83 lines
3.3 KiB
Markdown
83 lines
3.3 KiB
Markdown
[](https://travis-ci.org/Borewit/then-read-stream)
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[](https://npmjs.org/package/then-read-stream)
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[](https://npmjs.org/package/then-read-stream)
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[](https://david-dm.org/Borewit/then-read-stream)
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[](https://coveralls.io/github/Borewit/then-read-stream?branch=master)
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[](https://www.codacy.com/app/Borewit/then-read-stream?utm_source=github.com&utm_medium=referral&utm_content=Borewit/then-read-stream&utm_campaign=Badge_Grade)
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[](https://snyk.io/test/github/Borewit/then-read-stream?targetFile=package.json)
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# then-read-stream
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A promise based asynchronous stream reader, which makes reading from a stream easy.
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Allows to read from a [Readable Stream](https://nodejs.org/api/stream.html#stream_readable_streams)
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similar as you would read from a file.
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## Usage
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The `then-read-stream` contains one class: `StreamReader`, which reads from a [stream.Readable](https://nodejs.org/api/stream.html#stream_class_stream_readable).
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### Compatibility
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NPM module is compliant with [ECMAScript 2015 (ES6)](https://www.ecma-international.org/ecma-262/6.0/).
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#### Examples
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In the following example we read the first 16 bytes from a stream and store them in our buffer.
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Source code of examples can be found [here](test/examples.ts).
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```JavaScript
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import * as fs from 'fs';
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import * as path from 'path';
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import { StreamReader } from 'then-read-stream';
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const readable = fs.createReadStream('JPEG_example_JPG_RIP_001.jpg');
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const streamReader = new StreamReader(readable);
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const buffer = Buffer.alloc(16);
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return streamReader.read(buffer, 0, 16)
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.then( bytesRead => {
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// buf, contains bytesRead, which will be 16 if the end-of-stream has not been reached
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});
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```
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With peek you can read ahead:
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```JavaScript
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import * as fs from 'fs';
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import * as path from 'path';
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import { StreamReader } from 'then-read-stream';
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const fileReadStream = fs.createReadStream('JPEG_example_JPG_RIP_001.jpg');
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const streamReader = new StreamReader(fileReadStream);
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const buffer = Buffer.alloc(20);
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return streamReader.peek(buffer, 0, 3)
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.then(bytesRead => {
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if (bytesRead === 3 && buffer[0] === 0xFF && buffer[1] === 0xD8 && buffer[2] === 0xFF) {
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console.log('This is a JPEG file');
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return streamReader.read(buffer, 0, 20); // Read JPEG header
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} else {
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throw Error('Expected a JPEG file');
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}
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})
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.then(bytesRead => {
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if (bytesRead === 20) {
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console.log('Got the JPEG header');
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} else {
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throw Error('Failed to read JPEG header');
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}
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});
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```
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If you have to skip a part of the data, you can use ignore:
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```JavaScript
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return streamReader.ignore(16)
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.then( bytesIgnored => {
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if (bytesIgnored < 16){
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console.log(`Remaining stream length was ${bytesIgnored}, expected 16`);
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}
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});
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```
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