Refactor PDF data extraction

Hide the FileReader API behind an asnyc function. This makes it
easier to await the result and is less racy.

src/dbp-pdf-preview.js

@@ -10,7 +10,7 @@ import * as commonStyles from '@dbp-toolkit/common/styles';
 import pdfjs from 'pdfjs-dist/es5/build/pdf.js';
 import buildinfo from 'consts:buildinfo';
 import {name as pkgName} from './../package.json';
-import {getPDFSignatureCount} from './utils.js';
+import {getPDFSignatureCount, readBinaryFileContent} from './utils.js';
 
 const i18n = createI18nInstance();
 
@@ -209,36 +209,29 @@ export class PdfPreview extends ScopedElementsMixin(DBPLitElement) {
 
         this.isShowPlacement = isShowPlacement;
         this.isShowPage = true;
-        let reader = new FileReader();
 
-        reader.onload = async () => {
-            //this.isPageLoaded = false;
-            const data = reader.result;
+        const data = await readBinaryFileContent(file);
 
-            // get handle of pdf document
-            try {
-                this.pdfDoc = await pdfjs.getDocument({data: data}).promise;
-            } catch (error) {
-                console.error(error);
-
-                return;
-            }
-
-            // total pages in pdf
-            this.totalPages = this.pdfDoc.numPages;
-            const page = placementData.currentPage || 1;
+        // get handle of pdf document
+        try {
+            this.pdfDoc = await pdfjs.getDocument({data: data}).promise;
+        } catch (error) {
+            console.error(error);
+            return;
+        }
 
-            // show the first page
-            // if the placementData has no values we want to initialize the signature position
-            await this.showPage(page, placementData["scaleX"] === undefined);
+        // total pages in pdf
+        this.totalPages = this.pdfDoc.numPages;
+        const page = placementData.currentPage || 1;
 
-            this.isPageLoaded = true;
+        // show the first page
+        // if the placementData has no values we want to initialize the signature position
+        await this.showPage(page, placementData["scaleX"] === undefined);
 
-            // fix width adaption after "this.isPageLoaded = true"
-            await this.showPage(page);
-        };
+        this.isPageLoaded = true;
 
-        reader.readAsBinaryString(file);
+        // fix width adaption after "this.isPageLoaded = true"
+        await this.showPage(page);
 
         console.log(`Signature count: ${await getPDFSignatureCount(file)}`);
     }

src/utils.js

@@ -81,6 +81,25 @@ export const fabricjs2pdfasPosition = (data) => {
     };
 };
 
+/**
+ * Returns the content of the file
+ *
+ * @param {File} file The file to read
+ * @returns {string} The content
+ */
+export const readBinaryFileContent = async (file) => {
+    return new Promise((resolve, reject) => {
+        let reader = new FileReader();
+        reader.onload = () => {
+            resolve(reader.result);
+        };
+        reader.onerror = () => {
+            reject(reader.error);
+        };
+        reader.readAsBinaryString(file);
+    });
+};
+
 /**
  * Given a PDF file returns the amount of signatures found in it.
  *
@@ -94,22 +113,10 @@ export const getPDFSignatureCount = async (file) => {
     const sigRegex = new RegExp(
         "/Type\\s*/Sig\\s*/Filter\\s*/Adobe.PPKLite\\s*/SubFilter\\s*(/ETSI\\.CAdES\\.detached|/adbe\\.pkcs7\\.detached)",
         "g");
-
-    const promise = new Promise((resolve, reject) => {
-        let reader = new FileReader();
-        reader.onload = async () => {
-            let result = reader.result;
-            let matches = 0;
-            while (sigRegex.exec(result) !== null) {
-                matches++;
-            }
-            resolve(matches);
-        };
-        reader.onerror = async () => {
-            reject(reader.error);
-        };
-        reader.readAsBinaryString(file);
-    });
-
-    return promise;
+    const content = await readBinaryFileContent(file);
+    let matches = 0;
+    while (sigRegex.exec(content) !== null) {
+        matches++;
+    }
+    return matches;
 };
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