CoAP Adapter

The CoAP protocol adapter exposes CoAP based endpoints for Eclipse Hono™’s south bound Telemetry, Event and Command & Control APIs.

Device Authentication

The CoAP adapter by default requires clients (devices or gateway components) to authenticate during connection establishment. The adapter (currently) supports the use of pre-shared keys (PSK) and X.509 certificates as part of a DTLS handshake for that purpose. Additional variants mentioned in Securing CoAP might be added in the future.

Pre-Shared Key

The CoAP adapter supports authenticating clients using PSK based cipher suites as part of the DTLS handshake. This requires a client to provide a psk_identity in its ClientKeyExchange message as defined in RFC 4279, Section 2 during the DTLS handshake with the CoAP adapter. The adapter uses the provided information to verify the client’s identity as described in Pre-Shared Key based Authentication.

The examples below refer to devices 4711 and gw-1 of tenant DEFAULT_TENANT using auth-ids sensor1 and gw1 and corresponding secrets. The example deployment as described in the Deployment Guides comes pre-configured with the corresponding entities in its device registry component.

NB There is a subtle difference between the device identifier (device-id) and the auth-id a device uses for authentication. See Device Identity for a discussion of the concepts.

X.509

The CoAP adapter supports authenticating clients based on TLS cipher suites using the ECDHE_ECDSA key exchange algorithm as described in RFC 4492. This requires a client to provide an X.509 client certificate containing an ECDSA-capable public key. The adapter uses the information in the client certificate to verify the device’s identity as described in Client Certificate based Authentication.

NB The CoAP adapter needs to be configured for DTLS in order to support this mechanism.

Message Limits

The adapter rejects

  • a client’s request to upload data with status code 429 Too Many Requests and
  • any AMQP 1.0 message containing a command sent by a north bound application

if the message limit that has been configured for the device’s tenant is exceeded.

CoAP Content Format Codes

CoAP doesn’t use a textual identifier for content types. Instead, numbers are used which are maintained by the IANA. The IANA - CoAP Content Formats page lists all (currently) registered codes and the corresponding media types.

Publish Telemetry Data (authenticated Device)

  • URI: /telemetry
  • Method: POST
  • Type:
    • CON: at least once delivery semantics
    • NON: at most once delivery semantics
  • Request Options:
    • (optional) content-format: The type of payload contained in the request body. Required, if request contains payload.
  • Query Parameters:
    • (optional) hono-ttd: The number of seconds the device will wait for the response.
    • (optional) empty: Marks the request as an empty notification.
  • Request Body:
    • (optional) Arbitrary payload encoded according to the given content type. Maybe empty, if URI-query: empty is provided.
  • Response Options:
    • (optional) content-format: A media type describing the semantics and format of payload contained in the response body. This option will only be present if the response contains a command to be executed by the device which requires input data. Note that this option will be empty if the media type contained in the command (AMQP) message’s content-type property cannot be mapped to one of the registered CoAP content-format codes.
    • (optional) location-query: The hono-command query parameter contains the name of the command to execute. This option will only be present if the response contains a command to be executed by the device.
    • (optional) location-path: The location path is command for one-way-commands and command_response/<command-request-id> for commands expecting a response. In the latter case, the location-path option contains exactly the URI-path that the device must use when sending its response to the command. This option will only be present if the response contains a command to be executed by the device.
  • Response Body:
    • (optional) Arbitrary data serving as input to a command to be executed by the device.
    • (optional) Error details, if status code is >= 4.00.
  • Response Codes:
    • 2.04 (Changed): The data in the request body has been accepted for processing. The response may contain a command for the device to execute. Note that if the message type is NON (at most once semantics), this status code does not mean that the message has been delivered to any potential consumer (yet). However, if the message type is CON (at least once semantics), then the adapter waits for the message to be delivered and accepted by a downstream consumer before responding with this status code.
    • 4.00 (Bad Request): The request cannot be processed. Possible reasons include:
      • the request body is empty, and the URI-query option doesn’t contain the empty parameter.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The given tenant is not allowed to use this protocol adapter.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed. Possible reasons for this include:
      • There is no consumer of telemetry data for the given tenant connected to Hono, or the consumer has not indicated that it may receive further messages (not giving credits).
      • If the message type is CON (at least once semantics), the reason may be:
        • The consumer has indicated that it didn’t process the telemetry data.
        • The consumer failed to indicate in time whether it has processed the telemetry data.

