uplink/piecestore: Check SN piece hash timestamp (#3246)

Uplink must verify that every piece upload to a storage node return a
hash whose timestamp isn't older than the maximum elapsed time allowed
by the Satellite.

We cannot leave this check only to the Satellite site, because if there
is no error reported by this matter, the uplink cuts down the long tail.
When uplink submits the result uploads including these invalid ones, the
Satellite filters out the invalid ones and that can provoke that it gets
less than the optimal threshold amount of valid upload results, so it
rejects the request.

Detecting the error at this stage will allow the uplink to detect these
uploads as invalid and avoid to cut down the long tail prematurely.

uplink/piecestore/verification.go

@@ -6,6 +6,7 @@ package piecestore
 import (
 	"bytes"
 	"context"
+	"time"
 
 	"github.com/zeebo/errs"
 
@@ -14,6 +15,8 @@ import (
 	"storj.io/storj/pkg/signing"
 )
 
+const pieceHashExpiration = 2 * time.Hour
+
 var (
 	// ErrInternal is an error class for internal errors.
 	ErrInternal = errs.Class("internal")
@@ -21,6 +24,8 @@ var (
 	ErrProtocol = errs.Class("protocol")
 	// ErrVerifyUntrusted is an error in case there is a trust issue.
 	ErrVerifyUntrusted = errs.Class("untrusted")
+	// ErrStorageNodeInvalidResponse is an error when a storage node returns a response with invalid data
+	ErrStorageNodeInvalidResponse = errs.Class("storage node has returned an invalid response")
 )
 
 // VerifyPieceHash verifies piece hash which is sent by peer.
@@ -40,5 +45,11 @@ func (client *Client) VerifyPieceHash(ctx context.Context, peer *identity.PeerId
 		return ErrVerifyUntrusted.New("invalid hash signature: %v", err) // TODO: report rpc status bad message
 	}
 
+	if hash.Timestamp.Before(time.Now().Add(-pieceHashExpiration)) {
+		return ErrStorageNodeInvalidResponse.New("piece has timestamp is too old (%v). Required to be not older than %s",
+			hash.Timestamp, pieceHashExpiration,
+		)
+	}
+
 	return nil
 }