Dash Core

Dash Core Developer Documentation

Welcome to the Dash Core developer documentation. You'll find guides and documentation to help you start working with Dash Core as quickly as possible, as well as support if you get stuck. Let's jump right in!

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Data Messages

The following network messages all request or provide data related to transactions and blocks.

Overview Of P2P Protocol Data Request And Reply MessagesOverview Of P2P Protocol Data Request And Reply Messages

Many of the data messages use inventoriesinventories - A data type identifier and a hash; used to identify transactions, blocks, and objects available for download through the Dash P2P network. as unique identifiers for transactionstransactions - A transaction spending satoshis. and blocksblocks - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain.. Inventories have a simple 36-byte structure:

BytesNameData TypeDescription
4type identifieruint32_tThe type of object which was hashed. See list of type identifiers below.
32hashchar[32]SHA256(SHA256()) hash of the object in internal byte order.

The currently-available type identifiers are:

Type IdentifierNameDescription
1<<glossary:MSG_TX>>The hash is a TXID.
2<<glossary:MSG_BLOCK>>The hash is of a block header.
3<<glossary:MSG_FILTERED_BLOCK>>The hash is of a block header; identical to MSG_BLOCK. When used in a getdata message, this indicates the response should be a merkleblock message rather than a block message (but this only works if a bloom filter was previously configured). Only for use in getdata messages.
4<<glossary:MSG_LEGACY_TXLOCK_REQUEST>>MSG_TXLOCK_REQUEST prior to Dash Core 0.15.0. The hash is an Instant Send transaction lock request. Transactions received this way are automatically converted to a standard tx message as of Dash Core 0.15.0.
6<<glossary:MSG_SPORK>>The hash is Spork ID.
16<<glossary:MSG_DSTX>>The hash is Private Send (Dark Send) Broadcast TX.
17<<glossary:MSG_GOVERNANCE_OBJECT>>The hash is a Governance Object.
18<<glossary:MSG_GOVERNANCE_OBJECT_VOTE>>The hash is a Governance Object Vote.
20<<glossary:MSG_CMPCT_BLOCK>>The hash is of a block header; identical to MSG_BLOCK. When used in a getdata message, this indicates the response should be a cmpctblock message. Only for use in getdata messages.
21<<glossary:MSG_QUORUM_FINAL_COMMITMENT>>The hash is a long-living masternode quorum final commitment.
Added in 0.13.0
23<<glossary:MSG_QUORUM_CONTRIB>>The hash is a long-living masternode quorum contribution.
Added in 0.14.0
24<<glossary:MSG_QUORUM_COMPLAINT>>The hash is a long-living masternode quorum complaint.
Added in 0.14.0
25<<glossary:MSG_QUORUM_JUSTIFICATION>>The hash is a long-living masternode quorum justification.
Added in 0.14.0
26<<glossary:MSG_QUORUM_PREMATURE_COMMITMENT>>The hash is a long-living masternode quorum premature commitment.
Added in 0.14.0
28<<glossary:MSG_QUORUM_RECOVERED_SIG>>The hash is a long-living masternode quorum recovered signature.
Added in 0.14.0
29<<glossary:MSG_CLSIG>>The hash is a ChainLock signature.
Added in 0.14.0
30<<glossary:MSG_ISLOCK>>The hash is an LLMQ-based InstantSend lock.
Added in 0.14.0

The deprecated type identifiers are:

Type IdentifierNameDescription
5<<glossary:MSG_TXLOCK_VOTE>>Deprecated in 0.15.0

The hash is an Instant Send transaction vote.
7<<glossary:MSG_MASTERNODE_PAYMENT_VOTE>>Deprecated in 0.14.0

The hash is a Masternode Payment Vote.
8<<glossary:MSG_MASTERNODE_PAYMENT_BLOCK>>Deprecated in 0.14.0

The hash is a Masternode Payment Block.
8MSG_MASTERNODE_SCANNING_ERRORReplaced by MSG_MASTERNODE_PAYMENT_BLOCK
9<<glossary:MSG_BUDGET_VOTE>>Deprecated
10<<glossary:MSG_BUDGET_PROPOSAL>>Deprecated
11<<glossary:MSG_BUDGET_FINALIZED>>Deprecated
12<<glossary:MSG_BUDGET_FINALIZED_VOTE>>Deprecated
13<<glossary:MSG_MASTERNODE_QUORUM>>Not Implemented
14<<glossary:MSG_MASTERNODE_ANNOUNCE>>Deprecated in 0.14.0

The hash is a Masternode Broadcast.
15<<glossary:MSG_MASTERNODE_PING>>Deprecated in 0.14.0

The hash is a Masternode Ping.
19<<glossary:MSG_MASTERNODE_VERIFY>>Deprecated in 0.14.0

The hash is a Masternode Verify.
22MSG_QUORUM_DUMMY_COMMITMENTDeprecated in 0.14.0

Temporarily used on Testnet only.
27<<glossary:MSG_QUORUM_DEBUG_STATUS>>Deprecated in 0.14.0

Temporarily used on Testnet only.