This is the preferred way for devices to publish telemetry data. It is available only if the protocol adapter is configured to require devices to authenticate (which is the default).

Examples

The examples provided below make use of the coap-client command line tool which is part of the libcoap project. Precompiled packages should be available for different Linux variants.

Publish some JSON data for device 4711 using default message type CON (at least once):

coap-client -u sensor1@DEFAULT_TENANT -k hono-secret -m POST coaps://hono.eclipseprojects.io/telemetry -t application/json -e '{"temp": 5}'
Tip

coap-client only reports error response-codes, so the expected 2.04 response code will not be printed to the terminal.

Publish some JSON data for device 4711 using message type NON (at most once):

coap-client -u sensor1@DEFAULT_TENANT -k hono-secret -N -m POST coaps://hono.eclipseprojects.io/telemetry -t application/json -e '{"temp": 5}'

Publish some JSON data for device 4711, indicating that the device will wait for 10 seconds to receive the response:

coap-client -u sensor1@DEFAULT_TENANT -k hono-secret -m POST coaps://hono.eclipseprojects.io/telemetry?hono-ttd=10 -t application/json -e '{"temp": 5}'

{
  "brightness": 87
}
Info

In the example above the response actually contains payload that should be used as input to a command to be executed by the device. This is just for illustrative purposes. You will usually get an empty response because there is no downstream application attached which could send any commands to the device.

Publish Telemetry Data (unauthenticated Device)

  • URI: /telemetry/${tenantId}/${deviceId}
  • Method: PUT
  • Type:
    • CON: at least once delivery semantics
    • NON: at most once delivery semantics
  • Request Options:
    • (optional) content-format: The type of payload contained in the request body. Required, if request contains payload.
  • Query Parameters:
    • (optional) hono-ttd: The number of seconds the device will wait for the response.
    • (optional) empty: Marks the request as an empty notification.
  • Request Body:
    • (optional) Arbitrary payload encoded according to the given content type. Maybe empty, if URI-query: empty is provided.
  • Response Options:
    • (optional) content-format: A media type describing the semantics and format of payload contained in the response body. This option will only be present if the response contains a command to be executed by the device which requires input data. Note that this option will be empty if the media type contained in the command (AMQP) message’s content-type property cannot be mapped to one of the registered CoAP content-format codes.
    • (optional) location-query: The hono-command query parameter contains the name of the command to execute. This option will only be present if the response contains a command to be executed by the device.
    • (optional) location-path: The location path is command for one-way-commands and command_response/<command-request-id> for commands expecting a response. In the latter case, the location-path option contains exactly the URI-path that the device must use when sending its response to the command. This option will only be present if the response contains a command to be executed by the device.
  • Response Body:
    • (optional) Arbitrary data serving as input to a command to be executed by the device, if status code is 2.05 (Content).
    • (optional) Error details, if status code is >= 4.00.
  • Response Codes:
    • 2.04 (Changed): The data in the request body has been accepted for processing. The response may contain a command for the device to execute. Note that if the message type is NON (at most once semantics), this status code does not mean that the message has been delivered to any potential consumer (yet). However, if the message type is CON (at least once semantics), then the adapter waits for the message to be delivered and accepted by a downstream consumer before responding with this status code.
    • 4.00 (Bad Request): The request cannot be processed. Possible reasons include:
      • the request body is empty, and the URI-query option doesn’t contain the empty parameter.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The given tenant is not allowed to use this protocol adapter.
      • The given device does not belong to the given tenant.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed. Possible reasons for this include:
      • There is no consumer of telemetry data for the given tenant connected to Hono, or the consumer has not indicated that it may receive further messages (not giving credits).
      • If the message type is CON (at least once semantics), the reason may be:
        • The consumer has indicated that it didn’t process the telemetry data.
        • The consumer failed to indicate in time whether it has processed the telemetry data.

This resource MUST be used by devices that have not authenticated to the protocol adapter. Note that this requires the HONO_COAP_AUTHENTICATION_REQUIRED configuration property to be explicitly set to false.

