feature: Add Feature discovery API endpoint and plugin interface

docs/src/develop/plugins/server_plugin_api.md

@@ -2,12 +2,66 @@
 
 # Server API for plugins
 
-SignalK server provides an interface to allow plugins to access / update the full data model, operations and send / receive deltas (updates).
+SignalK server provides an interface to allow plugins to:
+- Discover Features.
+- Access / update the full data model
+- send / receive deltas (updates)
+- Interact with APIs
+- Expose HTTP endpoints
 
-These functions are available via the `app` passed to the plugin when it is invoked.
+
+These functions are available via the `app` object passed to the plugin when it is invoked.
 
 ---
 
+### Discover Features
+
+#### `app.getFeatures(enabed)`
+
+Returns an object detailing the available APIs and Plugins.
+
+The `enabled` parameter is optional and has the following values:
+- `undefined` (not provided): list all features
+- `true`: list only enabled features
+- `false`: list only disabled features
+
+_Example:_
+```javascript
+let features = app.getFeatures();
+
+{
+  "apis": [
+    "resources","course"
+  ],
+  "plugins": [
+    {
+      "id": "anchoralarm",
+      "name": "Anchor Alarm",
+      "version": "1.13.0",
+      "enabled": true
+    },
+    {
+      "id": "autopilot",
+      "name": "Autopilot Control",
+      "version": "1.4.0",
+      "enabled": false
+    },
+    {
+      "id": "sk-to-nmea2000",
+      "name": "Signal K to NMEA 2000",
+      "version": "2.17.0",
+      "enabled": false
+    },
+    {
+      "id": "udp-nmea-sender",
+      "name": "UDP NMEA0183 Sender",
+      "version": "2.0.0",
+      "enabled": false
+    }
+  ]
+}
+```
+
 ### Accessing the Data Model
 
