Subscribe to Events - Blockchain as a Service - Alibaba Cloud Documentation Center

Streams real-time blockchain events from a blockchain network over a persistent WebSocket connection.

Request syntax

GET /api/v1/networks/{network}/events/subscribe

Request parameters

Parameter	Description
`network`	The name of the channel.
`access_token`	The access token used to authenticate REST API requests.
`source`	The event types to subscribe to. Valid values: `Tx`, `Config`, `Contract`, `Block`. To subscribe to multiple types, separate them with commas (`,`). Use `*` to subscribe to all event types.

Message structure

Each message pushed over the WebSocket connection contains the following fields.

Parameter	Type	Description
`id`	String	The event ID, unique within the channel.
`name`	String	The event name.
`type`	EventType	The event type. Valid values: `Tx` (transaction creation), `Config` (blockchain system configuration change), `Contract` (smart contract event set in a transaction), `Block` (block creation).
`network`	String	The name of the channel.
`instance_id`	String	The instance ID of the subscribed event, unique within an organization.
`content`	Object	The event payload. The structure depends on the event type: when `type` is `Tx` or `Config`, the value follows the Transaction structure; when `type` is `Contract`, the value is a Base64-encoded string; when `type` is `Block`, the value follows the Block structure.

Transaction structure

Applies when type is Tx or Config.

Parameter	Type	Description
`id`	String	The transaction ID. Empty when `type` is `Config`.
`state`	String	The transaction state. `VALID` indicates a valid transaction. Any other value indicates an invalid transaction.
`from`	String	The transaction initiator, in the format `<Organization MSP>.<Username>`, where MSP is the Membership Service Provider (MSP) identifier.
`to`	String	The target chaincode called by the transaction. Empty when `type` is `Config`.
`input`	String	The JSON-encoded chaincode input parameters. When `type` is `Config`, this field contains the JSON-encoded `common.ConfigUpdate` value.
`events`	List\<Event\>	The blockchain events generated by the transaction.
`data`	Object	The full transaction payload. The data structure is `common.Payload`.

Block structure

Applies when type is Block.

Parameter	Type	Description
`number`	Integer	The block height.
`hash`	String	The hash of the current block, hex-encoded.
`previous_hash`	String	The hash of the previous block, hex-encoded.
`create_time`	Integer	The block creation time as a UNIX timestamp, representing the number of milliseconds elapsed since January 1, 1970, 00:00:00 UTC.
`transactions`	List\<String\>	The list of transaction IDs included in the block.

Examples

Connect to the event stream

wscat -c "ws://your.gateway.endpoint/api/v1/networks/channel3/events/subscribe?access_token=<Your URL Encoded Access Token>&source=%2A"

Sample block event message

{
  "type": "Block",
  "platform": "Fabric",
  "instance_id": "csi-e2ehmfqasth-bcw7tzao2dzeo",
  "network": "channel3",
  "id": "block-282",
  "name": "282",
  "content": {
    "number": 282,
    "hash": "f7b42d07509c463f8e8cde0fcc8325b42e8bf7fd6a7a24dd207eed297fcd6358",
    "create_time": 1581589504,
    "previous_hash": "b8de08d49217c1d8f4ea398c8c61fe2a5bc46ec7bb6c95f44dfd29eaf6c272ab",
    "transactions": [
      "dc90b701e27afa5120ee003ef9d51b86a2ff9e1a9d8537f65387bde6d92c5cba"
    ]
  }
}

Error codes

For more information, see Error codes.