Speed up unfurls by reusing puppeteer sessions

frontend/src/app/components/address/address-preview.component.ts

@@ -44,7 +44,6 @@ export class AddressPreviewComponent implements OnInit, OnDestroy {
   ) { }
 
   ngOnInit() {
-    this.openGraphService.setPreviewLoading();
     this.stateService.networkChanged$.subscribe((network) => this.network = network);
 
     this.addressLoadingStatus$ = this.route.paramMap
@@ -56,6 +55,7 @@ export class AddressPreviewComponent implements OnInit, OnDestroy {
     this.mainSubscription = this.route.paramMap
       .pipe(
         switchMap((params: ParamMap) => {
+          this.openGraphService.waitFor('address-data');
           this.error = undefined;
           this.isLoadingAddress = true;
           this.loadedConfirmedTxCount = 0;
@@ -90,7 +90,7 @@ export class AddressPreviewComponent implements OnInit, OnDestroy {
           this.address = address;
           this.updateChainStats();
           this.isLoadingAddress = false;
-          this.openGraphService.setPreviewReady();
+          this.openGraphService.waitOver('address-data');
         })
       )
       .subscribe(() => {},

frontend/src/app/components/block-overview-graph/block-overview-graph.component.ts

@@ -18,6 +18,7 @@ export class BlockOverviewGraphComponent implements AfterViewInit, OnDestroy {
   @Input() orientation = 'left';
   @Input() flip = true;
   @Output() txClickEvent = new EventEmitter<TransactionStripped>();
+  @Output() readyEvent = new EventEmitter();
 
   @ViewChild('blockCanvas')
   canvas: ElementRef<HTMLCanvasElement>;
@@ -37,6 +38,8 @@ export class BlockOverviewGraphComponent implements AfterViewInit, OnDestroy {
   selectedTx: TxView | void;
   tooltipPosition: Position;
 
+  readyNextFrame = false;
+
   constructor(
     readonly ngZone: NgZone,
     readonly elRef: ElementRef,
@@ -78,6 +81,7 @@ export class BlockOverviewGraphComponent implements AfterViewInit, OnDestroy {
   setup(transactions: TransactionStripped[]): void {
     if (this.scene) {
       this.scene.setup(transactions);
+      this.readyNextFrame = true;
       this.start();
     }
   }
@@ -258,6 +262,11 @@ export class BlockOverviewGraphComponent implements AfterViewInit, OnDestroy {
           this.gl.drawArrays(this.gl.TRIANGLES, 0, pointArray.length / TxSprite.vertexSize);
         }
       }
+
+      if (this.readyNextFrame) {
+        this.readyNextFrame = false;
+        this.readyEvent.emit();
+      }
     }
 
