# RPC

## Client

Client is provided as a Go package, so please refer to the
[relevant godocs page](https://godoc.org/github.com/nspcc-dev/neo-go/pkg/rpcclient).

## Server

The server is written to support as much of the [JSON-RPC 2.0 Spec](http://www.jsonrpc.org/specification) as possible. The server is run as part of the node currently.

### Example call

An example would be viewing the version of the node:

```bash
$ curl -X POST -d '{"jsonrpc": "2.0", "method": "getversion", "params": [], "id": 1}' http://localhost:20332
```

which would yield the response:

```json
{
  "result" : {
    "useragent" : "/NEO-GO:0.97.2/",
    "tcpport" : 10333,
    "network" : 860833102,
    "nonce" : 105745208
  },
  "jsonrpc" : "2.0",
  "id" : 1
}
```
### Supported methods

| Method  |
| ------- |
| `calculatenetworkfee` |
| `findstates` |
| `getapplicationlog` |
| `getbestblockhash` |
| `getblock` |
| `getblockcount` |
| `getblockhash` |
| `getblockheader` |
| `getblockheadercount` |
| `getcandidates` |
| `getcommittee` |
| `getconnectioncount` |
| `getcontractstate` |
| `getnativecontracts` |
| `getnep11balances` |
| `getnep11properties` |
| `getnep11transfers` |
| `getnep17balances` |
| `getnep17transfers` |
| `getnextblockvalidators` |
| `getpeers` |
| `getproof` |
| `getrawmempool` |
| `getrawtransaction` |
| `getstate` |
| `getstateheight` |
| `getstateroot` |
| `getstorage` |
| `gettransactionheight` |
| `getunclaimedgas` |
| `getversion` |
| `invokecontractverify` |
| `invokefunction` |
| `invokescript` |
| `sendrawtransaction` |
| `submitblock` |
| `submitoracleresponse` |
| `terminatesession` |
| `traverseiterator` |
| `validateaddress` |
| `verifyproof` |

#### Implementation notices

##### JSON representation of enumerations

C# implementation contains a number of enumerations and while it outputs them
into JSON as comma-separated strings (or just strings if only one value is
allowed for this type) it accepts pure numbers for input (see #2563 for
example). NeoGo currently doesn't support this behavior. This affects the
following data types:
 * transaction attribute type
 * oracle response code
 * transaction witness scope
 * rule witness action
 * condition rule witness type
 * function call flag
 * function call parameter type
 * execution trigger type
 * stack item type

Any call that takes any of these types for input in JSON format is affected.

##### Response error codes

NeoGo currently uses a different set of error codes in comparison to C# implementation, see 
[proposal](https://github.com/neo-project/proposals/pull/156).
NeoGo retains certain deprecated error codes, which will be removed once 
all nodes adopt the new error standard.

##### `calculatenetworkfee`

NeoGo tries to cover more cases with its calculatenetworkfee implementation,
whereas C# node support only standard signature contracts and deployed
contracts that can execute `verify` successfully on incomplete (not yet signed
properly) transaction, NeoGo also works with deployed contracts that fail at
this stage and executes non-standard contracts (that can fail
too). It's ignoring the result of any verification script (since the method
calculates fee and doesn't care about transaction validity). Invocation script
is used as is when provided, but absent it the system will try to infer one
based on the `verify` method signature (pushing dummy signatures or
hashes). If signature has some types which contents can't be adequately
guessed (arrays, maps, interop, void) they're ignored. See
neo-project/neo#2805 as well.

##### `invokefunction`, `invokescript`

neo-go implementation of `invokefunction` does not return `tx`
field in the answer because that requires signing the transaction with some
key in the server, which doesn't fit the model of our node-client interactions.
If this signature is lacking, the transaction is almost useless, so there is no point
in returning it.

It's possible to use `invokefunction` not only with a contract scripthash, but also 
with a contract name (for native contracts) or a contract ID (for all contracts). This
feature is not supported by the C# node.

If iterator is present on stack after function or script invocation then, depending
on `SessionEnable` RPC-server setting, iterator either will be marshalled as iterator
ID (corresponds to `SessionEnabled: true`) or as a set of traversed iterator values
up to `DefaultMaxIteratorResultItems` packed into array (corresponds to
`SessionEnabled: false`).

##### `getcontractstate`

It's possible to get non-native contract state by its ID, unlike with C# node where
it only works for native contracts.

##### `getrawtransaction`

VM state is included into verbose response along with other transaction fields if
the transaction is already on chain.

##### `getstateroot`

This method is able to accept state root hash instead of index, unlike the C# node
where only index is accepted.

##### `getstorage`

This method doesn't work for the Ledger contract, you can get data via regular
`getblock` and `getrawtransaction` calls. This method is able to get storage of
a native contract by its name (case-insensitive), unlike the C# node where
it only possible for index or hash.

##### `getnep11balances` and `getnep17balances`
neo-go implementation of `getnep11balances` and `getnep17balances` does not
perform tracking of NEP-11 and NEP-17 balances for each account as it is done
in the C# node. Instead, a neo-go node maintains a list of standard-compliant
contracts, i.e. those contracts that have `NEP-11` or `NEP-17` declared in the
supported standards section of the manifest. Each time balances are queried,
the neo-go node asks every NEP-11/NEP-17 contract for the account balance by
invoking `balanceOf` method with the corresponding args. Invocation GAS limit
is set to be 3 GAS. All non-zero balances are included in the RPC call result.

Thus, if a token contract doesn't have proper standard declared in the list of
supported standards but emits compliant NEP-11/NEP-17 `Transfer`
notifications, the token balance won't be shown in the list of balances
returned by the neo-go node (unlike the C# node behavior). However, transfer
logs of such tokens are still available via respective `getnepXXtransfers` RPC
calls.

