printer json FEATURE no prefix for nested nodes flag

New flag LYD_PRINT_NO_JSON_NESTED_PREFIX makes it possible to only
include the module name in the JSON data if it corresponds to the
top-level node in the schema. This is useful if you need libyang to only
print a subtree of the data which you may then wrap.

Author: Humblesaw

src/printer_data.h

@@ -111,6 +111,9 @@ struct ly_out;
                                                       are not explicitly present in the original data tree despite their
                                                       value is equal to their default value.  There is the same limitation regarding
                                                       the presence of ietf-netconf-with-defaults module in libyang context. */
+#define LYD_PRINT_JSON_NO_NESTED_PREFIX  0x100   /**< Do not print the prefix in JSON data for nested nodes (non-top-level). By nested
+                                                      we mean any node that does not appear in the top-level of a corresponding
+                                                      schema. */
 /**
  * @}
  */

src/printer_json.c

@@ -307,7 +307,7 @@ json_print_member(struct jsonpr_ctx *pctx, const struct lyd_node *node, const st
     }
 
     PRINT_COMMA;
-    if ((LEVEL == 1) || json_nscmp(node, snode, pctx->parent)) {
+    if (json_nscmp(node, snode, pctx->parent)) {
         /* print "namespace" */
         node_prefix(node, snode, &pref, NULL);
         ly_print_(pctx->out, "%*s\"%s%s:%s\":%s", INDENT, is_attr ? "@" : "", pref, name, DO_FORMAT ? " " : "");
@@ -1174,6 +1174,10 @@ json_print_data(struct ly_out *out, const struct lyd_node *root, uint32_t option
     /* content */
     LY_LIST_FOR(root, node) {
         pctx.root = node;
+        if (options & LYD_PRINT_JSON_NO_NESTED_PREFIX) {
+            /* update parent, if it has the same namespace it will not be printed */
+            pctx.parent = (const struct lyd_node *)(node->parent);
+        }
         LY_CHECK_RET(json_print_node(&pctx, node));
         if (!(options & LYD_PRINT_SIBLINGS)) {
             break;

tests/utests/data/test_printer_json.c

@@ -135,13 +135,35 @@ test_empty_leaf_list(void **state)
     lyd_free_all(tree);
 }
 
+static void
+test_no_json_nested_prefix(void **state)
+{
+    struct lyd_node *tree;
+    char *buffer = NULL;
+    const char *data = "{\"schema2:a\":{\"b\":{\"c\":\"dflt\"}}}";
+
+    CHECK_PARSE_LYD_PARAM(data, LYD_JSON, 0, LYD_VALIDATE_PRESENT, LY_SUCCESS, tree);
+    assert_int_equal(LY_SUCCESS, lyd_print_mem(&buffer, tree, LYD_JSON, LYD_PRINT_SHRINK | LYD_PRINT_WD_ALL |
+            LYD_PRINT_JSON_NO_NESTED_PREFIX));
+    CHECK_STRING(buffer, "{\"schema2:a\":{\"b\":{\"c\":\"dflt\"}}}");
+    free(buffer);
+
+    assert_int_equal(LY_SUCCESS, lyd_print_mem(&buffer, lyd_child(tree), LYD_JSON, LYD_PRINT_SHRINK | LYD_PRINT_WD_ALL |
+            LYD_PRINT_JSON_NO_NESTED_PREFIX));
+    CHECK_STRING(buffer, "{\"b\":{\"c\":\"dflt\"}}");
+    free(buffer);
+
+    lyd_free_all(tree);
+}
+
 int
 main(void)
 {
     const struct CMUnitTest tests[] = {
         UTEST(test_container_presence, setup),
         UTEST(test_empty_container_wd_trim, setup),
         UTEST(test_empty_leaf_list, setup),
+        UTEST(test_no_json_nested_prefix, setup),
     };
 
     return cmocka_run_group_tests(tests, NULL, NULL);