From e4f2d9eb4a592a9d8cbf2c999eea397a7fc502ec Mon Sep 17 00:00:00 2001
From: Konstantin Lebedev <lebedev_k@tochka.com>
Date: Mon, 5 Oct 2020 14:43:32 +0500
Subject: [PATCH] We return etag using the same algorithm as aws s3
 https://teppen.io/2018/06/23/aws_s3_etags/

---
 weed/filer/filechunks.go                    | 12 +++++++-----
 weed/server/volume_server_handlers_write.go |  3 ++-
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/weed/filer/filechunks.go b/weed/filer/filechunks.go
index db55eec00..c75a35f79 100644
--- a/weed/filer/filechunks.go
+++ b/weed/filer/filechunks.go
@@ -1,13 +1,15 @@
 package filer
 
 import (
+	"bytes"
+	"encoding/hex"
 	"fmt"
-	"hash/fnv"
 	"math"
 	"sort"
 	"sync"
 
 	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
+	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
 func TotalSize(chunks []*filer_pb.FileChunk) (size uint64) {
@@ -42,12 +44,12 @@ func ETagChunks(chunks []*filer_pb.FileChunk) (etag string) {
 	if len(chunks) == 1 {
 		return chunks[0].ETag
 	}
-
-	h := fnv.New32a()
+	md5_digests := [][]byte{}
 	for _, c := range chunks {
-		h.Write([]byte(c.ETag))
+		md5_decoded, _ := hex.DecodeString(c.ETag)
+		md5_digests = append(md5_digests, md5_decoded)
 	}
-	return fmt.Sprintf("%x", h.Sum32())
+	return fmt.Sprintf("%x-%d", util.Md5(bytes.Join(md5_digests, nil)), len(chunks))
 }
 
 func CompactFileChunks(lookupFileIdFn LookupFileIdFunctionType, chunks []*filer_pb.FileChunk) (compacted, garbage []*filer_pb.FileChunk) {
diff --git a/weed/server/volume_server_handlers_write.go b/weed/server/volume_server_handlers_write.go
index 78cbf08c5..01a77b901 100644
--- a/weed/server/volume_server_handlers_write.go
+++ b/weed/server/volume_server_handlers_write.go
@@ -13,6 +13,7 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/stats"
 	"github.com/chrislusf/seaweedfs/weed/storage/needle"
 	"github.com/chrislusf/seaweedfs/weed/topology"
+	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
 func (vs *VolumeServer) PostHandler(w http.ResponseWriter, r *http.Request) {
@@ -67,7 +68,7 @@ func (vs *VolumeServer) PostHandler(w http.ResponseWriter, r *http.Request) {
 		ret.Name = string(reqNeedle.Name)
 	}
 	ret.Size = uint32(originalSize)
-	ret.ETag = reqNeedle.Etag()
+	ret.ETag = fmt.Sprintf("%x", util.Base64Md5ToBytes(contentMd5))
 	ret.Mime = string(reqNeedle.Mime)
 	setEtag(w, ret.ETag)
 	w.Header().Set("Content-MD5", contentMd5)