# 6. Job Declaration Protocol
The Job Declaration Protocol is used to coordinate the creation of custom work, avoiding scenarios where Pools are unilaterally imposing work on miners.
Pools that opt into this protocol are only responsible for accounting shares and distributing rewards.
This is a key feature of Stratum V2 that improves Bitcoin decentralization.
# 6.1 Job Declarator Server
The Job Declarator Server (JDS) is deployed on Pool side, although it could be theoretically outsourced to a third party that is trusted by the Pool.
In order to fully implement the Server side of the Job Declaration Protocol, the JDS also needs to exchange RPCs (or similar) with a Bitcoin Node.
It is responsible for:
- Allocating tokens that JDC will use to declare Custom Jobs.
- Acknowledging declaration of Custom Jobs associated with specific allocated tokens.
- Maintaining an internal mempool (via RPCs (or similar) to a Bitcoin Node).
- Requesting identification for transactions on some declared Custom Job.
- Requesting missing transactions on some declared Custom Job.
- Publishing valid block submissions received from JDC.
# 6.2 Job Declarator Client
The Job Declarator Client (JDC) is deployed on the miner side.
In order to fully implement the Client side of the Job Declaration Protocol, the JDC also needs to operate under the Template Distribution and Mining Protocols.
It is responsible for:
- Receiving Templates from the Template Provider (via Template Distribution Protocol).
- Declaring Custom Jobs to JDS (via Job Declaration Protocol under Full-Template mode).
- Notifying declared Custom Jobs to Pool (via Mining Protocol).
- Receiving Shares from downstream Mining Devices working on Custom Jobs (via Mining Protocol).
- Submitting Shares for Custom Jobs to Pool.
- Publishing valid blocks found by downstream Mining Devices (both to Template Provider (TP) and JDS).
Additionally, if:
- JDS fails to respond with an
AllocateMiningJobToken.Successin a reasonable time. - JDS rejects some Custom Job declaration via
DeclareMiningJob.Error. - Pool rejects valid shares under a Custom Job that was previously acknowledged via
SetCustomMiningJob.Successand/orDeclareMiningJob.Success.
JDC is also responsible for switching to a new Pool+JDS (or solo mining as a last resort).
This fallback strategy incentivizes honesty on Pool side, otherwise it will lose hashrate by rejecting Shares for a Custom Job that was already acknowledged to be valid.
# 6.3 Job Declaration Modes
# 6.3.1 Coinbase-only Mode
Under Coinbase-only mode:
- JDS allocates
mining_job_tokento JDC (AllocateMiningJobToken/AllocateMiningJobToken.Success). - Pool evaluates fee revenue of some proposed work (uniquely identified by
mining_job_token) by looking at the coinbase. - JDC never reveals the tx data contained in the template (in other words, the transaction set).
- proposed work is acknowledged as valid by Pool via
SetCustomMiningJob.Success. - the
DeclareMiningJobmessage is never used. - if a valid block is found, JDC propagates it unilaterally.
In other words, Pool + JDS operating under Coinbase-only mode do not require to ever know which transactions are included in the miner template, preserving the privacy around the miner's mempool.
This leaves Pool arguably vulnerable to an attack where miner declares a coinbase with some fee revenue while one of the following situations is true:
- the template actually has a different fee revenue.
- the template has invalid transactions.
This potential attack vector is in many ways identical to block withholding and defenses against block withholding generally apply.
Some pools may wish to utilize additional mitigations. For example, Zero-Knowledge-Proof based protocol extensions, where JDC proves that the fee revenue on the coinbase belongs to a valid template, without ever revealing the template itself.
As soon as JDC has:
- a token (allocated by JDS), so it can use it to identify some unique work that it wants to advertise
- a new template
It SHOULD start sending the jobs downstream for hashing right away. The proof-of-work (shares) SHOULD be cached until JDC receives an acknowledgement via SetCustomMiningJob.Success.
We call this optimistic mining.
