of Object;

property OnError: TErrorEvent read FOnError write FOnError;

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally, the component raises an exception.

ErrorCode contains an error code and Description contains a textual description of the error. For a list of valid error codes and their descriptions, please refer to the Error Codes section.

ConnectionId indicates the connection for which the error is applicable.

Log Event (DTLSServer Component)

This event fires once for each log message.

Syntax

type TLogEvent = procedure (
  Sender: TObject;
  ConnectionId: Integer;
  LogLevel: Integer;
  const Message: String;
  const LogType: String
) of Object;

property OnLog: TLogEvent read FOnLog write FOnLog;

Remarks

This event fires once for each log message generated by the component. The verbosity is controlled by the LogLevel setting.

LogLevel indicates the level of message. Possible values are as follows:

The value 1 (Info) logs basic information, including users logging in and out, files transferred, and directories listed.

The value 2 (Verbose) includes logs from the PITrail event as well as basic information about data transfer channels.

The value 3 (Debug) logs additional debug information, such as extended socket connection and data transfer information.

Message is the log entry.

LogType identifies the type of log entry. Possible values are as follows:

• "Info"
• "Error"
• "Verbose"
• "Debug"

SSLClientAuthentication Event (DTLSServer Component)

This event is fired when the client presents its credentials to the server.

Syntax

type TSSLClientAuthenticationEvent = procedure (
  Sender: TObject;
  ConnectionId: Integer;
  const CertEncoded: String;
  const CertEncodedB: TBytes;
  const CertSubject: String;
  const CertIssuer: String;
  const Status: String;
  var Accept: Boolean
) of Object;

property OnSSLClientAuthentication: TSSLClientAuthenticationEvent read FOnSSLClientAuthentication write FOnSSLClientAuthentication;

Remarks

This event enables the server to decide whether or not to continue. The Accept parameter is a recommendation on whether to continue or to close the connection. This is just a suggestion: application software must use its own logic to determine whether or not to continue.

When Accept is False, Status shows why the verification failed (otherwise, Status contains the string "OK").

SSLStatus Event (DTLSServer Component)

This event is fired to show the progress of the secure connection.

Syntax

type TSSLStatusEvent = procedure (
  Sender: TObject;
  ConnectionId: Integer;
  const Message: String
) of Object;

property OnSSLStatus: TSSLStatusEvent read FOnSSLStatus write FOnSSLStatus;

Remarks

The event is fired for informational and logging purposes only. It is used to track the progress of the connection.

Certificate Type

This is the digital certificate being used.

Remarks

This type describes the current digital certificate. The certificate may be a public or private key. The fields are used to identify or select certificates.

Fields

Constructors

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constructor Create();

constructor Create(valEncoded: TBytes);

constructor Create(valStoreType: TipdCertStoreTypes; valStore: String; valStorePassword: String; valSubject: String);

constructor Create(valStoreType: TipdCertStoreTypes; valStore: TBytes; valStorePassword: String; valSubject: String);

DTLSConnection Type

This is a currently connected client.

Remarks

This type describes the connection of a client that is currently connected to the component. You may use the different fields of this type to manage the connection.

Fields

Constructors

constructor Create();

Config Settings (DTLSServer Component)

DTLSServer Config Settings

UDP Config Settings

Socket Config Settings

SSL Config Settings

-----BEGIN CERTIFICATE-----
MIIEKzCCAxOgAwIBAgIRANTET4LIkxdH6P+CFIiHvTowDQYJKoZIhvcNAQELBQAw
... Intermediate Cert ...
eWHV5OW1K53o/atv59sOiW5K3crjFhsBOd5Q+cJJnU+SWinPKtANXMht+EDvYY2w
F0I1XhM+pKj7FjDr+XNj
-----END CERTIFICATE-----
\r \n
-----BEGIN CERTIFICATE-----
MIIEFjCCAv6gAwIBAgIQetu1SMxpnENAnnOz1P+PtTANBgkqhkiG9w0BAQUFADBp
... Root Cert ...
d8q23djXZbVYiIfE9ebr4g3152BlVCHZ2GyPdjhIuLeH21VbT/dyEHHA
-----END CERTIFICATE-----

-----BEGIN CERTIFICATE-----
MIIEKzCCAxOgAwIBAgIRANTET4LIkxdH6P+CFIiHvTowDQYJKoZIhvcNAQELBQAw
... Intermediate Cert ...
eWHV5OW1K53o/atv59sOiW5K3crjFhsBOd5Q+cJJnU+SWinPKtANXMht+EDvYY2w
F0I1XhM+pKj7FjDr+XNj
-----END CERTIFICATE-----
\r \n
-----BEGIN CERTIFICATE-----
MIIEFjCCAv6gAwIBAgIQetu1SMxpnENAnnOz1P+PtTANBgkqhkiG9w0BAQUFADBp
... Root Cert ...
d8q23djXZbVYiIfE9ebr4g3152BlVCHZ2GyPdjhIuLeH21VbT/dyEHHA
-----END CERTIFICATE-----

-----BEGIN CERTIFICATE-----
MIIEKzCCAxOgAwIBAgIRANTET4LIkxdH6P+CFIiHvTowDQYJKoZIhvcNAQELBQAw
... Intermediate Cert...
eWHV5OW1K53o/atv59sOiW5K3crjFhsBOd5Q+cJJnU+SWinPKtANXMht+EDvYY2w
F0I1XhM+pKj7FjDr+XNj
-----END CERTIFICATE-----
\r \n
-----BEGIN CERTIFICATE-----
MIIEFjCCAv6gAwIBAgIQetu1SMxpnENAnnOz1P+PtTANBgkqhkiG9w0BAQUFADBp
... Root Cert...
d8q23djXZbVYiIfE9ebr4g3152BlVCHZ2GyPdjhIuLeH21VbT/dyEHHA
-----END CERTIFICATE-----

Base Config Settings

Trappable Errors (DTLSServer Component)

DTLSServer Errors