Work in progress! This part will be a new chapter later.

In PubSub the participating OPC UA Applications take their roles as Publishers and Subscribers. Publishers are the sources of data, while Subscribers consume that data. Communication in PubSub is message-based. Publishers send messages to a Message Oriented Middleware, without knowledge of what, if any, Subscribers there may be. Similarly, Subscribers express interest in specific types of data, and process messages that contain this data, without knowledge of what Publishers there are.

Message Oriented Middleware is software or hardware infrastructure that supports sending and receiving messages between distributed systems. OPC UA PubSub supports two different Message Oriented Middleware variants, namely the broker-less form and broker-based form. A broker-less form is where the Message Oriented Middleware is the network infrastructure that is able to route datagram-based messages. Subscribers and Publishers use datagram protocols like UDP. In a broker-based form, the core component of the Message Oriented Middleware is a message Broker. Subscribers and Publishers use standard messaging protocols like AMQP or MQTT to communicate with the Broker.

This makes PubSub suitable for applications where location independence and/or scalability are required.

The Publish/Subscribe (PubSub) extension for OPC UA enables fast and efficient 1:m communication. The PubSub extension is protocol agnostic and can be used with broker based protocols like MQTT and AMQP or brokerless implementations like UDP-Multicasting.

The PubSub API uses the following scheme:

  1. Create a configuration for the needed PubSub element.

  2. Call the add[element] function and pass in the configuration.

  3. The add[element] function returns the unique nodeId of the internally created element.

Take a look on the PubSub Tutorials for more details about the API usage.:

| UA_Server |
 |    |
 |    |
 |    |
 |    |  +----------------------+
 |    +--> UA_PubSubConnection  |  UA_Server_addPubSubConnection
 |       +----------------------+
 |        |    |
 |        |    |    +----------------+
 |        |    +----> UA_WriterGroup |  UA_PubSubConnection_addWriterGroup
 |        |         +----------------+
 |        |              |
 |        |              |    +------------------+
 |        |              +----> UA_DataSetWriter |  UA_WriterGroup_addDataSetWriter     +-+
 |        |                   +------------------+                                        |
 |        |                                                                               |
 |        |         +----------------+                                                    | r
 |        +---------> UA_ReaderGroup |    UA_PubSubConnection_addReaderGroup              | e
 |                  +----------------+                                                    | f
 |                       |                                                                |
 |                       |    +------------------+                                        |
 |                       +----> UA_DataSetReader |  UA_ReaderGroup_addDataSetReader       |
 |                            +------------------+                                        |
 |                                 |                                                      |
 |                                 |    +----------------------+                          |
 |                                 +----> UA_SubscribedDataSet |                          |
 |                                      +----------------------+                          |
 |                                           |                                            |
 |                                           |    +----------------------------+          |
 |                                           +----> UA_TargetVariablesDataType |          |
 |                                           |    +----------------------------+          |
 |                                           |                                            |
 |                                           |    +------------------------------------+  |
 |                                           +----> UA_SubscribedDataSetMirrorDataType |  |
 |                                                +------------------------------------+  |
 |                                                                                        |
 |       +---------------------------+                                                    |
 +-------> UA_PubSubPublishedDataSet |  UA_Server_addPublishedDataSet                   <-+
               |    +-----------------+
               +----> UA_DataSetField |  UA_PublishedDataSet_addDataSetField

PubSub compile flags


Enable the experimental OPC UA PubSub support. The option will include the PubSub UDP multicast plugin. Disabled by default.


The PubSub messages differentiate between keyframe (all published values contained) and deltaframe (only changed values contained) messages. Deltaframe messages creation consumes some additional ressources and can be disabled with this flag. Disabled by default. Compile the human-readable name of the StatusCodes into the binary. Disabled by default.


Enable loading OPC UA PubSub configuration from File/ByteString. Enabling PubSub informationmodel methods also will add a method to the Publish/Subscribe object which allows configuring PubSub at runtime.


Enable the information model representation of the PubSub configuration. For more details take a look at the following section PubSub Information Model Representation. Disabled by default.


