CopyObject must preserve checksums and encrypt them if required (#21399)

cmd/encryption-v1.go

@@ -1074,8 +1074,16 @@ func (o *ObjectInfo) metadataDecrypter(h http.Header) objectMetaDecryptFn {
 			return input, nil
 		}
 		var key []byte
-		if k, err := crypto.SSEC.ParseHTTP(h); err == nil {
+		if crypto.SSECopy.IsRequested(h) {
-			key = k[:]
+			sseCopyKey, err := crypto.SSECopy.ParseHTTP(h)
+			if err != nil {
+				return nil, err
+			}
+			key = sseCopyKey[:]
+		} else {
+			if k, err := crypto.SSEC.ParseHTTP(h); err == nil {
+				key = k[:]
+			}
 		}
 		key, err := decryptObjectMeta(key, o.Bucket, o.Name, o.UserDefined)
 		if err != nil {
@@ -1087,7 +1095,8 @@ func (o *ObjectInfo) metadataDecrypter(h http.Header) objectMetaDecryptFn {
 	}
 }
 
-// decryptPartsChecksums will attempt to decode checksums and return it/them if set.
+// decryptPartsChecksums will attempt to decrypt and decode part checksums, and save
+// only the decrypted part checksum values on ObjectInfo directly.
 // if part > 0, and we have the checksum for the part that will be returned.
 func (o *ObjectInfo) decryptPartsChecksums(h http.Header) {
 	data := o.Checksum
@@ -1112,6 +1121,23 @@ func (o *ObjectInfo) decryptPartsChecksums(h http.Header) {
 	}
 }
 
+// decryptChecksum will attempt to decrypt the ObjectInfo.Checksum, returns the decrypted value
+// An error is only returned if it was encrypted and the decryption failed.
+func (o *ObjectInfo) decryptChecksum(h http.Header) ([]byte, error) {
+	data := o.Checksum
+	if len(data) == 0 {
+		return data, nil
+	}
+	if _, encrypted := crypto.IsEncrypted(o.UserDefined); encrypted {
+		decrypted, err := o.metadataDecrypter(h)("object-checksum", data)
+		if err != nil {
+			return nil, err
+		}
+		data = decrypted
+	}
+	return data, nil
+}
+
 // metadataEncryptFn provides an encryption function for metadata.
 // Will return nil, nil if unencrypted.
 func (o *ObjectInfo) metadataEncryptFn(headers http.Header) (objectMetaEncryptFn, error) {

cmd/erasure-object.go

@@ -1470,7 +1470,17 @@ func (er erasureObjects) putObject(ctx context.Context, bucket string, object st
 			actualSize = n
 		}
 	}
-	if fi.Checksum == nil {
+	// If ServerSideChecksum is wanted for this object, it takes precedence
+	// over opts.WantChecksum.
+	if opts.WantServerSideChecksumType.IsSet() {
+		serverSideChecksum := r.RawServerSideChecksumResult()
+		if serverSideChecksum != nil {
+			fi.Checksum = serverSideChecksum.AppendTo(nil, nil)
+			if opts.EncryptFn != nil {
+				fi.Checksum = opts.EncryptFn("object-checksum", fi.Checksum)
+			}
+		}
+	} else if fi.Checksum == nil && opts.WantChecksum != nil {
 		// Trailing headers checksums should now be filled.
 		fi.Checksum = opts.WantChecksum.AppendTo(nil, nil)
 		if opts.EncryptFn != nil {

cmd/erasure-server-pool.go

@@ -1340,12 +1340,15 @@ func (z *erasureServerPools) CopyObject(ctx context.Context, srcBucket, srcObjec
 	}
 
 	putOpts := ObjectOptions{
-		ServerSideEncryption: dstOpts.ServerSideEncryption,
+		ServerSideEncryption:       dstOpts.ServerSideEncryption,
-		UserDefined:          srcInfo.UserDefined,
+		UserDefined:                srcInfo.UserDefined,
-		Versioned:            dstOpts.Versioned,
+		Versioned:                  dstOpts.Versioned,
-		VersionID:            dstOpts.VersionID,
+		VersionID:                  dstOpts.VersionID,
-		MTime:                dstOpts.MTime,
+		MTime:                      dstOpts.MTime,
-		NoLock:               true,
+		NoLock:                     true,
+		EncryptFn:                  dstOpts.EncryptFn,
+		WantChecksum:               dstOpts.WantChecksum,
+		WantServerSideChecksumType: dstOpts.WantServerSideChecksumType,
 	}
 
