Add HTTP API Server docs

docs/Docs/HTTP_API_Server.md

@@ -0,0 +1,47 @@
+# HTTP API Server
+
+PostalPoint runs a local HTTP server to allow communication with other devices on the LAN.
+
+With the `httpserver` plugin API, plugins can add their own local API endpoints.
+
+Valid HTTP API requests are POST requests with either a JSON request body, or an entirely empty body.
+
+The default HTTP server settings are to bind to all addresses on port 7678.  There is a basic API web client accessible on `/` for manual API access, for example, at http://localhost:7678/.
+
+## Security
+
+API requests are authenticated with a "Network Connection Key".  Each installation of PostalPoint maintains a user-configurable list of keys which are allowed to connect to that installation's API server.
+
+This means that, in order for a remote client to connect to PostalPoint, it must generate a random alphanumeric ID, which must be saved in the PostalPoint settings.
+
+## Adding an API endpoint
+
+This code adds an endpoint reachable by POST to `http://[local hostname]:[port]/testendpointname`.
+
+```js
+global.apis.httpserver.addEndpoint("testendpointname", async function (request) {
+    // `request` is an object parsed from the request body.
+    if (request.abc == "123") {
+        // A non-string `body` is converted to JSON before the HTTP reply is sent.
+        return {body: {json: true, abc: 123}, httpcode: 200, contentType: "application/json"};
+    }
+    // A string `body` is sent to the client as-is using whatever contentType you specify.
+    return {body: "abc", httpcode: 200, contentType: "text/plain"};
+});
+```
+
+## Connecting to a remote endpoint
+
+By default, `sendRequestToRemote` uses the configured "Host PC", but a different hostname/IP may be specified.
+
+This code hits the endpoint added above.
+
+```js
+try {
+    const responseObject = await global.apis.httpserver.sendRequestToRemote({abc: "123"}, "testendpointname");
+    // responseObject will be {json: true, abc: 123}
+    console.log(responseObject);
+} catch (ex) {
+    global.apis.alert(ex.message, "Request Error");
+}
+```

docs/Plugin API/httpserver.md

@@ -9,6 +9,7 @@ Add features to PostalPoint's integrated LAN HTTP API server.
     * [.addEndpoint(id, onCall)](#httpserver.addEndpoint)
     * [.getServerPort()](#httpserver.getServerPort) ⇒ <code>number</code>
     * [.getClientKey()](#httpserver.getClientKey) ⇒ <code>string</code>
+    * [.sendRequestToRemote(data, endpointID, serverAddress, serverPort)](#httpserver.sendRequestToRemote) ⇒ <code>Promise.&lt;Object&gt;</code>
 
 <a name="httpserver.addEndpoint"></a>
 
@@ -47,3 +48,22 @@ Get the local machine's HTTP client key it uses to authenticate with other
 installations of PostalPoint on the LAN.
 
 **Kind**: static method of [<code>httpserver</code>](#httpserver)  
+<a name="httpserver.sendRequestToRemote"></a>
+
+### httpserver.sendRequestToRemote(data, endpointID, serverAddress, serverPort) ⇒ <code>Promise.&lt;Object&gt;</code>
+Send a HTTP request to another PostalPoint installation on the local network.
+
+**Kind**: static method of [<code>httpserver</code>](#httpserver)  
+**Returns**: <code>Promise.&lt;Object&gt;</code> - - The JSON reply.  
+**Throws**:
+
+- <code>Error</code> When there's a network or other unrecoverable error while completing the request.  Error message is a human-readable description of the problem.
+
+
+| Param | Type | Description |
+| --- | --- | --- |
+| data | <code>Object</code> | Data to encode as JSON in the request body. |
+| endpointID | <code>string</code> | Endpoint to call. |
+| serverAddress | <code>string</code> \| <code>undefined</code> | Address of the PostalPoint server. If undefined, uses the host address configured in PostalPoint's Databases settings. |
+| serverPort | <code>number</code> \| <code>undefined</code> | Port of the PostalPoint server. If undefined, the default PostalPoint port number is used. |
+