Enable the experimental PubSub monitoring. This feature provides a basic framework to implement monitoring/timeout checks for PubSub components. Initially the MessageReceiveTimeout check of a DataSetReader is provided. It uses the internal server callback implementation. The monitoring backend can be changed by the application to satisfy realtime requirements. Disabled by default.


Enable the OPC UA Ethernet PubSub support to transport UADP NetworkMessages as payload of Ethernet II frame without IP or UDP headers. This option will include Publish and Subscribe based on EtherType B62C. Disabled by default.


Enable ETF feature to allow the user to transmit packets at calculated transmission time with nanosecond precision, in addition to the PubSub support to transport UADP NetworkMessages as payload of Ethernet II frame. Disabled by default.


Enable XDP feature to allow the user to receive packets using the eXpress Data Path (XDP), which bypasses TCP/IP layers and transfers the frames from hardware/netdev to user application thereby reducing the receiving time, in addition to the PubSub support to transport UADP NetworkMessages as payload of Ethernet II frame. Disabled by default.

PubSub Information Model Representation

The complete PubSub configuration is available inside the information model. The entry point is the node ‘PublishSubscribe, located under the Server node. The standard defines for PubSub no new Service set. The configuration can optionally done over methods inside the information model. The information model representation of the current PubSub configuration is generated automatically. This feature can enabled/disable by changing the UA_ENABLE_PUBSUB_INFORMATIONMODEL option.


The PubSub connections are the abstraction between the concrete transport protocol and the PubSub functionality. It is possible to create multiple connections with different transport protocols at runtime.

Take a look on the PubSub Tutorials for mor details about the API usage.

typedef enum  {
} UA_PubSubComponentEnumType;

typedef enum {
} UA_PublisherIdType;

typedef struct {
    UA_Int32 socketPriority;
    UA_Boolean sotxtimeEnabled;
    /* SO_TXTIME-specific additional socket config */
    UA_Int32 sotxtimeDeadlinemode;
    UA_Int32 sotxtimeReceiveerrors;
} UA_ETFConfiguration;

struct UA_PubSubConnectionConfig {
    UA_String name;
    UA_Boolean enabled;
    UA_PublisherIdType publisherIdType;
    union { /* std: valid types UInt or String */
        UA_UInt32 numeric;
        UA_String string;
    } publisherId;
    UA_String transportProfileUri;
    UA_Variant address;
    size_t connectionPropertiesSize;
    UA_KeyValuePair *connectionProperties;
    UA_Variant connectionTransportSettings;
    /* ETF related connection configuration - Not in PubSub specfication */
    UA_ETFConfiguration etfConfiguration;


typedef enum {
    // extend as needed
} UA_PubSubMonitoringType;

/* PubSub monitoring interface */
typedef struct {
    UA_StatusCode (*createMonitoring)(UA_Server *server, UA_NodeId Id, UA_PubSubComponentEnumType eComponentType,
                                      UA_PubSubMonitoringType eMonitoringType, void *data, UA_ServerCallback callback);
    UA_StatusCode (*startMonitoring)(UA_Server *server, UA_NodeId Id, UA_PubSubComponentEnumType eComponentType,
                                     UA_PubSubMonitoringType eMonitoringType, void *data);
    UA_StatusCode (*stopMonitoring)(UA_Server *server, UA_NodeId Id, UA_PubSubComponentEnumType eComponentType,
                                    UA_PubSubMonitoringType eMonitoringType, void *data);
    UA_StatusCode (*updateMonitoringInterval)(UA_Server *server, UA_NodeId Id, UA_PubSubComponentEnumType eComponentType,
                                              UA_PubSubMonitoringType eMonitoringType, void *data);
    UA_StatusCode (*deleteMonitoring)(UA_Server *server, UA_NodeId Id, UA_PubSubComponentEnumType eComponentType,
                                      UA_PubSubMonitoringType eMonitoringType, void *data);
} UA_PubSubMonitoringInterface;


