source-controller/controllers/bucket_controller.go

/*
Copyright 2020 The Flux 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 controllers

import (
	"context"
	"crypto/sha256"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	gcpstorage "cloud.google.com/go/storage"
	"github.com/fluxcd/pkg/runtime/events"
	"github.com/fluxcd/source-controller/pkg/gcp"
	"github.com/minio/minio-go/v7"
	"github.com/minio/minio-go/v7/pkg/credentials"
	"github.com/minio/minio-go/v7/pkg/s3utils"
	"golang.org/x/sync/errgroup"
	"golang.org/x/sync/semaphore"
	"google.golang.org/api/option"
	corev1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/types"
	kuberecorder "k8s.io/client-go/tools/record"
	ctrl "sigs.k8s.io/controller-runtime"
	"sigs.k8s.io/controller-runtime/pkg/client"
	"sigs.k8s.io/controller-runtime/pkg/controller"
	"sigs.k8s.io/controller-runtime/pkg/controller/controllerutil"
	"sigs.k8s.io/controller-runtime/pkg/predicate"

	"github.com/fluxcd/pkg/apis/meta"
	"github.com/fluxcd/pkg/runtime/conditions"
	helper "github.com/fluxcd/pkg/runtime/controller"
	"github.com/fluxcd/pkg/runtime/patch"
	"github.com/fluxcd/pkg/runtime/predicates"

	sourcev1 "github.com/fluxcd/source-controller/api/v1beta2"
	serror "github.com/fluxcd/source-controller/internal/error"
	sreconcile "github.com/fluxcd/source-controller/internal/reconcile"
	"github.com/fluxcd/source-controller/internal/reconcile/summarize"
	"github.com/fluxcd/source-controller/pkg/sourceignore"
)

// bucketReadyConditions contains all the conditions information needed
// for Bucket Ready status conditions summary calculation.
var bucketReadyConditions = summarize.Conditions{
	Target: meta.ReadyCondition,
	Owned: []string{
		sourcev1.ArtifactOutdatedCondition,
		sourcev1.FetchFailedCondition,
		meta.ReadyCondition,
		meta.ReconcilingCondition,
		meta.StalledCondition,
	},
	Summarize: []string{
		sourcev1.ArtifactOutdatedCondition,
		sourcev1.FetchFailedCondition,
		meta.StalledCondition,
		meta.ReconcilingCondition,
	},
	NegativePolarity: []string{
		sourcev1.ArtifactOutdatedCondition,
		sourcev1.FetchFailedCondition,
		meta.StalledCondition,
		meta.ReconcilingCondition,
	},
}

// +kubebuilder:rbac:groups=source.toolkit.fluxcd.io,resources=buckets,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=source.toolkit.fluxcd.io,resources=buckets/status,verbs=get;update;patch
// +kubebuilder:rbac:groups=source.toolkit.fluxcd.io,resources=buckets/finalizers,verbs=get;create;update;patch;delete
// +kubebuilder:rbac:groups="",resources=secrets,verbs=get;list;watch

// BucketReconciler reconciles a Bucket object
type BucketReconciler struct {
	client.Client
	kuberecorder.EventRecorder
	helper.Metrics

	Storage *Storage
}

type BucketReconcilerOptions struct {
	MaxConcurrentReconciles int
}

// bucketReconcilerFunc is the function type for all the bucket reconciler
// functions.
type bucketReconcilerFunc func(ctx context.Context, obj *sourcev1.Bucket, artifact *sourcev1.Artifact, dir string) (sreconcile.Result, error)

func (r *BucketReconciler) SetupWithManager(mgr ctrl.Manager) error {
	return r.SetupWithManagerAndOptions(mgr, BucketReconcilerOptions{})
}

func (r *BucketReconciler) SetupWithManagerAndOptions(mgr ctrl.Manager, opts BucketReconcilerOptions) error {
	return ctrl.NewControllerManagedBy(mgr).
		For(&sourcev1.Bucket{}).
		WithEventFilter(predicate.Or(predicate.GenerationChangedPredicate{}, predicates.ReconcileRequestedPredicate{})).
		WithOptions(controller.Options{MaxConcurrentReconciles: opts.MaxConcurrentReconciles}).
		Complete(r)
}

func (r *BucketReconciler) Reconcile(ctx context.Context, req ctrl.Request) (result ctrl.Result, retErr error) {
	start := time.Now()
	log := ctrl.LoggerFrom(ctx)

