json: add new API json_variant_filter() for dropping fields from objects

src/shared/json.c

@@ -1622,6 +1622,59 @@ void json_variant_dump(JsonVariant *v, JsonFormatFlags flags, FILE *f, const cha
                 fputc('\n', f); /* In case of SSE add a second newline */
 }
 
+int json_variant_filter(JsonVariant **v, char **to_remove) {
+        _cleanup_(json_variant_unrefp) JsonVariant *w = NULL;
+        _cleanup_free_ JsonVariant **array = NULL;
+        size_t i, n = 0, k = 0;
+        int r;
+
+        assert(v);
+
+        if (json_variant_is_blank_object(*v))
+                return 0;
+        if (!json_variant_is_object(*v))
+                return -EINVAL;
+
+        if (strv_isempty(to_remove))
+                return 0;
+
+        for (i = 0; i < json_variant_elements(*v); i += 2) {
+                JsonVariant *p;
+
+                p = json_variant_by_index(*v, i);
+                if (!json_variant_has_type(p, JSON_VARIANT_STRING))
+                        return -EINVAL;
+
+                if (strv_contains(to_remove, json_variant_string(p))) {
+                        if (!array) {
+                                array = new(JsonVariant*, json_variant_elements(*v) - 2);
+                                if (!array)
+                                        return -ENOMEM;
+
+                                for (k = 0; k < i; k++)
+                                        array[k] = json_variant_by_index(*v, k);
+                        }
+
+                        n++;
+                } else if (array) {
+                        array[k++] = p;
+                        array[k++] = json_variant_by_index(*v, i + 1);
+                }
+        }
+
+        if (n == 0)
+                return 0;
+
+        r = json_variant_new_object(&w, array, k);
+        if (r < 0)
+                return r;
+
+        json_variant_unref(*v);
+        *v = TAKE_PTR(w);
+
+        return (int) n;
+}
+
 static int json_variant_copy(JsonVariant **nv, JsonVariant *v) {
         JsonVariantType t;
         JsonVariant *c;

src/shared/json.h

@@ -167,6 +167,8 @@ typedef enum JsonFormatFlags {
 int json_variant_format(JsonVariant *v, JsonFormatFlags flags, char **ret);
 void json_variant_dump(JsonVariant *v, JsonFormatFlags flags, FILE *f, const char *prefix);
 
+int json_variant_filter(JsonVariant **v, char **to_remove);
+
 int json_parse(const char *string, JsonVariant **ret, unsigned *ret_line, unsigned *ret_column);
 int json_parse_continue(const char **p, JsonVariant **ret, unsigned *ret_line, unsigned *ret_column);
 int json_parse_file(FILE *f, const char *path, JsonVariant **ret, unsigned *ret_line, unsigned *ret_column);