re: https://github.com/Unidata/netcdf-c/issues/2119
H/T to [Egbert Eich](https://github.com/e4t) and [Bas Couwenberg](https://github.com/sebastic) for this PR.
It is undesirable to make netcdf be dependent on the availability
of libxml2, but it is desirable to allow its use if available.
In order to do this, a wrapper API (include/ncxml.h) was constructed
that supports either ezxml or libxml2 as the implementation.
Additionally, the xml support code was moved to a new directory
netcdf-c/libncxml.
Primary changes:
* Create a new sub-directory named netcdf-c/libncxml to hold all the xml implementation code.
* Move ezxml.c and ezxml.h to libncxml
* Create a wrapper API -- include/ncxml.h
* Create an implementation, ncxml_ezxml.c to support use of ezxml.
* Create an implementation, ncxml_xml2.c to support use of libxml2.
* Add a check for libxml2 in configure.ac and CMakeLists.txt
* Modify libdap to use the wrapper API instead of ezxml directly.
Misc. Other Changes:
* Change include/netcdf_json.h from built source to be part of the distribution.
re: Partly addresses issue https://github.com/Unidata/netcdf-c/issues/1712.
1. Turn on Hyrax Hack to accept Hyrax style attribute containers.
2. Support Url type as alias for String.
3. Accept the special attribute, "__DAP4_Checksum_CRC32",
to control per-variable checksums.
4. Make _DAP4_xxx attributes be reserved and only accessible
by name (ala _SuperBlock attribute).
5. Fix handling of checksums. There is a hack in the code
that uses an extra flag in the chunk header to indicate
that all variables have checksums. This violates the spec
and will be removed once it is possible to regenerate the
test cases.
Note that checksumming with the Hyrax test server has not
been tested. This, along with some other probable inconsistencies,
needs fixing when OPeNDAP and Unidata can agree on the proper
specification. Testing will be included.
Specific changes:
1. Add dap4 code: libdap4 and dap4_test.
Note that until the d4ts server problem is solved, dap4 is turned off.
2. Modify various files to support dap4 flags:
configure.ac, Makefile.am, CMakeLists.txt, etc.
3. Add nc_test/test_common.sh. This centralizes
the handling of the locations of various
things in the build tree: e.g. where is
ncgen.exe located. See nc_test/test_common.sh
for details.
4. Modify .sh files to use test_common.sh
5. Obsolete separate oc2 by moving it to be part of
netcdf-c. This means replacing code with netcdf-c
equivalents.
5. Add --with-testserver to configure.ac to allow
override of the servers to be used for --enable-dap-remote-tests.
6. There were multiple versions of nctypealignment code. Try to
centralize in libdispatch/doffset.c and include/ncoffsets.h
7. Add a unit test for the ncuri code because of its complexity.
8. Move the findserver code out of libdispatch and into
a separate, self contained program in ncdap_test and dap4_test.
9. Move the dispatch header files (nc{3,4}dispatch.h) to
.../include because they are now shared by modules.
10. Revamp the handling of TOPSRCDIR and TOPBUILDDIR for shell scripts.
11. Make use of MREMAP if available
12. Misc. minor changes e.g.
- #include <config.h> -> #include "config.h"
- Add some no-install headers to /include
- extern -> EXTERNL and vice versa as needed
- misc header cleanup
- clean up checking for misc. unix vs microsoft functions
13. Change copyright decls in some files to point to LICENSE file.
14. Add notes to RELEASENOTES.md