Type identifier zero and type identifiers greater than those shown in the table above are reserved for future implementations. Dash Core ignores all inventories with one of these unknown types.

block

The block message transmits a single serialized blockserialized block - A complete block in its binary format---the same format used to calculate total block byte size; often represented using hexadecimal. in the format described in the serialized blocks section. See that section for an example hexdump. It can be sent for two different reasons:

  1. GetData Response: Nodes will always send it in response to a getdata message that requests the block with an inventoryinventory - A data type identifier and a hash; used to identify transactions, blocks, and objects available for download through the Dash P2P network. type of MSG_BLOCK (provided the node has that block available for relay).

  2. Unsolicited: Some miners will send unsolicited block messages broadcasting their newly-mined blocks to all of their peerspeers - A computer that connects to the Dash network.. Many miningmining - Mining is the act of creating valid Dash blocks, which requires demonstrating proof of work, and miners are devices that mine or people who own those devices. pools do the same thing, although some may be misconfigured to send the block from multiple nodes, possibly sending the same block to some peers more than once.

blocktxn

Added in protocol version 70209 of Dash Core as described by BIP152

The blocktxn message sends requested blockblock - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain. transactionstransactions - A transaction spending satoshis. to a node which previously requested them with a getblocktxn message. It is defined as a message containing a serialized BlockTransactions message.

Upon receipt of a properly-formatted requested blocktxn message, nodesnodes - A computer that connects to the Dash network. should:

  1. Attempt to reconstruct the full block by taking the prefilledtxn transactions from the original cmpctblock message and placing them in the marked positions
  2. For each short transaction ID from the original cmpctblock message, in order, find the corresponding transaction (from either the blocktxn message or from other sources)
  3. Place each short transaction ID in the first available position in the block
  4. Once the block has been reconstructed, it shall be processed as normal.

Short transaction IDs are expected to occasionally collide. Nodes must not be penalized for such collisions.

The structure of BlockTransactions is defined below.

BytesNameData TypeEncodingDescription
32blockhashBinary blobThe output from a double-SHA256 of the block header, as used elsewhereThe blockhash of the block which the transactions being provided are in
1 or 3transactions
_length
CompactSizeAs used to encode array lengths elsewhereThe number of transactions provided
VariestransactionsList of transactionsAs encoded in tx messages in response to getdata MSG_TXThe transactions provided

The following annotated hexdump shows a blocktxn message. (The message header has been omitted.)

182327cb727da7d60541da793831fd0ab0509e79c8cd
3d654cdf3a0100000000 ....................... Block Hash

01 ......................................... Transactions Provided: 1

Transaction(s)
| Transaction 1
| | 01000000 ................................ Transaction Version: 1
| | 01 ...................................... Input count: 1
| |
| | Transaction input #1
| | |
| | | 0952617a516d956e2ecee71a6adc249f
| | | 4bb757adcc409452ab98c8e55c31e62a ..... Outpoint TXID
| | | 00000000 ............................. Outpoint index number: 0
| | |
| | | 6b ................................... Bytes in sig. script: 107
| | | 483045022100d10edf447252e1e69ff1
| | | 77330bb2c889a50be02e00cc5d79c0d0
| | | 79ae56518fc40220245d36905dc950fc
| | | d55694cfde8cde3109dc80b12aca3a6e
| | | 332033802ee36e1b01210272cc6e7660
| | | 2648831d8e80fca8eb24369cd0f23ff0
| | | 79cf20ae9d9beee05de6db ............... Secp256k1 signature
| | |
| | | ffffffff ............................. Sequence number: UINT32_MAX
| |
| | 02 ..................................... Number of outputs: 02
| |
| | Transaction output #1
| | | 0be0f50500000000 ..................... Duffs (0.99999755 Dash)
| | |
| | | 19 ................................... Bytes in pubkey script: 25
| | | | 76 ................................. OP_DUP
| | | | a9 ................................. OP_HASH160
| | | | 14 ................................. Push 20 bytes as data
| | | | | 923d91ed359f650eec6ea8b9030b340d
| | | | | ea63d590 ......................... PubKey hash
| | | | 88 ................................. OP_EQUALVERIFY
| | | | ac ................................. OP_CHECKSIG
| |
| | [...] .................................. 1 more tx output omitted
| |
| | 00000000 ............................... locktime: 0 (a block height)

cmpctblock

Added in protocol version 70209 of Dash Core as described by BIP152

The cmpctblock message is a reply to a getdata message which requested a blockblock - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain. using the inventoryinventory - A data type identifier and a hash; used to identify transactions, blocks, and objects available for download through the Dash P2P network. type MSG_CMPCT_BLOCK. If the requested block was recently announced and is close to the tip of the best chain of the receiver and after having sent the requesting peerpeer - A computer that connects to the Dash network. a sendcmpct message, nodes respond with a cmpctblock message containing data for the block.

If the requested block is too old, the node responds with a full non-compact block

Upon receipt of a cmpctblock message, after sending a sendcmpct message, nodes should calculate the short transaction ID for each unconfirmed transactionunconfirmed transaction - A score indicating the number of blocks on the best block chain that would need to be modified to remove or modify a particular transaction. A confirmed transaction has a confirmation score of one or higher. they have available (i.e. in their mempool) and compare each to each short transaction ID in the cmpctblock message. After finding already-available transactions, nodes which do not have all transactions available to reconstruct the full block should request the missing transactions using a getblocktxn message.

