postal-mime/src/base64-decoder.js

Email parser for Node.js and browser environments

import { decodeBase64, blobToArrayBuffer } from './decode-strings.js';

export default class Base64Decoder {
    constructor(opts) {
        opts = opts || {};

        this.decoder = opts.decoder || new TextDecoder();

        this.maxChunkSize = 100 * 1024;

        this.chunks = [];

        this.remainder = '';
    }

    update(buffer) {
        let str = this.decoder.decode(buffer);

        str = str.replace(/[^a-zA-Z0-9+\/]+/g, '');

        this.remainder += str;

        if (this.remainder.length >= this.maxChunkSize) {
            let allowedBytes = Math.floor(this.remainder.length / 4) * 4;
            let base64Str;

            if (allowedBytes === this.remainder.length) {
                base64Str = this.remainder;
                this.remainder = '';
            } else {
                base64Str = this.remainder.substr(0, allowedBytes);
                this.remainder = this.remainder.substr(allowedBytes);
            }

            if (base64Str.length) {
                this.chunks.push(decodeBase64(base64Str));
            }
        }
    }

    finalize() {
        if (this.remainder && !/^=+$/.test(this.remainder)) {
            this.chunks.push(decodeBase64(this.remainder));
        }

        return blobToArrayBuffer(new Blob(this.chunks, { type: 'application/octet-stream' }));
    }
}