commandconn: return original error while closing

Changes the `Read` and `Write` error handling
logic to return the original error while closing
the connection. We still skip calling `handleEOF`
if already closing the connection.

Fixes the flaky `TestCloseWhileWriting` and
`TestCloseWhileReading` tests.

Co-authored-by: Sebastiaan van Stijn <github@gone.nl>
Signed-off-by: Laura Brehm <laurabrehm@hey.com>

cli/connhelper/commandconn/commandconn.go

@@ -163,9 +163,8 @@ func (c *commandConn) Read(p []byte) (int, error) {
 	// Close might get called
 	if c.closing.Load() {
 		// If we're currently closing the connection
-		// we don't want to call onEOF, but we do want
-		// to return an io.EOF
-		return 0, io.EOF
+		// we don't want to call onEOF
+		return n, err
 	}
 
 	return n, c.handleEOF(err)
@@ -178,9 +177,8 @@ func (c *commandConn) Write(p []byte) (int, error) {
 	// Close might get called
 	if c.closing.Load() {
 		// If we're currently closing the connection
-		// we don't want to call onEOF, but we do want
-		// to return an io.EOF
-		return 0, io.EOF
+		// we don't want to call onEOF
+		return n, err
 	}
 
 	return n, c.handleEOF(err)

cli/connhelper/commandconn/commandconn_unix_test.go

@@ -5,6 +5,7 @@ package commandconn
 import (
 	"context"
 	"io"
+	"io/fs"
 	"testing"
 	"time"
 
@@ -178,7 +179,8 @@ func TestCloseWhileWriting(t *testing.T) {
 	assert.Check(t, !process.Alive(cmdConn.cmd.Process.Pid))
 
 	writeErr := <-writeErrC
-	assert.ErrorContains(t, writeErr, "EOF")
+	assert.ErrorContains(t, writeErr, "file already closed")
+	assert.Check(t, is.ErrorIs(writeErr, fs.ErrClosed))
 }
 
 func TestCloseWhileReading(t *testing.T) {
@@ -208,5 +210,5 @@ func TestCloseWhileReading(t *testing.T) {
 	assert.Check(t, !process.Alive(cmdConn.cmd.Process.Pid))
 
 	readErr := <-readErrC
-	assert.ErrorContains(t, readErr, "EOF")
+	assert.Check(t, is.ErrorIs(readErr, fs.ErrClosed))
 }