Understanding the “LastSend” and “LastRecv” Fields in Bitcoin RPC

The getpeerinfo RPC request is a fundamental interface provided by the Bitcoin Core software to retrieve information about peers connected to your local node. Among the various fields returned, two stand out: lastsend and lastrecv. These fields seem like they describe some sort of timestamp or time stamp, but what do they actually represent? In this article, we’ll break down the meaning behind these fields and explore their implications for P2P message transmission.

What does “LastSend” mean?

The lastsend field is expected to contain the UNIX epoch time (UTC) at which a peer last sent a transaction. This means that if you’re checking out of your local node using this method, lastsend will give you the timestamp when the corresponding transaction was committed.

To illustrate this concept further:

Imagine you’re on a P2P network and you send a new block to someone else (let’s call them Peer A). After the block is added to the chain by your local node, you can check out of it using getpeerinfo with the following parameters:

GETPEERINFO peeraddress 1234567890abcdef, lastsend=1643723401, lastrecv=1643723402

Here, lastsend is set to 1643723401 (the time in seconds since January 1, 1970, 00:00 UTC) when the transaction was committed by Peer A. Similarly, lastrecv would be 1643723414 (the time in seconds since January 1, 1970, 00:00 UTC), which is the current timestamp.

What does “LastRecv” mean?

The lastrecv field is expected to contain the UNIX epoch time at which a peer last received data from you. This means that if you’re checking out of your local node using this method, lastrecv will give you the timestamp when your local node last sent or received the corresponding data.

To put it another way: lastsend shows you what happened on the other side (the transaction), while lastrecv shows you what was happening on your end (your local node sending/receiving data).

Here’s an example:

GETPEERINFO peeraddress 1234567890abcdef, lastsend=1643723401, lastrecv=1643723412

In this case, lastsend is set to the time when Peer A committed their transaction. Meanwhile, lastrecv would be set to the current timestamp (1643723412), indicating that your local node was receiving data from Peer A at that time.

Implications for P2P message transmission

When using the getpeerinfo RPC with these fields, you can make informed decisions about whether a transaction or data has been sent and received. For example:

• If lastsend is non-zero and lastrecv is zero, it indicates that your local node has sent data to Peer A in recent times (since the last send).

• If both lastsend and lastrecv are non-zero, it suggests that multiple peers have exchanged data with you recently.

• If either field is zero, it might indicate that some type of error or loss occurred during transmission.

In conclusion, the lastsend and lastrecv fields in Bitcoin Core RPC provide a way to analyze P2P message transmission by checking when each peer last sent and received data. These values ​​offer valuable insights into your local node’s activity on the network, helping you refine your strategies for handling incoming messages and transactions.