/* General PubSub configuration */
struct UA_PubSubConfiguration {

    /* Callback for PubSub component state changes:
    If provided this callback informs the application about PubSub component state changes.
    E.g. state change from operational to error in case of a DataSetReader MessageReceiveTimeout.
    The status code provides additional information. */
    void (*pubsubStateChangeCallback)(UA_NodeId *Id,
                                      UA_PubSubState state,
                                      UA_StatusCode status);// TODO: maybe status code provides not enough information about the state change
    UA_PubSubMonitoringInterface monitoringInterface;

The UA_ServerConfig_addPubSubTransportLayer is used to add a transport layer to the server configuration. The list memory is allocated and will be freed with UA_PubSubManager_delete.


If the UA_String transportProfileUri was dynamically allocated the memory has to be freed when no longer required.


This has to be done before the server is started with UA_Server_run.

UA_ServerConfig_addPubSubTransportLayer(UA_ServerConfig *config,
                                        UA_PubSubTransportLayer *pubsubTransportLayer);

UA_Server_addPubSubConnection(UA_Server *server,
                              const UA_PubSubConnectionConfig *connectionConfig,
                              UA_NodeId *connectionIdentifier);

/* Returns a deep copy of the config */
UA_Server_getPubSubConnectionConfig(UA_Server *server,
                                    const UA_NodeId connection,
                                    UA_PubSubConnectionConfig *config);

/* Remove Connection, identified by the NodeId. Deletion of Connection
 * removes all contained WriterGroups and Writers. */
UA_Server_removePubSubConnection(UA_Server *server, const UA_NodeId connection);


The PublishedDataSets (PDS) are containers for the published information. The PDS contain the published variables and meta informations. The metadata is commonly autogenerated or given as constant argument as part of the template functions. The template functions are standard defined and intended for configuration tools. You should normally create a empty PDS and call the functions to add new fields.

/* The UA_PUBSUB_DATASET_PUBLISHEDITEMS has currently no additional members and
 * thus no dedicated config structure. */

typedef enum {
} UA_PublishedDataSetType;

typedef struct {
    UA_DataSetMetaDataType metaData;
    size_t variablesToAddSize;
    UA_PublishedVariableDataType *variablesToAdd;
} UA_PublishedDataItemsTemplateConfig;

typedef struct {
    UA_NodeId eventNotfier;
    UA_ContentFilter filter;
} UA_PublishedEventConfig;

typedef struct {
    UA_DataSetMetaDataType metaData;
    UA_NodeId eventNotfier;
    size_t selectedFieldsSize;
    UA_SimpleAttributeOperand *selectedFields;
    UA_ContentFilter filter;
} UA_PublishedEventTemplateConfig;

/* Configuration structure for PublishedDataSet */
typedef struct {
    UA_String name;
    UA_PublishedDataSetType publishedDataSetType;
    union {
        /* The UA_PUBSUB_DATASET_PUBLISHEDITEMS has currently no additional members
         * and thus no dedicated config structure.*/
        UA_PublishedDataItemsTemplateConfig itemsTemplate;
        UA_PublishedEventConfig event;
        UA_PublishedEventTemplateConfig eventTemplate;
    } config;
} UA_PublishedDataSetConfig;

UA_PublishedDataSetConfig_clear(UA_PublishedDataSetConfig *pdsConfig);

typedef struct {
    UA_StatusCode addResult;
    size_t fieldAddResultsSize;
    UA_StatusCode *fieldAddResults;
    UA_ConfigurationVersionDataType configurationVersion;
} UA_AddPublishedDataSetResult;

UA_Server_addPublishedDataSet(UA_Server *server,
                              const UA_PublishedDataSetConfig *publishedDataSetConfig,
                              UA_NodeId *pdsIdentifier);

/* Returns a deep copy of the config */
UA_Server_getPublishedDataSetConfig(UA_Server *server, const UA_NodeId pds,
                                    UA_PublishedDataSetConfig *config);

