# ESP Local Control

[中文]

## Overview

ESP Local Control (esp_local_ctrl) component in ESP-IDF provides capability to control an ESP device over HTTPS or Bluetooth® Low Energy. It provides access to application defined properties that are available for reading/writing via a set of configurable handlers.

Initialization of the esp_local_ctrl service over HTTPS transport is performed as follows:

>     /* Set the configuration */
>     httpd_ssl_config_t https_conf = HTTPD_SSL_CONFIG_DEFAULT();

>     /* Load server certificate */
>     extern const unsigned char servercert_start[] asm("_binary_servercert_pem_start");
>     extern const unsigned char servercert_end[]   asm("_binary_servercert_pem_end");
>     https_conf.servercert = servercert_start;
>     https_conf.servercert_len = servercert_end - servercert_start;

>     /* Load server private key */
>     extern const unsigned char prvtkey_pem_start[] asm("_binary_prvtkey_pem_start");
>     extern const unsigned char prvtkey_pem_end[]   asm("_binary_prvtkey_pem_end");
>     https_conf.prvtkey_pem = prvtkey_pem_start;
>     https_conf.prvtkey_len = prvtkey_pem_end - prvtkey_pem_start;

>     esp_local_ctrl_config_t config = {
>         .transport = ESP_LOCAL_CTRL_TRANSPORT_HTTPD,
>         .transport_config = {
>             .httpd = &https_conf
>         },
>         .proto_sec = {
>             .version = PROTOCOM_SEC0,
>             .custom_handle = NULL,
>             .sec_params = NULL,
>         },
>         .handlers = {
>             /* User defined handler functions */
>             .get_prop_values = get_property_values,
>             .set_prop_values = set_property_values,
>             .usr_ctx         = NULL,
>             .usr_ctx_free_fn = NULL
>         },
>         /* Maximum number of properties that may be set */
>         .max_properties = 10
>     };

>     /* Start esp_local_ctrl service */
>     ESP_ERROR_CHECK(esp_local_ctrl_start(&config));

You may set security for transport in ESP local control using following options:

1. `PROTOCOM_SEC2`: specifies that SRP6a-based key exchange and end-to-end encryption based on AES-GCM are used. This is the most preferred option as it adds a robust security with Augmented PAKE protocol, i.e., SRP6a.

2. `PROTOCOM_SEC1`: specifies that Curve25519-based key exchange and end-to-end encryption based on AES-CTR are used.

3. `PROTOCOM_SEC0`: specifies that data will be exchanged as a plain text (no security).

4. `PROTOCOM_SEC_CUSTOM`: you can define your own security requirement. Please note that you will also have to provide `custom_handle` of type `protocomm_security_t *` in this context.

Note

The respective security schemes need to be enabled through the project configuration menu. Please refer to the Enabling protocom security version section in Protocol Communication for more details.

## Creating a Property

Now that we know how to start the esp_local_ctrl service, let's add a property to it. Each property must have a unique `name` (string), a `type` (e.g., enum), `flags` (bit fields) and `size`.

The `size` is to be kept 0, if we want our property value to be of variable length (e.g., if it is a string or bytestream). For data types with fixed-length property value, like int, float, etc., setting the `size` field to the right value helps esp_local_ctrl to perform internal checks on arguments received with write requests.

The interpretation of `type` and `flags` fields is totally upto the application, hence they may be used as enumerations, bitfields, or even simple integers. One way is to use `type` values to classify properties, while `flags` to specify characteristics of a property.

Here is an example property which is to function as a timestamp. It is assumed that the application defines `TYPE_TIMESTAMP` and `READONLY`, which are used for setting the `type` and `flags` fields here.

>     /* Create a timestamp property */
>     esp_local_ctrl_prop_t timestamp = {
>         .name        = "timestamp",
>         .type        = TYPE_TIMESTAMP,
>         .size        = sizeof(int32_t),
>         .flags       = READONLY,
>         .ctx         = func_get_time,
>         .ctx_free_fn = NULL
>     };

>     /* Now register the property */
>     esp_local_ctrl_add_property(&timestamp);

Also notice that there is a ctx field, which is set to point to some custom func_get_time(). This can be used inside the property get/set handlers to retrieve timestamp.

Here is an example of `get_prop_values()` handler, which is used for retrieving the timestamp.

>     static esp_err_t get_property_values(size_t props_count,
>                                          const esp_local_ctrl_prop_t *props,
>                                          esp_local_ctrl_prop_val_t *prop_values,
>                                          void *usr_ctx)
>     {
>         for (uint32_t i = 0; i < props_count; i++) {
>             ESP_LOGI(TAG, "Reading %s", props[i].name);
>             if (props[i].type == TYPE_TIMESTAMP) {
>                 /* Obtain the timer function from ctx */
>                 int32_t (*func_get_time)(void) = props[i].ctx;

>                 /* Use static variable for saving the value. This is essential because the value has to be valid even after this function returns. Alternative is to use dynamic allocation and set the free_fn field */
>                 static int32_t ts = func_get_time();
>                 prop_values[i].data = &ts;
>             }
>         }
>         return ESP_OK;
>     }

Here is an example of `set_prop_values()` handler. Notice how we restrict from writing to read-only properties.