Examples

Publish some JSON data for device 4711 using default message type CON (at least once):

coap-client -m PUT coap://hono.eclipseprojects.io/telemetry/DEFAULT_TENANT/4711 -t application/json -e '{"temp": 5}'

Publish some JSON data for device 4711 using message type NON (at most once):

coap-client -N -m PUT coap://hono.eclipseprojects.io/telemetry/DEFAULT_TENANT/4711 -t application/json -e '{"temp": 5}'

Publish some JSON data for device 4711, indicating that the device will wait for 10 seconds to receive the response:

coap-client -m PUT coap://hono.eclipseprojects.io/telemetry/DEFAULT_TENANT/4711?hono-ttd=10 -t application/json -e '{"temp": 5}'

{
  "brightness": 87
}

Publish Telemetry Data (authenticated Gateway)

  • URI: /telemetry/${tenantId}/${deviceId}
  • Method: PUT
  • Type:
    • CON: at least once delivery semantics
    • NON: at most once delivery semantics
  • Request Options:
    • (optional) content-format: The type of payload contained in the request body. Required, if request contains payload.
  • Query Parameters:
    • (optional) hono-ttd: The number of seconds the device will wait for the response.
    • (optional) empty: Marks the request as an empty notification.
  • Request Body:
    • (optional) Arbitrary payload encoded according to the given content type. Maybe empty, if URI-query: empty is provided.
  • Response Options:
    • (optional) content-format: A media type describing the semantics and format of payload contained in the response body. This option will only be present if the response contains a command to be executed by the device which requires input data. Note that this option will be empty if the media type contained in the command (AMQP) message’s content-type property cannot be mapped to one of the registered CoAP content-format codes.
    • (optional) location-query: The hono-command query parameter contains the name of the command to execute. This option will only be present if the response contains a command to be executed by the device.
    • (optional) location-path: The location path is command/${tenantId}/${deviceId} for one-way-commands and command_response/${tenantId}/${deviceId}/<command-request-id> for commands expecting a response. In the latter case, the location-path option contains exactly the URI-path that the device must use when sending its response to the command. Note that in both cases the ${tenantId}/${deviceId} path segments indicate the device that the command is targeted at. This option will only be present if the response contains a command to be executed by the device.
  • Response Body:
    • (optional) Arbitrary data serving as input to a command to be executed by the device, if status code is 2.05 (Content).
    • (optional) Error details, if status code is >= 4.00.
  • Response Codes:
    • 2.04 (Changed): The data in the request body has been accepted for processing. The response may contain a command for a device to execute. Note that if the message type is NON (at most once semantics), this status code does not mean that the message has been delivered to any potential consumer (yet). However, if the message type is CON (at least once semantics), then the adapter waits for the message to be delivered and accepted by a downstream consumer before responding with this status code.
    • 4.00 (Bad Request): The request cannot be processed. Possible reasons include:
      • the request body is empty, and the URI-query option doesn’t contain the empty parameter.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The tenant that the gateway belongs to is not allowed to use this protocol adapter.
      • The device belongs to another tenant than the gateway.
      • The gateway is not authorized to act on behalf of the device.
      • The gateway associated with the device is not registered or disabled.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed. Possible reasons for this include:
      • There is no consumer of telemetry data for the given tenant connected to Hono, or the consumer has not indicated that it may receive further messages (not giving credits).
      • If the message type is CON (at least once semantics), the reason may be:
        • The consumer has indicated that it didn’t process the telemetry data.
        • The consumer failed to indicate in time whether it has processed the telemetry data.

This resource can be used by gateway components to publish data on behalf of other devices which do not connect to a protocol adapter directly but instead are connected to the gateway, e.g. using some low-bandwidth radio based technology like SigFox or LoRa. In this case the credentials provided by the gateway during connection establishment with the protocol adapter are used to authenticate the gateway whereas the parameters from the URI are used to identify the device that the gateway publishes data for.

The protocol adapter checks the gateway’s authority to publish data on behalf of the device implicitly by means of retrieving a registration assertion for the device from the configured Device Registration service.

Examples

Publish some JSON data for device 4712 using default message type CON (at least once):

coap-client -u gw@DEFAULT_TENANT -k gw-secret -m PUT coaps://hono.eclipseprojects.io/telemetry/DEFAULT_TENANT/4712 -t application/json -e '{"temp": 5}'

Publish some JSON data for device 4712 using message type NON (at most once):

coap-client -u gw@DEFAULT_TENANT -k gw-secret -N -m PUT coaps://hono.eclipseprojects.io/telemetry/DEFAULT_TENANT/4712 -t application/json -e '{"temp": 5}'

Publish some JSON data for device 4712, indicating that the gateway will wait for 10 seconds to receive the response:

coap-client -u gw@DEFAULT_TENANT -k gw-secret -m PUT coaps://hono.eclipseprojects.io/telemetry/DEFAULT_TENANT/4712?hono-ttd=10 -t application/json -e '{"temp": 5}'

{
  "brightness": 87
}

NB The examples above assume that a gateway device has been registered with psk credentials with auth-id gw and secret gw-secret which is authorized to publish data on behalf of device 4712.

