fix(write_flash): Fix --erase-all option

Closes https://github.com/espressif/esptool/issues/805

esptool/cmds.py

@@ -334,6 +334,8 @@ def write_flash(esp, args):
                 image = LoadFirmwareImage(esp.CHIP_NAME, argfile)
             except (FatalError, struct.error, RuntimeError):
                 continue
+            finally:
+                argfile.seek(0)  # LoadFirmwareImage changes the file handle position
             if image.chip_id != esp.IMAGE_CHIP_ID:
                 raise FatalError(
                     f"{argfile.name} is not an {esp.CHIP_NAME} image. "

test/test_esptool.py

@@ -513,6 +513,11 @@ class TestFlashing(EsptoolTestCase):
         assert "or higher (this chip is revision" in output
         assert "Use --force to flash anyway." in output
 
+    def test_erase_before_write(self):
+        output = self.run_esptool("write_flash --erase-all 0x0 images/one_kb.bin")
+        assert "Chip erase completed successfully" in output
+        assert "Hash of data verified" in output
+
 
 class TestFlashSizes(EsptoolTestCase):
     def test_high_offset(self):