A node must not send a cmpctblock message unless they are able to respond to a getblocktxn message which requests every transaction in the block. A node must not send a cmpctblock message without having validated that the headerheader - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. properly commits to each transaction in the block, and properly builds on top of the existing, fully-validated chain with a valid proof-of-work either as a part of the current most-work valid chain, or building directly on top of it. A node may send a cmpctblock message before validating that each transaction in the block validly spends existing UTXO set entries.

The cmpctblock message contains a vector of PrefilledTransaction whose structure is defined below. A PrefilledTransaction is used in HeaderAndShortIDs to provide a list of a few transactions explicitly.

BytesNameData TypeEncodingDescription
1 or 3indexCompactSizeCompact Size, differentially encoded since the last PrefilledTransaction in a listThe index into the block at which this transaction is
VariestxTransactionAs encoded in tx messages sent in response to getdata MSG_TXTransaction which is in the block at index index

The cmpctblock message is compromised of a serialized HeaderAndShortIDs structure which is defined below. A HeaderAndShortIDs structure is used to relay a block header, the short transactions IDs used for matching already-available transactions, and a select few transactions which we expect a peer may be missing.

BytesNameData TypeEncodingDescription
80headerBlock headerFirst 80 bytes of the block as defined by the encoding used by block messagesThe header of the block being provided
8nonceuint64_tLittle EndianA nonce for use in short transaction ID calculations
1 or 3shortids_
length
CompactSizeAs used to encode array lengths elsewhereThe number of short transaction IDs in shortids (i.e. block tx count - prefilledtxn
_length)
VariesshortidsList of 6-byte integersLittle EndianThe short transaction IDs calculated from the transactions which were not provided explicitly in prefilledtxn
1 or 3prefilledtxn
_length
CompactSizeAs used to encode array lengths elsewhereThe number of prefilled transactions in prefilledtxn (i.e. block tx count - shortids
_length)
VariesprefilledtxnList of Prefilled
Transactions
As defined by Prefilled
Transaction definition below
Used to provide the coinbase transaction and a select few which we expect a peer may be missing

Short Transaction ID calculation

Short transaction IDs are used to represent a transaction without sending a full 256-bit hash. They are calculated as follows,

  • A single-SHA256 hashing the block headerblock header - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. with the nonce appended (in little-endian)
  • Running SipHash-2-4 with the input being the transaction ID and the keys (k0/k1) set to the first two little-endian 64-bit integers from the above hash, respectively.
  • Dropping the 2 most significant bytes from the SipHash output to make it 6 bytes.

The following annotated hexdump shows a cmpctblock message. (The message header has been omitted.)

00000020981178a4342cec6316296b2ad84c9b7cdf9f
2688e5d0fe1a0003cd0000000000f64870f52a3d0125
1336c9464961216732b25fbf288a51f25a0e81bffb20
e9600194d85a64a50d1cc02b0181 ................ Block Header

3151b67e5b418b9d ............................ Nonce

01 .......................................... Short IDs Length: 1
483edcd3c799 ................................ Short IDs

01 .......................................... Prefilled Transaction Length: 1

Prefilled Transactions
| 00 ........................................ Index: 0
|
| Transaction 1 (Coinbase)
| | 01000000 ................................ Transaction Version: 1
| | 01 ...................................... Input count: 1
| |
| | Transaction input #1
| | |
| | | 00000000000000000000000000000000
| | | 00000000000000000000000000000000 ..... Outpoint TXID
| | | ffffffff ............................. Outpoint index number: UINT32_MAX
| | |
| | | 13 ................................... Bytes in sig. script: 19
| | | 03daaf010e2f5032506f6f6c2d74444153482f Secp256k1 signature
| | |
| | | ffffffff ............................. Sequence number: UINT32_MAX
| |
| | 04 ..................................... Number of outputs: 04
| |
| | Transaction output #1
| | | ffe5654200000000 ..................... Duffs (11.13974271 Dash)
| | |
| | | 19 ................................... Bytes in pubkey script: 25
| | | | 76 ................................. OP_DUP
| | | | a9 ................................. OP_HASH160
| | | | 14 ................................. Push 20 bytes as data
| | | | | b885cb21ad12e593c1a46d814df47ccb
| | | | | 450a7d84 ......................... PubKey hash
| | | | 88 ................................. OP_EQUALVERIFY
| | | | ac ................................. OP_CHECKSIG
| |
| | [...] .................................. 3 more tx outputs omitted
| |
| | 00000000 ............................... locktime: 0 (a block height)

getblocks

The getblocks message requests an inv message that provides block headerblock header - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. hashes starting from a particular point in the block chainblock chain - A chain of blocks with each block referencing the block that preceded it. The most-difficult-to-recreate chain is the best block chain.. It allows a peerpeer - A computer that connects to the Dash network. which has been disconnected or started for the first time to get the data it needs to request the blocks it hasn't seen.

Peers which have been disconnected may have stale blocksstale blocks - Blocks which were successfully mined but which aren't included on the current best block chain, likely because some other block at the same height had its chain extended first. in their locally-stored block chain, so the getblocks message allows the requesting peer to provide the receiving peer with multiple headerheader - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. hashes at heights on their local chain. This allows the receiving peer to find, within that list, the last header hash they had in common and reply with all subsequent header hashes.

