NodeJs

Introduction

• You cannot find ready-made solutions for every occasion, but if you understand inner mechanismsof a complex system, you will be able to analyze and critically evaluate other people's experience and come at your own conclusions.

• Concepts covered here:

  • Buffers
  • Streams
  • File system
  • Event emitters
  • Module system
  • HTTP, HTTPS, HTTP/2
  • NET
  • UDP/Datagram - sockets
  • DNS
  • OS, Path
  • Child Processes, Worker Threads
  • Deploying
  • Debugging
  • Async and Perf hooks.
  • N-API
  • V8
  • WASI

What is NodeJS?

• Built in Cpp
• A nodejs app runs in a single process, without creating a new thread for every request.
• Provides a set of asynchronous i/o primitives in its standard library that prevent Js code from blocking.
• Libraries in nodejs are written using non-blocking paradigms, making blocking the exception rather than the norm.
• Allows node to handle thousands of concurrent connections with a single server without introducing burden of managing thread concurrency.
• Javascript Engine - convert Js to Binary.
• V8 - introduced by Google.
• ECMAScript - javascript language specification.
• Embed V8 into your source code.
• Dependencies:
  • Libuv - C library, abstract non-blocking I/O ops to a consistent interface cross all supported platforms.
  • V8 -
  • Llhttp
  • C-ares
  • OpenSSL
  • Zlib
• Event Loop
• Setting to production:
  • logging kept at a minimum, essential level
  • more caching levels take place to optimise performance as opposed to recompilation.

EventEmitter

• is a module that facilitates communication/interaction between objects in Node.
• core of Node asynchronous event-driven architecture, many of node's built-in inherit from EventEmitter including Express.js
• Emitter objects emit named events that cause previously registered listeners to be called.
• So an emitter object basically has two main features
  • Emitting name events.
  • Registering and unregistering listener functions.
• MyEmitter.on('eventname', c1)
• MyEmitter.emit('eventname')

Buffers

• understand binary, decimals, hexadecimals.
• container that takes in data of some fixed length then sends it out.
• way to deal with raw binary data.
• always fixed size.
• great understanding of encodings.
• Each character in Hex is 4bits.

File System

• sequence of bits and depending on encoding could represent different things.
• file data - metadata of a file.
• Three ways to create a file
  • Promises API.
  • Callback API.
  • Synchronous API - blocks main thread.
• Async generator / iterator.
• Open - save a file descriptor.
• Watch functionality.

Streams

• Defn: An abstract interface for working with streaming data in Node.js.
• Data streaming.
• Writable streams
• Readable streams
• Duplex / Transform Streams
• create file -> create writestream -> create buffer -> point stream to buffer.
• 16KB chunks.
• Internal buffer - 16384 bytes, (stream.writableHighWaterMark), (stream.writableLength) - get filled space in buffer.
• Has events, properties and methods to it.
• reduce number of writes as waiting for buffer to fill before writing out.
• Drain before writing more.
• Read and Write streams have one internal buffer.
• writableLength should never be larger than writableHighWaterMark as this will lead to extreme buffering.
• Watch and compare memory impact of different implementations.
• Duplex Stream - Has Readable Internal buffer, Writable Internal buffer.
• Transform Stream --> read from Readable buffer process data then write to Writable buffer.

Networking

• Networking card come with unique MAC address. hex number.
• packet - data container. sent via switch to other computer.
• source and destination fields on the packet.
• Routers - work with IP addresses(unique to each device on network).
• Internet Service Provider (ISP)
• 127.0.0.1 - loop back address / localhost.
• Ports on addresses have to be configured to do sth.
• Network Layers
  • Physical layer --> Cable, Bits, Signal, Binary Transmission.
  • Data Link layer --> Cable, Frames, MAC Addresses
  • Network layer --> IP Addresses, Packets, Path Determination
  • Transport layer --> Segments, End-to-End connections, UDP/TCP
  • Application layer --> Data

• OSI Model

• current cables can move upto 1GB per second.
• net module base of all networking on node.
• TCP
  • data is received as exactly it was sent.
  • three way handshake
  • Headers
    • source port.
    • destination port(16 bits)
    • sequence number(32 bits)
    • ack numbers(32 bits)
    • Other headers
• UDP
  • Headers
    • source port(16 bits)
    • destination port(16 bits)
    • segment length(16 bits)
    • checksum(16 bits)
  • data prefers speed, highly lossy data, video, audio.