>     static esp_err_t set_property_values(size_t props_count,
>                                          const esp_local_ctrl_prop_t *props,
>                                          const esp_local_ctrl_prop_val_t *prop_values,
>                                          void *usr_ctx)
>     {
>         for (uint32_t i = 0; i < props_count; i++) {
>             if (props[i].flags & READONLY) {
>                 ESP_LOGE(TAG, "Cannot write to read-only property %s", props[i].name);
>                 return ESP_ERR_INVALID_ARG;
>             } else {
>                 ESP_LOGI(TAG, "Setting %s", props[i].name);

>                 /* For keeping it simple, lets only log the incoming data */
>                 ESP_LOG_BUFFER_HEX_LEVEL(TAG, prop_values[i].data,
>                                          prop_values[i].size, ESP_LOG_INFO);
>             }
>         }
>         return ESP_OK;
>     }

For complete example see protocols/esp_local_ctrl. The example demonstrates how to set up a secure `esp_local_ctrl` service over HTTPS transport for controlling devices on a local network.

## Client Side Implementation

The client side implementation establishes a protocomm session with the device first, over the supported mode of transport, and then send and receive protobuf messages understood by the esp_local_ctrl service. The service translates these messages into requests and then call the appropriate handlers (set/get). Then, the generated response for each handler is again packed into a protobuf message and transmitted back to the client.

See below the various protobuf messages understood by the esp_local_ctrl service:

1. `get_prop_count` : This should simply return the total number of properties supported by the service.

2. `get_prop_values` : This accepts an array of indices and should return the information (name, type, flags) and values of the properties corresponding to those indices.

3. `set_prop_values` : This accepts an array of indices and an array of new values, which are used for setting the values of the properties corresponding to the indices.

Note that indices may or may not be the same for a property, across multiple sessions. Therefore, the client must only use the names of the properties to uniquely identify them. So, every time a new session is established, the client should first call `get_prop_count` and then `get_prop_values`, hence form an index-to-name mapping for all properties. Now when calling `set_prop_values` for a set of properties, it must first convert the names to indexes, using the created mapping. As emphasized earlier, the client must refresh the index-to-name mapping every time a new session is established with the same device.

The various protocomm endpoints provided by esp_local_ctrl are listed below:

Endpoints provided by ESP Local Control
Endpoint Name (Bluetooth Low Energy + GATT Server) | URI (HTTPS Server + mDNS) | Description
--- | --- | ---
esp_local_ctrl/version | https://<mdns-hostname>.local/esp_local_ctrl/version | Endpoint used for retrieving version string
esp_local_ctrl/control | https://<mdns-hostname>.local/esp_local_ctrl/control | Endpoint used for sending or receiving control messages

## API Reference

### Header File

- components/esp_local_ctrl/include/esp_local_ctrl.h

- This header file can be included with:

  >     #include "esp_local_ctrl.h"

- This header file is a part of the API provided by the `esp_local_ctrl` component. To declare that your component depends on `esp_local_ctrl`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_local_ctrl

  > or

  >     PRIV_REQUIRES esp_local_ctrl

### Functions

const esp_local_ctrl_transport_t *esp_local_ctrl_get_transport_ble(void)

  Function for obtaining BLE transport mode.

const esp_local_ctrl_transport_t *esp_local_ctrl_get_transport_httpd(void)

  Function for obtaining HTTPD transport mode.

esp_err_t esp_local_ctrl_start(const esp_local_ctrl_config_t *config)

  Start local control service.

  Parameters:

    config -- [in] Pointer to configuration structure

  Returns:

    - ESP_OK : Success

    - ESP_FAIL : Failure

esp_err_t esp_local_ctrl_stop(void)

  Stop local control service.

esp_err_t esp_local_ctrl_add_property(const esp_local_ctrl_prop_t *prop)

  Add a new property.

  This adds a new property and allocates internal resources for it. The total number of properties that could be added is limited by configuration option `max_properties`

  Parameters:

    prop -- [in] Property description structure

  Returns:

    - ESP_OK : Success

    - ESP_FAIL : Failure

esp_err_t esp_local_ctrl_remove_property(const char *name)

  Remove a property.

  This finds a property by name, and releases the internal resources which are associated with it.

