BIP 0022

  BIP: 22
  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	Required	Type	Description
bits	Yes	String	the big-endian compressed difficulty in hexadecimal
curtime	Yes	Number	the current time as seen by the server (recommended for block time)
height	Should	Number	the height of the block we are looking for
previousblockhash	Yes	String	the hash of the previous block, in little endian converted to hexadecimal
transactions	Should	Array of Strings	Bitcoin transactions encoded in hexadecimal (byte-for-byte), not including coinbase
version	Yes	Number	always 1 (at least for bitcoin)
coinbasetxn	or ↓	String	hexadecimal byte-for-byte coinbase transaction
coinbasevalue	or ↑	Number	total funds available for the coinbase
coinbaseaux	No	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	No	Number	how many seconds (beginning from when the server sent the response) this work is valid for, at most
fulltarget	No	String	the number which full results should be less than, in little-endian hexadecimal (see "share/*" mutations)
longpoll	No	String	URI for long polling
maxtime	No	Number	the maximum time allowed
maxtimeoff	No	Number	the maximum time allowed (as a moving offset from "curtime" - every second, the actual maxtime is incremented by 1; for example, "maxtimeoff":0 means "time" may be incremented by 1 every second)
mintime	No	Number	the minimum time allowed
mintimeoff	No	Number	the minimum time allowed (as a moving offset from "curtime")
mutable	No	Array of Strings	different manipulations that the server explicitly allows to be made (see Mutations)
noncerange	No	String	two 32-bit integers, concatenated in big-endian hexadecimal, which represent the valid ranges of nonces the miner may scan
submitold	No	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
target	No	String	the number which valid results must be less than, in little-endian hexadecimal
txrequired	No	Number	this many of the first transactions provided must be present in the final block, even if the "transactions/remove" mutation is allowed
workid	No	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 (implied if "coinbasetxn" omitted)
generation	add or remove outputs from the coinbase/generation transaction (implied if "coinbasetxn" omitted)
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"
time/increment	change the time header to a value after "time" (implied if "maxtime" or "maxtimeoff" are provided)
time/decrement	change the time header to a value before "time" (implied if "mintime" is provided)
time	modify the time header of the block
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; implied if "transactions" omitted from result)
prevblock	use the work with other previous-blocks; this implicitly allows removing transactions that are no longer valid, unless they are part of the "txrequired" count; it also implies adjusting "height" as necessary

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

Long Polling

If the server supports long polling, it SHOULD include the "longpoll" key with a relative or absolute URI. The absolute URI MAY specify a different port than the original connection. Miners MAY start a request to this long polling URI with a standard JSON-RPC request (POST with data) and same basic authorization. This request SHOULD NOT be processed nor answered by the server until it wishes to replace the current block data. Clients SHOULD make this request with a very long request timeout and MUST accept the server sending response headers with "chunked" Transfer-Encoding delaying the completion of the final JSON response.

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.

If a client receives an incomplete or invalid response, it SHOULD retry the request with an exponential backoff. Clients MAY implement this backoff with limitations (such as maximum backoff time) or any algorithm as deemed suitable. It is however forbidden to simply retry immediately with no delay after more than one failure. In the case of a "Forbidden" response (for example, HTTP 403), a client SHOULD NOT attempt to retry without user intervention.

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 rejected, 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

• Eloipool
• bitcoind