From 6a3ad787d5d263d23e52a9f3bb23423266f4cbdd Mon Sep 17 00:00:00 2001
From: Fredrik Johansson <fredrik.johansson@intraphone.com>
Date: Thu, 2 Jul 2026 18:57:06 +0200
Subject: [PATCH] fix: register file-done channel before sending file-accept
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For small files, file-done arrives before wireFileRecv's goroutine
reaches the pendingDones registration — the message was discarded and
the goroutine timed out. Fix by registering doneCh in AcceptOffer
(before sending file-accept), carrying it through recvState, and
reading it in wireFileRecv without re-registering.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 cli/internal/transport/transport.go | 30 ++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/cli/internal/transport/transport.go b/cli/internal/transport/transport.go
index b8f3c5e..aaff774 100644
--- a/cli/internal/transport/transport.go
+++ b/cli/internal/transport/transport.go
@@ -777,13 +777,20 @@ func (s *Session) AcceptOffer(offer FileOffer, downloadDir string) {
 	if info, err := os.Stat(partPath); err == nil && info.Size() < offer.Size {
 		offset = info.Size()
 	}
-	s.controlSend(map[string]string{"type": "file-accept", "xid": offer.XID, "offset": fmt.Sprint(offset)})
+	// Register doneCh before sending file-accept so file-done can never arrive
+	// before the channel exists (small files finish before wireFileRecv runs).
+	doneCh := make(chan string, 1)
 	s.mu.Lock()
+	if s.pendingDones == nil {
+		s.pendingDones = make(map[string]chan string)
+	}
+	s.pendingDones[offer.XID] = doneCh
 	if s.pendingRecvs == nil {
 		s.pendingRecvs = make(map[string]*recvState)
 	}
-	s.pendingRecvs[offer.XID] = &recvState{offer: offer, dir: downloadDir, have: offset}
+	s.pendingRecvs[offer.XID] = &recvState{offer: offer, dir: downloadDir, have: offset, doneCh: doneCh}
 	s.mu.Unlock()
+	s.controlSend(map[string]string{"type": "file-accept", "xid": offer.XID, "offset": fmt.Sprint(offset)})
 }
 
 func (s *Session) RejectOffer(xid string) {
@@ -791,10 +798,11 @@ func (s *Session) RejectOffer(xid string) {
 }
 
 type recvState struct {
-	offer FileOffer
-	dir   string
-	have  int64
-	f     *os.File
+	offer  FileOffer
+	dir    string
+	have   int64
+	f      *os.File
+	doneCh chan string
 }
 
 func (s *Session) wireFileRecv(dc *webrtc.DataChannel) {
@@ -885,13 +893,9 @@ func (s *Session) wireFileRecv(dc *webrtc.DataChannel) {
 			}
 
 			// §9: wait for file-done and verify sha256 before reporting success.
-			doneCh := make(chan string, 1)
-			s.mu.Lock()
-			if s.pendingDones == nil {
-				s.pendingDones = make(map[string]chan string)
-			}
-			s.pendingDones[xid] = doneCh
-			s.mu.Unlock()
+			// doneCh was registered in AcceptOffer before file-accept was sent,
+			// so file-done can never arrive before the channel exists.
+			doneCh := rs.doneCh
 			var expectedSHA256 string
 			select {
 			case expectedSHA256 = <-doneCh: