# Hush Payment API

## Overview

Hush extends the Bitcoin Core API with new RPC calls to support private Hush payments involving shielded addresses (zaddrs).

Hush payments make use of two address formats:

* taddr - an address for transparent funds (just like a Bitcoin address, value stored in UTXOs)
* zaddr - an address for private funds (value stored in objects called notes)

As of Block 340000, taddrs cannot be recipients of transactions, they can only mine new coinbase funds, which must then be sent to a zaddr.

When a transfer involves zaddrs, you must use the new Hush RPC calls, such as `z_sendmany`.


## Compatibility with Bitcoin Core

Hush supports all commands in the Bitcoin Core API (as of version 0.11.2).   Where applicable, Hush will extend commands in a backwards-compatible way to enable additional functionality.

We do not recommend use of accounts which are now deprecated in Bitcoin Core.  Where the account parameter exists in the API, please use “” as its value, otherwise an error will be returned.

To support multiple users in a single node’s wallet, consider using getnewaddress or z_getnewaddress to obtain a new address for each user.  Also consider mapping multiple addresses to each user.

## List of Hush API commands

Optional parameters are denoted in [square brackets].

RPC calls by category:

* Accounting: z_getbalance, z_gettotalbalance
* Addresses : z_getnewaddress, z_listaddresses, z_validateaddress, z_exportviewingkey, z_importviewingkey
* Keys : z_exportkey, z_importkey, z_exportwallet, z_importwallet
* Operation: z_getoperationresult, z_getoperationstatus, z_listoperationids
* Payment : z_listreceivedbyaddress, z_listunspent, z_sendmany, z_shieldcoinbase

RPC parameter conventions:

* taddr : Transparent address
* zaddr : Private address
* address : Accepts both private and transparent addresses.
* amount : JSON format decimal number with at most 8 digits of precision, with 1 HUSH expressed as 1.00000000.
* memo : Metadata expressed in hexadecimal format.  Limited to 512 bytes, the current size of the memo field of a private transaction.  Zero padding is automatic.

### Accounting

Command | Parameters | Description
--- | --- | ---
z_getbalance<br>| address [minconf=1] | Returns the balance of a taddr or zaddr belonging to the node’s wallet.<br><br>Optionally set the minimum number of confirmations a private or transparent transaction must have in order to be included in the balance.  Use 0 to count unconfirmed transactions.
z_gettotalbalance<br>| [minconf=1] | Return the total value of funds stored in the node’s wallet.<br><br>Optionally set the minimum number of confirmations a private or transparent transaction must have in order to be included in the balance.  Use 0 to count unconfirmed transactions.<br><br>Output:<br>{<br>"transparent" : 1.23,<br>"private" : 4.56,<br>"total" : 5.79}

### Addresses

Command | Parameters | Description
--- | --- | ---
z_getnewaddress | | Return a new zaddr for sending and receiving payments. The spending key for this zaddr will be added to the node’s wallet.<br><br>Output:<br>zN68D8hSs3...
z_listaddresses | | Returns a list of all the zaddrs in this node’s wallet for which you have a spending key.<br><br>Output:<br>{ [“z123…”, “z456...”, “z789...”] }
z_validateaddress | zaddr | Return information about a given zaddr.<br><br>Output:<br>{"isvalid" : true,<br>"address" : "zcWsmq...",<br>"type" : "sprout",<br>"payingkey" : "f5bb3c...",<br>"transmissionkey" : "7a58c7...",<br>"ismine" : true}

