Limit to single inflight package syncing operation

client/httpclient.go

@@ -131,6 +131,7 @@ func (c *httpClient) runUntilStopped(ctx context.Context) {
 		&c.common.ClientSyncedState,
 		c.common.PackagesStateProvider,
 		c.common.Capabilities,
+		&c.common.PackageSyncMutex,
 	)
 }
 

client/internal/clientcommon.go

@@ -41,6 +41,9 @@ type ClientCommon struct {
 	// PackagesStateProvider provides access to the local state of packages.
 	PackagesStateProvider types.PackagesStateProvider
 
+	// PackageSyncMutex makes sure only one package syncing operation happens at a time.
+	PackageSyncMutex sync.Mutex
+
 	// The transport-specific sender.
 	sender Sender
 

client/internal/httpsender.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"sync"
 	"sync/atomic"
 	"time"
 
@@ -91,10 +92,11 @@ func (h *HTTPSender) Run(
 	clientSyncedState *ClientSyncedState,
 	packagesStateProvider types.PackagesStateProvider,
 	capabilities protobufs.AgentCapabilities,
+	packageSyncMutex *sync.Mutex,
 ) {
 	h.url = url
 	h.callbacks = callbacks
-	h.receiveProcessor = newReceivedProcessor(h.logger, callbacks, h, clientSyncedState, packagesStateProvider, capabilities)
+	h.receiveProcessor = newReceivedProcessor(h.logger, callbacks, h, clientSyncedState, packagesStateProvider, capabilities, packageSyncMutex)
 
 	for {
 		pollingTimer := time.NewTimer(time.Millisecond * time.Duration(atomic.LoadInt64(&h.pollingIntervalMs)))

client/internal/httpsender_test.go

@@ -183,7 +183,7 @@ func TestRequestInstanceUidFlagReset(t *testing.T) {
 	clientSyncedState := &ClientSyncedState{}
 	clientSyncedState.SetFlags(protobufs.AgentToServerFlags_AgentToServerFlags_RequestInstanceUid)
 	capabilities := protobufs.AgentCapabilities_AgentCapabilities_Unspecified
-	sender.receiveProcessor = newReceivedProcessor(&sharedinternal.NopLogger{}, sender.callbacks, sender, clientSyncedState, nil, capabilities)
+	sender.receiveProcessor = newReceivedProcessor(&sharedinternal.NopLogger{}, sender.callbacks, sender, clientSyncedState, nil, capabilities, new(sync.Mutex))
 