Note: the receiving peer itself may respond with an inv message containing header hashes of stale blocks. It is up to the requesting peer to poll all of its peers to find the best block chain.

If the receiving peer does not find a common header hash within the list, it will assume the last common block was the genesis blockgenesis block - The first block in the Dash block chain. (block zero), so it will reply with in inv message containing header hashes starting with block one (the first block after the genesis block).

BytesNameData TypeDescription
4versionuint32_tThe protocol version number; the same as sent in the version message.
Varieshash countcompactSize uintThe number of header hashes provided not including the stop hash. There is no limit except that the byte size of the entire message must be below the MAX_SIZE limit; typically from 1 to 200 hashes are sent.
Variesblock header hasheschar[32]One or more block header hashes (32 bytes each) in internal byte order. Hashes should be provided in reverse order of block height, so highest-height hashes are listed first and lowest-height hashes are listed last.
32stop hashchar[32]The header hash of the last header hash being requested; set to all zeroes to request an inv message with all subsequent header hashes (a maximum of 500 will be sent as a reply to this message; if you need more than 500, you will need to send another getblocks message with a higher-height header hash as the first entry in block header hash field).

The following annotated hexdump shows a getblocks message. (The message header has been omitted.)

71110100 ........................... Protocol version: 70001
02 ................................. Hash count: 2

d39f608a7775b537729884d4e6633bb2
105e55a16a14d31b0000000000000000 ... Hash #1

5c3e6403d40837110a2e8afb602b1c01
714bda7ce23bea0a0000000000000000 ... Hash #2

00000000000000000000000000000000
00000000000000000000000000000000 ... Stop hash

getblocktxn

Added in protocol version 70209 of Dash Core as described by BIP152

The getblocktxn message requests a blocktxn message for any transactions that it has not seen after a compact block is received. It is defined as a message containing a serialized BlockTransactionsRequest message. Upon receipt of a properly-formatted getblocktxn message, nodesnodes - A computer that connects to the Dash network. which recently provided the sender of such a message with a cmpctblock message for the block hash identified in this message must respond with either an appropriate blocktxn message, or a full block message.

A blocktxn message response must contain exactly and only each transaction which is present in the appropriate block at the index specified in the getblocktxn message indexes list, in the order requested.

The structure of BlockTransactionsRequest is defined below.

BytesNameData TypeEncodingDescription
32blockhashBinary blobThe output from a double-SHA256 of the block header, as used elsewhereThe blockhash of the block which the transactions being requested are in
Variesindexes_lengthCompactSize uintAs used to encode array lengths elsewhereThe number of transactions requested
VariesindexesCompactSize uint[]Differentially encodedVector of compactSize containing the indexes of the transactions being requested in the block.

The following annotated hexdump shows a getblocktxn message. (The message header has been omitted.)

182327cb727da7d60541da793831fd0a
b0509e79c8cd3d654cdf3a0100000000 ... Block Hash

01 ................................. Index length: 1
01 ................................. Index: 1

getdata

The getdata message requests one or more data objects from another nodenode - A computer that connects to the Dash network.. The objects are requested by an inventory, which the requesting node typically previously received by way of an inv message.

The response to a getdata message can be a tx message, block message, merkleblock message, ix message, txlvote message, mnw message, mnb message, mnp message, dstx message, govobj message, govobjvote message, mnv message, notfound message, or cmpctblock message.

This message cannot be used to request arbitrary data, such as historic transactions no longer in the memory pool or relay set. Full nodes may not even be able to provide older blocksblocks - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain. if they've pruned old transactions from their block database. For this reason, the getdata message should usually only be used to request data from a node which previously advertised it had that data by sending an inv message.

The format and maximum size limitations of the getdata message are identical to the inv message; only the message header differs.

getheaders

Added in protocol version 70077.

The getheaders message requests a headers message that provides block headers starting from a particular point in the block chainblock chain - A chain of blocks with each block referencing the block that preceded it. The most-difficult-to-recreate chain is the best block chain.. It allows a peerpeer - A computer that connects to the Dash network. which has been disconnected or started for the first time to get the headersheaders - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. it hasn’t seen yet.

The getheaders message is nearly identical to the getblocks message, with one minor difference: the inv reply to the getblocks message will include no more than 500 block headerblock header - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. hashes; the headers reply to the getheaders message will include as many as 2,000 block headers.

getmnlistd

Added in protocol version 70213

The getmnlistd message requests a mnlistdiff message that provides either:

  1. A full masternodemasternode - A computer that provides second-tier Dash functionality (InstantSend, PrivateSend, decentralized governance). Masternodes are incentivized by receiving part of the block reward, but must hold 1000 Dash as collateral to prevent sybil attacks. list (if baseBlockHash is all-zero)
  2. An update to a previously requested masternode list
BytesNameData typeRequiredDescription
32baseBlockHashuint256RequiredHash of a block the requester already has a valid masternode list of.
Note: Can be all-zero to indicate that a full masternode list is requested.
32blockHashuint256RequiredHash of the block for which the masternode list diff is requested

The following annotated hexdump shows a getmnlistd message. (The message header has been omitted.)

000001ee5108348a2c59396da29dc576
9b2a9bb303d7577aee9cd95136c49b9b ........... Base block hash

0000030f51f12e7069a7aa5f1bc9085d
db3fe368976296fd3b6d73fdaf898cc0 ........... Block hash

headers

Added in protocol version 31800 (of Bitcoin).