Publish an Event (authenticated Device)

  • URI: /event
  • Method: POST
  • Type:CON
  • Request Options:
    • (optional) content-format: The type of payload contained in the request body. Required, if request contains payload.
  • Query Parameters:
    • (optional) hono-ttd: The number of seconds the device will wait for the response.
    • (optional) empty: Marks the request as an empty notification.
  • Request Body:
    • (optional) Arbitrary payload encoded according to the given content type. Maybe empty, if URI-query: empty is provided.
  • Response Options:
    • (optional) content-format: A media type describing the semantics and format of payload contained in the response body. This option will only be present if the response contains a command to be executed by the device which requires input data. Note that this option will be empty if the media type contained in the command (AMQP) message’s content-type property cannot be mapped to one of the registered CoAP content-format codes.
    • (optional) location-query: The hono-command query parameter contains the name of the command to execute. This option will only be present if the response contains a command to be executed by the device.
    • (optional) location-path: The location path is command for one-way-commands and command_response/<command-request-id> for commands expecting a response. In the latter case, the location-path option contains exactly the URI-path that the device must use when sending its response to the command. This option will only be present if the response contains a command to be executed by the device.
  • Response Body:
    • (optional) Arbitrary data serving as input to a command to be executed by the device, if status code is 2.05 (Content).
    • (optional) Error details, if status code is >= 4.00.
  • Response Codes:
    • 2.04 (Changed): The data in the request body has been accepted for processing. The response may contain a command for the device to execute. Note that if the message type is NON (at most once semantics), this status code does not mean that the message has been delivered to any potential consumer (yet). However, if the message type is CON (at least once semantics), then the adapter waits for the message to be delivered and accepted by a downstream consumer before responding with this status code.
    • 4.00 (Bad Request): The request cannot be processed. Possible reasons include:
      • the request body is empty, and the URI-query option doesn’t contain the empty parameter.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The given tenant is not allowed to use this protocol adapter.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed because there is no consumer of events for the given tenant connected to Hono, or the consumer didn’t process the event.

This is the preferred way for devices to publish events. It is available only if the protocol adapter is configured to require devices to authenticate (which is the default).

Examples

The examples provided below make use of the coap-client command line tool which is part of the libcoap project. Precompiled packages should be available for different Linux variants.

Publish some JSON data for device 4711 using default message type CON (at least once):

coap-client -u sensor1@DEFAULT_TENANT -k hono-secret -m POST coaps://hono.eclipseprojects.io/event -t application/json -e '{"temp": 5}'
Tip

coap-client only reports error response-codes, so the expected 2.04 response code will not be printed to the terminal.

Publish some JSON data for device 4711, indicating that the device will wait for 10 seconds to receive the response:

coap-client -u sensor1@DEFAULT_TENANT -k hono-secret -m POST coaps://hono.eclipseprojects.io/event?hono-ttd=10 -t application/json -e '{"temp": 5}'

{
  "brightness": 87
}
Info

In the example above the response actually contains payload that should be used as input to a command to be executed by the device. This is just for illustrative purposes. You will usually get an empty response because there is no downstream application attached which could send any commands to the device.

Publish an Event (unauthenticated Device)

  • URI: /event/${tenantId}/${deviceId}
  • Method: PUT
  • Type:CON
  • Request Options:
    • (optional) content-format: The type of payload contained in the request body. Required, if request contains payload.
  • Query Parameters:
    • (optional) hono-ttd: The number of seconds the device will wait for the response.
    • (optional) empty: Marks the request as an empty notification.
  • Request Body:
    • (optional) Arbitrary payload encoded according to the given content type. Maybe empty, if URI-query: empty is provided.
  • Response Options:
    • (optional) content-format: A media type describing the semantics and format of payload contained in the response body. This option will only be present if the response contains a command to be executed by the device which requires input data. Note that this option will be empty if the media type contained in the command (AMQP) message’s content-type property cannot be mapped to one of the registered CoAP content-format codes.
    • (optional) location-query: The hono-command query parameter contains the name of the command to execute. This option will only be present if the response contains a command to be executed by the device.
    • (optional) location-path: The location path is command for one-way-commands and command_response/<command-request-id> for commands expecting a response. In the latter case, the location-path option contains exactly the URI-path that the device must use when sending its response to the command. This option will only be present if the response contains a command to be executed by the device.
  • Response Body:
    • (optional) Arbitrary data serving as input to a command to be executed by the device, if status code is 2.05 (Content).
    • (optional) Error details, if status code is >= 4.00.
  • Response Codes:
    • 2.04 (Changed): The data in the request body has been accepted for processing. The response may contain a command for the device to execute. Note that if the message type is NON (at most once semantics), this status code does not mean that the message has been delivered to any potential consumer (yet). However, if the message type is CON (at least once semantics), then the adapter waits for the message to be delivered and accepted by a downstream consumer before responding with this status code.
    • 4.00 (Bad Request): The request cannot be processed. Possible reasons include:
      • the request body is empty, and the URI-query option doesn’t contain the empty parameter.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The given tenant is not allowed to use this protocol adapter.
      • The given device does not belong to the given tenant.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed because there is no consumer of events for the given tenant connected to Hono, or the consumer didn’t process the event.

