Implement the dispatcher middleware framework, allowing users to
wrap method dispatching with their own code.
The Dispatcher functions have an untyped params arg, but expect its
value to be a typed, unmarshaled XXXParams struct. That required
splitting the elegant dispatch[P, R] function into two parts, one
to do the unmarshaling and one to call the method. The nicest way
I could find to do that was to map from method names to a pair
of functions, one to unmarshal and one to call. We could also write
it as two switches on method name, which would require less machinery
but would duplicate the list of method names, already a tad fragile
because they are literal strings.
I also exported the initialize params and result, so user Dispatchers
could access them. All Params and Result types will have to be exported
for that reason.
Change-Id: Ie2c95cc17b4ef3d3d095dccdadb294e5f1590796
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673515
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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