node.js Stream writable.end()用法及代码示例

writable.end()方法是Stream模块的内置应用程序编程接口，因此不再可以将更多数据写入Writable。参数块和编码是可选的，这将允许在关闭流之前立即写入一个最终的新数据块。此外，可选的回调函数被添加为可写流的“完成”事件的侦听器。

用法:

writable.end( chunk, encoding, callback)

参数：此方法接受上述和以下所述的三个参数：

• chunk:它是要写入的可选数据。块的值必须是字符串，缓冲区或Uint8Array。对于对象模式，块值可以是null以外的任何值。
• encoding:如果块是字符串值，它将保存编码值。
• callback:它是流的可选回调函数。

返回值：它返回在调用此方法之前写入的数据，如果end()方法具有大量新数据，则该数据也将在最后返回。

以下示例说明了Node.js中writable.end()方法的使用：

范例1：

// Node.js program to demonstrate the      
// writable.end() method   
  
// INcluding stream module 
const stream = require('stream'); 
  
// Creating a stream and creating  
// a write function 
const writable = new stream.Writable({ 
  
  // Write function with its  
  // parameters 
  write:function(chunk, encoding, next) { 
  
    // Converting the chunk of 
    // data to string 
    console.log(chunk.toString()); 
    next(); 
  } 
}); 
  
// Writing data 
writable.write('hi'); 
  
// Calling end method with its  
// all the parameters 
writable.end("last data", "utf8", () => { 
     console.log("Writable stream ended!"); 
});

输出：

hi
last data
Writable {
  _writableState:
   WritableState {
     objectMode:false,
     highWaterMark:16384,
     finalCalled:false,
     needDrain:false,
     ending:true,
     ended:true,
     finished:false,
     destroyed:false,
     decodeStrings:true,
     defaultEncoding:'utf8',
     length:0,
     writing:false,
     corked:0,
     sync:false,
     bufferProcessing:false,
     onwrite:[Function:bound onwrite],
     writecb:null,
     writelen:0,
     bufferedRequest:null,
     lastBufferedRequest:null,
     pendingcb:2,
     prefinished:true,
     errorEmitted:false,
     emitClose:true,
     autoDestroy:false,
     bufferedRequestCount:0,
     corkedRequestsFree:
      { next:null,
        entry:null,
        finish:[Function:bound onCorkedFinish] } },
  writable:false,
  _write:[Function:write],
  domain:null,
  _events:
   [Object:null prototype] {
     finish:{ [Function:bound onceWrapper] listener:[Function] } },
  _eventsCount:1,
  _maxListeners:undefined }
Writable stream ended!

范例2：

// Node.js program to demonstrate the      
// writable.end() method   
  
// INcluding stream module 
const stream = require('stream'); 
  
// Creating a stream and creating  
// a write function 
const writable = new stream.Writable({ 
  
  // Write function with its  
  // parameters 
  write:function(chunk, encoding, next) { 
  
    // Converting the chunk of 
    // data to string 
    console.log(chunk.toString()); 
    next(); 
  } 
}); 
  
// Writing data 
writable.write('hi'); 
  
// Calling end method with its  
// all the parameters 
writable.end("last data", "utf8", () => { 
     console.log("Writable stream ended!"); 
}); 
writable.write('GfG');

输出：

hi
last data
Error [ERR_STREAM_WRITE_AFTER_END]:write after end
    at writeAfterEnd (_stream_writable.js:248:12)
    at Writable.write (_stream_writable.js:296:5)
    at /home/runner/LuxuriousLegitimateObservation/index.js:30:10
    at Script.runInContext (vm.js:133:20)
    at Object. (/run_dir/interp.js:156:20)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)Writab
le stream ended!

此处显示错误，因为在end()方法之后调用了write()方法，这是不可能的。

参考： https://nodejs.org/api/stream.html#stream_writable_end_chunk_encoding_callback