add hash-set debugging currently supports SIPMOD (minio#13911)

fixes a bug in s3-check-md5 for single part
uploaded multipart objects.

.gitignore

@@ -28,3 +28,7 @@ xl-meta*
 healing-bin*
 inspect*
 200M*
+hash-set
+minio.RELEASE*
+mc
+nancy

docs/debugging/hash-set/main.go

@@ -0,0 +1,99 @@
+// Copyright (c) 2015-2021 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 main
+
+import (
+	"encoding/binary"
+	"flag"
+	"fmt"
+	"hash/crc32"
+	"log"
+
+	"github.com/dchest/siphash"
+	"github.com/google/uuid"
+)
+
+// hashes the key returning an integer based on the input algorithm.
+// This function currently supports
+// - SIPMOD
+func sipHashMod(key string, cardinality int, id [16]byte) int {
+	if cardinality <= 0 {
+		return -1
+	}
+	// use the faster version as per siphash docs
+	// https://github.com/dchest/siphash#usage
+	k0, k1 := binary.LittleEndian.Uint64(id[0:8]), binary.LittleEndian.Uint64(id[8:16])
+	sum64 := siphash.Hash(k0, k1, []byte(key))
+	return int(sum64 % uint64(cardinality))
+}
+
+// hashOrder - hashes input key to return consistent
+// hashed integer slice. Returned integer order is salted
+// with an input key. This results in consistent order.
+// NOTE: collisions are fine, we are not looking for uniqueness
+// in the slices returned.
+func hashOrder(key string, cardinality int) []int {
+	if cardinality <= 0 {
+		// Returns an empty int slice for cardinality < 0.
+		return nil
+	}
+
+	nums := make([]int, cardinality)
+	keyCrc := crc32.Checksum([]byte(key), crc32.IEEETable)
+
+	start := int(keyCrc % uint32(cardinality))
+	for i := 1; i <= cardinality; i++ {
+		nums[i-1] = 1 + ((start + i) % cardinality)
+	}
+	return nums
+}
+
+var (
+	object, deploymentID string
+	setCount, shards     int
+)
+
+func main() {
+	flag.StringVar(&object, "object", "", "Select an object")
+	flag.StringVar(&deploymentID, "deployment-id", "", "MinIO deployment ID, obtained from 'format.json'")
+	flag.IntVar(&setCount, "set-count", 0, "Total set count")
+	flag.IntVar(&shards, "shards", 0, "Total shards count")
+
+	flag.Parse()
+
+	if object == "" {
+		log.Fatalln("object name is mandatory")
+	}
+
+	if deploymentID == "" {
+		log.Fatalln("deployment ID is mandatory")
+	}
+
+	if setCount == 0 {
+		log.Fatalln("set count cannot be zero")
+	}
+
+	if shards == 0 {
+		log.Fatalln("total shards cannot be zero")
+	}
+
+	id := uuid.MustParse(deploymentID)
+
+	fmt.Println("Erasure distribution for the object", hashOrder(object, shards))
+	fmt.Println("Erasure setNumber for the object", sipHashMod(object, setCount, id)+1)
+}

docs/debugging/s3-check-md5/main.go

@@ -113,6 +113,7 @@ func main() {
 				continue
 			}
 			parts := 1
+			multipart := false
 			s := strings.Split(object.ETag, "-")
 			switch len(s) {
 			case 1:
@@ -124,6 +125,7 @@ func main() {
 					log.Println("ETAG: wrong format:", err)
 					continue
 				}
+				multipart = true
 			default:
 				log.Println("Unexpected ETAG format", object.ETag)
 				continue
@@ -148,13 +150,12 @@ func main() {
 
 			corrupted := false
 
-			switch parts {
-			case 1:
+			if !multipart {
 				md5sum := fmt.Sprintf("%x", partsMD5Sum[0])
 				if md5sum != object.ETag {
 					corrupted = true
 				}
-			default:
+			} else {
 				var totalMD5SumBytes []byte
 				for _, sum := range partsMD5Sum {
 					totalMD5SumBytes = append(totalMD5SumBytes, sum...)