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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, since/till block indexes.

  • new transaction in the block

    Contents: transaction. Filters: sender and signer.

  • notification generated during execution

    Contents: container hash, contract hash, notification name, stack item. Filters: contract hash, notification name.

  • transaction/persisting script executed

    Contents: application execution result. Filters: VM state, script container hash.

  • new/removed P2P notary request (if P2PSigExtensions are enabled)

    Contents: P2P notary request. Filters: request sender and main tx signer.

Filters use conjunctional logic.

Ordering and persistence guarantees

  • new block and header of this block are only announced after block's processing is complete and the chain is updated to the new height
  • no disk-level persistence guarantees are given
  • header of newly added block is announced after block processing, but before announcing the block itself
  • new in-block transaction is announced after block processing, but before announcing the block header and 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. First, OnPersist script execution is announced followed by notifications generated during the script execution. After that transaction execution is announced. It is then followed by notifications generated during this execution. Next, follows the transaction announcement. Transaction announcements are ordered the same way they're in the block. After all in-block transactions announcements PostPersist script execution is announced followed by notifications generated during the script execution. Finally, block header is announced followed by the block announcement itself.
  • notary request events announcements are not bound to the chain processing. Trigger for notary request notifications is notary request mempool content change, thus, notary request event is announced every time notary request enters or leaves notary pool.
  • 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_added Filter: primary as an integer with a valid range of 0-255 with primary (speaker) node index from ConsensusData and/or since field as an integer value with block index starting from which new block notifications will be received and/or till field as an integer values containing block index till which new block notifications will be received.
  • header_of_added_block Filter: primary as an integer with primary (speaker) node index from ConsensusData and/or since field as an integer value with header index starting from which new header notifications will be received and/or till field as an integer values containing header index till which new header notifications will be received.
  • transaction_added Filter: sender field containing a string with hex-encoded Uint160 (LE representation) for transaction's Sender and/or signer in the same format for one of transaction's Signers.
  • notification_from_execution Filter: contract field containing a string with hex-encoded Uint160 (LE representation) and/or name field containing a string with execution notification name which should be a valid UTF-8 string not longer than 32 bytes.
  • transaction_executed Filter: state field containing HALT or FAULT string for successful and failed executions respectively and/or container field containing script container (block/transaction) hash.
  • notary_request_event Filter: sender field containing a string with hex-encoded Uint160 (LE representation) for notary request's Sender and/or signer in the same format for one of main transaction's Signers. type field containing a string with event type, which could be one of "added" or "removed".

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 have not been delivered (usually when a client is unable to keep up with the event flow).

Verbose responses for various structures like blocks and transactions are used to simplify working with notifications on the 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

The first parameter (params section) contains a block converted to a JSON structure, which is similar to a verbose getblock response but with the following differences:

  • it doesn't have size field (you can calculate it client-side)
  • it doesn't have nextblockhash field (it's supposed to be the latest one anyway)
  • it doesn't have confirmations field (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,
               "signers" : [
                  {
                     "scopes" : 1,
                     "account" : "0x870958fd19ee3f6c7dc3c2df399d013910856e31"
                  }
               ],
               "validuntilblock" : 1200,
               "witnesses" : [
                  {
                     "invocation" : "0c4027727296b84853c5d9e07fb8a40e885246ae25641383b16eefbe92027ecb1635b794aacf6bbfc3e828c73829b14791c483d19eb758b57638e3191393dbf2d288",
                     "verification" : "0c2102b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc20b410a906ad4"
                  }
               ],
               "vout" : [],
               "txid" : "0xe1cd5e57e721d2a2e05fb1f08721b12057b25ab1dd7fd0f33ee1639932fdfad7"
            }
         ],
         "merkleroot" : "0xb2c7230ebee4cb83bc03afadbba413e6bca8fcdeaf9c077bea060918da0e52a1"
      }
   ],
   "jsonrpc" : "2.0",
   "method" : "block_added"
}

header_of_added_block notification

The first parameter (params section) contains a header of added block converted to a JSON structure, which is similar to a verbose getblockheader response but with the following differences:

  • it doesn't have size field (you can calculate it client-side)
  • it doesn't have nextblockhash field (it's supposed to be the latest one anyway)
  • it doesn't have confirmations field (see previous)

No other parameters are sent.

