BIP 0022

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  Title: getmemorypool
  Author: Luke Dashjr <>
  Status: Draft
  Type: Standards Track
  Created: 28-02-2012


This BIP describes a new JSON-RPC method for "smart" Bitcoin 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.


JSON-RPC Method: getmemorypool

A new JSON-RPC method is defined, called "getmemorypool". It takes no arguments. If arguments are provided, it may wrap the "submitblock" JSON-RPC method (described later), cast to a Boolean return value (true = share accepted).

getmemorypool MUST return a JSON Object containing at least the following keys, all of which relate to the block header:

Key Type Description
bits String the big-endian compressed difficulty in hexadecimal
curtime Number TODO?
mintime Number the minimum time allowed
previousblockhash String the hash of the previous block, in little endian converted to hexadecimal
time Number the recommended time
version Number always 1 (at least for bitcoin)

Additionally, getmemorypool SHOULD return a "transactions" key, which is an Array of Strings of Bitcoin transactions encoded in hexadecimal (byte-for-byte). The coinbase transaction is not included in this Array.

At least one of "coinbasevalue" (a Number of total funds available for the coinbase) or "coinbasetxn" (hexadecimal byte-for-byte coinbase transaction) must also be included.

Optional keys:

Key Type Description
coinbaseaux Object data that SHOULD or MUST (depending on mutable flags) be included in the coinbase's scriptSig content. Only the values (hexadecimal byte-for-byte) in this Object should be included, not the keys.
expires Number how many seconds (beginning from when the server sent the response) this work is valid for, at most
fulltarget String the number which full results should be less than, in little-endian hexadecimal (see "share/*" mutations)
mutable Array of Strings different manipulations that the server explicitly allows to be made (see later for details)
noncerange String two 32-bit integers, concatenated in big-endian hexadecimal, which represent the valid ranges of nonces the miner may scan
target String the number which valid results must be less than, in little-endian hexadecimal
transactionsrequired Number this many of the first transactions provided must be present in the final block, even if the "transactions/remove" mutation is allowed
workid String or Number if provided, this value must be returned with results (see "submitblock")


Any of these may be listed in the "mutable" key to signify modifications the miner is allowed to make:

Value Significance
coinbase/append append the provided coinbase scriptSig
coinbase provide their own coinbase; if one is provided, it may be replaced or modified
generation add or remove outputs from the coinbase/generation transaction
share/merkle if the block hash is less than "target", but not less than "fulltarget", only return the block header, coinbase transaction, and merkle tree connecting that transaction to the root (in the form of repeated right-side SHA256 hashes) in "submitblock"
share/truncate if the block hash is less than "target", but not less than "fulltarget", only return the block header in "submitblock"
transactions/add add other valid transactions to the block
transactions/remove remove transactions provided by the server
prevblock use the work with other previous-blocks; this implicitly allows removing transactions that are no longer valid, unless they are part of the "transactionsrequired" count

Note that miners are NOT required to implement any of these mutations.

JSON-RPC Method: submitblock

A new JSON-RPC method is defined, called "submitblock". It takes one to two arguments. The first argument is the block data; this may be truncated or merkle-ified depending on the "share/truncate" or "share/merkle" mutations, respectively. The second argument, if provided, is an Object. The only defined key of this Object is the "workid" provided by the server: if a "workid" was specified, it must be submitted with the share/block.

This method MUST return either null (when a share is accepted), a String describing briefly the reason the share was accepted, or an Object of these with a key for each merged-mining chain the share was submitted to.

Possible reasons a share may be rejected include, but are not limited to:

Reason Description
bad-cb-flag the server detected a feature-signifying flag that it does not allow
bad-cb-length the coinbase was too long (bitcoin limit is 100 bytes)
bad-cb-prefix the server only allows appending to the coinbase, but it was modified beyond that
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 the server didn't like something about the transactions in the block
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
stale-prevblk the previous-block is no longer the one the server intends to build on
stale-work the work this block was based on is no longer accepted
time-invalid the time was not acceptable
time-too-new the time was too far in the future
time-too-old the time was too far in the past
unknown-user the user submitting the block was not recognized
unknown-work the template or workid could not be identified


There is reasonable concerns about mining currently being too centralized on pools, and the amount of control these pools hold. By exposing the details of the block proposals to the miners, they are enabled to audit and possibly modify the block before hashing it.

There is also a very minor load reduction on the pool server, since it does not need to calculate SHA256 for the block's merkle tree.

Reference Implementation