test(microvm): read the host-loopback HTTP request up to its blank line

scripts/nvx_tools/microvm_tests.py

@@ -3008,6 +3008,32 @@ def run_ipv6_egress_policy(
             endpoint.close()
 
 
+HOST_LOOPBACK_HTTP_REQUEST_LIMIT = 8192
+
+
+def _read_http_request(connection: socket.socket, timeout: float) -> bytes:
+    """Read a request up to its blank line, however TCP splits it.
+
+    A request can arrive in several reads, so one ``recv`` is not enough. The
+    read stops at the header terminator, at the peer's close, or when the
+    request is too large or the deadline passes.
+    """
+    deadline = time.monotonic() + timeout
+    request = bytearray()
+    while b"\r\n\r\n" not in request:
+        remaining = deadline - time.monotonic()
+        if remaining <= 0:
+            raise TimeoutError("host-loopback HTTP request did not complete in time")
+        connection.settimeout(remaining)
+        chunk = connection.recv(4096)
+        if not chunk:
+            break
+        request.extend(chunk)
+        if len(request) > HOST_LOOPBACK_HTTP_REQUEST_LIMIT:
+            raise RuntimeError("host-loopback HTTP request exceeds its size limit")
+    return bytes(request)
+
+
 def _http_server(
     listener: socket.socket,
     expected_path: bytes,
@@ -3018,8 +3044,7 @@ def _http_server(
     try:
         connection, _ = listener.accept()
         with connection:
-            connection.settimeout(timeout)
-            request = connection.recv(4096)
+            request = _read_http_request(connection, timeout)
             if not request.startswith(b"GET " + expected_path + b" HTTP/1."):
                 raise RuntimeError(
                     f"unexpected host-loopback HTTP request: {request!r}"

scripts/test_microvm_tests.py

@@ -239,6 +239,46 @@ def _fresh_openvmm_command(*_args: object, **_kwargs: object) -> list[str]:
     return ["openvmm"]
 
 
+class HostLoopbackHttpFixtureTests(unittest.TestCase):
+    def _exchange(self, pieces: list[bytes]) -> tuple[bytes, list[Exception]]:
+        """Send the request in pieces with a gap, and return the reply and fixture errors."""
+        listener = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.addCleanup(listener.close)
+        listener.bind(("127.0.0.1", 0))
+        listener.listen(1)
+        errors: list[Exception] = []
+        server = threading.Thread(
+            target=microvm_tests._http_server,
+            args=(listener, b"/proxy", b"NVX-BODY", 2.0, errors),
+            daemon=True,
+        )
+        server.start()
+        response = b""
+        with socket.create_connection(listener.getsockname(), timeout=5) as client:
+            for index, piece in enumerate(pieces):
+                if index:
+                    time.sleep(0.25)
+                client.sendall(piece)
+            while chunk := client.recv(4096):
+                response += chunk
+        server.join(5)
+        return response, errors
+
+    def test_a_single_send_request_is_answered(self) -> None:
+        response, errors = self._exchange(
+            [b"GET /proxy HTTP/1.1\r\nHost: localhost\r\n\r\n"]
+        )
+        self.assertTrue(response.startswith(b"HTTP/1.1 200 OK"), response)
+        self.assertEqual(errors, [])
+
+    def test_a_request_split_across_reads_is_answered(self) -> None:
+        response, errors = self._exchange(
+            [b"GET ", b"/proxy HTTP/1.1\r\nHost: localhost\r\n\r\n"]
+        )
+        self.assertTrue(response.startswith(b"HTTP/1.1 200 OK"), response)
+        self.assertEqual(errors, [])
+
+
 class MicrovmTestParserTests(unittest.TestCase):
     def test_parser_defaults_to_all_correctness_scenarios(self):
         args = nvx.parse_args(["test-microvm", "--backend", "mshv"])