interface_http.py

#!/usr/bin/env python3
# Copyright (c) The Bitcoin Core developers
# Distributed under the MIT software license, see the accompanying
# file COPYING or http://www.opensource.org/licenses/mit-license.php.
"""Test the HTTP server basics."""

from test_framework.test_framework import BitcoinTestFramework
from test_framework.netutil import NETWORK_ERRORS
from test_framework.util import assert_equal, assert_raises, str_to_b64str

import concurrent.futures
import http.client
import socket
import threading
import time
import urllib.parse

# Configuration option for some tests
RPCSERVERTIMEOUT = 2
# Set in httpserver.h
MAX_HEADERS_SIZE = 8192
MAX_BODY_SIZE = 32 * 1024 * 1024

class BitcoinHTTPConnection:
    def __init__(self, node):
        self.url = urllib.parse.urlparse(node.url)
        self.authpair = f'{self.url.username}:{self.url.password}'
        self.headers = {"Authorization": f"Basic {str_to_b64str(self.authpair)}"}
        self.reset_conn()

    def reset_conn(self):
        self.conn = http.client.HTTPConnection(self.url.hostname, self.url.port)
        self.conn.connect()

    def sock_closed(self):
        if self.conn.sock is None:
            return True
        try:
            self.conn.request('GET', '/')
            self.conn.getresponse().read()
            return False
        except NETWORK_ERRORS:
            return True

    def close_sock(self):
        self.conn.close()

    def set_timeout(self, seconds):
        self.conn.sock.settimeout(seconds)

    def add_header(self, key, value):
        self.headers.update({key: value})

    def _request(self, method, path, data, connection_header, **kwargs):
        headers = self.headers.copy()
        if connection_header is not None:
            headers["Connection"] = connection_header
        self.conn.request(method, path, data, headers, **kwargs)
        return self.conn.getresponse()

    def post(self, path, data, connection_header=None, **kwargs):
        return self._request('POST', path, data, connection_header, **kwargs)

    def get(self, path, connection_header=None):
        return self._request('GET', path, '', connection_header)

    def send_raw(self, data):
        self.conn.sock.sendall(data)

    def post_raw(self, path, data):
        data_bytes = data.encode("utf-8")
        req = f"POST {path} HTTP/1.1\r\n"
        req += f'Authorization: Basic {str_to_b64str(self.authpair)}\r\n'
        req += f'Content-Length: {len(data_bytes)}\r\n\r\n'
        self.send_raw(req.encode("ascii") + data_bytes)

    def recv_raw(self):
        '''
        Blocking socket will wait until data is received and return up to 1024 bytes
        '''
        return self.conn.sock.recv(1024)

    def expect_timeout(self, seconds):
        # Wait for response, but expect a timeout disconnection
        start = time.time()
        response1 = self.recv_raw()
        stop = time.time()
        # Server disconnected with EOF
        assert_equal(response1, b"")
        # Server disconnected within an acceptable range of time:
        # not immediately, and not too far over the configured duration.
        # This allows for some jitter in the test between client and server.
        duration = stop - start
        assert duration <= seconds + 2, f"Server disconnected too slow: {duration} > {seconds}"
        assert duration >= seconds - 1, f"Server disconnected too fast: {duration} < {seconds}"
        # The connection is definitely closed.
        assert self.sock_closed()

class HTTPBasicsTest (BitcoinTestFramework):
    def set_test_params(self):
        self.num_nodes = 1

    def setup_network(self):
        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
        # so low on this one node, its connection will quickly timeout and get dropped by
        # the server. Negating this setting will force the AuthServiceProxy
        # for this node to create a fresh new HTTP connection for every command
        # called for the remainder of this test.
        self.node.reuse_http_connections = False

