Add node groups to opcua input plugin

plugins/inputs/opcua/README.md

@@ -9,8 +9,8 @@ Plugin minimum tested version: 1.16
 
 ```toml
 [[inputs.opcua]]
-  ## Device name
-  # name = "localhost"
+  ## Metric name
+  # name = "opcua"
   #
   ## OPC UA Endpoint URL
   # endpoint = "opc.tcp://localhost:4840"
@@ -47,34 +47,97 @@ Plugin minimum tested version: 1.16
   # password = ""
   #
   ## Node ID configuration
-  ## name       			- the variable name
-  ## namespace  			- integer value 0 thru 3
-  ## identifier_type		- s=string, i=numeric, g=guid, b=opaque
-  ## identifier			- tag as shown in opcua browser
-  ## data_type  			- boolean, byte, short, int, uint, uint16, int16,
-  ##                        uint32, int32, float, double, string, datetime, number
+  ## name              - field name to use in the output
+  ## namespace         - OPC UA namespace of the node (integer value 0 thru 3)
+  ## identifier_type   - OPC UA ID type (s=string, i=numeric, g=guid, b=opaque)
+  ## identifier        - OPC UA ID (tag as shown in opcua browser)
+  ## tags              - extra tags to be added to the output metric (optional)
   ## Example:
-  ## {name="ProductUri", namespace="0", identifier_type="i", identifier="2262", data_type="string", description="http://open62541.org"}
-  nodes = [
-    {name="", namespace="", identifier_type="", identifier="", data_type="", description=""},
-    {name="", namespace="", identifier_type="", identifier="", data_type="", description=""},
-  ]
+  ## {name="ProductUri", namespace="0", identifier_type="i", identifier="2262", tags=[["tag1","value1"],["tag2","value2]]}
+  # nodes = [
+  #  {name="", namespace="", identifier_type="", identifier=""},
+  #  {name="", namespace="", identifier_type="", identifier=""},
+  #]
+  #
+  ## Node Group
+  ## Sets defaults for OPC UA namespace and ID type so they aren't required in
+  ## every node.  A group can also have a metric name that overrides the main
+  ## plugin metric name.
+  ##
+  ## Multiple node groups are allowed
+  #[[inputs.opcua.group]]
+  ## Group Metric name. Overrides the top level name.  If unset, the
+  ## top level name is used.
+  # name =
+  #
+  ## Group default namespace. If a node in the group doesn't set its
+  ## namespace, this is used.
+  # namespace =
+  #
+  ## Group default identifier type. If a node in the group doesn't set its
+  ## namespace, this is used.
+  # identifier_type =
+  #
+  ## Node ID Configuration.  Array of nodes with the same settings as above.
+  # nodes = [
+  #  {name="", namespace="", identifier_type="", identifier=""},
+  #  {name="", namespace="", identifier_type="", identifier=""},
+  #]
 ```
 
-### Example Node Configuration
-An OPC UA node ID may resemble: "n=3,s=Temperature". In this example:
+### Node Configuration
+An OPC UA node ID may resemble: "n=3;s=Temperature". In this example:
 - n=3 is indicating the `namespace` is 3
 - s=Temperature is indicting that the `identifier_type` is a string and `identifier` value is 'Temperature'
-- This example temperature node has a value of 79.0, which makes the `data_type` a 'float'.
+- This example temperature node has a value of 79.0
 To gather data from this node enter the following line into the 'nodes' property above:
 ```
-{name="LabelName", namespace="3", identifier_type="s", identifier="Temperature", data_type="float", description="Description of node"},
+{field_name="temp", namespace="3", identifier_type="s", identifier="Temperature"},
+```
+
+This node configuration produces a metric like this:
+```
+opcua,id=n\=3;s\=Temperature temp=79.0,quality="OK (0x0)" 1597820490000000000
+
 ```
 
+### Group Configuration
+Groups can set default values for the namespace, identifier type, and
+tags settings.  The default values apply to all the nodes in the
+group.  If a default is set, a node may omit the setting altogether.
+This simplifies node configuration, especially when many nodes share
+the same namespace or identifier type.
 
-### Example Output
+The output metric will include tags set in the group and the node.  If
+a tag with the same name is set in both places, the tag value from the
+node is used.
 
+This example group configuration has two groups with two nodes each:
+```
+  [[inputs.opcua.group]]
+  name="group1_metric_name"
+  namespace="3"
+  identifier_type="i"
+  tags=[["group1_tag", "val1"]]
+  nodes = [
+    {name="name", identifier="1001", tags=[["node1_tag", "val2"]]},
+    {name="name", identifier="1002", tags=[["node1_tag", "val3"]]},
+  ]
+  [[inputs.opcua.group]]
+  name="group2_metric_name"
+  namespace="3"
+  identifier_type="i"
+  tags=[["group2_tag", "val3"]]
+  nodes = [
+    {name="saw", identifier="1003", tags=[["node2_tag", "val4"]]},
+    {name="sin", identifier="1004"},
+  ]
 ```
-opcua,host=3c70aee0901e,name=Random,type=double Random=0.018158170305814902 1597820490000000000
 
+It produces metrics like these:
+```
+group1_metric_name,group1_tag=val1,id=ns\=3;i\=1001,node1_tag=val2 name=0,Quality="OK (0x0)" 1606893246000000000
+group1_metric_name,group1_tag=val1,id=ns\=3;i\=1002,node1_tag=val3 name=-1.389117,Quality="OK (0x0)" 1606893246000000000
+group2_metric_name,group2_tag=val3,id=ns\=3;i\=1003,node2_tag=val4 Quality="OK (0x0)",saw=-1.6 1606893246000000000
+group2_metric_name,group2_tag=val3,id=ns\=3;i\=1004 sin=1.902113,Quality="OK (0x0)" 1606893246000000000
 ```