/* Returns a deep copy of the DataSetMetaData for an specific PDS */
UA_Server_getPublishedDataSetMetaData(UA_Server *server, const UA_NodeId pds,
                                      UA_DataSetMetaDataType *metaData);

/* Remove PublishedDataSet, identified by the NodeId. Deletion of PDS removes
 * all contained and linked PDS Fields. Connected WriterGroups will be also
 * removed. */
UA_Server_removePublishedDataSet(UA_Server *server, const UA_NodeId pds);


The description of published variables is named DataSetField. Each DataSetField contains the selection of one information model node. The DataSetField has additional parameters for the publishing, sampling and error handling process.

typedef struct{
    UA_ConfigurationVersionDataType configurationVersion;
    UA_String fieldNameAlias;
    UA_Boolean promotedField;
    UA_PublishedVariableDataType publishParameters;

    /* non std. field */
    struct {
        UA_Boolean rtFieldSourceEnabled;
        /* If the rtInformationModelNode is set, the nodeid in publishParameter must point
         * to a node with external data source backend defined
         * */
        UA_Boolean rtInformationModelNode;
        //TODO -> decide if suppress C++ warnings and use 'UA_DataValue * * const staticValueSource;'
        UA_DataValue ** staticValueSource;
    } rtValueSource;

} UA_DataSetVariableConfig;

typedef enum {
} UA_DataSetFieldType;

typedef struct {
    UA_DataSetFieldType dataSetFieldType;
    union {
        /* events need other config later */
        UA_DataSetVariableConfig variable;
    } field;
} UA_DataSetFieldConfig;

UA_DataSetFieldConfig_clear(UA_DataSetFieldConfig *dataSetFieldConfig);

typedef struct {
    UA_StatusCode result;
    UA_ConfigurationVersionDataType configurationVersion;
} UA_DataSetFieldResult;

UA_Server_addDataSetField(UA_Server *server,
                          const UA_NodeId publishedDataSet,
                          const UA_DataSetFieldConfig *fieldConfig,
                          UA_NodeId *fieldIdentifier);

/* Returns a deep copy of the config */
UA_Server_getDataSetFieldConfig(UA_Server *server, const UA_NodeId dsf,
                                UA_DataSetFieldConfig *config);

UA_Server_removeDataSetField(UA_Server *server, const UA_NodeId dsf);

Custom Callback Implementation

The user can use his own callback implementation for publishing and subscribing. The user must take care of the callback to call for every publishing or subscibing interval

typedef struct {
    UA_StatusCode (*addCustomCallback)(UA_Server *server, UA_NodeId identifier,
                                       UA_ServerCallback callback,
                                       void *data, UA_Double interval_ms, UA_UInt64 *callbackId);

    UA_StatusCode (*changeCustomCallbackInterval)(UA_Server *server, UA_NodeId identifier,
                                                  UA_UInt64 callbackId, UA_Double interval_ms);

    void (*removeCustomCallback)(UA_Server *server, UA_NodeId identifier, UA_UInt64 callbackId);

} UA_PubSub_CallbackLifecycle;


All WriterGroups are created within a PubSubConnection and automatically deleted if the connection is removed. The WriterGroup is primary used as container for DataSetWriter and network message settings. The WriterGroup can be imagined as producer of the network messages. The creation of network messages is controlled by parameters like the publish interval, which is e.g. contained in the WriterGroup.

typedef enum {
} UA_PubSubEncodingType;


The message publishing can be configured for realtime requirements. The RT-levels go along with different requirements. The below listed levels can be configured:

UA_PUBSUB_RT_NONE - —> Description: Default “none-RT” Mode —> Requirements: - —> Restrictions: - UA_PUBSUB_RT_DIRECT_VALUE_ACCESS (Preview - not implemented) —> Description: Normally, the latest value for each DataSetField is read out of the information model. Within this RT-mode, the value source of each field configured as static pointer to an DataValue. The publish cycle won’t use call the server read function. —> Requirements: All fields must be configured with a ‘staticValueSource’. —> Restrictions: - UA_PUBSUB_RT_FIXED_LENGTH (Preview - not implemented) —> Description: All DataSetFields have a known, non-changing length. The server will pre-generate some buffers and use only memcopy operations to generate requested PubSub packages. —> Requirements: DataSetFields with variable size can’t be used within this mode. —> Restrictions: The configuration must be frozen and changes are not allowed while the WriterGroup is ‘Operational’. UA_PUBSUB_RT_DETERMINISTIC (Preview - not implemented) —> Description: - —> Requirements: - —> Restrictions: -

