Merge 4005f2b5a9 into ec49fff583

Accept multipart uploads where the combined checksum provides the expected part count.

It seems this was added by AWS to make the API more consistent, even if the 
data is entirely superfluous on multiple levels.

Improves AWS S3 compatibility.

cmd/admin-handlers-users.go

@@ -1217,9 +1217,9 @@ func (a adminAPIHandlers) AccountInfoHandler(w http.ResponseWriter, r *http.Requ
 	}
 
 	bucketStorageCache.InitOnce(10*time.Second,
-		cachevalue.Opts{ReturnLastGood: true, NoWait: true},
-		func() (DataUsageInfo, error) {
-			ctx, done := context.WithTimeout(context.Background(), 2*time.Second)
+		cachevalue.Opts{ReturnLastGood: true},
+		func(ctx context.Context) (DataUsageInfo, error) {
+			ctx, done := context.WithTimeout(ctx, 2*time.Second)
 			defer done()
 
 			return loadDataUsageFromBackend(ctx, objectAPI)

cmd/bucket-quota.go

@@ -49,8 +49,8 @@ var bucketStorageCache = cachevalue.New[DataUsageInfo]()
 func (sys *BucketQuotaSys) Init(objAPI ObjectLayer) {
 	bucketStorageCache.InitOnce(10*time.Second,
 		cachevalue.Opts{ReturnLastGood: true, NoWait: true},
-		func() (DataUsageInfo, error) {
-			ctx, done := context.WithTimeout(context.Background(), 2*time.Second)
+		func(ctx context.Context) (DataUsageInfo, error) {
+			ctx, done := context.WithTimeout(ctx, 2*time.Second)
 			defer done()
 
 			return loadDataUsageFromBackend(ctx, objAPI)
@@ -59,8 +59,8 @@ func (sys *BucketQuotaSys) Init(objAPI ObjectLayer) {
 }
 
 // GetBucketUsageInfo return bucket usage info for a given bucket
-func (sys *BucketQuotaSys) GetBucketUsageInfo(bucket string) (BucketUsageInfo, error) {
-	dui, err := bucketStorageCache.Get()
+func (sys *BucketQuotaSys) GetBucketUsageInfo(ctx context.Context, bucket string) (BucketUsageInfo, error) {
+	dui, err := bucketStorageCache.GetWithCtx(ctx)
 	timedout := OperationTimedOut{}
 	if err != nil && !errors.Is(err, context.DeadlineExceeded) && !errors.As(err, &timedout) {
 		if len(dui.BucketsUsage) > 0 {
@@ -118,7 +118,7 @@ func (sys *BucketQuotaSys) enforceQuotaHard(ctx context.Context, bucket string,
 			return BucketQuotaExceeded{Bucket: bucket}
 		}
 
-		bui, err := sys.GetBucketUsageInfo(bucket)
+		bui, err := sys.GetBucketUsageInfo(ctx, bucket)
 		if err != nil {
 			return err
 		}

cmd/data-usage.go

@@ -79,12 +79,12 @@ func loadPrefixUsageFromBackend(ctx context.Context, objAPI ObjectLayer, bucket
 	prefixUsageCache.InitOnce(30*time.Second,
 		// No need to fail upon Update() error, fallback to old value.
 		cachevalue.Opts{ReturnLastGood: true, NoWait: true},
-		func() (map[string]uint64, error) {
+		func(ctx context.Context) (map[string]uint64, error) {
 			m := make(map[string]uint64)
 			for _, pool := range z.serverPools {
 				for _, er := range pool.sets {
 					// Load bucket usage prefixes
-					ctx, done := context.WithTimeout(context.Background(), 2*time.Second)
+					ctx, done := context.WithTimeout(ctx, 2*time.Second)
 					ok := cache.load(ctx, er, bucket+slashSeparator+dataUsageCacheName) == nil
 					done()
 					if ok {
@@ -107,7 +107,7 @@ func loadPrefixUsageFromBackend(ctx context.Context, objAPI ObjectLayer, bucket
 		},
 	)
 
