Using SCTP with Scamper and Netty

Using SCTP with Scamper and NettyUsing SCTP with Scamper and Netty
Tim BoudreauTim Boudreau
http://timboudreau.comhttp://timboudreau.com
October 2015October 2015

What is SCTP?What is SCTP?
●
Stream control transmission protocol
●
Alternative to TCP
–
Yes, that far down the network stack!
●
Message-oriented like UDP
●
Multiple streams per connection
–
No“head of line” blocking
●
Multiple addresses per connection
●
Heartbeats built-in

Why SCTP?Why SCTP?
●
Designed for multimedia & telephony
●
But good for anything message-oriented
–
Metrics / logging data in particular
●
Supported by most OS's
–
Need lksctp-tools on Linux

Anatomy of an SCTP connectionAnatomy of an SCTP connection
●
Multiple“channels” per connection
–
Send data in sequence on a channel
–
Does not block sends on other channels
●
Association – endpoint = more than one
socket address
–
Will take the shortest path
–
Provides network-level fault tolerance

What That MeansWhat That Means
●
You can decide if you care about message-order
●
Messages don't (have to) block each other
●
Messages are either completely delivered or not
–
The application doesn't have to deal with partial messages
●
Message size not limited (unlike UDP)
●
Reliable (unlike UDP)
●
Heartbeat built-in

Why isn't SCTP more used?Why isn't SCTP more used?
●
People use what they know
●
Home routers don't always support it well via
NAT
–
Not a problem for server-server communication

Use Case – statsd-like metricsUse Case – statsd-like metrics
●
Etsy's Statsd is a popular daemon for collecting real-time
metrics
●
Receives fire-and-forget small UDP packets that update
counters, etc.
●
Statsd stores them in a back-end for visualization &
reporting

Statsd issuesStatsd issues
●
You don't know if a UDP packet was
delivered
●
Packet size must be < network MTU
–
Or the packet may be silently dropped
●
Connection not redundant

SCTP Support in JavaSCTP Support in Java
●
Very low-level
–
com.sun.nio.sctp.SctpChannel
●
Complete but hard to work with
–
Implement message loop, handlers
–
Typical NIO network API

SCTP Support in NettySCTP Support in Netty
●
Also low-level
–
But better abstractions for writing async servers
–
Buffer memory pooling to reduce allocation and
other goodies
–
Still low-level

Why Scamper?Why Scamper?
●
I wanted some higher level abstractions
●
Writing asynchronous servers doesn't have to
feel like doing something hard
–
Follow the NodeJS model: Build a highly
concurrent system out of small blocks of simple
synchronous code

Scamper – Higher Level
Abstractions
Scamper – Higher Level
Abstractions
●
Messages are objects
●
Protocols are simple to write
–
5 byte message header + payload
●
Compression & encryption can be layered on top of any
protocol
●
Standards-based wire-format for messages
–
BSON / JSON / Java serialization / roll-your-own

Scamper – DetailsScamper – Details
Determines payload encoding –
BSON, JSON, Serializaton +/-
compression or encryption.
You define message types, map them to object classes.
The payload, which is encoded/decoded for you
public static final MessageType WHAT_TIME_IS_IT = new
MessageType("dateQuery", 1, 1);
public static final MessageType THE_TIME_IS = new
MessageType("dateResponse", 1, 2);
new SctpServerAndClientBuilder("datedemo")
.bind(WHAT_TIME_IS_IT, DateQueryHandler.class)
.bind(THE_TIME_IS, DateResponseHandler.class)
.start();

Using ScamperUsing Scamper
●
Define some POJOs (or use a Map)
●
Write a handler to receive POJOs
●
Register a MessageType
–
2 shorts, and a name (for logging)
–
Identifies which handler should be called with the message
●
Create an SctpServerAndClientBuilder
●
Bind MessageType+Handler pairs
●
Start the server, or retrieve a Sender if a client

Demo
A trivial client + serverA trivial client + server

Writing a Message TypeWriting a Message Type
public static final MessageType THE_TIME_IS = new
MessageType("dateResponse", 1, 2);
●
The 1 and 2 are message identifiers – you define them (16 bit Java
shorts)
●
The name is just for logging (not sent over the wire)
●
To create a message:
Message<DateResponse> msg = THE_TIME_IS.newMessage(new
DateResponse());
sender.send(address, msg);

Writing a Message HandlerWriting a Message Handler
●
Says what type it takes in its constructor
●
Implements onMessage() to receive POJOS
●
Can reply with a new message
static class DateResponseHandler extends MessageHandler<Map, DateRecord> {
DateResponseHandler() {
super(DateRecord.class);
}
public Message<Map> onMessage(Message<DateRecord> data, ChannelHandlerContext
ctx) {
System.out.println("RECEIVE " + new Date(data.body.when) + " from "
+ctx.channel().remoteAddress());
return null; //we could reply here
}
}
public static class DateRecord implements Serializable {
public long when = System.currentTimeMillis();
}

Is It Baked Yet?Is It Baked Yet?
●
The things that work, work
●
Uses pre-release Netty 5
–
Which has been very stable
●
Getting multi-homing working on a branch
●
In-progress patches for Netty for One-to-Many
support

Scamper – How to Get ItScamper – How to Get It
●
Maven dependency :
<dependency>
<groupId>com.mastfrog</groupId>
<artifactId>scamper</artifactId>
<version>1.3-dev</version>
</dependency>
●
Need my maven repo in your pom.xml
–
Follow instructions here: http://timboudreau.com/builds
–
Will be in Maven central Real Soon Now[tm]

LinksLinks
●
Sources: https://github.com/timboudreau/scamper
●
Info: http://timboudreau.com/blog/sctp/
●
Chat Demo:
https://github.com/timboudreau/scamper-chat
●
Maven repo: http://timboudreau.com/builds/
●
Me: http://timboudreau.com @kablosna

According to the RFCAccording to the RFC
●
Acknowledged error-free non-duplicated transfer of user
data
●
Data fragmentation to conform to discovered path MTU size
●
Sequenced delivery of user messages within multiple
streams, with an option for order-of-arrival delivery of
individual user messages
●
Optional bundling of multiple user messages into a single
SCTP packet, and
●
Network-level fault tolerance through supporting of multi-
homing at either or both ends of an association.

Using SCTP with Scamper and Netty

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