From 2d34a53a6a407c7566b50a59c8cacff8fb27426c Mon Sep 17 00:00:00 2001
From: Hilari Moragrega <hilari@hilarimoragrega.com>
Date: Thu, 17 Feb 2022 19:58:49 +0100
Subject: [PATCH 1/2] Return writer error if not nil in writeSequential

---
 client.go                  |  8 +++++---
 client_integration_test.go | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/client.go b/client.go
index 1587eb83..f5bd39ee 100644
--- a/client.go
+++ b/client.go
@@ -1176,11 +1176,13 @@ func (f *File) writeToSequential(w io.Writer) (written int64, err error) {
 		if n > 0 {
 			f.offset += int64(n)
 
-			m, err2 := w.Write(b[:n])
+			m, wErr := w.Write(b[:n])
 			written += int64(m)
 
-			if err == nil {
-				err = err2
+			if wErr != nil {
+				if err == nil || err == io.EOF {
+					err = wErr
+				}
 			}
 		}
 
diff --git a/client_integration_test.go b/client_integration_test.go
index b5083845..d7c10408 100644
--- a/client_integration_test.go
+++ b/client_integration_test.go
@@ -1249,6 +1249,44 @@ func TestClientReadSequential(t *testing.T) {
 	}
 }
 
+type writerFunc func(b []byte) (int, error)
+
+func (f writerFunc) Write(b []byte) (int, error) {
+	return f(b)
+}
+
+func TestClientWriteSequential_WriterErr(t *testing.T) {
+	sftp, cmd := testClient(t, READONLY, NODELAY)
+	defer cmd.Wait()
+	defer sftp.Close()
+
+	sftp.disableConcurrentReads = true
+	d, err := ioutil.TempDir("", "sftptest-writesequential")
+	require.NoError(t, err)
+
+	defer os.RemoveAll(d)
+
+	f, err := ioutil.TempFile(d, "write-sequential-test")
+	require.NoError(t, err)
+	fname := f.Name()
+	content := []byte("hello world")
+	f.Write(content)
+	f.Close()
+
+	sftpFile, err := sftp.Open(fname)
+	require.NoError(t, err)
+	defer sftpFile.Close()
+
+	want := errors.New("error writing")
+	n, got := io.Copy(writerFunc(func(b []byte) (int, error) {
+		return 10, want
+	}), sftpFile)
+
+	require.Error(t, got)
+	assert.ErrorIs(t, want, got)
+	assert.Equal(t, int64(10), n)
+}
+
 func TestClientReadDir(t *testing.T) {
 	sftp1, cmd1 := testClient(t, READONLY, NODELAY)
 	sftp2, cmd2 := testClientGoSvr(t, READONLY, NODELAY)

From 1c605bf1f54e6fc69bfeb318c96b22f5e5f14f3a Mon Sep 17 00:00:00 2001
From: Hilari Moragrega <hilari@hilarimoragrega.com>
Date: Mon, 21 Feb 2022 12:19:31 +0100
Subject: [PATCH 2/2] Improved test with CR feedback

---
 client.go                  |  4 +---
 client_integration_test.go | 47 ++++++++++++++++++++++++--------------
 2 files changed, 31 insertions(+), 20 deletions(-)

diff --git a/client.go b/client.go
index f5bd39ee..d8c979a0 100644
--- a/client.go
+++ b/client.go
@@ -1180,9 +1180,7 @@ func (f *File) writeToSequential(w io.Writer) (written int64, err error) {
 			written += int64(m)
 
 			if wErr != nil {
-				if err == nil || err == io.EOF {
-					err = wErr
-				}
+				return written, wErr
 			}
 		}
 
diff --git a/client_integration_test.go b/client_integration_test.go
index d7c10408..1a855d42 100644
--- a/client_integration_test.go
+++ b/client_integration_test.go
@@ -1249,10 +1249,19 @@ func TestClientReadSequential(t *testing.T) {
 	}
 }
 
-type writerFunc func(b []byte) (int, error)
+type lastChunkErrSequentialWriter struct {
+	expected      int
+	written       int
+	writtenReturn int
+}
 
-func (f writerFunc) Write(b []byte) (int, error) {
-	return f(b)
+func (w *lastChunkErrSequentialWriter) Write(b []byte) (int, error) {
+	chunkSize := len(b)
+	w.written += chunkSize
+	if w.written == w.expected {
+		return w.writtenReturn, errors.New("test error")
+	}
+	return chunkSize, nil
 }
 
 func TestClientWriteSequential_WriterErr(t *testing.T) {
@@ -1260,31 +1269,35 @@ func TestClientWriteSequential_WriterErr(t *testing.T) {
 	defer cmd.Wait()
 	defer sftp.Close()
 
-	sftp.disableConcurrentReads = true
-	d, err := ioutil.TempDir("", "sftptest-writesequential")
+	d, err := ioutil.TempDir("", "sftptest-writesequential-writeerr")
 	require.NoError(t, err)
 
 	defer os.RemoveAll(d)
 
-	f, err := ioutil.TempFile(d, "write-sequential-test")
+	var (
+		content    = []byte("hello world")
+		shortWrite = 2
+	)
+	w := lastChunkErrSequentialWriter{
+		expected:      len(content),
+		writtenReturn: shortWrite,
+	}
+
+	f, err := ioutil.TempFile(d, "write-sequential-writeerr-test")
 	require.NoError(t, err)
 	fname := f.Name()
-	content := []byte("hello world")
-	f.Write(content)
-	f.Close()
+	n, err := f.Write(content)
+	require.NoError(t, err)
+	require.Equal(t, n, len(content))
+	require.NoError(t, f.Close())
 
 	sftpFile, err := sftp.Open(fname)
 	require.NoError(t, err)
 	defer sftpFile.Close()
 
-	want := errors.New("error writing")
-	n, got := io.Copy(writerFunc(func(b []byte) (int, error) {
-		return 10, want
-	}), sftpFile)
-
-	require.Error(t, got)
-	assert.ErrorIs(t, want, got)
-	assert.Equal(t, int64(10), n)
+	gotWritten, gotErr := sftpFile.writeToSequential(&w)
+	require.NotErrorIs(t, io.EOF, gotErr)
+	require.Equal(t, int64(shortWrite), gotWritten)
 }
 
 func TestClientReadDir(t *testing.T) {