events: autogenerate fieldpath filters

To ensure consistent fieldpath matching for events, we generate the
fieldpath matching using protobuf definitions. This is done through a
plugin called "fieldpath" that defines a `Field` method for each type
with the plugin enabled. Generated code handles top-level envelope
fields, as well as deferred serialization for matching any types.

In practice, this means that we can cheaply match events on `topic` and
`namespace`. If we want to match on attributes within the event, we can
use the `event` prefix to address these fields. For example, the
following will match all envelopes that have a field named
`container_id` that has the value `testing`:

```
ctr events "event.container_id==testing"
```

The above will decode the underlying event and check that particular
field. Accordingly, if only `topic` or `namespace` is used, the event
will not be decoded and only match on the envelope.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

typeurl/types_test.go

@@ -1,12 +1,9 @@
 package typeurl
 
 import (
-	"fmt"
 	"path/filepath"
 	"reflect"
 	"testing"
-
-	eventsapi "github.com/containerd/containerd/api/services/events/v1"
 )
 
 type test struct {
@@ -106,41 +103,6 @@ func TestIs(t *testing.T) {
 	}
 }
 
-func TestMarshalEvent(t *testing.T) {
-	for _, testcase := range []struct {
-		event interface{}
-		url   string
-	}{
-		{
-			event: &eventsapi.TaskStart{},
-			url:   "types.containerd.io/containerd.services.events.v1.TaskStart",
-		},
-
-		{
-			event: &eventsapi.NamespaceUpdate{},
-			url:   "types.containerd.io/containerd.services.events.v1.NamespaceUpdate",
-		},
-	} {
-		t.Run(fmt.Sprintf("%T", testcase.event), func(t *testing.T) {
-			a, err := MarshalAny(testcase.event)
-			if err != nil {
-				t.Fatal(err)
-			}
-			if a.TypeUrl != testcase.url {
-				t.Fatalf("unexpected url: %v != %v", a.TypeUrl, testcase.url)
-			}
-
-			v, err := UnmarshalAny(a)
-			if err != nil {
-				t.Fatal(err)
-			}
-			if !reflect.DeepEqual(v, testcase.event) {
-				t.Fatalf("round trip failed %v != %v", v, testcase.event)
-			}
-		})
-	}
-}
-
 func TestRegisterDiffUrls(t *testing.T) {
 	clear()
 	defer func() {
@@ -151,20 +113,3 @@ func TestRegisterDiffUrls(t *testing.T) {
 	Register(&test{}, "test")
 	Register(&test{}, "test", "two")
 }
-
-func BenchmarkMarshalEvent(b *testing.B) {
-	ev := &eventsapi.TaskStart{}
-	expected, err := MarshalAny(ev)
-	if err != nil {
-		b.Fatal(err)
-	}
-	for i := 0; i < b.N; i++ {
-		a, err := MarshalAny(ev)
-		if err != nil {
-			b.Fatal(err)
-		}
-		if a.TypeUrl != expected.TypeUrl {
-			b.Fatalf("incorrect type url: %v != %v", a, expected)
-		}
-	}
-}