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Edit File: ephemeral.py

# This file is part of cloud-init. See LICENSE file for license information.

"""Module for ephemeral network context managers
"""
import contextlib
import logging
from functools import partial
from typing import Any, Callable, Dict, List, Literal, Optional, Tuple

import cloudinit.net as net
import cloudinit.netinfo as netinfo
from cloudinit.net.dhcp import NoDHCPLeaseError, maybe_perform_dhcp_discovery
from cloudinit.subp import ProcessExecutionError
from cloudinit.url_helper import UrlError, wait_for_url

LOG = logging.getLogger(__name__)

class EphemeralIPv4Network:
    """Context manager which sets up temporary static network configuration.

No operations are performed if the provided interface already has the
    specified configuration.
    This can be verified with the connectivity_urls_data.
    If unconnected, bring up the interface with valid ip, prefix and broadcast.
    If router is provided setup a default route for that interface. Upon
    context exit, clean up the interface leaving no configuration behind.
    """

def __init__(
        self,
        distro,
        interface,
        ip,
        prefix_or_mask,
        broadcast,
        interface_addrs_before_dhcp: dict,
        router=None,
        static_routes=None,
    ):
        """Setup context manager and validate call signature.

@param interface: Name of the network interface to bring up.
        @param ip: IP address to assign to the interface.
        @param prefix_or_mask: Either netmask of the format X.X.X.X or an int
            prefix.
        @param broadcast: Broadcast address for the IPv4 network.
        @param router: Optionally the default gateway IP.
        @param static_routes: Optionally a list of static routes from DHCP
        """
        if not all([interface, ip, prefix_or_mask, broadcast]):
            raise ValueError(
                "Cannot init network on {0} with {1}/{2} and bcast {3}".format(
                    interface, ip, prefix_or_mask, broadcast
                )
            )
        try:
            self.prefix = net.ipv4_mask_to_net_prefix(prefix_or_mask)
        except ValueError as e:
            raise ValueError(
                "Cannot setup network, invalid prefix or "
                "netmask: {0}".format(e)
            ) from e

self.interface = interface
        self.ip = ip
        self.broadcast = broadcast
        self.router = router
        self.static_routes = static_routes
        # List of commands to run to cleanup state.
        self.cleanup_cmds: List[Callable] = []
        self.distro = distro
        self.cidr = f"{self.ip}/{self.prefix}"
        self.interface_addrs_before_dhcp = interface_addrs_before_dhcp.get(
            self.interface, {}
        )

def __enter__(self):
        """Set up ephemeral network if interface is not connected.

This context manager handles the lifecycle of the network interface,
        addresses, routes, etc
        """

try:
            try:
                self._bringup_device()
            except ProcessExecutionError as e:
                if "File exists" not in str(
                    e.stderr
                ) and "Address already assigned" not in str(e.stderr):
                    raise

# rfc3442 requires us to ignore the router config *if*
            # classless static routes are provided.
            #
            # https://tools.ietf.org/html/rfc3442
            #
            # If the DHCP server returns both a Classless Static Routes
            # option and a Router option, the DHCP client MUST ignore
            # the Router option.
            #
            # Similarly, if the DHCP server returns both a Classless
            # Static Routes option and a Static Routes option, the DHCP
            # client MUST ignore the Static Routes option.
            if self.static_routes:
                self._bringup_static_routes()
            elif self.router:
                self._bringup_router()
        except ProcessExecutionError:
            self.__exit__(None, None, None)
            raise

def __exit__(self, excp_type, excp_value, excp_traceback):
        """Teardown anything we set up."""
        for cmd in self.cleanup_cmds:
            cmd()

def _bringup_device(self):
        """Perform the ip commands to fully set up the device.

Dhcp clients behave differently in how they leave link state and ip
        address assignment.

Attempt assigning address and setting up link if needed to be done.
        Set cleanup_cmds to return the interface state to how it was prior
        to execution of the dhcp client.
        """
        LOG.debug(
            "Attempting setup of ephemeral network on %s with %s brd %s",
            self.interface,
            self.cidr,
            self.broadcast,
        )
        interface_addrs_after_dhcp = netinfo.netdev_info().get(
            self.interface, {}
        )
        has_link = interface_addrs_after_dhcp.get("up")
        had_link = self.interface_addrs_before_dhcp.get("up")
        has_ip = self.ip in [
            ip.get("ip") for ip in interface_addrs_after_dhcp.get("ipv4", {})
        ]
        had_ip = self.ip in [
            ip.get("ip")
            for ip in self.interface_addrs_before_dhcp.get("ipv4", {})
        ]

