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# Channel Management
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Channel management provides client-side connection handling with support for secure and insecure connections, connectivity monitoring, interceptor chains, and comprehensive configuration options for production deployments.
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## Capabilities
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### Channel Creation
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Creates channels for client-side RPC communication with support for insecure and secure connections, including SSL/TLS, ALTS, and custom credentials.
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```python { .api }
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def insecure_channel(target: str, options=None, compression=None) -> Channel:
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    """
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    Creates an insecure Channel to a server.
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    Parameters:
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    - target: The server address (e.g., 'localhost:50051', 'dns:///example.com:443')
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    - options: Optional list of key-value pairs for channel configuration
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    - compression: Optional compression method (grpc.compression.Gzip, etc.)
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    Returns:
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    Channel: A thread-safe Channel object for making RPCs
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    """
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def secure_channel(target: str, credentials: ChannelCredentials, options=None, compression=None) -> Channel:
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    """
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    Creates a secure Channel to a server.
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    Parameters:
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    - target: The server address
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    - credentials: A ChannelCredentials instance for authentication
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    - options: Optional list of key-value pairs for channel configuration
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    - compression: Optional compression method
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    Returns:
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    Channel: A thread-safe secure Channel object
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    Raises:
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    ValueError: If called with insecure credentials
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    """
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```
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**Usage Examples:**
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```python
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# Basic insecure channel
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channel = grpc.insecure_channel('localhost:50051')
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# Secure channel with SSL
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credentials = grpc.ssl_channel_credentials()
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secure_chan = grpc.secure_channel('secure-server.com:443', credentials)
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# Channel with custom options
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options = [
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    ('grpc.keepalive_time_ms', 30000),
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    ('grpc.max_receive_message_length', 4 * 1024 * 1024),
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]
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channel = grpc.insecure_channel('localhost:50051', options=options)
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# Channel with compression
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channel = grpc.insecure_channel('localhost:50051', compression=grpc.compression.Gzip)
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```
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### Channel Interception
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Applies interceptor chains to channels for cross-cutting concerns like logging, metrics, authentication, and request/response transformation.
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```python { .api }
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def intercept_channel(channel: Channel, *interceptors) -> Channel:
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    """
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    Intercepts a channel through a set of interceptors.
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    Parameters:
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    - channel: A Channel object to intercept
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    - interceptors: Zero or more interceptor objects
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    Returns:
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    Channel: A Channel that applies interceptors to each invocation
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    Raises:
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    TypeError: If interceptor doesn't implement required interfaces
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    """
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```
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**Usage Example:**
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```python
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class LoggingInterceptor(grpc.UnaryUnaryClientInterceptor):
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    def intercept_unary_unary(self, continuation, client_call_details, request):
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        print(f"Calling {client_call_details.method}")
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        response = continuation(client_call_details, request)
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        print(f"Received response")
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        return response
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# Apply interceptor to channel
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channel = grpc.insecure_channel('localhost:50051')
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intercepted_channel = grpc.intercept_channel(channel, LoggingInterceptor())
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```
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### Channel Readiness
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Monitors channel connectivity state and provides futures for readiness notification, useful for connection pooling and health checking.
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```python { .api }
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def channel_ready_future(channel: Channel) -> Future:
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    """
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    Creates a Future that tracks when a Channel is ready.
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    Parameters:
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    - channel: A Channel object to monitor
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    Returns:
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    Future: A Future that completes when channel reaches READY state
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    Note:
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    Cancelling the Future does not affect the channel's state machine
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    """
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```
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**Usage Example:**
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```python
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channel = grpc.insecure_channel('localhost:50051')
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ready_future = grpc.channel_ready_future(channel)
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# Wait for channel to be ready (blocking)
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try:
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    ready_future.result(timeout=5.0)
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    print("Channel is ready")
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except grpc.FutureTimeoutError:
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    print("Channel not ready within timeout")
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```
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### Channel Interface
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Core channel interface providing RPC invocation methods and connectivity management.
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```python { .api }
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class Channel(abc.ABC):
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    """
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    Affords RPC invocation via generic methods on client-side.
