Silence stdout but still get JSON output via API

[bbczeuz]

Context

• Version of iperf3:

iperf 3.9 (cJSON 1.7.13)
Linux localhost 5.13.19-200.fc34.x86_64 #1 SMP Sat Sep 18 16:32:24 UTC 2021 x86_64
Optional features available: CPU affinity setting, IPv6 flow label, SCTP, TCP congestion algorithm setting, sendfile / zerocopy, socket pacing, authentication

• Hardware: x86_64

• Operating system (and distribution, if any): GNU/Linux, Fedora 34

• Other relevant information (for example, non-default compilers, libraries, cross-compiling, etc.):

Bug Report

• Expected Behavior I want to silcence output via stdout, but still get JSON output via iperf_get_test_json_output_string() API call. Silencing was done via iperf_set_test_logfile("/dev/null").

• Actual Behavior If output is being silenced, the iperf_get_test_json_output_string() API call returns NULL

• Steps to Reproduce

    //C++
    test_ = iperf_new_test();
    iperf_set_test_json_output(test_, 1);
    iperf_set_test_logfile("/dev/null");
[...]
    int rc = iperf_run_client(test_);
[...]
    auto res = iperf_get_test_json_output_string(test_);
    if (res == nullptr)
    {
          throw std::runtime_error("Iperf3: empty result");
    }

will throw the exception.

• Possible Workaround

    test_ = iperf_new_test();
    iperf_set_test_json_output(test_, 1);
    output_file_ = std::tmpnam(nullptr);
    iperf_set_test_logfile(output_file_);
[...]
    int rc = iperf_run_client(test_);
[...]
[open and read JSON from file output_file_]

[bmah888]

I'm trying to reproduce this problem but without much success. My test case is to start with examples/mic.c and add the following two lines before the call to iperf_run_client(), which should roughly simulate the setup in your C++ code:

    iperf_set_test_json_output( test, 1 );
    iperf_set_test_logfile( test, "/dev/null" );

Then I added these lines after the call to iperf_run_client(), to do a check similar to yours:

    char *res = iperf_get_test_json_output_string(test);
    if ( res == NULL ) {
        fprintf( stderr, "empty JSON result" );
    }
    else {
	printf("got %zd bytes of JSON\n",
		strlen(iperf_get_test_json_output_string(test)));
    }

This seems to be working correctly in my testing so far, in other words I always get the "got xxx bytes of JSON" output.

[t-higuchi]

I can reproduce this issue on Ubuntu 22.04, where installed version of iperf3 is iperf 3.9 (cJSON 1.7.13), and the issue is gone after iperf3 is upgraded to version 3.12.

I believe this bug is fixed by 98d87bd7e82b98775d9e4c62235132caa54233ab . It will be okay to close this issue.