Interface ISession

The client session to a server or cluster of servers.

Namespace: PushTechnology.ClientInterface.Client.Session

Assembly: Diffusion.Client.dll

Syntax

public interface ISession

Remarks

A new session can be created by connecting to a server using Open(String), specifying the server URL. There is also a non-blocking variant Open(String, ISessionOpenCallback). The session factory can be configured to control the behavior of the session.

The session provides a variety of operations to the application. These are grouped into feature interfaces, such as ITopics and IMessaging, exposed to the application through various properties.

Session lifecycle

Each session is managed by a server. The server assigns the session a unique identity (ISessionId), and manages the session's topic subscriptions, security details, and session properties.

A session can be terminated using Close(). A session may also be terminated by the server because of an error or a time out, or by other privileged sessions using the IClientControl feature.

A client can become disconnected from the server, and reconnect to the server without loss of the session. Reconnection can be configured using ReconnectionStrategy(IReconnectionStrategy). The server must be configured to allow reconnection.

If a session is connected to a server that belongs to a cluster with session replication enabled, and then becomes disconnected, it will attempt to reconnect to the original server. A properly configured load balancer can detect that the original server is unavailable and re-route the reconnection request to a second server in the cluster. The second server can recover session data and continue the session. This process is known as "fail over". Unlike reconnection, in-flight messages can be lost during failover, and the application will be unsubscribed and re-subscribed to topics.

The current state of the session can be retrieved with the State property. A listener can be registered with the StateChanged event which will be notified when the session state changes.

Session Properties

For each session, the server stores a set of session properties that describe various attributes of the session.

There are two types of session property. Fixed properties are assigned by the server. User-defined properties are assigned by the application.

Many operations use session filter expressions that use session properties to select sessions.

A privileged client can monitor other sessions, including changes to their session properties, using a ISessionPropertiesListener. When registering to receive session properties, special key values of ALL_FIXED_PROPERTIES and ALL_USER_PROPERTIES can be used.

Each property is identified by a key. Most properties have a single string value. The exception is the ROLES fixed property which has a set of string values.

Fixed properties are identified by keys with a $ prefix. The available fixed session properties are:

Key	Description
`$ClientIP` (CLIENT_IP)	The Internet address of the client in string format.
`$ClientType` (CLIENT_TYPE)	The client type of the session. One of `ANDROID`, `C`, `DOTNET`, `IOS`, `JAVA`, `JAVASCRIPT_BROWSER`, `MQTT`, `PYTHON`, or `OTHER`.
`$Connector` (CONNECTOR)	The configuration name of the server connector that the client connected to.
`$Country` (COUNTRY)	The country code for the country where the client's Internet address was allocated (for example, `NZ` for New Zealand). If the country code could not be determined, this will be a zero length `string`.
`$GatewayType` (GATEWAY_TYPE)	Gateway client type. Only set for gateway client sessions. If present it indicates the type of gateway client (e.g. Kafka).
`$GatewayId` (GATEWAY_ID)	The identity of a gateway client session. Only present if the $GatewayType session property is present.
`$Language` (LANGUAGE)	The language code for the official language of the country where the client's Internet address was allocated (for example, `en` for English). If the language could not be determined or is not applicable, this will be a zero length `string`.
`$Latitude` (LATITUDE)	The client's latitude, if available. This will be the `string` representation of a floating point number and will be `NaN` if not available.
`$Longitude` (LONGITUDE)	The client's longitude, if available. This will be the `string` representation of a floating point number and will be `NaN` if not available.
`$MQTTClientId` (MQTT_CLIENT_ID)	The MQTT client identifier. Only set for MQTT sessions. If present, the value of the `$ClientType` session property will be MQTT.
`$Principal` (PRINCIPAL)	The security principal associated with the client session.
`$Roles` (ROLES)	Authorisation roles assigned to the session. This is a set of roles represented as quoted strings (for example, `"role1","role2"`). The utility method StringToRoles(String) can be used to parse the `string` value into a set of roles.
`$ServerName` (SERVER_NAME)	The name of the server to which the session is connected.
`$SessionId` (SESSION_ID)	The session identifier. Equivalent to ISessionId's `ToString()` output.
`$StartTime` (START_TIME)	The session's start time in milliseconds since the epoch.
`$Transport` (TRANSPORT)	The session transport type. One of `WEBSOCKET`, `HTTP_LONG_POLL`, `TCP`, or `OTHER`.

