test: tolerate race condition in interface_http.py

Fixes #35632 by allowing both outcomes of a race condition.
The server behavior is unchanged: in response to a malformed request
we send an error code and disconnect. The issue is that sometimes
on Windows the RST is caught by the platform and the receive buffer
is discarded before the Python client can process it with recv().

We can also be much more polite to misbehaving clients by
implementing SO_LINGER as suggested in #35780 but that will require
more review.

test/functional/interface_http.py

@@ -104,6 +104,26 @@ class HTTPBasicsTest (BitcoinTestFramework):
         self.setup_nodes()
         self.node = self.nodes[0]
 
+    def send_bad_and_tolerate_disconnect(self, conn, predicate_fn):
+        '''
+        Tolerate a race condition when sending a malformed request that should result
+        in the server disconnecting the client. The server *should* be sending an error
+        response as well but in some conditions on some platforms (Windows) the python
+        client might encounter the socket error before processing the response.
+        '''
+        with self.node.assert_debug_log([f"HTTPResponse (status code: {http.client.BAD_REQUEST}"]):
+            try:
+                response = predicate_fn()
+                assert_equal(response.status, http.client.BAD_REQUEST)
+                self.log.info(f"Client received expected {http.client.BAD_REQUEST} response before connection was terminated")
+                # Drain server response
+                response.read()
+                conn.set_timeout(2)
+            except NETWORK_ERRORS:
+                self.log.info(f"Client did not receive expected {http.client.BAD_REQUEST} response before connection was terminated")
+        assert conn.sock_closed()
+
+
     def run_test(self):
         # The test framework typically reuses a single persistent HTTP connection
         # for all RPCs to a TestNode. Because we are setting -rpcservertimeout
@@ -192,8 +212,7 @@ class HTTPBasicsTest (BitcoinTestFramework):
 
         # Excessive URI size plus default headers breaks the limit.
         conn = BitcoinHTTPConnection(self.node)
-        response2 = conn.get(f'/{"x" * MAX_HEADERS_SIZE}')
-        assert_equal(response2.status, http.client.BAD_REQUEST)
+        self.send_bad_and_tolerate_disconnect(conn, lambda: conn.get(f'/{"x" * MAX_HEADERS_SIZE}'))
 
         # Compute how many short header lines need to be added to http.client
         # default headers to make / break the total limit in a single request.
@@ -212,8 +231,7 @@ class HTTPBasicsTest (BitcoinTestFramework):
         conn = BitcoinHTTPConnection(self.node)
         for i in range(headers_above_limit):
             conn.add_header(f"header_{i:04}", "foo")
-        response3 = conn.get('/x')
-        assert_equal(response3.status, http.client.BAD_REQUEST)
+        self.send_bad_and_tolerate_disconnect(conn, lambda: conn.get('/x'))
 
         # Compute how much data we can add to a request message body
         # to make / break the limit.
@@ -593,8 +611,7 @@ class HTTPBasicsTest (BitcoinTestFramework):
         # Extra whitespace before colon in header.
         conn = BitcoinHTTPConnection(self.node)
         conn.headers = {"Authorization ": f"Basic {str_to_b64str(conn.authpair)}"}
-        response = conn.post('/', '{"method": "getbestblockhash"}')
-        assert_equal(response.status, http.client.BAD_REQUEST)
+        self.send_bad_and_tolerate_disconnect(conn, lambda: conn.post('/', '{"method": "getbestblockhash"}'))
 
         # Extra whitespace at start of new line.
         # "line folding" as defined in
@@ -603,8 +620,7 @@ class HTTPBasicsTest (BitcoinTestFramework):
         # https://www.rfc-editor.org/rfc/rfc7230#section-3.2.4
         conn = BitcoinHTTPConnection(self.node)
         conn.headers = {"Authorization": f"Basic \n {str_to_b64str(conn.authpair)}"}
-        response = conn.post('/', '{"method": "getbestblockhash"}')
-        assert_equal(response.status, http.client.BAD_REQUEST)
+        self.send_bad_and_tolerate_disconnect(conn, lambda: conn.post('/', '{"method": "getbestblockhash"}'))
 
 
     def check_connection_limit(self):