The headers message sends block headers to a nodenode - A computer that connects to the Dash network. which previously requested certain headersheaders - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. with a getheaders message. A headers message can be empty.

BytesNameData TypeDescription
VariescountcompactSize uintNumber of block headers up to a maximum of 2,000. Note: headers-first sync assumes the sending node will send the maximum number of headers whenever possible.
Variesheadersblock_headerBlock headers: each 80-byte block header is in the format described in the block headers section with an additional 0x00 suffixed. This 0x00 is called the transaction count, but because the headers message doesn't include any transactions, the transaction count is always zero.

The following annotated hexdump shows a headers message. (The message header has been omitted.)

01 ................................. Header count: 1

02000000 ........................... Block version: 2
b6ff0b1b1680a2862a30ca44d346d9e8
910d334beb48ca0c0000000000000000 ... Hash of previous block's header
9d10aa52ee949386ca9385695f04ede2
70dda20810decd12bc9b048aaab31471 ... Merkle root
24d95a54 ........................... Unix time: 1415239972
30c31b18 ........................... Target (bits)
fe9f0864 ........................... Nonce

00 ................................. Transaction count (0x00)

inv

The inv message (inventory message) transmits one or more inventoriesinventories - A data type identifier and a hash; used to identify transactions, blocks, and objects available for download through the Dash P2P network. of objects known to the transmitting peerpeer - A computer that connects to the Dash network.. It can be sent unsolicited to announce new transactionstransactions - A transaction spending satoshis. or blocksblocks - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain., or it can be sent in reply to a getblocks message or mempool message.

The receiving peer can compare the inventories from an inv message against the inventories it has already seen, and then use a follow-up message to request unseen objects.

BytesNameData TypeDescription
VariescountcompactSize uintThe number of inventory entries.
VariesinventoryinventoryOne or more inventory entries up to a maximum of 50,000 entries.

The following annotated hexdump shows an inv message with two inventory entries. (The message header has been omitted.)

02 ................................. Count: 2

0f000000 ........................... Type: MSG_MASTERNODE_PING
dd6cc6c11211793b239c2e311f1496e2
2281b200b35233eaae465d2aa3c9d537 ... Hash (mnp)

05000000 ........................... Type: MSG_TXLOCK_VOTE
afc5b2f418f8c06c477a7d071240f5ee
ab17057f9ce4b50c2aef4fadf3729a2e ... Hash (txlvote)

mempool

Added in protocol version 60002 (of Bitcoin).

The mempool message requests the TXIDsTXIDs - An identifier used to uniquely identify a particular transaction; specifically, the sha256d hash of the transaction. of transactions that the receiving nodenode - A computer that connects to the Dash network. has verified as valid but which have not yet appeared in a blockblock - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain.. That is, transactions which are in the receiving node's memory pool. The response to the mempool message is one or more inv messages containing the TXIDs in the usual inventoryinventory - A data type identifier and a hash; used to identify transactions, blocks, and objects available for download through the Dash P2P network. format.

Sending the mempool message is mostly useful when a program first connects to the network. Full nodes can use it to quickly gather most or all of the unconfirmed transactions available on the network; this is especially useful for miners trying to gather transactions for their transaction fees. SPV clients can set a filter before sending a mempool to only receive transactions that match that filter; this allows a recently-started client to get most or all unconfirmed transactions related to its wallet.

📘

Mempool Synchronization

Since Dash Core 0.15.0, the mempool message was expanded to include syncing of InstantSend Lock inventories. Additionally, nodes now attempt to sync their mempool with peers at startup by default (limited to peers using protocol version 70216 or higher). This allows nodes to more quickly detect any double-spend attempts as well as show InstantSend lock status correctly for transactions received while offline.

The inv response to the mempool message is, at best, one node's view of the network---not a complete list of every unconfirmed transactionunconfirmed transaction - A score indicating the number of blocks on the best block chain that would need to be modified to remove or modify a particular transaction. A confirmed transaction has a confirmation score of one or higher. on the network. Here are some additional reasons the list might not be complete:

  • The mempool message is not currently fully compatible with the filterload message's BLOOM_UPDATE_ALL and BLOOM_UPDATE_P2PUBKEY_ONLY flags. Mempool transactions are not sorted like in-block transactions, so a transaction (tx2) spending an outputoutput - An output in a transaction which contains two fields: a value field for transferring zero or more duffs and a pubkey script for indicating what conditions must be fulfilled for those duffs to be further spent. can appear before the transaction (tx1) containing that output, which means the automatic filter update mechanism won't operate until the second-appearing transaction (tx1) is seen---missing the first-appearing transaction (tx2). It has been proposed in Bitcoin Core issue #2381 that the transactions should be sorted before being processed by the filter.

There is no payload in a mempool message. See the message header section for an example of a message without a payload.

merkleblock

Added in protocol version 70001 as described by BIP37.

The merkleblock message is a reply to a getdata message which requested a blockblock - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain. using the inventory type MSG_MERKLEBLOCK. It is only part of the reply: if any matching transactions are found, they will be sent separately as tx messages.

