configure: --with-only-libndpi triggers pcap check on MinGW instead of skipping it

[drnpkr]

Bug

On MinGW/MSYS2, passing --with-only-libndpi to configure triggers a PKG_CHECK_MODULES check for libpcap, causing configure to fail if libpcap-dev is not installed. This is the opposite of the intended behavior — building only the library should not require pcap.

Root cause

In configure.ac line 344, the AS_IF condition for the MinGW pcap check is inverted:

AS_IF([test "${enable_npcap+set}" != set && test "${with_only_libndpi+set}" != set],,
      [PKG_CHECK_MODULES([PCAP], [libpcap], [PCAP_LIB="" PCAP_INC="${pkg_cv_PCAP_CFLAGS}"])
       AC_CHECK_LIB([pcap], [pcap_open_live],, [AC_MSG_ERROR([Missing msys2/mingw libpcap library. ...])])])

The empty then-body (,,) means:

• When neither flag is set (default): pcap check skipped (correct)
• When --with-only-libndpi is set: pcap check runs (incorrect)

Compare with the non-MinGW path (line 365) which correctly skips pcap when --with-only-libndpi is set:

elif test "${with_only_libndpi+set}" != set; then :
   AC_CHECK_LIB([pcap], [pcap_open_live], [PCAP_LIB="-lpcap"])

Error output

checking for libpcap... no
configure: error: Package requirements (libpcap) were not met:

Package 'libpcap' not found

Steps to reproduce

On MSYS2/MinGW64:

./autogen.sh
./configure --with-only-libndpi

Suggested fix

The MinGW pcap check should only run when npcap is explicitly enabled and --with-only-libndpi is not set.

[IvanNardi]

@drnpkr, @aouinizied: any news? I see you tried to push a few PRs but you closed them....

[aouinizied]

I did one PR and then gave up as it broke other builds so we went with handling this edge case on nfstream side.