[azeventhubs] Fixing checkpoint store race condition (#20727)

The checkpoint store wasn't guarding against multiple owners claiming for the first time - fixing this by using IfNoneMatch

Fixes #20717

sdk/messaging/azeventhubs/CHANGELOG.md

@@ -14,6 +14,7 @@
 - Potential leaks for $cbs and $management when there was a partial failure. (PR#20564)
 - Latest go-amqp changes have been merged in with fixes for robustness.
 - Sending a message to an entity that is full will no longer retry. (PR#20722)
+- Checkpoint store handles multiple initial owners properly, allowing only one through. (PR#20727)
 
 ## 0.6.0 (2023-03-07)
 

sdk/messaging/azeventhubs/checkpoints/blob_store.go

@@ -44,6 +44,9 @@ func NewBlobStore(containerClient *container.Client, options *BlobStoreOptions)
 
 // ClaimOwnership attempts to claim ownership of the partitions in partitionOwnership and returns
 // the actual partitions that were claimed.
+//
+// If we fail to claim ownership because of another update then it will be omitted from the
+// returned slice of [Ownership]'s. It is not considered an error.
 func (b *BlobStore) ClaimOwnership(ctx context.Context, partitionOwnership []azeventhubs.Ownership, options *azeventhubs.ClaimOwnershipOptions) ([]azeventhubs.Ownership, error) {
 	var ownerships []azeventhubs.Ownership
 
@@ -54,13 +57,12 @@ func (b *BlobStore) ClaimOwnership(ctx context.Context, partitionOwnership []aze
 		if err != nil {
 			return nil, err
 		}
-		lastModified, etag, err := b.setMetadata(ctx, blobName, newOwnershipBlobMetadata(po), po.ETag)
+		lastModified, etag, err := b.setOwnershipMetadata(ctx, blobName, po)
 
 		if err != nil {
-			if bloberror.HasCode(err, bloberror.ConditionNotMet) {
-				// we can fail to claim ownership and that's okay - it's expected that clients will
-				// attempt to claim with whatever state they hold locally. If they fail it just means
-				// someone else claimed ownership before them.
+			if bloberror.HasCode(err,
+				bloberror.ConditionNotMet,     // updated before we could update it
+				bloberror.BlobAlreadyExists) { // created before we could create it
 				continue
 			}
 
@@ -179,25 +181,28 @@ func (b *BlobStore) ListOwnership(ctx context.Context, fullyQualifiedNamespace s
 }
 
 // UpdateCheckpoint updates a specific checkpoint with a sequence and offset.
+//
+// NOTE: This function doesn't attempt to prevent simultaneous checkpoint updates - ownership is assumed.
 func (b *BlobStore) UpdateCheckpoint(ctx context.Context, checkpoint azeventhubs.Checkpoint, options *azeventhubs.UpdateCheckpointOptions) error {
 	blobName, err := nameForCheckpointBlob(checkpoint)
 
 	if err != nil {
 		return err
 	}
 
-	_, _, err = b.setMetadata(ctx, blobName, newCheckpointBlobMetadata(checkpoint), nil)
+	_, _, err = b.setCheckpointMetadata(ctx, blobName, checkpoint)
 	return err
 }
 
-func (b *BlobStore) setMetadata(ctx context.Context, blobName string, blobMetadata map[string]*string, etag *azcore.ETag) (*time.Time, azcore.ETag, error) {
+func (b *BlobStore) setOwnershipMetadata(ctx context.Context, blobName string, ownership azeventhubs.Ownership) (*time.Time, azcore.ETag, error) {
+	blobMetadata := newOwnershipBlobMetadata(ownership)
 	blobClient := b.cc.NewBlockBlobClient(blobName)
 
-	if etag != nil {
+	if ownership.ETag != nil {
 		setMetadataResp, err := blobClient.SetMetadata(ctx, blobMetadata, &blob.SetMetadataOptions{
 			AccessConditions: &blob.AccessConditions{
 				ModifiedAccessConditions: &blob.ModifiedAccessConditions{
-					IfMatch: etag,
+					IfMatch: ownership.ETag,
 				},
 			},
 		})
@@ -207,29 +212,52 @@ func (b *BlobStore) setMetadata(ctx context.Context, blobName string, blobMetada
 		}
 
 		return setMetadataResp.LastModified, *setMetadataResp.ETag, nil
-	} else {
-		setMetadataResp, err := blobClient.SetMetadata(ctx, blobMetadata, nil)
+	}
 
