[rafa-br34]

Currently, Masscan does not flush the file buffer when using the -oL - flags. This does not allow other programs (in my case, Python) to easily parse the output stream.

Here's the code I'm using in case anyone wants to reproduce the issue.

import subprocess

def masscan_iterate(path, port, rate=1000):
        process = subprocess.Popen(
                [
                        path,
                        "-oL", "-",
                        "-p", str(port),
                        "--rate", str(rate),
                        "--exclude", "255.255.255.255",
                        "0.0.0.0/0",
                        "--output-flush", # Added by this PR
                ],
                stdout = subprocess.PIPE,
                stderr = subprocess.DEVNULL
        )

        while process.poll() == None:
                line = process.stdout.readline() # Hangs with the current Masscan version, works with the PR

                if line != b'':
                        print(line)

masscan_iterate("./masscan", 22)

[Frky]

Thanks for the contribution. Could you do two small modifications to your PR?

1. Could you add the same logic for the banner output as well (in output_report_banner)?
2. In order to avoid unnecessary overhead when not needed (for instance when flushing regularly is not a requirement), could you add a command line option to enable the flush only when necessary?

[rafa-br34]

Of course! I'll do that tomorrow.

[rafa-br34]

@Frky
Please let me know if I missed anything or if you would like me to change anything.

[Frky]

Thanks, just a few remarks if you don't mind:

• I suggest to rename the option to --output-flush to match other output options (such as --output-show, etc.)
• Could you add the option to print_nmap_help? (don't mind the function name)
• As mentioned in a comment in the review, maybe the check for fp == stdout isn't necessary anymore now that there is a CLI option to flush explicitly?

What do you think?

[rafa-br34]

Done! Anything else you would like to change?

[Frky]

No, looks good to me. Thank you.

[rafa-br34]

You're welcome!