@apr144/generic-filehandle/esm/blobFile.js

uniform interface for accessing binary data from local files, remote HTTP resources, and browser Blob data

import { Buffer } from 'buffer';
// Using this you can "await" the file like a normal promise
// https://blog.shovonhasan.com/using-promises-with-filereader/
function readBlobAsArrayBuffer(blob) {
    const fileReader = new FileReader();
    return new Promise((resolve, reject) => {
        fileReader.onerror = () => {
            fileReader.abort();
            reject(new Error('problem reading blob'));
        };
        fileReader.onabort = () => {
            reject(new Error('blob reading was aborted'));
        };
        fileReader.onload = () => {
            if (fileReader.result && typeof fileReader.result !== 'string') {
                resolve(fileReader.result);
            }
            else {
                reject(new Error('unknown error reading blob'));
            }
        };
        fileReader.readAsArrayBuffer(blob);
    });
}
function readBlobAsText(blob) {
    const fileReader = new FileReader();
    return new Promise((resolve, reject) => {
        fileReader.onerror = () => {
            fileReader.abort();
            reject(new Error('problem reading blob'));
        };
        fileReader.onabort = () => {
            reject(new Error('blob reading was aborted'));
        };
        fileReader.onload = () => {
            if (fileReader.result && typeof fileReader.result === 'string') {
                resolve(fileReader.result);
            }
            else {
                reject(new Error('unknown error reading blob'));
            }
        };
        fileReader.readAsText(blob);
    });
}
/**
 * Blob of binary data fetched from a local file (with FileReader).
 *
 * Adapted by Robert Buels and Garrett Stevens from the BlobFetchable object in
 * the Dalliance Genome Explorer, which is copyright Thomas Down 2006-2011.
 */
export default class BlobFile {
    constructor(blob) {
        this.blob = blob;
        this.size = blob.size;
    }
    async read(buffer, offset = 0, length, position = 0) {
        // short-circuit a read of 0 bytes here, because browsers actually sometimes
        // crash if you try to read 0 bytes from a local file!
        if (!length) {
            return { bytesRead: 0, buffer };
        }
        const start = position;
        const end = start + length;
        const result = await readBlobAsArrayBuffer(this.blob.slice(start, end));
        const resultBuffer = Buffer.from(result);
        const bytesCopied = resultBuffer.copy(buffer, offset);
        return { bytesRead: bytesCopied, buffer: resultBuffer };
    }
    async readFile(options) {
        let encoding;
        if (typeof options === 'string') {
            encoding = options;
        }
        else {
            encoding = options && options.encoding;
        }
        if (encoding === 'utf8') {
            return readBlobAsText(this.blob);
        }
        if (encoding) {
            throw new Error(`unsupported encoding: ${encoding}`);
        }
        const result = await readBlobAsArrayBuffer(this.blob);
        return Buffer.from(result);
    }
    async stat() {
        return { size: this.size };
    }
    async close() {
        return;
    }
}
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