     /* LOOP */

frontend/src/app/components/block/block-preview.component.html

@@ -30,44 +30,42 @@
             <td i18n="block.weight">Weight</td>
             <td [innerHTML]="'&lrm;' + (block?.weight | wuBytes: 2)"></td>
           </tr>
-          <ng-template [ngIf]="webGlEnabled">
+          <tr *ngIf="block?.extras?.medianFee != undefined">
-            <tr *ngIf="block?.extras?.medianFee != undefined">
+            <td class="td-width" i18n="block.median-fee">Median fee</td>
-              <td class="td-width" i18n="block.median-fee">Median fee</td>
+            <td>~{{ block?.extras?.medianFee | number:'1.0-0' }} <span class="symbol" i18n="shared.sat-vbyte|sat/vB">sat/vB</span></td>
-              <td>~{{ block?.extras?.medianFee | number:'1.0-0' }} <span class="symbol" i18n="shared.sat-vbyte|sat/vB">sat/vB</span></td>
+          </tr>
-            </tr>
+          <ng-template [ngIf]="fees !== undefined">
-            <ng-template [ngIf]="fees !== undefined">
+            <tr>
-              <tr>
+              <td i18n="block.total-fees|Total fees in a block">Total fees</td>
-                <td i18n="block.total-fees|Total fees in a block">Total fees</td>
+              <td *ngIf="network !== 'liquid' && network !== 'liquidtestnet'; else liquidTotalFees">
-                <td *ngIf="network !== 'liquid' && network !== 'liquidtestnet'; else liquidTotalFees">
+                <app-amount [satoshis]="block?.extras.totalFees" digitsInfo="1.2-3" [noFiat]="true"></app-amount>
-                  <app-amount [satoshis]="block?.extras.totalFees" digitsInfo="1.2-3" [noFiat]="true"></app-amount>
+              </td>
+              <ng-template #liquidTotalFees>
+                <td>
+                  <app-amount [satoshis]="fees * 100000000" digitsInfo="1.2-2" [noFiat]="true"></app-amount>
                 </td>
-                <ng-template #liquidTotalFees>
+              </ng-template>
-                  <td>
-                    <app-amount [satoshis]="fees * 100000000" digitsInfo="1.2-2" [noFiat]="true"></app-amount>
-                  </td>
-                </ng-template>
-              </tr>
-            </ng-template>
-            <tr *ngIf="network !== 'liquid' && network !== 'liquidtestnet'">
-              <td i18n="block.miner">Miner</td>
-              <td *ngIf="stateService.env.MINING_DASHBOARD">
-                <a [attr.data-cy]="'block-details-miner-badge'" placement="bottom" [routerLink]="['/mining/pool' | relativeUrl, block?.extras.pool.slug]" class="badge"
-                  [class]="block?.extras.pool.name === 'Unknown' ? 'badge-secondary' : 'badge-primary'">
-                  {{ block?.extras.pool.name }}
-                </a>
-              </td>
-              <td *ngIf="!stateService.env.MINING_DASHBOARD && stateService.env.BASE_MODULE === 'mempool'">
-                <span [attr.data-cy]="'block-details-miner-badge'" placement="bottom" class="badge"
-                  [class]="block?.extras.pool.name === 'Unknown' ? 'badge-secondary' : 'badge-primary'">
-                  {{ block?.extras.pool.name }}
-              </span>
-              </td>
             </tr>
           </ng-template>
+          <tr *ngIf="network !== 'liquid' && network !== 'liquidtestnet'">
+            <td i18n="block.miner">Miner</td>
+            <td *ngIf="stateService.env.MINING_DASHBOARD">
+              <a [attr.data-cy]="'block-details-miner-badge'" placement="bottom" [routerLink]="['/mining/pool' | relativeUrl, block?.extras.pool.slug]" class="badge"
+                [class]="block?.extras.pool.name === 'Unknown' ? 'badge-secondary' : 'badge-primary'">
+                {{ block?.extras.pool.name }}
+              </a>
+            </td>
+            <td *ngIf="!stateService.env.MINING_DASHBOARD && stateService.env.BASE_MODULE === 'mempool'">
+              <span [attr.data-cy]="'block-details-miner-badge'" placement="bottom" class="badge"
+                [class]="block?.extras.pool.name === 'Unknown' ? 'badge-secondary' : 'badge-primary'">
+                {{ block?.extras.pool.name }}
+            </span>
+            </td>
+          </tr>
         </tbody>
       </table>
     </div>
-    <div class="col-sm chart-container" *ngIf="webGlEnabled">
+    <div class="col-sm chart-container">
       <app-block-overview-graph
         #blockGraph
         [isLoading]="false"
@@ -75,7 +73,7 @@
         [blockLimit]="stateService.blockVSize"
         [orientation]="'top'"
         [flip]="false"
-        (txClickEvent)="onTxClick($event)"
+        (readyEvent)="onGraphReady()"
       ></app-block-overview-graph>
     </div>
   </div>

frontend/src/app/components/block/block-preview.component.ts

@@ -1,11 +1,153 @@
-import { Component } from '@angular/core';
+import { Component, OnInit, OnDestroy, ViewChild, ElementRef } from '@angular/core';
-import { BlockComponent } from './block.component';
+import { ActivatedRoute, ParamMap } from '@angular/router';
+import { ElectrsApiService } from '../../services/electrs-api.service';
+import { switchMap, tap, throttleTime, catchError, shareReplay, startWith, pairwise } from 'rxjs/operators';
+import { of, Subscription, asyncScheduler } from 'rxjs';
+import { StateService } from '../../services/state.service';
+import { SeoService } from 'src/app/services/seo.service';
+import { OpenGraphService } from 'src/app/services/opengraph.service';
+import { BlockExtended, TransactionStripped } from 'src/app/interfaces/node-api.interface';
+import { ApiService } from 'src/app/services/api.service';
+import { BlockOverviewGraphComponent } from 'src/app/components/block-overview-graph/block-overview-graph.component';
 
