BIP 0022

  BIP: TBD
  Title: getmemorypool
  Author: Luke Dashjr <luke+bipgmp@dashjr.org>
  Status: Draft
  Type: Standards Track
  Created: 28-02-2012

Abstract

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.

Specification

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
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.
curtime	Number	TODO?
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)
maxtime	Number	the maximum time allowed
maxtimeoff	Number	the maximum time allowed (as a moving offset from 'time')
mintime	Number	the minimum time allowed
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")

Mutations

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
transactions	add or remove transactions (both of the above)
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

Motivation

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

• https://gitorious.org/bitcoin/eloipool
• bitcoind