        self.check_default_connection()
        self.check_socket_exclusivity()
        self.check_keepalive_connection()
        self.check_close_connection()
        self.check_excessive_request_size()
        self.check_pipelining(with_invalid_second_request=False)
        self.check_pipelining(with_invalid_second_request=True)
        self.check_chunked_transfer()
        self.check_idle_timeout()
        self.check_server_busy_idle_timeout()
        self.check_auth_required()
        self.check_wrong_credentials()
        self.check_malformed_auth_headers()
        self.check_disallowed_http_methods()
        self.check_path_traversal()
        self.check_request_smuggling_cl_te()
        self.check_duplicate_content_length()
        self.check_null_byte_in_uri()
        self.check_invalid_http_version()
        self.check_whitespace_in_headers()
        self.check_connection_limit()
        self.check_pipelined_data_is_throttled()


    def check_default_connection(self):
        self.log.info("Checking default HTTP/1.1 connection persistence")
        conn = BitcoinHTTPConnection(self.node)
        # Make request without explicit "Connection" header
        response1 = conn.post('/', '{"method": "getbestblockhash"}').read()
        assert b'"error":null' in response1
        # Connection still open after request
        assert not conn.sock_closed()
        # Make second request without explicit "Connection" header
        response2 = conn.post('/', '{"method": "getchaintips"}').read()
        assert b'"error":null' in response2
        # Connection still open after second request
        assert not conn.sock_closed()
        # Close
        conn.close_sock()
        assert conn.sock_closed()


    def check_socket_exclusivity(self):
        self.log.info("Checking that another process cannot bind the HTTP listen port")
        url = urllib.parse.urlparse(self.node.url)
        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as competing_listener:
            competing_listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
            # Ill-configured sockets permit port reuse unless the original
            # listener requested exclusive address use.
            assert_raises(
                OSError,
                lambda: competing_listener.bind((url.hostname, url.port)))


    def check_keepalive_connection(self):
        self.log.info("Checking keep-alive connection persistence")
        conn = BitcoinHTTPConnection(self.node)
        # Make request with explicit "Connection: keep-alive" header
        response1 = conn.post('/', '{"method": "getbestblockhash"}', connection_header='keep-alive').read()
        assert b'"error":null' in response1
        # Connection still open after request
        assert not conn.sock_closed()
        # Make second request with explicit "Connection" header
        response2 = conn.post('/', '{"method": "getchaintips"}', connection_header='keep-alive').read()
        assert b'"error":null' in response2
        # Connection still open after second request
        assert not conn.sock_closed()
        # Close
        conn.close_sock()
        assert conn.sock_closed()


    def check_close_connection(self):
        self.log.info("Checking close connection after response")
        conn = BitcoinHTTPConnection(self.node)
        # Make request with explicit "Connection: close" header
        response1 = conn.post('/', '{"method": "getbestblockhash"}', connection_header='close').read()
        assert b'"error":null' in response1
        # Connection closed after response
        assert conn.sock_closed()


    def check_excessive_request_size(self):
        self.log.info("Checking excessive request size")

        # Large URI plus up to 1000 bytes of default headers
        # added by python's http.client still below total limit.
        conn = BitcoinHTTPConnection(self.node)
        response1 = conn.get(f'/{"x" * (MAX_HEADERS_SIZE - 1000)}')
        assert_equal(response1.status, http.client.NOT_FOUND)

        # Excessive URI size plus default headers breaks the limit.
        conn = BitcoinHTTPConnection(self.node)
        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.
        header_line_length = len("header_0000: foo\r\n")
        headers_below_limit = (MAX_HEADERS_SIZE - 1000) // header_line_length
        headers_above_limit = MAX_HEADERS_SIZE // header_line_length

        # Many small header lines is ok
        conn = BitcoinHTTPConnection(self.node)
        for i in range(headers_below_limit):
            conn.add_header(f"header_{i:04}", "foo")
        response3 = conn.get('/x')
        assert_equal(response3.status, http.client.NOT_FOUND)

