add walk+handler (emicklei#63)

* add proto.Walk + Handlers per Visitee type

walk.go

@@ -0,0 +1,97 @@
+// Copyright (c) 2018 Ernest Micklei
+//
+// MIT License
+//
+// Permission is hereby granted, free of charge, to any person obtaining
+// a copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to
+// permit persons to whom the Software is furnished to do so, subject to
+// the following conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+package proto
+
+// Handler is a type of function that accepts a Visitee.
+type Handler func(v Visitee)
+
+// Walk recursively pays a visit to all Visitees of a Proto and calls each handler with it.
+func Walk(proto *Proto, handlers ...Handler) {
+	walk(proto, handlers...)
+}
+
+func walk(container elementContainer, handlers ...Handler) {
+	for _, eachElement := range container.elements() {
+		for _, eachFilter := range handlers {
+			eachFilter(eachElement)
+		}
+		if next, ok := eachElement.(elementContainer); ok {
+			walk(next, handlers...)
+		}
+	}
+}
+
+// WithMessage returns a Handler that will call the apply function when the Visitee is a Message.
+func WithMessage(apply func(*Message)) Handler {
+	return func(v Visitee) {
+		if s, ok := v.(*Message); ok {
+			apply(s)
+		}
+	}
+}
+
+// WithOption returns a Handler that will call the apply function when the Visitee is a Option.
+func WithOption(apply func(*Option)) Handler {
+	return func(v Visitee) {
+		if s, ok := v.(*Option); ok {
+			apply(s)
+		}
+	}
+}
+
+// WithEnum returns a Handler that will call the apply function when the Visitee is a Enum.
+func WithEnum(apply func(*Enum)) Handler {
+	return func(v Visitee) {
+		if s, ok := v.(*Enum); ok {
+			apply(s)
+		}
+	}
+}
+
+// WithOneof returns a Handler that will call the apply function when the Visitee is a Oneof.
+func WithOneof(apply func(*Oneof)) Handler {
+	return func(v Visitee) {
+		if s, ok := v.(*Oneof); ok {
+			apply(s)
+		}
+	}
+}
+
+// WithService returns a Handler that will call the apply function when the Visitee is a Service.
+func WithService(apply func(*Service)) Handler {
+	return func(v Visitee) {
+		if s, ok := v.(*Service); ok {
+			apply(s)
+		}
+	}
+}
+
+// WithRPC returns a Handler that will call the apply function when the Visitee is a RPC.
+func WithRPC(apply func(*RPC)) Handler {
+	return func(v Visitee) {
+		if s, ok := v.(*RPC); ok {
+			apply(s)
+		}
+	}
+}

walk_test.go

@@ -0,0 +1,28 @@
+package proto
+
+import (
+	"os"
+	"testing"
+)
+
+type counter struct {
+	counts map[string]int
+}
+
+func (c counter) handleService(s *Service) {
+	c.counts["service"] = c.counts["service"] + 1
+}
+
+func (c counter) handleRPC(r *RPC) {
+	c.counts["rpc"] = c.counts["rpc"] + 1
+}
+
+func TestWalkGoogleApisDLP(t *testing.T) {
+	if len(os.Getenv("PB")) == 0 {
+		t.Skip("PB test not run")
+	}
+	proto := fetchAndParse(t, "https://raw.githubusercontent.com/googleapis/googleapis/master/google/privacy/dlp/v2beta2/dlp.proto")
+	count := counter{counts: map[string]int{}}
+	Walk(proto, WithService(count.handleService), WithRPC(count.handleRPC))
+	t.Logf("%#v", count)
+}