 	return z.serverPools[poolIdx].PutObject(ctx, dstBucket, dstObject, srcInfo.PutObjReader, putOpts)

cmd/erasure-sets.go

@@ -868,11 +868,14 @@ func (s *erasureSets) CopyObject(ctx context.Context, srcBucket, srcObject, dstB
 	}
 
 	putOpts := ObjectOptions{
-		ServerSideEncryption: dstOpts.ServerSideEncryption,
+		ServerSideEncryption:       dstOpts.ServerSideEncryption,
-		UserDefined:          srcInfo.UserDefined,
+		UserDefined:                srcInfo.UserDefined,
-		Versioned:            dstOpts.Versioned,
+		Versioned:                  dstOpts.Versioned,
-		VersionID:            dstOpts.VersionID,
+		VersionID:                  dstOpts.VersionID,
-		MTime:                dstOpts.MTime,
+		MTime:                      dstOpts.MTime,
+		EncryptFn:                  dstOpts.EncryptFn,
+		WantChecksum:               dstOpts.WantChecksum,
+		WantServerSideChecksumType: dstOpts.WantServerSideChecksumType,
 	}
 
 	return dstSet.putObject(ctx, dstBucket, dstObject, srcInfo.PutObjReader, putOpts)

cmd/logging.go

@@ -152,6 +152,10 @@ func encLogIf(ctx context.Context, err error, errKind ...interface{}) {
 	logger.LogIf(ctx, "encryption", err, errKind...)
 }
 
+func encLogOnceIf(ctx context.Context, err error, id string, errKind ...interface{}) {
+	logger.LogOnceIf(ctx, "encryption", err, id, errKind...)
+}
+
 func storageLogIf(ctx context.Context, err error, errKind ...interface{}) {
 	logger.LogIf(ctx, "storage", err, errKind...)
 }

cmd/object-api-datatypes.go

@@ -654,6 +654,7 @@ type objectAttributesChecksum struct {
 	ChecksumSHA1      string `xml:",omitempty"`
 	ChecksumSHA256    string `xml:",omitempty"`
 	ChecksumCRC64NVME string `xml:",omitempty"`
+	ChecksumType      string `xml:",omitempty"`
 }
 
 type objectAttributesParts struct {

cmd/object-api-interface.go

@@ -86,6 +86,8 @@ type ObjectOptions struct {
 
 	WantChecksum *hash.Checksum // x-amz-checksum-XXX checksum sent to PutObject/ CompleteMultipartUpload.
 
+	WantServerSideChecksumType hash.ChecksumType // if set, we compute a server-side checksum of this type
+
 	NoDecryption                        bool      // indicates if the stream must be decrypted.
 	PreserveETag                        string    // preserves this etag during a PUT call.
 	NoLock                              bool      // indicates to lower layers if the caller is expecting to hold locks.

cmd/object-api-utils.go

@@ -1096,6 +1096,16 @@ func NewPutObjReader(rawReader *hash.Reader) *PutObjReader {
 	return &PutObjReader{Reader: rawReader, rawReader: rawReader}
 }
 
+// RawServerSideChecksumResult returns the ServerSideChecksumResult from the
+// underlying rawReader, since the PutObjReader might be encrypted data and
+// thus any checksum from that would be incorrect.
+func (p *PutObjReader) RawServerSideChecksumResult() *hash.Checksum {
+	if p.rawReader != nil {
+		return p.rawReader.ServerSideChecksumResult
+	}
+	return nil
+}
+
 func sealETag(encKey crypto.ObjectKey, md5CurrSum []byte) []byte {
 	var emptyKey [32]byte
 	if bytes.Equal(encKey[:], emptyKey[:]) {

cmd/object-handlers.go

@@ -641,6 +641,7 @@ func (api objectAPIHandlers) getObjectAttributesHandler(ctx context.Context, obj
 				ChecksumSHA1:      strings.Split(chkSums["SHA1"], "-")[0],
 				ChecksumSHA256:    strings.Split(chkSums["SHA256"], "-")[0],
 				ChecksumCRC64NVME: strings.Split(chkSums["CRC64NVME"], "-")[0],
+				ChecksumType:      chkSums[xhttp.AmzChecksumType],
 			}
 		}
 	}
@@ -1465,6 +1466,46 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 			targetSize, _ = srcInfo.DecryptedSize()
 		}
 
