Add regression tests modifying attributes 2^16 times

This commit adds three new tests:

- a test documenting the limitation originally reported in Unidata#350 (in
  general modifying an attribute about 2^16 times makes it impossible
  to modify this file in ways requiring nc_redef() and nc_enddef() calls).
- a test ensuring that a scalar attribute can be modified 2^16 times
  as long as its type and size remain the same
- a test ensuring that a text attribute can be modified 2^16 times as
  long as its size remains the same

This version uses the nc_redef(), nc_put_att_...(), nc_enddef()
sequence. One could also use nc_open(), nc_put_att_...(), nc_close()
but that would make these tests significantly slower.

nc_test4/tst_atts.c

@@ -424,5 +424,99 @@ main(int argc, char **argv)
  free(data_in);
  }
  SUMMARIZE_ERR;
+ printf("*** testing modification of an attribute 2^16 times (changing size)...");
+ {
+ /* This test documents that if the size of an attribute changes
+ * from one modification to the next we have to delete and
+ * re-create it, incrementing HDF5's attribute creation order
+ * index. In this case after about 2^16 modifications this
+ * index reaches its maximum, making it impossible to modify
+ * this file's metadata because nc_enddef() will fail. */
+ int ncid = -1, i = -1, error_code = NC_NOERR;
+ int data[2] = {1, 2};
+
+ /* Create a file. Note that we use a different file name here
+ * because we will not be able to close this file. */
+ if (nc_create("tst_att_modification.nc", NC_NETCDF4|NC_CLOBBER, &ncid)) ERR;
+ if (nc_enddef(ncid)) ERR;
+
+ /* Modify an attribute 2^16 times. */
+ for (i = 0; i < 65536; ++i)
+ {
+ if (nc_redef(ncid)) ERR;
+
+ /* Note that the attribute size changes every time. */
+ if (nc_put_att_int(ncid, NC_GLOBAL, "attribute", NC_INT,
+ 1 + i % 2, data)) ERR;
+
+ /* nc_enddef() synchronizes attributes. */
+ error_code = nc_enddef(ncid);
+
+ /* After a number of iterations nc_enddef() will fail with
+ * NC_EATTMETA. */
+ if (error_code == NC_EATTMETA)
+ break;
+
+ /* Catch other errors. */
+ if (error_code != NC_NOERR) ERR;
+ }
+
+ /* nc_close() will fail too: just like nc_enddef() it tries to
+ * write dirty attributes to disc. */
+ if (nc_close(ncid) != NC_EATTMETA) ERR;
+
+ /* In this test reaching the end of the loop without encountering
+ * NC_EATTMETA is a failure. */
+ if (error_code != NC_EATTMETA) ERR;
+ }
+ SUMMARIZE_ERR;
+ printf("*** testing modification of a scalar attribute 2^16 times (same type and size)...");
+ {
+ /* This test ensures that a scalar attribute can be modified
+ * 2^16 times as long as its type and size remain the same. */
+ int ncid = -1, i = -1;
+
+ /* Create a file. */
+ if (nc_create(FILE_NAME, NC_NETCDF4|NC_CLOBBER, &ncid)) ERR;
+ if (nc_enddef(ncid)) ERR;
+
+ /* Modify an attribute 2^16 times. */
+ for (i = 0; i < 65536; ++i)
+ {
+ if (nc_redef(ncid)) ERR;
+ /* All built-in attribute types except for NC_CHAR (but
+ * including NC_STRING) use the same logic so it is enough
+ * to test nc_put_att_int(). */
+ if (nc_put_att_int(ncid, NC_GLOBAL, "attribute", NC_INT, 1, &i)) ERR;
+ /* nc_enddef() synchronizes attributes. */
+ if (nc_enddef(ncid)) ERR;
+ }
+
+ if (nc_close(ncid)) ERR;
+ }
+ SUMMARIZE_ERR;
+ printf("*** testing modification of a text attribute 2^16 times (same size)...");
+ {
+ /* This test ensures that a text attribute can be modified
+ * 2^16 times as long as its size remains the same. */
+ int ncid = -1, i = -1;
+ const char *string = "test string"; /* 11 characters */
+
+ /* Create a file. */
+ if (nc_create(FILE_NAME, NC_NETCDF4|NC_CLOBBER, &ncid)) ERR;
+ if (nc_enddef(ncid)) ERR;
+
+ /* Modify an attribute 2^16 times. */
+ for (i = 0; i < 65536; ++i)
+ {
+ if (nc_redef(ncid)) ERR;
+ if (nc_put_att_text(ncid, NC_GLOBAL, "attribute", 11, string)) ERR;
+ /* nc_enddef() synchronizes attributes */
+ if (nc_enddef(ncid)) ERR;
+ }
+
+ if (nc_close(ncid)) ERR;
+ }
+ SUMMARIZE_ERR;
  FINAL_RESULTS;
 }