-	return prefixUsageCache.Get()
+	return prefixUsageCache.GetWithCtx(ctx)
 }
 
 func loadDataUsageFromBackend(ctx context.Context, objAPI ObjectLayer) (DataUsageInfo, error) {

cmd/erasure-multipart.go

@@ -1231,7 +1231,7 @@ func (er erasureObjects) CompleteMultipartUpload(ctx context.Context, bucket str
 	}
 
 	if opts.WantChecksum != nil {
-		err := opts.WantChecksum.Matches(checksumCombined)
+		err := opts.WantChecksum.Matches(checksumCombined, len(parts))
 		if err != nil {
 			return oi, err
 		}

cmd/erasure-server-pool.go

@@ -1962,8 +1962,8 @@ func (z *erasureServerPools) ListBuckets(ctx context.Context, opts BucketOptions
 	if opts.Cached {
 		listBucketsCache.InitOnce(time.Second,
 			cachevalue.Opts{ReturnLastGood: true, NoWait: true},
-			func() ([]BucketInfo, error) {
-				ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+			func(ctx context.Context) ([]BucketInfo, error) {
+				ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
 				defer cancel()
 
 				buckets, err = z.s3Peer.ListBuckets(ctx, opts)
@@ -1980,7 +1980,7 @@ func (z *erasureServerPools) ListBuckets(ctx context.Context, opts BucketOptions
 			},
 		)
 
-		return listBucketsCache.Get()
+		return listBucketsCache.GetWithCtx(ctx)
 	}
 
 	buckets, err = z.s3Peer.ListBuckets(ctx, opts)

cmd/metrics-v2.go

@@ -361,7 +361,7 @@ type MetricsGroupOpts struct {
 func (g *MetricsGroupV2) RegisterRead(read func(context.Context) []MetricV2) {
 	g.metricsCache = cachevalue.NewFromFunc(g.cacheInterval,
 		cachevalue.Opts{ReturnLastGood: true},
-		func() ([]MetricV2, error) {
+		func(ctx context.Context) ([]MetricV2, error) {
 			if g.metricsGroupOpts.dependGlobalObjectAPI {
 				objLayer := newObjectLayerFn()
 				// Service not initialized yet

cmd/metrics-v3-cache.go

@@ -18,6 +18,7 @@
 package cmd
 
 import (
+	"context"
 	"sync"
 	"time"
 
@@ -57,7 +58,7 @@ type nodesOnline struct {
 }
 
 func newNodesUpDownCache() *cachevalue.Cache[nodesOnline] {
-	loadNodesUpDown := func() (v nodesOnline, err error) {
+	loadNodesUpDown := func(ctx context.Context) (v nodesOnline, err error) {
 		v.Online, v.Offline = globalNotificationSys.GetPeerOnlineCount()
 		return
 	}
@@ -84,7 +85,7 @@ type storageMetrics struct {
 }
 
 func newDataUsageInfoCache() *cachevalue.Cache[DataUsageInfo] {
-	loadDataUsage := func() (u DataUsageInfo, err error) {
+	loadDataUsage := func(ctx context.Context) (u DataUsageInfo, err error) {
 		objLayer := newObjectLayerFn()
 		if objLayer == nil {
 			return
@@ -100,7 +101,7 @@ func newDataUsageInfoCache() *cachevalue.Cache[DataUsageInfo] {
 }
 
 func newESetHealthResultCache() *cachevalue.Cache[HealthResult] {
-	loadHealth := func() (r HealthResult, err error) {
+	loadHealth := func(ctx context.Context) (r HealthResult, err error) {
 		objLayer := newObjectLayerFn()
 		if objLayer == nil {
 			return
@@ -157,7 +158,7 @@ func newDriveMetricsCache() *cachevalue.Cache[storageMetrics] {
 		prevDriveIOStatsRefreshedAt time.Time
 	)
 
