sol-bus: Add a helper to parse dictionaries

In D-Bus, there isn't the concept of dictionaries, only dictionary
entries and arrays, and using them is pretty common, so it makes sense
to provide a helper to parse dictionaries.

Signed-off-by: Vinicius Costa Gomes <[email protected]>

src/lib/common/sol-bus.c

@@ -950,3 +950,67 @@ sol_bus_log_callback(sd_bus_message *reply, void *userdata,
 
     return -1;
 }
+
+SOL_API int
+sol_bus_parse_dict(sd_bus_message *m, const struct sol_bus_dict_entry *dict)
+{
+    int r;
+
+    r = sd_bus_message_enter_container(m, SD_BUS_TYPE_ARRAY, "{sv}");
+    SOL_INT_CHECK(r, < 0, r);
+
+    do {
+        const struct sol_bus_dict_entry *entry;
+        const char *member, *contents;
+        char type;
+
+        r = sd_bus_message_enter_container(m, SD_BUS_TYPE_DICT_ENTRY, "sv");
+        if (r <= 0) {
+            r = 0;
+            break;
+        }
+
+        r = sd_bus_message_read_basic(m, SD_BUS_TYPE_STRING, &member);
+        SOL_INT_CHECK_GOTO(r, < 0, end);
+
+        r = sd_bus_message_peek_type(m, &type, &contents);
+        SOL_INT_CHECK_GOTO(r, < 0, end);
+
+        for (entry = dict; entry && entry->name; entry++) {
+            if (streq(entry->name, member))
+                break;
+        }
+
+        if (entry->name) {
+            size_t len;
+
+            r = sd_bus_message_enter_container(m, SD_BUS_TYPE_VARIANT, contents);
+            SOL_INT_CHECK_GOTO(r, < 0, end);
+
+            len = strlen(contents);
+
+            if (entry->type == 'v' && entry->parse_variant)
+                r = entry->parse_variant(m, entry->value);
+            else if (len == 1 && entry->type == contents[0])
+                r = sd_bus_message_read_basic(m, entry->type, entry->value);
+            else {
+                SOL_WRN("Invalid type in message '%s', expecting '%c'",
+                    contents, entry->type);
+                r = -EINVAL;
+            }
+            SOL_INT_CHECK_GOTO(r, < 0, end);
+
+            r = sd_bus_message_exit_container(m);
+            SOL_INT_CHECK_GOTO(r, < 0, end);
+        } else {
+            r = sd_bus_message_skip(m, "v");
+            SOL_INT_CHECK_GOTO(r, < 0, end);
+        }
+
+        r = sd_bus_message_exit_container(m);
+        SOL_INT_CHECK_GOTO(r, < 0, end);
+    } while (1);
+
+end:
+    return r;
+}

src/lib/common/sol-bus.h

@@ -272,3 +272,44 @@ int sol_bus_remove_interfaces_watch(struct sol_bus_client *client,
  */
 int sol_bus_log_callback(sd_bus_message *reply, void *userdata,
     sd_bus_error *ret_error);
+
+/**
+ * @brief Represents an entry in a D-Bus dictionary
+ *
+ * A common idiom in D-Bus is having an array of type 'a{sv}', representing
+ * a dictionary, this struct and sol_bus_parse_dict() help parsing those
+ * data structures.
+ */
+struct sol_bus_dict_entry {
+    /**
+     * @brief The name of the dictionary entry
+     */
+    const char *name;
+    /**
+     * @brief The type of value of the property in the dictionary
+     *
+     * It can be any of the basic types, or 'v' (SD_BUS_TYPE_VARIANT), in
+     * case the type is not basic, the function parse_variant() will be called.
+     */
+    char type;
+    /**
+     * @brief In which place to store the parsed value
+     */
+    void *value;
+    /**
+     * @brief Function to be called in case the value being parsed is not basic.
+     */
+    int (*parse_variant)(sd_bus_message *m, void *value);
+};
+
+/**
+ * @brief Helper to parse D-Bus dictionaries
+ *
+ * @see #sol_bus_dict_entry, the @a dict array must be terminated by an empty entry.
+ *
+ * @param m D-Bus message containing the D-Bus dictionary array
+ * @param dict Dictionary representation, informing how to parse the dictionary.
+ *
+ * @return 0 on success, -errno otherwise.
+ */
+int sol_bus_parse_dict(sd_bus_message *m, const struct sol_bus_dict_entry *dict);