Blockchain Network

It use the Bitcoin broadcast network to propagate transactions and blocks. All communications are done over TCP (ipv6 and tor is supported). The Header structure is:

name	description	size	data type
version	Block version information	4 bits	int32
prev_block	The hash value of the previous block this particular block references	32 bits	char[32]
merkle_root	The reference to a Merkle tree collection which is a hash of all transactions related to this block	32 bytes	char[32]
timestamp	A timestamp recording when this block was created	4 bits	int32
bits	The calculated difficulty target being used for this block	4 bits	uint32
nonce	The nonce used to generate this block… to allow variations of the header and compute different hashes	4 bits	uint32
txn_count	Number of transaction entries, this value is always 0	1+ bits	var_int

Inside the payload there is a message with the following structure

name	description	size	data type
magic	Magic value indicating message origin network, and used to seek to next message when stream state is unknown	4	uint32
command	ASCII string identifying the packet content, NULL padded (non-NULL padding results in packet rejected)	12	char[12]
lengt	Length of payload in number of bytes	4	uint32
checksum	First 4 bytes of sha256(sha256(payload))	4	uint32
payload	The actual data	?	char[]

The possible commands messages are:

• version - Information about program version and block count. Exchanged when first connecting.
• verack - Sent in response to a version message to acknowledge that we are willing to connect.
• addr - List of one or more IP addresses and ports.
• inv - "I have these blocks/transactions: ..." Normally sent only when a new block or transaction is being relayed. This is only a list, not the actual data.
• getdata - Request a single block or transaction by hash.
• getblocks - Request an inv of all blocks in a range.
• getheaders - Request a headers message containing all block headers in a range.
• tx - Send a transaction. This is sent only in response to a getdata request.
• block - Send a block. This is sent only in response to a getdata request.
• headers - Send up to 2,000 block headers. Non-generators can download the headers of blocks instead of entire blocks.
• getaddr - Request an addr message containing a bunch of known-active peers (for bootstrapping).
• submitorder, checkorder, and reply - Used when performing an IP transaction.
• alert - Send a network alert.
• ping - Does nothing. Used to check that the connection is still online. A TCP error will occur if the connection has died.