Protocol Communication¶

Overview¶

Protocol Communication (protocomm) component manages secure sessions and provides framework for multiple transports. The application can also use protocomm layer directly to have application specific extensions for the provisioning (or non-provisioning) use cases.

Following features are available for provisioning :

Communication security at application level -
- protocomm_security0 (no security)
- protocomm_security1 (curve25519 key exchange + AES-CTR encryption)
Proof-of-possession (support with protocomm_security1 only)

Protocomm internally uses protobuf (protocol buffers) for secure session establishment. Though users can implement their own security (even without using protobuf). One can even use protocomm without any security layer.

Protocomm provides framework for various transports - WiFi (SoftAP+HTTPD), BLE, console - in which case the handler invocation is automatically taken care of on the device side (see Transport Examples below for code snippets).

Note that the client still needs to establish session (only for protocomm_security1) by performing the two way handshake. See Unified Provisioning for more details about the secure handshake logic.

Transport Example (SoftAP + HTTP) with Security 1¶

For complete example see provisioning/legacy/softap_prov

/* Endpoint handler to be registered with protocomm.
 * This simply echoes back the received data. */
esp_err_t echo_req_handler (uint32_t session_id,
                            const uint8_t *inbuf, ssize_t inlen,
                            uint8_t **outbuf, ssize_t *outlen,
                            void *priv_data)
{
    /* Session ID may be used for persistence */
    printf("Session ID : %d", session_id);

    /* Echo back the received data */
    *outlen = inlen;            /* Output data length updated */
    *outbuf = malloc(inlen);    /* This will be deallocated outside */
    memcpy(*outbuf, inbuf, inlen);

    /* Private data that was passed at the time of endpoint creation */
    uint32_t *priv = (uint32_t *) priv_data;
    if (priv) {
        printf("Private data : %d", *priv);
    }

    return ESP_OK;
}

/* Example function for launching a protocomm instance over HTTP */
protocomm_t *start_pc(const char *pop_string)
{
    protocomm_t *pc = protocomm_new();


    /* Config for protocomm_httpd_start() */
    protocomm_httpd_config_t pc_config = {
        .data = {
        .config = PROTOCOMM_HTTPD_DEFAULT_CONFIG()
        }
    };

    /* Start protocomm server on top of HTTP */
    protocomm_httpd_start(pc, &pc_config);

    /* Create Proof of Possession object from pop_string. It must be valid
     * throughout the scope of protocomm endpoint. This need not be static,
     * ie. could be dynamically allocated and freed at the time of endpoint
     * removal */
    const static protocomm_security_pop_t pop_obj = {
        .data = (const uint8_t *) strdup(pop_string),
        .len = strlen(pop_string)
    };

    /* Set security for communication at application level. Just like for
     * request handlers, setting security creates an endpoint and registers
     * the handler provided by protocomm_security1. One can similarly use
     * protocomm_security0. Only one type of security can be set for a
     * protocomm instance at a time. */
    protocomm_set_security(pc, "security_endpoint", &protocomm_security1, &pop_obj);

    /* Private data passed to the endpoint must be valid throughout the scope
     * of protocomm endpoint. This need not be static, ie. could be dynamically
     * allocated and freed at the time of endpoint removal */
    static uint32_t priv_data = 1234;

    /* Add a new endpoint for the protocomm instance, identified by a unique name
     * and register a handler function along with private data to be passed at the
     * time of handler execution. Multiple endpoints can be added as long as they
     * are identified by unique names */
    protocomm_add_endpoint(pc, "echo_req_endpoint",
                           echo_req_handler, (void *) &priv_data);
    return pc;
}

/* Example function for stopping a protocomm instance */
void stop_pc(protocomm_t *pc)
{
    /* Remove endpoint identified by it's unique name */
    protocomm_remove_endpoint(pc, "echo_req_endpoint");

    /* Remove security endpoint identified by it's name */
    protocomm_unset_security(pc, "security_endpoint");

    /* Stop HTTP server */
    protocomm_httpd_stop(pc);