if has_ip:
            LOG.debug(
                "Skip adding ip address: %s already has address %s",
                self.interface,
                self.ip,
            )
        else:
            self.distro.net_ops.add_addr(
                self.interface, self.cidr, self.broadcast
            )
        if has_link:
            LOG.debug(
                "Skip bringing up network link: interface %s is already up",
                self.interface,
            )
        else:
            self.distro.net_ops.link_up(self.interface, family="inet")
        if had_link:
            LOG.debug(
                "Not queueing link down: link [%s] was up prior before "
                "receiving a dhcp lease",
                self.interface,
            )
        else:
            self.cleanup_cmds.append(
                partial(
                    self.distro.net_ops.link_down,
                    self.interface,
                    family="inet",
                )
            )
        if had_ip:
            LOG.debug(
                "Not queueing address removal: address %s was assigned before "
                "receiving a dhcp lease",
                self.ip,
            )
        else:
            self.cleanup_cmds.append(
                partial(
                    self.distro.net_ops.del_addr, self.interface, self.cidr
                )
            )

def _bringup_static_routes(self):
        # static_routes = [("169.254.169.254/32", "130.56.248.255"),
        #                  ("0.0.0.0/0", "130.56.240.1")]
        for net_address, gateway in self.static_routes:
            # Use "append" rather than "add" since the DHCP server may provide
            # rfc3442 classless static routes with multiple routes to the same
            # subnet via different routers or local interface addresses.
            #
            # In this scenario, `ip r add` fails.
            #
            # RHBZ: #2003231
            self.distro.net_ops.append_route(
                self.interface, net_address, gateway
            )
            self.cleanup_cmds.insert(
                0,
                partial(
                    self.distro.net_ops.del_route,
                    self.interface,
                    net_address,
                    gateway=gateway,
                ),
            )

def _bringup_router(self):
        """Perform the ip commands to fully setup the router if needed."""
        # Check if a default route exists and exit if it does
        out = self.distro.net_ops.get_default_route()
        if "default" in out:
            LOG.debug(
                "Skip ephemeral route setup. %s already has default route: %s",
                self.interface,
                out.strip(),
            )
            return
        self.distro.net_ops.add_route(
            self.interface, self.router, source_address=self.ip
        )
        self.cleanup_cmds.insert(
            0,
            partial(
                self.distro.net_ops.del_route,
                self.interface,
                self.router,
                source_address=self.ip,
            ),
        )
        self.distro.net_ops.add_route(
            self.interface, "default", gateway=self.router
        )
        self.cleanup_cmds.insert(
            0,
            partial(self.distro.net_ops.del_route, self.interface, "default"),
        )

class EphemeralIPv6Network:
    """Context manager which sets up a ipv6 link local address

The linux kernel assigns link local addresses on link-up, which is
    sufficient for link-local communication.
    """

def __init__(self, distro, interface):
        """Setup context manager and validate call signature.

@param interface: Name of the network interface to bring up.
        @param ip: IP address to assign to the interface.
        @param prefix: IPv6 uses prefixes, not netmasks
        """
        if not interface:
            raise ValueError("Cannot init network on {0}".format(interface))

self.interface = interface
        self.distro = distro

def __enter__(self):
        """linux kernel does autoconfiguration even when autoconf=0

https://www.kernel.org/doc/html/latest/networking/ipv6.html
        """
        if net.read_sys_net(self.interface, "operstate") != "up":
            self.distro.net_ops.link_up(self.interface)

def __exit__(self, *_args):
        """No need to set the link to down state"""

class EphemeralDHCPv4:
    def __init__(
        self,
        distro,
        iface=None,
        connectivity_urls_data: Optional[List[Dict[str, Any]]] = None,
        dhcp_log_func=None,
    ):
        self.iface = iface
        self._ephipv4: Optional[EphemeralIPv4Network] = None
        self.lease: Optional[Dict[str, Any]] = None
        self.dhcp_log_func = dhcp_log_func
        self.connectivity_urls_data = connectivity_urls_data or []
        self.distro = distro
        self.interface_addrs_before_dhcp = netinfo.netdev_info()

def __enter__(self):
        """Setup sandboxed dhcp context, unless connectivity_url can already be
        reached."""
        if imds_reached_at_url := _check_connectivity_to_imds(
            self.connectivity_urls_data
        ):
            LOG.debug(
                "Skip ephemeral DHCP setup, instance has connectivity"
                " to %s",
                imds_reached_at_url,
            )
            return None
        # If we don't have connectivity, perform dhcp discovery
        return self.obtain_lease()

def __exit__(self, excp_type, excp_value, excp_traceback):
        """Teardown sandboxed dhcp context."""
        self.clean_network()

def clean_network(self):
        """Exit _ephipv4 context to teardown of ip configuration performed."""
        self.lease = None
        if self._ephipv4:
            self._ephipv4.__exit__(None, None, None)

def obtain_lease(self):
        """Perform dhcp discovery in a sandboxed environment if possible.