 #### `app.getPath(path)`

docs/src/develop/webapps.md

@@ -93,6 +93,55 @@ GET /signalk/v1/applicationData/user/my-application
 [ "1.0", "1.1"]
 ```
 
+## Discovering Server Features
+
+To assist in tailoring a WebApps UI, it can "discover" the features supported by the server by sending a request to `/signalk/v2/features`.
+
+The response wil contain an object detailing the available APIs and Plugins.
+
+You can use the `enabled` parameter to specify to only return enabled or disabled features.
+
+To list only enabled features:
+`/signalk/v2/features?enable=1`
+
+To list only disabled features:
+`/signalk/v2/features?enable=0`
+
+_Example response:_
+```JSON
+{
+  "apis": [
+    "resources","course"
+  ],
+  "plugins": [
+    {
+      "id": "anchoralarm",
+      "name": "Anchor Alarm",
+      "version": "1.13.0",
+      "enabled": true
+    },
+    {
+      "id": "autopilot",
+      "name": "Autopilot Control",
+      "version": "1.4.0",
+      "enabled": false
+    },
+    {
+      "id": "sk-to-nmea2000",
+      "name": "Signal K to NMEA 2000",
+      "version": "2.17.0",
+      "enabled": false
+    },
+    {
+      "id": "udp-nmea-sender",
+      "name": "UDP NMEA0183 Sender",
+      "version": "2.0.0",
+      "enabled": false
+    }
+  ]
+}
+```
+
 ## Embedded Components and Admin UI / Server interfaces
 
 Embedded components are implemented using [Webpack Federated Modules](https://webpack.js.org/concepts/module-federation/) and [React Code Splitting](https://reactjs.org/docs/code-splitting.html).

packages/server-api/src/index.ts

@@ -31,6 +31,16 @@ import { PointDestination, RouteDestination, CourseInfo } from './coursetypes'
 
 export * from './autopilotapi'
 
+export type SignalKApiId =
+  | 'resources'
+  | 'course'
+  | 'history'
+  | 'autopilot'
+  | 'anchor'
+  | 'logbook'
+  | 'historyplayback' //https://signalk.org/specification/1.7.0/doc/streaming_api.html#history-playback
+  | 'historysnapshot' //https://signalk.org/specification/1.7.0/doc/rest_api.html#history-snapshot-retrieval
+
 export {
   PropertyValue,
   PropertyValues,
@@ -113,6 +123,16 @@ export interface Metadata {
   description?: string
 }
 
+export interface FeatureInfo {
+  apis: SignalKApiId[]
+  plugins: Array<{
+    id: string
+    name: string
+    version: string
+    enabled: boolean
+  }>
+}
+
 export interface ServerAPI extends PluginServerApp {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   getSelfPath: (path: string) => any
@@ -172,6 +192,9 @@ export interface ServerAPI extends PluginServerApp {
     ) => void
   }) => void
   getSerialPorts: () => Promise<Ports>
+
+  getFeatures: () => FeatureInfo
+
   getCourse: () => Promise<CourseInfo>
   clearDestination: () => Promise<void>
   setDestination: (

src/api/discovery/index.ts

@@ -0,0 +1,40 @@
+import { createDebug } from '../../debug'
+const debug = createDebug('signalk-server:api:features')
+
+import { IRouter, Request, Response } from 'express'
+
+import { WithFeatures } from '../../app'
+
+const FEATURES_API_PATH = `/signalk/v2/features`
+
+interface FeaturesApplication extends IRouter, WithFeatures {}
+
+export class FeaturesApi {
+  constructor(private app: FeaturesApplication) {}
+
+  async start() {
+    return new Promise<void>((resolve) => {
+      this.initApiRoutes()
+      resolve()
+    })
+  }
+
+  private initApiRoutes() {
+    debug(`** Initialise ${FEATURES_API_PATH} path handlers **`)
+    // return Feature information
+    this.app.get(
+      `${FEATURES_API_PATH}`,
+      async (req: Request, res: Response) => {
+        debug(`** GET ${req.path}`)
+
+        const enabled = ['true', '1'].includes(req.query.enabled as string)
+          ? true
+          : ['false', '0'].includes(req.query.enabled as string)
+          ? false
+          : undefined
+
+        res.json(await this.app.getFeatures(enabled))
+      }
+    )
+  }
+}

src/api/discovery/openApi.json

@@ -14,10 +14,19 @@
   },
   "servers": [
     {
-      "url": "/"
+      "url": "/signalk"
+    }
+  ],
+  "tags": [
+    {
+      "name": "server",
+      "description": "Signal K Server."
+    },
+    {
+      "name": "features",
+      "description": "Signal K Server features."
     }
   ],
-  "tags": [],
   "components": {
     "schemas": {
       "DiscoveryData": {
@@ -70,6 +79,46 @@
             }
           }
         }
+      },
+      "PluginMetaData": {
+        "type": "object",
+        "required": ["id", "name", "version"],
+        "description": "Plugin metadata.",
+        "properties": {
+          "id": {
+            "type": "string",
+            "description": "Plugin ID."
+          },
+          "name": {
+            "type": "string",
+            "description": "Plugin name."
+          },
+          "version": {
+            "type": "string",
+            "description": "Plugin verison."
+          }
+        }
+      },
+      "FeaturesModel": {
+        "type": "object",
+        "required": ["apis", "plugins"],
+        "description": "Features response",
+        "properties": {
+          "apis": {
+            "type": "array",
+            "description": "Implemented APIs.",
+            "items": {
+              "type": "string"
+            }
+          },
+          "plugins": {
+            "type": "array",
+            "description": "Installed Plugins.",
+            "items": {
+              "$ref": "#/components/schemas/PluginMetaData"
+            }
+          }
+        }
       }
     },
     "responses": {
@@ -82,21 +131,107 @@
             }
           }
         }
+      },
+      "200Ok": {
+        "description": "OK",
+        "content": {
+          "application/json": {
+            "schema": {
+              "type": "object",
+              "properties": {
+                "state": {
+                  "type": "string",
+                  "enum": ["COMPLETED"]
+                },
+                "statusCode": {
+                  "type": "number",
+                  "enum": [200]
+                }
+              },
+              "required": ["state", "statusCode"]
+            }
+          }
+        }
+      },
+      "ErrorResponse": {
+        "description": "Failed operation",
+        "content": {
+          "application/json": {
+            "schema": {
+              "type": "object",
+              "description": "Request error response",
+              "properties": {
+                "state": {
+                  "type": "string",
+                  "enum": ["FAILED"]
+                },
+                "statusCode": {
+                  "type": "number",
+                  "enum": [404]
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "required": ["state", "statusCode", "message"]
+            }
+          }
+        }
+      },
+      "FeaturesResponse": {
+        "description": "Server features response.",
+        "content": {
+          "application/json": {
+            "schema": {
+              "description": "Features response.",
+              "$ref": "#/components/schemas/FeaturesModel"
+            }
+          }
+        }
       }
     }
   },
 
   "paths": {
-    "/signalk": {
+    "/": {
       "get": {
-        "tags": [],
+        "tags": ["server"],
+        "summary": "Retrieve server version and service endpoints.",
         "description": "Returns data about server's endpoints and versions.",
         "responses": {
           "200": {
             "$ref": "#/components/responses/DiscoveryResponse"
           }
         }
       }
+    },
+    "/v2/features": {
+      "get": {
+        "tags": ["features"],
+        "parameters": [
+          {
+            "name": "enabled",
+            "in": "query",
+            "description": "Limit results to enabled features.",
+            "required": false,
+            "explode": false,
+            "schema": {
+              "type": "string",
+              "enum": ["enabled", "1", "false", "0"]
+            }
+          }
+        ],
+        "summary": "Retrieve available server features.",
+        "description": "Returns object detailing the available server features.",
+        "responses": {
+          "200": {
+            "$ref": "#/components/responses/FeaturesResponse"
+          },
+          "default": {
+            "$ref": "#/components/responses/ErrorResponse"
+          }
+        }
+      }
     }
   }
 }