 @Component({
   selector: 'app-block-preview',
   templateUrl: './block-preview.component.html',
-  styleUrls: ['./block.component.scss', './block-preview.component.scss']
+  styleUrls: ['./block-preview.component.scss']
 })
-export class BlockPreviewComponent extends BlockComponent {
+export class BlockPreviewComponent implements OnInit, OnDestroy {
-  
+  network = '';
+  block: BlockExtended;
+  blockHeight: number;
+  blockHash: string;
+  isLoadingBlock = true;
+  strippedTransactions: TransactionStripped[];
+  overviewTransitionDirection: string;
+  isLoadingOverview = true;
+  error: any;
+  blockSubsidy: number;
+  fees: number;
+  overviewError: any = null;
+
+  overviewSubscription: Subscription;
+  networkChangedSubscription: Subscription;
+
+  @ViewChild('blockGraph') blockGraph: BlockOverviewGraphComponent;
+
+  constructor(
+    private route: ActivatedRoute,
+    private electrsApiService: ElectrsApiService,
+    public stateService: StateService,
+    private seoService: SeoService,
+    private openGraphService: OpenGraphService,
+    private apiService: ApiService
+  ) { }
+
+  ngOnInit() {
+    this.network = this.stateService.network;
+
+    const block$ = this.route.paramMap.pipe(
+      switchMap((params: ParamMap) => {
+        this.openGraphService.waitFor('block-viz');
+        this.openGraphService.waitFor('block-data');
+
+        const blockHash: string = params.get('id') || '';
+        this.block = undefined;
+        this.error = undefined;
+        this.fees = undefined;
+
+        let isBlockHeight = false;
+        if (/^[0-9]+$/.test(blockHash)) {
+          isBlockHeight = true;
+        } else {
+          this.blockHash = blockHash;
+        }
+
+        this.isLoadingBlock = true;
+        this.isLoadingOverview = true;
+
+        if (isBlockHeight) {
+          return this.electrsApiService.getBlockHashFromHeight$(parseInt(blockHash, 10))
+            .pipe(
+              switchMap((hash) => {
+                this.blockHash = hash;
+                return this.apiService.getBlock$(hash);
+              })
+            );
+        }
+        return this.apiService.getBlock$(blockHash);
+      }),
+      tap((block: BlockExtended) => {
+        this.block = block;
+        this.blockHeight = block.height;
+
+        this.seoService.setTitle($localize`:@@block.component.browser-title:Block ${block.height}:BLOCK_HEIGHT:: ${block.id}:BLOCK_ID:`);
+        this.isLoadingBlock = false;
+        this.setBlockSubsidy();
+        if (block?.extras?.reward !== undefined) {
+          this.fees = block.extras.reward / 100000000 - this.blockSubsidy;
+        }
+        this.stateService.markBlock$.next({ blockHeight: this.blockHeight });
+        this.isLoadingOverview = true;
+        this.overviewError = null;
+
+        this.openGraphService.waitOver('block-data');
+      }),
+      throttleTime(50, asyncScheduler, { leading: true, trailing: true }),
+      shareReplay(1)
+    );
+
+    this.overviewSubscription = block$.pipe(
+      startWith(null),
+      pairwise(),
+      switchMap(([prevBlock, block]) => this.apiService.getStrippedBlockTransactions$(block.id)
+        .pipe(
+          catchError((err) => {
+            this.overviewError = err;
+            return of([]);
+          }),
+          switchMap((transactions) => {
+            return of({ transactions, direction: 'down' });
+          })
+        )
+      ),
+    )
+    .subscribe(({transactions, direction}: {transactions: TransactionStripped[], direction: string}) => {
+      this.strippedTransactions = transactions;
+      this.isLoadingOverview = false;
+      if (this.blockGraph) {
+        this.blockGraph.destroy();
+        this.blockGraph.setup(this.strippedTransactions);
+      }
+    },
+    (error) => {
+      this.error = error;
+      this.isLoadingOverview = false;
+      if (this.blockGraph) {
+        this.blockGraph.destroy();
+      }
+    });
+
+    this.networkChangedSubscription = this.stateService.networkChanged$
+      .subscribe((network) => this.network = network);
+  }
+
+  ngOnDestroy() {
+    if (this.overviewSubscription) {
+      this.overviewSubscription.unsubscribe();
+    }
+    if (this.networkChangedSubscription) {
+      this.networkChangedSubscription.unsubscribe();
+    }
+  }
+
+  // TODO - Refactor this.fees/this.reward for liquid because it is not
+  // used anymore on Bitcoin networks (we use block.extras directly)
+  setBlockSubsidy() {
+    this.blockSubsidy = 0;
+  }
+
+  onGraphReady(): void {
+    this.openGraphService.waitOver('block-viz');
+  }
 }

