Found and hopefullyfixed a bug with fenrir watchdog.

src/fenrirscreenreader/screenDriver/vcsaDriver.py

@@ -263,9 +263,10 @@ class driver(screenDriver):
             while True:
                 # Read from file
                 try:
-                    d += file.readline(1)
+                    chunk = file.readline(1)
-                    if not d:
+                    if not chunk:
                         break
+                    d += chunk
                 except Exception as e:
                     break
         return d

tests/unit/test_vcsa_driver.py

@@ -0,0 +1,35 @@
+from unittest.mock import Mock
+
+from fenrirscreenreader.screenDriver.vcsaDriver import driver as VcsaDriver
+
+
+class BulkReadFailure:
+    def __init__(self, chunks):
+        self.chunks = iter(chunks)
+        self.readline_calls = 0
+
+    def seek(self, offset):
+        assert offset == 0
+
+    def read(self):
+        raise OSError(22, "Invalid argument")
+
+    def readline(self, size):
+        assert size == 1
+        self.readline_calls += 1
+        if self.readline_calls > 3:
+            raise RuntimeError("read continued after EOF")
+        return next(self.chunks)
+
+
+def test_vcsa_read_fallback_stops_at_eof():
+    vcsa_driver = VcsaDriver.__new__(VcsaDriver)
+    vcsa_driver.env = {
+        "runtime": {
+            "DebugManager": Mock(),
+        }
+    }
+    screen_file = BulkReadFailure([b"a", b"b", b""])
+
+    assert vcsa_driver.read_file(screen_file) == b"ab"
+    assert screen_file.readline_calls == 3