 	// If we process a message with a nil AgentIdentification, or an incorrect NewInstanceUid.
 	sender.receiveProcessor.ProcessReceivedMessage(ctx,
@@ -208,3 +208,123 @@ func TestRequestInstanceUidFlagReset(t *testing.T) {
 	assert.Equal(t, sender.receiveProcessor.clientSyncedState.flags, protobufs.AgentToServerFlags_AgentToServerFlags_Unspecified)
 	cancel()
 }
+
+func TestPackageUpdatesInParallel(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	localPackageState := NewInMemPackagesStore()
+	sender := NewHTTPSender(&sharedinternal.NopLogger{})
+	ch := make(chan struct{})
+	doneCh := make([]<-chan struct{}, 0)
+
+	// Use this to simulate blocking behavior on the first call to Sync().
+	localPackageState.onAllPackagesHash = func() {
+		if localPackageState.lastReportedStatuses != nil {
+			<-ch
+		}
+	}
+
+	var messages atomic.Int32
+	var mux sync.Mutex
+	sender.callbacks = types.CallbacksStruct{
+		OnMessageFunc: func(ctx context.Context, msg *types.MessageData) {
+			err := msg.PackageSyncer.Sync(ctx)
+			assert.NoError(t, err)
+			messages.Add(1)
+			doneCh = append(doneCh, msg.PackageSyncer.Done())
+		},
+	}
+
+	clientSyncedState := &ClientSyncedState{}
+	capabilities := protobufs.AgentCapabilities_AgentCapabilities_AcceptsPackages
+	sender.receiveProcessor = newReceivedProcessor(&sharedinternal.NopLogger{}, sender.callbacks, sender, clientSyncedState, localPackageState, capabilities, &mux)
+
+	sender.receiveProcessor.ProcessReceivedMessage(ctx,
+		&protobufs.ServerToAgent{
+			PackagesAvailable: &protobufs.PackagesAvailable{
+				Packages: map[string]*protobufs.PackageAvailable{
+					"package1": {
+						Type:    protobufs.PackageType_PackageType_TopLevel,
+						Version: "1.0.0",
+						File: &protobufs.DownloadableFile{
+							DownloadUrl: "foo",
+							ContentHash: []byte{4, 5},
+						},
+						Hash: []byte{1, 2, 3},
+					},
+				},
+				AllPackagesHash: []byte{1, 2, 3, 4, 5},
+			},
+		})
+	sender.receiveProcessor.ProcessReceivedMessage(ctx,
+		&protobufs.ServerToAgent{
+			PackagesAvailable: &protobufs.PackagesAvailable{
+				Packages: map[string]*protobufs.PackageAvailable{
+					"package22": {
+						Type:    protobufs.PackageType_PackageType_TopLevel,
+						Version: "1.0.0",
+						File: &protobufs.DownloadableFile{
+							DownloadUrl: "bar",
+							ContentHash: []byte{4, 5},
+						},
+						Hash: []byte{1, 2, 3},
+					},
+				},
+				AllPackagesHash: []byte{1, 2, 3, 4, 5},
+			},
+		})
+
+	// Make sure that both Sync calls have gone through _before_ releasing the first.
+	// This means that they're both called in parallel, but locking makes sure
+	// that this is not a race condition.
+	assert.Eventually(t, func() bool {
+		return messages.Load() == 2
+	}, 2*time.Second, 100*time.Millisecond, "both messages must have been processed successfully")
+
+	// Release the first Sync call so it can continue and wait for both of them to complete.
+	ch <- struct{}{}
+	<-doneCh[0]
+	<-doneCh[1]
+
+	cancel()
+}
+
+func TestPackageUpdatesWithError(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	sender := NewHTTPSender(&sharedinternal.NopLogger{})
+
+	// We'll pass in a nil PackageStateProvider to force the Sync call to return with an error.
+	localPackageState := types.PackagesStateProvider(nil)
+	var messages atomic.Int32
+	var mux sync.Mutex
+	sender.callbacks = types.CallbacksStruct{
+		OnMessageFunc: func(ctx context.Context, msg *types.MessageData) {
+			// Make sure the call to Sync will return an error due to a nil PackageStateProvider
+			err := msg.PackageSyncer.Sync(ctx)
+			assert.Error(t, err)
+			messages.Add(1)
+		},
+	}
+
+	clientSyncedState := &ClientSyncedState{}
+
+	capabilities := protobufs.AgentCapabilities_AgentCapabilities_AcceptsPackages
+	sender.receiveProcessor = newReceivedProcessor(&sharedinternal.NopLogger{}, sender.callbacks, sender, clientSyncedState, localPackageState, capabilities, &mux)
+
+	// Send two messages in parallel.
+	sender.receiveProcessor.ProcessReceivedMessage(ctx,
+		&protobufs.ServerToAgent{
+			PackagesAvailable: &protobufs.PackagesAvailable{},
+		})
+	sender.receiveProcessor.ProcessReceivedMessage(ctx,
+		&protobufs.ServerToAgent{
+			PackagesAvailable: &protobufs.PackagesAvailable{},
+		})
+
+	// Make sure that even though the call to Sync errored out early, the lock
+	// was still released properly for both messages to be processed.
+	assert.Eventually(t, func() bool {
+		return messages.Load() == 2
+	}, 5*time.Second, 100*time.Millisecond, "both messages must have been processed successfully")
+
+	cancel()
+}

client/internal/inmempackagestore.go

@@ -15,6 +15,8 @@ type InMemPackagesStore struct {
 	fileContents         map[string][]byte
 	fileHashes           map[string][]byte
 	lastReportedStatuses *protobufs.PackageStatuses
+
+	onAllPackagesHash func()
 }
 
 var _ types.PackagesStateProvider = (*InMemPackagesStore)(nil)
@@ -28,6 +30,9 @@ func NewInMemPackagesStore() *InMemPackagesStore {
 }
 
 func (l *InMemPackagesStore) AllPackagesHash() ([]byte, error) {
+	if l.onAllPackagesHash != nil {
+		l.onAllPackagesHash()
+	}
 	return l.allPackagesHash, nil
 }
 

client/internal/packagessyncer.go

@@ -6,6 +6,7 @@
 	"errors"
 	"fmt"
 	"net/http"
+	"sync"
 
 	"github.com/open-telemetry/opamp-go/client/types"
 	"github.com/open-telemetry/opamp-go/protobufs"
@@ -20,6 +21,7 @@
 	sender            Sender
 
 	statuses *protobufs.PackageStatuses
+	mux      *sync.Mutex
 	doneCh   chan struct{}
 }
 