@return: A dict representing dhcp options on the most recent lease
            obtained from the dhclient discovery if run, otherwise an error
            is raised.

@raises: NoDHCPLeaseError if no leases could be obtained.
        """
        if self.lease:
            return self.lease
        self.lease = maybe_perform_dhcp_discovery(
            self.distro, self.iface, self.dhcp_log_func
        )
        if not self.lease:
            raise NoDHCPLeaseError()
        LOG.debug(
            "Received dhcp lease on %s for %s/%s",
            self.lease["interface"],
            self.lease["fixed-address"],
            self.lease["subnet-mask"],
        )
        nmap = {
            "interface": "interface",
            "ip": "fixed-address",
            "prefix_or_mask": "subnet-mask",
            "broadcast": "broadcast-address",
            "static_routes": [
                "rfc3442-classless-static-routes",
                "classless-static-routes",
                "static_routes",
                "unknown-121",
            ],
            "router": "routers",
        }
        kwargs = self.extract_dhcp_options_mapping(nmap)
        if not kwargs["broadcast"]:
            kwargs["broadcast"] = net.mask_and_ipv4_to_bcast_addr(
                kwargs["prefix_or_mask"], kwargs["ip"]
            )
        if kwargs["static_routes"]:
            kwargs["static_routes"] = (
                self.distro.dhcp_client.parse_static_routes(
                    kwargs["static_routes"]
                )
            )
        ephipv4 = EphemeralIPv4Network(
            self.distro,
            interface_addrs_before_dhcp=self.interface_addrs_before_dhcp,
            **kwargs,
        )
        ephipv4.__enter__()
        self._ephipv4 = ephipv4
        return self.lease

def extract_dhcp_options_mapping(self, nmap):
        result = {}
        for internal_reference, lease_option_names in nmap.items():
            if isinstance(lease_option_names, list):
                self.get_first_option_value(
                    internal_reference, lease_option_names, result
                )
            else:
                result[internal_reference] = self.lease.get(lease_option_names)
        return result

def get_first_option_value(
        self, internal_mapping, lease_option_names, result
    ):
        for different_names in lease_option_names:
            if not result.get(internal_mapping):
                result[internal_mapping] = self.lease.get(different_names)

class EphemeralIPNetwork:
    """Combined ephemeral context manager for IPv4 and IPv6

Either ipv4 or ipv6 ephemeral network may fail to initialize, but if either
    succeeds, then this context manager will not raise exception. This allows
    either ipv4 or ipv6 ephemeral network to succeed, but requires that error
    handling for networks unavailable be done within the context.
    """

def __init__(
        self,
        distro,
        interface,
        ipv6: bool = False,
        ipv4: bool = True,
        connectivity_urls_data: Optional[List[Dict[str, Any]]] = None,
    ):
        """
        Args:
            distro: The distro object
            interface: The interface to bring up
            ipv6: Whether to bring up an ipv6 network
            ipv4: Whether to bring up an ipv4 network
            connectivity_urls_data: List of url data to use for connectivity
                check before attempting to bring up ephemeral networks. If
                connectivity can be established to any of the urls, then the
                ephemeral network setup is skipped.
        """
        self.interface = interface
        self.ipv4 = ipv4
        self.ipv6 = ipv6
        self.stack = contextlib.ExitStack()
        self.state_msg: str = ""
        self.distro = distro
        self.connectivity_urls_data = connectivity_urls_data

def __enter__(self):
        if not self.ipv4 and not self.ipv6:
            # no ephemeral network requested, but this object still needs to
            # function as a context manager
            return self
        exceptions = []
        ephemeral_obtained = False

# short-circuit if we already have connectivity to IMDS
        if imds_url := _check_connectivity_to_imds(
            self.connectivity_urls_data
        ):
            LOG.debug(
                "We already have connectivity to IMDS at %s, skipping DHCP.",
                imds_url,
            )
            return self

# otherwise, attempt to bring up ephemeral network
        LOG.debug("No connectivity to IMDS, attempting DHCP setup.")

# first try to bring up ephemeral network for ipv4 (if enabled)
        # then try to bring up ephemeral network for ipv6 (if enabled)
        if self.ipv4:
            ipv4_ephemeral_obtained, ipv4_exception = (
                self._perform_ephemeral_network_setup(ip_version="ipv4")
            )
            ephemeral_obtained |= ipv4_ephemeral_obtained
            if ipv4_exception:
                exceptions.append(ipv4_exception)
        if self.ipv6:
            ipv6_ephemeral_obtained, ipv6_exception = (
                self._perform_ephemeral_network_setup(ip_version="ipv6")
            )
            ephemeral_obtained |= ipv6_ephemeral_obtained
            if ipv6_exception:
                exceptions.append(ipv6_exception)

