Re: [lwip-users] netconn_write semantic with NETCONN_NOCOPY flag

[Simon Goldschmidt]

MaX <address@hidden> wrote:

I'm looking to the netconn interface and I don't completely understand the semantic of the netconn_write.

The signature of the function is:

err netcon_write(struct netcon * aNetcon, void* aData, size_t, aSize, u8_t API_Flags);

With the NETCONN_NOCOPY flag, the data should remain unattached until it has been transmitted. 

Therefore, what mechanisms can I use to know when a sent buffer can be reused in a safe way?

TCP has to keep data buffer for retransmission until it is ACKed by the remote host. There'd ere, it needs to maintain unchanged for a while. You can either pass *static* data to netconn_write (NOCOPY), or tell netconn_write to copy data into internal buffers. However, this means extra memcpy plus extra buffer allocation (up to the amount of the TCP window).

Simon