    /* Delete (deallocate) the protocomm instance */
    protocomm_delete(pc);
}

Transport Example (BLE) with Security 0¶

For complete example see provisioning/legacy/ble_prov

/* Example function for launching a secure protocomm instance over BLE */
protocomm_t *start_pc()
{
    protocomm_t *pc = protocomm_new();

    /* Endpoint UUIDs */
    protocomm_ble_name_uuid_t nu_lookup_table[] = {
        {"security_endpoint", 0xFF51},
        {"echo_req_endpoint", 0xFF52}
    };

    /* Config for protocomm_ble_start() */
    protocomm_ble_config_t config = {
        .service_uuid = {
            /* LSB <---------------------------------------
            * ---------------------------------------> MSB */
            0xfb, 0x34, 0x9b, 0x5f, 0x80, 0x00, 0x00, 0x80,
            0x00, 0x10, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00,
        },
        .nu_lookup_count = sizeof(nu_lookup_table)/sizeof(nu_lookup_table[0]),
        .nu_lookup = nu_lookup_table
    };

    /* Start protocomm layer on top of BLE */
    protocomm_ble_start(pc, &config);

    /* For protocomm_security0, Proof of Possession is not used, and can be kept NULL */
    protocomm_set_security(pc, "security_endpoint", &protocomm_security0, NULL);
    protocomm_add_endpoint(pc, "echo_req_endpoint", echo_req_handler, NULL);
    return pc;
}

/* Example function for stopping a protocomm instance */
void stop_pc(protocomm_t *pc)
{
    protocomm_remove_endpoint(pc, "echo_req_endpoint");
    protocomm_unset_security(pc, "security_endpoint");

    /* Stop BLE protocomm service */
    protocomm_ble_stop(pc);

    protocomm_delete(pc);
}

API Reference¶

Header File¶

protocomm/include/common/protocomm.h

Functions¶

protocomm_t *protocomm_new(void)¶

Create a new protocomm instance.

This API will return a new dynamically allocated protocomm instance with all elements of the protocomm_t structure initialized to NULL.

Return

protocomm_t* : On success
NULL : No memory for allocating new instance

void protocomm_delete(protocomm_t *pc)¶

Delete a protocomm instance.

This API will deallocate a protocomm instance that was created using protocomm_new().

Parameters

[in] pc: Pointer to the protocomm instance to be deleted

esp_err_t protocomm_add_endpoint(protocomm_t *pc, const char *ep_name, protocomm_req_handler_t h, void *priv_data)¶

Add endpoint request handler for a protocomm instance.

This API will bind an endpoint handler function to the specified endpoint name, along with any private data that needs to be pass to the handler at the time of call.

Note

An endpoint must be bound to a valid protocomm instance, created using protocomm_new().
This function internally calls the registered add_endpoint() function of the selected transport which is a member of the protocomm_t instance structure.

Return

ESP_OK : Success
ESP_FAIL : Error adding endpoint / Endpoint with this name already exists
ESP_ERR_NO_MEM : Error allocating endpoint resource
ESP_ERR_INVALID_ARG : Null instance/name/handler arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] ep_name: Endpoint identifier(name) string
[in] h: Endpoint handler function
[in] priv_data: Pointer to private data to be passed as a parameter to the handler function on call. Pass NULL if not needed.

esp_err_t protocomm_remove_endpoint(protocomm_t *pc, const char *ep_name)¶

Remove endpoint request handler for a protocomm instance.

This API will remove a registered endpoint handler identified by an endpoint name.

Note

This function internally calls the registered remove_endpoint() function which is a member of the protocomm_t instance structure.

Return

ESP_OK : Success
ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist
ESP_ERR_INVALID_ARG : Null instance/name arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] ep_name: Endpoint identifier(name) string

esp_err_t protocomm_open_session(protocomm_t *pc, uint32_t session_id)¶

Allocates internal resources for new transport session.

