Very scary test here. Trying to see if we can boost speed on very large terminals.

src/fenrirscreenreader/screenDriver/vcsaDriver.py

@@ -10,6 +10,7 @@
 # blink = 5 if attr & 1 else 0
 # bold = 1 if attr & 16 else 0
 
+import errno
 import fcntl
 import glob
 import os
@@ -53,6 +54,9 @@ class driver(screenDriver):
         fgColorValues: Foreground color value mappings
         hichar: High character mask for Unicode support
     """
+    read_retry_attempts = 10
+    read_retry_delay = 0.05
+
     def __init__(self):
         screenDriver.__init__(self)
         self.ListSessions = None
@@ -251,23 +255,39 @@ class driver(screenDriver):
             bytes: File content as bytes
         """
         d = b""
+        for attempt in range(self.read_retry_attempts + 1):
             file.seek(0)
             try:
-            d = file.read()
+                return file.read()
-        except Exception as e:
+            except OSError as e:
+                if (
+                    e.errno == errno.EINVAL
+                    and attempt < self.read_retry_attempts
+                ):
+                    time.sleep(self.read_retry_delay)
+                    continue
                 self.env["runtime"]["DebugManager"].write_debug_out(
-                "vcsaDriver get_screen_text: Error reading file: " + str(e),
+                    "vcsaDriver get_screen_text: Error reading file: "
+                    + str(e),
                     debug.DebugLevel.ERROR,
                 )
+                break
+            except Exception as e:
+                self.env["runtime"]["DebugManager"].write_debug_out(
+                    "vcsaDriver get_screen_text: Error reading file: "
+                    + str(e),
+                    debug.DebugLevel.ERROR,
+                )
+                break
+
         file.seek(0)
         while True:
-                # Read from file
             try:
                 chunk = file.readline(1)
                 if not chunk:
                     break
                 d += chunk
-                except Exception as e:
+            except Exception:
                 break
         return d
 

tests/unit/test_vcsa_driver.py

@@ -22,14 +22,49 @@ class BulkReadFailure:
         return next(self.chunks)
 
 
-def test_vcsa_read_fallback_stops_at_eof():
+class TransientInvalidArgumentRead:
+    def __init__(self, payload):
+        self.payload = payload
+        self.read_calls = 0
+        self.readline_calls = 0
+
+    def seek(self, offset):
+        assert offset == 0
+
+    def read(self):
+        self.read_calls += 1
+        if self.read_calls == 1:
+            raise OSError(22, "Invalid argument")
+        return self.payload
+
+    def readline(self, size):
+        self.readline_calls += 1
+        return b""
+
+
+def build_vcsa_driver():
     vcsa_driver = VcsaDriver.__new__(VcsaDriver)
     vcsa_driver.env = {
         "runtime": {
             "DebugManager": Mock(),
         }
     }
+    vcsa_driver.read_retry_delay = 0
+    return vcsa_driver
+
+
+def test_vcsa_read_fallback_stops_at_eof():
+    vcsa_driver = build_vcsa_driver()
     screen_file = BulkReadFailure([b"a", b"b", b""])
 
     assert vcsa_driver.read_file(screen_file) == b"ab"
     assert screen_file.readline_calls == 3
+
+
+def test_vcsa_read_retries_transient_invalid_argument():
+    vcsa_driver = build_vcsa_driver()
+    screen_file = TransientInvalidArgumentRead(b"\x01\x02\x00\x00x")
+
+    assert vcsa_driver.read_file(screen_file) == b"\x01\x02\x00\x00x"
+    assert screen_file.read_calls == 2
+    assert screen_file.readline_calls == 0