# Copyright 2025 Flower Labs GmbH. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Flower client app."""
import time
from contextlib import AbstractContextManager
from logging import ERROR, INFO, WARN
from pathlib import Path
from typing import Callable, Optional, Union
from cryptography.hazmat.primitives.asymmetric import ec
from grpc import RpcError
from flwr.app.error import Error
from flwr.cli.config_utils import get_fab_metadata
from flwr.cli.install import install_from_fab
from flwr.client.client import Client
from flwr.client.client_app import ClientApp, LoadClientAppError
from flwr.client.grpc_adapter_client.connection import grpc_adapter
from flwr.client.grpc_rere_client.connection import grpc_request_response
from flwr.client.message_handler.message_handler import handle_control_message
from flwr.client.numpy_client import NumPyClient
from flwr.client.run_info_store import DeprecatedRunInfoStore
from flwr.client.typing import ClientFnExt
from flwr.common import GRPC_MAX_MESSAGE_LENGTH, Context, EventType, Message, event
from flwr.common.address import parse_address
from flwr.common.constant import (
MAX_RETRY_DELAY,
TRANSPORT_TYPE_GRPC_ADAPTER,
TRANSPORT_TYPE_GRPC_BIDI,
TRANSPORT_TYPE_GRPC_RERE,
TRANSPORT_TYPE_REST,
TRANSPORT_TYPES,
ErrorCode,
)
from flwr.common.exit import ExitCode, flwr_exit
from flwr.common.logger import log, warn_deprecated_feature
from flwr.common.retry_invoker import RetryInvoker, RetryState, exponential
from flwr.common.typing import Fab, Run, RunNotRunningException, UserConfig
from flwr.compat.client.grpc_client.connection import grpc_connection
from flwr.supernode.nodestate import NodeStateFactory
def _check_actionable_client(
client: Optional[Client], client_fn: Optional[ClientFnExt]
) -> None:
if client_fn is None and client is None:
raise ValueError(
"Both `client_fn` and `client` are `None`, but one is required"
)
if client_fn is not None and client is not None:
raise ValueError(
"Both `client_fn` and `client` are provided, but only one is allowed"
)
# pylint: disable=import-outside-toplevel
# pylint: disable=too-many-branches
# pylint: disable=too-many-locals
# pylint: disable=too-many-statements
# pylint: disable=too-many-arguments
[docs]
def start_client(
*,
server_address: str,
client_fn: Optional[ClientFnExt] = None,
client: Optional[Client] = None,
grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,
root_certificates: Optional[Union[bytes, str]] = None,
insecure: Optional[bool] = None,
transport: Optional[str] = None,
authentication_keys: Optional[
tuple[ec.EllipticCurvePrivateKey, ec.EllipticCurvePublicKey]
] = None,
max_retries: Optional[int] = None,
max_wait_time: Optional[float] = None,
) -> None:
"""Start a Flower client node which connects to a Flower server.
Warning
-------
This function is deprecated since 1.13.0. Use :code:`flower-supernode` command
instead to start a SuperNode.
Parameters
----------
server_address : str
The IPv4 or IPv6 address of the server. If the Flower
server runs on the same machine on port 8080, then `server_address`
would be `"[::]:8080"`.
client_fn : Optional[ClientFnExt]
A callable that instantiates a Client. (default: None)
client : Optional[flwr.client.Client]
An implementation of the abstract base
class `flwr.client.Client` (default: None)
grpc_max_message_length : int (default: 536_870_912, this equals 512MB)
The maximum length of gRPC messages that can be exchanged with the
Flower server. The default should be sufficient for most models.
Users who train very large models might need to increase this
value. Note that the Flower server needs to be started with the
same value (see `flwr.server.start_server`), otherwise it will not
know about the increased limit and block larger messages.
root_certificates : Optional[Union[bytes, str]] (default: None)
The PEM-encoded root certificates as a byte string or a path string.
If provided, a secure connection using the certificates will be
established to an SSL-enabled Flower server.
insecure : bool (default: True)
Starts an insecure gRPC connection when True. Enables HTTPS connection
when False, using system certificates if `root_certificates` is None.
transport : Optional[str] (default: None)
Configure the transport layer. Allowed values:
- 'grpc-bidi': gRPC, bidirectional streaming
- 'grpc-rere': gRPC, request-response (experimental)
- 'rest': HTTP (experimental)
authentication_keys : Optional[Tuple[PrivateKey, PublicKey]] (default: None)
Tuple containing the elliptic curve private key and public key for
authentication from the cryptography library.