	// Fetch the Bucket
	obj := &sourcev1.Bucket{}
	if err := r.Get(ctx, req.NamespacedName, obj); err != nil {
		return ctrl.Result{}, client.IgnoreNotFound(err)
	}

	// Record suspended status metric
	r.RecordSuspend(ctx, obj, obj.Spec.Suspend)

	// Return early if the object is suspended
	if obj.Spec.Suspend {
		log.Info("reconciliation is suspended for this object")
		return ctrl.Result{}, nil
	}

	// Initialize the patch helper with the current version of the object.
	patchHelper, err := patch.NewHelper(obj, r.Client)
	if err != nil {
		return ctrl.Result{}, err
	}

	// recResult stores the abstracted reconcile result.
	var recResult sreconcile.Result

	// Always attempt to patch the object and status after each reconciliation
	// NOTE: The final runtime result and error are set in this block.
	defer func() {
		summarizeHelper := summarize.NewHelper(r.EventRecorder, patchHelper)
		summarizeOpts := []summarize.Option{
			summarize.WithConditions(bucketReadyConditions),
			summarize.WithReconcileResult(recResult),
			summarize.WithReconcileError(retErr),
			summarize.WithIgnoreNotFound(),
			summarize.WithProcessors(
				summarize.RecordContextualError,
				summarize.RecordReconcileReq,
			),
			summarize.WithResultBuilder(sreconcile.AlwaysRequeueResultBuilder{RequeueAfter: obj.GetInterval().Duration}),
		}
		result, retErr = summarizeHelper.SummarizeAndPatch(ctx, obj, summarizeOpts...)

		// Always record readiness and duration metrics
		r.Metrics.RecordReadiness(ctx, obj)
		r.Metrics.RecordDuration(ctx, obj, start)
	}()

	// Add finalizer first if not exist to avoid the race condition between init and delete
	if !controllerutil.ContainsFinalizer(obj, sourcev1.SourceFinalizer) {
		controllerutil.AddFinalizer(obj, sourcev1.SourceFinalizer)
		recResult = sreconcile.ResultRequeue
		return
	}

	// Examine if the object is under deletion
	if !obj.ObjectMeta.DeletionTimestamp.IsZero() {
		recResult, retErr = r.reconcileDelete(ctx, obj)
		return
	}

	// Reconcile actual object
	reconcilers := []bucketReconcilerFunc{
		r.reconcileStorage,
		r.reconcileSource,
		r.reconcileArtifact,
	}
	recResult, retErr = r.reconcile(ctx, obj, reconcilers)
	return
}

// reconcile steps iterates through the actual reconciliation tasks for objec,
// it returns early on the first step that returns ResultRequeue or produces an
// error.
func (r *BucketReconciler) reconcile(ctx context.Context, obj *sourcev1.Bucket, reconcilers []bucketReconcilerFunc) (sreconcile.Result, error) {
	if obj.Generation != obj.Status.ObservedGeneration {
		conditions.MarkReconciling(obj, "NewGeneration", "reconciling new generation %d", obj.Generation)
	}

	var artifact sourcev1.Artifact

	// Create temp working dir
	tmpDir, err := os.MkdirTemp("", fmt.Sprintf("%s-%s-%s-", obj.Kind, obj.Namespace, obj.Name))
	if err != nil {
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("failed to create temporary directory: %w", err),
			Reason: sourcev1.StorageOperationFailedReason,
		}
	}
	defer os.RemoveAll(tmpDir)