        # Too many small header lines exceeds total headers size allowed
        conn = BitcoinHTTPConnection(self.node)
        for i in range(headers_above_limit):
            conn.add_header(f"header_{i:04}", "foo")
        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.
        base_request_body_size = len('{"jsonrpc": "2.0", "id": "0", "method": "submitblock", "params": [""]}}')
        bytes_below_limit = MAX_BODY_SIZE - base_request_body_size
        bytes_above_limit = MAX_BODY_SIZE - base_request_body_size + 2

        # Large request body size is ok
        conn = BitcoinHTTPConnection(self.node)
        response4 = conn.post('/', f'{{"jsonrpc": "2.0", "id": "0", "method": "submitblock", "params": ["{"0" * bytes_below_limit}"]}}')
        assert_equal(response4.status, http.client.OK)

        conn = BitcoinHTTPConnection(self.node)

        # Split off the send into a background thread. When the server detects
        # the excessive size it will stop reading from the socket, but the client
        # will continue trying to write until the backpressure eventually
        # drops the TCP window size to 0. While the send operation is blocking until
        # it times out, we can still receive the server's response in the foreground.

        def send_excessive_body(self, conn):
            try:
                # Excessive body size is invalid
                conn.post_raw('/', f'{{"jsonrpc": "2.0", "id": "0", "method": "submitblock", "params": ["{"0" * bytes_above_limit}"]}}')
                # On some platforms (e.g. Windows) the whole request may be
                # accepted into the OS send buffer before the server disconnects.
                # It's ok to allow that, the server-side behavior is asserted in
                # the foreground thread via the 413 response.
                self.log.info("Client finished sending request before connection was terminated")
            except NETWORK_ERRORS:
                self.log.info("Client did not finish sending request before connection was terminated")

        send_thread = threading.Thread(target=send_excessive_body, args=(self, conn))
        send_thread.start()

        response5 = conn.recv_raw().decode()
        assert "413 Content too large" in response5

        try:
            conn.conn.sock.shutdown(socket.SHUT_RDWR)
            self.log.info("Send thread force-closed by test framework")
        except OSError:
            self.log.info("Send thread was already closed by RST from server")
        send_thread.join()


    def check_pipelining(self, with_invalid_second_request):
        """
        Requests are responded to in the order in which they were received
        See https://www.rfc-editor.org/rfc/rfc7230#section-6.3.2
        """
        self.log.info("Check pipelining" + (" with invalid second request" if with_invalid_second_request else ""))
        tip_height = self.node.getblockcount()
        conn = BitcoinHTTPConnection(self.node)
        conn.set_timeout(5)

        # Send two requests in a row.
        # The first request will block the second indefinitely
        conn.post_raw('/', f'{{"method": "waitforblockheight", "params": [{tip_height + 1}]}}')
        if with_invalid_second_request:
            conn.post_raw(f'/{"x" * MAX_HEADERS_SIZE * 2}', '{"method": "getblockcount"}')
        else:
            conn.post_raw('/', '{"method": "getblockcount"}')

        # The server should not respond to the second request until the first
        # request has been handled. Since the server will not respond at all
        # to the first request until we generate a block we expect a socket timeout.
        assert_raises(TimeoutError, lambda: conn.recv_raw())

        # Use a separate http connection to generate a block
        self.generate(self.node, 1, sync_fun=self.no_op)

        # Wait for responses to be received
        if with_invalid_second_request:
            OK = 1
            BAD = 1
        else:
            OK = 2
            BAD = 0
        res = b""
        while True:
            res += conn.recv_raw()
            if res.count(b"HTTP/1.1 200") == OK and res.count(b"HTTP/1.1 400") == BAD:
                break

