Streamline integration by linking socket libraries only when required

[jcfr]

DCMTK no longer unconditionally test or link against nsl and socket. These libraries are now only considered on pre-11.4 Solaris systems, where functions such as gethostbyname were historically provided outside libc.

On modern systems (Linux, BSD, macOS, Solaris >= 11.4), networking APIs (gethostbyname, getaddrinfo, socket, etc.) are provided directly by libc, so linking -lnsl or -lsocket is unnecessary.

This streamlines integration of DCMTK into external projects by removing dependencies on libraries that may directly or indirectly pull in a different OpenSSL version than the one bundled with the application.

Background:

• Solaris historically required -lsocket -lnsl for basic networking.
• Since Solaris 11.4, libnsl functionality has been folded into libc.

Verification:

• Confirmed that no libnsl-only symbols are referenced in DCMTK by grepping sources against the exported symbol set of libnsl.

References:

• https://man7.org/linux/man-pages/man3/gethostbyname.3.html
• https://man7.org/linux/man-pages/man3/getaddrinfo.3.html
• https://man7.org/linux/man-pages/man2/socket.2.html
• https://docs.oracle.com/cd/E88353_01/html/E37842/libnsl-3lib.html

[jcfr]

For reference, the following was used to check that no libnsl-only symbols are referenced in DCMTK by grepping sources against the exported symbol set of libnsl:

cd /path/to/src/dcmtk
for func in $(readelf -C --wide --dynamic -s /usr/lib/x86_64-linux-gnu/libnsl.so.2.0.1 | \
    grep -v ' UND ' |  \
    grep " FUNC " | \
    awk '{print $NF}' | \
    sed -E 's/(.+)@@.+/\1/');
do
  ack "$func"
done

[jcfr]

Related:

• Investigate GSSAPI Symbol Conflicts with libtirpc on Modern Linux Systems Slicer/Slicer#8626
• Identify What Introduces libtirpc Dependency on Ubuntu 25.04 Slicer/Slicer#8627

cc: @Punzo @pieper @lassoan

[pieper]

Looks good to me 👍

[michaelonken]

@eichelberg Marco, since you are our Solaris guy, maybe this is something for you.

[eichelberg]

Merged into DCMTK's testing branch.