ObjectLayer/GetObject: Should return the right error value. Fix done in FS and XL. (#2133)

fixes #2117

xl-v1-utils.go

@@ -23,6 +23,59 @@ import (
 	"path"
 )
 
+// Returns nil even if one of the slice elements is nil.
+// Else returns the error which occours the most.
+func reduceErrs(errs []error) error {
+	// In case the error type is not in the known error list.
+	var unknownErr = errors.New("unknown error")
+	var errTypes = []struct {
+		err   error // error type
+		count int   // occurance count
+	}{
+		// List of known error types. Any new type that can be returned from StorageAPI should
+		// be added to this list. Most common errors are listed here.
+		{errDiskNotFound, 0}, {errFaultyDisk, 0}, {errFileAccessDenied, 0},
+		{errFileNotFound, 0}, {errFileNameTooLong, 0}, {errVolumeNotFound, 0},
+		{errDiskFull, 0},
+		// unknownErr count - count of the number of unknown errors.
+		{unknownErr, 0},
+	}
+	// In case unknownErr count occours maximum number of times, unknownErrType is used to
+	// to store it so that it can be used for the return error type.
+	var unknownErrType error
+
+	// For each err in []errs increment the corresponding count value.
+	for _, err := range errs {
+		if err == nil {
+			// Return nil even if one of the elements is nil.
+			return nil
+		}
+		for i := range errTypes {
+			if errTypes[i].err == err {
+				errTypes[i].count++
+				break
+			}
+			if errTypes[i].err == unknownErr {
+				errTypes[i].count++
+				unknownErrType = err
+				break
+			}
+		}
+	}
+	max := 0
+	// Get the error type which has the maximum count.
+	for i, errType := range errTypes {
+		if errType.count > errTypes[max].count {
+			max = i
+		}
+	}
+	if errTypes[max].err == unknownErr {
+		// Return the unknown error.
+		return unknownErrType
+	}
+	return errTypes[max].err
+}
+
 // Validates if we have quorum based on the errors with errDiskNotFound.
 func isQuorum(errs []error, minQuorumCount int) bool {
 	var diskFoundCount int