Fix segfault on user compound dtype conversion callback (#3842)

* Fix segfault on user compound conversion

* Check if lib conversion func is in use

src/H5T.c

@@ -5174,10 +5174,10 @@ H5T_path_noop(const H5T_path_t *p)
 /*-------------------------------------------------------------------------
  * Function:  H5T_path_compound_subset
  *
- * Purpose:   Checks if the source and destination types are both compound.
- *            Tells whether whether the source members are a subset of
- *            destination, and the order is the same, and no conversion
- *            is needed.  For example:
+ * Purpose:   Checks if the library's compound conversion function
+ *            is in use. Tells whether whether the source members are
+ *            a subset of destination, and the order is the same, and
+ *            no conversion is needed.  For example:
  *                  struct source {            struct destination {
  *                      TYPE1 A;      -->          TYPE1 A;
  *                      TYPE2 B;      -->          TYPE2 B;
@@ -5186,8 +5186,9 @@ H5T_path_noop(const H5T_path_t *p)
  *                                                 TYPE5 E;
  *                                             };
  *
- * Return:    A pointer to the subset info struct in p, or NULL if there are
- *            no compounds.  Points directly into the H5T_path_t structure.
+ * Return:    A pointer to the subset info struct in p, or NULL if the
+ *            library's compound conversion function is not in use.
+ *            Points directly into the H5T_path_t structure.
  *
  *-------------------------------------------------------------------------
  */
@@ -5200,7 +5201,9 @@ H5T_path_compound_subset(const H5T_path_t *p)
 
     assert(p);
 
-    if (p->are_compounds)
+    /* Only retrieve private info if the library compound conversion
+     * function is in use */
+    if (!p->conv.is_app && (p->conv.u.lib_func == H5T__conv_struct))
         ret_value = H5T__conv_struct_subset(&(p->cdata));
 
     FUNC_LEAVE_NOAPI(ret_value)

test/dtypes.c

@@ -100,6 +100,15 @@ typedef enum dtype_t {
     OTHER
 } dtype_t; /* This doesn't seem to be used anywhere... -BMR */
 
+typedef struct src_cmpd_t {
+    uint32_t a;
+    float    b;
+} src_cmpd_t;
+
+typedef struct dst_cmpd_t {
+    float b;
+} dst_cmpd_t;
+
 typedef enum { E1_RED, E1_GREEN, E1_BLUE, E1_ORANGE, E1_YELLOW } color_t;
 
 /* Constant for size of conversion buffer for int <-> float exception test */
@@ -160,6 +169,28 @@ reset_hdf5(void)
 #endif
 }
 
+/* Conversion function to test user compound conversion functions */
+static herr_t
+user_compound_convert(hid_t H5_ATTR_UNUSED src_id, hid_t H5_ATTR_UNUSED dst_id, H5T_cdata_t *cdata,
+                      size_t nelmts, size_t H5_ATTR_UNUSED buf_stride, size_t H5_ATTR_UNUSED bkg_stride,
+                      void *buf, void H5_ATTR_UNUSED *bkg, hid_t H5_ATTR_UNUSED dxpl)
+{
+    herr_t retval = EXIT_SUCCESS;
+    switch (cdata->command) {
+        case H5T_CONV_INIT:
+            break;
+        case H5T_CONV_CONV:
+            for (size_t i = 0; i < nelmts; ++i)
+                ((dst_cmpd_t *)buf)[i].b = ((src_cmpd_t *)buf)[i].b;
+            break;
+        case H5T_CONV_FREE:
+            break;
+        default:
+            break;
+    }
+    return retval;
+}
+
 /*-------------------------------------------------------------------------
  * Function:    test_classes
  *
@@ -3788,6 +3819,99 @@ test_compound_18(void)
     return 1;
 } /* end test_compound_18() */
 
