# Metadata handling ### *group* Metadata handling Handle JSON-formatted metadata. ### Enums ### enum jsdrv_meta_flag_e Metadata flag bits (mirrors minibitty’s mb_pubsub_meta_flags_e). *Values:* ### enumerator JSDRV_META_FLAG_RO Topic is read-only; cannot be updated by the host. ### enumerator JSDRV_META_FLAG_HIDE Topic should not appear in the user interface. ### enumerator JSDRV_META_FLAG_DEV Developer option; not for production use. ### Functions ### int32_t jsdrv_meta_syntax_check(const char \*meta) Check the JSON metadata syntax. * **Parameters:** **meta** – The JSON metadata. * **Returns:** 0 or error code. ### int32_t jsdrv_meta_dtype(const char \*meta, uint8_t \*dtype) Get the data type. * **Parameters:** * **meta** – The JSON metadata. * **dtype** – **[out]** The [jsdrv_union_e](https://docs.joulescope.com/en/software/joulescope_driver/h_union.md#group__jsdrv__union_1ga2a05d885f40b41bfd2c499659678b597) data type. * **Returns:** 0 or error code. ### int32_t jsdrv_meta_default(const char \*meta, struct [jsdrv_union_s](https://docs.joulescope.com/en/software/joulescope_driver/h_union.md#_CPPv413jsdrv_union_s) \*value) Get the default value. * **Parameters:** * **meta** – The JSON metadata. * **value** – **[out]** The parsed default value. * **Returns:** 0 or error code. ### int32_t jsdrv_meta_value(const char \*meta, struct [jsdrv_union_s](https://docs.joulescope.com/en/software/joulescope_driver/h_union.md#_CPPv413jsdrv_union_s) \*value) Validate a parameter value using the metadata. * **Parameters:** * **meta** – The JSON metadata. * **value** – **[inout]** The value, which is modified in place. * **Returns:** 0 or error code. ### int32_t jsdrv_meta_flags(const char \*meta, uint32_t \*flags) Get the flags bitmask from the metadata. Parses the “flags” key from the JSON metadata, which is a list of string tokens: “ro”, “hide”, “dev”. Returns a bitmask of [jsdrv_meta_flag_e](#group__jsdrv__meta_1ga444d12671864661f302b6712ae76de86). If “flags” is absent, \*flags is set to 0. * **Parameters:** * **meta** – The JSON metadata. * **flags** – **[out]** The resulting bitmask. * **Returns:** 0 or error code. ## Host-side metadata The driver defines its own topic metadata, such as JS320 `h/fs` and the memory buffer `m/` topics, in `jsdrvp_param_s` tables in `src/**/*_params.c`. Tables in `src/devices//` apply to that device model. Other tables are global driver topics. Topics may contain `{buf}` and `{sig}` placeholders for the buffer and signal ids. `pyjoulescope_driver.metadata_extract` parses these tables into the packaged `host_params.json`. After editing a table, regenerate it with: ```default python -m pyjoulescope_driver.metadata_extract --write ``` A unit test fails when `host_params.json` is stale. The `metadata` entry point combines this host-side metadata with the firmware build’s `pubsub_metadata.json` files to document all topics without a device: ```default python -m pyjoulescope_driver metadata --firmware js320.zip --out js320.html ``` With a connected device, `--diff` compares the live metadata against a saved JSON file to verify the offline output: ```default python -m pyjoulescope_driver metadata --diff js320.json ```