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Getting Started With
STREAMS IN NODE JS
By:!Kushal Likhi!!Daytime: !Innox Technologies
Streams Vs Full load
WHY? Why do we need streams and why they are great?
Why Streams?
"We should have some ways of connecting programs like garden
hose--screw in another segment when it becomes necessary to
massage data in another way. This is the way of IO also.”!
- Doug McIlroy
❖ Process large amounts of data with least memory footprint.!
❖ Manage Throttle - Producer consumer.!
❖ Separation of concerns, enforces building reusable components with defined behaviour.
3
Understanding Streams
CONCEPTUAL Let’s understand conceptually what streams are in programming world.
The General Idea { readableStream.pipe(writableStream) }
What are Streams? Here we let the data flow in small units from source to destination.
Glacier!Source Of Data!
Readable Stream
Ocean!Target For Data!
Writeable Stream
Pipe!Connection between the streams
Streams: Event Flow
Event : START / READABLE
Source!Readable Stream
Sink!Writable Stream
START COMMUNICATION
Streams: Event Flow
Event : DATA
Source!Readable Stream
Sink!Writable Stream
SENDING DATA
Streams: Event Flow
Event : DATA
Source!Readable Stream
Sink!Writable Stream
SENDING DATA
Streams: Event Flow
Event : END
Source!Readable Stream
Sink!Writable Stream
END COMMUNICATION
Streams: Event Flow
Event : CLOSE
Source!Readable Stream
Sink!Writable Stream
CLOSE COMMUNICATION
Understanding Streams
PROGRAMATICALLY Lets see how we can use them in NodeJS
Some Basics
EVENT EMITTERS
Event Emitters are objects with following methods:!❖ .on(eventName, handler)!❖ .emit(eventName, [optional data])!And Following behaviour:!❖ On call to “on” method it will register a
handler for the specified event.!❖ On call to “emit” method it will call all
registered handlers for specified event.
Streams Implementation❖ Streams are EventEmitters. Or in concrete words
Classes inheriting EventEmitter.!❖ They emit specific events:!
❖ start!❖ data!❖ end, finish!❖ error!❖ pipe, unpipe, drain!
❖ They have specific methods (Common ones):!❖ .pause()!❖ .pipe()!❖ .resume()!❖ .read()!❖ .write()
Readable Stream
❖ Readable streams produce data that can be fed into a writable, transform, or duplex stream by calling .pipe()!
❖ readableStream.pipe(dest);!
❖ Readable streams will emit data events each time they get a "chunk" of data and then they will emit end when they are all finished.
Readable Stream Example
❖ Lets make a program which can print the input strings in new lines and is pipe able in shell.
Example!&!
Demo Time
Writable Stream❖ A writable stream is a stream you
can .pipe() to but not from:!❖ src.pipe(writableStream)!
❖ Examples:!❖ http requests, on the client!
❖ http responses, on the server!
❖ fs write streams!
❖ crypto streams!
❖ tcp sockets!
❖ child process stdin!
❖ process.stdout, process.stderr
Writable stream Implementation❖ Writable streams must implement two functions: !
❖ write!
❖ end !
❖ When you write data to a writable stream it will return either true or false. !
❖ true means cool, keep sending more data with write.!
❖ false means Uh-oh I am backed up -- don't write any more data until I emit drain.
What is?
DUPLEX STREAM Combination of both readable and writable stream.
What is?
TRANSFORM STREAM
Same as Duplex, though their output is derived from input. They transform input to a different form and size output.
What next?
More Complex Examples
Lets see them!
Complex Examples
❖ STREAMS……
Example!&!
Demo Time
–Thank You
“presentation.pipe(audience)”