If a filter has been previously set with the filterload message, the merkleblock message will contain the TXIDsTXIDs - An identifier used to uniquely identify a particular transaction; specifically, the sha256d hash of the transaction. of any transactions in the requested block that matched the filter, as well as any parts of the block's merkle treemerkle tree - A tree constructed by hashing paired data (the leaves), then pairing and hashing the results until a single hash remains, the merkle root. In Dash, the leaves are almost always transactions from a single block. necessary to connect those transactions to the block header's merkle rootmerkle root - The root node of a merkle tree, a descendant of all the hashed pairs in the tree. Block headers must include a valid merkle root descended from all transactions in that block.. The message also contains a complete copy of the block headerblock header - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. to allow the client to hash it and confirm its proof of workproof of work - A hash below a target value which can only be obtained, on average, by performing a certain amount of brute force work---therefore demonstrating proof of work..

BytesNameData TypeDescription
80block headerblock_headerThe block header in the format described in the block header section.
4transaction countuint32_tThe number of transactions in the block (including ones that don't match the filter).
Varieshash countcompactSize uintThe number of hashes in the following field.
Varieshasheschar[32]One or more hashes of both transactions and merkle nodes in internal byte order. Each hash is 32 bytes.
Variesflag byte countcompactSize uintThe number of flag bytes in the following field.
Variesflagsbyte[]A sequence of bits packed eight in a byte with the least significant bit first. May be padded to the nearest byte boundary but must not contain any more bits than that. Used to assign the hashes to particular nodes in the merkle tree as described below.

The annotated hexdump below shows a merkleblock message which corresponds to the examples below. (The message header has been omitted.)

01000000 ........................... Block version: 1
82bb869cf3a793432a66e826e05a6fc3
7469f8efb7421dc88067010000000000 ... Hash of previous block's header
7f16c5962e8bd963659c793ce370d95f
093bc7e367117b3c30c1f8fdd0d97287 ... Merkle root
76381b4d ........................... Time: 1293629558
4c86041b ........................... nBits: 0x04864c * 256**(0x1b-3)
554b8529 ........................... Nonce

07000000 ........................... Transaction count: 7
04 ................................. Hash count: 4

3612262624047ee87660be1a707519a4
43b1c1ce3d248cbfc6c15870f6c5daa2 ... Hash #1
019f5b01d4195ecbc9398fbf3c3b1fa9
bb3183301d7a1fb3bd174fcfa40a2b65 ... Hash #2
41ed70551dd7e841883ab8f0b16bf041
76b7d1480e4f0af9f3d4c3595768d068 ... Hash #3
20d2a7bc994987302e5b1ac80fc425fe
25f8b63169ea78e68fbaaefa59379bbf ... Hash #4

01 ................................. Flag bytes: 1
1d ................................. Flags: 1 0 1 1 1 0 0 0

Note: when fully decoded, the above merkleblock message provided the TXID for a single transaction that matched the filter. In the networknetwork - The Dash P2P network which broadcasts transactions and blocks. traffic dump this output was taken from, the full transaction belonging to that TXID was sent immediately after the merkleblock message as a tx message.

Parsing A MerkleBlock Message

As seen in the annotated hexdump above, the merkleblock message provides three special data types: a transaction count, a list of hashes, and a list of one-bit flags.

You can use the transaction count to construct an empty merkle treemerkle tree - A tree constructed by hashing paired data (the leaves), then pairing and hashing the results until a single hash remains, the merkle root. In Dash, the leaves are almost always transactions from a single block.. We'll call each entry in the tree a node; on the bottom are TXID nodes---the hashes for these nodes are TXIDsTXIDs - An identifier used to uniquely identify a particular transaction; specifically, the sha256d hash of the transaction.; the remaining nodes (including the merkle rootmerkle root - The root node of a merkle tree, a descendant of all the hashed pairs in the tree. Block headers must include a valid merkle root descended from all transactions in that block.) are non-TXID nodes---they may actually have the same hash as a TXID, but we treat them differently.

Example Of Parsing A MerkleBlock MessageExample Of Parsing A MerkleBlock Message

Keep the hashes and flags in the order they appear in the merkleblock message. When we say "next flag" or "next hash", we mean the next flag or hash on the list, even if it's the first one we've used so far.

Start with the merkle root node and the first flag. The table below describes how to evaluate a flag based on whether the node being processed is a TXID node or a non-TXID node. Once you apply a flag to a node, never apply another flag to that same node or reuse that same flag again.

FlagTXID NodeNon-TXID Node
0Use the next hash as this node's TXID, but this transaction didn't match the filter.Use the next hash as this node's hash. Don't process any descendant nodes.
1Use the next hash as this node's TXID, and mark this transaction as matching the filter.The hash needs to be computed. Process the left child node to get its hash; process the right child node to get its hash; then concatenate the two hashes as 64 raw bytes and hash them to get this node's hash.

Any time you begin processing a node for the first time, evaluate the next flag. Never use a flag at any other time.

When processing a child node, you may need to process its children (the grandchildren of the original node) or further-descended nodes before returning to the parent node. This is expected---keep processing depth first until you reach a TXID node or a non-TXID node with a flag of 0.

After you process a TXID node or a non-TXID node with a flag of 0, stop processing flags and begin to ascend the tree. As you ascend, compute the hash of any nodes for which you now have both child hashes or for which you now have the sole child hash. See the merkle tree section for hashing instructions. If you reach a node where only the left hash is known, descend into its right child (if present) and further descendants as necessary.