  Parameters:

    name -- [in] Name of the property to remove

  Returns:

    - ESP_OK : Success

    - ESP_ERR_NOT_FOUND : Failure

const esp_local_ctrl_prop_t *esp_local_ctrl_get_property(const char *name)

  Get property description structure by name.

  This API may be used to get a property's context structure `esp_local_ctrl_prop_t` when its name is known

  Parameters:

    name -- [in] Name of the property to find

  Returns:

    - Pointer to property

    - NULL if not found

esp_err_t esp_local_ctrl_set_handler(const char *ep_name, protocomm_req_handler_t handler, void *user_ctx)

  Register protocomm handler for a custom endpoint.

  This API can be called by the application to register a protocomm handler for an endpoint after the local control service has started.

  Note

  In case of BLE transport the names and uuids of all custom endpoints must be provided beforehand as a part of the `protocomm_ble_config_t` structure set in `esp_local_ctrl_config_t`, and passed to `esp_local_ctrl_start()`.

  Parameters:

    - ep_name -- [in] Name of the endpoint

    - handler -- [in] Endpoint handler function

    - user_ctx -- [in] User data

  Returns:

    - ESP_OK : Success

    - ESP_FAIL : Failure

### Unions

union esp_local_ctrl_transport_config_t
  #include <esp_local_ctrl.h>

  Transport mode (BLE / HTTPD) configuration.

  Public Members

  esp_local_ctrl_transport_config_ble_t *ble

    This is same as `protocomm_ble_config_t`. See `protocomm_ble.h` for available configuration parameters.

  esp_local_ctrl_transport_config_httpd_t *httpd

    This is same as `httpd_ssl_config_t`. See `esp_https_server.h` for available configuration parameters.

### Structures

struct esp_local_ctrl_prop

  Property description data structure, which is to be populated and passed to the `esp_local_ctrl_add_property()` function.

  Once a property is added, its structure is available for read-only access inside `get_prop_values()` and `set_prop_values()` handlers.

  Public Members

  char *name

    Unique name of property

  uint32_t type

    Type of property. This may be set to application defined enums

  size_t size

    Size of the property value, which:

    - if zero, the property can have values of variable size

    - if non-zero, the property can have values of fixed size only, therefore, checks are performed internally by esp_local_ctrl when setting the value of such a property

  uint32_t flags

    Flags set for this property. This could be a bit field. A flag may indicate property behavior, e.g. read-only / constant

  void *ctx

    Pointer to some context data relevant for this property. This will be available for use inside the `get_prop_values` and `set_prop_values` handlers as a part of this property structure. When set, this is valid throughout the lifetime of a property, till either the property is removed or the esp_local_ctrl service is stopped.

  void (*ctx_free_fn)(void *ctx)

    Function used by esp_local_ctrl to internally free the property context when `esp_local_ctrl_remove_property()` or `esp_local_ctrl_stop()` is called.

struct esp_local_ctrl_prop_val

  Property value data structure. This gets passed to the `get_prop_values()` and `set_prop_values()` handlers for the purpose of retrieving or setting the present value of a property.

  Public Members

  void *data

    Pointer to memory holding property value

  size_t size

    Size of property value

  void (*free_fn)(void *data)

    This may be set by the application in `get_prop_values()` handler to tell `esp_local_ctrl` to call this function on the data pointer above, for freeing its resources after sending the `get_prop_values` response.

struct esp_local_ctrl_handlers

  Handlers for receiving and responding to local control commands for getting and setting properties.

  Public Members

  esp_err_t (*get_prop_values)(size_t props_count, const esp_local_ctrl_prop_t props[], esp_local_ctrl_prop_val_t prop_values[], void *usr_ctx)

    Handler function to be implemented for retrieving current values of properties.

    Note

    If any of the properties have fixed sizes, the size field of corresponding element in `prop_values` need to be set

    Param props_count:

      [in] Total elements in the props array

    Param props:

      [in] Array of properties, the current values for which have been requested by the client

    Param prop_values:

      [out] Array of empty property values, the elements of which need to be populated with the current values of those properties specified by props argument

    Param usr_ctx:

      [in] This provides value of the `usr_ctx` field of `esp_local_ctrl_handlers_t` structure

    Return:

      Returning different error codes will convey the corresponding protocol level errors to the client :

      - ESP_OK : Success

      - ESP_ERR_INVALID_ARG : InvalidArgument

      - ESP_ERR_INVALID_STATE : InvalidProto

      - All other error codes : InternalError

  esp_err_t (*set_prop_values)(size_t props_count, const esp_local_ctrl_prop_t props[], const esp_local_ctrl_prop_val_t prop_values[], void *usr_ctx)

    Handler function to be implemented for changing values of properties.

    Note

    If any of the properties have variable sizes, the size field of the corresponding element in `prop_values` must be checked explicitly before making any assumptions on the size.

