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Contents

namespaceInter-App Communication3 functions

datumhue.messaging

Topic-based publish/subscribe between apps; a message's scope decides which apps it reaches.

Returns handles
Subscription, Presence

Functions 3

datumhue.messaging.publish

function
datumhue.messaging.publish(opts: messaging.PublishOptions)

Publish payload on topic to every subscriber in scope. Requires the network capability when scope is "network". Raises for a payload that holds a table inside itself, nests tables more than 127 deep, or is larger than the memory the app has left.

Example
datumhue.messaging.publish({
    topic = "scores",
    payload = { player = "Ada", best = 42 },
})

opts messaging.PublishOptions options 4 keys, 3 inherited

KeyTypeDefaultDescription
payload requiredanyno defaultMessage payload; each subscriber receives its own copy of it, in which a table the payload holds twice is two tables.
From messaging.MessageOptions
topic requiredstringno defaultTopic to publish or subscribe on. A network topic is kept within this app's @scope and where its package came from, unless shared is set.
scope"local" | "network""local"Which apps the message reaches.
sharedbooleanfalseUse the network topic of this name that every app setting shared uses, whatever its @scope and wherever its package came from. Network scope only: a local topic reaches every app on this workstation either way.

In the guide: Messages, events and shared state

datumhue.messaging.subscribe

function
datumhue.messaging.subscribe(opts: messaging.SubscribeOptions) -> Subscription

Subscribe callback to topic in scope. Returns a subscription; call :unsubscribe() to stop it. Requires the network capability when scope is "network".

Example
local sub = datumhue.messaging.subscribe({
    topic = "scores",
    callback = function(msg)
        print(msg.payload.best) --> 42
    end,
})
-- A publisher never hears itself, so another app sends.
local send = [[
local msg = { topic = "scores", payload = { best = 42 } }
datumhue.messaging.publish(msg)
]]
datumhue.app.spawn({ name = "sender", service = true, code = send })

opts messaging.SubscribeOptions options 4 keys, 3 inherited

KeyTypeDefaultDescription
callback requiredfunctionno defaultCalled with each message received, as a table whose payload is the published value. A message published with local scope also holds sender, the publishing app (nil once it has ended), type, the topic, id, unique on this workstation, and timestamp, in seconds since the workstation started. One published with network scope holds topic instead.
From messaging.MessageOptions
topic requiredstringno defaultTopic to publish or subscribe on. A network topic is kept within this app's @scope and where its package came from, unless shared is set.
scope"local" | "network""local"Which apps the message reaches.
sharedbooleanfalseUse the network topic of this name that every app setting shared uses, whatever its @scope and wherever its package came from. Network scope only: a local topic reaches every app on this workstation either way.

In the guide: Messages, events and shared state How your app runs

datumhue.messaging.presence

functionneeds network
datumhue.messaging.presence(topic: string, opts?: messaging.PresenceOptions) -> Presence

Join a presence group on a topic. Handles on the same topic in the apps of this app's @scope whose packages came from the same place (one registry or a folder) see each other's beacons; an app under another @scope, or a copy of this one that came another way, joins a different group under the same name, and with shared every app that also sets it joins one. A member disappears from peers() when its beacons stop for ttl seconds. Beacons carry a per-handle id, not an identity — they prove liveness only.

Example
local lobby = datumhue.messaging.presence("lobby", { ttl = 5 })
lobby:publish({ name = "Ada" })

opts messaging.PresenceOptions options 3 keys

KeyTypeDefaultDescription
ttlnumber10Seconds a member stays listed after its last beacon.
maxinteger64Member cap, at most 1024; past it the least recently seen member is evicted.
sharedbooleanfalseJoin the group of this name that every app setting shared joins, whatever its @scope and wherever its package came from, instead of one kept within this app's @scope.

In the guide: Messages, events and shared state

Types 2

messaging.MessageOptions

options

options 3 keys

KeyTypeDefaultDescription
topic requiredstringno defaultTopic to publish or subscribe on. A network topic is kept within this app's @scope and where its package came from, unless shared is set.
scope"local" | "network""local"Which apps the message reaches.
sharedbooleanfalseUse the network topic of this name that every app setting shared uses, whatever its @scope and wherever its package came from. Network scope only: a local topic reaches every app on this workstation either way.

Extended by: messaging.PublishOptions, messaging.SubscribeOptions

messaging.Scope

enum
ValueDescription
"local"Reaches the apps on this workstation.
"network"Reaches the apps of this app's @scope whose packages came from the same place (one registry or a folder), on this workstation and on the others connected to the same deployment. An app under another @scope, or a copy of this one that came another way, reaches a different topic under the same name; with shared, every app that also sets it reaches one topic.

Nested in: messaging.MessageOptions

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