Implement index (fast) scrubbing for regular/EC volumes. (#8207)

Implement index (fast) scrubbing for regular/EC volumes via `ScrubVolume()`/`ScrubEcVolume()`.

Also rearranges existing index test files for reuse across unit tests for different modules.

weed/storage/idx/check.go

@@ -0,0 +1,103 @@
+package idx
+
+import (
+	"fmt"
+	"io"
+	"sort"
+
+	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+)
+
+type indexEntry struct {
+	index  int
+	id     types.NeedleId
+	offset int64
+	size   types.Size
+}
+
+func (ie *indexEntry) Compare(other *indexEntry) int {
+	if ie.offset < other.offset {
+		return -1
+	}
+	if ie.offset > other.offset {
+		return 1
+	}
+	if ie.size < other.size {
+		return -1
+	}
+	if ie.size > other.size {
+		return 1
+	}
+	return 0
+}
+
+// CheckIndexFile verifies the integrity of a IDX/ECX index file. Returns a count of processed file entries, and slice of found errors.
+func CheckIndexFile(r io.ReaderAt, indexFileSize int64, version needle.Version) (int64, []error) {
+	errs := []error{}
+
+	entries := []*indexEntry{}
+	var i int
+	err := WalkIndexFile(r, 0, func(id types.NeedleId, offset types.Offset, size types.Size) error {
+		entries = append(entries, &indexEntry{
+			index:  i,
+			id:     id,
+			offset: offset.ToActualOffset(),
+			size:   size,
+		})
+		i++
+		return nil
+	})
+	if err != nil {
+		errs = append(errs, err)
+	}
+
+	sort.Slice(entries, func(i, j int) bool {
+		return entries[i].Compare(entries[j]) < 0
+	})
+
+	for i, e := range entries {
+		if i == 0 {
+			// nothing to check for the first entry
+			continue
+		}
+
+		start, end := e.offset, e.offset
+		if size := needle.GetActualSize(e.size, version); size != 0 {
+			end += size - 1
+		}
+
+		last := entries[i-1]
+		lastStart, lastEnd := last.offset, last.offset
+		if lastSize := needle.GetActualSize(last.size, version); lastSize != 0 {
+			lastEnd += lastSize - 1
+		}
+
+		// check if needles overlap
+		if start <= lastEnd {
+			errs = append(errs, fmt.Errorf(
+				"needle %d (#%d) at [%d-%d] overlaps needle %d at [%d-%d]",
+				e.id, e.index+1,
+				start, end,
+				last.id,
+				lastStart, lastEnd))
+		}
+
+		// The check below is intended to ensure all index entries are contiguous; unfortunately, Seaweed
+		// can delete index entries for files while keeping their data, so volumes with deleted files
+		// will fail this test :(
+		// See https://github.com/seaweedfs/seaweedfs/issues/8204 for details.
+		/*
+			if e.offset != lastEnd + 1 {
+				errs = append(errs, fmt.Errorf("offset %d for needle %d (#%d) doesn't match end of needle %d at %d", e.offset, e.id, e.index+1, last.id, lastEnd))
+			}
+		*/
+	}
+
+	count := int64(len(entries))
+	if got, want := count*types.NeedleMapEntrySize, indexFileSize; got != want {
+		errs = append(errs, fmt.Errorf("expected an index file of size %d, got %d", want, got))
+	}
+
+	return count, errs
+}