+		// Client can request that a different type of checksum is computed server-side for the
+		// destination object using the x-amz-checksum-algorithm header.
+		headerChecksumType := hash.NewChecksumHeader(r.Header)
+		if headerChecksumType.IsSet() {
+			dstOpts.WantServerSideChecksumType = headerChecksumType.Base()
+			srcInfo.Reader.AddServerSideChecksumHasher(headerChecksumType)
+			dstOpts.WantChecksum = nil
+		} else {
+			// Check the source object for checksum.
+			// If Checksum is not encrypted, decryptChecksum will be a no-op and return
+			// the already unencrypted value.
+			srcChecksumDecrypted, err := srcInfo.decryptChecksum(r.Header)
+			if err != nil {
+				encLogOnceIf(GlobalContext,
+					fmt.Errorf("Unable to decryptChecksum for object: %s/%s, error: %w", srcBucket, srcObject, err),
+					"copy-object-decrypt-checksums-"+srcBucket+srcObject)
+			}
+
+			// The source object has a checksum set, we need the destination to have one too.
+			if srcChecksumDecrypted != nil {
+				dstOpts.WantChecksum = hash.ChecksumFromBytes(srcChecksumDecrypted)
+
+				// When an object is being copied from a source that is multipart, the destination will
+				// no longer be multipart, and thus the checksum becomes full-object instead. Since
+				// the CopyObject API does not require that the caller send us this final checksum, we need
+				// to compute it server-side, with the same type as the source object.
+				if dstOpts.WantChecksum != nil && dstOpts.WantChecksum.Type.IsMultipartComposite() {
+					dstOpts.WantServerSideChecksumType = dstOpts.WantChecksum.Type.Base()
+					srcInfo.Reader.AddServerSideChecksumHasher(dstOpts.WantServerSideChecksumType)
+					dstOpts.WantChecksum = nil
+				}
+			} else {
+				// S3: All copied objects without checksums and specified destination checksum algorithms
+				// automatically gain a CRC-64NVME checksum algorithm.
+				dstOpts.WantServerSideChecksumType = hash.ChecksumCRC64NVME
+				srcInfo.Reader.AddServerSideChecksumHasher(dstOpts.WantServerSideChecksumType)
+				dstOpts.WantChecksum = nil
+			}
+		}
+
 		if isTargetEncrypted {
 			var encReader io.Reader
 			kind, _ := crypto.IsRequested(r.Header)
@@ -1498,6 +1539,7 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 			if dstOpts.IndexCB != nil {
 				dstOpts.IndexCB = compressionIndexEncrypter(objEncKey, dstOpts.IndexCB)
 			}
+			dstOpts.EncryptFn = metadataEncrypter(objEncKey)
 		}
 	}
 
@@ -1633,6 +1675,13 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 		return
 	}
 
+	// After we've checked for an invalid copy (above), if a server-side checksum type
+	// is requested, we need to read the source to recompute the checksum.
+	if dstOpts.WantServerSideChecksumType.IsSet() {
+		srcInfo.metadataOnly = false
+	}
+
+	// Federation only.
 	remoteCallRequired := isRemoteCopyRequired(ctx, srcBucket, dstBucket, objectAPI)
 
 	var objInfo ObjectInfo

internal/hash/checksum.go

@@ -230,6 +230,11 @@ func (c ChecksumType) FullObjectRequested() bool {
 	return c&(ChecksumFullObject) == ChecksumFullObject || c.Is(ChecksumCRC64NVME)
 }
 
+// IsMultipartComposite returns true if the checksum is multipart and full object was not requested.
+func (c ChecksumType) IsMultipartComposite() bool {
+	return c.Is(ChecksumMultipart) && !c.FullObjectRequested()
+}
+
 // ObjType returns a string to return as x-amz-checksum-type.
 func (c ChecksumType) ObjType() string {
 	if c.FullObjectRequested() {
@@ -269,7 +274,7 @@ func (c ChecksumType) Trailing() bool {
 	return c.Is(ChecksumTrailing)
 }
 