        # waitforblockheight was responded to first, and then getblockcount
        # which includes the block added after the request was made
        chunks = res.split(b'"result":')
        assert chunks[1].startswith(b'{"hash":')
        if with_invalid_second_request:
            # The response to the in-flight first request is sent before the
            # error generated by parsing the second one, even though the second
            # request could have been rejected much earlier.
            assert res.index(b"HTTP/1.1 200") < res.index(b"HTTP/1.1 400")
        else:
            assert chunks[2].startswith(bytes(f'{tip_height + 1}', 'utf8'))


    def check_chunked_transfer(self):
        self.log.info("Check HTTP request encoded with chunked transfer")
        conn = BitcoinHTTPConnection(self.node)
        headers_chunked = conn.headers.copy()
        headers_chunked.update({"Transfer-encoding": "chunked"})
        body_chunked = [
            b'{"method": "submitblock", "params": ["',
            b'0' * 1000000,
            b'1' * 1000000,
            b'2' * 1000000,
            b'3' * 1000000,
            b'"]}'
        ]
        conn.conn.request(
            method='POST',
            url='/',
            body=iter(body_chunked),
            headers=headers_chunked,
            encode_chunked=True)
        response1 = conn.recv_raw()
        assert b'{"result":"high-hash","error":null}\n' in response1

        self.log.info("Check excessive size HTTP request encoded with chunked transfer")
        conn = BitcoinHTTPConnection(self.node)
        headers_chunked = conn.headers.copy()
        headers_chunked.update({"Transfer-encoding": "chunked"})
        body_chunked = [
            b'{"method": "submitblock", "params": ["',
            b'0' * 10000000,
            b'1' * 10000000,
            b'2' * 10000000,
            b'3' * 10000000,
            b'"]}'
        ]

        # Split off the send into a background thread. When the server detects
        # the excessive size it will stop reading from the socket, but the client
        # will continue trying to write until the backpressure eventually
        # drops the TCP window size to 0. While the send operation is blocking until
        # it times out, we can still receive the server's response in the foreground.

        def send_excessive_chunked(self, conn):
            try:
                conn.conn.request(
                    method='POST',
                    url='/',
                    body=iter(body_chunked),
                    headers=headers_chunked,
                    encode_chunked=True)
                # On some platforms (e.g. Windows) the whole request may be
                # accepted into the OS send buffer before the server disconnects.
                # It's ok to allow that, the server-side behavior is asserted in
                # the foreground thread via the 413 response.
                self.log.info("Client finished sending request before connection was terminated")
            except NETWORK_ERRORS:
                self.log.info("Client did not finish sending request before connection was terminated")

        send_thread = threading.Thread(target=send_excessive_chunked, args=(self, conn))
        send_thread.start()

        response2 = conn.recv_raw().decode()
        assert "413 Content too large" in response2

        try:
            conn.conn.sock.shutdown(socket.SHUT_RDWR)
            self.log.info("Send thread force-closed by test framework")
        except OSError:
            self.log.info("Send thread was already closed by RST from server")
        send_thread.join()


    def check_idle_timeout(self):
        self.log.info("Check -rpcservertimeout")

        # This is the amount of time the server will wait for a client to
        # send a complete request. Test it by sending an incomplete but
        # so-far otherwise well-formed HTTP request, and never finishing it.
        self.restart_node(0, extra_args=[f"-rpcservertimeout={RPCSERVERTIMEOUT}"])

        # Copied from http_incomplete_test_() in regress_http.c in libevent.
        # A complete request would have an additional "\r\n" at the end.
        bad_http_request = "GET /test1 HTTP/1.1\r\nHost: somehost\r\n"
        conn = BitcoinHTTPConnection(self.node)
        conn.send_raw(bad_http_request.encode("ascii"))

        conn.expect_timeout(RPCSERVERTIMEOUT)

        # Sanity check -- complete requests don't timeout waiting for completion
        good_http_request = "GET /test2 HTTP/1.1\r\nHost: somehost\r\n\r\n"
        conn.reset_conn()
        conn.send_raw(good_http_request.encode("ascii"))
        response = conn.recv_raw()
        assert response.startswith(b"HTTP/1.1 404 Not Found")

