BIP: 22 Layer: API/RPC Title: getblocktemplate - Fundamentals Author: Luke Dashjr <luke+bip22@dashjr.org> Comments-Summary: No comments yet. Status: Final Dash-Status: Modified Active Type: Standards Track Created: 2012-02-28 License: BSD-2-Clause
This BIP describes a new JSON-RPC method for "smart" miners and proxies. Instead of sending a simple block header for hashing, the entire block structure is sent, and left to the miner to (optionally) customize and assemble.
This BIP is licensed under the BSD 2-clause license.
A JSON-RPC method is defined, called "getblocktemplate". It accepts exactly one argument, which MUST be an Object of request parameters. If the request parameters include a "mode" key, that is used to explicitly select between the default "template" request or a "proposal".
Block template creation can be influenced by various parameters:
| template request | |||
|---|---|---|---|
| Key | Required | Type | Description |
| capabilities | No | Array of Strings | SHOULD contain a list of the following, to indicate client-side support: "longpoll", "coinbasetxn", "coinbasevalue", "proposal", "serverlist", "workid", and any of the mutations |
| mode | No | String | MUST be "template" or omitted |
getblocktemplate MUST return a JSON Object containing the following keys:
| template | |||
|---|---|---|---|
| Key | Required | Type | Description |
| bits | Yes | String | the compressed difficulty in hexadecimal |
| curtime | Yes | Number | the current time as seen by the server (recommended for block time) - note this is not necessarily the system clock, and must fall within the mintime/maxtime rules |
| height | Yes | Number | the height of the block we are looking for |
| previousblockhash | Yes | String | the hash of the previous block, in big-endian hexadecimal |
| sigoplimit | No | Number | number of sigops allowed in blocks |
| sizelimit | No | Number | number of bytes allowed in blocks |
| transactions | Should | Array of Objects | Objects containing information for transactions (excluding coinbase) |
| version | Yes | Number | always 1 or 2 (at least for bitcoin) - clients MUST understand the implications of the version they use (eg, comply with BIP 0034 for version 2) |
| coinbaseaux | No | Object | data that SHOULD be included in the coinbase's scriptSig content. Only the values (hexadecimal byte-for-byte) in this Object should be included, not the keys. This does not include the block height, which is required to be included in the scriptSig by BIP 0034. It is advisable to encode values inside "PUSH" opcodes, so as to not inadvertently expend SIGOPs (which are counted toward limits, despite not being executed). |
| coinbasetxn | this or ↓ | Object | information for coinbase transaction |
| coinbasevalue | this or ↑ | Number | total funds available for the coinbase (in duffs - 1/100,000,000 DASH) |
| workid | No | String | if provided, this value must be returned with results (see Block Submission) |
| masternode | Yes | Object | Object containing required masternode payee that must be included in the next block (see Masternode Payee information) |
| masternode_payments_started | Yes | Boolean | True, if masternode payments started |
| masternode_payments_enforced | Yes | Boolean | True, if masternode payments are enforced |
| superblock | Yes | Array | Objects containing required superblock payees that must be included in the next block (see Superblock payee information) |
| superblocks_started | Yes | Boolean | True, if superblock payments started |
| superblocks_enforced | Yes | Boolean | True, if superblock payments are enabled |
The Objects listed in the response's "transactions" key contains these keys:
| template "transactions" element | ||
|---|---|---|
| Key | Type | Description |
| data | String | transaction data encoded in hexadecimal (byte-for-byte) |
| depends | Array of Numbers | other transactions before this one (by 1-based index in "transactions" list) that must be present in the final block if this one is; if key is not present, dependencies are unknown and clients MUST NOT assume there aren't any |
| fee | Number | difference in value between transaction inputs and outputs (in Duffs); for coinbase transactions, this is a negative Number of the total collected block fees (ie, not including the block subsidy); if key is not present, fee is unknown and clients MUST NOT assume there isn't one |
| hash | String | hash/id encoded in little-endian hexadecimal |
| required | Boolean | if provided and true, this transaction must be in the final block |
| sigops | Number | total number of SigOps, as counted for purposes of block limits; if key is not present, sigop count is unknown and clients MUST NOT assume there aren't any |
Only the "data" key is required, but servers should provide the others if they are known.
The Object listed in the response's "masternode" key contains these keys:
| template "masternode" element | ||
|---|---|---|
| Key | Type | Description |
| payee | String | Payee address |
| script | String | Payee scriptPubKey |
| amount | Number | Required amount to pay |
The Objects listed in the response's "superblock" key contains these keys:
| template "superblock" element | ||
|---|---|---|
| Key | Type | Description |
| payee | String | Payee address |
| script | String | Payee scriptPubKey |
| amount | Number | Required amount to pay |
A JSON-RPC method is defined, called "submitblock", to submit potential blocks (or shares). It accepts two arguments: the first is always a String of the hex-encoded block data to submit; the second is an Object of parameters, and is optional if parameters are not needed.
