What's the meaning of return value "0" of s2n_send?

[Mavis-Dong]

Hi, I got a question on s2n_send. I found that for s2n_recv, in the example, the "0" return value means the connection is closed: https://github.com/aws/s2n-tls/blob/main/docs/examples/s2n_recv.c#L29
However in s2n_send, it's regarded as normal processing: https://github.com/aws/s2n-tls/blob/main/docs/examples/s2n_send.c#L24
What could lead to "0" return value in s2n_send? Thanks!

[maddeleine]

s2n_send can be called with a buffer of size zero. In this case nothing would be sent and the function would return zero bytes sent. It's not considered an error as it is an allowed way of calling this function.