The behavior of the `LastUpdatedBlock` tracking for archival nodes as far as for
governing token balances matches the C# node's one. For non-archival nodes and
other NEP-11/NEP-17 tokens, if transfer's `LastUpdatedBlock` is lower than the
latest state synchronization point P the node working against,
`LastUpdatedBlock` equals P. For NEP-11 NFTs `LastUpdatedBlock` is equal for
all tokens of the same asset.

##### `getversion`

NeoGo can return additional fields in the `protocol` object depending on the
extensions enabled. Specifically that's `p2psigextensions` and
`staterootinheader` booleans and `committeehistory` and `validatorshistory`
objects (that are effectively maps from stringified integers to other
integers. These fields are only returned when corresponding settings are
enabled in the server's protocol configuration.

##### `getnep11transfers` and `getnep17transfers`
`transfernotifyindex` is not tracked by NeoGo, thus this field is always zero.

##### `traverseiterator` and `terminatesession`

NeoGo returns an error when it is unable to find a session or iterator, unlike 
the error-free C# response that provides a default result.

##### `verifyProof`

NeoGo can generate an error in response to an invalid proof, unlike
the error-free C# implementation.

### Unsupported methods

Methods listed below are not going to be supported for various reasons
and we're not accepting issues related to them.

| Method  | Reason |
| ------- | ------------|
| `closewallet` | Doesn't fit neo-go wallet model |
| `dumpprivkey` | Shouldn't exist for security reasons, see `closewallet` comment also |
| `getnewaddress` | See `closewallet` comment, use CLI to do that |
| `getwalletbalance` | See `closewallet` comment, use `getnep17balances` for that |
| `getwalletunclaimedgas` | See `closewallet` comment, use `getunclaimedgas` for that |
| `importprivkey` | Not applicable to neo-go, see `closewallet` comment |
| `listaddress` | Not applicable to neo-go, see `closewallet` comment |
| `listplugins` | neo-go doesn't have any plugins, so it makes no sense |
| `openwallet` | Doesn't fit neo-go wallet model |
| `sendfrom` | Not applicable to neo-go, see `openwallet` comment |
| `sendmany` | Not applicable to neo-go, see `openwallet` comment |
| `sendtoaddress` | Not applicable to neo-go, see `claimgas` comment |

### Extensions

Some additional extensions are implemented as a part of this RPC server.

#### `getblocksysfee` call

This method returns cumulative system fee for all transactions included in a
block. It can be removed in future versions, but at the moment you can use it
to see how much GAS is burned with a particular block (because system fees are
burned).

#### `invokecontractverifyhistoric`, `invokefunctionhistoric` and `invokescripthistoric` calls

These methods provide the ability of *historical* calls and accept block hash or
block index or stateroot hash as the first parameter and the list of parameters
that is the same as of `invokecontractverify`, `invokefunction` and
`invokescript` correspondingly. The historical call assumes that the contracts'
storage state has all its values got from MPT with the specified stateroot (or,
which is the same, with the stateroot of the block of the specified height) and
the transaction will be invoked using interop context with block which is next to
the block with the specified height. This allows to perform test invocation using
the specified past chain state. These methods may be useful for debugging
purposes.

Behavior note: any historical RPC call need the historical chain state to be
presented in the node storage, thus if the node keeps only latest MPT state
the historical call can not be handled properly.The historical calls only
guaranteed to correctly work on archival node that stores all MPT data. If a
node keeps the number of latest states and has the GC on (this setting
corresponds to the `RemoveUntraceableBlocks` set to `true`), then the behaviour
of historical RPC call is undefined. GC can always kick some data out of the
storage while the historical call is executing, thus keep in mind that the call
can be processed with `RemoveUntraceableBlocks` only with limitations on
available data.

#### `submitnotaryrequest` call

This method can be used on P2P Notary enabled networks to submit new notary
payloads to be relayed from RPC to P2P.

#### Limits and paging for getnep11transfers and getnep17transfers

`getnep11transfers` and `getnep17transfers` RPC calls never return more than
1000 results for one request (within the specified time frame). You can pass your
own limit via an additional parameter and then use paging to request the next
batch of transfers.

An example of requesting 10 events for address NbTiM6h8r99kpRtb428XcsUk1TzKed2gTc
within 0-1600094189000 timestamps:

```json
{ "jsonrpc": "2.0", "id": 5, "method": "getnep17transfers", "params":
["NbTiM6h8r99kpRtb428XcsUk1TzKed2gTc", 0, 1600094189000, 10] }
```

Get the next 10 transfers for the same account within the same time frame:

```json
{ "jsonrpc": "2.0", "id": 5, "method": "getnep17transfers", "params":
["NbTiM6h8r99kpRtb428XcsUk1TzKed2gTc", 0, 1600094189000, 10, 1] }
```

#### Websocket server

This server accepts websocket connections on `ws://$BASE_URL/ws` address. You
can use it to perform regular RPC calls over websockets (it's supposed to be a
little faster than going regular HTTP route) and you can also use it for
additional functionality provided only via websockets (like notifications).

#### Notification subsystem

Notification subsystem consists of two additional RPC methods (`subscribe` and
`unsubscribe` working only over websocket connection) that allow to subscribe
to various blockchain events (with simple event filtering) and receive them on
the client as JSON-RPC notifications. More details on that are written in the
[notifications specification](notifications.md).

## Reference

* [JSON-RPC 2.0 Specification](http://www.jsonrpc.org/specification)
* [Neo JSON-RPC 2.0 docs](https://docs.neo.org/docs/en-us/reference/rpc/latest-version/api.html)