15 KiB
Notification subsystem
Original motivation, requirements and general solution strategy are described in the issue #895.
This extension allows a websocket client to subscribe to various events and receive them as JSON-RPC notifications from the server.
Events
Currently supported events:
- new block added Contents: block. Filters: primary ID.
- new transaction in the block Contents: transaction. Filters: sender and cosigner.
- notification generated during execution Contents: container hash, contract script hash, stack item. Filters: contract script hash.
- transaction executed Contents: application execution result. Filters: VM state.
Filters use conjunctional logic.
Ordering and persistence guarantees
- new block is only announced after its processing is complete and the chain is updated to the new height
- no disk-level persistence guarantees are given
- new in-block transaction is announced after block processing, but before announcing the block itself
- transaction notifications are only announced for successful transactions
- all announcements are being done in the same order they happen on the chain At first transaction execution is announced, then followed by notifications generated during this execution, then followed by transaction announcement. Transaction announcements are ordered the same way they're in the block.
- unsubscription may not cancel pending, but not yet sent events
Subscription management
To receive events clients need to subscribe to them first via subscribe
method. Upon successful subscription clients receive subscription ID for
subsequent management of this subscription. Subscription is only valid for
connection lifetime, no long-term client identification is being made.
Errors are not described down below, but they can be returned as standard JSON-RPC errors (most often caused by invalid parameters).
subscribe method
Parameters: event stream name, stream-specific filter rules hash (can be omitted if empty).
Recognized stream names:
block_addedFilter:primaryas an integer with primary (speaker) node index from ConsensusData.transaction_addedFilter:senderfield containing string with hex-encoded Uint160 (LE representation) for transaction'sSenderand/orcosignerin the same format for one of transaction'sCosigners.notification_from_executionFilter:contractfield containing string with hex-encoded Uint160 (LE representation).transaction_executedFilter:statefield containingHALTorFAULTstring for successful and failed executions respectively.
Response: returns subscription ID (string) as a result. This ID can be used to cancel this subscription and has no meaning other than that.
Example request (subscribe to notifications from contract 0x6293a440ed80a427038e175a507d3def1e04fb67 generated when executing transactions):
{
"jsonrpc": "2.0",
"method": "subscribe",
"params": ["notification_from_execution", {"contract": "6293a440ed80a427038e175a507d3def1e04fb67"}],
"id": 1
}
Example response:
{
"jsonrpc": "2.0",
"id": 1,
"result": "55aaff00"
}
unsubscribe method
Parameters: subscription ID as a string.
Response: boolean true.
Example request (unsubscribe from "55aaff00"):
{
"jsonrpc": "2.0",
"method": "unsubscribe",
"params": ["55aaff00"],
"id": 1
}
Example response:
{
"jsonrpc": "2.0",
"id": 1,
"result": true
}
Events
Events are sent as JSON-RPC notifications from the server with method field
being used for notification names. Notification names are identical to stream
names described for subscribe method with one important addition for
event_missed which can be sent for any subscription to signify that some
events were not delivered (usually when client isn't able to keep up with
event flow).
Verbose responses for various structures like blocks and transactions are used to simplify working with notifications on client side. Returned structures mostly follow the one used by standard Neo RPC calls, but may have some minor differences.
If a server-side event matches several subscriptions from one client, it's only sent once.
block_added notification
As a first parameter (params section) contains block converted to JSON
structure which is similar to verbose getblock response but with the
following differences:
- it doesn't have
sizefield (you can calculate it client-side) - it doesn't have
nextblockhashfield (it's supposed to be the latest one anyway) - it doesn't have
confirmationsfield (see previous)
No other parameters are sent.
Example:
{
"params" : [
{
"index" : 207,
"time" : 1590006200,
"nextconsensus" : "AXSvJVzydxXuL9da4GVwK25zdesCrVKkHL",
"consensusdata" : {
"primary" : 0,
"nonce" : "0000000000000457"
},
"previousblockhash" : "0x04f7580b111ec75f0ce68d3a9fd70a0544b4521b4a98541694d8575c548b759e",
"witnesses" : [
{
"invocation" : "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",
"verification" : "130c2102103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e0c2102a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd620c2102b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc20c2103d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699140b413073b3bb"
}
],
"version" : 0,
"hash" : "0x239fea00c54c2f6812612874183b72bef4473fcdf68bf8da08d74fd5b6cab030",
"tx" : [
{
"txid" : "0xf736cd91ab84062a21a09b424346b241987f6245ffe8c2b2db39d595c3c222f7",
"witnesses" : [
{
"verification" : "0c2102b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc20b410a906ad4",
"invocation" : "0c4016e7a112742409cdfaad89dcdbcb52c94c5c1a69dfe5d8b999649eaaa787e31ca496d1734d6ea606c749ad36e9a88892240ae59e0efa7f544e0692124898d512"
}
],
"vout" : [],
"cosigners" : [],
"validuntilblock" : 1200,
"nonce" : 8,
"netfee" : "0.0030421",
"sender" : "ALHF9wsXZVEuCGgmDA6ZNsCLtrb4A1g4yG",
"sysfee" : "0",
"type" : "InvocationTransaction",
"attributes" : [],
"version" : 1,
"vin" : [],
"size" : 204,
"script" : "10c00c04696e69740c14769162241eedf97c2481652adf1ba0f5bf57431b41627d5b52"
},
{
"script" : "01e8030c14316e851039019d39dfc2c37d6c3fee19fd5809870c14769162241eedf97c2481652adf1ba0f5bf57431b13c00c087472616e736665720c14769162241eedf97c2481652adf1ba0f5bf57431b41627d5b5238",
"size" : 277,
"attributes" : [],
"version" : 1,
"vin" : [],
"netfee" : "0.0037721",
"sender" : "ALHF9wsXZVEuCGgmDA6ZNsCLtrb4A1g4yG",
"sysfee" : "0",
"type" : "InvocationTransaction",
"nonce" : 9,
"cosigners" : [
{
"scopes" : 1,
"account" : "0x870958fd19ee3f6c7dc3c2df399d013910856e31"
}
],
"validuntilblock" : 1200,
"witnesses" : [
{
"invocation" : "0c4027727296b84853c5d9e07fb8a40e885246ae25641383b16eefbe92027ecb1635b794aacf6bbfc3e828c73829b14791c483d19eb758b57638e3191393dbf2d288",
"verification" : "0c2102b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc20b410a906ad4"
}
],
"vout" : [],
"txid" : "0xe1cd5e57e721d2a2e05fb1f08721b12057b25ab1dd7fd0f33ee1639932fdfad7"
}
],
"merkleroot" : "0xb2c7230ebee4cb83bc03afadbba413e6bca8fcdeaf9c077bea060918da0e52a1"
}
],
"jsonrpc" : "2.0",
"method" : "block_added"
}
transaction_added notification
In the first parameter (params section) contains transaction converted to
JSON which is similar to verbose getrawtransaction response, but with the
following differences:
- block's metadata is missing (
blockhash,confirmations,blocktime)
No other parameters are sent.
