Improve error message when trying to do nc_def_var_deflate() on vlen type variable

[mrsalo]

trafficstars

Using netcdf 4.9.0 the following snippet of code produces an error message that is hard to understand:

#include <netcdf.h>
#include <stdio.h>

#define BAIL(e)                                                          \
    do {                                                                 \
        printf("Bailing out in file %s, line %d, error:%s.\n", __FILE__, \
               __LINE__, nc_strerror(e));                                \
        return e;                                                        \
    } while (0)

#define CHECK(f) \
    if ((res = f)) BAIL(res);

int main() {
    int res = 0;

    int nc_id = 0;
    CHECK(nc_create("test.nc", NC_NETCDF4, &nc_id));

    int dim_id = 0;
    CHECK(nc_def_dim(nc_id, "number_tm_packets", 100, &dim_id));

    int grp_id = 0;
    CHECK(nc_def_grp(nc_id, "data", &grp_id));

    int vlen_id = 0;
    CHECK(nc_def_vlen(nc_id, "row_of_bytes", NC_BYTE, &vlen_id));

    int dims[] = {dim_id};
    int var_id = 0;
    CHECK(nc_def_var(grp_id, "number_tm_packets", vlen_id, 1, dims, &var_id));

    CHECK(nc_def_var_deflate(grp_id, var_id, 1, 1, 2));
}

The error message is:

error:NetCDF: Filter error: bad id or parameters or duplicate filter.

Could this error message be improved to say something like:

error:NetCDF: Filter error: unsupported operation deflate on vlen type variable

?

See https://github.com/Unidata/netcdf4-python/issues/1175

[DennisHeimbigner]

error:NetCDF: Filter error: unsupported operation deflate on vlen type variable

No, because thata error message is the generic one for NC_EFILTER, which is used in several places to signal a number of different errors. We could however ensure that a log message is generated to give more detailed info. This requires figuring out where in the code, the error is signalled.

[edwardhartnett]

I think that def_var_deflate() should check for legal types and return a NC_EINVAL.

[DennisHeimbigner]

Actually the check is currently made for nc_def_var_filter, but apparently nc_def_var_deflate bypasses that code.