reference: https://nodesource.com/blog/understanding-streams-in-nodejs/
Advantage：
- In a http example, do not need to put all file size into memories anymore
- prevent the low response speed or even crash caused by memory's over-limited
- process one chunk data each time
Principle：
Event Emitter of Node.js
Category：
- readable：可读
- writable：可写
- duplex：双工。可读也可写，互不干扰。
- transform：转换。从可写转成可读，链式调用，做数据处理
Implement：
- native api:
- stream
- fs.createReadStream
- http
- socket
- process.stdin(out)
- zlib.createGzip: one of the most common transform stream
- inherit
to diy your own specific stream:
- inherit class (like Readable)
- redefine _read function
API：
- pipe/unpipe
- pipeline: multiple process in one line
- resume/pause
- push
- event:
readable, data,
error, finish, close, drain
Concept :
- mode: flowing & pause and several related events
- back pressure：背压，eg: 写不进去，wait the drain(下水道) event to continue
Streams Cheat Sheet:
fundamental
practice
flowing
readable & transform
writable & compound
