go get github.com/codemodus/chain
Package chain aids the composition of nested http.Handler instances.
Nesting functions is a simple concept. If your nested handler order does not need to be composable, please do not use this or any similar package and avoid adding a dependency to your project.
type Chain
func New(handlers ...func(http.Handler) http.Handler) *Chain
func (c *Chain) Append(handlers ...func(http.Handler) http.Handler) *Chain
func (c *Chain) Copy(chain *Chain)
func (c *Chain) End(handler http.Handler) http.Handler
func (c *Chain) EndFn(handlerFunc http.HandlerFunc) http.Handler
func (c *Chain) Merge(chains ...*Chain) *Chainimport (
// ...
"github.com/codemodus/chain"
)
func main() {
// ...
// Nested handlers write either "0" or "1" to the response body before
// and after ServeHTTP() is called.
//
// endHandler writes "_END_" to the response body.
ch00 := New(nestedHandler0, nestedHandler0)
ch001 := ch00.Append(nestedHandler1)
ch1 := New(nestedHandler1)
ch1001 := ch1.Merge(ch001)
mux := http.NewServeMux()
mux.Handle("/00_End", ch00.EndFn(endHandler)) // Resp Body: "00_END_00"
mux.Handle("/001_End", ch001.EndFn(endHandler)) // Resp Body: "001_END_100"
mux.Handle("/1001_End", ch1001.EndFn(endHandler)) // Resp Body: "1001_END_1001"
// ...
}func nestableHandler(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// ...
next.ServeHTTP(w, r)
// ...
})
}As of Go 1.7, the http package's Request type includes a field (accessed via the Context() method) which holds an implementation of context.Context. Further, the context package has been added to the standard library. There is now no need for the custom Handler defined in previous versions of chain. Please refer to the following command to ease the process of updating your source.
sed -r -e 's/chain\.Handler/http.Handler/g' \
-e 's/[a-zA-Z0-9]+ context\.Context, ([a-zA-Z0-9]+) (http\.ResponseWriter)/\1 \2/' \
-e 's/ServeHTTPContext\([a-zA-Z0-9]+, /ServeHTTP(/'
Beyond this, any usage of chain.Set(context.Context) will need to be modified manually. Adding the affected logic as a nested handler is a simple and effective alternative. Don't forget to run gofmt/goimports.
View the GoDoc
These results are for comparison of normally nested functions, and chained functions. Each benchmark includes 10 functions prior to the final handler.
go1.7
benchmark iter time/iter bytes alloc allocs
--------- ---- --------- ----------- ------
BenchmarkChain10 20000 61.01 μs/op 3684 B/op 51 allocs/op
BenchmarkChain10-4 20000 68.62 μs/op 3691 B/op 51 allocs/op
BenchmarkChain10-8 20000 69.33 μs/op 3696 B/op 51 allocs/op
BenchmarkNest10 20000 60.36 μs/op 3684 B/op 51 allocs/op
BenchmarkNest10-4 20000 70.82 μs/op 3692 B/op 51 allocs/op
BenchmarkNest10-8 20000 71.03 μs/op 3697 B/op 51 allocs/op