# 6.3.2 Full-Template Mode
Under Full-Template mode:
- JDS allocates
mining_job_tokento JDC (AllocateMiningJobToken/AllocateMiningJobToken.Success). - JDC sends
DeclareMiningJobto JDS (containing thetxidof every transaction in the template). - JDS could potentially request for JDC to reveal
txdata(viaProvideMissingTransactions). - JDS acknowledges proposed work via
DeclareMiningJob.Success. - JDC notifies work to Pool via
SetCustomMiningJob, acknowledged viaSetCustomMiningJob.Success. - if a valid block is found, both JDC and JDS propagate it.
Similarly to Coinbase-only, as soon as JDC has:
- a token (allocated by JDS), so it can use it to identify some unique work that it wants to advertise
- a new template
It SHOULD do optimistic mining by sending the jobs downstream for hashing right away. The proof-of-work (shares) SHOULD be cached until JDC receives an acknowledgement via SetCustomMiningJob.Success.
# 6.3.3 Coinbase-only vs Full-Template
The table below shows a comparison between the two Sv2 Job Declation Modes:
| Coinbase-only | Full-Template | |
|---|---|---|
| knowledge of fee revenue | • JDC • Pool (while blind against tx data) | • JDC • Pool (while blind against tx data) • JDS (verifying against revealed tx data on behalf of Pool) |
| knowledge of txdata on the template | • JDC | • JDC • JDS (on behalf of Pool) |
| ability to broadcast mined block | • JDC | • JDC • JDS (on behalf of Pool) |
# 6.4 Job Declaration Protocol Messages
# 6.4.1 SetupConnection Flags for Job Declaration Protocol
Flags usable in SetupConnection.flags and SetupConnection.Error::flags:
| Field Name | Bit | Description |
|---|---|---|
| DECLARE_TX_DATA | 0 | JDC agrees to reveal the template's txdata via DeclareMiningJob and ProvideMissingTransactions. |
No flags are yet defined for use in SetupConnection.Success.
# 6.4.2 AllocateMiningJobToken (JDC -> JDS)
A request to get an identifier for a future-submitted mining job.
Rate limited to a rather slow rate and only available on connections where this has been negotiated. Otherwise, only mining_job_token(s) from AllocateMiningJobToken.Success are valid.
| Field Name | Data Type | Description |
|---|---|---|
| user_identifier | STR0_255 | Unconstrained sequence of bytes. Whatever is needed by the pool to identify/authenticate the client, e.g. "braiinstest". Additional restrictions can be imposed by the pool. It is highly recommended that UTF-8 encoding is used. |
| request_id | U32 | Unique identifier for pairing the response |
# 6.4.3 AllocateMiningJobToken.Success (Server -> Client)
The Server MUST NOT change the value of coinbase_output_max_additional_size in AllocateMiningJobToken.Success messages unless required for changes to the pool’s configuration.
Notably, if the pool intends to change the space it requires for coinbase transaction outputs regularly, it should simply prefer to use the maximum of all such output sizes as the coinbase_output_max_additional_size value.
| Field Name | Data Type | Description |
|---|---|---|
| request_id | U32 | Unique identifier for pairing the response |
| mining_job_token | B0_255 | Token that makes the client eligible for committing a mining job for approval/transaction declaration or for identifying custom mining job on mining connection. |
| coinbase_output_max_additional_size | U32 | The maximum additional serialized bytes which the pool will add in coinbase transaction outputs. See discussion in the Template Distribution Protocol's CoinbaseOutputConstraints message for more details. |
| coinbase_output_max_additional_sigops | U16 | The maximum additional sigops which the pool will add in coinbase transaction outputs. See discussion in the Template Distribution Protocol's CoinbaseOutputConstraints message for more details. |
| coinbase_tx_outputs | B0_64K | Bitcoin transaction outputs added by the pool |
# 6.4.4 DeclareMiningJob (Client -> Server)
Only used in Full-Template mode.