	// Run the sub-reconcilers and build the result of reconciliation.
	var res sreconcile.Result
	var resErr error
	for _, rec := range reconcilers {
		recResult, err := rec(ctx, obj, &artifact, tmpDir)
		// Exit immediately on ResultRequeue.
		if recResult == sreconcile.ResultRequeue {
			return sreconcile.ResultRequeue, nil
		}
		// If an error is received, prioritize the returned results because an
		// error also means immediate requeue.
		if err != nil {
			resErr = err
			res = recResult
			break
		}
		// Prioritize requeue request in the result.
		res = sreconcile.LowestRequeuingResult(res, recResult)
	}
	return res, resErr
}

// reconcileStorage ensures the current state of the storage matches the desired and previously observed state.
//
// All artifacts for the resource except for the current one are garbage collected from the storage.
// If the artifact in the Status object of the resource disappeared from storage, it is removed from the object.
// If the hostname of the URLs on the object do not match the current storage server hostname, they are updated.
func (r *BucketReconciler) reconcileStorage(ctx context.Context, obj *sourcev1.Bucket, artifact *sourcev1.Artifact, dir string) (sreconcile.Result, error) {
	// Garbage collect previous advertised artifact(s) from storage
	_ = r.garbageCollect(ctx, obj)

	// Determine if the advertised artifact is still in storage
	if artifact := obj.GetArtifact(); artifact != nil && !r.Storage.ArtifactExist(*artifact) {
		obj.Status.Artifact = nil
		obj.Status.URL = ""
	}

	// Record that we do not have an artifact
	if obj.GetArtifact() == nil {
		conditions.MarkReconciling(obj, "NoArtifact", "no artifact for resource in storage")
		return sreconcile.ResultSuccess, nil
	}

	// Always update URLs to ensure hostname is up-to-date
	// TODO(hidde): we may want to send out an event only if we notice the URL has changed
	r.Storage.SetArtifactURL(obj.GetArtifact())
	obj.Status.URL = r.Storage.SetHostname(obj.Status.URL)

	return sreconcile.ResultSuccess, nil
}

// reconcileSource reconciles the upstream bucket with the client for the given object's Provider, and returns the
// result.
// If a SecretRef is defined, it attempts to fetch the Secret before calling the provider. If the fetch of the Secret
// fails, it records v1beta1.FetchFailedCondition=True and returns early.
func (r *BucketReconciler) reconcileSource(ctx context.Context, obj *sourcev1.Bucket, artifact *sourcev1.Artifact, dir string) (sreconcile.Result, error) {
	var secret *corev1.Secret
	if obj.Spec.SecretRef != nil {
		secretName := types.NamespacedName{
			Namespace: obj.GetNamespace(),
			Name:      obj.Spec.SecretRef.Name,
		}
		secret = &corev1.Secret{}
		if err := r.Get(ctx, secretName, secret); err != nil {
			e := &serror.Event{
				Err:    fmt.Errorf("failed to get secret '%s': %w", secretName.String(), err),
				Reason: sourcev1.AuthenticationFailedReason,
			}
			conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.AuthenticationFailedReason, e.Err.Error())
			// Return error as the world as observed may change
			return sreconcile.ResultEmpty, e
		}
	}

	switch obj.Spec.Provider {
	case sourcev1.GoogleBucketProvider:
		return r.reconcileGCPSource(ctx, obj, artifact, secret, dir)
	default:
		return r.reconcileMinioSource(ctx, obj, artifact, secret, dir)
	}
}

// reconcileMinioSource ensures the upstream Minio client compatible bucket can be reached and downloaded from using the
// declared configuration, and observes its state.
//
// The bucket contents are downloaded to the given dir using the defined configuration, while taking ignore rules into
// account. In case of an error during the download process (including transient errors), it records
// v1beta1.FetchFailedCondition=True and returns early.
// On a successful download, it removes v1beta1.FetchFailedCondition, and compares the current revision of HEAD to
// the artifact on the object, and records v1beta1.ArtifactOutdatedCondition if they differ.
// If the download was successful, the given artifact pointer is set to a new artifact with the available metadata.
func (r *BucketReconciler) reconcileMinioSource(ctx context.Context, obj *sourcev1.Bucket, artifact *sourcev1.Artifact,
	secret *corev1.Secret, dir string) (sreconcile.Result, error) {
	// Build the client with the configuration from the object and secret
	s3Client, err := r.buildMinioClient(obj, secret)
	if err != nil {
		e := &serror.Event{
			Err:    fmt.Errorf("failed to construct S3 client: %w", err),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		// Return error as the contents of the secret may change
		return sreconcile.ResultEmpty, e
	}

