You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: watcher.go
    path of file: ./repos/etcd/server/proxy/grpcproxy
    
    the code of the file until where you have to start completion: // Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package grpcproxy

import (
	"time"

	pb "go.etcd.io/etcd/api/v3/etcdserverpb"
	"go.etcd.io/etcd/api/v3/mvccpb"
	clientv3 "go.etcd.io/etcd/client/v3"
	"go.etcd.io/etcd/server/v3/storage/mvcc"
)

type watchRange struct {
	key, end string
}

func (wr *watchRange) valid() bool {
	retu
    
func (w *watcher) send(wr clientv3.WatchResponse) {
	if wr.IsProgressNotify() && !w.progress {
		return
	}
	if w.nextrev > wr.Header.Revision && len(wr.Events) > 0 {
		return
	}
	if w.nextrev == 0 {
		// current watch; expect updates following this revision
		w.nextrev = wr.Header.Revision + 1
	}

	events := make([]*mvccpb.Event, 0, len(wr.Events))

	var lastRev int64
	for i := range wr.Events {
		ev := (*mvccpb.Event)(wr.Events[i])
		if ev.Kv.ModRevision < w.nextrev {
			continue
		} else {
			// We cannot update w.rev here.
			// txn can have multiple events with the same rev.
			// If w.nextrev updates here, it would skip events in the same txn.
			lastRev = ev.Kv.ModRevision
		}

		filtered := false
		for _, filter := range w.filters {
			if filter(*ev) {
				filtered = true
				break
			}
		}
		if filtered {
			continue
		}

		if !w.prevKV {
			evCopy := *ev
			evCopy.PrevKv = nil
			ev = &evCopy
		}
		events = append(events, ev)
	}

	if lastRev >= w.nextrev {
		w.nextrev = lastRev + 1
	}

	// all events are filtered out?
	if !wr.IsProgressNotify() && !wr.Created && len(events) == 0 && wr.CompactRevision == 0 {
		return
	}

	w.lastHeader = wr.Header
	w.post(&pb.WatchResponse{
		Header:          &wr.Header,
		Created:         wr.Created,
		CompactRevision: wr.CompactRevision,
		Canceled:        wr.Canceled,
		WatchId:         w.id,
		Events:          events,
	})
}