Example:
{
"method" : "transaction_added",
"params" : [
{
"validuntilblock" : 1200,
"version" : 1,
"txid" : "0xe1cd5e57e721d2a2e05fb1f08721b12057b25ab1dd7fd0f33ee1639932fdfad7",
"witnesses" : [
{
"invocation" : "0c4027727296b84853c5d9e07fb8a40e885246ae25641383b16eefbe92027ecb1635b794aacf6bbfc3e828c73829b14791c483d19eb758b57638e3191393dbf2d288",
"verification" : "0c2102b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc20b410a906ad4"
}
],
"sysfee" : "0",
"sender" : "ALHF9wsXZVEuCGgmDA6ZNsCLtrb4A1g4yG",
"vout" : [],
"netfee" : "0.0037721",
"size" : 277,
"attributes" : [],
"script" : "01e8030c14316e851039019d39dfc2c37d6c3fee19fd5809870c14769162241eedf97c2481652adf1ba0f5bf57431b13c00c087472616e736665720c14769162241eedf97c2481652adf1ba0f5bf57431b41627d5b5238",
"nonce" : 9,
"vin" : [],
"type" : "InvocationTransaction",
"cosigners" : [
{
"account" : "0x870958fd19ee3f6c7dc3c2df399d013910856e31",
"scopes" : 1
}
]
}
],
"jsonrpc" : "2.0"
}
notification_from_execution notification
Contains three parameters: container hash (hex-encoded LE Uint256 in a
string), contract script hash (hex-encoded LE Uint160 in a string) and stack
item (encoded the same way as state field contents for notifications from
getapplicationlog response).
Example:
{
"jsonrpc" : "2.0",
"method" : "notification_from_execution",
"params" : [
{
"state" : {
"value" : [
{
"value" : "636f6e74726163742063616c6c",
"type" : "ByteString"
},
{
"value" : "7472616e73666572",
"type" : "ByteString"
},
{
"value" : [
{
"value" : "769162241eedf97c2481652adf1ba0f5bf57431b",
"type" : "ByteString"
},
{
"value" : "316e851039019d39dfc2c37d6c3fee19fd580987",
"type" : "ByteString"
},
{
"value" : "1000",
"type" : "Integer"
}
],
"type" : "Array"
}
],
"type" : "Array"
},
"contract" : "0x1b4357bff5a01bdf2a6581247cf9ed1e24629176"
}
]
}
transaction_executed notification
Contains the same result as from getapplicationlog method in the first
parameter and no other parameters. One difference from getapplicationlog is
that it always contains zero in the contract field.
Example:
{
"method" : "transaction_executed",
"params" : [
{
"txid" : "0xe1cd5e57e721d2a2e05fb1f08721b12057b25ab1dd7fd0f33ee1639932fdfad7",
"executions" : [
{
"trigger" : "Application",
"gasconsumed" : "2.291",
"contract" : "0x0000000000000000000000000000000000000000",
"stack" : [],
"notifications" : [
{
"state" : {
"type" : "Array",
"value" : [
{
"value" : "636f6e74726163742063616c6c",
"type" : "ByteString"
},
{
"type" : "ByteString",
"value" : "7472616e73666572"
},
{
"value" : [
{
"value" : "769162241eedf97c2481652adf1ba0f5bf57431b",
"type" : "ByteString"
},
{
"type" : "ByteString",
"value" : "316e851039019d39dfc2c37d6c3fee19fd580987"
},
{
"value" : "1000",
"type" : "Integer"
}
],
"type" : "Array"
}
]
},
"contract" : "0x1b4357bff5a01bdf2a6581247cf9ed1e24629176"
},
{
"contract" : "0x1b4357bff5a01bdf2a6581247cf9ed1e24629176",
"state" : {
"value" : [
{
"value" : "7472616e73666572",
"type" : "ByteString"
},
{
"value" : "769162241eedf97c2481652adf1ba0f5bf57431b",
"type" : "ByteString"
},
{
"value" : "316e851039019d39dfc2c37d6c3fee19fd580987",
"type" : "ByteString"
},
{
"value" : "1000",
"type" : "Integer"
}
],
"type" : "Array"
}
}
],
"vmstate" : "HALT"
}
]
}
],
"jsonrpc" : "2.0"
}
event_missed notification
Never has any parameters. Example:
{
"jsonrpc": "2.0",
"method": "event_missed",
"params": []
}