A request sent by JDC that proposes a selected set of transactions to JDS.
| Field Name | Data Type | Description |
|---|---|---|
| request_id | U32 | Unique identifier for pairing the response |
| mining_job_token | B0_255 | Previously reserved mining job token received by AllocateMiningJobToken.Success |
| version | U32 | Version header field. To be later modified by BIP320-consistent changes. |
| prev_hash | U256 | Optional. Contains the chain tip that the template is based on. JDS SHOULD accept templates based on different tips, as long as they are on the best block height and don't contain double spends. |
| coinbase_tx_prefix | B0_64K | Serialized bytes representing the initial part of the coinbase transaction (not including extranonce) |
| coinbase_tx_suffix | B0_64K | Serialized bytes representing the final part of the coinbase transaction (after extranonce) |
| tx_ids_list | SEQ0_64K[U256] | List of hashes of the transaction set contained in the template. JDS checks the list against its mempool and requests missing txs via ProvideMissingTransactions. Does not include the coinbase transaction (as there is no corresponding full data for it yet). |
| excess_data | B0_64K | Extra data which the Pool may require to validate the work (as defined in the Template Distribution Protocol) |
# 6.4.5 DeclareMiningJob.Success (Server -> Client)
A response sent by JDS acknowledging some Custom Job declaration.
JDS MAY request txdata via ProvideMissingTransactions before making this commitment.
Since JDS could be third party (not necessarily integrated to Pool), DeclareMiningJob.Success.new_mining_job_token MAY carry a cryptographic commitment from JDS where:
- JDS acknowledges that the template declared under
DeclareMiningJob.mining_job_tokenis valid - it signals to JDC that it should use
SetCustomMininingJob.mining_job_token = DeclareMiningJob.Success.new_mining_job_tokenwhen declaring Custom Jobs to Pool as a way to prove it went through the Full-Template declaration process
| Field Name | Data Type | Description |
|---|---|---|
| request_id | U32 | Identifier of the original request. |
| new_mining_job_token | B0_255 | Unique custom work identifier. |
# 6.4.6 DeclareMiningJob.Error (Server->Client)
A response sent by JDS rejecting some Custom Job declaration.
This should be a trigger for fallback into some other Pool+JDS or solo mining.
| Field Name | Data Type | Description |
|---|---|---|
| request_id | U32 | Identifier of the original request |
| error_code | STR0_255 | |
| error_details | B0_64K | Optional data providing further details to given error |
Possible error codes:
invalid-mining-job-tokeninvalid-job-param-value-{}-{}is replaced by a particular field name fromDeclareMiningJobmessage
# 6.4.7 ProvideMissingTransactions (Server->Client)
Only used in Full-Template mode.
If DeclareMiningJob includes some transactions that JDS's mempool has not yet seen, then JDS needs to request that JDC provides those missing ones.
| Field Name | Data Type | Description |
|---|---|---|
| request_id | U32 | Identifier of the original AllocateMiningJobToken request |
| unknown_tx_position_list | SEQ0_64K[U16] | A list of unrecognized transactions that need to be supplied by the Job Declarator in full. They are specified by their position in the original DeclareMiningJob message, 0-indexed not including the coinbase transaction transaction. |
# 6.4.8 ProvideMissingTransactions.Success (Client->Server)
This is a message to push transactions that the server did not recognize and requested them to be supplied in ProvideMissingTransactions.
| Field Name | Data Type | Description |
|---|---|---|
| request_id | U32 | Identifier of the original AllocateMiningJobToken request "" |
| transaction_list | SEQ0_64K[B0_16M] | List of full transactions as requested by ProvideMissingTransactions, in the order they were requested in ProvideMissingTransactions |
# 6.4.9 PushSolution (Client -> Server)
Only used in Full-Template mode.
Sent by JDC as soon as a valid block is found, so that it can be propagated also by JDS.
In the meantime, the block is also transmitted to the network by JDC through the SubmitSolution message under in Template Distribution Protocol.
In this way, a valid solution is immediately propagated on both client and server sides, decreasing the chance of the block being orphaned by the network.
| Field Name | Data Type | Description |
|---|---|---|
| extranonce | B0_32 | Extranonce bytes which need to be added to coinbase to form a fully valid submission. (This is the full extranonce) |
| prev hash | U256 | Hash of the last block |
| nonce | U32 | Nonce leading to the hash being submitted |
| ntime | U32 | The nTime field in the block header. |
| nbits | U32 | The nBits field in the block header. |
| version | U32 | Version header field. |