nodejs Node.js Stream.pipeline()方法

Node.js Stream.pipeline()方法

原文:https://www . geesforgeks . org/node-js-stream-pipeline-method/

stream.pipeline()方法是一种模块方法，用于链接传递错误的流，并在管道完成时准确清理和提供回调函数。

语法:

stream.pipeline(...streams, callback)

参数:该方法接受两个参数，如上所述，如下所述。

... Stream: These are two or more streams that will be connected together by pipelines.
Callback: This function is called when the pipeline is completely completed. If the pipeline is not completed, "Error" will be displayed.

返回值:返回一个清理函数。

下面的例子说明了 stream.pipeline()方法在 Node.js 中的使用:

例 1:

// Node.js program to demonstrate the     
// stream.pipeline() method

// Including fs and zlib module
var fs = require('fs');
const zlib = require('zlib');

// Constructing finished from stream
const { pipeline } = require('stream');

// Constructing promisify from
// util
const { promisify } = require('util');

// Defining pipelineAsync method
const pipelineAsync = promisify(pipeline);

// Constructing readable stream
const readable = fs.createReadStream("input.text");

// Constructing writable stream
var writable = fs.createWriteStream("output.text");

// Creating transform stream
const transform = zlib.createGzip();

// Async function
(async function run() {
  try{ 

    // pipelining three streams
    await pipelineAsync(
      readable,
      transform,
      writable
    );
    console.log("pipeline accomplished.");
    }

  // Shows error
  catch(err) {
    console.error('pipeline failed with error:', err);
  }
  })();

输出:

Promise {  }
pipeline accomplished.

例 2:

// Node.js program to demonstrate the     
// stream.pipeline() method

// Including fs and zlib module
var fs = require('fs');
const zlib = require('zlib');

// Constructing finished from stream
const { pipeline } = require('stream');

// Constructing promisify from
// util
const { promisify } = require('util');

// Defining pipelineAsync method
const pipelineAsync = promisify(pipeline);

// Constructing readable stream
const readable = fs.createReadStream("input.text");

// Constructing writable stream
var writable = fs.createWriteStream("output.text");

// Creating transform stream
const transform = zlib.createGzip();

// Async function
(async function run() {
  try{ 

    // pipelining three streams
    await pipelineAsync(
      readable,
      writable,
      transform
    );
    console.log("pipeline accomplished.");
    }

  // Shows error
  catch(err) {
    console.error('pipeline failed with error:', err);
  }
  })();

输出:这里，管道传输时，流的顺序不正确，因此出现错误。

Promise {  }
pipeline failed with error: Error [ERR_STREAM_CANNOT_PIPE]: Cannot pipe, not readable
    at WriteStream.Writable.pipe (_stream_writable.js:243:24)
    at pipe (internal/streams/pipeline.js:57:15)
    at Array.reduce ()
    at pipeline (internal/streams/pipeline.js:88:18)
    at Promise (internal/util.js:274:30)
    at new Promise ()
    at pipeline (internal/util.js:273:12)
    at run (/home/runner/ThirstyTimelyKey/index.js:33:11)
    at /home/runner/ThirstyTimelyKey/index.js:45:5
    at Script.runInContext (vm.js:133:20)

参考:https://nodejs . org/API/stream . html # stream _ stream _ pipeline _ streams _ callback。