        # Still open
        assert not conn.sock_closed()


    def check_server_busy_idle_timeout(self):
        self.log.info("Check that -rpcservertimeout won't close on a delayed response")

        self.restart_node(0, extra_args=[f"-rpcservertimeout={RPCSERVERTIMEOUT}"])

        tip_height = self.node.getblockcount()
        conn = BitcoinHTTPConnection(self.node)
        conn.post_raw('/', f'{{"method": "waitforblockheight", "params": [{tip_height + 1}]}}')

        # Wait until after the timeout, then generate a block with a second HTTP connection
        time.sleep(RPCSERVERTIMEOUT + 1)
        generated_block = self.generate(self.node, 1, sync_fun=self.no_op)[0]

        # The first connection gets the response it is patiently waiting for
        response1 = conn.recv_raw().decode()
        assert generated_block in response1
        # The connection is still open
        assert not conn.sock_closed()

        # Now it will actually close due to idle timeout
        conn.expect_timeout(RPCSERVERTIMEOUT)


    def check_auth_required(self):
        self.log.info("Check that requests without credentials return 401 Unauthorized with WWW-Authenticate")
        conn = BitcoinHTTPConnection(self.node)
        conn.headers = {}
        response = conn.post('/', '{"method": "getbestblockhash"}')
        assert_equal(response.status, http.client.UNAUTHORIZED)
        assert response.getheader('WWW-Authenticate') is not None


    def check_wrong_credentials(self):
        self.log.info("Check that incorrect credentials return 401 Unauthorized")
        conn = BitcoinHTTPConnection(self.node)
        wrong_pair = f"{conn.url.username}:wrong_password"
        conn.headers = {"Authorization": f"Basic {str_to_b64str(wrong_pair)}"}
        response = conn.post('/', '{"method": "getbestblockhash"}')
        assert_equal(response.status, http.client.UNAUTHORIZED)
        assert response.getheader('WWW-Authenticate') is not None


    def check_malformed_auth_headers(self):
        self.log.info("Check that malformed Authorization headers return 401 Unauthorized")
        cases = [
            "Bearer sometoken123",
            'Digest username="user", realm="test"',
            "Basic !!!notbase64!!!",
            f"Basic {str_to_b64str('nocolon')}",
            "Basic ",
        ]
        for auth_value in cases:
            conn = BitcoinHTTPConnection(self.node)
            conn.headers = {"Authorization": f"{auth_value}"}
            response = conn.post('/', '{"method": "getbestblockhash"}')
            assert_equal(response.status, http.client.UNAUTHORIZED)
            assert response.getheader('WWW-Authenticate') is not None


    def check_disallowed_http_methods(self):
        self.log.info("Check that unsafe or unsupported HTTP methods are rejected")
        for method, err in [
            ['TRACE',   http.client.METHOD_NOT_ALLOWED],
            ['CONNECT', http.client.METHOD_NOT_ALLOWED],
            ['DELETE',  http.client.METHOD_NOT_ALLOWED],
            ['PATCH',   http.client.METHOD_NOT_ALLOWED],
            ['OPTIONS', http.client.METHOD_NOT_ALLOWED],
            ['GET',     http.client.METHOD_NOT_ALLOWED] # RPC endpoint '/' only handles POST
        ]:
            conn = BitcoinHTTPConnection(self.node)
            response = conn._request(method, '/', data=None, connection_header=None)
            assert_equal(response.status, err)


    def check_path_traversal(self):
        self.log.info("Check that path traversal attempts are safely rejected")
        traversal_paths = [
            '/../etc/passwd',
            '/../../etc/shadow',
            '/%2e%2e/%2e%2e/etc/passwd',     # URL-encoded dots
            '/..%2Fetc%2Fpasswd',            # URL-encoded slash
            '/.%2e/.%2e/etc/passwd',         # mixed encoding
            '/valid/../../../etc/passwd',
        ]
        for path in traversal_paths:
            conn = BitcoinHTTPConnection(self.node)
            response = conn.get(path)
            assert_equal(response.status, http.client.NOT_FOUND)