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    Supports context manager protocol for automatic cleanup.
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    """
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    def subscribe(self, callback, try_to_connect=False):
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        """
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        Subscribe to this Channel's connectivity state machine.
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        Parameters:
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        - callback: Callable invoked with ChannelConnectivity argument
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        - try_to_connect: Whether channel should attempt immediate connection
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        """
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    def unsubscribe(self, callback):
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        """
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        Unsubscribes a callback from connectivity notifications.
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        Parameters:
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        - callback: Previously registered callback function
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        """
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    def unary_unary(self, method: str, request_serializer=None, response_deserializer=None, _registered_method=False) -> UnaryUnaryMultiCallable:
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        """
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        Creates a UnaryUnaryMultiCallable for a unary-unary method.
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        Parameters:
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        - method: The name of the RPC method (e.g., '/service.Method')
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        - request_serializer: Optional serializer for request messages
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        - response_deserializer: Optional deserializer for response messages
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        - _registered_method: Internal parameter for registered methods
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        Returns:
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        UnaryUnaryMultiCallable: Object for making unary-unary calls
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        """
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    def unary_stream(self, method: str, request_serializer=None, response_deserializer=None, _registered_method=False) -> UnaryStreamMultiCallable:
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        """Creates a UnaryStreamMultiCallable for a unary-stream method."""
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    def stream_unary(self, method: str, request_serializer=None, response_deserializer=None, _registered_method=False) -> StreamUnaryMultiCallable:
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        """Creates a StreamUnaryMultiCallable for a stream-unary method."""
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    def stream_stream(self, method: str, request_serializer=None, response_deserializer=None, _registered_method=False) -> StreamStreamMultiCallable:
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        """Creates a StreamStreamMultiCallable for a stream-stream method."""
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    def close(self):
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        """
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        Closes this Channel and releases all resources.
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        Terminates all active RPCs and prevents new ones.
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        This method is idempotent.
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        """
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    def __enter__(self):
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        """Enters the runtime context for context manager usage."""
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    def __exit__(self, exc_type, exc_val, exc_tb):
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        """Exits the runtime context and closes the channel."""
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```
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**Usage Examples:**
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```python
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# Context manager usage (recommended)
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with grpc.insecure_channel('localhost:50051') as channel:
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    stub = MyServiceStub(channel)
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    response = stub.MyMethod(request)
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    # Channel automatically closed
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# Manual lifecycle management
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channel = grpc.insecure_channel('localhost:50051')
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try:
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    stub = MyServiceStub(channel)
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    response = stub.MyMethod(request)
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finally:
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    channel.close()
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# Connectivity monitoring
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def connectivity_callback(connectivity):
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    print(f"Channel state: {connectivity}")
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channel = grpc.insecure_channel('localhost:50051')
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channel.subscribe(connectivity_callback, try_to_connect=True)
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```
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### Channel Options
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Common channel configuration options for production deployments:
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```python
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# Keepalive settings
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('grpc.keepalive_time_ms', 30000),
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('grpc.keepalive_timeout_ms', 5000),
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('grpc.keepalive_permit_without_calls', True),
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# Message size limits
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('grpc.max_send_message_length', 4 * 1024 * 1024),
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('grpc.max_receive_message_length', 4 * 1024 * 1024),
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# Connection settings
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('grpc.max_connection_idle_ms', 300000),
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('grpc.max_connection_age_ms', 600000),
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('grpc.http2.max_pings_without_data', 0),
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# Load balancing
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('grpc.lb_policy_name', 'round_robin'),
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('grpc.service_config', '{"loadBalancingConfig": [{"round_robin":{}}]}'),
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```
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## Types
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```python { .api }
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class ChannelConnectivity(enum.Enum):
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    """Channel connectivity states."""
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    IDLE = ...  # Channel is idle
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    CONNECTING = ...  # Channel is connecting
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    READY = ...  # Channel is ready to conduct RPCs
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    TRANSIENT_FAILURE = ...  # Channel has seen a recoverable failure
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    SHUTDOWN = ...  # Channel has seen an unrecoverable failure
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```