fix(jadepy): avoid blocking large serial reads

jadepy/jade_serial.py

@@ -85,4 +85,11 @@ def write(self, bytes_):
 
     def read(self, n):
         assert self.ser is not None
-        return self.ser.read(n)
+
+        if not n:
+            return bytes()
+
+        waiting = getattr(self.ser, 'in_waiting', 0) or 0
+        read_size = min(n, waiting) if waiting > 0 else 1
+
+        return self.ser.read(read_size)

tests/test_jade_serial.py

@@ -0,0 +1,58 @@
+import sys
+import types
+import unittest
+
+serial_module = types.ModuleType('serial')
+serial_module.Serial = object
+
+serialutil_module = types.ModuleType('serial.serialutil')
+serialutil_module.SerialException = Exception
+serial_module.serialutil = serialutil_module
+
+tools_module = types.ModuleType('serial.tools')
+list_ports_module = types.ModuleType('serial.tools.list_ports')
+list_ports_module.comports = lambda: []
+tools_module.list_ports = list_ports_module
+
+sys.modules.setdefault('serial', serial_module)
+sys.modules.setdefault('serial.serialutil', serialutil_module)
+sys.modules.setdefault('serial.tools', tools_module)
+sys.modules.setdefault('serial.tools.list_ports', list_ports_module)
+
+from jadepy.jade_serial import JadeSerialImpl
+
+
+class FakeSerial:
+    def __init__(self, *, in_waiting, payload):
+        self.in_waiting = in_waiting
+        self.payload = payload
+        self.read_calls = []
+
+    def read(self, n):
+        self.read_calls.append(n)
+        return self.payload[:n]
+
+
+class JadeSerialImplReadTest(unittest.TestCase):
+    def make_impl(self, fake_serial):
+        impl = JadeSerialImpl('/dev/ttyACM0', 115200, 1)
+        impl.ser = fake_serial
+        return impl
+
+    def test_read_uses_buffered_bytes_instead_of_requested_chunk_size(self):
+        fake_serial = FakeSerial(in_waiting=3, payload=b'abc')
+        impl = self.make_impl(fake_serial)
+
+        result = impl.read(4096)
+
+        self.assertEqual(result, b'abc')
+        self.assertEqual(fake_serial.read_calls, [3])
+
+    def test_read_uses_single_byte_when_no_bytes_are_buffered(self):
+        fake_serial = FakeSerial(in_waiting=0, payload=b'z')
+        impl = self.make_impl(fake_serial)
+
+        result = impl.read(4096)
+
+        self.assertEqual(result, b'z')
+        self.assertEqual(fake_serial.read_calls, [1])