mirror of
https://github.com/bitcoin/bips.git
synced 2024-11-19 01:40:05 +01:00
107 lines
5.1 KiB
Plaintext
107 lines
5.1 KiB
Plaintext
<pre>
|
|
BIP: 64
|
|
Layer: Peer Services
|
|
Title: getutxo message
|
|
Author: Mike Hearn <hearn@vinumeris.com>
|
|
Comments-Summary: No comments yet.
|
|
Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0064
|
|
Status: Obsolete
|
|
Type: Standards Track
|
|
Created: 2014-06-10
|
|
</pre>
|
|
|
|
==Abstract==
|
|
|
|
This document describes a small P2P protocol extension that performs UTXO lookups given a set of outpoints.
|
|
|
|
==Motivation==
|
|
|
|
All full Bitcoin nodes maintain a database called the unspent transaction output set. This set is
|
|
how double spending is checked for: to be valid a transaction must identify unspent outputs in this
|
|
set using an identifier called an "outpoint", which is merely the hash of the output's containing
|
|
transaction plus an index.
|
|
|
|
The ability to query this can sometimes be useful for a lightweight/SPV client which does not have
|
|
the full UTXO set at hand. For example, it can be useful in applications implementing assurance
|
|
contracts to do a quick check when a new pledge becomes visible to test whether that pledge was
|
|
already revoked via a double spend. Although this message is not strictly necessary because e.g.
|
|
such an app could be implemented by fully downloading and storing the block chain, it is useful for
|
|
obtaining acceptable performance and resolving various UI cases.
|
|
|
|
Another example of when this data can be useful is for performing floating fee calculations in an
|
|
SPV wallet. This use case requires some other changes to the Bitcoin protocol however, so we will
|
|
not dwell on it here.
|
|
|
|
==Specification==
|
|
|
|
Two new messages are defined. The "getutxos" message has the following structure:
|
|
|
|
{|class="wikitable"
|
|
! Field Size !! Description !! Data type !! Comments
|
|
|-
|
|
| 1 || check mempool || bool || Whether to apply mempool transactions during the calculation, thus exposing their UTXOs and removing outputs that they spend.
|
|
|-
|
|
| ? || outpoints || vector<COutPoint> || The list of outpoints to be queried. Each outpoint is serialized in the same way it is in a tx message.
|
|
|}
|
|
|
|
The response message "utxos" has the following structure:
|
|
|
|
{|class="wikitable"
|
|
! Field Size !! Description !! Data type !! Comments
|
|
|-
|
|
| 4 || chain height || uint32 || The height of the chain at the moment the result was calculated.
|
|
|-
|
|
| 32 || chain tip hash || uint256 || Block hash of the top of the chain at the moment the result was calculated.
|
|
|-
|
|
| ? || hit bitmap || byte[] || An array of bytes encoding one bit for each outpoint queried. Each bit indicates whether the queried outpoint was found in the UTXO set or not.
|
|
|-
|
|
| ? || result utxos || result[] || A list of result objects (defined below), one for each outpoint that is unspent (i.e. has a bit set in the bitmap).
|
|
|}
|
|
|
|
The result object is defined as:
|
|
|
|
{|class="wikitable"
|
|
! Field Size !! Description !! Data type !! Comments
|
|
|-
|
|
| 4 || tx version || uint32 || The version number of the transaction the UTXO was found in.
|
|
|-
|
|
| 4 || height || uint32 || The height of the block containing the defining transaction, or 0x7FFFFFFF if the tx is in the mempool.
|
|
|-
|
|
| ? || output || CTxOut || The output itself, serialized in the same way as in a tx message.
|
|
|}
|
|
|
|
==Backward compatibility==
|
|
|
|
Nodes indicate support by advertising a protocol version above 70003 and by setting a new
|
|
NODE_GETUTXO flag in their nServices field, which has a value of 2 (the second bit of the field).
|
|
|
|
==Authentication==
|
|
|
|
The UTXO set is not currently authenticated by anything. There are proposals to resolve this by
|
|
introducing a new consensus rule that commits to a root hash of the UTXO set in blocks, however this
|
|
feature is not presently available in the Bitcoin protocol. Once it is, the utxos message could be
|
|
upgraded to include Merkle branches showing inclusion of the UTXOs in the committed sets.
|
|
|
|
If the requesting client is looking up outputs for a signed transaction that they have locally, the
|
|
client can partly verify the returned output by running the input scripts with it. Currently this
|
|
verifies only that the script is correct. A future version of the Bitcoin protocol is likely to also
|
|
allow the value to be checked in this way. It does not show that the output is really unspent or was
|
|
ever actually created in the block chain however. Additionally, the form of the provided scriptPubKey
|
|
should be checked before execution to ensure the remote peer doesn't just set the script to OP_TRUE.
|
|
|
|
If the requesting client has a mapping of chain heights to block hashes in the best chain e.g.
|
|
obtained via getheaders, then they can obtain a proof that the output did at one point exist by
|
|
requesting the block and searching for the output within it. When combined with Bloom filtering this
|
|
can be reasonably efficient.
|
|
|
|
Note that even when the outputs are being checked against something this protocol has the same
|
|
security model as Bloom filtering: a remote node can lie through omission by claiming the requested
|
|
UTXO does not exist / was already spent (they are the same, from the perspective of a full node).
|
|
Querying multiple nodes and combining their answers can be a partial solution to this, although as
|
|
nothing authenticates the Bitcoin P2P network a man in the middle could still yield incorrect
|
|
results.
|
|
|
|
==Implementation==
|
|
|
|
https://github.com/bitcoin/bitcoin/pull/4351/files
|