feature request: make client report after specific number of bytes transferred

[khimaros]

Context

• Version of iperf3: 3.13

• Hardware: x86

• Operating system (and distribution, if any): Debian 12

Enhancement Request

• Current behavior

it is currently possible to generate a report every number of seconds using -i flag, however, there is no way to report after a specific number of bytes are transferred.

• Desired behavior

provide a new flag to report every number of bytes, for example:

$ iperf3 --interval-bytes=1M

would report after each 1MB was transferred regardless of how much time has elapsed.

it's fine if -i 0 also needs to be passed along to disable time based intervals

• Implementation notes

i'm using this to generate a sound each time a number of bytes is successfully sent on my phone. this helps me search for reception while traveling in remote areas. more frequent sound means higher bandwidth.

i tried to do this using repeated invocations to iperf3, but the startup time (connecting initial server connection/handshake) ends up being the majority of the time and puts an upper bound on the frequency of notifications.

[khimaros]

if i am reading correctly, this could be done with only one or two new variables on the stack in iperf_run_client and no other api or data structure changes.

for client only implementation, it seems like the implementation of this could go somewhere near here: https://github.com/esnet/iperf/blob/master/src/iperf_client_api.c#L651

making use of test->bytes_sent and/or test->bytes_received and tracking them in the while loop with another variable which is reset each time the threshold is reached (rolling over the remaining bytes to the next iteration).

[khimaros]

created this tool to work around the limitation: https://github.com/khimaros/iperf3_watch