All listed property keys constants can be found in SessionProperty.

All user-defined property keys are non-empty strings and are case-sensitive. The characters ' ', '\t', '\r', '\n', '\"', '\'', '(', ')' are not allowed.

Session properties are initially associated with a session as follows:

When a client starts a new session, it can optionally propose user-defined session properties (see Property(String, String) and Properties(IDictionary<String, String>)). Session properties proposed in this way must be accepted by the authenticator. This safeguard prevents abuse by a rogue, unprivileged client.
The server allocates all fixed property values.
The new session is authenticated by registered authenticators. An authenticator that accepts a session can veto or change the user-defined session properties and add new user-defined session properties. The authenticator can also change certain fixed properties.

Once a session is established, its user-defined session properties can be modified by clients with VIEW_SESSION and MODIFY_SESSION permissions using IClientControl. A privileged client can also modify its own session properties.

If a session re-authenticates (see ChangePrincipalAsync(String, ICredentials)), the authenticator that allows the re-authentication can modify the user-defined session properties and a subset of the fixed properties as mentioned above.

Session Filters

Session filters are query expressions for session properties. They can be used to address a set of sessions based on their session properties. For example, it is possible to send a message to all sessions that satisfy a specified filter. Session filters are parsed and evaluated on the server.

A session filter expression consists of either a single clause, or multiple clauses connected by the binary operators and and or. The and operator takes precedence over or but parentheses can be used to override the precedence. For example:

Department is "Accounts"
hasRoles[ "operator" "trading desk" ]
Department is "Payroll" and Status is "Closed"
(Department is "Accounts" or Department is "Payroll") and Status is "Closed"

The unary not operator can be used to negate the following clause or an expression within parentheses:

not Department is "Payroll"
not (Department is "Payroll" or Department is "Accounts")

An equality clause has the form key operator value where key is the name of a session property and value is the property value. The supported operators are is or eq, both of which mean "equals", and ne which means "does not equal". Values are strings enclosed within single or double quotes. Special characters (", ', or \) can be included within the value by preceding with the escape character \. The utility method EscapeString(String) can be used to insert escape characters into a value.

The all operator matches all sessions.

The has operator may be used to check if a property is present. This is useful for determining whether a user-defined property or an optional fixed property is set for a session.

hasRoles is a special operator for querying the $Roles session property. A hasRoles clause has the form hasRoles[ "role1" "role2"... "roleN" ]. The clause will match sessions that have all the specified authorisation roles. Each role is a string enclosed within either single or double quotes. Roles can be space or comma separated.

The in operator allows for the querying of a specific session property to see if it exists in a defined set. An example of this would be to filter all sessions from a set of countries, say Germany, France, and the UK. The query would be $Country in 'UK','DE','FR'.

The lists provided to in and hasRoles can optionally use square brackets and commas as delimiters. For example $Country in ['UK','DE','FR'].

The $Roles session property can also be queried with an equality clause, for example, $Roles eq '"admin","client"', but the hasRoles clause is usually more convenient. An equality clause will match sessions that have exactly the listed roles. In contrast, a hasRoles clause will match any sessions with the listed roles, regardless of whether they have other roles. The equality clause requires the value to be in the canonical form produced by the RolesToString(IReadOnlyCollection<String>) utility method.

All operators are case insensitive.

The following are further examples of valid session filter expressions:

$Principal is "Alice"
Department is "Accounts" and $Country ne "US"
$Language EQ "en" and $Country NE "US"
not (Department is "Accounts" or Department is "Payroll") and $Country is "FR"
Text is "xyz\"\\"
hasRoles ["operator"]
$Transport is "wss" and hasRoles ["accountancy" "administrator"]
$Version in {"6","7","8"}
$Country in ['UK','DE','FR']
hasRoles ["operator"] and not hasRoles ["administrator"]
has Department
all

Session locks

The actions of multiple sessions can be coordinated using session locks. See ISessionLock.

