config/snapshot/config_snapshot.go

/*
Copyright 2022 The TestGrid 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 snapshot

import (
	"context"
	"fmt"
	"time"

	"cloud.google.com/go/storage"
	"github.com/GoogleCloudPlatform/testgrid/config"
	configpb "github.com/GoogleCloudPlatform/testgrid/pb/config"
	"github.com/GoogleCloudPlatform/testgrid/util/gcs"
	"github.com/sethvargo/go-retry"
	"github.com/sirupsen/logrus"
)

// Config is a mapped representation of the config at a particular point in time.
// Not concurrency-safe; meant for reading only
type Config struct {
	DashboardGroups map[string]*configpb.DashboardGroup
	Dashboards      map[string]*configpb.Dashboard
	Groups          map[string]*configpb.TestGroup
	Attrs           storage.ReaderObjectAttrs
}

// Observe reads the config at configPath and return a ConfigSnapshot initially and, if a ticker is supplied, when the config changes
// Returns an error instead if there is no file at configPath
func Observe(ctx context.Context, log logrus.FieldLogger, client gcs.ConditionalClient, configPath gcs.Path, ticker <-chan time.Time) (<-chan *Config, error) {
	ch := make(chan *Config)
	if log == nil {
		log = logrus.New()
	}
	log = log.WithField("observed-path", configPath.String())

	initialSnap, err := updateHash(ctx, client, configPath)
	if err != nil {
		return nil, fmt.Errorf("can't read %q: %w", configPath.String(), err)
	}
	cond := storage.Conditions{
		GenerationNotMatch: initialSnap.Attrs.Generation,
	}
	client = client.If(&cond, nil)

	go func() {
		defer close(ch)
		ch <- initialSnap
		if ticker == nil {
			return
		}
	nextTick:
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker:
				snap, err := updateHash(ctx, client, configPath)
				if err != nil {
					if !gcs.IsPreconditionFailed(err) {
						log.WithError(err).Warning("Error fetching updated config")
					}
					continue nextTick
				}
				// Configuration changed
				select {
				case <-ctx.Done():
					return
				case ch <- snap:
					cond.GenerationNotMatch = snap.Attrs.Generation
				}
			}

		}
	}()

	return ch, nil
}

func updateHash(ctx context.Context, client gcs.Opener, configPath gcs.Path) (*Config, error) {
	var cs Config
	cfg, attrs, err := fetchConfig(ctx, client, configPath)
	if err != nil {
		return nil, err
	}

	namedDashboardGroups := make(map[string]*configpb.DashboardGroup, len(cfg.DashboardGroups))
	for _, dg := range cfg.DashboardGroups {
		namedDashboardGroups[dg.Name] = dg
	}
	namedDashboards := make(map[string]*configpb.Dashboard, len(cfg.Dashboards))
	for _, d := range cfg.Dashboards {
		namedDashboards[d.Name] = d
	}
	namedGroups := make(map[string]*configpb.TestGroup, len(cfg.TestGroups))
	for _, tg := range cfg.TestGroups {
		namedGroups[tg.Name] = tg
	}

	cs.DashboardGroups = namedDashboardGroups
	cs.Dashboards = namedDashboards
	cs.Groups = namedGroups
	if attrs != nil {
		cs.Attrs = *attrs
	}
	return &cs, nil
}

func fetchConfig(ctx context.Context, client gcs.Opener, configPath gcs.Path) (*configpb.Configuration, *storage.ReaderObjectAttrs, error) {
	backoff := retry.WithMaxRetries(2, retry.NewExponential(5*time.Second))

	var cfg *configpb.Configuration
	var attrs *storage.ReaderObjectAttrs
	err := retry.Do(ctx, backoff, func(innerCtx context.Context) error {
		var onceErr error
		cfg, attrs, onceErr = fetchConfigOnce(innerCtx, client, configPath)
		if onceErr != nil {
			return retry.RetryableError(onceErr)
		}
		return nil
	})
	return cfg, attrs, err
}

func fetchConfigOnce(ctx context.Context, client gcs.Opener, configPath gcs.Path) (*configpb.Configuration, *storage.ReaderObjectAttrs, error) {
	r, attrs, err := client.Open(ctx, configPath)
	if err != nil {
		return nil, nil, fmt.Errorf("open: %w", err)
	}

	cfg, err := config.Unmarshal(r)
	if err != nil {
		return nil, nil, fmt.Errorf("unmarshal: %v", err)
	}
	return cfg, attrs, nil
}