Note

An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

Return

ESP_OK : Request handled successfully
ESP_ERR_NO_MEM : Error allocating internal resource
ESP_ERR_INVALID_ARG : Null instance/name arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] session_id: Unique ID for a communication session

esp_err_t protocomm_close_session(protocomm_t *pc, uint32_t session_id)¶

Frees internal resources used by a transport session.

Note

An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

Return

ESP_OK : Request handled successfully
ESP_ERR_INVALID_ARG : Null instance/name arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] session_id: Unique ID for a communication session

esp_err_t protocomm_req_handle(protocomm_t *pc, const char *ep_name, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen)¶

Calls the registered handler of an endpoint session for processing incoming data and generating the response.

Note

An endpoint must be bound to a valid protocomm instance, created using protocomm_new().
Resulting output buffer must be deallocated by the caller.

Return

ESP_OK : Request handled successfully
ESP_FAIL : Internal error in execution of registered handler
ESP_ERR_NO_MEM : Error allocating internal resource
ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist
ESP_ERR_INVALID_ARG : Null instance/name arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] ep_name: Endpoint identifier(name) string
[in] session_id: Unique ID for a communication session
[in] inbuf: Input buffer contains input request data which is to be processed by the registered handler
[in] inlen: Length of the input buffer
[out] outbuf: Pointer to internally allocated output buffer, where the resulting response data output from the registered handler is to be stored
[out] outlen: Buffer length of the allocated output buffer

esp_err_t protocomm_set_security(protocomm_t *pc, const char *ep_name, const protocomm_security_t *sec, const protocomm_security_pop_t *pop)¶

Add endpoint security for a protocomm instance.

This API will bind a security session establisher to the specified endpoint name, along with any proof of possession that may be required for authenticating a session client.

Note

An endpoint must be bound to a valid protocomm instance, created using protocomm_new().
The choice of security can be any protocomm_security_t instance. Choices protocomm_security0 and protocomm_security1 are readily available.

Return

ESP_OK : Success
ESP_FAIL : Error adding endpoint / Endpoint with this name already exists
ESP_ERR_INVALID_STATE : Security endpoint already set
ESP_ERR_NO_MEM : Error allocating endpoint resource
ESP_ERR_INVALID_ARG : Null instance/name/handler arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] ep_name: Endpoint identifier(name) string
[in] sec: Pointer to endpoint security instance
[in] pop: Pointer to proof of possession for authenticating a client

esp_err_t protocomm_unset_security(protocomm_t *pc, const char *ep_name)¶

Remove endpoint security for a protocomm instance.

This API will remove a registered security endpoint identified by an endpoint name.

Return

ESP_OK : Success
ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist
ESP_ERR_INVALID_ARG : Null instance/name arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] ep_name: Endpoint identifier(name) string

esp_err_t protocomm_set_version(protocomm_t *pc, const char *ep_name, const char *version)¶

Set endpoint for version verification.

This API can be used for setting an application specific protocol version which can be verified by clients through the endpoint.

Note

An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

Return

ESP_OK : Success
ESP_FAIL : Error adding endpoint / Endpoint with this name already exists
ESP_ERR_INVALID_STATE : Version endpoint already set
ESP_ERR_NO_MEM : Error allocating endpoint resource
ESP_ERR_INVALID_ARG : Null instance/name/handler arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] ep_name: Endpoint identifier(name) string
[in] version: Version identifier(name) string

esp_err_t protocomm_unset_version(protocomm_t *pc, const char *ep_name)¶

Remove version verification endpoint from a protocomm instance.

This API will remove a registered version endpoint identified by an endpoint name.

Return

ESP_OK : Success
ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist
ESP_ERR_INVALID_ARG : Null instance/name arguments

Parameters

[in] pc: Pointer to the protocomm instance
[in] ep_name: Endpoint identifier(name) string

Type Definitions¶

typedef esp_err_t (*protocomm_req_handler_t)(uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen, void *priv_data)¶: Function prototype for protocomm endpoint handler.

typedef struct protocomm protocomm_t¶

This structure corresponds to a unique instance of protocomm returned when the API protocomm_new() is called. The remaining Protocomm APIs require this object as the first parameter.