frontend/src/app/services/opengraph.service.ts

@@ -1,4 +1,4 @@
-import { Injectable } from '@angular/core';
+import { Injectable, NgZone } from '@angular/core';
 import { Meta } from '@angular/platform-browser';
 import { Router, ActivatedRoute, NavigationEnd } from '@angular/router';
 import { filter, map, switchMap } from 'rxjs/operators';
@@ -12,8 +12,11 @@ import { LanguageService } from './language.service';
 export class OpenGraphService {
   network = '';
   defaultImageUrl = '';
+  previewLoadingEvents = {};
+  previewLoadingCount = 0;
 
   constructor(
+    private ngZone: NgZone,
     private metaService: Meta,
     private stateService: StateService,
     private LanguageService: LanguageService,
@@ -39,6 +42,9 @@ export class OpenGraphService {
         this.clearOgImage();
       }
     });
+
+    // expose this service to global scope, so we can access it from the unfurler
+    window['ogService'] = this;
   }
 
   setOgImage() {
@@ -59,13 +65,44 @@ export class OpenGraphService {
     this.metaService.updateTag({ property: 'og:image:height', content: '500' });
   }
 
-  /// signal that the unfurler should wait for a 'ready' signal before taking a screenshot
+  /// register an event that needs to resolve before we can take a screenshot
-  setPreviewLoading() {
+  waitFor(event) {
-    this.metaService.updateTag({ property: 'og:loading', content: 'loading'});
+    if (!this.previewLoadingEvents[event]) {
+      this.previewLoadingEvents[event] = 1;
+      this.previewLoadingCount++;
+    } else {
+      this.previewLoadingEvents[event]++;
+    }
+    this.metaService.updateTag({ property: 'og:preview:loading', content: 'loading'});
   }
 
-  // signal to the unfurler that the page is ready for a screenshot
+  // signal that an event has resolved
-  setPreviewReady() {
+  // if all registered events have resolved, signal we are ready for a screenshot
-    this.metaService.updateTag({ property: 'og:ready', content: 'ready'});
+  waitOver(event) {
+    if (this.previewLoadingEvents[event]) {
+      this.previewLoadingEvents[event]--;
+      if (this.previewLoadingEvents[event] === 0) {
+        delete this.previewLoadingEvents[event]
+        this.previewLoadingCount--;
+      }
+    }
+    if (this.previewLoadingCount === 0) {
+      this.metaService.updateTag({ property: 'og:preview:ready', content: 'ready'});
+    }
+  }
+
+  resetLoading() {
+    this.previewLoadingEvents = {};
+    this.previewLoadingCount = 0;
+    this.metaService.removeTag("property='og:preview:loading'");
+    this.metaService.removeTag("property='og:preview:ready'");
+    this.metaService.removeTag("property='og:meta:ready'");
+  }
+
+  loadPage(path) {
+    this.resetLoading();
+    this.ngZone.run(() => {
+      this.router.navigateByUrl(path);
+    })
   }
 }

frontend/src/app/services/seo.service.ts

@@ -21,12 +21,14 @@ export class SeoService {
     this.titleService.setTitle(newTitle + ' - ' + this.getTitle());
     this.metaService.updateTag({ property: 'og:title', content: newTitle});
     this.metaService.updateTag({ property: 'twitter:title', content: newTitle});
+    this.metaService.updateTag({ property: 'og:meta:ready', content: 'ready'});
   }
 
   resetTitle(): void {
     this.titleService.setTitle(this.getTitle());
     this.metaService.updateTag({ property: 'og:title', content: this.getTitle()});
     this.metaService.updateTag({ property: 'twitter:title', content: this.getTitle()});
+    this.metaService.updateTag({ property: 'og:meta:ready', content: 'ready'});
   }
 
   setEnterpriseTitle(title: string) {

unfurler/config.sample.json

@@ -9,6 +9,7 @@
   },
   "PUPPETEER": {
     "CLUSTER_SIZE": 2,
-    "EXEC_PATH": "/usr/local/bin/chrome" // optional
+    "EXEC_PATH": "/usr/local/bin/chrome", // optional
+    "MAX_PAGE_AGE": 86400 // maximum lifetime of a page session (in seconds)
   }
 }