Source: https://cryptography.io/en/latest/hazmat/primitives/asymmetric/ec/
Used to establish an authenticated connection with the server.
max_retries: Optional[int] (default: None)
The maximum number of times the client will try to connect to the
server before giving up in case of a connection error. If set to None,
there is no limit to the number of tries.
max_wait_time: Optional[float] (default: None)
The maximum duration before the client stops trying to
connect to the server in case of connection error.
If set to None, there is no limit to the total time.
Examples
--------
Starting a gRPC client with an insecure server connection::
start_client(
server_address=localhost:8080,
client_fn=client_fn,
)
Starting a TLS-enabled gRPC client using system certificates::
def client_fn(context: Context):
return FlowerClient().to_client()
start_client(
server_address=localhost:8080,
client_fn=client_fn,
insecure=False,
)
Starting a TLS-enabled gRPC client using provided certificates::
from pathlib import Path
start_client(
server_address=localhost:8080,
client_fn=client_fn,
root_certificates=Path("/crts/root.pem").read_bytes(),
)
"""
msg = (
"flwr.client.start_client() is deprecated."
"\n\tInstead, use the `flower-supernode` CLI command to start a SuperNode "
"as shown below:"
"\n\n\t\t$ flower-supernode --insecure --superlink='<IP>:<PORT>'"
"\n\n\tTo view all available options, run:"
"\n\n\t\t$ flower-supernode --help"
"\n\n\tUsing `start_client()` is deprecated."
)
warn_deprecated_feature(name=msg)
event(EventType.START_CLIENT_ENTER)
start_client_internal(
server_address=server_address,
node_config={},
load_client_app_fn=None,
client_fn=client_fn,
client=client,
grpc_max_message_length=grpc_max_message_length,
root_certificates=root_certificates,
insecure=insecure,
transport=transport,
authentication_keys=authentication_keys,
max_retries=max_retries,
max_wait_time=max_wait_time,
)
event(EventType.START_CLIENT_LEAVE)
# pylint: disable=import-outside-toplevel
# pylint: disable=too-many-branches
# pylint: disable=too-many-locals
# pylint: disable=too-many-statements
def start_client_internal(
*,
server_address: str,
node_config: UserConfig,
load_client_app_fn: Optional[Callable[[str, str, str], ClientApp]] = None,
client_fn: Optional[ClientFnExt] = None,
client: Optional[Client] = None,
grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,
root_certificates: Optional[Union[bytes, str]] = None,
insecure: Optional[bool] = None,
transport: Optional[str] = None,
authentication_keys: Optional[
tuple[ec.EllipticCurvePrivateKey, ec.EllipticCurvePublicKey]
] = None,
max_retries: Optional[int] = None,
max_wait_time: Optional[float] = None,
flwr_path: Optional[Path] = None,
) -> None:
"""Start a Flower client node which connects to a Flower server.
Parameters
----------
server_address : str
The IPv4 or IPv6 address of the server. If the Flower
server runs on the same machine on port 8080, then `server_address`
would be `"[::]:8080"`.
node_config: UserConfig
The configuration of the node.
load_client_app_fn : Optional[Callable[[], ClientApp]] (default: None)
A function that can be used to load a `ClientApp` instance.
client_fn : Optional[ClientFnExt]
A callable that instantiates a Client. (default: None)
client : Optional[flwr.client.Client]
An implementation of the abstract base
class `flwr.client.Client` (default: None)
grpc_max_message_length : int (default: 536_870_912, this equals 512MB)
The maximum length of gRPC messages that can be exchanged with the
Flower server. The default should be sufficient for most models.
Users who train very large models might need to increase this
value. Note that the Flower server needs to be started with the
same value (see `flwr.server.start_server`), otherwise it will not
know about the increased limit and block larger messages.
root_certificates : Optional[Union[bytes, str]] (default: None)
The PEM-encoded root certificates as a byte string or a path string.
