go/{zeo,neo}: handshake: Report "unexpected EOF" if peer sends only partial data

NEO was already doing this, but let's use xio.NoEOF everywhere for
uniformity.

go/neo/neonet/newlink.go

-// Copyright (C) 2016-2018  Nexedi SA and Contributors.
+// Copyright (C) 2016-2020  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -29,6 +29,7 @@ import (
 	"sync"
 
 	"lab.nexedi.com/kirr/go123/xnet"
+	"lab.nexedi.com/kirr/neo/go/internal/xio"
 	"lab.nexedi.com/kirr/neo/go/neo/proto"
 )
 
@@ -84,9 +85,7 @@ func handshake(ctx context.Context, conn net.Conn, version uint32) (err error) {
 	go func() {
 		var b [4]byte
 		_, err := io.ReadFull(conn, b[:])
-		if err == io.EOF {
-			err = io.ErrUnexpectedEOF // can be returned with n = 0
-		}
+		err = xio.NoEOF(err) // can be returned with n = 0
 		if err == nil {
 			peerVersion := binary.BigEndian.Uint32(b[:]) // XXX -> ntoh32 ?
 			if peerVersion != version {

go/zodb/storage/zeo/zrpc.go

@@ -479,7 +479,7 @@ func handshake(ctx context.Context, conn net.Conn) (_ *zLink, err error) {
 		// first letter is preferred encoding: 'M' (msgpack), or 'Z' (pickles).
 		pkb, err := zl.recvPkt()
 		if err != nil {
-			return fmt.Errorf("rx: %s", err)
+			return fmt.Errorf("rx: %s", xio.NoEOF(err))
 		}
 
 		proto := string(pkb.Payload())