Data Types

This page summarizes the Lua representations used by the OPC UA stack. Values are ordinary Lua values unless a table structure is shown.

Built-in Types

OPC UA type	Lua representation	Notes
`SByte`	number	Signed 8-bit integer.
`Byte`	number	Unsigned 8-bit integer.
`Int16`	number	Signed 16-bit integer.
`UInt16`	number	Unsigned 16-bit integer.
`Int32`	number	Signed 32-bit integer.
`UInt32`	number	Unsigned 32-bit integer.
`Int64`	number	Signed 64-bit integer.
`UInt64`	number	Unsigned 64-bit integer.
`Float`	number	32-bit floating-point value.
`Double`	number	64-bit floating-point value.
`DateTime`	number	Unix timestamp in seconds, usually from `compat.gettime()` or `os.time()`. Encoders convert this to the OPC UA wire format.
`String`	string	UTF-8 string.
`ByteString`	string	Binary byte sequence stored in a Lua string.
`Guid`	string	GUID string, for example `12345678-1234-1234-1234-123456789012`.
`StatusCode`	number	OPC UA status code, for example `ua.StatusCode.Good`.

LocalizedText

Localized text is represented as a table.

Field	Type	Description
`Locale`	string, optional	Locale name such as `"en-US"`. If omitted, the default locale is used.
`Text`	string	Localized text content.

local text = {Locale = "en-US", Text = "This is localized text"}
local textDefaultLocale = {Text = "This is localized text"}

QualifiedName

A QualifiedName is the service identifier of a node. It combines a namespace index with a name.

Field	Type	Description
`ns`	number	Namespace index.
`Name`	string	Name within the namespace.

local qualifiedName = {ns = 1, Name = "Node Name"}

NodeId

A NodeId is encoded as a string:

[ns=<namespace_index>;]<type>=<value>

Part	Value	Description
`namespace_index`	unsigned 16-bit integer	Optional. Omit when the namespace index is `0`.
`type`	`i`, `s`, `g`, or `b`	Identifier type: integer, string, GUID, or opaque byte string.
`value`	type-specific string	Decimal integer, UTF-8 string, lowercase GUID, or base64 byte string.

Type code	Identifier type	Example
`i`	Integer	`i=85` or `ns=2;i=1001`
`s`	String	`ns=2;s=Temperature`
`g`	GUID	`ns=2;g=12345678-1234-1234-1234-123456789012`
`b`	Opaque byte string	`ns=2;b=AQIDBA==`

Additional examples are available in node_id.lua. The official syntax is described in the OPC Foundation NodeId reference.

NodeId helpers

Function	Parameters	Return value
`toString(id, ns)`	`id` is a number, string, GUID, byte array, or bytes. `ns` is a namespace index or `nil`.	Encoded NodeId string.
`toString({id = value, ns = number})`	Table form of the same parameters.	Encoded NodeId string.
`fromString(string)`	Encoded NodeId string.	Table with `ns` and `id` fields.

Variant

A Variant wraps a value with an OPC UA type. It can represent a scalar or an array.

Field	Type	Description
`Type`	`ua.VariantType`	Type of the stored value.
`Value`	any supported Lua value	Value to encode.
`IsArray`	boolean, optional	Set to `true` when `Value` is an array.
`ArrayDimensions`	number array, optional	Dimensions for array values.

local uint32 = {Type = ua.VariantType.UInt32, Value = 0}
local uint32Array = {
  Type = ua.VariantType.UInt32,
  Value = {1, 2, 3, 4},
  IsArray = true,
  ArrayDimensions = {4}
}

VariantType constants

Name	Value	Name	Value
`Null`	0	`Boolean`	1
`SByte`	2	`Byte`	3
`Int16`	4	`UInt16`	5
`Int32`	6	`UInt32`	7
`Int64`	8	`UInt64`	9
`Float`	10	`Double`	11
`String`	12	`DateTime`	13
`Guid`	14	`ByteString`	15
`XmlElement`	16	`NodeId`	17
`ExpandedNodeId`	18	`StatusCode`	19
`QualifiedName`	20	`LocalizedText`	21
`ExtensionObject`	22	`DataValue`	23
`Variant`	24	`DiagnosticInfo`	25

DataValue

A DataValue is a Variant value plus optional status and timestamp fields.

