cloud using a variant of the Zarr protocol and storage
format. This enhancement is generically referred to as "NCZarr".
The data model supported by NCZarr is netcdf-4 minus the user-defined
types and the String type. In this sense it is similar to the CDF-5
data model.
More detailed information about enabling and using NCZarr is
described in the document NUG/nczarr.md and in a
[Unidata Developer's blog entry](https://www.unidata.ucar.edu/blogs/developer/en/entry/overview-of-zarr-support-in).
WARNING: this code has had limited testing, so do use this version
for production work. Also, performance improvements are ongoing.
Note especially the following platform matrix of successful tests:
Platform | Build System | S3 support
------------------------------------
Linux+gcc | Automake | yes
Linux+gcc | CMake | yes
Visual Studio | CMake | no
Additionally, and as a consequence of the addition of NCZarr,
major changes have been made to the Filter API. NOTE: NCZarr
does not yet support filters, but these changes are enablers for
that support in the future. Note that it is possible
(probable?) that there will be some accidental reversions if the
changes here did not correctly mimic the existing filter testing.
In any case, previously filter ids and parameters were of type
unsigned int. In order to support the more general zarr filter
model, this was all converted to char*. The old HDF5-specific,
unsigned int operations are still supported but they are
wrappers around the new, char* based nc_filterx_XXX functions.
This entailed at least the following changes:
1. Added the files libdispatch/dfilterx.c and include/ncfilter.h
2. Some filterx utilities have been moved to libdispatch/daux.c
3. A new entry, "filter_actions" was added to the NCDispatch table
and the version bumped.
4. An overly complex set of structs was created to support funnelling
all of the filterx operations thru a single dispatch
"filter_actions" entry.
5. Move common code to from libhdf5 to libsrc4 so that it is accessible
to nczarr.
Changes directly related to Zarr:
1. Modified CMakeList.txt and configure.ac to support both C and C++
-- this is in support of S3 support via the awd-sdk libraries.
2. Define a size64_t type to support nczarr.
3. More reworking of libdispatch/dinfermodel.c to
support zarr and to regularize the structure of the fragments
section of a URL.
Changes not directly related to Zarr:
1. Make client-side filter registration be conditional, with default off.
2. Hack include/nc4internal.h to make some flags added by Ed be unique:
e.g. NC_CREAT, NC_INDEF, etc.
3. cleanup include/nchttp.h and libdispatch/dhttp.c.
4. Misc. changes to support compiling under Visual Studio including:
* Better testing under windows for dirent.h and opendir and closedir.
5. Misc. changes to the oc2 code to support various libcurl CURLOPT flags
and to centralize error reporting.
6. By default, suppress the vlen tests that have unfixed memory leaks; add option to enable them.
7. Make part of the nc_test/test_byterange.sh test be contingent on remotetest.unidata.ucar.edu being accessible.
Changes Left TO-DO:
1. fix provenance code, it is too HDF5 specific.
This consists of a persistent attribute named
_NCProperties plus two computed attributes
_IsNetcdf4 and _SuperblockVersion.
See the 'Provenance Attributes' section
of docs/attribute_conventions.md for details.
The code for handling character constants
in datalists in ncgen has some problems.
1. It failed on large constants
2. It did not handle e.g. var = 'a', 'b', ...
in the same way that ncgen3 did.
3. The code for generate.c and genchar.c needed
some refactoring to make it a little simpler
(but not simple).
should be under ENABLE_DAP_REMOTE_TESTS.
Fixed to make sure that this is so.
Also attempted to fix ncdap_test/CMakeLists.txt,
but probably got it wrong.
HT to Nico Schlomer.
2. Attempted to reduce the number of conversion errors
when -Wconversion is set. Fixed oc2, but
rest of netcdf remains to be done.
HT to Nico Schlomer.
3. When doing #2, I discovered an error in ncgen.y
that has remained hidden. This required some other
test case fixes.
Ncgen is unable to resolve
ambiguous references to an enum
constant when two different enums
have same econstant name.
Solved by allowing more specific
forms for econstant references.
1. /.../enumname.enumconstname
2. enumname.enumconstname
3. enumconstname
Case 1 is resolved by using the econstant
in the specific enum definition. If none is
found, an error is reported.
Case 2 is resolved by
1. finding an enclosing group with an
enum definition with the specified name
and containing the specified econstant.
If there are more than one, then an error is reported
2. finding all enum definitions in the dataset that have
the specified enum name and contain the specified
econstant. If more than one is found, then an error is reported.
If the above two methods fail, then report an error.
Case 3 is similar to case 2, but all enums, irrespective
of name are used if they contains the specified enum constant.
The ref_tst_econst.cdl test in ncdump is causing ncdump
to fail. So there may be yet some problem.
