Satoshi Client Operation: Transaction Exchange
---------------------------------------------------------
The Satoshi client advertises locally generated transactions and relays
transactions from other nodes. This article describes the operations
that deal with this exchange of transactions.
See this article for more information on how transactions are validated:
https://en.bitcoin.it/wiki/Protocol_rules#.22tx.22_messages-- Wallet Send --
The client periodically calls SendMessages() (in main.cpp) which calls
ResendWalletTransactions to send transactions generated locallly.
This routine looks to see if there has been a new block since last time,
and if so, and the local transaction are still not in a block,
then the transactions are sent to all nodes.
This is done only about every 30 minutes.
Transactions are only rebroadcast if they have a timestamp at least
5 minutes older than the last block was received. They are sorted
and sent oldest first.[1]
-- Periodic Advertisement --
The client periodically calls SendMessages() (in main.cpp) which
determines if a message should be sent to a remote node.
For each message processing iteration, one node is chosen as the
"trickle node".[2] This node is the only one chosen to receive
an "addr" message, if appropriate.[3]
In the section for inventory, the client sends 1/4 of the transaction
inventory, determined randomly [4], UNLESS they are the trickle node,
in which case they receive ALL transactions.[5] Yes that seems reversed,
but it is what it is. If the node is to receive 1/4 (not all), then the
code also avoids sending any transactions that came from the local
wallet.[6] The comments indicate this is intended to increase privacy.
-- Relay --
When the client receives a transaction via a "tx" messages,
it calls RelayMessage, which calls RelayInventory, which queues the
inventory to be sent to all other nodes.[7]
Footnotes
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1. See CWallet::ResendWalletTransactions in wallet.cpp.
2. See:
pnodeTrickle = vNodesCopy[GetRand(vNodesCopy.size())];
... and ...
SendMessages(pnode, pnode == pnodeTrickle);
in ThreadMessageHandler2() in net.cpp.
3. See:
//
// Message: addr
//
if (fSendTrickle)
{
in SendMessages() in main.cpp.
4. See:
bool fTrickleWait = ((hashRand & 3) != 0);
in SendMessages() in main.cpp.
5. See:
// trickle out tx inv to protect privacy
if (inv.type == MSG_TX && !fSendTrickle)
{
in SendMessages() in main.cpp.
6. See:
// always trickle our own transactions
if (!fTrickleWait)
{
CWalletTx wtx;
if (GetTransaction(inv.hash, wtx))
if (wtx.fFromMe)
fTrickleWait = true;
}
in SendMessages() in main.cpp.
7. Both RelayMessage and RelayInventory in net.h.
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