Unused prototype objects from V8 FunctionTemplate initialization

[TimothyGu]

• Version: all
• Platform: all
• Subsystem: src

> typeof process.binding('udp_wrap').UDP.prototype.bind6.prototype
'object'

We don't need these prototypes, and we can get rid of them either through v8::FunctionTemplate::RemovePrototype() or indirectly, by specifying v8::ConstructorBehavior::kThrow when creating the v8::FunctionTemplate.

[brandontruggles]

Hello, I'd like to work on this! Any tips on where I should look?

[addaleax]

@brandonrninefive I think Environment::SetMethod, Environment::SetProtoMethod and Environment::SetTemplateMethod in env-inl.h are the relevant places where this would apply.

[brandontruggles]

@addaleax Great! Thank you. I think I've figured out how this works. The udp_wrap binding and its associated prototypes/functions are defined within udp_wrap.cc. From there, I can use RemovePrototype() on FunctionTemplate objects to remove their prototype objects. Furthermore, I can use the Environment methods that you listed above to define methods outside or within prototype objects.

For clarification regarding this exact issue, am I just getting rid of the last prototype object listed in
> typeof process.binding('udp_wrap').UDP.prototype.bind6.prototype ?

Or am getting rid of that prototype and also the prototype object after UDP, and replacing its prototype methods with regular methods defined either by Environment::SetMethod or Environment::SetTemplateMethod?

I appreciate the help, and please let me know if any of my above conclusions are incorrect.

[TimothyGu]

@brandonrninefive My recommendation is that you do not use RemovePrototype(), instead using v8::ConstructorBehavior::kThrow when creating such methods in Environment::SetProtoMethod. (You will need to tweak Environment::NewFunctionTemplate() (decl, impl) to accept a third optional parameter of type v8::ConstructorBehavior, to allow passing this information to V8.) There are several reasons for this:

• This way, not only udp_wrap's classes are fixed but also other bindings. In the original issue, I only used udp_wrap as an example. The same issue applies to all other bindings.
• As a bonus, this would make new (process.binding('udp_wrap').UDP.prototype.bind6)() throw. One should never do something like that in the first place, and since process.binding is considered internal API this makes the code more robust.

With regards to your last question, you are only getting rid of the last prototype. If you look at built-in methods like Number.prototype.toString, you will notice that they don't have a prototype property. That's what we are trying to accomplish here as well.

[brandontruggles]

@TimothyGu Thank you for all the tips! I'm working on implementing this now, and I should have a PR ready over the next few days.