    def check_request_smuggling_cl_te(self):
        self.log.info("Check request smuggling is not possible")
        # https://www.rfc-editor.org/rfc/rfc7230#section-3.3.3
        # Transfer-Encoding takes precedence over Content-Length.
        # Sending both creates a smuggling vector: a front-end proxy that
        # uses Content-Length while the back-end uses Transfer-Encoding lets an
        # attacker prepend arbitrary bytes to the next victim's request.

        # The real JSON-RPC body sent as a single chunk.
        body = b'{"method":"getblockcount"}'
        # Content-Length is set to the length of just the chunk-size line
        # ("1a\r\n" = 4 bytes), not the full chunked body — the ambiguity that
        # smuggling exploits. A server using Transfer-Encoding reads the complete
        # chunk and responds with the block count; a server confused by the
        # mismatch may stall, close the connection, or return an error.
        chunk_size_line = f"{len(body):x}\r\n".encode("ascii")
        # Signals end of body
        empty_chunk = b'\r\n0\r\n\r\n'
        chunk_body = chunk_size_line + body + empty_chunk

        conn = BitcoinHTTPConnection(self.node)
        raw = (
            f"POST / HTTP/1.1\r\n"
            f"Host: {conn.url.hostname}\r\n"
            f"Authorization: Basic {str_to_b64str(conn.authpair)}\r\n"
            f"Content-Length: {len(chunk_size_line)}\r\n"
            f"Transfer-Encoding: chunked\r\n"
            f"\r\n"
        ).encode("ascii") + chunk_body
        conn.send_raw(raw)
        response = conn.recv_raw().decode()
        assert "HTTP/1.1 200 OK" in response
        count = self.node.getblockcount()
        assert f'"result":{count}' in response


    def check_duplicate_content_length(self):
        self.log.info("Check that duplicate Content-Length headers are handled")
        # https://www.rfc-editor.org/rfc/rfc7230#section-3.3.3
        # Multiple Content-Length headers with differing values "MUST"
        # result in an error.
        conn = BitcoinHTTPConnection(self.node)
        body = '{"method":"getblockcount"}'
        raw = (
            f"POST / HTTP/1.1\r\n"
            f"Host: {conn.url.hostname}\r\n"
            f"Authorization: Basic {str_to_b64str(conn.authpair)}\r\n"
            f"Content-Length: {len(body)}\r\n"
            f"Content-Length: 999\r\n"
            f"\r\n"
            f"{body}"
        ).encode("ascii")
        conn.send_raw(raw)
        response = conn.recv_raw().decode()
        assert response.startswith("HTTP/1.1 400")


    def check_null_byte_in_uri(self):
        self.log.info("Check that null bytes in the URI are safely rejected")
        # Null-byte injection can truncate the path string in C environments,
        # bypassing suffix/extension checks and causing unexpected file access.
        conn = BitcoinHTTPConnection(self.node)
        raw = (
            "GET /safe\x00/../etc/passwd HTTP/1.1\r\n"
            f"Host: {conn.url.hostname}\r\n"
            f"Authorization: Basic {str_to_b64str(conn.authpair)}\r\n"
            "\r\n"
        ).encode("ascii")
        conn.send_raw(raw)
        response = conn.recv_raw().decode()
        assert response.startswith("HTTP/1.1 400")


    def check_invalid_http_version(self):
        self.log.info("Check that requests with invalid HTTP versions are safely rejected")
        cases = [
            b"GET / \r\n\r\n",                                    # HTTP/0.9 — no version
            b"GET / HTTP/9.9\r\nHost: localhost\r\n\r\n",         # far-future version
            b"GET / HTTP/INVALID\r\nHost: localhost\r\n\r\n",     # non-numeric version
            b"GET / NOTHTTP/1.1\r\nHost: localhost\r\n\r\n",      # wrong protocol name
        ]
        for raw in cases:
            conn = BitcoinHTTPConnection(self.node)
            conn.send_raw(raw)
            response = conn.recv_raw().decode()
            assert response.startswith("HTTP/1.1 400")


