Introduction to Stream Module in Stream and how to use streams for data processing

1. Stream module in

• The basic concept of flow：
• Stream is an abstract interface used to process streaming data.
• It is an efficient data processing mechanism suitable for handling large files or high data throughput scenarios.
• There are four main types of streams:
  • Readable: Readable stream, used to read data from source (such as files, HTTP responses).
  • Writable: Writable stream, used to write data to the target (such as files, HTTP requests).
  • Duplex: Bilateral streams, both readable and writable (such as TCP sockets).
  • Transform: Converted stream, a special bilateral stream that converts data (such as compressed streams) during writing and reading.

2. How to use streams for data processing

Basic example: Read file content and write to console

const fs = require('fs');
const http = require('http');
const url = '';
// Create a readable stream to read the fileconst readableStream = ('');
// Create a writable stream to write to the consoleconst writableStream = ;
// Pipe the readable stream to the writable stream(writableStream);

Code parsing

• Create a readable stream that is used to read the file contents.
• is a default writable stream for outputting data to the console.
• .pipeThe method is the core feature of a stream, which is used to pass the output of one stream directly to another stream as input, efficiently without additional memory buffering.

Advanced example: Read data from HTTP requests and write files

const https = require('https');
const fs = require('fs');
// Create a write stream to save data to local fileconst fileStream = ('');
// Initiate HTTP request(url, (response) => {
  // Pipe the readable stream of HTTP response to the file to the write stream  (fileStream);
  // Listen to complete events  ('end', () => {
    ('The file download is complete!  ');
  });
});

Data transformation using Transform streams

const zlib = require('zlib');
const fs = require('fs');
// Create a readable stream (compressed file)const gzipStream = ('');
// Create a decompression streamconst unzip = ();
// Create a writable stream (decompressed file)const outStream = ('');
// Process flow through pipeline(unzip).pipe(outStream);

3. Rational use suggestions

Processing large files with stream

• When dealing with super large files, avoid loading the entire file into memory, and use stream chunking instead.
• Example: Extracting data from a large CSV file

const fs = require('fs');
const parse = require('csv-parse');
const parser = parse({ delimiter: ',' });
const readableStream = ('large_dataset.csv');
(parser);
('data', (row) => {
  (row); // Process each row of data});
('end', () => {
  ('The processing is completed!  ');
});

Used in combination with third-party modules

• Stream can be used withrequest-promise、fastifyThe modules are used in conjunction with each other to achieve efficient network communication and data transmission.
• Example: Receive video streams and save them through the API

const request = require('request');
const fs = require('fs');
('/video')
  .pipe(('video.mp4'))
  .on('finish', () => {
    ('The video download is completed!  ');
  });

Implement flow multiplexing

• passpumpThe module securely connects multiple streams to ensure the integrity of the stream in error and shutdown.
• Example:

const pump = require('pump');
const fs = require('fs');
const http = require('http');
const server = ((req, res) => {
  const fileStream = ('');
  pump(fileStream, res, (err) => {
    if (err) {
      ('Streaming error:', err);
    }
  });
});
(3000);

4. Points to be noted in actual development

Error handling

• Always listen to streamserrorEvents to avoid uncaught exceptions causing program crash.
• Example:

const readable = ('');
('error', (err) => {
  ('An error occurred while reading the file:', err);
});

Resource Management

• Make sure to call after the stream is used.destroy()Method orpumpAllow modules to release resources to prevent memory leakage.
• Example:

const stream = ('');
('finish', () => {
  (); // Free up resources});

Avoid blocking event loops

• The flow operation is asynchronous, ensuring proper buffering and backpressure mechanisms to avoid event loops being blocked.
• Example: UsehighWaterMarkLimit buffer size

const readable = ('', { highWaterMark: 1024 * 1024 }); // 1MB

Performance optimization

• Using streamingpipeThe method can significantly improve performance because it is optimized in-built.
• Manually process streaming data events when needed (e.g.data、end) to implement more complex logic.

5. Summary

• flowIt is one of the core mechanisms for medium and efficient data processing, suitable for large files and high throughput scenarios.
• Read/write streams, pipe operations, convert streamsis the main way to use streams.
• In actual development, we must make rational use of the advantages of flow, and pay attention to details such as error handling, resource management, and performance optimization.

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