However, if you find a node whose left and right children both have the same hash, fail. This is related to CVE-2012-2459.

Continue descending and ascending until you have enough information to obtain the hash of the merkle root node. If you run out of flags or hashes before that condition is reached, fail. Then perform the following checks (order doesn't matter):

  • Fail if there are unused hashes in the hashes list.

  • Fail if there are unused flag bits---except for the minimum number of bits necessary to pad up to the next full byte.

  • Fail if the hash of the merkle root node is not identical to the merkle root in the block headerblock header - An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work..

  • Fail if the block header is invalid. Remember to ensure that the hash of the header is less than or equal to the target thresholdtarget threshold - The target is the threshold below which a block header hash must be in order for the block to be valid, and nBits is the encoded form of the target threshold as it appears in the block header. encoded by the nBits header field. Your program should also, of course, attempt to ensure the header belongs to the best block chain and that the user knows how many confirmations this block has.

For a detailed example of parsing a merkleblock message, please see the corresponding merkle block examples section.

Creating A MerkleBlock Message

It's easier to understand how to create a merkleblock message after you understand how to parse an already-created message, so we recommend you read the parsing section above first.

Create a complete merkle tree with TXIDsTXIDs - An identifier used to uniquely identify a particular transaction; specifically, the sha256d hash of the transaction. on the bottom row and all the other hashes calculated up to the merkle rootmerkle root - The root node of a merkle tree, a descendant of all the hashed pairs in the tree. Block headers must include a valid merkle root descended from all transactions in that block. on the top row. For each transaction that matches the filter, track its TXID node and all of its ancestor nodes.

Example Of Creating A MerkleBlock MessageExample Of Creating A MerkleBlock Message

Start processing the tree with the merkle rootmerkle root - The root node of a merkle tree, a descendant of all the hashed pairs in the tree. Block headers must include a valid merkle root descended from all transactions in that block. node. The table below describes how to process both TXID nodes and non-TXID nodes based on whether the node is a match, a match ancestor, or neither a match nor a match ancestor.

TXID NodeNon-TXID Node
Neither Match Nor Match AncestorAppend a 0 to the flag list; append this node's TXID to the hash list.Append a 0 to the flag list; append this node's hash to the hash list. Do not descend into its child nodes.
Match Or Match AncestorAppend a 1 to the flag list; append this node's TXID to the hash list.Append a 1 to the flag list; process the left child node. Then, if the node has a right child, process the right child. Do not append a hash to the hash list for this node.

Any time you begin processing a node for the first time, a flag should be appended to the flag list. Never put a flag on the list at any other time, except when processing is complete to pad out the flag list to a byte boundary.

When processing a child node, you may need to process its children (the grandchildren of the original node) or further-descended nodes before returning to the parent node. This is expected---keep processing depth first until you reach a TXID node or a node which is neither a TXID nor a match ancestor.

After you process a TXID node or a node which is neither a TXID nor a match ancestor, stop processing and begin to ascend the tree until you find a node with a right child you haven't processed yet. Descend into that right child and process it.

After you fully process the merkle root node according to the instructions in the table above, processing is complete. Pad your flag list to a byte boundary and construct the merkleblock message using the template near the beginning of this subsection.

mnlistdiff

Added in protocol version 70213

The mnlistdiff message is a reply to a getmnlistd message which requested either a full masternodemasternode - A computer that provides second-tier Dash functionality (InstantSend, PrivateSend, decentralized governance). Masternodes are incentivized by receiving part of the block reward, but must hold 1000 Dash as collateral to prevent sybil attacks. list or a diff for a range of blocksblocks - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain..

BytesNameData
type
RequiredDescription
32baseBlockHashuint256RequiredHash of a block the requester already has a valid masternode list of. Can be all-zero to indicate that a full masternode list is requested.
32blockHashuint256RequiredHash of the block for which the masternode list diff is requested
4totalTransactionsuint32_tRequiredNumber of total transactions in blockHash
1-9merkleHashes
Count
compactSize uintRequiredNumber of Merkle hashes
variablemerkleHashesvectorRequiredMerkle hashes in depth-first order
1-9merkleFlags
Count
compactSize uintRequiredNumber of Merkle flag bytes
variablemerkleFlagsvector<uint8_t>RequiredMerkle flag bits, packed per 8 in a byte, least significant bit first
variablecbTxCTransactionRequiredThe fully serialized coinbase transaction of blockHash
1-9deletedMNsCountcompactSize uintRequiredNumber of ProRegTx hashes which were deleted after baseBlockHash
variabledeletedMNsvectorRequiredA list of ProRegTx hashes for masternode which were deleted after baseBlockHash
variablemnListvectorRequiredThe list of Simplified Masternode List (SML) entries which were added or updated since baseBlockHash
1-9deletedQuorums
Count
compactSize uintRequiredAdded in protocol version 70214

Number of LLMQs which were deleted from the active set after baseBlockHash
variabledeletedQuorums(uint8_t+uint256)[]RequiredAdded in protocol version 70214

A list of LLMQ type and quorum hashes for LLMQs which were deleted after baseBlockHash
1-9newQuorumsCountcompactSize uintRequiredAdded in protocol version 70214