-		if err == nil {
-			return setMetadataResp.LastModified, *setMetadataResp.ETag, nil
-		}
+	uploadResp, err := blobClient.Upload(ctx, streaming.NopCloser(bytes.NewReader([]byte{})), &blockblob.UploadOptions{
+		Metadata: blobMetadata,
+		AccessConditions: &blob.AccessConditions{
+			ModifiedAccessConditions: &blob.ModifiedAccessConditions{
+				IfNoneMatch: to.Ptr(azcore.ETag("*")),
+			},
+		},
+	})
 
-		if !bloberror.HasCode(err, bloberror.BlobNotFound) {
-			return nil, "", err
-		}
+	if err != nil {
+		return nil, "", err
+	}
 
-		// in JS they check to see if the error is BlobNotFound. If it is, then they
-		// do a full upload of a blob instead.
-		uploadResp, err := blobClient.Upload(ctx, streaming.NopCloser(bytes.NewReader([]byte{})), &blockblob.UploadOptions{
-			Metadata: blobMetadata,
-		})
+	return uploadResp.LastModified, *uploadResp.ETag, nil
+}
 
-		if err != nil {
-			return nil, "", err
-		}
+// setCheckpointMetadata sets the metadata for a checkpoint, falling back to creating
+// the blob if it doesn't already exist.
+//
+// NOTE: unlike [setOwnershipMetadata] this function doesn't attempt to prevent simultaneous
+// checkpoint updates - ownership is assumed.
+func (b *BlobStore) setCheckpointMetadata(ctx context.Context, blobName string, checkpoint azeventhubs.Checkpoint) (*time.Time, azcore.ETag, error) {
+	blobMetadata := newCheckpointBlobMetadata(checkpoint)
+	blobClient := b.cc.NewBlockBlobClient(blobName)
+
+	setMetadataResp, err := blobClient.SetMetadata(ctx, blobMetadata, nil)
+
+	if err == nil {
+		return setMetadataResp.LastModified, *setMetadataResp.ETag, nil
+	}
 
-		return uploadResp.LastModified, *uploadResp.ETag, nil
+	if !bloberror.HasCode(err, bloberror.BlobNotFound) {
+		return nil, "", err
 	}
+
+	uploadResp, err := blobClient.Upload(ctx, streaming.NopCloser(bytes.NewReader([]byte{})), &blockblob.UploadOptions{
+		Metadata: blobMetadata,
+	})
+
+	if err != nil {
+		return nil, "", err
+	}
+
+	return uploadResp.LastModified, *uploadResp.ETag, nil
 }
 
 func nameForCheckpointBlob(a azeventhubs.Checkpoint) (string, error) {

sdk/messaging/azeventhubs/checkpoints/blob_store_test.go

@@ -4,6 +4,7 @@ package checkpoints_test
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"strconv"
 	"testing"
@@ -216,6 +217,126 @@ func TestBlobStore_ListAndClaim(t *testing.T) {
 	require.Empty(t, claimedOwnerships)
 }
 