WARNING! For hard real time requirements the underlying system must be rt-capable.

typedef enum {
} UA_PubSubRTLevel;

typedef struct {
    UA_String name;
    UA_Boolean enabled;
    UA_UInt16 writerGroupId;
    UA_Duration publishingInterval;
    UA_Double keepAliveTime;
    UA_Byte priority;
    UA_MessageSecurityMode securityMode;
    UA_ExtensionObject transportSettings;
    UA_ExtensionObject messageSettings;
    size_t groupPropertiesSize;
    UA_KeyValuePair *groupProperties;
    UA_PubSubEncodingType encodingMimeType;
    /* PubSub Manager Callback */
    UA_PubSub_CallbackLifecycle pubsubManagerCallback;
    /* non std. config parameter. maximum count of embedded DataSetMessage in
     * one NetworkMessage */
    UA_UInt16 maxEncapsulatedDataSetMessageCount;
    /* non std. field */
    UA_PubSubRTLevel rtLevel;
} UA_WriterGroupConfig;

UA_WriterGroupConfig_clear(UA_WriterGroupConfig *writerGroupConfig);

/* Add a new WriterGroup to an existing Connection */
UA_Server_addWriterGroup(UA_Server *server, const UA_NodeId connection,
                         const UA_WriterGroupConfig *writerGroupConfig,
                         UA_NodeId *writerGroupIdentifier);

/* Returns a deep copy of the config */
UA_Server_getWriterGroupConfig(UA_Server *server, const UA_NodeId writerGroup,
                               UA_WriterGroupConfig *config);

UA_Server_updateWriterGroupConfig(UA_Server *server, UA_NodeId writerGroupIdentifier,
                                  const UA_WriterGroupConfig *config);

/* Get state of WriterGroup */
UA_Server_WriterGroup_getState(UA_Server *server, UA_NodeId writerGroupIdentifier,
                               UA_PubSubState *state);

UA_Server_removeWriterGroup(UA_Server *server, const UA_NodeId writerGroup);

UA_Server_freezeWriterGroupConfiguration(UA_Server *server, const UA_NodeId writerGroup);

UA_Server_unfreezeWriterGroupConfiguration(UA_Server *server, const UA_NodeId writerGroup);

UA_Server_setWriterGroupOperational(UA_Server *server, const UA_NodeId writerGroup);

UA_Server_setWriterGroupDisabled(UA_Server *server, const UA_NodeId writerGroup);


The DataSetWriters are the glue between the WriterGroups and the PublishedDataSets. The DataSetWriter contain configuration parameters and flags which influence the creation of DataSet messages. These messages are encapsulated inside the network message. The DataSetWriter must be linked with an existing PublishedDataSet and be contained within a WriterGroup.

typedef struct {
    UA_String name;
    UA_UInt16 dataSetWriterId;
    UA_DataSetFieldContentMask dataSetFieldContentMask;
    UA_UInt32 keyFrameCount;
    UA_ExtensionObject messageSettings;
    UA_ExtensionObject transportSettings;
    UA_String dataSetName;
    size_t dataSetWriterPropertiesSize;
    UA_KeyValuePair *dataSetWriterProperties;
} UA_DataSetWriterConfig;

UA_DataSetWriterConfig_clear(UA_DataSetWriterConfig *pdsConfig);

/* Add a new DataSetWriter to a existing WriterGroup. The DataSetWriter must be
 * coupled with a PublishedDataSet on creation.
 * Part 14, defines: The link between the PublishedDataSet and
 * DataSetWriter shall be created when an instance of the DataSetWriterType is
 * created. */
UA_Server_addDataSetWriter(UA_Server *server,
                           const UA_NodeId writerGroup, const UA_NodeId dataSet,
                           const UA_DataSetWriterConfig *dataSetWriterConfig,
                           UA_NodeId *writerIdentifier);