-	loadDriveMetrics := func() (v storageMetrics, err error) {
+	loadDriveMetrics := func(ctx context.Context) (v storageMetrics, err error) {
 		objLayer := newObjectLayerFn()
 		if objLayer == nil {
 			return
@@ -203,7 +204,7 @@ func newDriveMetricsCache() *cachevalue.Cache[storageMetrics] {
 }
 
 func newCPUMetricsCache() *cachevalue.Cache[madmin.CPUMetrics] {
-	loadCPUMetrics := func() (v madmin.CPUMetrics, err error) {
+	loadCPUMetrics := func(ctx context.Context) (v madmin.CPUMetrics, err error) {
 		var types madmin.MetricType = madmin.MetricsCPU
 
 		m := collectLocalMetrics(types, collectMetricsOpts{
@@ -228,7 +229,7 @@ func newCPUMetricsCache() *cachevalue.Cache[madmin.CPUMetrics] {
 }
 
 func newMemoryMetricsCache() *cachevalue.Cache[madmin.MemInfo] {
-	loadMemoryMetrics := func() (v madmin.MemInfo, err error) {
+	loadMemoryMetrics := func(ctx context.Context) (v madmin.MemInfo, err error) {
 		var types madmin.MetricType = madmin.MetricsMem
 
 		m := collectLocalMetrics(types, collectMetricsOpts{
@@ -253,7 +254,7 @@ func newMemoryMetricsCache() *cachevalue.Cache[madmin.MemInfo] {
 }
 
 func newClusterStorageInfoCache() *cachevalue.Cache[storageMetrics] {
-	loadStorageInfo := func() (v storageMetrics, err error) {
+	loadStorageInfo := func(ctx context.Context) (v storageMetrics, err error) {
 		objLayer := newObjectLayerFn()
 		if objLayer == nil {
 			return storageMetrics{}, nil

cmd/peer-rest-client.go

@@ -116,7 +116,7 @@ func (client *peerRESTClient) call(method string, values url.Values, body io.Rea
 // permanently. The only way to restore the connection is at the xl-sets layer by xlsets.monitorAndConnectEndpoints()
 // after verifying format.json
 func (client *peerRESTClient) callWithContext(ctx context.Context, method string, values url.Values, body io.Reader, length int64) (respBody io.ReadCloser, err error) {
-	if client == nil || !client.IsOnline() {
+	if client == nil {
 		return nil, errPeerNotReachable
 	}
 
@@ -129,6 +129,10 @@ func (client *peerRESTClient) callWithContext(ctx context.Context, method string
 		return respBody, nil
 	}
 
+	if xnet.IsNetworkOrHostDown(err, true) {
+		return nil, errPeerNotReachable
+	}
+
 	return nil, err
 }
 
@@ -139,7 +143,11 @@ func (client *peerRESTClient) String() string {
 
 // IsOnline returns true if the peer client is online.
 func (client *peerRESTClient) IsOnline() bool {
-	return client.restClient.IsOnline()
+	conn := client.gridConn()
+	if conn == nil {
+		return false
+	}
+	return client.restClient.IsOnline() || conn.State() == grid.StateConnected
 }
 
 // Close - marks the client as closed.

cmd/storage-rest-client.go

@@ -191,8 +191,13 @@ func (client *storageRESTClient) String() string {
 	return client.endpoint.String()
 }
 
-// IsOnline - returns whether RPC client failed to connect or not.
+// IsOnline - returns whether client failed to connect or not.
 func (client *storageRESTClient) IsOnline() bool {
+	return client.restClient.IsOnline() || client.IsOnlineWS()
+}
+
+// IsOnlineWS - returns whether websocket client failed to connect or not.
+func (client *storageRESTClient) IsOnlineWS() bool {
 	return client.gridConn.State() == grid.StateConnected
 }
 
@@ -254,7 +259,7 @@ func (client *storageRESTClient) NSScanner(ctx context.Context, cache dataUsageC
 }
 
 func (client *storageRESTClient) GetDiskID() (string, error) {
-	if !client.IsOnline() {
+	if !client.IsOnlineWS() {
 		// make sure to check if the disk is offline, since the underlying
 		// value is cached we should attempt to invalidate it if such calls
 		// were attempted. This can lead to false success under certain conditions
@@ -275,7 +280,7 @@ func (client *storageRESTClient) SetDiskID(id string) {
 }
 
 func (client *storageRESTClient) DiskInfo(ctx context.Context, opts DiskInfoOptions) (info DiskInfo, err error) {
-	if !client.IsOnline() {
+	if !client.IsOnlineWS() {
 		// make sure to check if the disk is offline, since the underlying
 		// value is cached we should attempt to invalidate it if such calls
 		// were attempted. This can lead to false success under certain conditions
@@ -302,10 +307,9 @@ func (client *storageRESTClient) DiskInfo(ctx context.Context, opts DiskInfoOpti
 		return info, nil
 	} // In all other cases cache the value upto 1sec.
 