+func TestBlobStore_OnlyOneOwnershipClaimSucceeds(t *testing.T) {
+	testData := getContainerClient(t)
+	defer testData.Cleanup()
+
+	cc, err := container.NewClientFromConnectionString(testData.ConnectionString, testData.ContainerName, nil)
+	require.NoError(t, err)
+
+	store, err := checkpoints.NewBlobStore(cc, nil)
+	require.NoError(t, err)
+
+	// we're going to make multiple calls to the blob store but only _one_ should succeed
+	// since it's "first one in wins"
+	claimsCh := make(chan []azeventhubs.Ownership, 20)
+
+	t.Logf("Starting %d goroutines to claim ownership without an etag", cap(claimsCh))
+
+	// attempt to claim the same partition from multiple goroutines. Only _one_ of the
+	// goroutines should walk away thinking it claimed the partition.
+	for i := 0; i < cap(claimsCh); i++ {
+		go func() {
+			ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+			defer cancel()
+
+			ownerships, err := store.ClaimOwnership(ctx, []azeventhubs.Ownership{
+				{ConsumerGroup: azeventhubs.DefaultConsumerGroup, EventHubName: "name", FullyQualifiedNamespace: "ns", PartitionID: "0", OwnerID: "ownerID"},
+			}, nil)
+
+			if err != nil {
+				claimsCh <- nil
+				require.NoError(t, err)
+			} else {
+				claimsCh <- ownerships
+			}
+		}()
+	}
+
+	claimed := map[string]bool{}
+	numFailedClaims := 0
+
+	for i := 0; i < cap(claimsCh); i++ {
+		claims := <-claimsCh
+
+		if claims == nil {
+			numFailedClaims++
+			continue
+		}
+
+		for _, claim := range claims {
+			require.False(t, claimed[claim.PartitionID], fmt.Sprintf("Partition ID %s was claimed more than once", claim.PartitionID))
+			require.NotNil(t, claim.ETag)
+			claimed[claim.PartitionID] = true
+		}
+	}
+
+	require.Equal(t, cap(claimsCh)-1, numFailedClaims, fmt.Sprintf("One of the 1/%d wins and the rest all fail to claim", cap(claimsCh)))
+}
+
+func TestBlobStore_OnlyOneOwnershipUpdateSucceeds(t *testing.T) {
+	testData := getContainerClient(t)
+	defer testData.Cleanup()
+
+	cc, err := container.NewClientFromConnectionString(testData.ConnectionString, testData.ContainerName, nil)
+	require.NoError(t, err)
+
+	store, err := checkpoints.NewBlobStore(cc, nil)
+	require.NoError(t, err)
+
+	// we're going to make multiple calls to the blob store but only _one_ should succeed
+	// since it's "first one in wins"
+	claimsCh := make(chan []azeventhubs.Ownership, 20)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+
+	ownerships, err := store.ClaimOwnership(ctx, []azeventhubs.Ownership{
+		{ConsumerGroup: azeventhubs.DefaultConsumerGroup, EventHubName: "name", FullyQualifiedNamespace: "ns", PartitionID: "0", OwnerID: "ownerID"},
+	}, nil)
+	require.NoError(t, err)
+	require.Equal(t, "0", ownerships[0].PartitionID)
+	require.NotNil(t, ownerships[0].ETag)
+
+	t.Logf("Starting %d goroutines to claim ownership without an etag", cap(claimsCh))
+
+	// attempt to claim the same partition from multiple goroutines. Only _one_ of the
+	// goroutines should walk away thinking it claimed the partition.
+	for i := 0; i < cap(claimsCh); i++ {
+		go func() {
+
+			ownerships, err := store.ClaimOwnership(ctx, ownerships, nil)
+
+			if err != nil {
+				claimsCh <- nil
+				require.NoError(t, err)
+			} else {
+				claimsCh <- ownerships
+			}
+		}()
+	}
+
+	claimed := map[string]bool{}
+	numFailedClaims := 0
+
+	for i := 0; i < cap(claimsCh); i++ {
+		claims := <-claimsCh
+
+		if claims == nil {
+			numFailedClaims++
+			continue
+		}
+
+		for _, claim := range claims {
+			require.False(t, claimed[claim.PartitionID], fmt.Sprintf("Partition ID %s was claimed more than once", claim.PartitionID))
+			require.NotNil(t, claim.ETag)
+			claimed[claim.PartitionID] = true
+		}
+	}
+
+	require.Equal(t, cap(claimsCh)-1, numFailedClaims, fmt.Sprintf("One of the 1/%d wins and the rest all fail to claim", cap(claimsCh)))
+}
+
 func getContainerClient(t *testing.T) struct {
 	ConnectionString string
 	ContainerName    string

sdk/messaging/azeventhubs/internal/test/test_helpers.go

@@ -40,6 +40,13 @@ func CaptureLogsForTest() func() []string {
 
 func CaptureLogsForTestWithChannel(messagesCh chan string) func() []string {
 	setAzLogListener(func(e azlog.Event, s string) {
+		defer func() {
+			if err := recover(); err != nil {
+				fmt.Printf("FAILED SENDING MESSAGE (%s), message was: [%s] %s\n", err, e, s)
+				panic(err)
+			}
+		}()
+
 		messagesCh <- fmt.Sprintf("[%s] %s", e, s)
 	})