/* Returns a deep copy of the config */
UA_Server_getDataSetWriterConfig(UA_Server *server, const UA_NodeId dsw,
                                 UA_DataSetWriterConfig *config);

/* Get state of DataSetWriter */
UA_Server_DataSetWriter_getState(UA_Server *server, UA_NodeId dataSetWriterIdentifier,
                               UA_PubSubState *state);

UA_Server_removeDataSetWriter(UA_Server *server, const UA_NodeId dsw);


SubscribedDataSet describes the processing of the received DataSet. SubscribedDataSet defines which field in the DataSet is mapped to which Variable in the OPC UA Application. SubscribedDataSet has two sub-types called the TargetVariablesType and SubscribedDataSetMirrorType. SubscribedDataSetMirrorType is currently not supported. SubscribedDataSet is set to TargetVariablesType and then the list of target Variables are created in the Subscriber AddressSpace. TargetVariables are a list of variables that are to be added in the Subscriber AddressSpace. It defines a list of Variable mappings between received DataSet fields and added Variables in the Subscriber AddressSpace.

/* SubscribedDataSetDataType Definition */
typedef enum {
} UA_SubscribedDataSetEnumType;

typedef struct {
    /* Standard-defined FieldTargetDataType */
    UA_FieldTargetDataType targetVariable;

    /* If realtime-handling is required, set this pointer non-NULL and it will be used
     * to memcpy the value instead of using the Write service.
     * If the afterWrite method pointer is set, it will be called after a memcpy update
     * to the value. */
    UA_DataValue **externalDataValue;
    void *targetVariableContext; /* user-defined pointer */
    void (*afterWrite)(UA_Server *server,
                       const UA_NodeId *readerIdentifier,
                       const UA_NodeId *readerGroupIdentifier,
                       const UA_NodeId *targetVariableIdentifier,
                       void *targetVariableContext,
                       UA_DataValue **externalDataValue);
} UA_FieldTargetVariable;

typedef struct {
    size_t targetVariablesSize;
    UA_FieldTargetVariable *targetVariables;
} UA_TargetVariables;

/* Return Status Code after creating TargetVariables in Subscriber AddressSpace */
UA_Server_DataSetReader_createTargetVariables(UA_Server *server,
                                              UA_NodeId dataSetReaderIdentifier,
                                              size_t targetVariablesSize,
                                              const UA_FieldTargetVariable *targetVariables);

/* To Do:Implementation of SubscribedDataSetMirrorType
 * UA_StatusCode
 * A_PubSubDataSetReader_createDataSetMirror(UA_Server *server, UA_NodeId dataSetReaderIdentifier,
 * UA_SubscribedDataSetMirrorDataType* mirror) */


DataSetReader can receive NetworkMessages with the DataSetMessage of interest sent by the Publisher. DataSetReaders represent the configuration necessary to receive and process DataSetMessages on the Subscriber side. DataSetReader must be linked with a SubscribedDataSet and be contained within a ReaderGroup.

/* Parameters for PubSubSecurity */
typedef struct {
    UA_Int32 securityMode;          /* placeholder datatype 'MessageSecurityMode' */
    UA_String securityGroupId;
    size_t keyServersSize;
    UA_Int32 *keyServers;
} UA_PubSubSecurityParameters;

/* Parameters for PubSub DataSetReader Configuration */
typedef struct {
    UA_String name;
    UA_Variant publisherId;
    UA_UInt16 writerGroupId;
    UA_UInt16 dataSetWriterId;
    UA_DataSetMetaDataType dataSetMetaData;
    UA_DataSetFieldContentMask dataSetFieldContentMask;
    UA_Double messageReceiveTimeout;
    UA_PubSubSecurityParameters securityParameters;
    UA_ExtensionObject messageSettings;
    UA_ExtensionObject transportSettings;
    UA_SubscribedDataSetEnumType subscribedDataSetType;
    /* TODO UA_SubscribedDataSetMirrorDataType subscribedDataSetMirror */
    union {
        UA_TargetVariables subscribedDataSetTarget;
        // UA_SubscribedDataSetMirrorDataType subscribedDataSetMirror;
    } subscribedDataSet;
} UA_DataSetReaderConfig;