If provided, a secure connection using the certificates will be
established to an SSL-enabled Flower server.
insecure : Optional[bool] (default: None)
Starts an insecure gRPC connection when True. Enables HTTPS connection
when False, using system certificates if `root_certificates` is None.
transport : Optional[str] (default: None)
Configure the transport layer. Allowed values:
- 'grpc-bidi': gRPC, bidirectional streaming
- 'grpc-rere': gRPC, request-response (experimental)
- 'rest': HTTP (experimental)
authentication_keys : Optional[Tuple[PrivateKey, PublicKey]] (default: None)
Tuple containing the elliptic curve private key and public key for
authentication from the cryptography library.
Source: https://cryptography.io/en/latest/hazmat/primitives/asymmetric/ec/
Used to establish an authenticated connection with the server.
max_retries: Optional[int] (default: None)
The maximum number of times the client will try to connect to the
server before giving up in case of a connection error. If set to None,
there is no limit to the number of tries.
max_wait_time: Optional[float] (default: None)
The maximum duration before the client stops trying to
connect to the server in case of connection error.
If set to None, there is no limit to the total time.
flwr_path: Optional[Path] (default: None)
The fully resolved path containing installed Flower Apps.
"""
if insecure is None:
insecure = root_certificates is None
if load_client_app_fn is None:
_check_actionable_client(client, client_fn)
if client_fn is None:
# Wrap `Client` instance in `client_fn`
def single_client_factory(
context: Context, # pylint: disable=unused-argument
) -> Client:
if client is None: # Added this to keep mypy happy
raise ValueError(
"Both `client_fn` and `client` are `None`, but one is required"
)
return client # Always return the same instance
client_fn = single_client_factory
def _load_client_app(_1: str, _2: str, _3: str) -> ClientApp:
return ClientApp(client_fn=client_fn)
load_client_app_fn = _load_client_app
# At this point, only `load_client_app_fn` should be used
# Both `client` and `client_fn` must not be used directly
# Initialize connection context manager
connection, address, connection_error_type = _init_connection(
transport, server_address
)
def _on_sucess(retry_state: RetryState) -> None:
if retry_state.tries > 1:
log(
INFO,
"Connection successful after %.2f seconds and %s tries.",
retry_state.elapsed_time,
retry_state.tries,
)
def _on_backoff(retry_state: RetryState) -> None:
if retry_state.tries == 1:
log(WARN, "Connection attempt failed, retrying...")
else:
log(
WARN,
"Connection attempt failed, retrying in %.2f seconds",
retry_state.actual_wait,
)
retry_invoker = RetryInvoker(
wait_gen_factory=lambda: exponential(max_delay=MAX_RETRY_DELAY),
recoverable_exceptions=connection_error_type,
max_tries=max_retries + 1 if max_retries is not None else None,
max_time=max_wait_time,
on_giveup=lambda retry_state: (
log(
WARN,
"Giving up reconnection after %.2f seconds and %s tries.",
retry_state.elapsed_time,
retry_state.tries,
)
if retry_state.tries > 1
else None
),
on_success=_on_sucess,
on_backoff=_on_backoff,
)
# DeprecatedRunInfoStore gets initialized when the first connection is established
run_info_store: Optional[DeprecatedRunInfoStore] = None
state_factory = NodeStateFactory()
state = state_factory.state()
runs: dict[int, Run] = {}
while True:
sleep_duration: int = 0
with connection(
address,
insecure,
retry_invoker,
grpc_max_message_length,
root_certificates,
authentication_keys,
) as conn:
receive, send, create_node, delete_node, get_run, get_fab = conn
# Register node when connecting the first time
if run_info_store is None:
if create_node is None:
if transport not in ["grpc-bidi", None]:
raise NotImplementedError(
"All transports except `grpc-bidi` require "
"an implementation for `create_node()`.'"
