@sounisi5011/stream-transform-from
v1.1.1
Published
Create a transform stream from an async iterator
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@sounisi5011/stream-transform-from
Create a transform stream from an async iterator. This is the last piece needed to convert between streams and async iterators/generators.
Features
No dependencies
This package uses only the Node.js built-in
stream.Transform
class.Strict type definition
The exact type definitions for arguments and return values will be generated based on the
objectMode
option.Encoding arguments can be used
You can use
encoding
, which is passed as the second argument of thetransform._transform()
method. This allows you to safely convert a string toBuffer
object.
Installation
npm install @sounisi5011/stream-transform-from
yarn add @sounisi5011/stream-transform-from
pnpm add @sounisi5011/stream-transform-from
Usage
Convert Buffer
objects
const fs = require('fs');
const stream = require('stream');
const { transformFrom } = require('@sounisi5011/stream-transform-from');
stream.pipeline(
fs.createReadStream('input.txt', 'utf8'),
transformFrom(async function*(source) {
for await (const { chunk } of source) {
yield chunk.toString('utf8').toUpperCase();
}
}),
fs.createWriteStream('output.txt'),
error => {
if (error) {
console.error(error);
} else {
console.log('done!');
}
}
);
Convert any type value
const stream = require('stream');
const { transformFrom } = require('@sounisi5011/stream-transform-from');
stream.pipeline(
stream.Readable.from([1, 2, 3]),
transformFrom(
async function*(source) {
for await (const { chunk } of source) {
yield chunk + 2;
}
},
{ objectMode: true }
),
// ...
error => {
if (error) {
console.error(error);
} else {
console.log('done!');
}
}
);
Convert string to Buffer
using encoding
const stream = require('stream');
const { transformFrom } = require('@sounisi5011/stream-transform-from');
stream.pipeline(
// ...
transformFrom(
async function*(source) {
for await (const { chunk, encoding } of source) {
if (typeof chunk === 'string') {
yield Buffer.from(chunk, encoding);
}
}
},
{ writableObjectMode: true }
),
// ...
error => {
if (error) {
console.error(error);
} else {
console.log('done!');
}
}
);
API
const { transformFrom } = require('@sounisi5011/stream-transform-from');
// The return value is a Transform stream.
const transformStream = transformFrom(
async function*(source) {
// `source` is `AsyncIterableIterator<{ chunk: Buffer, encoding: BufferEncoding }>`
// or `AsyncIterableIterator<{ chunk: unknown, encoding: BufferEncoding }>` type
// The value returned by `yield` keyword will be passed as the first argument of `transform.push()` method.
},
// The second argument is an options for the Transform stream.
// The options are passed to the constructor function of the Transform class.
// However, the following fields are not allowed:
// + `construct`
// + `read`
// + `write`
// + `writev`
// + `final`
// + `destroy`
// + `transform`
// + `flush`
// The fields listed above will be ignored if specified.
{}
);