1/*
2 *
3 * Copyright 2018 gRPC authors.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 *     http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 */
18
19package health
20
21import (
22	"context"
23	"fmt"
24	"io"
25	"time"
26
27	"google.golang.org/grpc"
28	"google.golang.org/grpc/codes"
29	"google.golang.org/grpc/connectivity"
30	healthpb "google.golang.org/grpc/health/grpc_health_v1"
31	"google.golang.org/grpc/internal"
32	"google.golang.org/grpc/internal/backoff"
33	"google.golang.org/grpc/status"
34)
35
36var (
37	backoffStrategy = backoff.DefaultExponential
38	backoffFunc     = func(ctx context.Context, retries int) bool {
39		d := backoffStrategy.Backoff(retries)
40		timer := time.NewTimer(d)
41		select {
42		case <-timer.C:
43			return true
44		case <-ctx.Done():
45			timer.Stop()
46			return false
47		}
48	}
49)
50
51func init() {
52	internal.HealthCheckFunc = clientHealthCheck
53}
54
55const healthCheckMethod = "/grpc.health.v1.Health/Watch"
56
57// This function implements the protocol defined at:
58// https://github.com/grpc/grpc/blob/master/doc/health-checking.md
59func clientHealthCheck(ctx context.Context, newStream func(string) (interface{}, error), setConnectivityState func(connectivity.State), service string) error {
60	tryCnt := 0
61
62retryConnection:
63	for {
64		// Backs off if the connection has failed in some way without receiving a message in the previous retry.
65		if tryCnt > 0 && !backoffFunc(ctx, tryCnt-1) {
66			return nil
67		}
68		tryCnt++
69
70		if ctx.Err() != nil {
71			return nil
72		}
73		setConnectivityState(connectivity.Connecting)
74		rawS, err := newStream(healthCheckMethod)
75		if err != nil {
76			continue retryConnection
77		}
78
79		s, ok := rawS.(grpc.ClientStream)
80		// Ideally, this should never happen. But if it happens, the server is marked as healthy for LBing purposes.
81		if !ok {
82			setConnectivityState(connectivity.Ready)
83			return fmt.Errorf("newStream returned %v (type %T); want grpc.ClientStream", rawS, rawS)
84		}
85
86		if err = s.SendMsg(&healthpb.HealthCheckRequest{Service: service}); err != nil && err != io.EOF {
87			// Stream should have been closed, so we can safely continue to create a new stream.
88			continue retryConnection
89		}
90		s.CloseSend()
91
92		resp := new(healthpb.HealthCheckResponse)
93		for {
94			err = s.RecvMsg(resp)
95
96			// Reports healthy for the LBing purposes if health check is not implemented in the server.
97			if status.Code(err) == codes.Unimplemented {
98				setConnectivityState(connectivity.Ready)
99				return err
100			}
101
102			// Reports unhealthy if server's Watch method gives an error other than UNIMPLEMENTED.
103			if err != nil {
104				setConnectivityState(connectivity.TransientFailure)
105				continue retryConnection
106			}
107
108			// As a message has been received, removes the need for backoff for the next retry by resetting the try count.
109			tryCnt = 0
110			if resp.Status == healthpb.HealthCheckResponse_SERVING {
111				setConnectivityState(connectivity.Ready)
112			} else {
113				setConnectivityState(connectivity.TransientFailure)
114			}
115		}
116	}
117}
118