/* Update configuration to the dataSetReader */
UA_Server_DataSetReader_updateConfig(UA_Server *server, UA_NodeId dataSetReaderIdentifier,
                                     UA_NodeId readerGroupIdentifier,
                                     const UA_DataSetReaderConfig *config);

/* Get configuration of the dataSetReader */
UA_Server_DataSetReader_getConfig(UA_Server *server, UA_NodeId dataSetReaderIdentifier,
                                  UA_DataSetReaderConfig *config);

/* Get state of DataSetReader */
UA_Server_DataSetReader_getState(UA_Server *server, UA_NodeId dataSetReaderIdentifier,
                               UA_PubSubState *state);


ReaderGroup is used to group a list of DataSetReaders. All ReaderGroups are created within a PubSubConnection and automatically deleted if the connection is removed. All network message related filters are only available in the DataSetReader.

The RT-levels go along with different requirements. The below listed levels can be configured for a ReaderGroup. UA_PUBSUB_RT_NONE –> No RT applied to this level PUBSUB_CONFIG_FASTPATH_FIXED_OFFSETS –> Extends PubSub RT functionality and implements fast path message decoding in the Subscriber. Uses a buffered network message and only decodes the necessary offsets stored in an offset buffer.

/* ReaderGroup configuration */
typedef struct {
    UA_String name;
    UA_PubSubSecurityParameters securityParameters;
    /* PubSub Manager Callback */
    UA_PubSub_CallbackLifecycle pubsubManagerCallback;
    /* non std. field */
    UA_PubSubRTLevel rtLevel;
} UA_ReaderGroupConfig;

/* Add DataSetReader to the ReaderGroup */
UA_Server_addDataSetReader(UA_Server *server, UA_NodeId readerGroupIdentifier,
                                      const UA_DataSetReaderConfig *dataSetReaderConfig,
                                      UA_NodeId *readerIdentifier);

/* Remove DataSetReader from ReaderGroup */
UA_Server_removeDataSetReader(UA_Server *server, UA_NodeId readerIdentifier);

/* To Do: Update Configuration of ReaderGroup
 * UA_StatusCode
 * UA_Server_ReaderGroup_updateConfig(UA_Server *server, UA_NodeId readerGroupIdentifier,
 *                                    const UA_ReaderGroupConfig *config);

/* Get configuraiton of ReaderGroup */
UA_Server_ReaderGroup_getConfig(UA_Server *server, UA_NodeId readerGroupIdentifier,
                               UA_ReaderGroupConfig *config);

/* Get state of ReaderGroup */
UA_Server_ReaderGroup_getState(UA_Server *server, UA_NodeId readerGroupIdentifier,
                               UA_PubSubState *state);

/* Add ReaderGroup to the created connection */
UA_Server_addReaderGroup(UA_Server *server, UA_NodeId connectionIdentifier,
                                   const UA_ReaderGroupConfig *readerGroupConfig,
                                   UA_NodeId *readerGroupIdentifier);

/* Remove ReaderGroup from connection */
UA_Server_removeReaderGroup(UA_Server *server, UA_NodeId groupIdentifier);

UA_Server_freezeReaderGroupConfiguration(UA_Server *server, const UA_NodeId readerGroupId);

UA_Server_unfreezeReaderGroupConfiguration(UA_Server *server, const UA_NodeId readerGroupId);

UA_Server_setReaderGroupOperational(UA_Server *server, const UA_NodeId readerGroupId);

UA_Server_setReaderGroupDisabled(UA_Server *server, const UA_NodeId readerGroupId);

#endif /* UA_ENABLE_PUBSUB */