node.js - Why crypto.createHash() is not writable until setEncoding() is called? -

i use request package crypto. seems request implements legacy stream protocol , don't write data piped destination until it's writable.

stream.prototype.pipe = function(dest, options) {   var source = this;    function ondata(chunk) {     if (dest.writable) {       if (false === dest.write(chunk) && source.pause) {         source.pause();       }     }   } ... 

so, if use next code:

const crypto = require('crypto');  const request = require('request');  var hasher = crypto.createhash('sha256');  // uncomment line below fix! // hasher.setencoding('hex'); console.log(hasher.writable);  request('http://ya.ru').pipe(hasher).on('finish', function() {     console.log('hash is', hasher.read());  }); 

it produces sha256('') (i.e. empty value). when use hasher.setencoding('hex') code produces sha256(<response_body>) , hasher.writable gives true.

i can't understand reason of acting way? , stated in documentation?

finally, there bug in node. here smaller code sample reproduce it:

var hasher = crypto.createhash('sha256');  const _ = hasher._writablestate;  // don't have call .setenconding() here console.log(hasher.writable); 

stream1 implementation required this.writable true in destination stream.

stream.prototype.pipe = function(dest, options) {   var source = this;    function ondata(chunk) {     if (dest.writable) {       if (false === dest.write(chunk) && source.pause) {         source.pause();       }     }   }    source.on('data', ondata);   ... 

calling hasher.setencoding('hex') (or other access this._writablestate) triggered call actual constructor of stream. before this.writable undefined.