unfurler/src/concurrency/ReusablePage.ts

@@ -0,0 +1,119 @@
+import * as puppeteer from 'puppeteer';
+import ConcurrencyImplementation, { ResourceData } from 'puppeteer-cluster/dist/concurrency/ConcurrencyImplementation';
+import { timeoutExecute } from 'puppeteer-cluster/dist/util';
+
+import config from '../config';
+const mempoolHost = config.MEMPOOL.HTTP_HOST + (config.MEMPOOL.HTTP_PORT ? ':' + config.MEMPOOL.HTTP_PORT : '');
+
+const BROWSER_TIMEOUT = 5000;
+// maximum lifetime of a single page session
+const maxAgeMs = (config.PUPPETEER.MAX_PAGE_AGE || (24 * 60 * 60)) * 1000;
+
+interface repairablePage extends puppeteer.Page {
+  repairRequested?: boolean;
+}
+
+export default class ReusablePage extends ConcurrencyImplementation {
+
+  protected browser: puppeteer.Browser | null = null;
+  protected currentPage: repairablePage | null = null;
+  protected pageCreatedAt: number = 0;
+  private repairing: boolean = false;
+  private repairRequested: boolean = false;
+  private openInstances: number = 0;
+  private waitingForRepairResolvers: (() => void)[] = [];
+
+  public constructor(options: puppeteer.LaunchOptions, puppeteer: any) {
+    super(options, puppeteer);
+  }
+
+  private async repair() {
+    if (this.openInstances !== 0 || this.repairing) {
+      // already repairing or there are still pages open? wait for start/finish
+      await new Promise<void>(resolve => this.waitingForRepairResolvers.push(resolve));
+      return;
+    }
+
+    this.repairing = true;
+    console.log('Starting repair');
+
+    try {
+      // will probably fail, but just in case the repair was not necessary
+      await (<puppeteer.Browser>this.browser).close();
+    } catch (e) {
+      console.log('Unable to close browser.');
+    }
+
+    try {
+      this.browser = await this.puppeteer.launch(this.options) as puppeteer.Browser;
+    } catch (err) {
+      throw new Error('Unable to restart chrome.');
+    }
+    this.currentPage = null;
+    this.repairRequested = false;
+    this.repairing = false;
+    this.waitingForRepairResolvers.forEach(resolve => resolve());
+    this.waitingForRepairResolvers = [];
+    await this.createResources();
+  }
+
+  public async init() {
+    this.browser = await this.puppeteer.launch(this.options);
+  }
+
+  public async close() {
+    await (this.browser as puppeteer.Browser).close();
+  }
+
+  protected async createResources(): Promise<ResourceData> {
+    if (!this.currentPage) {
+      this.currentPage = await (this.browser as puppeteer.Browser).newPage();
+      this.pageCreatedAt = Date.now();
+      const defaultUrl = mempoolHost + '/preview/block/1';
+      this.currentPage.on('pageerror', (err) => {
+        this.repairRequested = true;
+      });
+      await this.currentPage.goto(defaultUrl, { waitUntil: "load" });
+    }
+    return {
+      page: this.currentPage
+    }
+  }
+
+  public async workerInstance() {
+    let resources: ResourceData;
+
+    return {
+      jobInstance: async () => {
+        if (this.repairRequested || this.currentPage?.repairRequested) {
+          await this.repair();
+        }
+
+        await timeoutExecute(BROWSER_TIMEOUT, (async () => {
+          resources = await this.createResources();
+        })());
+        this.openInstances += 1;
+
+        return {
+          resources,
+
+          close: async () => {
+            this.openInstances -= 1; // decrement first in case of error
+
+            if (this.repairRequested || this.currentPage?.repairRequested || (Date.now() - this.pageCreatedAt > maxAgeMs)) {
+              await this.repair();
+            }
+          },
+        };
+      },
+
+      close: async () => {},
+
+      repair: async () => {
+        console.log('Repair requested');
+        this.repairRequested = true;
+        await this.repair();
+      },
+    };
+  }
+}

unfurler/src/config.ts

@@ -12,6 +12,7 @@ interface IConfig {
   PUPPETEER: {
     CLUSTER_SIZE: number;
     EXEC_PATH?: string;
+    MAX_PAGE_AGE?: number;
   };
 }
 

unfurler/src/index.ts

@@ -3,6 +3,7 @@ import { Application, Request, Response, NextFunction } from 'express';
 import * as http from 'http';
 import config from './config';
 import { Cluster } from 'puppeteer-cluster';
+import ReusablePage from './concurrency/ReusablePage';
 const puppeteerConfig = require('../puppeteer.config.json');
 
