issues/266: use http.Handler as the http middleware instead of http.HandlerFunc

[komuw]

What:

• Use http.Handler as the http middleware instead of http.HandlerFunc
• With this change, a middleware accepts a http.Handler and returns a http.HandlerFunc.
  This is more in line with the mantra; accept interfaces, return concrete types

Why:

• http.Handler is a more idiomatic middleware since it is an interface whereas http.HandlerFunc is an implementation of that interface
• Fixes use http.Handler instead of http.HandlerFunc #266

Benchmarks:

func oneMiddleware(wrappedHandler http.HandlerFunc) http.HandlerFunc {
	count := 0
	return func(w http.ResponseWriter, r *http.Request) {
		count = count + 1
		r.Header.Set("MY-COUNT", fmt.Sprint(count))
		wrappedHandler(w, r)
	}
}

func twoMiddleware(wrappedHandler http.Handler) http.HandlerFunc {
	count := 0
	return func(w http.ResponseWriter, r *http.Request) {
		count = count + 1
		r.Header.Set("MY-COUNT", fmt.Sprint(count))
		wrappedHandler.ServeHTTP(w, r)
	}
}

func threeMiddleware(wrappedHandler http.Handler) http.Handler {
	count := 0
	return http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			count = count + 1
			r.Header.Set("MY-COUNT", fmt.Sprint(count))
			wrappedHandler.ServeHTTP(w, r)
		},
	)
}

go test -benchmem -run=^$ -bench ^BenchmarkMid$ github.com/komuw/ong/mux -count=5
BenchmarkMid/oneMiddleware-8      358.7 ns/op
BenchmarkMid/oneMiddleware-8      371.8 ns/op
BenchmarkMid/oneMiddleware-8      343.6 ns/op
BenchmarkMid/oneMiddleware-8      289.0 ns/op
BenchmarkMid/oneMiddleware-8      291.4 ns/op

BenchmarkMid/twoMiddleware-8      296.7 ns/op
BenchmarkMid/twoMiddleware-8      353.3 ns/op
BenchmarkMid/twoMiddleware-8      363.2 ns/op
BenchmarkMid/twoMiddleware-8      366.2 ns/op
BenchmarkMid/twoMiddleware-8      315.2 ns/op

BenchmarkMid/threeMiddleware-8    299.0 ns/op
BenchmarkMid/threeMiddleware-8    307.6 ns/op
BenchmarkMid/threeMiddleware-8    324.9 ns/op
BenchmarkMid/threeMiddleware-8    367.6 ns/op
BenchmarkMid/threeMiddleware-8    373.3 ns/op

The change we want is twoMiddleware and it seems competitive with the others.

[codecov-commenter]

Codecov Report

Patch coverage: 96.66% and project coverage change: +0.48 🎉

Comparison is base (ce5ce80) 77.58% compared to head (1b6c919) 78.06%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #269      +/-   ##
==========================================
+ Coverage   77.58%   78.06%   +0.48%     
==========================================
  Files          36       36              
  Lines        3337     3360      +23     
==========================================
+ Hits         2589     2623      +34     
+ Misses        623      612      -11     
  Partials      125      125              

Impacted Files	Coverage Δ
mux/mux.go	76.11% <84.21%> (+4.96%)	⬆️
middleware/auth.go	100.00% <100.00%> (ø)
middleware/client_ip.go	100.00% <100.00%> (ø)
middleware/cors.go	96.44% <100.00%> (ø)
middleware/csrf.go	88.07% <100.00%> (ø)
middleware/fingerprint.go	75.00% <100.00%> (ø)
middleware/gzip.go	68.15% <100.00%> (ø)
middleware/loadshed.go	76.71% <100.00%> (ø)
middleware/log.go	64.38% <100.00%> (ø)
middleware/middleware.go	100.00% <100.00%> (ø)
... and 8 more

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