NodeCallback<T, R>: New type to simplify callback declarations

Just trying to reduce some boilerplate.  I kept this as a separate commit to
illustrate clearly how this type of things is done since we'll have people
learning TypeScript.

* src/types/misc.ts (NodeCallback<T,R>): New type.
* src/server/dapi/TokenedDataApi.ts: Use it.
* test/server/dapi/TokenedDataApiTest.ts: Use it.

src/server/dapi/TokenedDataApi.ts

@@ -79,7 +79,7 @@ export class TokenedDataApi implements DataApi
      */
     request(
         data:     DataApiInput,
-        callback: ( e: Error | null, data: DataApiResult | null ) => void,
+        callback: NodeCallback<DataApiResult>,
         id:       string
     ): this
     {
@@ -144,7 +144,7 @@ export class TokenedDataApi implements DataApi
     private _replyUnlessStale(
         newtok:    Token<TokenState.DONE>,
         resp_data: DataApiResult,
-        callback:  ( e: Error | null, data: DataApiResult | null ) => void,
+        callback:  NodeCallback<DataApiResult>,
         id:        string
     ): void
     {

src/types/misc.d.ts

@@ -44,3 +44,13 @@ type NominalType<K, T> = K & { __nominal_type__: T };
  * Number of seconds since the Unix epoch (1970-01-01 UTC).
  */
 type UnixTimestamp = NominalType<number, 'UnixTimestamp'>;
+
+
+/**
+ * Oldschool NodeJS callback
+ *
+ * We should migrate to promises over time.  The purpose of this type is to
+ * reduce the boilerplate of these function definitions, and to clearly
+ * document that this pattern is something that used to be done frequently.
+ */
+type NodeCallback<T, R = void> = ( e: Error | null, result: T | null ) => R;

test/server/dapi/TokenedDataApiTest.ts

@@ -121,9 +121,9 @@ describe( 'TokenedDataApi', () =>
         const mock_dapi = new class implements DataApi
         {
             request(
-                given_data:     DataApiInput,
-                callback: ( e: Error|null, data: DataApiResult|null ) => void,
-                given_id:       string
+                given_data: DataApiInput,
+                callback:   NodeCallback<DataApiResult>,
+                given_id:   string,
             ): this
             {
                 expect( given_data ).to.equal( expected_data );
@@ -141,7 +141,7 @@ describe( 'TokenedDataApi', () =>
             return mock_tstore;
         };
 
-        const callback = ( e: Error|null, data: DataApiResult|null ) =>
+        const callback: NodeCallback<DataApiResult> = ( e, data ) =>
         {
             expect( tok_completed ).to.be.true;
 
@@ -197,8 +197,8 @@ describe( 'TokenedDataApi', () =>
         const mock_dapi = new class implements DataApi
         {
             request(
-                _: any,
-                callback: ( e: Error|null, data: DataApiResult|null ) => void,
+                _:        any,
+                callback: NodeCallback<DataApiResult>,
             )
             {
                 callback( expected_err, null );
@@ -206,7 +206,7 @@ describe( 'TokenedDataApi', () =>
             }
         };
 
-        const callback = ( e: Error|null, data: DataApiResult|null ) =>
+        const callback: NodeCallback<DataApiResult> = ( e, data ) =>
         {
             expect( data ).to.equal( null );
             expect( e ).to.equal( expected_err );