Determining that all outbound packets are sent ...

[kolban]

Imagine I have an app that wishes to wake up, connect to an access point, send data and then disconnect from the access point. I am planning to use UDP datagram messages for transmission. In my logic I was coding:

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sendto(socket, ...); // Send the data gram packet
close(socket); // Close the socket
esp_wifi_disconnect(); // Disconnect from the access point

My concern here is that it initially "appears" that when I issue esp_wifi_disconnect(), the outbound packets may not be being sent before the network connections are shutdown. If I change my logic to be:

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sendto(socket, ...); // Send the data gram packet
close(socket); // Close the socket
sleep(1); // Sleep for a second
esp_wifi_disconnect(); // Disconnect from the access point

I don't appear to have an issue. Should esp_wifi_disconnect() honor buffered transmissions before disconnecting? Is there some other logic that I should be using such as some kind of blocking flush() type API call?

[SpenZerX]

I think, before closing the connection you have to check that it is writeable.

sendto(socket, ...); // Send the data gram packet
check/wait writeability or get write finnished callback
sendto(socket, ...); // Send the data gram packet
check/wait writeability or get write finnished callback
close(socket); // Close the socket

if sendto(socket, ...) = write(FD/SD, Buff, Len)

[WiFive]

I think, before closing the connection you have to check that it is writeable.

sendto(socket, ...); // Send the data gram packet
check/wait writeability or get write finnished callback
sendto(socket, ...); // Send the data gram packet
check/wait writeability or get write finnished callback
close(socket); // Close the socket

if sendto(socket, ...) = write(FD/SD, Buff, Len)

But what if the data was copied out of the socket buffer to the WiFi tx buffer and still sending at the RF layer?

[SpenZerX]

But what if the data was copied out of the socket buffer to the WiFi tx buffer and still sending at the RF layer?

Iam not 100% sure, but i think the socket is writeable again when the data is transmitted and the receiver confirmed ok.

[WiFive]

But what if the data was copied out of the socket buffer to the WiFi tx buffer and still sending at the RF layer?

Iam not 100% sure, but i think the socket is writeable again when the data is transmitted and the receiver confirmed ok.

UDP doesn't have ACK