How to create streams from string in Node Js

Question

I am using a library  ya-csv  that expects either a file or a stream as input  but I have a string   How do I convert that string into a stream in Node

User · Answer

I got tired of having to re-learn this every six months, so I just published an npm module to abstract away the implementation details:

https://www.npmjs.com/package/streamify-string

This is the core of the module:

const Readable = require('stream').Readable;
const util     = require('util');

function Streamify(str, options) {

  if (! (this instanceof Streamify)) {
    return new Streamify(str, options);
  }

  Readable.call(this, options);
  this.str = str;
}

util.inherits(Streamify, Readable);

Streamify.prototype._read = function (size) {

  var chunk = this.str.slice(0, size);

  if (chunk) {
    this.str = this.str.slice(size);
    this.push(chunk);
  }

  else {
    this.push(null);
  }

};

module.exports = Streamify;

str is the string that must be passed to the constructor upon invokation, and will be outputted by the stream as data. options are the typical options that may be passed to a stream, per the documentation.

According to Travis CI, it should be compatible with most versions of node.

User · Answer

JavaScript is duck-typed  so if you just copy a readable stream s API  it ll work just fine  In fact  you can probably not implement most of those methods or just leave them as stubs  all you ll need to implement is what the library uses  You can use Node s pre-built EventEmitter class to deal with events  too  so you don t have to implement addListener and such yourself   Here s how you might implement it in CoffeeScript     class StringStream extends require  events   EventEmitter   constructor    string  - gt  super      readable  true   writable  false    setEncoding  - gt  throw  not implemented    pause  - gt       nothing to do   resume  - gt      nothing to do   destroy  - gt     nothing to do   pipe  - gt  throw  not implemented     send  - gt       emit  data    string      emit  end    Then you could use it like so   stream   new StringStream someString doSomethingWith stream stream send

User · Answer

Edit  Garth s answer is probably better   My old answer text is preserved below     To convert a string to a stream  you can use a paused through stream   through   pause   queue  your string   end     Example   var through   require  through       Create a paused stream and buffer some data into it  var stream   through   pause   queue  your string   end       Pass stream around  callback null  stream      Now that a consumer has attached  remember to resume the stream  stream resume

User · Answer

Just create a new instance of the stream module and customize it according to your needs   var Stream   require  stream    var stream   new Stream     stream pipe   function dest      dest write  your string      return dest      stream pipe process stdout      in this case the terminal  change to ya-csv   or  var Stream   require  stream    var stream   new Stream     stream on  data   function data      process stdout write data      change process stdout to ya-csv      stream emit  data    this is my string

User · Answer

Do not use Jo Liss s resumer answer  It will work in most cases  but in my case it lost me a good 4 or 5 hours bug finding  There is no need for third party modules to do this    NEW ANSWER   var Readable   require  stream   Readable  var s   new Readable   s push  beep         the string you want s push null          indicates end-of-file basically - the end of the stream   This should be a fully compliant Readable stream  See here for more info on how to use streams properly   OLD ANSWER  Just use the native PassThrough stream   var stream   require  stream   var a   new stream PassThrough   a write  your string   a end    a pipe process stdout     piping will work as normal   stream on  data   function x          using the  data  event works too    console log  data   x         setTimeout function           you can even pipe after the scheduler has had time to do other things    a pipe process stdout     100     a on  end   function         console log  ended      the end event will be called properly      Note that the  close  event is not emitted  which is not required by the stream interfaces

User · Answer

Another solution is passing the read function to the constructor of Readable  cf doc stream readeable options   var s   new Readable  read size        this push  your string here       this push null           you can after use s pipe for exemple

User · Answer

Heres a tidy solution in TypeScript   import   Readable   from  stream   class ReadableString extends Readable       private sent   false      constructor          private str  string                 super                read             if   this sent                this push Buffer from this str                this sent   true                   else               this push null                     const stringStream   new ReadableString  string to be streamed

User · Answer

As  substack corrected me in  node  the new streams API in Node v10 makes this easier  const Readable   require  stream   Readable  const s   new Readable    s  read        gt         redundant  see update below s push  your text here    s push null        after which you can freely pipe it or otherwise pass it to your intended consumer  It s not as clean as the resumer one-liner  but it does avoid the extra dependency   Update  in v0 10 26 through v9 2 1 so far  a call to push directly from the REPL prompt will crash with a not implemented exception if you didn t set  read  It won t crash inside a function or a script  If inconsistency makes you nervous  include the noop

User · Answer

From node 10 17  stream Readable have a from method to easily create streams from any iterable  which includes array literals    const   Readable     require  stream    const readable   Readable from   input string     readable on  data    chunk    gt      console log chunk     will be called once with   input string        Note that at least between 10 17 and 12 3  a string is itself a iterable  so Readable from  input string   will work  but emit one event per character  Readable from   input string    will emit one event per item in the array  in this case  one item    Also note that in later nodes  probably 12 3  since the documentation says the function was changed then   it is no longer necessary to wrap the string in an array   https   nodejs org api stream html stream stream readable from iterable options

User · Answer

in coffee-script   class StringStream extends Readable   constructor    str  - gt      super       read   size  - gt       push  str      push null   use it   new StringStream  text here   pipe stream1  pipe stream2

User · Answer

There s a module for that  https   www npmjs com package string-to-stream  var str   require  string-to-stream   str  hi there   pipe process stdout       gt   hi there

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