Watch feature (#1527)

* Add part 1 watch functionality. (squashed)

* add funcs for service/endpoint fqdns

* add endpoints watch

* document exposed funcs

* only send subset deltas

* locking for watch map

* tests and docs

* add pod watch

* remove debugs prints

* feedback part 1

* add error reporting to proto

* inform clients of server stop+errors

* add grpc options param

* use proper context

* Review feedback:
 * Removed client (will move to another repo)
 * Use new log functions
 * Change watchChan to be for string not []string
 * Rework how k8s plugin stores watch tracking info to simplify
 * Normalize the qname on watch request

* Add blank line back

* Revert another spurious change

* Fix tests

* Add stop channel.
Fix tests.
Better docs for plugin interface.

* fmt.Printf -> log.Warningf

* Move from dnsserver to plugin/pkg/watch

* gofmt

* remove dead client watches

* sate linter

* linter omg

1 files changed, 37 insertions, 0 deletions

diff --git a/pb/dns.proto b/pb/dns.proto
index 8461f01e6..e4ac2eb2c 100644
--- a/pb/dns.proto
+++ b/pb/dns.proto
@@ -9,4 +9,41 @@ message DnsPacket {
 
 service DnsService {
 	rpc Query (DnsPacket) returns (DnsPacket);
+	rpc Watch (stream WatchRequest) returns (stream WatchResponse);
+}
+
+message WatchRequest {
+  // request_union is a request to either create a new watcher or cancel an existing watcher.
+  oneof request_union {
+    WatchCreateRequest create_request = 1;
+    WatchCancelRequest cancel_request = 2;
+  }
+}
+
+message WatchCreateRequest {
+  DnsPacket query = 1;
+}
+
+message WatchCancelRequest {
+  // watch_id is the watcher id to cancel
+  int64 watch_id = 1;
+}
+
+message WatchResponse {
+	// watch_id is the ID of the watcher that corresponds to the response.
+	int64 watch_id = 1;
+
+	// created is set to true if the response is for a create watch request.
+	// The client should record the watch_id and expect to receive DNS replies
+	// from the same stream.
+	// All replies sent to the created watcher will attach with the same watch_id.
+	bool created = 2;
+
+	// canceled is set to true if the response is for a cancel watch request.
+	// No further events will be sent to the canceled watcher.
+	bool canceled = 3;
+
+	string qname = 4;
+
+	string err = 5;
 }