Buffer and transform the n first bytes of a stream
npm install first-chunk-stream> Buffer and transform the n first bytes of a stream
``sh`
npm install first-chunk-stream
`js
import fs from 'node:fs';
import getStream from 'get-stream';
import FirstChunkStream from 'first-chunk-stream';
import {uint8ArrayToString} from 'uint8array-extras';
// unicorn.txt => unicorn rainbow
const stream = fs.createReadStream('unicorn.txt')
.pipe(new FirstChunkStream({chunkSize: 7}, async (chunk, encoding) => {
return uint8ArrayToString(chunk).toUpperCase();
}));
const data = await getStream(stream);
if (data.length < 7) {
throw new Error('Couldn\'t get the minimum required first chunk length');
}
console.log(data);
//=> 'UNICORN rainbow'
`
FirstChunkStream constructor.
#### transform(chunk, encoding)
Type: Function
Async function that receives the required options.chunkSize bytes.
Expected to return an buffer-like object or string or object of form {buffer: Uint8Array, encoding: string} to send to stream or firstChunkStream.stop to end stream right away.
An error thrown from this function will be emitted as stream errors.
Note that the buffer can have a smaller length than the required one. In that case, it will be due to the fact that the complete stream contents has a length less than the options.chunkSize value. You should check for this yourself if you strictly depend on the length.
`js
import FirstChunkStream from 'first-chunk-stream';
new FirstChunkStream({chunkSize: 7}, async (chunk, encoding) => {
return chunk.toString(encoding).toUpperCase(); // Send string to stream
});
new FirstChunkStream({chunkSize: 7}, async (chunk, encoding) => {
return chunk; // Send buffer to stream
});
new FirstChunkStream({chunkSize: 7}, async (chunk, encoding) => {
return {
buffer: chunk,
encoding: encoding,
}; // Send buffer with encoding to stream
});
new FirstChunkStream({chunkSize: 7}, async (chunk, encoding) => {
return FirstChunkStream.stop; // End the stream early
});
new FirstChunkStream({chunkSize: 7}, async (chunk, encoding) => {
throw new Error('Unconditional error'); // Emit stream error
});
`
#### options
Type: object
The options object is passed to the Duplex stream constructor allowing you to customize your stream behavior. In addition, you can specify the following option:
###### chunkSize
Type: number`
The number of bytes to buffer.