* gen_udp and gen_tcp * managing pool of sockets using dynamic supervisors * pattern matching on binary data * sending chunks of data over the socket

1. gen_udp/tcp and data streaming
github.com/stepnivlk
---
Streetbees
(we’re hiring)

2. Why should I even care about gen_*?
● Relatively low-level interface to udp/tcp sockets
● We can control how messages are received
● Socket can be reconfigured on the fly
● Useful when we need to stream binary data to clients
We may need to define chunks of data being sent,
control when we send those chunks
or handle interrupts (my use case - mp3 streaming)
● Allows us to understand how various libraries
work ‘behind curtains’

3. And BTW those are Erlang modules!

4. UDP
● Stateless / No session
● Broken into packets
● Untagged
● No order guarantee
● No ‘receive’ guarantee

5. TCP
● Stateful, connection-based
● Handshake before data sending
● Tagged packets
● Order guarantee
● Receive guarantee
● Multiple communications over
single port
Client
Server

6. Let’s build echoing server

7. NaiveTcp

8. NaiveTcp

9. NaiveTcp

10. (1/9) Wait, what is that <<”quit”, _::binary>>?

11. (2/9)Wait, what is that <<”quit”, _::binary>> ?

12. (3/9) Wait, what is that <<”quit”, _::binary>>?

13. (4/9) Wait, what is that <<”quit”, _::binary>>?

14. (5/9) Wait, what is that <<”quit”, _::binary>>?
The ID3v2 tag size is encoded with four bytes where the most significant
bit (bit 7) is set to zero in every byte, making a total of 28 bits.

15. (6/9) Wait, what is that <<”quit”, _::binary>>?

16. (7/9) Wait, what is that <<”quit”, _::binary>>?

17. (8/9) Wait, what is that <<”quit”, _::binary>>?

18. (9/9) Wait, what is that <<”quit”, _::binary>>?

19. ● Can only handle requests coming one-by-one
● Sequential flow - acceptor sets itself up, then spawns new process
NaiveTcp

20. ● More parallel - pool of processes ready to accept client
● We need supervisor with many acceptor workers
● Supervisor passes listen socket to each worker
BetterTcp

21. Typical Supervisor

22. Dynamic Supervisor

23. Dynamic Supervisor

24. BetterTcpSup (supervisor)

25. BetterTcpSup (supervisor)

26. BetterTcpServ (worker)

27. BetterTcpServ (worker)

28. Ok, what about something real?
Meet my radio project [massive WIP]
● Shoutcast compatible mp3 streaming server
● Each listener has own process and identity
● Based on preferences server picks songs for user and serves it to them
● Underground spotify (think radio23.cz + ektoplazm.com)

29. (1/5) Shoutcast?
Client has access to a server using *.pls file containing information about server itself

30. (2/5) Shoutcast?
Server responds to client with simple informations about itself, mainly data chunk size

31. (3/5) Shoutcast?
Server sends mp3 chunk by chunk to a client. Server has to send mp3 files without any id3 tag

32. (4/5) Shoutcast?
Server sends mp3 chunk by chunk to a client. Server has to send mp3 files without any id3 tag

33. (5/5) Shoutcast?
Server sends mp3 chunk by chunk to a client. Server has to send mp3 files without any id3 tag

35. The end, thx for listening