-	client.diskInfoCache.InitOnce(time.Second,
-		cachevalue.Opts{CacheError: true},
-		func() (info DiskInfo, err error) {
-			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	client.diskInfoCache.InitOnce(time.Second, cachevalue.Opts{},
+		func(ctx context.Context) (info DiskInfo, err error) {
+			ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
 			defer cancel()
 
 			nopts := DiskInfoOptions{DiskID: *client.diskID.Load(), Metrics: true}
@@ -321,7 +325,7 @@ func (client *storageRESTClient) DiskInfo(ctx context.Context, opts DiskInfoOpti
 		},
 	)
 
-	return client.diskInfoCache.Get()
+	return client.diskInfoCache.GetWithCtx(ctx)
 }
 
 // MakeVolBulk - create multiple volumes in a bulk operation.

cmd/veeam-sos-api.go

@@ -156,7 +156,7 @@ func veeamSOSAPIGetObject(ctx context.Context, bucket, object string, rs *HTTPRa
 		}
 
 		q, _ := globalBucketQuotaSys.Get(ctx, bucket)
-		binfo, _ := globalBucketQuotaSys.GetBucketUsageInfo(bucket)
+		binfo, _ := globalBucketQuotaSys.GetBucketUsageInfo(ctx, bucket)
 
 		ci := capacityInfo{
 			Used: int64(binfo.Size),

cmd/xl-storage-disk-id-check.go

@@ -99,7 +99,7 @@ type xlStorageDiskIDCheck struct {
 func (p *xlStorageDiskIDCheck) getMetrics() DiskMetrics {
 	p.metricsCache.InitOnce(5*time.Second,
 		cachevalue.Opts{},
-		func() (DiskMetrics, error) {
+		func(ctx context.Context) (DiskMetrics, error) {
 			diskMetric := DiskMetrics{
 				LastMinute: make(map[string]AccElem, len(p.apiLatencies)),
 				APICalls:   make(map[string]uint64, len(p.apiCalls)),
@@ -114,7 +114,7 @@ func (p *xlStorageDiskIDCheck) getMetrics() DiskMetrics {
 		},
 	)
 
-	diskMetric, _ := p.metricsCache.Get()
+	diskMetric, _ := p.metricsCache.GetWithCtx(context.Background())
 	// Do not need this value to be cached.
 	diskMetric.TotalErrorsTimeout = p.totalErrsTimeout.Load()
 	diskMetric.TotalErrorsAvailability = p.totalErrsAvailability.Load()

cmd/xl-storage.go

@@ -331,7 +331,7 @@ func newXLStorage(ep Endpoint, cleanUp bool) (s *xlStorage, err error) {
 
 	// Initialize DiskInfo cache
 	s.diskInfoCache.InitOnce(time.Second, cachevalue.Opts{},
-		func() (DiskInfo, error) {
+		func(ctx context.Context) (DiskInfo, error) {
 			dcinfo := DiskInfo{}
 			di, err := getDiskInfo(s.drivePath)
 			if err != nil {
@@ -752,8 +752,8 @@ func (s *xlStorage) setWriteAttribute(writeCount uint64) error {
 
 // DiskInfo provides current information about disk space usage,
 // total free inodes and underlying filesystem.
-func (s *xlStorage) DiskInfo(_ context.Context, _ DiskInfoOptions) (info DiskInfo, err error) {
-	info, err = s.diskInfoCache.Get()
+func (s *xlStorage) DiskInfo(ctx context.Context, _ DiskInfoOptions) (info DiskInfo, err error) {
+	info, err = s.diskInfoCache.GetWithCtx(ctx)
 	info.NRRequests = s.nrRequests
 	info.Rotational = s.rotational
 	info.MountPath = s.drivePath

internal/cachevalue/cache.go

@@ -18,6 +18,7 @@
 package cachevalue
 
 import (
+	"context"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -30,11 +31,6 @@ type Opts struct {
 	// Returns the last good value AND the error.
 	ReturnLastGood bool
 
