[Screenshotting/PDF Worker Thread] Add type to GeneratePdfResponse (e…

…lastic#196860)

## Summary

This PR adds a `type` to `GeneratePdfResponse` and introduces more
logging for PDF worker.

Closes: elastic#194493
(cherry picked from commit c25a97b)

x-pack/plugins/screenshotting/server/formats/pdf/pdf_maker/pdfmaker.ts

@@ -22,7 +22,12 @@ import {
 } from './constants';
 import { REPORTING_TABLE_LAYOUT } from './get_doc_options';
 import { getFont } from './get_font';
-import type { GeneratePdfRequest, GeneratePdfResponse, WorkerData } from './worker';
+import {
+  GeneratePdfResponseType,
+  type GeneratePdfRequest,
+  type WorkerData,
+  GeneratePdfResponse,
+} from './worker';
 
 // Ensure that all dependencies are included in the release bundle.
 import './worker_dependencies';
@@ -32,6 +37,8 @@ export class PdfMaker {
   private content: Content[];
 
   private worker?: Worker;
+  private workerLogger: Logger;
+
   private pageCount: number = 0;
   private transferList: ArrayBuffer[] = [];
 
@@ -71,6 +78,7 @@ export class PdfMaker {
   ) {
     this.title = '';
     this.content = [];
+    this.workerLogger = logger.get('pdf-worker');
 
     // running in dist: `worker.ts` becomes `worker.js`
     // running in source: `worker_src_harness.ts` needs to be wrapped in JS and have a ts-node environment initialized.
@@ -209,26 +217,37 @@ export class PdfMaker {
         const { port1: myPort, port2: theirPort } = new MessageChannel();
         this.worker = this.createWorker(theirPort);
         this.worker.on('error', (workerError: NodeJS.ErrnoException) => {
+          this.workerLogger.error(`Worker error: ${workerError}`);
           if (workerError.code === 'ERR_WORKER_OUT_OF_MEMORY') {
             reject(new errors.PdfWorkerOutOfMemoryError(workerError.message));
           } else {
             reject(workerError);
           }
         });
-        this.worker.on('exit', () => {});
+        this.worker.on('exit', () => {
+          this.workerLogger.debug('Worker exited');
+        });
 
-        // We expect one message from the worker generating the PDF buffer.
-        myPort.on('message', ({ error, data }: GeneratePdfResponse) => {
-          if (error) {
+        myPort.on('message', ({ type, error, data, message }: GeneratePdfResponse) => {
+          if (type === GeneratePdfResponseType.Log && message) {
+            this.workerLogger.debug(message);
+            return;
+          }
+
+          if (type === GeneratePdfResponseType.Error) {
             reject(new Error(`PDF worker returned the following error: ${error}`));
             return;
           }
-          if (!data) {
+
+          if (type === GeneratePdfResponseType.Data && !data) {
             reject(new Error(`Worker did not generate a PDF!`));
             return;
           }
-          this.pageCount = data.metrics.pages;
-          resolve(data.buffer);
+
+          if (data) {
+            this.pageCount = data.metrics.pages;
+            resolve(data.buffer);
+          }
         });
 
         // Send the request

x-pack/plugins/screenshotting/server/formats/pdf/pdf_maker/worker.ts

@@ -34,23 +34,44 @@ export interface GeneratePdfRequest {
   data: GenerateReportRequestData;
 }
 
-export type GeneratePdfResponse = SuccessResponse | ErrorResponse;
-
-export interface SuccessResponse {
-  error?: undefined;
-  data: {
-    buffer: Uint8Array;
-    metrics: {
-      pages: number;
-    };
+export interface GeneratePdfData {
+  buffer: Uint8Array;
+  metrics: {
+    pages: number;
   };
 }
 
-export interface ErrorResponse {
-  error: string;
-  data: null;
+export enum GeneratePdfResponseType {
+  Log,
+  Data,
+  Error,
+}
+
+interface GeneratePdfLogResponse {
+  type: GeneratePdfResponseType.Log;
+  data?: GeneratePdfData;
+  error?: string;
+  message?: string;
+}
+
+interface GeneratePdfDataResponse {
+  type: GeneratePdfResponseType.Data;
+  data?: GeneratePdfData;
+  error?: string;
+  message?: string;
 }
 
+interface GeneratePdfErrorResponse {
+  type: GeneratePdfResponseType.Error;
+  data?: GeneratePdfData;
+  error?: string;
+  message?: string;
+}
+export type GeneratePdfResponse =
+  | GeneratePdfLogResponse
+  | GeneratePdfDataResponse
+  | GeneratePdfErrorResponse;
+
 if (!isMainThread) {
   const { port } = workerData as WorkerData;
   port.on('message', execute);
@@ -68,6 +89,11 @@ const getPageCount = (pdfDoc: PDFKit.PDFDocument): number => {
 
 async function execute({ data: { layout, logo, title, content } }: GeneratePdfRequest) {
   const { port } = workerData as WorkerData;
+  port.postMessage({
+    type: GeneratePdfResponseType.Log,
+    message: 'Starting execution',
+  });
+
   try {
     const tableBorderWidth = 1;
 
@@ -89,6 +115,11 @@ async function execute({ data: { layout, logo, title, content } }: GeneratePdfRe
       },
     };
 
+    port.postMessage({
+      type: GeneratePdfResponseType.Log,
+      message: 'Initializing PDF printer',
+    });
+
     const printer = new Printer(fonts);
 
     const docDefinition = _.assign(getTemplate(layout, logo, title, tableBorderWidth, assetPath), {
@@ -103,6 +134,11 @@ async function execute({ data: { layout, logo, title, content } }: GeneratePdfRe
       ),
     });
 
+    port.postMessage({
+      type: GeneratePdfResponseType.Log,
+      message: 'Generating document stream',
+    });
+
     const pdfDoc = printer.createPdfKitDocument(docDefinition, {
       tableLayouts: {
         noBorder: {
@@ -121,6 +157,11 @@ async function execute({ data: { layout, logo, title, content } }: GeneratePdfRe
       throw new Error('Document stream has not been generated');
     }
 
+    port.postMessage({
+      type: GeneratePdfResponseType.Log,
+      message: 'Document stream has been generated',
+    });
+
     const buffer = await new Promise<Buffer>((resolve, reject) => {
       const buffers: Buffer[] = [];
       pdfDoc.on('error', reject);
@@ -133,7 +174,13 @@ async function execute({ data: { layout, logo, title, content } }: GeneratePdfRe
       pdfDoc.end();
     });
 
-    const successResponse: SuccessResponse = {
+    port.postMessage({
+      type: GeneratePdfResponseType.Log,
+      message: 'PDF buffer has been generated',
+    });
+
+    const successResponse: GeneratePdfResponse = {
+      type: GeneratePdfResponseType.Data,
       data: {
         buffer,
         metrics: {
@@ -143,7 +190,10 @@ async function execute({ data: { layout, logo, title, content } }: GeneratePdfRe
     };
     port.postMessage(successResponse, [buffer.buffer /* Transfer buffer instead of copying */]);
   } catch (error) {
-    const errorResponse: ErrorResponse = { error: error.message, data: null };
+    const errorResponse: GeneratePdfResponse = {
+      type: GeneratePdfResponseType.Error,
+      error: error.message,
+    };
     port.postMessage(errorResponse);
   } finally {
     process.nextTick(() => {