)
# gRPC-bidi doesn't have the concept of node_id,
# so we set it to -1
run_info_store = DeprecatedRunInfoStore(
node_id=-1,
node_config={},
)
else:
# Call create_node fn to register node
# and store node_id in state
if (node_id := create_node()) is None:
raise ValueError(
"Failed to register SuperNode with the SuperLink"
)
state.set_node_id(node_id)
run_info_store = DeprecatedRunInfoStore(
node_id=state.get_node_id(),
node_config=node_config,
)
# pylint: disable=too-many-nested-blocks
while True:
try:
# Receive
message = receive()
if message is None:
time.sleep(3) # Wait for 3s before asking again
continue
log(INFO, "")
if len(message.metadata.group_id) > 0:
log(
INFO,
"[RUN %s, ROUND %s]",
message.metadata.run_id,
message.metadata.group_id,
)
log(
INFO,
"Received: %s message %s",
message.metadata.message_type,
message.metadata.message_id,
)
# Handle control message
out_message, sleep_duration = handle_control_message(message)
if out_message:
send(out_message)
break
# Get run info
run_id = message.metadata.run_id
if run_id not in runs:
if get_run is not None:
runs[run_id] = get_run(run_id)
# If get_run is None, i.e., in grpc-bidi mode
else:
runs[run_id] = Run.create_empty(run_id=run_id)
run: Run = runs[run_id]
if get_fab is not None and run.fab_hash:
fab = get_fab(run.fab_hash, run_id)
# If `ClientApp` runs in the same process, install the FAB
install_from_fab(fab.content, flwr_path, True)
fab_id, fab_version = get_fab_metadata(fab.content)
else:
fab = None
fab_id, fab_version = run.fab_id, run.fab_version
run.fab_id, run.fab_version = fab_id, fab_version
# Register context for this run
run_info_store.register_context(
run_id=run_id,
run=run,
flwr_path=flwr_path,
fab=fab,
)
# Retrieve context for this run
context = run_info_store.retrieve_context(run_id=run_id)
# Create an error reply message that will never be used to prevent
# the used-before-assignment linting error
reply_message = Message(
Error(code=ErrorCode.UNKNOWN, reason="Unknown"),
reply_to=message,
)
# Handle app loading and task message
try:
# Load ClientApp instance
client_app: ClientApp = load_client_app_fn(
fab_id, fab_version, run.fab_hash
)
# Execute ClientApp
reply_message = client_app(message=message, context=context)
except Exception as ex: # pylint: disable=broad-exception-caught
# Legacy grpc-bidi
if transport in ["grpc-bidi", None]:
log(ERROR, "Client raised an exception.", exc_info=ex)
# Raise exception, crash process
raise ex
# Don't update/change DeprecatedRunInfoStore
e_code = ErrorCode.CLIENT_APP_RAISED_EXCEPTION
# Ex fmt: "<class 'ZeroDivisionError'>:<'division by zero'>"
reason = str(type(ex)) + ":<'" + str(ex) + "'>"
exc_entity = "ClientApp"
if isinstance(ex, LoadClientAppError):
reason = (
"An exception was raised when attempting to load "
"`ClientApp`"
)
e_code = ErrorCode.LOAD_CLIENT_APP_EXCEPTION
exc_entity = "SuperNode"
log(ERROR, "%s raised an exception", exc_entity, exc_info=ex)
# Create error message
reply_message = Message(
Error(code=e_code, reason=reason),
reply_to=message,
)
else:
# No exception, update node state
run_info_store.update_context(
run_id=run_id,
context=context,
)
# Send
send(reply_message)
log(INFO, "Sent reply")
except RunNotRunningException:
log(INFO, "")
log(
INFO,
"SuperNode aborted sending the reply message. "
"Run ID %s is not in `RUNNING` status.",
run_id,
)
log(INFO, "")
# pylint: enable=too-many-nested-blocks
# Unregister node
if delete_node is not None:
delete_node() # pylint: disable=not-callable
if sleep_duration == 0:
log(INFO, "Disconnect and shut down")
break
# Sleep and reconnect afterwards
log(
INFO,
"Disconnect, then re-establish connection after %s second(s)",
sleep_duration,
)
time.sleep(sleep_duration)
[docs]
def start_numpy_client(
*,
server_address: str,
client: NumPyClient,
grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,
root_certificates: Optional[bytes] = None,
insecure: Optional[bool] = None,
transport: Optional[str] = None,
) -> None:
"""Start a Flower NumPyClient which connects to a gRPC server.
Warning
-------
This function is deprecated since 1.7.0. Use :code:`flwr.client.start_client`
instead and first convert your :code:`NumPyClient` to type
:code:`flwr.client.Client` by executing its :code:`to_client()` method.
Parameters
----------
server_address : str
The IPv4 or IPv6 address of the server. If the Flower server runs on
the same machine on port 8080, then `server_address` would be
`"[::]:8080"`.
client : flwr.client.NumPyClient
An implementation of the abstract base class `flwr.client.NumPyClient`.
grpc_max_message_length : int (default: 536_870_912, this equals 512MB)
The maximum length of gRPC messages that can be exchanged with the
Flower server. The default should be sufficient for most models.