+/*-------------------------------------------------------------------------
+ * Function:    test_user_compound_conversion
+ *
+ * Purpose:     Tests that library correctly handles a user-defined
+ *              conversion function between two compound types.
+ *
+ * Return:      Success:        0
+ *              Failure:        number of errors
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+test_user_compound_conversion(void)
+{
+    hid_t             file_id = H5I_INVALID_HID;
+    hid_t             dset_id = H5I_INVALID_HID;
+    hid_t             src = H5I_INVALID_HID, dst = H5I_INVALID_HID;
+    hid_t             space_id = H5I_INVALID_HID;
+    struct src_cmpd_t buf[]    = {{1, 1.0}};
+
+    hsize_t dim = 1;
+    char    filename[1024];
+
+    TESTING("compound conversion via user conversion callback");
+
+    /* Create the source compound datatype */
+    if ((src = H5Tcreate(H5T_COMPOUND, sizeof(struct src_cmpd_t))) < 0)
+        TEST_ERROR;
+
+    if (H5Tinsert(src, "a", HOFFSET(struct src_cmpd_t, a), H5T_NATIVE_UINT32) < 0)
+        TEST_ERROR;
+
+    if (H5Tinsert(src, "b", HOFFSET(struct src_cmpd_t, b), H5T_NATIVE_FLOAT) < 0)
+        TEST_ERROR;
+
+    /* Create the destination compound datatype */
+    if ((dst = H5Tcreate(H5T_COMPOUND, sizeof(struct dst_cmpd_t))) < 0)
+        TEST_ERROR;
+
+    if (H5Tinsert(dst, "b", HOFFSET(struct dst_cmpd_t, b), H5T_IEEE_F32LE) < 0)
+        TEST_ERROR;
+
+    if (H5Tregister(H5T_PERS_SOFT, "src_cmpd_t->dst_cmpd_t", src, dst, &user_compound_convert) < 0)
+        TEST_ERROR;
+
+    /* Create File */
+    h5_fixname(FILENAME[0], H5P_DEFAULT, filename, sizeof filename);
+    if ((file_id = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)) < 0)
+        TEST_ERROR;
+
+    /* Create a dataspace to use */
+    if ((space_id = H5Screate_simple(1, &dim, NULL)) < 0)
+        TEST_ERROR;
+
+    /* Create a dataset with the destination compound datatype */
+    if ((dset_id = H5Dcreate2(file_id, "dataset", dst, space_id, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0)
+        TEST_ERROR;
+
+    if (H5Dwrite(dset_id, src, space_id, H5S_ALL, H5P_DEFAULT, buf) < 0)
+        TEST_ERROR;
+
+    /* Close IDs */
+    if (H5Tunregister(H5T_PERS_SOFT, "src_cmpd_t->dst_cmpd_t", src, dst, &user_compound_convert) < 0)
+        TEST_ERROR;
+    if (H5Tclose(src) < 0)
+        TEST_ERROR;
+    if (H5Tclose(dst) < 0)
+        TEST_ERROR;
+    if (H5Sclose(space_id) < 0)
+        TEST_ERROR;
+    if (H5Dclose(dset_id) < 0)
+        TEST_ERROR;
+    if (H5Fclose(file_id) < 0)
+        TEST_ERROR;
+
+    PASSED();
+    return 0;
+
+error:
+    H5E_BEGIN_TRY
+    {
+        H5Tunregister(H5T_PERS_SOFT, "src_cmpd_t->dst_cmpd_t", src, dst, &user_compound_convert);
+        H5Tclose(src);
+        H5Tclose(dst);
+        H5Sclose(space_id);
+        H5Dclose(dset_id);
+        H5Fclose(file_id);
+    }
+    H5E_END_TRY;
+
+    return 1;
+} /* end test_user_compound_conversion() */
+
 /*-------------------------------------------------------------------------
  * Function:    test_query
  *
@@ -8786,6 +8910,7 @@ main(void)
     nerrors += test_compound_16();
     nerrors += test_compound_17();
     nerrors += test_compound_18();
+    nerrors += test_user_compound_conversion();
     nerrors += test_conv_enum_1();
     nerrors += test_conv_enum_2();
     nerrors += test_conv_bitfield();