xl: GetCheckSumInfo() shouldn't fail if hash not available. (#2984)

In a multipart upload scenario disks going down and coming backup
can lead to certain parts missing on the disk/server which was
going down. This is a valid case since these blocks can be
missing and should be healed through heal operation. But we are
not supposed to fail prematurely since we have enough data on
the other disks as well within read-quorum.

This fix relaxes previous assumption, fixes a major corruption
issue reproduced by @vadmeste.

Fixes #2976

cmd/xl-v1-healing.go

@@ -171,10 +171,7 @@ func (xl xlObjects) HealObject(bucket, object string) error {
 		partName := latestMeta.Parts[partIndex].Name
 		partSize := latestMeta.Parts[partIndex].Size
 		erasure := latestMeta.Erasure
-		sumInfo, err := latestMeta.Erasure.GetCheckSumInfo(partName)
-		if err != nil {
-			return err
-		}
+		sumInfo := latestMeta.Erasure.GetCheckSumInfo(partName)
 		// Heal the part file.
 		checkSums, err := erasureHealFile(latestDisks, outDatedDisks,
 			bucket, pathJoin(object, partName),

cmd/xl-v1-metadata.go

@@ -81,14 +81,14 @@ func (e *erasureInfo) AddCheckSumInfo(ckSumInfo checkSumInfo) {
 }
 
 // GetCheckSumInfo - get checksum of a part.
-func (e erasureInfo) GetCheckSumInfo(partName string) (ckSum checkSumInfo, err error) {
+func (e erasureInfo) GetCheckSumInfo(partName string) (ckSum checkSumInfo) {
 	// Return the checksum.
 	for _, sum := range e.Checksum {
 		if sum.Name == partName {
-			return sum, nil
+			return sum
 		}
 	}
-	return checkSumInfo{}, traceError(errUnexpected)
+	return checkSumInfo{Algorithm: bitRotAlgo}
 }
 
 // statInfo - carries stat information of the object.
@@ -197,7 +197,7 @@ func (m xlMetaV1) ObjectToPartOffset(offset int64) (partIndex int, partOffset in
 func pickValidXLMeta(metaArr []xlMetaV1, modTime time.Time) xlMetaV1 {
 	// Pick latest valid metadata.
 	for _, meta := range metaArr {
-		if meta.IsValid() && meta.Stat.ModTime == modTime {
+		if meta.IsValid() && meta.Stat.ModTime.Equal(modTime) {
 			return meta
 		}
 	}

cmd/xl-v1-multipart.go

@@ -386,8 +386,6 @@ func (xl xlObjects) PutObjectPart(bucket, object, uploadID string, partID int, s
 	tmpSuffix := getUUID()
 	tmpPartPath := path.Join(tmpMetaPrefix, tmpSuffix)
 
-	lreader := data
-
 	// Initialize md5 writer.
 	md5Writer := md5.New()
 
@@ -401,12 +399,16 @@ func (xl xlObjects) PutObjectPart(bucket, object, uploadID string, partID int, s
 
 	mw := io.MultiWriter(writers...)
 
+	var lreader io.Reader
 	// Limit the reader to its provided size > 0.
 	if size > 0 {
 		// This is done so that we can avoid erroneous clients sending
 		// more data than the set content size.
 		lreader = io.LimitReader(data, size)
-	} // else we read till EOF.
+	} else {
+		// else we read till EOF.
+		lreader = data
+	}
 
 	// Construct a tee reader for md5sum.
 	teeReader := io.TeeReader(lreader, mw)

cmd/xl-v1-object.go

@@ -187,10 +187,7 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
 				checkSums[index] = ""
 				continue
 			}
-			ckSumInfo, err := metaArr[index].Erasure.GetCheckSumInfo(partName)
-			if err != nil { // FIXME - relook at returning error here.
-				return toObjectErr(err, bucket, object)
-			}
+			ckSumInfo := metaArr[index].Erasure.GetCheckSumInfo(partName)
 			checkSums[index] = ckSumInfo.Hash
 			// Set checksum algo only once, while it is possible to have
 			// different algos per block because of our `xl.json`.

cmd/xl-v1-utils_test.go

@@ -209,7 +209,7 @@ func compareXLMetaV1(t *testing.T, unMarshalXLMeta, gjsonXLMeta xlMetaV1) {
 	if unMarshalXLMeta.Stat.Size != gjsonXLMeta.Stat.Size {
 		t.Errorf("Expected the stat size to be %v, but got %v.", unMarshalXLMeta.Stat.Size, gjsonXLMeta.Stat.Size)
 	}
-	if unMarshalXLMeta.Stat.ModTime != gjsonXLMeta.Stat.ModTime {
+	if !unMarshalXLMeta.Stat.ModTime.Equal(gjsonXLMeta.Stat.ModTime) {
 		t.Errorf("Expected the modTime to be \"%v\", but got \"%v\".", unMarshalXLMeta.Stat.ModTime, gjsonXLMeta.Stat.ModTime)
 	}
 	if unMarshalXLMeta.Erasure.Algorithm != gjsonXLMeta.Erasure.Algorithm {