	// Confirm bucket exists
	ctxTimeout, cancel := context.WithTimeout(ctx, obj.Spec.Timeout.Duration)
	defer cancel()
	exists, err := s3Client.BucketExists(ctxTimeout, obj.Spec.BucketName)
	if err != nil {
		e := &serror.Event{
			Err:    fmt.Errorf("failed to verify existence of bucket '%s': %w", obj.Spec.BucketName, err),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		return sreconcile.ResultEmpty, e
	}
	if !exists {
		e := &serror.Event{
			Err:    fmt.Errorf("bucket '%s' does not exist", obj.Spec.BucketName),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		return sreconcile.ResultEmpty, e
	}

	// Look for file with ignore rules first
	path := filepath.Join(dir, sourceignore.IgnoreFile)
	if err := s3Client.FGetObject(ctxTimeout, obj.Spec.BucketName, sourceignore.IgnoreFile, path, minio.GetObjectOptions{}); err != nil {
		if resp, ok := err.(minio.ErrorResponse); ok && resp.Code != "NoSuchKey" {
			e := &serror.Event{
				Err:    fmt.Errorf("failed to get '%s' file: %w", sourceignore.IgnoreFile, err),
				Reason: sourcev1.BucketOperationFailedReason,
			}
			conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
			return sreconcile.ResultEmpty, e
		}
	}
	ps, err := sourceignore.ReadIgnoreFile(path, nil)
	if err != nil {
		e := &serror.Event{
			Err:    fmt.Errorf("failed to read '%s' file: %w", sourceignore.IgnoreFile, err),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		return sreconcile.ResultEmpty, e
	}
	// In-spec patterns take precedence
	if obj.Spec.Ignore != nil {
		ps = append(ps, sourceignore.ReadPatterns(strings.NewReader(*obj.Spec.Ignore), nil)...)
	}
	matcher := sourceignore.NewMatcher(ps)

	// Build up an index of object keys and their etags
	// As the keys define the paths and the etags represent a change in file contents, this should be sufficient to
	// detect both structural and file changes
	var index = make(etagIndex)
	for object := range s3Client.ListObjects(ctxTimeout, obj.Spec.BucketName, minio.ListObjectsOptions{
		Recursive: true,
		UseV1:     s3utils.IsGoogleEndpoint(*s3Client.EndpointURL()),
	}) {
		if err = object.Err; err != nil {
			e := &serror.Event{
				Err:    fmt.Errorf("failed to list objects from bucket '%s': %w", obj.Spec.BucketName, err),
				Reason: sourcev1.BucketOperationFailedReason,
			}
			conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
			return sreconcile.ResultEmpty, e
		}

		// Ignore directories and the .sourceignore file
		if strings.HasSuffix(object.Key, "/") || object.Key == sourceignore.IgnoreFile {
			continue
		}
		// Ignore matches
		if matcher.Match(strings.Split(object.Key, "/"), false) {
			continue
		}

		index[object.Key] = object.ETag
	}

	// Calculate revision checksum from the collected index values
	revision, err := index.Revision()
	if err != nil {
		ctrl.LoggerFrom(ctx).Error(err, "failed to calculate revision")
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("failed to calculate revision: %w", err),
			Reason: meta.FailedReason,
		}
	}

	if !obj.GetArtifact().HasRevision(revision) {
		// Mark observations about the revision on the object
		message := fmt.Sprintf("new upstream revision '%s'", revision)
		conditions.MarkTrue(obj, sourcev1.ArtifactOutdatedCondition, "NewRevision", message)
		conditions.MarkReconciling(obj, "NewRevision", message)

