From 97ec0f1fc43fc197369c92775e1c4b094e5ae0a7 Mon Sep 17 00:00:00 2001
From: Ofer Chen <oferchen@gmail.com>
Date: Wed, 27 Aug 2025 19:26:11 +0200
Subject: [PATCH] refactor: share write-only helper

---
 cmd/dump/client.go                |  9 +++------
 internal/common/writeonly.go      |  9 +++++++++
 internal/common/writeonly_test.go | 23 +++++++++++++++++++++++
 transfer/delta.go                 |  7 ++-----
 4 files changed, 37 insertions(+), 11 deletions(-)
 create mode 100644 internal/common/writeonly.go
 create mode 100644 internal/common/writeonly_test.go

diff --git a/cmd/dump/client.go b/cmd/dump/client.go
index 579a93f2..6da7f93d 100644
--- a/cmd/dump/client.go
+++ b/cmd/dump/client.go
@@ -16,6 +16,7 @@ import (
 	rootcmd "lvmsync_go/cmd/root"
 	"lvmsync_go/common"
 	"lvmsync_go/device"
+	internalcommon "lvmsync_go/internal/common"
 	"lvmsync_go/internal/config"
 	cpufeatures "lvmsync_go/internal/cpufeatures"
 	digestpkg "lvmsync_go/internal/digest"
@@ -197,10 +198,6 @@ var copyBufferPool = sync.Pool{New: func() any {
 	return &buf
 }}
 
-type writeOnlyReadWriter struct{ io.Writer }
-
-func (writeOnlyReadWriter) Read(p []byte) (int, error) { return 0, io.EOF }
-
 type contextReader struct {
 	ctx context.Context
 	r   io.Reader
@@ -549,7 +546,7 @@ func (r *Runner) StreamToRemote(ctx context.Context, cfg *config.Config, remoteS
 		return fmt.Errorf("compute digest: %w", err)
 	}
 
-	rw := writeOnlyReadWriter{remoteStdin}
+	rw := internalcommon.WriteOnlyReadWriter{Writer: remoteStdin}
 	cl := rsyncwire.NewClient(rsyncwire.NewStream(rw, maxFrame))
 	if err := cl.SendDigest(ctx, alg, sum); err != nil {
 		remoteStdin.Close()
@@ -582,7 +579,7 @@ func (r *Runner) streamRsyncDelta(ctx context.Context, cfg *config.Config, remot
 	}
 	defer common.CloseWithErr(orig, &err, "close origin")
 
-	rw := writeOnlyReadWriter{remoteStdin}
+	rw := internalcommon.WriteOnlyReadWriter{Writer: remoteStdin}
 	cl := rsyncwire.NewClient(rsyncwire.NewStream(rw, maxFrame))
 	esc, err := privilege.New(ctx, logger)
 	if err != nil {
diff --git a/internal/common/writeonly.go b/internal/common/writeonly.go
new file mode 100644
index 00000000..f8a6df05
--- /dev/null
+++ b/internal/common/writeonly.go
@@ -0,0 +1,9 @@
+package common
+
+import "io"
+
+// WriteOnlyReadWriter wraps an io.Writer to satisfy io.ReadWriter.
+type WriteOnlyReadWriter struct{ io.Writer }
+
+// Read always returns io.EOF, making it safe to use where a read side is required.
+func (WriteOnlyReadWriter) Read([]byte) (int, error) { return 0, io.EOF }
diff --git a/internal/common/writeonly_test.go b/internal/common/writeonly_test.go
new file mode 100644
index 00000000..046d1b23
--- /dev/null
+++ b/internal/common/writeonly_test.go
@@ -0,0 +1,23 @@
+package common
+
+import (
+	"bytes"
+	"io"
+	"testing"
+)
+
+func TestWriteOnlyReadWriter(t *testing.T) {
+	var buf bytes.Buffer
+	rw := WriteOnlyReadWriter{Writer: &buf}
+	if _, err := rw.Write([]byte("hello")); err != nil {
+		t.Fatalf("unexpected write error: %v", err)
+	}
+	b := make([]byte, 1)
+	n, err := rw.Read(b)
+	if n != 0 || err != io.EOF {
+		t.Fatalf("Read() = %d, %v; want 0, io.EOF", n, err)
+	}
+	if got := buf.String(); got != "hello" {
+		t.Fatalf("unexpected buffer content: %q", got)
+	}
+}
diff --git a/transfer/delta.go b/transfer/delta.go
index e9ba1eb9..8d33d8cd 100644
--- a/transfer/delta.go
+++ b/transfer/delta.go
@@ -13,6 +13,7 @@ import (
 	"lvmsync_go/common"
 	"lvmsync_go/dedup"
 	"lvmsync_go/device"
+	internalcommon "lvmsync_go/internal/common"
 	"lvmsync_go/internal/config"
 	digestpkg "lvmsync_go/internal/digest"
 	"lvmsync_go/internal/privilege"
@@ -22,10 +23,6 @@ import (
 
 const rsyncMaxFrame = 1 << 20
 
-type writeOnlyReadWriter struct{ io.Writer }
-
-func (w writeOnlyReadWriter) Read([]byte) (int, error) { return 0, io.EOF }
-
 // streamRsyncDelta performs a byte-level delta pre-pass using rsyncwire.
 // It streams signatures and deltas followed by a digest frame.
 // When out implements io.Closer, it is closed on completion.
@@ -57,7 +54,7 @@ func (t *Transfer) streamRsyncDelta(ctx context.Context, cfg *config.Config, sna
 		rwOK   bool
 	)
 	if rw, rwOK = out.(io.ReadWriter); !rwOK {
-		rw = writeOnlyReadWriter{out}
+		rw = internalcommon.WriteOnlyReadWriter{Writer: out}
 	}
 	stream = rsyncwire.NewStream(rw, rsyncMaxFrame)
 	cl := rsyncwire.NewClient(stream)