-// NewChecksumFromData returns a new checksum from specified algorithm and base64 encoded value.
+// NewChecksumFromData returns a new Checksum, using specified algorithm type on data.
 func NewChecksumFromData(t ChecksumType, data []byte) *Checksum {
 	if !t.IsSet() {
 		return nil
@@ -311,8 +316,6 @@ func ReadCheckSums(b []byte, part int) (cs map[string]string, isMP bool) {
 			}
 			if !typ.FullObjectRequested() {
 				cs = fmt.Sprintf("%s-%d", cs, t)
-			} else if part <= 0 {
-				res[xhttp.AmzChecksumType] = xhttp.AmzChecksumTypeFullObject
 			}
 			b = b[n:]
 			if part > 0 {
@@ -337,6 +340,13 @@ func ReadCheckSums(b []byte, part int) (cs map[string]string, isMP bool) {
 		}
 		if cs != "" {
 			res[typ.String()] = cs
+			res[xhttp.AmzChecksumType] = typ.ObjType()
+			if !typ.Is(ChecksumMultipart) {
+				// Single part PUTs are always FULL_OBJECT checksum
+				// Refer https://docs.aws.amazon.com/AmazonS3/latest/API/API_PutObject.html
+				// **For PutObject uploads, the checksum type is always FULL_OBJECT.**
+				res[xhttp.AmzChecksumType] = ChecksumFullObject.ObjType()
+			}
 		}
 	}
 	if len(res) == 0 {
@@ -468,6 +478,65 @@ func (c *Checksum) AppendTo(b []byte, parts []byte) []byte {
 	return b
 }
 
+// ChecksumFromBytes reconstructs a Checksum struct from the serialized bytes created in AppendTo()
+// Returns nil if the bytes are invalid or empty.
+// AppendTo() can append a serialized Checksum to another already-serialized Checksum,
+// however, in practice, we only use one at a time.
+// ChecksumFromBytes only returns the first one and no part checksums.
+func ChecksumFromBytes(b []byte) *Checksum {
+	if len(b) == 0 {
+		return nil
+	}
+
+	// Read checksum type
+	t, n := binary.Uvarint(b)
+	if n <= 0 {
+		return nil
+	}
+	b = b[n:]
+
+	typ := ChecksumType(t)
+	length := typ.RawByteLen()
+	if length == 0 || len(b) < length {
+		return nil
+	}
+
+	// Read raw checksum bytes
+	raw := make([]byte, length)
+	copy(raw, b[:length])
+	b = b[length:]
+
+	c := &Checksum{
+		Type:    typ,
+		Raw:     raw,
+		Encoded: base64.StdEncoding.EncodeToString(raw),
+	}
+
+	// Handle multipart checksums
+	if typ.Is(ChecksumMultipart) {
+		parts, n := binary.Uvarint(b)
+		if n <= 0 {
+			return nil
+		}
+		b = b[n:]
+
+		c.WantParts = int(parts)
+
+		if typ.Is(ChecksumIncludesMultipart) {
+			wantLen := int(parts) * length
+			if len(b) < wantLen {
+				return nil
+			}
+		}
+	}
+
+	if !c.Valid() {
+		return nil
+	}
+
+	return c
+}
+
 // Valid returns whether checksum is valid.
 func (c Checksum) Valid() bool {
 	if c.Type == ChecksumInvalid {
@@ -506,12 +575,26 @@ func (c Checksum) Matches(content []byte, parts int) error {
 	return nil
 }
 
-// AsMap returns the
+// AsMap returns the checksum as a map[string]string.
 func (c *Checksum) AsMap() map[string]string {
 	if c == nil || !c.Valid() {
 		return nil
 	}
-	return map[string]string{c.Type.String(): c.Encoded}
+	return map[string]string{
+		c.Type.String():       c.Encoded,
+		xhttp.AmzChecksumType: c.Type.ObjType(),
+	}
+}
+
+// Equal returns whether two checksum structs are equal in all their fields.
+func (c *Checksum) Equal(s *Checksum) bool {
+	if c == nil || s == nil {
+		return c == s
+	}
+	return c.Type == s.Type &&
+		c.Encoded == s.Encoded &&
+		bytes.Equal(c.Raw, s.Raw) &&
+		c.WantParts == s.WantParts
 }
 