Field	Type	Description
`Type`	`ua.VariantType`	Type of `Value`.
`Value`	any supported Lua value	Value to encode.
`StatusCode`	status code, optional	Value status, for example `ua.StatusCode.Good`.
`SourceTimestamp`	DateTime, optional	Source timestamp.
`ServerTimestamp`	DateTime, optional	Server timestamp.
`SourcePicoseconds`	UInt16, optional	Fractional source timestamp precision.
`ServerPicoseconds`	UInt16, optional	Fractional server timestamp precision.

local dataValue = {
  Type = ua.VariantType.UInt32,
  Value = 100,
  StatusCode = ua.StatusCode.Good,
  SourceTimestamp = os.time()
}

TimestampsToReturn

ua.TimestampsToReturn selects which timestamps the Server includes in returned DataValues.

Constant	Value	Description
`ua.TimestampsToReturn.Source`	0	Return the source timestamp only.
`ua.TimestampsToReturn.Server`	1	Return the server timestamp only.
`ua.TimestampsToReturn.Both`	2	Return both source and server timestamps.
`ua.TimestampsToReturn.Neither`	3	Do not return source or server timestamps.

MonitoringMode

ua.MonitoringMode controls whether a MonitoredItem samples and reports values.

Constant	Value	Description
`ua.MonitoringMode.Disabled`	0	Do not sample or report values.
`ua.MonitoringMode.Sampling`	1	Sample and queue values without reporting them.
`ua.MonitoringMode.Reporting`	2	Sample, queue, and report values through Publish responses.

DataChangeTrigger

ua.DataChangeTrigger selects which DataValue changes create notifications.

Constant	Value	Description
`ua.DataChangeTrigger.Status`	0	Report changes to the StatusCode.
`ua.DataChangeTrigger.StatusValue`	1	Report changes to the StatusCode or value.
`ua.DataChangeTrigger.StatusValueTimestamp`	2	Report changes to the StatusCode, value, or source timestamp.

DeadbandType

ua.DeadbandType selects how a DataChangeFilter suppresses small value changes.

Constant	Value	Description
`ua.DeadbandType.None`	0	Do not apply a deadband.
`ua.DeadbandType.Absolute`	1	Require an absolute difference greater than `DeadbandValue`.
`ua.DeadbandType.Percent`	2	Require a percentage difference based on the Variable’s engineering range. The compact Server does not support this mode.

ExtensionObject

An ExtensionObject represents a structured value. It is also used when a field can contain one of several structure types, such as node attributes for AddNodes.

Field	Type	Description
`TypeId`	NodeId	NodeId of the structure type. This is the decoded structure NodeId, not the binary, XML, or JSON encoding NodeId.
`Body`	table, ByteString, XML string, or JSON string	Decoded body table when the structure is known. Otherwise, the body is left opaque and must be decoded by application code.

local extensionObject = {
  TypeId = "i=338", -- BuildInfo
  Body = {
    ProductUri = ua.Version.ProductUri,
    ManufacturerName = ua.Version.ManufacturerName,
    ProductName = ua.Version.ProductName,
    SoftwareVersion = ua.Version.Version,
    BuildNumber = ua.Version.BuildNumber,
    BuildDate = compat.gettime()
  }
}

Service Structures

NotificationData

NotificationMessage.NotificationData is an array of ExtensionObject notification payloads returned by both Publish and Republish responses. The array is empty when the NotificationMessage is a keep-alive.

A data-change notification is an ExtensionObject with TypeId = "i=811". Its Body contains:

Field	Type	Description
`MonitoredItems[]`	array	Values reported for the MonitoredItems that produced notifications.
`MonitoredItems[].ClientHandle`	UInt32	Application-defined handle supplied in the MonitoredItem’s `RequestedParameters`.
`MonitoredItems[].Value`	DataValue	Sampled value, StatusCode, and requested timestamps.
`DiagnosticInfos[]`	array	Optional diagnostics corresponding to `MonitoredItems`.

ResponseHeader

Every OPC UA service response contains a ResponseHeader with service-level status and diagnostic information.

Field	Type	Description
`Timestamp`	DateTime	Server time when the response was created.
`RequestHandle`	UInt32	Handle copied from the corresponding request. The Client uses it to associate asynchronous responses with callbacks.
`ServiceResult`	StatusCode	Overall result of the service call. Per-operation failures can still be present in a successful response’s `Results` array.
`ServiceDiagnostics`	DiagnosticInfo	Service-level diagnostic details. String indexes in this structure refer to entries in `StringTable`.
`StringTable[]`	String array	Strings referenced by indexes in `ServiceDiagnostics` and other diagnostic structures in the response.
`AdditionalHeader`	ExtensionObject	Additional service-defined response data. A null ExtensionObject means that no additional header was supplied.