@@ -30,6 +32,7 @@
 	sender Sender,
 	clientSyncedState *ClientSyncedState,
 	packagesStateProvider types.PackagesStateProvider,
+	mux *sync.Mutex,
 ) *packagesSyncer {
 	return &packagesSyncer{
 		logger:            logger,
@@ -38,6 +41,7 @@
 		clientSyncedState: clientSyncedState,
 		localState:        packagesStateProvider,
 		doneCh:            make(chan struct{}),
+		mux:               mux,
 	}
 }
 
@@ -49,15 +53,24 @@
 	}()
 
 	// Prepare package statuses.
+	// Grab a lock to make sure that package statuses are not overriden by
+	// another call to Sync running in parallel.
+	// In case Sync returns early with an error, take care of unlocking the
+	// mutex in this goroutine; otherwise it will be unlocked at the end
+	// of the sync operation.
+	s.mux.Lock()
 	if err := s.initStatuses(); err != nil {
+		s.mux.Unlock()
 		return err
 	}
 
 	if err := s.clientSyncedState.SetPackageStatuses(s.statuses); err != nil {
+		s.mux.Unlock()
 		return err
 	}
 
-	// Now do the actual syncing in the background.
+	// Now do the actual syncing in the background and release the lock from
+	// inside of the goroutine.
 	go s.doSync(ctx)
 
 	return nil
@@ -99,6 +112,10 @@
 
 // doSync performs the actual syncing process.
 func (s *packagesSyncer) doSync(ctx context.Context) {
+	// Once doSync returns  in a separate goroutine, make sure to release the
+	// mutex so that a new syncing process can take place.
+	defer s.mux.Unlock()
+
 	hash, err := s.localState.AllPackagesHash()
 	if err != nil {
 		s.logger.Errorf(ctx, "Package syncing failed: %V", err)

client/internal/receivedprocessor.go

@@ -3,6 +3,7 @@ package internal
 import (
 	"context"
 	"fmt"
+	"sync"
 
 	"github.com/open-telemetry/opamp-go/client/types"
 	"github.com/open-telemetry/opamp-go/protobufs"
@@ -24,6 +25,9 @@ type receivedProcessor struct {
 
 	packagesStateProvider types.PackagesStateProvider
 
+	// packageSyncMutex protects against multiple package syncing operations at the same time.
+	packageSyncMutex *sync.Mutex
+
 	// Agent's capabilities defined at Start() time.
 	capabilities protobufs.AgentCapabilities
 }
@@ -35,6 +39,7 @@ func newReceivedProcessor(
 	clientSyncedState *ClientSyncedState,
 	packagesStateProvider types.PackagesStateProvider,
 	capabilities protobufs.AgentCapabilities,
+	packageSyncMutex *sync.Mutex,
 ) receivedProcessor {
 	return receivedProcessor{
 		logger:                logger,
@@ -43,6 +48,7 @@ func newReceivedProcessor(
 		clientSyncedState:     clientSyncedState,
 		packagesStateProvider: packagesStateProvider,
 		capabilities:          capabilities,
+		packageSyncMutex:      packageSyncMutex,
 	}
 }
 
@@ -122,6 +128,7 @@ func (r *receivedProcessor) ProcessReceivedMessage(ctx context.Context, msg *pro
 					r.sender,
 					r.clientSyncedState,
 					r.packagesStateProvider,
+					r.packageSyncMutex,
 				)
 			} else {
 				r.logger.Debugf(ctx, "Ignoring PackagesAvailable, agent does not have AcceptsPackages capability")

client/internal/wsreceiver.go

@@ -3,6 +3,7 @@ package internal
 import (
 	"context"
 	"fmt"
+	"sync"
 
 	"github.com/gorilla/websocket"
 	"github.com/open-telemetry/opamp-go/client/types"
@@ -32,13 +33,14 @@ func NewWSReceiver(
 	clientSyncedState *ClientSyncedState,
 	packagesStateProvider types.PackagesStateProvider,
 	capabilities protobufs.AgentCapabilities,
+	packageSyncMutex *sync.Mutex,
 ) *wsReceiver {
 	w := &wsReceiver{
 		conn:      conn,
 		logger:    logger,
 		sender:    sender,
 		callbacks: callbacks,
-		processor: newReceivedProcessor(logger, callbacks, sender, clientSyncedState, packagesStateProvider, capabilities),
+		processor: newReceivedProcessor(logger, callbacks, sender, clientSyncedState, packagesStateProvider, capabilities, packageSyncMutex),
 		stopped:   make(chan struct{}),
 	}