 // TransferChecksumHeader will transfer any checksum value that has been checked.

internal/hash/checksum_test.go

@@ -0,0 +1,162 @@
+// Copyright (c) 2015-2025 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package hash
+
+import (
+	"net/http/httptest"
+	"testing"
+)
+
+// TestChecksumAddToHeader tests that adding and retrieving a checksum on a header works
+func TestChecksumAddToHeader(t *testing.T) {
+	tests := []struct {
+		name     string
+		checksum ChecksumType
+		fullobj  bool
+	}{
+		{"CRC32-composite", ChecksumCRC32, false},
+		{"CRC32-full-object", ChecksumCRC32, true},
+		{"CRC32C-composite", ChecksumCRC32C, false},
+		{"CRC32C-full-object", ChecksumCRC32C, true},
+		{"CRC64NVME-full-object", ChecksumCRC64NVME, false}, // testing with false, because it always is full object.
+		{"ChecksumSHA1-composite", ChecksumSHA1, false},
+		{"ChecksumSHA256-composite", ChecksumSHA256, false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			myData := []byte("this-is-a-checksum-data-test")
+			chksm := NewChecksumFromData(tt.checksum, myData)
+			if tt.fullobj {
+				chksm.Type |= ChecksumFullObject
+			}
+
+			w := httptest.NewRecorder()
+			AddChecksumHeader(w, chksm.AsMap())
+			gotChksm, err := GetContentChecksum(w.Result().Header)
+			if err != nil {
+				t.Fatalf("GetContentChecksum failed: %v", err)
+			}
+
+			// In the CRC64NVM case, it is always full object, so add the flag for easier equality comparison
+			if chksm.Type.Base().Is(ChecksumCRC64NVME) {
+				chksm.Type |= ChecksumFullObject
+			}
+			if !chksm.Equal(gotChksm) {
+				t.Fatalf("Checksum mismatch: expected %+v, got %+v", chksm, gotChksm)
+			}
+		})
+	}
+}
+
+// TestChecksumSerializeDeserialize checks AppendTo can be reversed by ChecksumFromBytes
+func TestChecksumSerializeDeserialize(t *testing.T) {
+	myData := []byte("this-is-a-checksum-data-test")
+	chksm := NewChecksumFromData(ChecksumCRC32, myData)
+	if chksm == nil {
+		t.Fatal("NewChecksumFromData returned nil")
+	}
+	// Serialize the checksum to bytes
+	b := chksm.AppendTo(nil, nil)
+	if b == nil {
+		t.Fatal("AppendTo returned nil")
+	}
+
+	// Deserialize the checksum from bytes
+	chksmOut := ChecksumFromBytes(b)
+	if chksmOut == nil {
+		t.Fatal("ChecksumFromBytes returned nil")
+	}
+
+	// Assert new checksum matches the content
+	matchError := chksmOut.Matches(myData, 0)
+	if matchError != nil {
+		t.Fatalf("Checksum mismatch on chksmOut: %v", matchError)
+	}
+
+	// Assert they are exactly equal
+	if !chksmOut.Equal(chksm) {
+		t.Fatalf("Checksum mismatch: expected %+v, got %+v", chksm, chksmOut)
+	}
+}
+
+// TestChecksumSerializeDeserializeMultiPart checks AppendTo can be reversed by ChecksumFromBytes
+// for multipart checksum
+func TestChecksumSerializeDeserializeMultiPart(t *testing.T) {
+	// Create dummy data that we'll split into 3 parts
+	dummyData := []byte("The quick brown fox jumps over the lazy dog. " +
+		"Pack my box with five dozen brown eggs. " +
+		"Have another go it will all make sense in the end!")
+
+	// Split data into 3 parts
+	partSize := len(dummyData) / 3
+	part1Data := dummyData[0:partSize]
+	part2Data := dummyData[partSize : 2*partSize]
+	part3Data := dummyData[2*partSize:]
+
+	// Calculate CRC32C checksum for each part using NewChecksumFromData
+	checksumType := ChecksumCRC32C
+
+	part1Checksum := NewChecksumFromData(checksumType, part1Data)
+	part2Checksum := NewChecksumFromData(checksumType, part2Data)
+	part3Checksum := NewChecksumFromData(checksumType, part3Data)
+
+	// Combine the raw checksums (this is what happens in CompleteMultipartUpload)
+	var checksumCombined []byte
+	checksumCombined = append(checksumCombined, part1Checksum.Raw...)
+	checksumCombined = append(checksumCombined, part2Checksum.Raw...)
+	checksumCombined = append(checksumCombined, part3Checksum.Raw...)
+
+	// Create the final checksum (checksum of the combined checksums)
+	// Add BOTH the multipart flag AND the includes-multipart flag
+	finalChecksumType := checksumType | ChecksumMultipart | ChecksumIncludesMultipart
+	finalChecksum := NewChecksumFromData(finalChecksumType, checksumCombined)
+
+	// Set WantParts to indicate 3 parts
+	finalChecksum.WantParts = 3
+
+	// Test AppendTo serialization
+	var serialized []byte
+	serialized = finalChecksum.AppendTo(serialized, checksumCombined)
+
+	// Use ChecksumFromBytes to deserialize the final checksum
+	chksmOut := ChecksumFromBytes(serialized)
+	if chksmOut == nil {
+		t.Fatal("ChecksumFromBytes returned nil")
+	}
+
+	// Assert they are exactly equal
+	if !chksmOut.Equal(finalChecksum) {
+		t.Fatalf("Checksum mismatch: expected %+v, got %+v", finalChecksum, chksmOut)
+	}
+
+	// Serialize what we got from ChecksumFromBytes
+	serializedOut := chksmOut.AppendTo(nil, checksumCombined)
+
+	// Read part checksums from serializedOut
+	readParts := ReadPartCheckSums(serializedOut)
+	expectedChecksums := []string{
+		part1Checksum.Encoded,
+		part2Checksum.Encoded,
+		part3Checksum.Encoded,
+	}
+	for i, expected := range expectedChecksums {
+		if got := readParts[i][ChecksumCRC32C.String()]; got != expected {
+			t.Fatalf("want part%dChecksum.Encoded %s, got %s", i+1, expected, got)
+		}
+	}
+}

