I am currently exploring ways to save PDF files in local or session storage using Angular.
My current understanding is that we can convert the file into a string by encoding it into base64 before storing it. However, I am unsure about how to retrieve the original blob/file later on.
Is there any recommended library or snippet that simplifies this conversion process? Any insights would be greatly appreciated!
Utilizing the base64Decoder helper provided below, a base64 string can be converted into an ArrayBuffer
/* eslint-disable no-bitwise */
const chars =
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
// Utilizing a lookup table to determine the index.
const lookup = typeof Uint8Array === 'undefined' ? [] : new Uint8Array(256);
for (let i = 0; i < chars.length; i++) {
lookup[chars.charCodeAt(i)] = i;
}
export const encode = (arraybuffer: ArrayBuffer): string => {
const bytes = new Uint8Array(arraybuffer);
let i;
const len = bytes.length;
let base64 = '';
for (i = 0; i < len; i += 3) {
base64 += chars[bytes[i] >> 2];
base64 += chars[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
base64 += chars[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
base64 += chars[bytes[i + 2] & 63];
}
if (len % 3 === 2) {
base64 = base64.substring(0, base64.length - 1) + '=';
} else if (len % 3 === 1) {
base64 = base64.substring(0, base64.length - 2) + '==';
}
return base64;
};
export const decode = (base64: string): ArrayBuffer => {
let bufferLength = base64.length * 0.75;
const len = base64.length;
let i;
let p = 0;
let encoded1;
let encoded2;
let encoded3;
let encoded4;
if (base64[base64.length - 1] === '=') {
bufferLength--;
if (base64[base64.length - 2] === '=') {
bufferLength--;
}
}
const arraybuffer = new ArrayBuffer(bufferLength);
const bytes = new Uint8Array(arraybuffer);
for (i = 0; i < len; i += 4) {
encoded1 = lookup[base64.charCodeAt(i)];
encoded2 = lookup[base64.charCodeAt(i + 1)];
encoded3 = lookup[base64.charCodeAt(i + 2)];
encoded4 = lookup[base64.charCodeAt(i + 3)];
bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
}
return arraybuffer;
};
An example implementation using this helper could be:
import { decode } from '../path-to-your-base64-decoder'
const base64Pdf = // retrieve base64 string pdf
const pdfBlob = new Blob([decode(base64Pdf)]);
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