From 6cd9860681d391e9b1ffc556cf102f1c8417eca2 Mon Sep 17 00:00:00 2001
From: Viktor Varland <varl@vlv.io>
Date: Tue, 30 Sep 2025 12:39:49 +0200
Subject: [PATCH] fix: avoid bind mount read errors

---
 internal/server/queue.go      | 34 +++++++++++++++++++++-----
 internal/server/queue_test.go | 46 +++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 6 deletions(-)

diff --git a/internal/server/queue.go b/internal/server/queue.go
index 14766dd..38b5e39 100644
--- a/internal/server/queue.go
+++ b/internal/server/queue.go
@@ -9,9 +9,15 @@ import (
 	"path/filepath"
 	"sync"
 	"sync/atomic"
+	"syscall"
 	"time"
 )
 
+var (
+	osWriteFile = os.WriteFile
+	osRename    = os.Rename
+)
+
 type VideoRequest struct {
 	URL          string `json:"url"`
 	OutDir       string `json:"out_dir"`
@@ -169,12 +175,7 @@ func (q *Queue) persistLocked() error {
 		return err
 	}
 
-	tmp := q.persist + ".tmp"
-	if err := os.WriteFile(tmp, data, 0o644); err != nil {
-		return err
-	}
-
-	return os.Rename(tmp, q.persist)
+	return writeFileAtomic(q.persist, data)
 }
 
 var idCounter uint64
@@ -183,3 +184,24 @@ func generateID() string {
 	count := atomic.AddUint64(&idCounter, 1)
 	return fmt.Sprintf("%d-%d", time.Now().UTC().UnixNano(), count)
 }
+
+func writeFileAtomic(path string, data []byte) error {
+	tmp := path + ".tmp"
+	if err := osWriteFile(tmp, data, 0o644); err != nil {
+		return err
+	}
+
+	if err := osRename(tmp, path); err != nil {
+		if errors.Is(err, syscall.EBUSY) {
+			if writeErr := osWriteFile(path, data, 0o644); writeErr != nil {
+				_ = os.Remove(tmp)
+				return writeErr
+			}
+			return os.Remove(tmp)
+		}
+		_ = os.Remove(tmp)
+		return err
+	}
+
+	return nil
+}
diff --git a/internal/server/queue_test.go b/internal/server/queue_test.go
index 7c7533b..1e4efb6 100644
--- a/internal/server/queue_test.go
+++ b/internal/server/queue_test.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"os"
 	"path/filepath"
+	"syscall"
 	"testing"
 	"time"
 )
@@ -90,3 +91,48 @@ func TestQueuePersistence(t *testing.T) {
 		t.Fatalf("expected queue file removed after draining, got %v", err)
 	}
 }
+
+func TestWriteFileAtomicFallback(t *testing.T) {
+	// Simulate EBUSY by replacing os.Rename temporarily.
+	origRename := osRename
+	origWriteFile := osWriteFile
+	defer func() {
+		osRename = origRename
+		osWriteFile = origWriteFile
+	}()
+
+	tmpDir := t.TempDir()
+	path := filepath.Join(tmpDir, "queue.json")
+	odyssey := filepath.Join(tmpDir, "queue.json.tmp")
+
+	osWriteFile = func(name string, data []byte, perm os.FileMode) error {
+		if name == path {
+			if err := os.WriteFile(name, data, perm); err != nil {
+				return err
+			}
+			return nil
+		}
+		return os.WriteFile(name, data, perm)
+	}
+
+	osRename = func(oldpath, newpath string) error {
+		return syscall.EBUSY
+	}
+
+	if err := writeFileAtomic(path, []byte("{}")); err != nil {
+		t.Fatalf("writeFileAtomic: %v", err)
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read path: %v", err)
+	}
+
+	if string(data) != "{}" {
+		t.Fatalf("expected file contents '{}', got %q", data)
+	}
+
+	if _, err := os.Stat(odyssey); !os.IsNotExist(err) {
+		t.Fatalf("expected tmp removed, got %v", err)
+	}
+}