internal/hash/reader.go

@@ -51,11 +51,18 @@ type Reader struct {
 	checksum      etag.ETag
 	contentSHA256 []byte
 
-	// Content checksum
+	// Client-provided content checksum
 	contentHash   Checksum
 	contentHasher hash.Hash
 	disableMD5    bool
 
+	// Server side computed checksum. In some cases, like CopyObject, a new checksum
+	// needs to be computed and saved on the destination object, but the client
+	// does not provide it. Not calculated if client-side contentHash is set.
+	ServerSideChecksumType   ChecksumType
+	ServerSideHasher         hash.Hash
+	ServerSideChecksumResult *Checksum
+
 	trailer http.Header
 
 	sha256 hash.Hash
@@ -247,6 +254,16 @@ func (r *Reader) AddNonTrailingChecksum(cs *Checksum, ignoreValue bool) error {
 	return nil
 }
 
+// AddServerSideChecksumHasher adds a new hasher for computing the server-side checksum.
+func (r *Reader) AddServerSideChecksumHasher(t ChecksumType) {
+	h := t.Hasher()
+	if h == nil {
+		return
+	}
+	r.ServerSideHasher = h
+	r.ServerSideChecksumType = t
+}
+
 func (r *Reader) Read(p []byte) (int, error) {
 	n, err := r.src.Read(p)
 	r.bytesRead += int64(n)
@@ -255,6 +272,8 @@ func (r *Reader) Read(p []byte) (int, error) {
 	}
 	if r.contentHasher != nil {
 		r.contentHasher.Write(p[:n])
+	} else if r.ServerSideHasher != nil {
+		r.ServerSideHasher.Write(p[:n])
 	}
 
 	if err == io.EOF { // Verify content SHA256, if set.
@@ -293,6 +312,9 @@ func (r *Reader) Read(p []byte) (int, error) {
 				}
 				return n, err
 			}
+		} else if r.ServerSideHasher != nil {
+			sum := r.ServerSideHasher.Sum(nil)
+			r.ServerSideChecksumResult = NewChecksumWithType(r.ServerSideChecksumType, base64.StdEncoding.EncodeToString(sum))
 		}
 	}
 	if err != nil && err != io.EOF {