Note: Structure of the protocomm object is kept private

Header File¶

protocomm/include/security/protocomm_security.h

Structures¶

struct protocomm_security_pop¶

Proof Of Possession for authenticating a secure session.

Public Members

const uint8_t *data¶: Pointer to buffer containing the proof of possession data

uint16_t len¶: Length (in bytes) of the proof of possession data

struct protocomm_security¶

Protocomm security object structure.

The member functions are used for implementing secure protocomm sessions.

Note: This structure should not have any dynamic members to allow re-entrancy

Public Members

int ver¶: Unique version number of security implementation

esp_err_t (*init)(protocomm_security_handle_t *handle)¶: Function for initializing/allocating security infrastructure

esp_err_t (*cleanup)(protocomm_security_handle_t handle)¶: Function for deallocating security infrastructure

esp_err_t (*new_transport_session)(protocomm_security_handle_t handle, uint32_t session_id)¶: Starts new secure transport session with specified ID

esp_err_t (*close_transport_session)(protocomm_security_handle_t handle, uint32_t session_id)¶: Closes a secure transport session with specified ID

esp_err_t (*security_req_handler)(protocomm_security_handle_t handle, const protocomm_security_pop_t *pop, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen, void *priv_data)¶: Handler function for authenticating connection request and establishing secure session

esp_err_t (*encrypt)(protocomm_security_handle_t handle, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t *outbuf, ssize_t *outlen)¶: Function which implements the encryption algorithm

esp_err_t (*decrypt)(protocomm_security_handle_t handle, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t *outbuf, ssize_t *outlen)¶: Function which implements the decryption algorithm

Type Definitions¶

typedef struct protocomm_security_pop protocomm_security_pop_t¶: Proof Of Possession for authenticating a secure session.

typedef void *protocomm_security_handle_t¶

typedef struct protocomm_security protocomm_security_t¶

Protocomm security object structure.

The member functions are used for implementing secure protocomm sessions.

Note: This structure should not have any dynamic members to allow re-entrancy

Functions¶

esp_err_t protocomm_httpd_start(protocomm_t *pc, const protocomm_httpd_config_t *config)¶

Start HTTPD protocomm transport.

This API internally creates a framework to allow endpoint registration and security configuration for the protocomm.

Note

This is a singleton. ie. Protocomm can have multiple instances, but only one instance can be bound to an HTTP transport layer.

Return

ESP_OK : Success
ESP_ERR_INVALID_ARG : Null arguments
ESP_ERR_NOT_SUPPORTED : Transport layer bound to another protocomm instance
ESP_ERR_INVALID_STATE : Transport layer already bound to this protocomm instance
ESP_ERR_NO_MEM : Memory allocation for server resource failed
ESP_ERR_HTTPD_* : HTTP server error on start

Parameters

[in] pc: Protocomm instance pointer obtained from protocomm_new()
[in] config: Pointer to config structure for initializing HTTP server

esp_err_t protocomm_httpd_stop(protocomm_t *pc)¶

Stop HTTPD protocomm transport.

This API cleans up the HTTPD transport protocomm and frees all the handlers registered with the protocomm.

Return

ESP_OK : Success
ESP_ERR_INVALID_ARG : Null / incorrect protocomm instance pointer

Parameters

[in] pc: Same protocomm instance that was passed to protocomm_httpd_start()

Unions¶

union protocomm_httpd_config_data_t¶

#include <protocomm_httpd.h>

Protocomm HTTPD Configuration Data

Public Members

void *handle¶: HTTP Server Handle, if ext_handle_provided is set to true

protocomm_http_server_config_t config¶: HTTP Server Configuration, if a server is not already active

Structures¶

struct protocomm_http_server_config_t¶

Config parameters for protocomm HTTP server.