Users who train very large models might need to increase this
value. Note that the Flower server needs to be started with the
same value (see `flwr.server.start_server`), otherwise it will not
know about the increased limit and block larger messages.
root_certificates : bytes (default: None)
The PEM-encoded root certificates as a byte string or a path string.
If provided, a secure connection using the certificates will be
established to an SSL-enabled Flower server.
insecure : Optional[bool] (default: None)
Starts an insecure gRPC connection when True. Enables HTTPS connection
when False, using system certificates if `root_certificates` is None.
transport : Optional[str] (default: None)
Configure the transport layer. Allowed values:
- 'grpc-bidi': gRPC, bidirectional streaming
- 'grpc-rere': gRPC, request-response (experimental)
- 'rest': HTTP (experimental)
Examples
--------
Starting a gRPC client with an insecure server connection::
start_numpy_client(
server_address=localhost:8080,
client=FlowerClient(),
)
Starting a TLS-enabled gRPC client using system certificates::
start_numpy_client(
server_address=localhost:8080,
client=FlowerClient(),
insecure=False,
)
Starting a TLS-enabled gRPC client using provided certificates::
from pathlib import Path
start_numpy_client(
server_address=localhost:8080,
client=FlowerClient(),
root_certificates=Path("/crts/root.pem").read_bytes(),
)
"""
mssg = (
"flwr.client.start_numpy_client() is deprecated. \n\tInstead, use "
"`flwr.client.start_client()` by ensuring you first call "
"the `.to_client()` method as shown below: \n"
"\tflwr.client.start_client(\n"
"\t\tserver_address='<IP>:<PORT>',\n"
"\t\tclient=FlowerClient().to_client(),"
" # <-- where FlowerClient is of type flwr.client.NumPyClient object\n"
"\t)\n"
"\tUsing `start_numpy_client()` is deprecated."
)
warn_deprecated_feature(name=mssg)
# Calling this function is deprecated. A warning is thrown.
# We first need to convert the supplied client to `Client.`
wrp_client = client.to_client()
start_client(
server_address=server_address,
client=wrp_client,
grpc_max_message_length=grpc_max_message_length,
root_certificates=root_certificates,
insecure=insecure,
transport=transport,
)
def _init_connection(transport: Optional[str], server_address: str) -> tuple[
Callable[
[
str,
bool,
RetryInvoker,
int,
Union[bytes, str, None],
Optional[tuple[ec.EllipticCurvePrivateKey, ec.EllipticCurvePublicKey]],
],
AbstractContextManager[
tuple[
Callable[[], Optional[Message]],
Callable[[Message], None],
Optional[Callable[[], Optional[int]]],
Optional[Callable[[], None]],
Optional[Callable[[int], Run]],
Optional[Callable[[str, int], Fab]],
]
],
],
str,
type[Exception],
]:
# Parse IP address
parsed_address = parse_address(server_address)
if not parsed_address:
flwr_exit(
ExitCode.COMMON_ADDRESS_INVALID,
f"SuperLink address ({server_address}) cannot be parsed.",
)
host, port, is_v6 = parsed_address
address = f"[{host}]:{port}" if is_v6 else f"{host}:{port}"
# Set the default transport layer
if transport is None:
transport = TRANSPORT_TYPE_GRPC_BIDI
# Use either gRPC bidirectional streaming or REST request/response
if transport == TRANSPORT_TYPE_REST:
try:
from requests.exceptions import ConnectionError as RequestsConnectionError
from flwr.client.rest_client.connection import http_request_response
except ModuleNotFoundError:
flwr_exit(ExitCode.COMMON_MISSING_EXTRA_REST)
if server_address[:4] != "http":
flwr_exit(ExitCode.SUPERNODE_REST_ADDRESS_INVALID)
connection, error_type = http_request_response, RequestsConnectionError
elif transport == TRANSPORT_TYPE_GRPC_RERE:
connection, error_type = grpc_request_response, RpcError
elif transport == TRANSPORT_TYPE_GRPC_ADAPTER:
connection, error_type = grpc_adapter, RpcError
elif transport == TRANSPORT_TYPE_GRPC_BIDI:
connection, error_type = grpc_connection, RpcError # type: ignore[assignment]
else:
raise ValueError(
f"Unknown transport type: {transport} (possible: {TRANSPORT_TYPES})"
)
return connection, address, error_type