		// Download the files in parallel, but with a limited number of workers
		group, groupCtx := errgroup.WithContext(ctx)
		group.Go(func() error {
			const workers = 4
			sem := semaphore.NewWeighted(workers)
			for key := range index {
				k := key
				if err := sem.Acquire(groupCtx, 1); err != nil {
					return err
				}
				group.Go(func() error {
					defer sem.Release(1)
					localPath := filepath.Join(dir, k)
					if err := s3Client.FGetObject(ctxTimeout, obj.Spec.BucketName, k, localPath, minio.GetObjectOptions{}); err != nil {
						return fmt.Errorf("failed to get '%s' file: %w", k, err)
					}
					return nil
				})
			}
			return nil
		})
		if err = group.Wait(); err != nil {
			e := &serror.Event{
				Err:    fmt.Errorf("download from bucket '%s' failed: %w", obj.Spec.BucketName, err),
				Reason: sourcev1.BucketOperationFailedReason,
			}
			conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
			return sreconcile.ResultEmpty, e
		}
		r.eventLogf(ctx, obj, events.EventTypeTrace, sourcev1.BucketOperationSucceedReason,
			"downloaded %d files with revision '%s' from '%s'", len(index), revision, obj.Spec.BucketName)
	}
	conditions.Delete(obj, sourcev1.FetchFailedCondition)

	// Create potential new artifact
	*artifact = r.Storage.NewArtifactFor(obj.Kind, obj, revision, fmt.Sprintf("%s.tar.gz", revision))
	return sreconcile.ResultSuccess, nil
}

// reconcileGCPSource ensures the upstream Google Cloud Storage bucket can be reached and downloaded from using the
// declared configuration, and observes its state.
//
// The bucket contents are downloaded to the given dir using the defined configuration, while taking ignore rules into
// account. In case of an error during the download process (including transient errors), it records
// v1beta1.DownloadFailedCondition=True and returns early.
// On a successful download, it removes v1beta1.DownloadFailedCondition, and compares the current revision of HEAD to
// the artifact on the object, and records v1beta1.ArtifactOutdatedCondition if they differ.
// If the download was successful, the given artifact pointer is set to a new artifact with the available metadata.
func (r *BucketReconciler) reconcileGCPSource(ctx context.Context, obj *sourcev1.Bucket, artifact *sourcev1.Artifact,
	secret *corev1.Secret, dir string) (sreconcile.Result, error) {
	gcpClient, err := r.buildGCPClient(ctx, secret)
	if err != nil {
		e := &serror.Event{
			Err:    fmt.Errorf("failed to construct GCP client: %w", err),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		// Return error as the contents of the secret may change
		return sreconcile.ResultEmpty, e
	}
	defer gcpClient.Close(ctrl.LoggerFrom(ctx))

	// Confirm bucket exists
	ctxTimeout, cancel := context.WithTimeout(ctx, obj.Spec.Timeout.Duration)
	defer cancel()
	exists, err := gcpClient.BucketExists(ctxTimeout, obj.Spec.BucketName)
	if err != nil {
		e := &serror.Event{
			Err:    fmt.Errorf("failed to verify existence of bucket '%s': %w", obj.Spec.BucketName, err),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		return sreconcile.ResultEmpty, e
	}
	if !exists {
		e := &serror.Event{
			Err:    fmt.Errorf("bucket '%s' does not exist", obj.Spec.BucketName),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		return sreconcile.ResultEmpty, e
	}

	// Look for file with ignore rules first
	path := filepath.Join(dir, sourceignore.IgnoreFile)
	if err := gcpClient.FGetObject(ctxTimeout, obj.Spec.BucketName, sourceignore.IgnoreFile, path); err != nil {
		if err != gcpstorage.ErrObjectNotExist {
			e := &serror.Event{
				Err:    fmt.Errorf("failed to get '%s' file: %w", sourceignore.IgnoreFile, err),
				Reason: sourcev1.BucketOperationFailedReason,
			}
			conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
			return sreconcile.ResultEmpty, e
		}
	}
	ps, err := sourceignore.ReadIgnoreFile(path, nil)
	if err != nil {
		e := &serror.Event{
			Err:    fmt.Errorf("failed to read '%s' file: %w", sourceignore.IgnoreFile, err),
			Reason: sourcev1.BucketOperationFailedReason,
		}
		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
		return sreconcile.ResultEmpty, e
	}
	// In-spec patterns take precedence
	if obj.Spec.Ignore != nil {
		ps = append(ps, sourceignore.ReadPatterns(strings.NewReader(*obj.Spec.Ignore), nil)...)
	}
	matcher := sourceignore.NewMatcher(ps)

