compactBlockHeaders1 (50)

The compactBlockHeaders1 message is the specialized response sent to a light client after it makes a getRelevantBlockTransactions request.

This message serves two purposes:

1. It provides the client with the headers for the requested block range, allowing it to validate the chain's structure.
2. It echoes the original request parameters, confirming what data the response corresponds to.

Crucially, this message only contains the headers. The actual transactions that matched the client's filter are sent in separate transactionsChunk3 messages.

Core Data Types

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

Payload Structure

Field	Data Type	Min	Max	Description
Entire Payload	byte[]		50MB	The total size of the message payload must not exceed the global maximum.
fromBlockNum	IxiVarUInt	1		(Echoed) The starting block number from the original request.
count	IxiVarUInt	1		(Echoed) The number of blocks requested in the original request.
cuckooFilter	IxiBytes			(Echoed) The Cuckoo Filter from the original request.
compactHeaders	CompactHeader[]			An array of one or more compact block header entries.

Compact Header Entry Structure

Each entry in the compactHeaders array is a serialized Block Header where the signatures have been stripped out to save space.

Field	Data Type	Description
headerData	IxiBytes	The 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 light client receiving this message should parse the compactHeaders to build a local understanding of the blockchain's structure for the given range.
• This message provides the block context. The client should expect to receive transactionsChunk3 messages that contain the transactions belonging to the blocks described in this message.
• The echoed fields (fromBlockNum, count, cuckooFilter) allow the client to confirm that this response corresponds to its original request.