From e0b01c802e39c06004f67a3fcd010c5280828138 Mon Sep 17 00:00:00 2001
From: Dustin Long <me@dustmop.io>
Date: Tue, 17 Mar 2020 13:15:52 -0400
Subject: [PATCH] fix(dsync): Don't call the finalize hook more than once

---
 dsync/dsync.go   |  4 ++--
 dsync/session.go | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/dsync/dsync.go b/dsync/dsync.go
index 88d8286..b9a7c4e 100644
--- a/dsync/dsync.go
+++ b/dsync/dsync.go
@@ -393,8 +393,8 @@ func (ds *Dsync) ReceiveBlock(sid, hash string, data []byte) ReceiveResponse {
 	res := sess.ReceiveBlock(hash, bytes.NewReader(data))
 	log.Debugf("received block: %s", res.Hash)
 
-	// if we're done transferring, finalize!
-	if res.Status == StatusOk && sess.Complete() {
+	// check if transfer has completed, if so finalize it, but only once
+	if res.Status == StatusOk && sess.IsFinalizedOnce() {
 		if err := ds.finalizeReceive(sess); err != nil {
 			return ReceiveResponse{
 				Hash:   sess.info.RootCID().String(),
diff --git a/dsync/session.go b/dsync/session.go
index 583479c..65559fc 100644
--- a/dsync/session.go
+++ b/dsync/session.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"math/rand"
+	"sync"
 
 	ipld "github.com/ipfs/go-ipld-format"
 	coreiface "github.com/ipfs/interface-go-ipfs-core"
@@ -23,6 +24,8 @@ type session struct {
 	diff   *dag.Manifest
 	prog   dag.Completion
 	progCh chan dag.Completion
+	lock   sync.Mutex
+	fin    bool
 }
 
 // newSession creates a receive state machine
@@ -99,6 +102,22 @@ func (s *session) completionChanged() {
 	s.progCh <- s.prog
 }
 
+// IsFinalizedOnce will return true if the session is complete, but only the first time it is
+// called, even if multiple threads call this function at the same time
+func (s *session) IsFinalizedOnce() bool {
+	if !s.Complete() {
+		return false
+	}
+	ret := false
+	s.lock.Lock()
+	if !s.fin {
+		ret = true
+		s.fin = true
+	}
+	defer s.lock.Unlock()
+	return ret
+}
+
 // the best stack overflow answer evaarrr: https://stackoverflow.com/a/22892986/9416066
 const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
 const (