	// Build up an index of object keys and their etags
	// As the keys define the paths and the etags represent a change in file contents, this should be sufficient to
	// detect both structural and file changes
	var index = make(etagIndex)
	objects := gcpClient.ListObjects(ctxTimeout, obj.Spec.BucketName, nil)
	for {
		object, err := objects.Next()
		if err != nil {
			if err == gcp.IteratorDone {
				break
			}
			e := &serror.Event{
				Err:    fmt.Errorf("failed to list objects from bucket '%s': %w", obj.Spec.BucketName, err),
				Reason: sourcev1.BucketOperationFailedReason,
			}
			conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
			return sreconcile.ResultEmpty, e
		}

		if strings.HasSuffix(object.Name, "/") || object.Name == sourceignore.IgnoreFile {
			continue
		}

		if matcher.Match(strings.Split(object.Name, "/"), false) {
			continue
		}

		index[object.Name] = object.Etag
	}

	// Calculate revision checksum from the collected index values
	revision, err := index.Revision()
	if err != nil {
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("failed to calculate revision: %w", err),
			Reason: meta.FailedReason,
		}
	}

	if !obj.GetArtifact().HasRevision(revision) {
		// Mark observations about the revision on the object
		message := fmt.Sprintf("new upstream revision '%s'", revision)
		conditions.MarkTrue(obj, sourcev1.ArtifactOutdatedCondition, "NewRevision", message)
		conditions.MarkReconciling(obj, "NewRevision", message)

		// Download the files in parallel, but with a limited number of workers
		group, groupCtx := errgroup.WithContext(ctx)
		group.Go(func() error {
			const workers = 4
			sem := semaphore.NewWeighted(workers)
			for key := range index {
				k := key
				if err := sem.Acquire(groupCtx, 1); err != nil {
					return err
				}
				group.Go(func() error {
					defer sem.Release(1)
					localPath := filepath.Join(dir, k)
					if err := gcpClient.FGetObject(ctxTimeout, obj.Spec.BucketName, k, localPath); err != nil {
						return fmt.Errorf("failed to get '%s' file: %w", k, err)
					}
					return nil
				})
			}
			return nil
		})
		if err = group.Wait(); err != nil {
			e := &serror.Event{
				Err:    fmt.Errorf("download from bucket '%s' failed: %w", obj.Spec.BucketName, err),
				Reason: sourcev1.BucketOperationFailedReason,
			}
			conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, sourcev1.BucketOperationFailedReason, e.Err.Error())
			return sreconcile.ResultEmpty, e
		}
		r.eventLogf(ctx, obj, events.EventTypeTrace, sourcev1.BucketOperationSucceedReason,
			"downloaded %d files from bucket '%s'", len(index), obj.Spec.BucketName)
	}
	conditions.Delete(obj, sourcev1.FetchFailedCondition)

	// Create potential new artifact
	*artifact = r.Storage.NewArtifactFor(obj.Kind, obj, revision, fmt.Sprintf("%s.tar.gz", revision))
	return sreconcile.ResultSuccess, nil
}

// reconcileArtifact archives a new artifact to the storage, if the current observation on the object does not match the
// given data.
//
// The inspection of the given data to the object is differed, ensuring any stale observations as
// If the given artifact does not differ from the object's current, it returns early.
// On a successful archive, the artifact in the status of the given object is set, and the symlink in the storage is
// updated to its path.
func (r *BucketReconciler) reconcileArtifact(ctx context.Context, obj *sourcev1.Bucket, artifact *sourcev1.Artifact, dir string) (sreconcile.Result, error) {
	// Always restore the Ready condition in case it got removed due to a transient error
	defer func() {
		if obj.GetArtifact().HasRevision(artifact.Revision) {
			conditions.Delete(obj, sourcev1.ArtifactOutdatedCondition)
			conditions.MarkTrue(obj, meta.ReadyCondition, meta.SucceededReason,
				"stored artifact for revision '%s'", artifact.Revision)
		}
	}()