Note

This interface does not require user implementation and is only used to hide implementation details.

Added in 5.0.

Examples

Opening a session to localhost using the WebSocket protocol on port 8080.

var session = Diffusion.Sessions.Open( "ws://localhost:8080" );

Properties

Attributes

Gets attributes of this session.

Declaration

ISessionAttributes Attributes { get; }

Property Value

Type	Description
ISessionAttributes	The attributes of this session.

Remarks

Added in 5.0.

Examples

Retrieving the session attributes.

// session is a previously obtained ISession instance.
var attributes = session.Attributes;

AuthenticationControl

Gets the authentication-control feature.

Declaration

IAuthenticationControl AuthenticationControl { get; }

Property Value

Type	Description
IAuthenticationControl	The authentication-control feature.

Remarks

Added in 5.0.

Examples

Retrieving the authentication-control feature.

// session is a previously obtained ISession instance.
var authenticationControl = session.AuthenticationControl;

ClientControl

Gets the client-control feature.

Declaration

IClientControl ClientControl { get; }

Property Value

Type	Description
IClientControl	The client-control feature.

Remarks

Added in 5.0.

Examples

Retrieving the client-control feature.

// session is a previously obtained ISession instance.
var clientControl = session.ClientControl;

Messaging

Gets the messaging feature.

Declaration

IMessaging Messaging { get; }

Property Value

Type	Description
IMessaging	The messaging feature.

Remarks

Added in 5.0.

Examples

Retrieving the messaging feature.

// session is a previously obtained ISession instance.
var messaging = session.Messaging;

Metrics

Gets the metrics feature.

Declaration

IMetrics Metrics { get; }

Property Value

Type	Description
IMetrics	The metrics feature.

Remarks

The Metrics feature allows a client to configure metric collectors.

Added in 6.7.

Examples

Retrieving the metrics feature.

// session is a previously obtained ISession instance.
var metrics = session.Metrics;

Ping

Gets the pings feature.

Declaration

IPings Ping { get; }

Property Value

Type	Description
IPings	The pings feature.

Remarks

Added in 5.0.

Examples

Retrieving the pings feature.

// session is a previously obtained ISession instance.
var pings = session.Ping;

Principal

Gets the name of the security principal associated with the session.

Declaration

string Principal { get; }

Property Value

Type	Description
String	The principal name.

Remarks

If the session was opened with no associated principal, (it is an "anonymous session"), an empty string will be returned.

Added in 5.0.

Examples

Retrieving the session principal.

// session is a previously obtained ISession instance.
var principal = session.Principal;

RemoteServers

Gets the remote servers feature.

Declaration

IRemoteServers RemoteServers { get; }

Property Value

Type	Description
IRemoteServers	The remote servers feature.

Remarks

The Remote Servers feature allows a client session to create, remove, list and check remote servers.

Added in 6.5.

Examples

Retrieving the remote servers feature.

// session is a previously obtained ISession instance.
var remoteServers = session.RemoteServers;

Security

Gets the security feature.

Declaration

ISecurity Security { get; }

Property Value

Type	Description
ISecurity	The security feature.

Remarks

Added in 5.0.

Examples

Retrieving the security feature.

// session is a previously obtained ISession instance.
var security = session.Security;

SecurityControl

Gets the security-control feature.

Declaration

ISecurityControl SecurityControl { get; }

Property Value

Type	Description
ISecurityControl	The security-control feature.

Remarks

Added in 5.3.

Examples

Retrieving the security-control feature.

// session is a previously obtained ISession instance.
var securityControl = session.SecurityControl;

SessionId

Gets the unique identifier of this session.

Declaration

ISessionId SessionId { get; }

Property Value

Type	Description
ISessionId	The session identifier.

Remarks

The session identifier will be assigned by the first server this session connected to.

Added in 5.0.

Examples

Retrieving the session identifier.

// session is a previously obtained ISession instance.
var sessionId = session.SessionId;

SessionTrees

Gets the session trees feature.