### Key Management

Command | Parameters | Description
--- | --- | ---
z_exportkey | zaddr | _Requires an unlocked wallet or an unencrypted wallet._<br><br>Return a zkey for a given zaddr belonging to the node’s wallet.<br><br>The key will be returned as a string formatted using Base58Check as described in the Hush protocol spec.<br><br>Output:AKWUAkypwQjhZ6LLNaMuuuLcmZ6gt5UFyo8m3jGutvALmwZKLdR5
z_importkey | zkey [rescan=true] | _Wallet must be unlocked._<br><br>Add a zkey as returned by z_exportkey to a node's wallet.<br><br>The key should be formatted using Base58Check as described in the Hush protocol spec.<br><br>Set rescan to true (the default) to rescan the entire local block database for transactions affecting any address or pubkey script in the wallet (including transactions affecting the newly-added address for this spending key).
z_exportwallet | filename | _Requires an unlocked wallet or an unencrypted wallet._<br><br>Creates or overwrites a file with taddr private keys and zaddr private keys in a human-readable format.<br><br>Filename is the file in which the wallet dump will be placed. May be prefaced by an absolute file path. An existing file with that name will be overwritten.<br><br>No value is returned but a JSON-RPC error will be reported if a failure occurred.
z_importwallet | filename | _Requires an unlocked wallet or an unencrypted wallet._<br><br>Imports private keys from a file in wallet export file format (see z_exportwallet). These keys will be added to the keys currently in the wallet. This call may need to rescan all or parts of the block chain for transactions affecting the newly-added keys, which may take several minutes.<br><br>Filename is the file to import. The path is relative to hushd’s working directory.<br><br>No value is returned but a JSON-RPC error will be reported if a failure occurred.
z_exportviewingkey | zaddr | Reveals the viewing key corresponding to 'zaddr'. Then the z_importviewingkey can be used with this output.
z_importviewingkey | vkey [rescan=whenkeyisnew] [startHeight=0] | Adds a viewing key (as returned by z_exportviewingkey) to your wallet.


### Payment

Command | Parameters | Description
--- | --- | ---
z_listreceivedbyaddress<br> | zaddr [minconf=1] | Return a list of amounts received by a zaddr belonging to the node’s wallet.<br><br>Optionally set the minimum number of confirmations which a received amount must have in order to be included in the result.  Use 0 to count unconfirmed transactions.<br><br>Output:<br>[{<br>“txid”: “4a0f…”,<br>“amount”: 0.54,<br>“memo”:”F0FF…”,}, {...}, {...}<br>]
z_listunspent | [minconf=1] [maxconf=9999999] [includeWatchonly=false] [zaddrs] | Returns array of unspent shielded notes with between minconf and maxconf (inclusive) confirmations.<br><br>Optionally filter to only include notes sent to specified addresses.<br><br>When minconf is 0, unspent notes with zero confirmations are returned, even though they are not immediately spendable.<br><br>Results are an array of Objects, each of which has: {txid, jsindex, jsoutindex, confirmations, address, amount, memo}
z_sendmany<br> | fromaddress amounts [minconf=1] [fee=0.0001] | _This is an Asynchronous RPC call_<br><br>Send funds from an address to multiple outputs.  The address can be either a taddr or a zaddr.<br><br>Amounts is a list containing key/value pairs corresponding to the addresses and amount to pay.  Each output address can be in taddr or zaddr format.<br><br>When sending to a zaddr, you also have the option of attaching a memo in hexadecimal format.<br><br>**NOTE:**When sending coinbase funds to a zaddr, the node's wallet does not allow any change. Put another way, spending a partial amount of a coinbase utxo is not allowed. This is not a consensus rule but a local wallet rule due to the current implementation of z_sendmany. In future, this rule may be removed.<br><br>Example of Outputs parameter:<br>[{“address”:”t123…”, “amount”:0.005},<br>,{“address”:”z010…”,”amount”:0.03, “memo”:”f508af…”}]<br><br>Optionally set the minimum number of confirmations which a private or transparent transaction must have in order to be used as an input.  When sending from a zaddr, minconf must be greater than zero.<br><br>Optionally set a transaction fee, which by default is 0.0001 HUSH.<br><br>Any transparent change will be sent to a new transparent address.  Any private change will be sent back to the zaddr being used as the source of funds.<br><br>Returns an operationid.  You use the operationid value with z_getoperationstatus and z_getoperationresult to obtain the result of sending funds, which if successful, will be a txid.
z_shieldcoinbase<br> | fromaddress toaddress [fee=0.0001] [limit=50] | _This is an Asynchronous RPC call_<br><br>Shield transparent coinbase funds by sending to a shielded z address.  Utxos selected for shielding will be locked.  If there is an error, they are unlocked.  The RPC call `listlockunspent` can be used to return a list of locked utxos.<br><br>The number of coinbase utxos selected for shielding can be set with the limit parameter, which has a default value of 50.  If the parameter is set to 0, the number of utxos selected is limited by the `-mempooltxinputlimit` option.  Any limit is constrained by a consensus rule defining a maximum transaction size of 100000 bytes.  <br><br>The from address is a taddr or "*" for all taddrs belonging to the wallet.  The to address is a zaddr. The default fee is 0.0001.<br><br>Returns an object containing an operationid which can be used with z_getoperationstatus and z_getoperationresult, along with key-value pairs regarding how many utxos are being shielded in this transaction and what remains to be shielded.