-	// If CacheError is set, errors will be cached as well
-	// and not continuously try to update.
-	// Should not be combined with ReturnLastGood.
-	CacheError bool
-
 	// If NoWait is set, Get() will return the last good value,
 	// if TTL has expired but 2x TTL has not yet passed,
 	// but will fetch a new value in the background.
@@ -50,7 +46,7 @@ type Cache[T any] struct {
 	// Only one caller will call this function at any time, others will be blocking.
 	// The returned value can no longer be modified once returned.
 	// Should be set before calling Get().
-	updateFn func() (T, error)
+	updateFn func(ctx context.Context) (T, error)
 
 	// ttl for a cached value.
 	ttl time.Duration
@@ -62,10 +58,7 @@ type Cache[T any] struct {
 	Once sync.Once
 
 	// Managed values.
-	valErr atomic.Pointer[struct {
-		v T
-		e error
-	}]
+	val          atomic.Pointer[T]
 	lastUpdateMs atomic.Int64
 	updating     sync.Mutex
 }
@@ -78,7 +71,7 @@ func New[T any]() *Cache[T] {
 
 // NewFromFunc allocates a new cached value instance and initializes it with an
 // update function, making it ready for use.
-func NewFromFunc[T any](ttl time.Duration, opts Opts, update func() (T, error)) *Cache[T] {
+func NewFromFunc[T any](ttl time.Duration, opts Opts, update func(ctx context.Context) (T, error)) *Cache[T] {
 	return &Cache[T]{
 		ttl:      ttl,
 		updateFn: update,
@@ -88,7 +81,7 @@ func NewFromFunc[T any](ttl time.Duration, opts Opts, update func() (T, error))
 
 // InitOnce initializes the cache with a TTL and an update function. It is
 // guaranteed to be called only once.
-func (t *Cache[T]) InitOnce(ttl time.Duration, opts Opts, update func() (T, error)) {
+func (t *Cache[T]) InitOnce(ttl time.Duration, opts Opts, update func(ctx context.Context) (T, error)) {
 	t.Once.Do(func() {
 		t.ttl = ttl
 		t.updateFn = update
@@ -96,61 +89,68 @@ func (t *Cache[T]) InitOnce(ttl time.Duration, opts Opts, update func() (T, erro
 	})
 }
 
-// Get will return a cached value or fetch a new one.
+// GetWithCtx will return a cached value or fetch a new one.
+// passes a caller context, if caller context cancels nothing
+// is cached.
 // Tf the Update function returns an error the value is forwarded as is and not cached.
-func (t *Cache[T]) Get() (T, error) {
-	v := t.valErr.Load()
+func (t *Cache[T]) GetWithCtx(ctx context.Context) (T, error) {
+	v := t.val.Load()
 	ttl := t.ttl
 	vTime := t.lastUpdateMs.Load()
 	tNow := time.Now().UnixMilli()
 	if v != nil && tNow-vTime < ttl.Milliseconds() {
-		if v.e == nil {
-			return v.v, nil
-		}
-		if v.e != nil && t.opts.CacheError || t.opts.ReturnLastGood {
-			return v.v, v.e
-		}
+		return *v, nil
 	}
 
-	// Fetch new value.
-	if t.opts.NoWait && v != nil && tNow-vTime < ttl.Milliseconds()*2 && (v.e == nil || t.opts.CacheError) {
+	// Fetch new value asynchronously, while we do not return an error
+	// if v != nil value or
+	if t.opts.NoWait && v != nil && tNow-vTime < ttl.Milliseconds()*2 {
 		if t.updating.TryLock() {
 			go func() {
 				defer t.updating.Unlock()
-				t.update()
+				t.update(context.Background())
 			}()
 		}
-		return v.v, v.e
+		return *v, nil
 	}
 