Declaration

ISessionTrees SessionTrees { get; }

Property Value

Type	Description
ISessionTrees	The session trees feature.

Remarks

The Session Trees feature allows the creation and alteration of branch mapping tables.

Added in 6.7.

Examples

Retrieving the session trees feature.

// session is a previously obtained ISession instance.
var sessionTrees = session.SessionTrees;

State

Gets the current state of this session.

Declaration

SessionState State { get; }

Property Value

Type	Description
SessionState	The current state of this session.

Remarks

Added in 5.0.

Examples

Retrieving the session state.

// session is a previously obtained ISession instance.
var state = session.State;

SubscriptionControl

Gets the subscription-control feature.

Declaration

ISubscriptionControl SubscriptionControl { get; }

Property Value

Type	Description
ISubscriptionControl	The subscription-control feature.

Remarks

Added in 5.0.

Examples

Retrieving the subscription-control feature.

// session is a previously obtained ISession instance.
var subscriptionControl = session.SubscriptionControl;

SystemAuthenticationControl

Gets the system-authentication-control feature.

Declaration

ISystemAuthenticationControl SystemAuthenticationControl { get; }

Property Value

Type	Description
ISystemAuthenticationControl	The system-authentication-control feature.

Remarks

Added in 5.2.

Examples

Retrieving the system-authentication-control feature.

// session is a previously obtained ISession instance.
var systemAuthenticationControl = session.SystemAuthenticationControl;

TimeSeries

Gets the time-series feature.

Declaration

ITimeSeries TimeSeries { get; }

Property Value

Type	Description
ITimeSeries	The time-series feature.

Remarks

Added in 6.1.

Examples

Retrieving the time-series feature.

// session is a previously obtained ISession instance.
var timeSeries = session.TimeSeries;

TopicControl

Gets the topic-control feature.

Declaration

ITopicControl TopicControl { get; }

Property Value

Type	Description
ITopicControl	The topic-control feature.

Remarks

Added in 5.0.

Examples

Retrieving the topic-control feature.

// session is a previously obtained ISession instance.
var topicControl = session.TopicControl;

TopicNotifications

Gets the topic-notifications feature.

Declaration

ITopicNotifications TopicNotifications { get; }

Property Value

Type	Description
ITopicNotifications	The topic-notifications feature.

Remarks

Added in 6.1.

Examples

Retrieving the topic-notifications feature.

// session is a previously obtained ISession instance.
var topicNotifications = session.TopicNotifications;

Topics

Gets the topics feature.

Declaration

ITopics Topics { get; }

Property Value

Type	Description
ITopics	The topics feature.

Remarks

Added in 5.0.

Examples

Retrieving the topics feature.

// session is a previously obtained ISession instance.
var topics = session.Topics;

TopicUpdate

Gets the topic-update feature.

Declaration

ITopicUpdate TopicUpdate { get; }

Property Value

Type	Description
ITopicUpdate	The topic-update feature.

Remarks

Added in 6.2.

Examples

Retrieving the topic-update feature.

// session is a previously obtained ISession instance.
var topicUpdate = session.TopicUpdate;

TopicViews

Gets the topic-views feature.

Declaration

ITopicViews TopicViews { get; }

Property Value

Type	Description
ITopicViews	The topic-views feature.

Remarks

Added in 6.3.

Examples

Retrieving the topic-views feature.

// session is a previously obtained ISession instance.
var topicViews = session.TopicViews;

Methods

Close()

Closes the session.

Declaration

void Close()

Remarks

Has no effect if the session is already closed.

Added in 5.0.

Examples

Closing an active session.

// session is a previously obtained ISession instance.
session.Close();

LockAsync(String)

Attempts to acquire a ISessionLock.

Declaration

Task<ISessionLock> LockAsync(string lockName)

Parameters

Type	Name	Description
String	lockName	The name of the session lock.

Returns

Type	Description
Task<ISessionLock>	The `Task` representing the current operation.

Remarks

If the operation completes successfully, the Task result will be the requested ISessionLock assigned to the calling session by the server. The session owns the returned lock and is responsible for unlocking it.