 if (config.PUPPETEER.EXEC_PATH) {
@@ -32,7 +33,7 @@ class Server {
       ;
 
     this.cluster = await Cluster.launch({
-        concurrency: Cluster.CONCURRENCY_CONTEXT,
+        concurrency: ReusablePage,
         maxConcurrency: config.PUPPETEER.CLUSTER_SIZE,
         puppeteerOptions: puppeteerConfig,
     });
@@ -52,47 +53,40 @@ class Server {
     this.app.get('*', (req, res) => { return this.renderHTML(req, res) })
   }
 
-  async clusterTask({ page, data: { url, action } }) {
+  async clusterTask({ page, data: { url, path, action } }) {
-    await page.goto(url, { waitUntil: "networkidle0" });
+    try {
-    switch (action) {
+      if (action === 'screenshot' || action === 'html') {
-      case 'screenshot': {
+        const loaded = await page.evaluate(async (path) => {
-        await page.evaluate(async () => {
+          if (window['ogService']) {
-          // wait for all images to finish loading
+            window['ogService'].loadPage(path);
-          const imgs = Array.from(document.querySelectorAll("img"));
+            return true;
-          await Promise.all([
+          } else {
-            document.fonts.ready,
+            return false;
-            ...imgs.map((img) => {
-              if (img.complete) {
-                if (img.naturalHeight !== 0) return;
-                throw new Error("Image failed to load");
-              }
-              return new Promise((resolve, reject) => {
-                img.addEventListener("load", resolve);
-                img.addEventListener("error", reject);
-              });
-            }),
-          ]);
-        });
-        const waitForReady = await page.$('meta[property="og:loading"]');
-        const alreadyReady = await page.$('meta[property="og:ready"]');
-        if (waitForReady != null && alreadyReady == null) {
-          try {
-            await page.waitForSelector('meta[property="og:ready]"', { timeout: 10000 });
-          } catch (e) {
-            // probably timed out
           }
+        }, path)
+
+        if (!loaded) {
+          throw new Error('failed to access open graph service');
         }
-        return page.screenshot();
+
-      } break;
+        if (action === 'screenshot') {
-      default: {
+          const waitForReady = await page.$('meta[property="og:preview:loading"]');
-        try {
+          const alreadyReady = await page.$('meta[property="og:preview:ready"]');
-          await page.waitForSelector('meta[property="og:title"]', { timeout: 10000 })
+          if (waitForReady != null && alreadyReady == null) {
-          const tag = await page.$('meta[property="og:title"]');
+            await page.waitForSelector('meta[property="og:preview:ready"]', { timeout: 8000 });
-        } catch (e) {
+          }
-          // probably timed out
+          return page.screenshot();
+        } else if (action === 'html') {
+          const alreadyReady = await page.$('meta[property="og:meta:ready"]');
+          if (alreadyReady == null) {
+            await page.waitForSelector('meta[property="og:meta:ready"]', { timeout: 8000 });
+          }
+          return page.content();
         }
-        return page.content();
       }
+    } catch (e) {
+      console.log(`failed to render page for ${action}`, e instanceof Error ? e.message : e);
+      page.repairRequested = true;
     }
   }
 
@@ -100,8 +94,11 @@ class Server {
     try {
       // strip default language code for compatibility
       const path = req.params[0].replace('/en/', '/');
-      const img = await this.cluster?.execute({ url: this.mempoolHost + path, action: 'screenshot' });
+      const img = await this.cluster?.execute({ url: this.mempoolHost + path, path: path, action: 'screenshot' });
 
+      if (!img) {
+        throw new Error('failed to render preview image');
+      }
       res.contentType('image/png');
       res.send(img);
     } catch (e) {
@@ -120,9 +117,14 @@ class Server {
     }
 
     try {
-      let html = await this.cluster?.execute({ url: this.mempoolHost + req.params[0], action: 'html' });
+      // strip default language code for compatibility
+      const path = req.params[0].replace('/en/', '/');
 
-      res.send(html)
+      let html = await this.cluster?.execute({ url: this.mempoolHost + req.params[0], path: req.params[0], action: 'html' });
+      if (!html) {
+        throw new Error('failed to render preview image');
+      }
+      res.send(html);
     } catch (e) {
       console.log(e);
       res.status(500).send(e instanceof Error ? e.message : e);