ActivateSessionResponse

Field	Type	Description
`ServerNonce`	ByteString	Random value that should not be reused.
`Results`	StatusCode array	User identity token validation results.

AddNodesResponse

Field	Type	Description
`Results[]`	array	One result per requested node.
`Results[].StatusCode`	StatusCode	Status of the add operation.
`Results[].AddedNodeId`	NodeId	Server-assigned NodeId, or `nil` if the operation failed.

BrowseParameters

Field	Type	Description
`RequestedMaxReferencesPerNode`	UInt32	Maximum number of references to return. `0` means unlimited.
`NodesToBrowse[]`	array	Nodes to browse.
`NodesToBrowse[].NodeId`	NodeId	Node to browse.
`NodesToBrowse[].ReferenceTypeId`	NodeId	Reference type to follow.
`NodesToBrowse[].BrowseDirection`	`ua.BrowseDirection`	Browse direction.
`NodesToBrowse[].NodeClassMask`	`ua.NodeClass`	Node classes to include.
`NodesToBrowse[].ResultMask`	`ua.BrowseResultMask`	Fields to include in the response.
`NodesToBrowse[].IncludeSubtypes`	boolean	Include subtypes of `ReferenceTypeId`.

BrowseResult

Field	Type	Description
`Results[]`	array	One result per requested node.
`Results[].StatusCode`	StatusCode	Browse status for the requested node.
`Results[].References[]`	array	References returned by the browse operation.
`References[].NodeId`	NodeId	Target node identifier.
`References[].ReferenceTypeId`	NodeId	Reference type identifier.
`References[].IsForward`	boolean	Reference direction.
`References[].BrowseName`	QualifiedName	Service name of the node.
`References[].DisplayName`	LocalizedText	User-facing node label.
`References[].NodeClass`	Int32	Node class.
`References[].TypeDefinition`	NodeId	Node type definition.

CloseSecureChannelResponse

Empty table.

CloseSessionResponse

Empty table.

CreateSessionResponse

Field	Type	Description
`ResponseHeader`	ResponseHeader	Standard OPC UA response header.
`SessionId`	NodeId	Unique NodeId assigned by the server to the session.
`AuthenticationToken`	NodeId	Unique token assigned by the server to the session.
`RevisedSessionTimeout`	Double	Actual maximum session idle time in milliseconds.
`ServerNonce`	ByteString	Random value that should not be reused in another request.
`ServerCertificate`	ByteString	Server application instance certificate.
`ServerEndpoints`	array	Endpoint descriptions supported by the server.
`ServerSignature`	table	Signature generated with the server certificate private key.
`MaxRequestMessageSize`	UInt32	Maximum request body size in bytes.

FindServersResponse

Field	Type	Description
`Servers[]`	array	Servers that match the request criteria.
`ApplicationUri`	string	Application URI.
`ProductUri`	string	Product URI.
`ApplicationName`	LocalizedText	Human-readable application name.
`ApplicationType`	number	OPC UA application type.
`GatewayServerUri`	string	Gateway server URI, if used.
`DiscoveryProfileUri`	string	Discovery profile URI, if used.
`DiscoveryUrls`	string array	Discovery endpoint URLs.

GetEndpointsResponse

Field	Type	Description
`Endpoints[]`	array	Endpoint descriptions.
`EndpointUrl`	string	Endpoint URL.
`Server`	table	Server application description.
`ServerCertificate`	ByteString	Server certificate.
`SecurityMode`	number	Message security mode.
`SecurityPolicyUri`	string	Security policy URI.
`UserIdentityTokens`	array	Supported user identity token policies.
`TransportProfileUri`	string	Transport profile URI.
`SecurityLevel`	Byte	Relative endpoint security level.

OpenSecureChannelResponse

Field	Type	Description
`ResponseHeader`	ResponseHeader	Standard OPC UA response header.
`SecurityToken`	table	Secure channel token.
`SecurityToken.ChannelId`	UInt32	Unique SecureChannel identifier.
`SecurityToken.TokenId`	UInt32	Unique token identifier within the channel.
`SecurityToken.CreatedAt`	DateTime	Token creation time.
`SecurityToken.RevisedLifetime`	UInt32	Token lifetime in milliseconds.

ReadResponse

Field	Type	Description
`Results[]`	DataValue array	Attribute values returned by the server.

WriteResponse

Field	Type	Description
`Results[]`	StatusCode array	Results for the nodes written by the request.