dynamic palette

Design notes for #322

Currently, the palette of nodes is loaded when the runtime starts and does not change.

The runtime needs to allow nodes to be added/removed dynamically.

Some points that need to be considered:

• nodes can be added by dropping files into the node path, or by npm. Both of these mechanisms should be supported by this feature
  • adding by file will expect the file to have already been copied into node path
  • adding by npm will trigger an npm install of the module
  • future support for importing a zip or files themselves?
• removing a node cannot 'unload' the module - care must be taken if the node creates any 'static' resources
• removing a node in the editor must allow it to remove any artefacts added to the page (eg, debug node's tab)
• a node file or module can contain multiple nodes. Making a request to remove a single node type may trigger the removal of multiple node types.
• what to do if the node is being used in the current flow? Safest option is to reject the removal.
• removing a node, without also removing the files, will mean it returns to the palette on the next restart. That would be unexpected.

Adding a node type

To add a new node to the palette:

1. a request is POSTed to {admin root}/nodes to trigger the add. The post body is a JSON structure that identifies where the node information comes from, either a local file (filename) or an npm module (npm).

    {
        filename: "path to local node .js file or package.json",
        npm: "npm module name"
    }
   

2. For filename, we require that the files already exist somewhere under NODE_RED_HOME/nodes/ This reduces security concerns over exposing arbitrary files and removes the need for the runtime to remember what extra nodes have been added.

   For npm, we npm install the node.

3. The node's .js is then loaded using the existing node loading code. This generates a unique id for the set of nodes loaded (ie hash of the filename/module name)

4. An event is fired over the comms link telling any connected editors that nodes have been added. This triggers a HTTP Get back to {admin root}/nodes/{node-set-id} to load the node definition/help/edit template.

Remove node type

To remove a node from the palette:

1. a DELETE http request is sent to {admin root}/nodes/{node-set-id} to trigger the removal.
2. If the any of the corresponding nodes are in use, the request is rejected
3. The runtime registry removes the corresponding nodes.
4. An event is fired over the comms link telling any connected editors that the nodes have been removed.

In the case of filename being specified, the user is expected to delete the files after the request completes. For npm, the system will uninstall the module.