Acquiring the lock can take an arbitrarily long time if other sessions are competing for the lock. The server will retain the session's request for the lock until it is assigned to the session, the session is closed.

A session can call this method multiple times. If the lock is acquired, all calls will complete successfully with equal ISessionLock.

A session that acquires a lock will remain its owner until it is unlocked (via UnlockAsync()) or the session closes. The LockAsync(String, SessionLockScope) variant of this method takes a scope argument that provides the further option of releasing the lock when the session loses its connection to the server.

Access control

To allow fine-grained access control, lock names are interpreted as path names, controlled with the ACQUIRE_LOCK topic permission. This allows permission to be granted to a session to acquire the lock update-topic/a while preventing the session from acquiring the lock update-topic/b, for example.

This method is the same as calling LockAsync(String, CancellationToken) with System.Threading.CancellationToken.None.

Added in 6.2.

Examples

Acquiring a session lock.

try {
    // session is a previously obtained ISession instance.
    var sessionLock = await session.LockAsync( "lock name" );
    Console.WriteLine( $"Lock {sessionLock.Name} acquired." );
} catch ( SessionSecurityException ex ) {
    Console.WriteLine( $"Acquiring lock failed because of security reasons: {ex}" );
} catch ( SessionClosedException ex ) {
    Console.WriteLine( "Acquiring lock failed because the session is closed." );
}

Exceptions

Type	Condition
SessionSecurityException	The calling session does not have ACQUIRE_LOCK permission for `lockName`. Thrown by the returned `Task`.
SessionClosedException	The calling session is closed. Thrown by the returned `Task`.

LockAsync(String, CancellationToken)

Attempts to acquire a ISessionLock.

Declaration

Task<ISessionLock> LockAsync(string lockName, CancellationToken cancellationToken)

Parameters

Type	Name	Description
String	lockName	The name of the session lock.
CancellationToken	cancellationToken	The cancellation token used to cancel the current operation.

Returns

Type	Description
Task<ISessionLock>	The `Task` representing the current operation.

Remarks

A session can call this method multiple times. If the lock is acquired, all calls will complete successfully with equal ISessionLock.

Canceling the returned Task has no effect on other pending lock calls made by the session.

A session that acquires a lock will remain its owner until it is unlocked (via UnlockAsync(CancellationToken)) or the session closes. The LockAsync(String, SessionLockScope, CancellationToken) variant of this method takes a scope argument that provides the further option of releasing the lock when the session loses its connection to the server.

Access control

Added in 6.2.

Examples

Acquiring a session lock.

var cancellationTokenSource = new CancellationTokenSource();
var token = cancellationTokenSource.Token;

try {
    // session is a previously obtained ISession instance.
    var sessionLock = await session.LockAsync( "lock name", token );
    Console.WriteLine( $"Lock {sessionLock.Name} acquired." );
} catch ( SessionSecurityException ex ) {
    Console.WriteLine( $"Acquiring lock failed because of security reasons: {ex}" );
} catch ( SessionClosedException ex ) {
    Console.WriteLine( "Acquiring lock failed because the session is closed." );
}

Exceptions

Type	Condition
SessionSecurityException	The calling session does not have ACQUIRE_LOCK permission for `lockName`. Thrown by the returned `Task`.
SessionClosedException	The calling session is closed. Thrown by the returned `Task`.

LockAsync(String, SessionLockScope)

Attempts to acquire a ISessionLock with a given scope.

Declaration

Task<ISessionLock> LockAsync(string lockName, SessionLockScope scope)

Parameters

Type	Name	Description
String	lockName	The name of the session lock.
SessionLockScope	scope	The scope of the session lock.

Returns

Type	Description
Task<ISessionLock>	The `Task` representing the current operation.

Remarks

A session can call this method multiple times. If the lock is acquired, all calls will complete successfully with equal ISessionLock.

A session that acquires a lock will remain its owner until it is unlocked (via UnlockAsync()) or the session closes.

If called with a scope of UNLOCK_ON_SESSION_LOSS, this method behaves exactly like LockAsync(String).

If called with a scope of UNLOCK_ON_CONNECTION_LOSS, any lock that is returned will be unlocked if the session loses its connection to the server. This is useful to allow another session to take ownership of the lock while this session is reconnecting.

