feat: core.ToContext(ctx, v) for ctx initialization

[rurirei]

related #831 #841

this brings a method to check and create Instance for ctx, while may someone needs this. (like me ::)

[xiaokangwang]

Hi, I have to revert some of your change: you have created an exported API, which is an unsupported usage and enable so many other unsupported usages.

You shouldn't use

//go:linkname mustToContextForced github.com/v2fly/v2ray-core/v4.mustToContext
func mustToContextForced(ctx context.Context, v *Instance) context.Context

to forcefully export this function into your package to create a context suitable for interact with V2Ray's internal component.
This kind of usage is unsupported and may break at any time.

[rurirei]

@xiaokangwang ok. i don't know how to design a func MustToContext (i see there is a func MustFromContext as i created a similar one), and i wait for your opinion on this pr (sorry for no extra comment for this). you can do your way kindly, thanks.

[xiaokangwang]

The reason I did so is that V2Ray have so many internal components that may change behavior at any time, you shouldn't depend on them remain unchanged. You could develop software that interact with them, but it may stop working any time.

[rurirei]

@xiaokangwang thanks for your explaination.

maybe there is a purpose to make a public ToContext(ctx, v) for go test.

v2ray-core/app/proxyman/outbound/handler_test.go

Line 70 in 1822504

ctx := context.WithValue(context.Background(), v2rayKey, v)