	// The artifact is up-to-date
	if obj.GetArtifact().HasRevision(artifact.Revision) {
		ctrl.LoggerFrom(ctx).Info("artifact up-to-date", "revision", artifact.Revision)
		return sreconcile.ResultSuccess, nil
	}

	// Mark reconciling because the artifact and remote source are different.
	// and they have to be reconciled.
	conditions.MarkReconciling(obj, "NewRevision", "new upstream revision '%s'", artifact.Revision)

	// Ensure target path exists and is a directory
	if f, err := os.Stat(dir); err != nil {
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("failed to stat source path: %w", err),
			Reason: sourcev1.StorageOperationFailedReason,
		}
	} else if !f.IsDir() {
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("source path '%s' is not a directory", dir),
			Reason: sourcev1.StorageOperationFailedReason,
		}
	}

	// Ensure artifact directory exists and acquire lock
	if err := r.Storage.MkdirAll(*artifact); err != nil {
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("failed to create artifact directory: %w", err),
			Reason: sourcev1.StorageOperationFailedReason,
		}
	}
	unlock, err := r.Storage.Lock(*artifact)
	if err != nil {
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("failed to acquire lock for artifact: %w", err),
			Reason: meta.FailedReason,
		}
	}
	defer unlock()

	// Archive directory to storage
	if err := r.Storage.Archive(artifact, dir, nil); err != nil {
		return sreconcile.ResultEmpty, &serror.Event{
			Err:    fmt.Errorf("unable to archive artifact to storage: %s", err),
			Reason: sourcev1.StorageOperationFailedReason,
		}
	}
	r.AnnotatedEventf(obj, map[string]string{
		"revision": artifact.Revision,
		"checksum": artifact.Checksum,
	}, corev1.EventTypeNormal, "NewArtifact", "stored artifact for revision '%s'", artifact.Revision)

	// Record it on the object
	obj.Status.Artifact = artifact.DeepCopy()

	// Update symlink on a "best effort" basis
	url, err := r.Storage.Symlink(*artifact, "latest.tar.gz")
	if err != nil {
		r.eventLogf(ctx, obj, corev1.EventTypeWarning, sourcev1.StorageOperationFailedReason,
			"failed to update status URL symlink: %s", err)
	}
	if url != "" {
		obj.Status.URL = url
	}
	return sreconcile.ResultSuccess, nil
}

// reconcileDelete handles the deletion of an object. It first garbage collects all artifacts for the object from the
// artifact storage, if successful, the finalizer is removed from the object.
func (r *BucketReconciler) reconcileDelete(ctx context.Context, obj *sourcev1.Bucket) (sreconcile.Result, error) {
	// Garbage collect the resource's artifacts
	if err := r.garbageCollect(ctx, obj); err != nil {
		// Return the error so we retry the failed garbage collection
		return sreconcile.ResultEmpty, err
	}

	// Remove our finalizer from the list
	controllerutil.RemoveFinalizer(obj, sourcev1.SourceFinalizer)

	// Stop reconciliation as the object is being deleted
	return sreconcile.ResultEmpty, nil
}

// garbageCollect performs a garbage collection for the given v1beta1.Bucket. It removes all but the current
// artifact except for when the deletion timestamp is set, which will result in the removal of all artifacts for the
// resource.
func (r *BucketReconciler) garbageCollect(ctx context.Context, obj *sourcev1.Bucket) error {
	if !obj.DeletionTimestamp.IsZero() {
		if deleted, err := r.Storage.RemoveAll(r.Storage.NewArtifactFor(obj.Kind, obj.GetObjectMeta(), "", "*")); err != nil {
			return &serror.Event{
				Err:    fmt.Errorf("garbage collection for deleted resource failed: %s", err),
				Reason: "GarbageCollectionFailed",
			}
		} else if deleted != "" {
			r.eventLogf(ctx, obj, events.EventTypeTrace, "GarbageCollectionSucceeded",
				"garbage collected artifacts for deleted resource")
		}
		obj.Status.Artifact = nil
		return nil
	}
	if obj.GetArtifact() != nil {
		if deleted, err := r.Storage.RemoveAllButCurrent(*obj.GetArtifact()); err != nil {
			return &serror.Event{
				Err:    fmt.Errorf("garbage collection of old artifacts failed: %s", err),
				Reason: "GarbageCollectionFailed",
			}
		} else if len(deleted) > 0 {
			r.eventLogf(ctx, obj, events.EventTypeTrace, "GarbageCollectionSucceeded",
				"garbage collected old artifacts")
		}
	}
	return nil
}

