Added onUsed and wrapper support

[PlasmaPower]

Yet another wrapper implementation. Created this to play with the idea. Requires koajs/compose#53 to work.

[jonathanong]

what's the pros and cons with #694? seems quite convoluted.

@koajs anyone have opinions on this or #694?

[PlasmaPower]

@jonathanong Pros:

• It will be a lot easier for profilers to generate a tree of middleware
• Middleware can be converted before any request arrives, speeding things up
• The onUsed API is more general than just wrapping, and could be used for other things

Cons:

• The most complicated option

[codecov-io]

Current coverage is 54.27%

Merging #707 into v2.x will decrease coverage by 45.73%

@@               v2.x    #707   diff @@
=======================================
  Files             4       4          
  Lines           414     339    -75   
  Methods          80       0    -80   
  Branches         99      96     -3   
=======================================
- Hits            414     184   -230   
- Misses            0     153   +153   
- Partials          0       2     +2   

Powered by Codecov. Last updated by d47d0f9...72c8318

[PlasmaPower]

@jonathanong I added tests for nested middleware, look good?

[PlasmaPower]

I've rebased this to v2.x, but actual server tests will still fail until koajs/compose#53 is merged.

[jonathanong]

would really love more people to express their opinion :)

[miwnwski]

I'll just close this as it has little relevance today IMO. Maybe there's still a need for wrappers but I doubt it personally and the same functionality can be approached in user land. Also, over the years I haven't really seen any requests for wrappers. If I remember correctly, this was brought to light due to TJ's original issue to simplify mw profiling, though today this can be solved with async_hooks which seems more like native approach Koa should aim towards. Please reopen if I'm wrong :)