Peer channel-based event services¶
General overview¶
In previous versions of Fabric, the peer event service was known as the event hub. This service sent events any time a new block was added to the peer’s ledger, regardless of the channel to which that block pertained, and it was only accessible to members of the organization running the eventing peer (i.e., the one being connected to for events).
Starting with v1.1, there are new services which provide events. These services use an entirely different design to provide events on a per-channel basis. This means that registration for events occurs at the level of the channel instead of the peer, allowing for fine-grained control over access to the peer’s data. Requests to receive events are accepted from identities outside of the peer’s organization (as defined by the channel configuration). This also provides greater reliability and a way to receive events that may have been missed (whether due to a connectivity issue or because the peer is joining a network that has already been running).
Available services¶
Deliver
This service sends entire blocks that have been committed to the ledger. If
any events were set by a chaincode, these can be found within the
ChaincodeActionPayload
of the block.
DeliverWithPrivateData
This service sends the same data as the Deliver
service, and additionally
includes any private data from collections that the client’s organization is
authorized to access.
DeliverFiltered
This service sends «filtered» blocks, minimal sets of information about blocks
that have been committed to the ledger. It is intended to be used in a network
where owners of the peers wish for external clients to primarily receive
information about their transactions and the status of those transactions. If
any events were set by a chaincode, these can be found within the
FilteredChaincodeAction
of the filtered block.
Nota
The payload of chaincode events will not be included in filtered blocks.
How to register for events¶
Registration for events is done by sending an envelope
containing a deliver seek info message to the peer that contains the desired start
and stop positions, the seek behavior (block until ready or fail if not ready).
There are helper variables SeekOldest
and SeekNewest
that can be used to
indicate the oldest (i.e. first) block or the newest (i.e. last) block on the ledger.
To have the services send events indefinitely, the SeekInfo
message should
include a stop position of MAXINT64
.
Nota
If mutual TLS is enabled on the peer, the TLS certificate hash must be set in the envelope’s channel header.
By default, the event services use the Channel Readers policy to determine whether to authorize requesting clients for events.
Overview of deliver response messages¶
The event services send back DeliverResponse
messages.
Each message contains one of the following:
- status – HTTP status code. Each of the services will return the appropriate failure code if any failure occurs; otherwise, it will return
200 - SUCCESS
once the service has completed sending all information requested by theSeekInfo
message.- block – returned only by the
Deliver
service.- block and private data – returned only by the
DeliverWithPrivateData
service.- filtered block – returned only by the
DeliverFiltered
service.
A filtered block contains:
- channel ID.
- number (i.e. the block number).
- array of filtered transactions.
- transaction ID.
- type (e.g.
ENDORSER_TRANSACTION
,CONFIG
).- transaction validation code.
- filtered transaction actions.
- array of filtered chaincode actions.
- chaincode event for the transaction (with the payload nilled out).
SDK event documentation¶
For further details on using the event services, refer to the SDK documentation.