# Notification subsystem Original motivation, requirements and general solution strategy are described in the [issue #895](https://github.com/nspcc-dev/neo-go/issues/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 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. 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 announcement is followed. * 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 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. * `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. * `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" } ``` ### `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": [] } ```