# need to set this if we only have ipv6 ephemeral network
        if (self.ipv6 and ipv6_ephemeral_obtained) or not self.ipv4:
            self.state_msg = "using link-local ipv6"

if not ephemeral_obtained:
            # Ephemeral network setup failed in linkup for both ipv4 and
            # ipv6. Raise only the first exception found.
            LOG.error(
                "Failed to bring up EphemeralIPNetwork. "
                "Datasource setup cannot continue"
            )
            raise exceptions[0]
        return self

def _perform_ephemeral_network_setup(
        self,
        ip_version: Literal["ipv4", "ipv6"],
    ) -> Tuple[bool, Optional[Exception]]:
        """
        Attempt to bring up an ephemeral network for the specified IP version.

Args:
            ip_version (str): The IP version to bring up ("ipv4" or "ipv6").

Returns:
            Tuple: A tuple containing:
                - a boolean indicating whether an ephemeral network was
                    successfully obtained
                - an optional exception if ephemeral network setup failed
                    or None if successful
        """
        try:
            if ip_version == "ipv4":
                self.stack.enter_context(
                    EphemeralDHCPv4(
                        distro=self.distro,
                        iface=self.interface,
                    )
                )
            elif ip_version == "ipv6":
                self.stack.enter_context(
                    EphemeralIPv6Network(
                        self.distro,
                        self.interface,
                    )
                )
            else:
                raise ValueError(f"Unsupported IP version: {ip_version}")

LOG.debug(
                "Successfully brought up %s for ephemeral %s networking.",
                self.interface,
                ip_version,
            )
            return True, None
        except (ProcessExecutionError, NoDHCPLeaseError) as e:
            LOG.debug(
                "Failed to bring up %s for ephemeral %s networking.",
                self.interface,
                ip_version,
            )
            return False, e

def __exit__(self, *_args):
        self.stack.close()

def _check_connectivity_to_imds(
    connectivity_urls_data: List[Dict[str, Any]],
) -> Optional[str]:
    """
    Perform a connectivity check to the provided URLs to determine if the
    ephemeral network setup is necessary.

This function attempts to reach one of the provided URLs and returns the
    URL that was successfully reached. If none of the URLs can be reached,
    it returns None.

The timeout for the request is determined by the highest timeout value
    provided in the connectivity URLs data. If no timeout is provided, a
    default timeout of 5 seconds is used.

Args:
        connectivity_urls_data: A list of dictionaries, each containing
            the following keys:
            - "url" (str): The URL to check connectivity for.
            - "headers" (dict, optional): Headers to include in the request.
            - "timeout" (int, optional): Timeout for the request in seconds.

Returns:
        Optional[str]: The URL that was successfully reached, or None if no
        connectivity was established.
    """

def _headers_cb(url):
        """
        Helper function to get headers for a given URL from the connectivity
        URLs data provided to _check_connectivity_to_imds.
        """
        headers = [
            url_data.get("headers")
            for url_data in connectivity_urls_data
            if url_data["url"] == url
        ][0]
        return headers

if not connectivity_urls_data:
        LOG.debug(
            "No connectivity URLs provided. "
            "Skipping connectivity check before ephemeral network setup."
        )
        return None

# if the user has provided timeout, use the highest value provided
    timeout = (
        max(url_data.get("timeout", 0) for url_data in connectivity_urls_data)
        or 5
    )  # this *should* be sufficient if connectivity is actually available

try:
        url_that_worked, _ = wait_for_url(
            urls=[url_data["url"] for url_data in connectivity_urls_data],
            headers_cb=_headers_cb,  # get headers per URL
            timeout=timeout,
            connect_synchronously=False,  # use happy eyeballs
            max_wait=0,  # only try once
        )

# wait_for_url will raise a UrlError if:
    # - request fails
    # - response is empty
    # - response is not OK
    # which is exactly what we want to catch here since if any of these
    # conditions are met, we don't have connectivity to IMDS
    except UrlError as e:
        LOG.debug(
            "Failed to reach IMDS without ephemeral network setup: %s",
            e,
        )
    else:
        # if an error occurs inside wait_for_url that does not result in a
        # UrlError, it won't raise an exception, so we need to check if
        # url_that_worked is None to determine if we have connectivity
        if not url_that_worked:
            LOG.debug("Failed to reach IMDS without ephemeral network setup.")
            return None

return url_that_worked
    return None