    def check_whitespace_in_headers(self):
        self.log.info("Check that requests with whitespace in headers are rejected")
        # Extra whitespace before colon in header.
        conn = BitcoinHTTPConnection(self.node)
        conn.headers = {"Authorization ": f"Basic {str_to_b64str(conn.authpair)}"}
        self.send_bad_and_tolerate_disconnect(conn, lambda: conn.post('/', '{"method": "getbestblockhash"}'))

        # Extra whitespace at start of new line.
        # "line folding" as defined in
        # https://www.rfc-editor.org/rfc/rfc2616#section-2.2
        # is considered unsafe and is explicitly deprecated in
        # 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)}"}
        self.send_bad_and_tolerate_disconnect(conn, lambda: conn.post('/', '{"method": "getbestblockhash"}'))


    def check_connection_limit(self):
        self.log.info("Check connection limits")

        # Disable timeout so the initial batch of clients stays connected
        # until the end of the test.
        for comment,                  extra_args,                                      limit in [
            ("default (16)",          ["-rpcservertimeout=0", "-rest"],                16),
            ("-rpcmaxconnections=64", ["-rpcservertimeout=0", "-rest",
                                       "-rpcmaxconnections=64", "-maxconnections=16"], 64)
        ]:
            self.log.info(f"Using connection limit: {comment}")
            self.restart_node(0, extra_args=extra_args)

            # Close the persistent HTTP connection to this node by replacing it with
            # a new AuthServiceProxy, reducing HTTPServer::GetConnectionsCount() to 0.
            # The new AuthServiceProxy won't actually open an HTTP connection until
            # it needs to send an RPC (for example, to stop the node at the end of the test).
            self.node._rpc = self.node.create_new_rpc_connection(mode="AUTHPROXY")

            MAX_HTTP_CONNECTIONS = limit
            connections = []

            # Connections all succeed up to the limit
            with self.node.assert_debug_log(
                expected_msgs = [f"method=invalidrpc_{i} " for i in range(1, MAX_HTTP_CONNECTIONS + 1)]
            ):
                for i in range(1, MAX_HTTP_CONNECTIONS + 1):
                    conn = BitcoinHTTPConnection(self.node)
                    # Each client makes a unique request so it's easy to find in the log
                    conn.post('/', f'{{"method": "invalidrpc_{i}"}}', connection_header='keep-alive').read()
                    connections.append(conn)

            # The next connection is over the limit, expect it to timeout
            with self.node.assert_debug_log(
                expected_msgs = [],
                unexpected_msgs = ["method=never_accepted"]
            ):
                conn = BitcoinHTTPConnection(self.node)
                conn.set_timeout(5)
                assert_raises(TimeoutError, lambda: conn.post('/', '{"method": "never_accepted"}', connection_header='keep-alive').read())

            # All original clients are still connected
            assert_equal(len(connections), MAX_HTTP_CONNECTIONS)
            for client in connections:
                assert not client.sock_closed()

            # Try connecting again, but this time we'll wait for acceptance.
            # Because the send is blocking, we'll execute in a background thread.

            def wait_for_send(conn):
                return conn.get('/rest/blockhashbyheight/0.json').read()

            conn = BitcoinHTTPConnection(self.node)
            conn.set_timeout(None)
            executor = concurrent.futures.ThreadPoolExecutor(max_workers=1)
            waiting_request = executor.submit(
                wait_for_send,
                conn
            )

            # We are waiting
            assert not waiting_request.done()

            # Close one of the original connections
            popped_client = connections.pop()
            popped_client.close_sock()

