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Node.js rendering and font diagnostics

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This example shows how to collect the most useful diagnostics for rendering and font investigations in DWS Viewer API.

The script fetches:

  • Document fonts
  • Global fonts
  • Global font substitutions
  • Document information
  • Document properties
  • A rendered preview image for one page

It then saves the results locally so they can be attached to a support ticket or compared across environments.

Prerequisites

  • A DWS Viewer API key in NUTRIENT_DWS_VIEWER_API_KEY
  • A documentId for the file you want to investigate
  • Node.js 18 or later

Complete example

The following code is a complete example. You can copy and paste it into a file named diagnostics.mjs and run it with Node.js:

import { mkdir, writeFile } from "node:fs/promises";
import path from "node:path";


const apiKey = process.env.NUTRIENT_DWS_VIEWER_API_KEY;
const documentId = process.argv[2];
const pageIndex = Number(process.argv[3] ?? 0);
const outputDir = path.resolve(process.argv[4] ?? `./dws-diagnostics-${documentId}`);


if (!apiKey) {
  throw new Error("Missing NUTRIENT_DWS_VIEWER_API_KEY");
}


if (!documentId) {
  throw new Error("Usage: node diagnostics.mjs <documentId> [pageIndex] [outputDir]");
}


await mkdir(outputDir, { recursive: true });


const requestJson = async (pathname) => {
  const response = await fetch(`https://api.nutrient.io${pathname}`, {
    headers: {
      Authorization: `Bearer ${apiKey}`,
      Accept: "application/json",
    },
  });


  if (!response.ok) {
    const errorText = await response.text();
    throw new Error(`${pathname} failed: ${response.status} ${errorText}`);
  }


  return response.json();
};


const requestBinary = async (pathname, accept) => {
  const response = await fetch(`https://api.nutrient.io${pathname}`, {
    headers: {
      Authorization: `Bearer ${apiKey}`,
      Accept: accept,
    },
  });


  if (!response.ok) {
    const errorText = await response.text();
    throw new Error(`${pathname} failed: ${response.status} ${errorText}`);
  }


  return Buffer.from(await response.arrayBuffer());
};


const diagnostics = {
  documentFonts: await requestJson(`/viewer/documents/${documentId}/fonts`),
  globalFonts: await requestJson("/viewer/fonts"),
  fontSubstitutions: await requestJson("/viewer/font_substitutions"),
  documentInfo: await requestJson(`/viewer/documents/${documentId}/document_info`),
  documentProperties: await requestJson(`/viewer/documents/${documentId}/properties`),
};


const previewImage = await requestBinary(
  `/viewer/documents/${documentId}/pages/${pageIndex}/image?width=1600`,
  "image/png",
);


await Promise.all([
  writeFile(
    path.join(outputDir, "document-fonts.json"),
    JSON.stringify(diagnostics.documentFonts, null, 2),
  ),
  writeFile(
    path.join(outputDir, "global-fonts.json"),
    JSON.stringify(diagnostics.globalFonts, null, 2),
  ),
  writeFile(
    path.join(outputDir, "font-substitutions.json"),
    JSON.stringify(diagnostics.fontSubstitutions, null, 2),
  ),
  writeFile(
    path.join(outputDir, "document-info.json"),
    JSON.stringify(diagnostics.documentInfo, null, 2),
  ),
  writeFile(
    path.join(outputDir, "document-properties.json"),
    JSON.stringify(diagnostics.documentProperties, null, 2),
  ),
  writeFile(path.join(outputDir, `page-${pageIndex}.png`), previewImage),
]);


console.log(`Saved diagnostics to ${outputDir}`);

Run the script

Run the script with your API key and a document ID. Optionally, specify a page index (default 0) and an output directory (default ./dws-diagnostics-<documentId>):

Terminal window
export NUTRIENT_DWS_VIEWER_API_KEY=your_api_key_here
node diagnostics.mjs <document_id> 0

Example output directory:

./dws-diagnostics-<document_id>/
├── document-fonts.json
├── document-info.json
├── document-properties.json
├── font-substitutions.json
├── global-fonts.json
└── page-0.png

How to read the output

  • document-fonts.json — Font faces referenced by the document
  • global-fonts.json — Font faces globally available in DWS Viewer API
  • font-substitutions.json — Configured replacement patterns for missing fonts
  • document-info.json — Page count, page sizes, metadata, and permissions
  • document-properties.json — File properties such as byte size, SHA-256, storage type, and password-protection status
  • page-0.png — A server-rendered preview you can compare with what you see in the browser