 	// Get lock. Either we get it or we wait for it.
 	t.updating.Lock()
+	defer t.updating.Unlock()
+
 	if time.Since(time.UnixMilli(t.lastUpdateMs.Load())) < ttl {
 		// There is a new value, release lock and return it.
-		v = t.valErr.Load()
-		t.updating.Unlock()
-		return v.v, v.e
-	}
-	t.update()
-	v = t.valErr.Load()
-	t.updating.Unlock()
-	return v.v, v.e
-}
-
-func (t *Cache[T]) update() {
-	val, err := t.updateFn()
-	if err != nil {
-		if t.opts.ReturnLastGood {
-			// Keep last good value.
-			v := t.valErr.Load()
-			if v != nil {
-				val = v.v
-			}
+		if v = t.val.Load(); v != nil {
+			return *v, nil
 		}
 	}
-	t.valErr.Store(&struct {
-		v T
-		e error
-	}{v: val, e: err})
-	t.lastUpdateMs.Store(time.Now().UnixMilli())
+
+	if err := t.update(ctx); err != nil {
+		var empty T
+		return empty, err
+	}
+
+	return *t.val.Load(), nil
+}
+
+// Get will return a cached value or fetch a new one.
+// Tf the Update function returns an error the value is forwarded as is and not cached.
+func (t *Cache[T]) Get() (T, error) {
+	return t.GetWithCtx(context.Background())
+}
+
+func (t *Cache[T]) update(ctx context.Context) error {
+	val, err := t.updateFn(ctx)
+	if err != nil {
+		if t.opts.ReturnLastGood && t.val.Load() != nil {
+			// Keep last good value, so update
+			// does not return an error.
+			return nil
+		}
+		return err
+	}
+
+	t.val.Store(&val)
+	t.lastUpdateMs.Store(time.Now().UnixMilli())
+	return nil
 }

internal/cachevalue/cache_test.go

@@ -18,15 +18,76 @@
 package cachevalue
 
 import (
+	"context"
+	"errors"
 	"testing"
 	"time"
 )
 
+func slowCaller(ctx context.Context) error {
+	sl := time.NewTimer(time.Second)
+	defer sl.Stop()
+
+	select {
+	case <-sl.C:
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+
+	return nil
+}
+
+func TestCacheCtx(t *testing.T) {
+	cache := New[time.Time]()
+	t.Parallel()
+	cache.InitOnce(2*time.Second, Opts{},
+		func(ctx context.Context) (time.Time, error) {
+			return time.Now(), slowCaller(ctx)
+		},
+	)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // cancel context to test.
+
+	_, err := cache.GetWithCtx(ctx)
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("expected context.Canceled err, got %v", err)
+	}
+
+	ctx, cancel = context.WithCancel(context.Background())
+	defer cancel()
+
+	t1, err := cache.GetWithCtx(ctx)
+	if err != nil {
+		t.Fatalf("expected nil err, got %v", err)
+	}
+
+	t2, err := cache.GetWithCtx(ctx)
+	if err != nil {
+		t.Fatalf("expected nil err, got %v", err)
+	}
+
+	if !t1.Equal(t2) {
+		t.Fatalf("expected time to be equal: %s != %s", t1, t2)
+	}
+
+	time.Sleep(3 * time.Second)
+
+	t3, err := cache.GetWithCtx(ctx)
+	if err != nil {
+		t.Fatalf("expected nil err, got %v", err)
+	}
+
+	if t1.Equal(t3) {
+		t.Fatalf("expected time to be un-equal: %s == %s", t1, t3)
+	}
+}
+
 func TestCache(t *testing.T) {
 	cache := New[time.Time]()
 	t.Parallel()
 	cache.InitOnce(2*time.Second, Opts{},
-		func() (time.Time, error) {
+		func(ctx context.Context) (time.Time, error) {
 			return time.Now(), nil
 		},
 	)
@@ -50,7 +111,7 @@ func TestCache(t *testing.T) {
 func BenchmarkCache(b *testing.B) {
 	cache := New[time.Time]()
 	cache.InitOnce(1*time.Millisecond, Opts{},
-		func() (time.Time, error) {
+		func(ctx context.Context) (time.Time, error) {
 			return time.Now(), nil
 		},
 	)

internal/hash/checksum.go

@@ -27,6 +27,7 @@ import (
 	"hash"
 	"hash/crc32"
 	"net/http"
+	"strconv"
 	"strings"
 
