fix: flush SLIP reader after ReadFlash to prevent stale data corruption

pkg/espflasher/flasher.go

@@ -178,6 +178,12 @@ func (f *Flasher) Close() error {
 	return f.port.Close()
 }
 
+// FlushInput discards any unread data from the serial port and SLIP reader.
+// Useful when reusing a flasher connection across multiple operations.
+func (f *Flasher) FlushInput() {
+	f.conn.flushInput()
+}
+
 // reopenPort closes and reopens the serial port after a USB device
 // re-enumeration. TinyUSB CDC devices may briefly disappear during reset.
 func (f *Flasher) reopenPort() error {
@@ -799,9 +805,9 @@ func (f *Flasher) GetSecurityInfo() (*SecurityInfo, error) {
 	return f.readSecurityInfo()
 }
 
-// GetMD5 returns the MD5 hash of a flash region.
+// GetFlashMD5 returns the MD5 hash of a flash region.
 // Requires the stub loader to be running.
-func (f *Flasher) GetMD5(offset, size uint32) (string, error) {
+func (f *Flasher) GetFlashMD5(offset, size uint32) (string, error) {
 	if !f.conn.isStub() {
 		return "", &UnsupportedCommandError{Command: "flash MD5 (requires stub)"}
 	}
@@ -828,7 +834,12 @@ func (f *Flasher) ReadFlash(offset, size uint32) ([]byte, error) {
 		return nil, err
 	}
 
-	return f.conn.readFlash(offset, size)
+	data, err := f.conn.readFlash(offset, size)
+	// Clear any stale data left in the serial buffer and SLIP reader
+	// after the raw block-read protocol. Without this, leftover bytes
+	// can corrupt subsequent command responses.
+	f.conn.flushInput()
+	return data, err
 }
 
 // Reset performs a hard reset of the device, causing it to run user code.

pkg/espflasher/flasher_test.go

@@ -434,11 +434,11 @@ func TestFlashSizeFromJEDECMatchesChipSizes(t *testing.T) {
 	}
 }
 
-func TestGetMD5RequiresStub(t *testing.T) {
+func TestFlashMD5RequiresStub(t *testing.T) {
 	mock := &mockConnection{}
 	mock.stubMode = false // ROM mode
 	f := &Flasher{conn: mock, chip: chipDefs[ChipESP32]}
-	_, err := f.GetMD5(0, 1024)
+	_, err := f.GetFlashMD5(0, 1024)
 	if err == nil {
 		t.Fatal("expected error when stub is not running")
 	}

pkg/espflasher/protocol.go

@@ -630,9 +630,10 @@ func (c *conn) flashWriteSize() uint32 {
 	return flashWriteSizeROM
 }
 
-// flushInput discards any unread data from the serial port.
+// flushInput discards any unread data from the serial port and SLIP reader.
 func (c *conn) flushInput() {
 	c.port.ResetInputBuffer() //nolint:errcheck
+	c.reader.reset()
 }
 
 // eraseTimeoutForSize calculates an appropriate timeout for erase operations.

pkg/espflasher/protocol_test.go

@@ -737,3 +737,45 @@ func TestReadFlashParameterValidation(t *testing.T) {
 		t.Errorf("cmdReadFlash opcode mismatch")
 	}
 }
+
+// flushTrackingPort embeds mockPort and records ResetInputBuffer calls.
+type flushTrackingPort struct {
+	mockPort
+	resetCount int
+}
+
+func (f *flushTrackingPort) ResetInputBuffer() error {
+	f.resetCount++
+	return nil
+}
+
+func TestConnFlushInputResetsPortAndReader(t *testing.T) {
+	port := &flushTrackingPort{}
+	c := newConn(port)
+	c.reader.leftover = []byte{0xDE, 0xAD, 0xBE, 0xEF}
+
+	c.flushInput()
+
+	if port.resetCount != 1 {
+		t.Errorf("ResetInputBuffer called %d times, want 1", port.resetCount)
+	}
+	if c.reader.leftover != nil {
+		t.Errorf("reader.leftover = %X after flushInput, want nil", c.reader.leftover)
+	}
+}
+
+func TestFlasherFlushInputDelegatesToConn(t *testing.T) {
+	port := &flushTrackingPort{}
+	c := newConn(port)
+	c.reader.leftover = []byte{0x01, 0x02}
+	f := &Flasher{conn: c}
+
+	f.FlushInput()
+
+	if port.resetCount != 1 {
+		t.Errorf("ResetInputBuffer called %d times, want 1", port.resetCount)
+	}
+	if c.reader.leftover != nil {
+		t.Errorf("reader.leftover not cleared by Flasher.FlushInput")
+	}
+}

pkg/espflasher/slip.go

@@ -77,6 +77,11 @@ func newSlipReader(port serial.Port) *slipReader {
 	return &slipReader{port: port}
 }
 
+// reset clears any buffered data from the SLIP reader.
+func (r *slipReader) reset() {
+	r.leftover = nil
+}
+
 // ReadFrame reads a single SLIP-framed packet from the serial port.
 // It blocks until a complete frame is received or the timeout expires.
 func (r *slipReader) ReadFrame(timeout time.Duration) ([]byte, error) {

pkg/espflasher/slip_test.go

@@ -155,3 +155,23 @@ t.Errorf("raw 0xC0 found at inner byte %d in encoded data %X", i, encoded)
 }
 }
 }
+
+func TestSlipReaderResetClearsLeftover(t *testing.T) {
+	r := newSlipReader(nil)
+	r.leftover = []byte{0xDE, 0xAD, 0xBE, 0xEF}
+
+	r.reset()
+
+	if r.leftover != nil {
+		t.Errorf("leftover after reset = %X, want nil", r.leftover)
+	}
+}
+
+func TestSlipReaderResetIsIdempotent(t *testing.T) {
+	r := newSlipReader(nil)
+	r.reset()
+	r.reset()
+	if r.leftover != nil {
+		t.Errorf("leftover after double reset = %X, want nil", r.leftover)
+	}
+}

tools/update-stubs.go

@@ -54,7 +54,9 @@ func download(url, dest string) error {
 	if err != nil {
 		return err
 	}
-	defer resp.Body.Close()
+	defer func() {
+		_ = resp.Body.Close()
+	}()
 
 	if resp.StatusCode != http.StatusOK {
 		return fmt.Errorf("HTTP %s for %s", resp.Status, url)
@@ -64,7 +66,9 @@ func download(url, dest string) error {
 	if err != nil {
 		return err
 	}
-	defer f.Close()
+	defer func() {
+		_ = f.Close()
+	}()
 
 	_, err = io.Copy(f, resp.Body)
 	return err