### Operations

Asynchronous calls return an OperationStatus object which is a JSON object with the following defined key-value pairs:

* operationid : unique identifier for the async operation.  Use this value with z_getoperationstatus or z_getoperationresult to poll and query the operation and obtain its result.
* status : current status of operation
  * queued : operation is pending execution
  * executing : operation is currently being executed
  * cancelled
  * failed.
  * success
* result : result object if the status is ‘success’.  The exact form of the result object is dependent on the call itself.
* error: error object if the status is ‘failed’. The error object has the following key-value pairs:
  * code : number
  * message: error message

Depending on the type of asynchronous call, there may be other key-value pairs.  For example, a z_sendmany operation will also include the following in an OperationStatus object:

* method : name of operation e.g. z_sendmany
* params : an object containing the parameters to z_sendmany

Currently, as soon as you retrieve the operation status for an operation which has finished, that is it has either succeeded, failed, or been cancelled, the operation and any associated information is removed.

It is currently not possible to cancel operations.

Command | Parameters | Description
--- | --- | ---
z_getoperationresult <br>| [operationids] | Return OperationStatus JSON objects for all completed operations the node is currently aware of, and then remove the operation from memory.<br><br>Operationids is an optional array to filter which operations you want to receive status objects for.<br><br>Output is a list of operation status objects, where the status is either "failed", "cancelled" or "success".<br>[<br>{“operationid”: “opid-11ee…”,<br>“status”: “cancelled”},<br>{“operationid”: “opid-9876”, “status”: ”failed”},<br>{“operationid”: “opid-0e0e”,<br>“status”:”success”,<br>“execution_time”:”25”,<br>“result”: {“txid”:”af3887654…”,...}<br>},<br>]<br><br> Examples:<br>hush-cli z_getoperationresult '["opid-8120fa20-5ee7-4587-957b-f2579c2d882b"]'<br> hush-cli z_getoperationresult
z_getoperationstatus <br>| [operationids] | Return OperationStatus JSON objects for all operations the node is currently aware of.<br><br>Operationids is an optional array to filter which operations you want to receive status objects for.<br><br>Output is a list of operation status objects.<br>[<br>{“operationid”: “opid-12ee…”,<br>“status”: “queued”},<br>{“operationid”: “opd-098a…”, “status”: ”executing”},<br>{“operationid”: “opid-9876”, “status”: ”failed”}<br>]<br><br>When the operation succeeds, the status object will also include the result.<br><br>{“operationid”: “opid-0e0e”,<br>“status”:”success”,<br>“execution_time”:”25”,<br>“result”: {“txid”:”af3887654…”,...}<br>}
z_listoperationids <br>| [state] | Return a list of operationids for all operations which the node is currently aware of.<br><br>State is an optional string parameter to filter the operations you want listed by their state.  Acceptable parameter values are ‘queued’, ‘executing’, ‘success’, ‘failed’, ‘cancelled’.<br><br>[“opid-0e0e…”, “opid-1af4…”, … ]

## Asynchronous RPC call Error Codes

Hush error codes are defined in https://git.hush.is/hush/hush3/src/branch/master/src/rpc/protocol.h