 	"github.com/minio/minio/internal/hash/sha256"
@@ -71,9 +72,10 @@ const (
 
 // Checksum is a type and base 64 encoded value.
 type Checksum struct {
-	Type    ChecksumType
-	Encoded string
-	Raw     []byte
+	Type      ChecksumType
+	Encoded   string
+	Raw       []byte
+	WantParts int
 }
 
 // Is returns if c is all of t.
@@ -260,13 +262,14 @@ func ReadPartCheckSums(b []byte) (res []map[string]string) {
 		}
 		// Skip main checksum
 		b = b[length:]
-		if !typ.Is(ChecksumIncludesMultipart) {
-			continue
-		}
 		parts, n := binary.Uvarint(b)
 		if n <= 0 {
 			break
 		}
+		if !typ.Is(ChecksumIncludesMultipart) {
+			continue
+		}
+
 		if len(res) == 0 {
 			res = make([]map[string]string, parts)
 		}
@@ -292,11 +295,25 @@ func NewChecksumWithType(alg ChecksumType, value string) *Checksum {
 	if !alg.IsSet() {
 		return nil
 	}
+	wantParts := 0
+	if strings.ContainsRune(value, '-') {
+		valSplit := strings.Split(value, "-")
+		if len(valSplit) != 2 {
+			return nil
+		}
+		value = valSplit[0]
+		nParts, err := strconv.Atoi(valSplit[1])
+		if err != nil {
+			return nil
+		}
+		alg |= ChecksumMultipart
+		wantParts = nParts
+	}
 	bvalue, err := base64.StdEncoding.DecodeString(value)
 	if err != nil {
 		return nil
 	}
-	c := Checksum{Type: alg, Encoded: value, Raw: bvalue}
+	c := Checksum{Type: alg, Encoded: value, Raw: bvalue, WantParts: wantParts}
 	if !c.Valid() {
 		return nil
 	}
@@ -325,12 +342,15 @@ func (c *Checksum) AppendTo(b []byte, parts []byte) []byte {
 	b = append(b, crc...)
 	if c.Type.Is(ChecksumMultipart) {
 		var checksums int
+		if c.WantParts > 0 && !c.Type.Is(ChecksumIncludesMultipart) {
+			checksums = c.WantParts
+		}
 		// Ensure we don't divide by 0:
 		if c.Type.RawByteLen() == 0 || len(parts)%c.Type.RawByteLen() != 0 {
 			hashLogIf(context.Background(), fmt.Errorf("internal error: Unexpected checksum length: %d, each checksum %d", len(parts), c.Type.RawByteLen()))
 			checksums = 0
 			parts = nil
-		} else {
+		} else if len(parts) > 0 {
 			checksums = len(parts) / c.Type.RawByteLen()
 		}
 		if !c.Type.Is(ChecksumIncludesMultipart) {
@@ -358,7 +378,7 @@ func (c Checksum) Valid() bool {
 }
 
 // Matches returns whether given content matches c.
-func (c Checksum) Matches(content []byte) error {
+func (c Checksum) Matches(content []byte, parts int) error {
 	if len(c.Encoded) == 0 {
 		return nil
 	}
@@ -368,6 +388,13 @@ func (c Checksum) Matches(content []byte) error {
 		return err
 	}
 	sum := hasher.Sum(nil)
+	if c.WantParts > 0 && c.WantParts != parts {
+		return ChecksumMismatch{
+			Want: fmt.Sprintf("%s-%d", c.Encoded, c.WantParts),
+			Got:  fmt.Sprintf("%s-%d", base64.StdEncoding.EncodeToString(sum), parts),
+		}
+	}
+
 	if !bytes.Equal(sum, c.Raw) {
 		return ChecksumMismatch{
 			Want: c.Encoded,