Add grpc prometheus metrics

This provideds generic grpc metrics via prometheus

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

vendor/github.com/grpc-ecosystem/go-grpc-prometheus/client.go

@@ -0,0 +1,72 @@
+// Copyright 2016 Michal Witkowski. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+// gRPC Prometheus monitoring interceptors for client-side gRPC.
+
+package grpc_prometheus
+
+import (
+	"io"
+
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+)
+
+// UnaryClientInterceptor is a gRPC client-side interceptor that provides Prometheus monitoring for Unary RPCs.
+func UnaryClientInterceptor(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+	monitor := newClientReporter(Unary, method)
+	monitor.SentMessage()
+	err := invoker(ctx, method, req, reply, cc, opts...)
+	if err != nil {
+		monitor.ReceivedMessage()
+	}
+	monitor.Handled(grpc.Code(err))
+	return err
+}
+
+// StreamServerInterceptor is a gRPC client-side interceptor that provides Prometheus monitoring for Streaming RPCs.
+func StreamClientInterceptor(ctx context.Context, desc *grpc.StreamDesc, cc *grpc.ClientConn, method string, streamer grpc.Streamer, opts ...grpc.CallOption) (grpc.ClientStream, error) {
+	monitor := newClientReporter(clientStreamType(desc), method)
+	clientStream, err := streamer(ctx, desc, cc, method, opts...)
+	if err != nil {
+		monitor.Handled(grpc.Code(err))
+		return nil, err
+	}
+	return &monitoredClientStream{clientStream, monitor}, nil
+}
+
+func clientStreamType(desc *grpc.StreamDesc) grpcType {
+	if desc.ClientStreams && !desc.ServerStreams {
+		return ClientStream
+	} else if !desc.ClientStreams && desc.ServerStreams {
+		return ServerStream
+	}
+	return BidiStream
+}
+
+// monitoredClientStream wraps grpc.ClientStream allowing each Sent/Recv of message to increment counters.
+type monitoredClientStream struct {
+	grpc.ClientStream
+	monitor *clientReporter
+}
+
+func (s *monitoredClientStream) SendMsg(m interface{}) error {
+	err := s.ClientStream.SendMsg(m)
+	if err == nil {
+		s.monitor.SentMessage()
+	}
+	return err
+}
+
+func (s *monitoredClientStream) RecvMsg(m interface{}) error {
+	err := s.ClientStream.RecvMsg(m)
+	if err == nil {
+		s.monitor.ReceivedMessage()
+	} else if err == io.EOF {
+		s.monitor.Handled(codes.OK)
+	} else {
+		s.monitor.Handled(grpc.Code(err))
+	}
+	return err
+}