Public Members

uint16_t port¶: Port on which the HTTP server will listen

size_t stack_size¶: Stack size of server task, adjusted depending upon stack usage of endpoint handler

unsigned task_priority¶: Priority of server task

struct protocomm_httpd_config_t¶

Config parameters for protocomm HTTP server.

Public Members

bool ext_handle_provided¶: Flag to indicate of an external HTTP Server Handle has been provided. In such as case, protocomm will use the same HTTP Server and not start a new one internally.

protocomm_httpd_config_data_t data¶: Protocomm HTTPD Configuration Data

Macros¶

PROTOCOMM_HTTPD_DEFAULT_CONFIG()¶

Header File¶

protocomm/include/transports/protocomm_ble.h

Functions¶

esp_err_t protocomm_ble_start(protocomm_t *pc, const protocomm_ble_config_t *config)¶

Start Bluetooth Low Energy based transport layer for provisioning.

Initialize and start required BLE service for provisioning. This includes the initialization for characteristics/service for BLE.

Return

ESP_OK : Success
ESP_FAIL : Simple BLE start error
ESP_ERR_NO_MEM : Error allocating memory for internal resources
ESP_ERR_INVALID_STATE : Error in ble config
ESP_ERR_INVALID_ARG : Null arguments

Parameters

[in] pc: Protocomm instance pointer obtained from protocomm_new()
[in] config: Pointer to config structure for initializing BLE

esp_err_t protocomm_ble_stop(protocomm_t *pc)¶

Stop Bluetooth Low Energy based transport layer for provisioning.

Stops service/task responsible for BLE based interactions for provisioning

Note

You might want to optionally reclaim memory from Bluetooth. Refer to the documentation of esp_bt_mem_release in that case.

Return

ESP_OK : Success
ESP_FAIL : Simple BLE stop error
ESP_ERR_INVALID_ARG : Null / incorrect protocomm instance

Parameters

[in] pc: Same protocomm instance that was passed to protocomm_ble_start()

Structures¶

struct name_uuid¶

This structure maps handler required by protocomm layer to UUIDs which are used to uniquely identify BLE characteristics from a smartphone or a similar client device.

Public Members

const char *name¶: Name of the handler, which is passed to protocomm layer

uint16_t uuid¶: UUID to be assigned to the BLE characteristic which is mapped to the handler

struct protocomm_ble_config¶

Config parameters for protocomm BLE service.

Public Members

char device_name[MAX_BLE_DEVNAME_LEN]¶: BLE device name being broadcast at the time of provisioning

uint8_t service_uuid[BLE_UUID128_VAL_LENGTH]¶: 128 bit UUID of the provisioning service

uint8_t *manufacturer_data¶: BLE device manufacturer data pointer in advertisement

ssize_t manufacturer_data_len¶: BLE device manufacturer data length in advertisement

ssize_t nu_lookup_count¶: Number of entries in the Name-UUID lookup table

protocomm_ble_name_uuid_t *nu_lookup¶: Pointer to the Name-UUID lookup table

unsigned ble_bonding : 1¶: BLE bonding

unsigned ble_sm_sc : 1¶: BLE security flag

Macros¶

MAX_BLE_DEVNAME_LEN¶: BLE device name cannot be larger than this value 31 bytes (max scan response size) - 1 byte (length) - 1 byte (type) = 29 bytes

BLE_UUID128_VAL_LENGTH¶

MAX_BLE_MANUFACTURER_DATA_LEN¶: Theoretically, the limit for max manufacturer length remains same as BLE device name i.e. 31 bytes (max scan response size) - 1 byte (length) - 1 byte (type) = 29 bytes However, manufacturer data goes along with BLE device name in scan response. So, it is important to understand the actual length should be smaller than (29 - (BLE device name length) - 2).

Type Definitions¶

typedef struct name_uuid protocomm_ble_name_uuid_t¶: This structure maps handler required by protocomm layer to UUIDs which are used to uniquely identify BLE characteristics from a smartphone or a similar client device.

typedef struct protocomm_ble_config protocomm_ble_config_t¶: Config parameters for protocomm BLE service.

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