blockHeaders3 (47)

The blockHeaders3 message is the response to a getBlockHeaders3 request. It contains a batch of full, serialized block headers.

If the number of requested headers is large, the responding node will split them across multiple blockHeaders3 messages to ensure no single message exceeds the maximum network message size.

Core Data Types

• IxiVarUInt: See IxiVarInt Encoding.
• IxiBytes: See IxiBytes Encoding.

Payload Structure

The payload consists of a repeating series of Block Header entries. There is no explicit count field; the number of headers is determined by parsing the stream until it ends.

Field	Data Type	Min	Max	Description
Entire Payload	byte[]		50MB	The total size of the message payload must not exceed the global maximum.
headers	BlockHeader[]	1	5000*	An array of one or more serialized block header entries.

* The maximum number of headers per chunk is determined by the node configuration (CoreConfig.maximumBlockHeadersPerChunk), which defaults to 5000.

Block Header Entry Structure

Each entry in the headers array is a complete, serialized Block Header.

Field	Data Type	Description
headerData	IxiBytes	The full binary representation of a single block header. The internal structure is a subset of the blockData2 message, excluding the Block Body fields (signatures and transaction IDs).

Behavioral Notes

• A node receiving this message should parse each block header, validate it, and connect it to its local chain.
• Validation includes checking the lastBlockChecksum to ensure it links to the previous header, verifying the block's internal consistency, and checking the Proof of Work if applicable.
• The recipient should be prepared to receive multiple blockHeaders3 messages in response to a single large getBlockHeaders3 request.