Number of new LLMQs which were added to the active set since baseBlockHash
variablenewQuorumsqfcommit[]RequiredAdded in protocol version 70214

The list of LLMQ commitments for the LLMQs which were added since baseBlockHash

Simplified Masternode List (SML) Entry

BytesNameData typeDescription
32proRegTxHashuint256The hash of the ProRegTx that identifies the masternode
32confirmedHashuint256The hash of the block at which the masternode got confirmed
16ipAddressbyte[]IPv6 address in network byte order. Only IPv4 mapped addresses are allowed (to be extended in the future)
2portuint_16Port (network byte order)
48pubKeyOperatorBLSPubKeyThe operators public key
20keyIDVotingCKeyIDThe public key hash used for voting.
1isValidboolTrue if a masternode is not PoSe-banned

The following annotated hexdump shows a mnlistdiff message. (The message header has been omitted.)

000001ee5108348a2c59396da29dc576
9b2a9bb303d7577aee9cd95136c49b9b ........... Base block hash

0000030f51f12e7069a7aa5f1bc9085d
db3fe368976296fd3b6d73fdaf898cc0 ........... Block hash

05000000 ................................... Transactions: 5

04 ......................................... Merkle hash count: 4

4488a599e5d61709664c32305befd58b
ef29e33bc6e718af0233f938557a57a9 ........... Merkle hash 1
5c8119b7b136d94e477a0d2917d5f724
5ff299cc6e31994f6236a8fb34fec88f ........... Merkle hash 2
905efa3e6743c889823f00147d36d12f
d12ad401c19089f0affcabd423deef67 ........... Merkle hash 3
3f3a7f84d7ad33214994b5aecf4c1e19
2cb65b86750b1377e069073d1eba477a ........... Merkle hash 4

01 ......................................... Merkle flag count: 1
0f ......................................... Flags: 0 0 0 0 1 1 1 1

[...]....................................... Coinbase Tx (Not shown)

00 ......................................... Deleted masternodes: 0

02 ......................................... Masternode list entries: 2

00 ......................................... Deleted quorums: 0

00 ......................................... New quorums: 0

Masternode List
| Masternode 1
| | 01040eb32f760490054543356cff4638
| | 65633439dd073cffa570305eb086f70e ....... ProRegTx hash
| |
| | 000001ee5108348a2c59396da29dc576
| | 9b2a9bb303d7577aee9cd95136c49b9b ....... Confirmed block hash
| |
| | 00000000000000000000000000000000 ....... IP Address: ::ffff:0.0.0.0
| | 0000 ................................... Port: 0
| |
| | 0000000000000000000000000000000000000000
| | 0000000000000000000000000000000000000000
| | 0000000000000000 ....................... Operator public key (BLS)
| | c2ae01fb4084cbc3bc31e7f59b36be228a320404 Voting pubkey hash (ECDSA)
| |
| | 0 ...................................... Valid (0 - No)
|
| Masternode 2
| | f7737beb39779971e9bc59632243e13f
| | c5fc9ada93b69bf48c2d4c463296cd5a ....... ProRegTx hash
| |
| | 0000030f51f12e7069a7aa5f1bc9085d
| | db3fe368976296fd3b6d73fdaf898cc0 ....... Confirmed block hash
| |
| | 000000000000000000000000cf9af40d ....... IP Address: ::ffff:207.154.244.13
| | 4e1f ................................... Port: 19999
| |
| | 88d719278eef605d9c19037366910b59bc28d437
| | de4a8db4d76fda6d6985dbdf10404fb9bb5cd0e8
| | c22f4a914a6c5566 ....................... Operator public key (BLS)
| | 43ce12751c4ba45dcdfe2c16cefd61461e17a54d Voting pubkey hash (ECDSA)
| |
| | 1 ...................................... Valid (1 - Yes)

notfound

Added in protocol version 70001.

The notfound message is a reply to a getdata message which requested an object the receiving nodenode - A computer that connects to the Dash network. does not have available for relay. (Nodes are not expected to relay historic transactions which are no longer in the memory pool or relay set. Nodes may also have pruned spent transactions from older blocksblocks - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain., making them unable to send those blocks.)

The format and maximum size limitations of the notfound message are identical to the inv message; only the message header differs.

tx

The tx message transmits a single transaction in the raw transactionraw transaction - Complete transactions in their binary format; often represented using hexadecimal. Sometimes called raw format because of the various Dash Core commands with "raw" in their names. format. It can be sent in a variety of situations;

  • Transaction Response: Dash Core will send it in response to a getdata message that requests the transaction with an inventoryinventory - A data type identifier and a hash; used to identify transactions, blocks, and objects available for download through the Dash P2P network. type of MSG_TX.

  • MerkleBlock Response: Dash Core will send it in response to a getdata message that requests a merkle blockmerkle block - A partial merkle tree connecting transactions matching a bloom filter to the merkle root of a block. with an inventoryinventory - A data type identifier and a hash; used to identify transactions, blocks, and objects available for download through the Dash P2P network. type of MSG_MERKLEBLOCK. (This is in addition to sending a merkleblock message.) Each tx message in this case provides a matched transaction from that blockblock - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain..

For an example hexdump of the raw transaction format, see the raw transaction section.

Updated 8 months ago



Data Messages


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