// buildMinioClient constructs a minio.Client with the data from the given object and Secret.
// It returns an error if the Secret does not have the required fields, or if there is no credential handler
// configured.
func (r *BucketReconciler) buildMinioClient(obj *sourcev1.Bucket, secret *corev1.Secret) (*minio.Client, error) {
	opts := minio.Options{
		Region: obj.Spec.Region,
		Secure: !obj.Spec.Insecure,
	}
	if secret != nil {
		var accessKey, secretKey string
		if k, ok := secret.Data["accesskey"]; ok {
			accessKey = string(k)
		}
		if k, ok := secret.Data["secretkey"]; ok {
			secretKey = string(k)
		}
		if accessKey == "" || secretKey == "" {
			return nil, fmt.Errorf("invalid '%s' secret data: required fields 'accesskey' and 'secretkey'", secret.Name)
		}
		opts.Creds = credentials.NewStaticV4(accessKey, secretKey, "")
	} else if obj.Spec.Provider == sourcev1.AmazonBucketProvider {
		opts.Creds = credentials.NewIAM("")
	}
	return minio.New(obj.Spec.Endpoint, &opts)
}

// buildGCPClient constructs a gcp.GCPClient with the data from the given Secret.
// It returns an error if the Secret does not have the required field, or if the client construction fails.
func (r *BucketReconciler) buildGCPClient(ctx context.Context, secret *corev1.Secret) (*gcp.GCPClient, error) {
	var client *gcp.GCPClient
	var err error
	if secret != nil {
		if err := gcp.ValidateSecret(secret.Data, secret.Name); err != nil {
			return nil, err
		}
		client, err = gcp.NewClient(ctx, option.WithCredentialsJSON(secret.Data["serviceaccount"]))
		if err != nil {
			return nil, err
		}
	} else {
		client, err = gcp.NewClient(ctx)
		if err != nil {
			return nil, err
		}
	}
	return client, nil
}

// etagIndex is an index of bucket keys and their Etag values.
type etagIndex map[string]string

// Revision calculates the SHA256 checksum of the index.
// The keys are sorted to ensure a stable order, and the SHA256 sum is then calculated for the string representations of
// the key/value pairs, each pair written on a newline
// The sum result is returned as a string.
func (i etagIndex) Revision() (string, error) {
	keyIndex := make([]string, 0, len(i))
	for k := range i {
		keyIndex = append(keyIndex, k)
	}
	sort.Strings(keyIndex)
	sum := sha256.New()
	for _, k := range keyIndex {
		if _, err := sum.Write([]byte(fmt.Sprintf("%s  %s\n", k, i[k]))); err != nil {
			return "", err
		}
	}
	return fmt.Sprintf("%x", sum.Sum(nil)), nil
}

// eventLog records event and logs at the same time. This log is different from
// the debug log in the event recorder in the sense that this is a simple log,
// the event recorder debug log contains complete details about the event.
func (r *BucketReconciler) eventLogf(ctx context.Context, obj runtime.Object, eventType string, reason string, messageFmt string, args ...interface{}) {
	msg := fmt.Sprintf(messageFmt, args...)
	// Log and emit event.
	if eventType == corev1.EventTypeWarning {
		ctrl.LoggerFrom(ctx).Error(errors.New(reason), msg)
	} else {
		ctrl.LoggerFrom(ctx).Info(msg)
	}
	r.Eventf(obj, eventType, reason, msg)
}