Value Downlink

A ValueDownlink synchronizes a shared real-time value with a remote value lane. In addition to the standard Downlink callbacks, ValueDownlink supports registering a did_set callback to observe changes to downlinked state — whether remote or local.

Create a ValueDownlink with a SwimClient’s downlink_value method.

Use the get method to get the current state value, and the set method to set the current state value. For the most part, client code can treat a ValueDownlink like an ordinary mutable variable; the Swim client will ensure that the downlink is continuously made consistent with the remote lane.

from swimos import SwimClient

with SwimClient() as swim_client:
    host_uri = 'warp://example.com'
    node_uri = '/hotel/room/123'
    lane_uri = 'light'

    value_downlink = swim_client.downlink_value()
    value_downlink.set_host_uri(host_uri)
    value_downlink.set_node_uri(node_uri)
    value_downlink.set_lane_uri(lane_uri)

    value_downlink.open()

    value_downlink.get()  # get the current local state of the downlink
    value_downlink.set(True)  # update the local and remote state of the downlink

Using did_set callbacks, applications can update dependent components to keep them consistent with the shared state of the remote value lane in network real-time. The did_set callback can be defined as shown below.

from swimos import SwimClient


async def custom_did_set(new_value, old_value):
    print(f'Link watched info change TO {new_value} from {old_value}')


with SwimClient() as swim_client:
    host_uri = 'warp://example.com'
    node_uri = '/hotel/room/123'
    lane_uri = 'light'

    value_downlink = swim_client.downlink_value()
    value_downlink.set_host_uri(host_uri)
    value_downlink.set_node_uri(node_uri)
    value_downlink.set_lane_uri(lane_uri)

    value_downlink.did_set(custom_did_set)

    value_downlink.open()
Downlinks
Map Downlink