            # The waiting connection gets processed
            delayed_response = waiting_request.result(timeout=5)
            assert "0f9188f13cb7b2c71f2a335e3a4fc328bf5beb436012afca590b1a11466e2206" in delayed_response.decode()

            # Close all remaining connections for clean up
            for client in connections:
                client.close_sock()


    def check_pipelined_data_is_throttled(self):
        self.log.info("Check that pipelined data is throttled while a request is in flight")
        self.restart_node(0, extra_args=["-rpcservertimeout=0"])

        conn = BitcoinHTTPConnection(self.node)

        # A blocking RPC request: the server reads it fully and it enters the
        # worker pool as "in flight" (m_req_busy) until a new block arrives.
        tip_height = self.node.getblockcount()
        conn.post_raw('/', f'{{"method": "waitforblockheight", "params": [{tip_height + 1}]}}')

        # Flood the same connection with big pipelined requests:
        # Large garbage submitblock (just under MAX_BODY_SIZE each, including HTTP/jsonrpc overhead)
        garbage_block = "0" * (MAX_BODY_SIZE - 100)
        body = f'{{"method": "submitblock", "params": ["{garbage_block}"]}}'
        flood = (
            f'POST / HTTP/1.1\r\nAuthorization: Basic {str_to_b64str(conn.authpair)}\r\n'
            f'Content-Length: {len(body)}\r\n\r\n' +
            body
        ).encode("ascii")

        # Non-blocking send: When the server stops reading from the buffer
        # due to TCP backpressure, Python will raise an error. If the socket
        # was set to blocking, we would have to wait for an ambiguous timeout.
        conn.conn.sock.setblocking(False)

        # Kernel socket buffer sizes vary widely across platforms,
        # so we can't rely on counting sent() bytes to determine if the
        # server is actually draining its end of the socket.
        # When the server is busy, a continuous flood from the client SHOULD,
        # at some point, stall indefinitely. An unpatched server will continue
        # to accept data from the socket, at some rate, indefinitely.

        # If send() is blocked for this many seconds, we assume the server
        # is behaving correctly.
        STALL_TIMEOUT = 5
        # If send() continues to progress for this many seconds, we assume
        # the server is vulnerable to memory exhaustion.
        PROGRESS_TIMEOUT = 10

        sent = 0
        stuck_since = None
        start = time.monotonic()
        while True:
            try:
                sent += conn.conn.sock.send(flood[sent % len(flood):])
                # Progress: the server is still reading
                stuck_since = None
                self.log.debug(f"sent: {sent}")
                assert sent <= len(flood) * 10, (
                    f"Server accepted {sent} bytes of pipelined data while a "
                    "request was still in flight: the receive buffer is not throttled")
            except BlockingIOError:
                # The kernel send buffer is full (EAGAIN).
                # That's good, but we still need to determine if we are
                # feeling backpressure from the server or the client-side buffer.
                if stuck_since is None:
                    stuck_since = time.monotonic()
                elif time.monotonic() - stuck_since > STALL_TIMEOUT:
                    # No progress: the server has stopped reading.
                    break
            if stuck_since is None and time.monotonic() - start > PROGRESS_TIMEOUT:
                # Continuous progress: the server is still draining the
                # receive buffer while a request is in flight.
                raise AssertionError(
                    f"Server kept reading pipelined data ({sent} bytes) while a "
                    f"request was still in flight for {PROGRESS_TIMEOUT}s.")
            time.sleep(0.05)

        self.log.info(f"Pipelined flood stalled after {sent} bytes; no progress for {STALL_TIMEOUT}s.")

        # Unblock the client request queue.
        conn.conn.sock.settimeout(10)
        generated_block = self.generate(self.node, 1, sync_fun=self.no_op)[0]
        # First reply is for the blocking request.
        response = conn.recv_raw().decode()
        assert generated_block in response


if __name__ == '__main__':
    HTTPBasicsTest(__file__).main()