http/endpoint: extract common pipe code (#1113)

defaultResultWriter and odataJsonWriter use identical code for piping results to
response.  This commit extracts the shared code into its own function.

lib/http/endpoint.js

@@ -191,21 +191,27 @@ const endpointBase = ({ preprocessor = noop, before = noop, resultWriter, errorW
 ////////////////////////////////////////////////////////////////////////////////
 // ENDPOINT FORMAT SPECIALIZATIONS
 
-////////////////////////////////////////
-// JSON/default
-
 const streamErrorHandler = (response) => () => {
   response.addTrailers({ Status: 'Error' }); // TODO: improve response content.
 };
-const defaultResultWriter = (result, request, response, next) => {
-  if (!response.hasHeader('Content-Type')) response.type('json');
-
+const pipelineResult = (result, response, next) => {
   if (result instanceof PartialPipe) {
     result.streams.at(-1).on('error', streamErrorHandler(response));
     result.with(response).pipeline((err) => next?.(err));
+    return true;
   } else if (result.pipe != null) {
     result.on('error', streamErrorHandler(response));
     pipeline(result, response, (err) => err && next?.(err));
+    return true;
+  }
+  return false;
+};
+
+const defaultResultWriter = (result, request, response, next) => {
+  if (!response.hasHeader('Content-Type')) response.type('json');
+
+  if (pipelineResult(result, response, next)) {
+    // handled
   } else if (isJsonType(response.getHeader('Content-Type'))) {
     response.send(jsonSerialize(result));
   } else {
@@ -349,16 +355,11 @@ const odataPreprocessor = (format) => (_, context) => {
 // respond with the appropriate OData version (section 8.1.5).
 const odataBefore = (response) => { response.setHeader('OData-Version', '4.0'); };
 
-// TODO refactor to share common code with defaultResultWriter?
 const odataJsonWriter = (result, request, response, next) => {
   if (!response.hasHeader('Content-Type')) response.type('json');
 
-  if (result instanceof PartialPipe) {
-    result.streams.at(-1).on('error', streamErrorHandler(response));
-    result.with(response).pipeline((err) => next?.(err));
-  } else if (result.pipe != null) {
-    result.on('error', streamErrorHandler(response));
-    pipeline(result, response, (err) => err && next?.(err));
+  if (pipelineResult(result, response, next)) {
+    // handled
   } else {
     // OData JSON endpoints craft JSON by hand
     response.send(result);