### z_sendmany error codes

RPC_INVALID_PARAMETER (-8) | _Invalid, missing or duplicate parameter_
---------------------------| -------------------------------------------------
"Minconf cannot be zero when sending from zaddr" | Cannot accept minimum confirmation value of zero when sending from zaddr.
"Minconf cannot be negative" | Cannot accept negative minimum confirmation number.
"Minimum number of confirmations cannot be less than 0" | Cannot accept negative minimum confirmation number.
"From address parameter missing" | Missing an address to send funds from.
"No recipients" | Missing recipient addresses.
"Memo must be in hexadecimal format" | Encrypted memo field data must be in hexadecimal format.
"Memo size of __ is too big, maximum allowed is __ " | Encrypted memo field data exceeds maximum size of 512 bytes.
"From address does not belong to this node, zaddr spending key not found." | Sender address spending key not found.
"Invalid parameter, expected object" | Expected object.
"Invalid parameter, unknown key: __" | Unknown key.
"Invalid parameter, expected valid size" | Invalid size.
"Invalid parameter, expected hex txid" | Invalid txid.
"Invalid parameter, vout must be positive" | Invalid vout.
"Invalid parameter, duplicated address" | Address is duplicated.
"Invalid parameter, amounts array is empty" | Amounts array is empty.
"Invalid parameter, unknown key" | Key not found.
"Invalid parameter, unknown address format" | Unknown address format.
"Invalid parameter, size of memo" | Invalid memo field size.
"Invalid parameter, amount must be positive" | Invalid or negative amount.
"Invalid parameter, too many zaddr outputs" | z_address outputs exceed maximum allowed.
"Invalid parameter, expected memo data in hexadecimal format" | Encrypted memo field is not in hexadecimal format.
"Invalid parameter, size of memo is larger than maximum allowed __ " | Encrypted memo field data exceeds maximum size of 512 bytes.


RPC_INVALID_ADDRESS_OR_KEY (-5) | _Invalid address or key_
--------------------------------| ---------------------------
"Invalid from address, no spending key found for zaddr" | z_address spending key not found.
"Invalid output address, not a valid taddr."            | Transparent output address is invalid.
"Invalid from address, should be a taddr or zaddr."     | Sender address is invalid.
"From address does not belong to this node, zaddr spending key not found."  | Sender address spending key not found.


RPC_WALLET_INSUFFICIENT_FUNDS (-6) | _Not enough funds in wallet or account_
-----------------------------------| ------------------------------------------
"Insufficient funds, no UTXOs found for taddr from address." | Insufficient funds for sending address.
"Could not find any non-coinbase UTXOs to spend. Coinbase UTXOs can only be sent to a single zaddr recipient." | Must send Coinbase UTXO to a single z_address.
"Could not find any non-coinbase UTXOs to spend." | No available non-coinbase UTXOs.
"Insufficient funds, no unspent notes found for zaddr from address." | Insufficient funds for sending address.
"Insufficient transparent funds, have __, need __ plus fee __" | Insufficient funds from transparent address.
"Insufficient protected funds, have __, need __ plus fee __" | Insufficient funds from shielded address.

RPC_WALLET_ERROR (-4) | _Unspecified problem with wallet_
----------------------| -------------------------------------
"Could not find witness for note commitment" | Try restarting node with `-rescan`.
"Witness for note commitment is null" | Missing witness for note commitment.
"Witness for spendable note does not have same anchor as change input" | Invalid anchor for spendable note witness.
"Not enough funds to pay miners fee" | Retry with sufficient funds.
"Missing hex data for raw transaction" | Raw transaction data is null.
"Missing hex data for signed transaction" | Hex value for signed transaction is null.
"Send raw transaction did not return an error or a txid." |

RPC_WALLET_ENCRYPTION_FAILED (-16)                                       | _Failed to encrypt the wallet_
-------------------------------------------------------------------------| -------------------------------------
"Failed to sign transaction"                                             | Transaction was not signed, sign transaction and retry.

RPC_WALLET_KEYPOOL_RAN_OUT (-12)                                         | _Keypool ran out, call keypoolrefill first_
-------------------------------------------------------------------------| -----------------------------------------------
"Could not generate a taddr to use as a change address"                  | Call keypoolrefill and retry.