| submitblock parameters (2nd argument) | ||
|---|---|---|
| Key | Type | Description |
| workid | String | if the server provided a workid, it MUST be included with submissions |
This method MUST return either null (when a share is accepted), a String describing briefly the reason the share was rejected, or an Object of these with a key for each merged-mining chain the share was submitted to.
| template request | ||
|---|---|---|
| Key | Type | Description |
| capabilities | Array of Strings | miners which support long polling SHOULD provide a list including the String "longpoll" |
| longpollid | String | "longpollid" of job to monitor for expiration; required and valid only for long poll requests |
| template | ||
|---|---|---|
| Key | Type | Description |
| longpollid | String | identifier for long poll request; MUST be omitted if the server does not support long polling |
| longpolluri | String | if provided, an alternate URI to use for long poll requests |
| submitold | Boolean | only relevant for long poll responses: indicates if work received prior to this response remains potentially valid (default) and should have its shares submitted; if false, the miner may wish to discard its share queue |
If the server supports long polling, it MUST include a "longpollid" key in block templates, and it MUST be unique for each event: any given "longpollid" should check for only one condition and not be reused. For example, a server which has a long poll wakeup only for new blocks might use the previous block hash. However, clients should not assume the "longpollid" has any specific meaning. It MAY supply the "longpolluri" key with a relative or absolute URI, which MAY specify a completely different resource than the original connection, including port number. If "longpolluri" is provided by the server, clients MUST only attempt to use that URI for longpoll requests.
Clients MAY start a longpoll request with a standard JSON-RPC request (in the case of HTTP transport, POST with data) and same authorization, setting the "longpollid" parameter in the request to the value provided by the server.
This request SHOULD NOT be processed nor answered by the server until it wishes to replace the current block data as identified by the "longpollid". Clients SHOULD make this request with a very long request timeout and MUST accept servers sending a partial response in advance (such as HTTP headers with "chunked" Transfer-Encoding), and only delaying the completion of the final JSON response until processing.
Upon receiving a completed response:
- Only if "submitold" is provided and false, the client MAY discard the results of past operations and MUST begin working on the new work immediately.
- The client SHOULD begin working on the new work received as soon as possible, if not immediately.
- The client SHOULD make a new request to the same long polling URI.
| template request | ||
|---|---|---|
| Key | Type | Description |
| sigoplimit | Number or Boolean | maximum number of sigops to include in template |
| sizelimit | Number or Boolean | maximum number of bytes to use for the entire block |
| maxversion | Number | highest block version number supported |
For "sigoplimit" and "sizelimit", negative values and zero are offset from the server-determined block maximum. If a Boolean is provided and true, the default limit is used; if false, the server is instructed not to use any limits on returned template. Servers SHOULD respect these desired maximums, but are NOT required to: clients SHOULD check that the returned template satisfies their requirements appropriately.
Possible reasons a share may be rejected include, but are not limited to:
| share rejection reasons | |
|---|---|
| Reason | Description |
| bad-cb-amount | the coinbase amount was invalid |
| bad-cb-length | the coinbase was too long (Dash limit is 100 bytes) |
| bad-cb-payee | invalid masternode or superblock payee |
| bad-cb-missing | first transaction is not a coinbase |
| bad-cb-multiple | more than one coinbase |
| bad-diffbits | "bits" were changed |
| bad-prevblk | the previous-block is not the one the server intends to build on |
| bad-txnmrklroot | the block header's merkle root did not match the transaction merkle tree |
| bad-txns-BIP30 | tried to overwrite older unspent transaction (BIP34 makes this impossible) |
| bad-txns-inputs-missingorspent | inputs missing or already spent |
| bad-txns-inputs-nonfinal | contains a non-BIP68-final transaction |
| bad-txns-duplicate | duplicate transaction |
| bad-version | the version was wrong |
| duplicate | the server already processed this block data |
| high-hash | the block header did not hash to a value lower than the specified target |
| rejected | a generic rejection without details |
| time-too-new | the time was too far in the future |
| time-too-old | the time was too far in the past |
bitcoind's JSON-RPC server can no longer support the load of generating the work required to productively mine, and external software specializing in work generation has become necessary. At the same time, new independent node implementations are maturing to the point where they will also be able to support miners.
A common standard for communicating block construction details is necessary to ensure compatibility between the full nodes and work generation software.
Why not just deal with transactions as hashes (txids)?
- Servers might not have access to the transaction database, or miners may wish to include transactions not broadcast to the network as a whole.
- Miners may opt not to do full transaction verification, and may not have access to the transaction database on their end.
- If servers allow all mutations, it may be hard to identify which job it is based on. While it may be possible to verify the submission by its content, it is much easier to compare it to the job issued. It is very easy for the miner to keep track of this. Therefore, using a "workid" is a very cheap solution to enable more mutations.
- Due to the BIP 0016 changes regarding rules on block sigops, it is impossible to count sigops from the transactions themselves (the sigops in the scriptCheck must also be included in the count).
- Add Dash specific masternode / superblock template items
- Updated example rejection reasons