imports.md

World imports

• Imports:
  • interface wasi:messaging/[email protected]
  • interface wasi:messaging/[email protected]
  • interface wasi:messaging/[email protected]

Import interface wasi:messaging/[email protected]

---

Types

resource client

A connection to a message-exchange service (e.g., buffer, broker, etc.).

resource error

TODO(danbugs): This should be eventually extracted as an underlying type for other wasi-cloud-core interfaces.

type channel

string

There are two types of channels: - publish-subscribe channel, which is a broadcast channel, and - point-to-point channel, which is a unicast channel.

The interface doesn't highlight this difference in the type itself as that's uniquely a consumer issue.

record guest-configuration

Configuration includes a required list of channels the guest is subscribing to, and an optional list of extensions key-value pairs (e.g., partitions/offsets to read from in Kafka/EventHubs, QoS etc.).

Record Fields

• channels: list<channel>
• extensions: option<list<(string, string)>>

enum format-spec

Format specification for messages

• more info: https://github.com/clemensv/spec/blob/registry-extensions/registry/spec.md#message-formats
• message metadata can further decorate w/ things like format version, and so on.

Enum Cases

• cloudevents
• http
• amqp
• mqtt
• kafka
• raw

record message

A message with a binary payload, a format specification, and decorative metadata.

Record Fields

• data: list<u8>
• format: format-spec
• metadata: option<list<(string, string)>>

---

Functions

[static]client.connect: func

Params

• name: string

Return values

• result<own<client>, own<error>>

[static]error.trace: func

Return values

• string

Import interface wasi:messaging/[email protected]

---

Types

type client

client

#### `type channel` [`channel`](#channel)

#### `type message` [`message`](#message)

#### `type error` [`error`](#error)

----

Functions

send: func

Params

• c: own<client>
• ch: channel
• m: list<message>

Return values

• result<_, own<error>>

Import interface wasi:messaging/[email protected]

---

Types

type client

client

#### `type message` [`message`](#message)

#### `type channel` [`channel`](#channel)

#### `type error` [`error`](#error)

#### `type guest-configuration` [`guest-configuration`](#guest_configuration)

----

Functions

subscribe-try-receive: func

Blocking receive for t-milliseconds with ephemeral subscription – if no message is received, returns None

Params

• c: own<client>
• ch: channel
• t-milliseconds: u32

Return values

• result<option<list<message>>, own<error>>

subscribe-receive: func

Blocking receive until message with ephemeral subscription

Params

• c: own<client>
• ch: channel

Return values

• result<list<message>, own<error>>

update-guest-configuration: func

'Fit-all' type function for updating a guest's configuration – this could be useful for:

• unsubscribing from a channel,
• checkpointing,
• etc..

Params

• gc: guest-configuration

Return values

• result<_, own<error>>

complete-message: func

A message can exist under several statuses: (1) available: the message is ready to be read, (2) acquired: the message has been sent to a consumer (but still exists in the queue), (3) accepted (result of complete-message): the message has been received and ACK-ed by a consumer and can be safely removed from the queue, (4) rejected (result of abandon-message): the message has been received and NACK-ed by a consumer, at which point it can be:

• deleted,
• sent to a dead-letter queue, or
• kept in the queue for further processing.

Params

• m: message

Return values

• result<_, own<error>>

abandon-message: func

Params

• m: message

Return values

• result<_, own<error>>