first_stage_test: Add test_timeout_error

Signed-off-by: Marc Hartmayer <[email protected]>

Author: mhartmay

tests/first_stage_test.py

@@ -2,6 +2,7 @@
 import os
 import select
 import subprocess
+import sys
 
 try:
     from io import StringIO
@@ -339,3 +340,42 @@ def test_eof_too_early(self):
             finally:
                 proc.stdout.close()
                 proc.stderr.close()
+
+    def test_timeout_error(self):
+        """
+        The boot command should write an ECO marker to stdout, read the
+        preamble from stdin, then execute it.
+
+        This test attaches closes stdin to create a specific failure
+        1. Fork child tries to read from STDIN, but fails as it is closed
+        2. Fork child raises TimeoutError
+        3. Fork child's file descriptors (write pipes) are closed by the OS
+        4. Fork parent does `dup(<read pipe>, <stdin>)` and `exec(<python>)`
+        5. Python reads `b''` (i.e. EOF) from stdin (a closed pipe)
+        6. Python runs `''` (a valid script) and exits with success
+        """
+
+        # We do not want to wait the default of 10s, change it to 0.3s
+        self.conn._first_stage_timeout = 0.3
+        args = self.conn.get_boot_command()
+
+        proc = subprocess.Popen(
+            args=args,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            preexec_fn=sys.stdin.close,
+        )
+        try:
+            try:
+                stdout, stderr = proc.communicate(timeout=12)
+            except TypeError:
+                stdout, stderr = proc.communicate()
+        except:
+            proc.kill()
+            self.fail("Timeout situation was not recognized")
+        self.assertEqual(0, proc.returncode)
+        self.assertEqual(stdout, mitogen.parent.BootstrapProtocol.EC0_MARKER + b("\n"))
+        self.assertIn(
+            b("TimeoutError"),
+            stderr,
+        )