If a session makes multiple requests for a lock using different scopes, and the server assigns the lock to the session fulfilling the requests, the lock will be given the weakest scope (UNLOCK_ON_CONNECTION_LOSS).

Access control

This method is the same as calling LockAsync(String, SessionLockScope, CancellationToken) with System.Threading.CancellationToken.None.

Added in 6.2.

Examples

Acquiring a session lock.

var scope = SessionLockScope.UNLOCK_ON_CONNECTION_LOSS;

try {
    // session is a previously obtained ISession instance.
    var sessionLock = await session.LockAsync( "lock name", scope );
    Console.WriteLine( $"Lock {sessionLock.Name} acquired." );
} catch ( SessionSecurityException ex ) {
    Console.WriteLine( $"Acquiring lock failed because of security reasons: {ex}" );
} catch ( SessionClosedException ex ) {
    Console.WriteLine( "Acquiring lock failed because the session is closed." );
}

Exceptions

Type	Condition
SessionSecurityException	The calling session does not have ACQUIRE_LOCK permission for `lockName`. Thrown by the returned `Task`.
SessionClosedException	The calling session is closed. Thrown by the returned `Task`.

LockAsync(String, SessionLockScope, CancellationToken)

Attempts to acquire a ISessionLock with a given scope.

Declaration

Task<ISessionLock> LockAsync(string lockName, SessionLockScope scope, CancellationToken cancellationToken)

Parameters

Type	Name	Description
String	lockName	The name of the session lock.
SessionLockScope	scope	The scope of the session lock.
CancellationToken	cancellationToken	The cancellation token used to cancel the current operation.

Returns

Type	Description
Task<ISessionLock>	The `Task` representing the current operation.

Remarks

A session can call this method multiple times. If the lock is acquired, all calls will complete successfully with equal ISessionLock.

Canceling the returned Task has no effect on other pending lock calls made by the session.

A session that acquires a lock will remain its owner until it is unlocked (by calling UnlockAsync(CancellationToken)) or the session closes.

If called with a scope of UNLOCK_ON_SESSION_LOSS, this method behaves exactly like LockAsync(String).

Access control

Added in 6.2.

Examples

Acquiring a session lock.

var cancellationTokenSource = new CancellationTokenSource();
var token = cancellationTokenSource.Token;
var scope = SessionLockScope.UNLOCK_ON_CONNECTION_LOSS;

try {
    // session is a previously obtained ISession instance.
    var sessionLock = await session.LockAsync( "lock name", scope, token );
    Console.WriteLine( $"Lock {sessionLock.Name} acquired." );
} catch ( SessionSecurityException ex ) {
    Console.WriteLine( $"Acquiring lock failed because of security reasons: {ex}" );
} catch ( SessionClosedException ex ) {
    Console.WriteLine( "Acquiring lock failed because the session is closed." );
}

Exceptions

Type	Condition
SessionSecurityException	The calling session does not have ACQUIRE_LOCK permission for `lockName`. Thrown by the returned `Task`.
SessionClosedException	The calling session is closed. Thrown by the returned `Task`.

Events

ErrorNotified

The event for session errors.

Declaration

event EventHandler<SessionErrorHandlerEventArgs> ErrorNotified

Event Type

Type	Description
EventHandler<SessionErrorHandlerEventArgs>	The event for session errors.

Remarks

Added in 5.0.

Examples

Subscribe to the event.

// session is a previously obtained ISession instance.
session.ErrorNotified += ( sender, e ) => {
    Console.WriteLine( $"Session Error: {e.Error}." );
};

StateChanged

The event for session state changes.

Declaration

event EventHandler<SessionListenerEventArgs> StateChanged

Event Type

Type	Description
EventHandler<SessionListenerEventArgs>	The event for session state changes.

Remarks

Added in 5.0.

Examples

Subscribe to the event.

// session is a previously obtained ISession instance.
session.StateChanged += ( sender, e ) => {
    Console.WriteLine( $"{e.Session.SessionId} state changed from {e.OldState} to {e.NewState}." );
};