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We observed a regression behavior in iperf3 when using the -n (fixed data size) option.

Under identical test conditions:

iperf3 v3.20 (client) hangs after completing the specified data transfer.

iperf3 v3.1.4 (client) works correctly and exits normally.

This suggests a potential regression introduced after v3.1.4.

Environment

Client OS: Windows 11 24H2 v26100.7840

Server OS: Windows

Tool versions tested:

Client v3.1.4 + Server v3.1.4→ PASS

Client v3.20 + Server v3.1.4 → FAIL

Client v3.20 + Server v3.20 → FAIL

Network: Wlan (192.168.x.x)

Command Used

Client:

iperf3 -c 192.168.x.x -n 50M -i 5

Server:

iperf3 -s

Expected Behavior

After transmitting 50M bytes:

Client should terminate normally.

Server should print final summary.

TCP session should close cleanly.

Actual Behavior (v3.20)

Data transfer appears to complete.

Client hangs and does not exit.

Server continues printing interval lines with:

0.00 Bytes/sec

Manual interruption (Ctrl+C) required.

Working Behavior (v3.1.4)

Transfer completes.

Client exits normally.

Server prints final summary.

No hang observed.

Reproducibility

Issue is consistently reproducible with v3.20.