The Perl Conference 2019 in Pittsburgh Lightning Talks

1. Perl5 VS JSON
The Perl Conference 2019 in Pittsburgh - Lightning Talks
Kenta SATO (a.k.a. @karupanerura)

2. Kenta SATO a.k.a. @karupanerura
• PAUSE ID: KARUPA
• TOML::Parser, Time::Strptime, DBD::BlackHole, etc..
• Japan Perl Association - 3rd Representative Director
• Shibuya.pm - Leader
• DeNA, Co,. LTD. - Software Engineer

3. tl;dr
• JSON is de facto standard serialization format for IPC in today
• JSON data type is important for almost other languages
• Typed data schema is great solution for JSON encoding
• JSON::Types is match for simple cases
• Cpanel::JSON::XS::Type is match for almost cases

4. Background

5. Modern Web Application Development
• JavaScript side DOM rendering
• e.g.) React.js, Vue.js, etc..
• Minimam HTML rendering on Server-side application
• Almost data is provided by JSON Web API.

6. JSON is used for many many cases
• Authentication/Authorization
• JWT(JWS), OIDC, etc..
• Mobile (Android/iOS) applications
• (Internal/External) Web APIs
• microservices, customer’s application, etc..

7. JSON is a de facto standard
serialization format for IPC today

8. Perl5 can encode/decode JSON!
JSON::(PP|XS)
Cpanel::JSON::(PP|XS)

9. No problem!

10. Really?

11. JSON encoding

12. JSON value has a type

13. Perl5 value can be 3 container types:
Scalar(SV), Array(AV), Hash(HV)

14. JSON value can be 6 data types:
null, boolean, number,
string, array, object

15. How to translate to JSON's data type
from Perl's container type?

16. Perl5 to JSON
• Hash -> object
• Array -> array
• Scalar(undef) -> null
• Scalar(special boolean blessed object) -> boolean
• Scalar -> number OR string

17. Perl5 to JSON
• Hash -> object
• Array -> array
• Scalar(undef) -> null
• Scalar(special boolean blessed object) -> boolean
• Scalar -> number OR string What’s going on?

18. Scalar to JSON (string|number)
• Looking internal SV flags
• Basic examples:
• PV(Literal: ‘a’) -> “a” (string)
• IV(Literal: 1) -> 1 (number)
• PVIV(Literal: ‘1’) -> “1” (string)

19. Looks like good for almost cases!

20. Really…?

21. Problem: SV flags is changed implicitly
• Too easy to change SV flags implicitly
# Example
my $x = 1; # IV (JSON encoding as number)
print "DEBUG: x = $xn"; # <-- Creates PV slot implicitly!
$x; # PVIV (JSON encoding as string)

22. Problem: JSON typing is important
// Java Script Example
const response = JSON.parse(`{"expiresTime":"3600"}`);
const expiresTime = response.expiresTime;
const nowEpoch = Math.floor(Date.now() / 1000);
const expiresAt = expiresTime + nowEpoch; // concat
console.log(expiresAt); // 3600XXXXXXXX
Strictly typing is serious problem for almost other languages.
Almost static typing languages throw error if type mismatch.
Almost dynamic typing languages change some behaviours
by the data type.

23. It’s too messy…

24. Solutions

25. JSON::Types
• Type annotation likes SV converter for JSON::(PP|XS)
use JSON::XS qw/encode_json/;
use JSON::Types;
my $json = encode_json([bool 0, number 1, string 2]);
say $json; # => [false,1,"2"]

26. Good: JSON::Types
• Very very simple implementation
• Easy to use it :)

27. Bad: JSON::Types
• SHOULD use it ONLY just before encoding
• Because, the converted SVs can be re-changed
• By after processes
• No converter from JSON Schema / OpenAPI (Swagger) / etc

28. Cpanel::JSON::XS::Type
• Typed data structure schema for Cpanel::JSON::XS
use Cpanel::JSON::XS;
use Cpanel::JSON::XS::Type;
my $schema =
[JSON_TYPE_BOOL, JSON_TYPE_INT, JSON_TYPE_STRING];
my $json = encode_json([0, 1, 2], $schema);
say $json; # => [false,1,"2"]

29. Good: Cpanel::JSON::XS::Type
• Never implicitly change the JSON data type
• Don’t look SV flags
• Explicitly type control

30. Bad: Cpanel::JSON::XS::Type
• No converter from JSON Schema / OpenAPI (Swagger) / etc
• Or exists...? (Maybe I don't know yet?)

31. Conclution

32. Conclution
• JSON is de facto standard serialization format for IPC today
• JSON data type is important for almost other languages
• Typed data schema is great solution for JSON encoding
• JSON::Types is match for simple cases
• Cpanel::JSON::XS::Type is match for almost cases

33. Thank you
Executable example codes in the slide
https://gist.github.com/karupanerura/223b2d862f0c0c966e706e7062cb8cc9