    Param props_count:

      [in] Total elements in the props array

    Param props:

      [in] Array of properties, the values for which the client requests to change

    Param prop_values:

      [in] Array of property values, the elements of which need to be used for updating those properties specified by props argument

    Param usr_ctx:

      [in] This provides value of the `usr_ctx` field of `esp_local_ctrl_handlers_t` structure

    Return:

      Returning different error codes will convey the corresponding protocol level errors to the client :

      - ESP_OK : Success

      - ESP_ERR_INVALID_ARG : InvalidArgument

      - ESP_ERR_INVALID_STATE : InvalidProto

      - All other error codes : InternalError

  void *usr_ctx

    Context pointer to be passed to above handler functions upon invocation. This is different from the property level context, as this is valid throughout the lifetime of the `esp_local_ctrl` service, and freed only when the service is stopped.

  void (*usr_ctx_free_fn)(void *usr_ctx)

    Pointer to function which will be internally invoked on `usr_ctx` for freeing the context resources when `esp_local_ctrl_stop()` is called.

struct esp_local_ctrl_proto_sec_cfg

  Protocom security configs

  Public Members

  esp_local_ctrl_proto_sec_t version

    This sets protocom security version, sec0/sec1 or custom If custom, user must provide handle via `proto_sec_custom_handle` below

  void *custom_handle

    Custom security handle if security is set custom via `proto_sec` above This handle must follow `protocomm_security_t` signature

  const void *pop

    Proof of possession to be used for local control. Could be NULL.

  const void *sec_params

    Pointer to security params (NULL if not needed). This is not needed for protocomm security 0 This pointer should hold the struct of type esp_local_ctrl_security1_params_t for protocomm security 1 and esp_local_ctrl_security2_params_t for protocomm security 2 respectively. Could be NULL.

struct esp_local_ctrl_config

  Configuration structure to pass to `esp_local_ctrl_start()`

  Public Members

  const esp_local_ctrl_transport_t *transport

    Transport layer over which service will be provided

  esp_local_ctrl_transport_config_t transport_config

    Transport layer over which service will be provided

  esp_local_ctrl_proto_sec_cfg_t proto_sec

    Security version and POP

  esp_local_ctrl_handlers_t handlers

    Register handlers for responding to get/set requests on properties

  size_t max_properties

    This limits the number of properties that are available at a time

### Macros

ESP_LOCAL_CTRL_TRANSPORT_BLE

ESP_LOCAL_CTRL_TRANSPORT_HTTPD

### Type Definitions

typedef struct esp_local_ctrl_prop esp_local_ctrl_prop_t

  Property description data structure, which is to be populated and passed to the `esp_local_ctrl_add_property()` function.

  Once a property is added, its structure is available for read-only access inside `get_prop_values()` and `set_prop_values()` handlers.

typedef struct esp_local_ctrl_prop_val esp_local_ctrl_prop_val_t

  Property value data structure. This gets passed to the `get_prop_values()` and `set_prop_values()` handlers for the purpose of retrieving or setting the present value of a property.

typedef struct esp_local_ctrl_handlers esp_local_ctrl_handlers_t

  Handlers for receiving and responding to local control commands for getting and setting properties.

typedef struct esp_local_ctrl_transport esp_local_ctrl_transport_t

  Transport mode (BLE / HTTPD) over which the service will be provided.

  This is forward declaration of a private structure, implemented internally by `esp_local_ctrl`.

typedef struct protocomm_ble_config esp_local_ctrl_transport_config_ble_t

  Configuration for transport mode BLE.

  This is a forward declaration for `protocomm_ble_config_t`. To use this, application must set CONFIG_BT_ENABLED and include `protocomm_ble.h`.

typedef struct httpd_config esp_local_ctrl_transport_config_httpd_t

  Configuration for transport mode HTTPD.

  This is a forward declaration for `httpd_ssl_config_t` (for HTTPS) or `httpd_config_t` (for HTTP)

typedef enum esp_local_ctrl_proto_sec esp_local_ctrl_proto_sec_t

  Security types for esp_local_control.

typedef protocomm_security1_params_t esp_local_ctrl_security1_params_t

typedef protocomm_security2_params_t esp_local_ctrl_security2_params_t

typedef struct esp_local_ctrl_proto_sec_cfg esp_local_ctrl_proto_sec_cfg_t

  Protocom security configs

typedef struct esp_local_ctrl_config esp_local_ctrl_config_t

  Configuration structure to pass to `esp_local_ctrl_start()`

### Enumerations

enum esp_local_ctrl_proto_sec

  Security types for esp_local_control.

  Values:

  enumerator PROTOCOM_SEC0
  enumerator PROTOCOM_SEC1
  enumerator PROTOCOM_SEC2
  enumerator PROTOCOM_SEC_CUSTOM

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