Example:

{
   "jsonrpc": "2.0",
   "method": "header_of_added_block",
   "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",
         "merkleroot" : "0xb2c7230ebee4cb83bc03afadbba413e6bca8fcdeaf9c077bea060918da0e52a1"
      }
   ]
}

transaction_added notification

The first parameter (params section) contains a transaction converted to JSON, which is similar to a 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",
         "signers" : [
            {
               "account" : "0x870958fd19ee3f6c7dc3c2df399d013910856e31",
               "scopes" : 1
            }
         ]
      }
   ],
   "jsonrpc" : "2.0"
}

notification_from_execution notification

Contains four parameters: container hash (block's or transaction's hex-encoded LE Uint256 hash in a string), contract hash (hex-encoded LE Uint160 in a string), notification name 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",
         "name" : "transfer",
         "container" : "0xe1cd5e57e721d2a2e05fb1f08721b12057b25ab1dd7fd0f33ee1639932fdfad7",
      }
   ]
}

transaction_executed notification

It contains the same result as from getapplicationlog method in the first parameter and no other parameters. The difference from getapplicationlog is that it has block's or transaction's hex-encoded LE Uint256 hash in the container field instead of two separate txid and blockhash fields and a single execution instead of an executions array.

Example:

{
   "method" : "transaction_executed",
   "params" : [
      {
         "container" : "0xe1cd5e57e721d2a2e05fb1f08721b12057b25ab1dd7fd0f33ee1639932fdfad7",
         "trigger" : "Application",
         "gasconsumed" : "2.291",
         "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"
}

notary_request_event notification

It contains two parameters: event type, which could be one of "added" or "removed", and added (or removed) notary request.

Example:

{
   "jsonrpc" : "2.0",
   "method" : "notary_request_event",
   "params" : [
      {
         "notaryrequest" : {
            "Witness" : {
               "verification" : "DCECs2Ir9AF73+MXxYrtX0x1PyBrfbiWBG+n13S7xL9/jcJBVuezJw==",
               "invocation" : "DECWLkFhNqBMCewLxjAWiXXA1YE/GmX6EWmIRM17F9lwwpXyWtzp+hkxvJNWHpDlslDvpXizGiB/YBd05kadXlSv"
            },
            "fallbacktx" : {
               "validuntilblock" : 115,
               "attributes" : [
                  {
                     "type" : "NotValidBefore",
                     "height" : 65
                  },
                  {
                     "type" : "Conflicts",
                     "hash" : "0x03c564ed28ba3d50beb1a52dcb751b929e1d747281566bd510363470be186bc0"
                  },
                  {
                     "type" : "NotaryAssisted",
                     "nkeys" : 0
                  }
               ],
               "sender" : "NRNp25VPHahL3umVxBcMLuEENGZR9cHxtc",
               "size" : 291,
               "netfee" : "200000000",
               "witnesses" : [
                  {
                     "invocation" : "DEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
                     "verification" : ""
                  },
                  {
                     "invocation" : "DEBnVePpwnsM54K72RmxZR8cWTGxQveJ1cAdd3/zQUh6KVDnj+G5F8AI6gYlbnEK5qJwP40WfGWlmy3A8mYHGVLm",
                     "verification" : "DCECs2Ir9AF73+MXxYrtX0x1PyBrfbiWBG+n13S7xL9/jcJBVuezJw=="
                  }
               ],
               "nonce" : 0,
               "sysfee" : "0",
               "signers" : [
                  {
                     "scopes" : "None",
                     "account" : "0xc1e14f19c3e60d0b9244d06dd7ba9b113135ec3b"
                  },
                  {
                     "account" : "0xb248508f4ef7088e10c48f14d04be3272ca29eee",
                     "scopes" : "None"
                  }
               ],
               "version" : 0,
               "hash" : "0x5eb5f89d04648d43ba7563130e8bfd1710392ab97cba8e35857aed4206db3643",
               "script" : "QA=="
            },
            "maintx" : {
               "sender" : "Nhfg3TbpwogLvDGVvAvqyThbsHgoSUKwtn",
               "attributes" : [
                  {
                     "nkeys" : 1,
                     "type" : "NotaryAssisted"
                  }
               ],
               "validuntilblock" : 115,
               "witnesses" : [
                  {
                     "invocation" : "AQQH",
                     "verification" : "AwYJ"
                  }
               ],
               "netfee" : "0",
               "size" : 62,
               "version" : 0,
               "signers" : [
                  {
                     "scopes" : "None",
                     "account" : "0xb248508f4ef7088e10c48f14d04be3272ca29eee"
                  }
               ],
               "sysfee" : "0",
               "nonce" : 1,
               "script" : "QA==",
               "hash" : "0x03c564ed28ba3d50beb1a52dcb751b929e1d747281566bd510363470be186bc0"
            }
         },
         "type" : "added"
      }
   ]
}

event_missed notification

Never has any parameters. Example:

{
  "jsonrpc": "2.0",
  "method": "event_missed",
  "params": []
}