alterx silently ignores -l when stdin is a pipe, and hangs forever when that pipe is empty

Summary

When stdin is a pipe, alterx ignores -l/-list entirely. Two consequences:

1. Silent data loss — if stdin has data, -l is discarded without a warning and only stdin is processed.
2. Indefinite hang — if stdin is an open pipe that never sends data (the normal situation when alterx is invoked from a script, cron job, or as a subprocess), alterx blocks forever instead of falling back to -l.

This differs from httpx, which merges both sources.

Reproduce

printf 'api.example.com\ndev.example.com\nstaging.example.com\n' > in.txt

1. -l is silently discarded when stdin has data

# -l alone
alterx -l in.txt -limit 100000 -silent </dev/null | wc -l
# 1842   — all derived from example.com

# stdin alone
printf 'zzz.other.com\n' | alterx -limit 100000 -silent | wc -l
# 696    — all derived from other.com

# both together
printf 'zzz.other.com\n' | alterx -l in.txt -limit 100000 -silent | grep -c 'example\.com'
# 0      — every result comes from stdin; in.txt contributed nothing

No warning is printed. A pipeline that passes -l and happens to have data on stdin silently processes the wrong input.

2. Hangs when stdin is open but empty

# stdin redirected — completes instantly
alterx -l in.txt -limit 10 -silent </dev/null
# exit 0, 10 results

# stdin inherited from a parent process that holds it open — hangs forever
alterx -l in.txt -limit 10 -silent > out.txt
# no output, no error, no timeout

This is the common case when alterx runs inside a shell script or is spawned by another program, which is how most people use it.

Comparison with httpx

printf 'example.com\nexample.org\n' > two.txt
printf 'scanme.sh\n' | httpx -l two.txt -silent -nc
# https://example.com
# https://example.org
# https://scanme.sh          <- merged: 2 from -l + 1 from stdin

printf 'zzz.other.com\n' | alterx -l two.txt -limit 100 -silent
# only permutations of zzz.other.com   <- -l dropped

Expected

Either behaviour would be fine, as long as it is consistent and never silent:

• merge stdin with -l, as httpx does; or
• have -l take precedence and skip the stdin read entirely; or
• at minimum, log a warning when stdin overrides -l, and don't block on stdin when -l is set.

The hang in particular seems worth avoiding regardless: if -l was supplied, there is no reason to wait on stdin.

Possibly related

#110 ("Severe process hangs") describes hangs "in a call to it from an external program" and was closed without a reproduction. Being called from an external program is exactly the condition that triggers case 2 above, so this may be the same underlying cause.

Environment

alterx v0.1.0 (reported as latest)
Linux 7.1.5 x86_64
go install github.com/projectdiscovery/alterx/cmd/alterx@latest