This resource MUST be used by devices that have not authenticated to the protocol adapter. Note that this requires the HONO_COAP_AUTHENTICATION_REQUIRED configuration property to be explicitly set to false.

Examples

Publish some JSON data for device 4711 using default message type CON (at least once):

coap-client -m PUT coap://hono.eclipseprojects.io/event/DEFAULT_TENANT/4711 -t application/json -e '{"temp": 5}'

Publish some JSON data for device 4711, indicating that the device will wait for 10 seconds to receive the response:

coap-client -m PUT coap://hono.eclipseprojects.io/event/DEFAULT_TENANT/4711?hono-ttd=10 -t application/json -e '{"temp": 5}'

{
  "brightness": 87
}

Publish an Event (authenticated Gateway)

  • URI: /event/${tenantId}/${deviceId}
  • Method: PUT
  • Type:CON
  • Request Options:
    • (optional) content-format: The type of payload contained in the request body. Required, if request contains payload.
  • Query Parameters:
    • (optional) hono-ttd: The number of seconds the device will wait for the response.
    • (optional) empty: Marks the request as an empty notification.
  • Request Body:
    • (optional) Arbitrary payload encoded according to the given content type. Maybe empty, if URI-query: empty is provided.
  • Response Options:
    • (optional) content-format: A media type describing the semantics and format of payload contained in the response body. This option will only be present if the response contains a command to be executed by the device which requires input data. Note that this option will be empty if the media type contained in the command (AMQP) message’s content-type property cannot be mapped to one of the registered CoAP content-format codes.
    • (optional) location-query: The hono-command query parameter contains the name of the command to execute. This option will only be present if the response contains a command to be executed by the device.
    • (optional) location-path: The location path is command/${tenantId}/${deviceId} for one-way-commands and command_response/${tenantId}/${deviceId}/<command-request-id> for commands expecting a response. In the latter case, the location-path option contains exactly the URI-path that the device must use when sending its response to the command. Note that in both cases the ${tenantId}/${deviceId} path segments indicate the device that the command is targeted at. This option will only be present if the response contains a command to be executed by the device.
  • Response Body:
    • (optional) Arbitrary data serving as input to a command to be executed by the device, if status code is 2.05 (Content).
    • (optional) Error details, if status code is >= 4.00.
  • Response Codes:
    • 2.04 (Changed): The data in the request body has been accepted for processing. The response may contain a command for a device to execute. Note that if the message type is NON (at most once semantics), this status code does not mean that the message has been delivered to any potential consumer (yet). However, if the message type is CON (at least once semantics), then the adapter waits for the message to be delivered and accepted by a downstream consumer before responding with this status code.
    • 4.00 (Bad Request): The request cannot be processed. Possible reasons include:
      • the request body is empty, and the URI-query option doesn’t contain the empty parameter.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The tenant that the gateway belongs to is not allowed to use this protocol adapter.
      • The device belongs to another tenant than the gateway.
      • The gateway is not authorized to act on behalf of the device.
      • The gateway associated with the device is not registered or disabled.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed because there is no consumer of events for the given tenant connected to Hono, or the consumer didn’t process the event.

This resource can be used by gateway components to publish data on behalf of other devices which do not connect to a protocol adapter directly but instead are connected to the gateway, e.g. using some low-bandwidth radio based technology like SigFox or LoRa. In this case the credentials provided by the gateway during connection establishment with the protocol adapter are used to authenticate the gateway whereas the parameters from the URI are used to identify the device that the gateway publishes data for.

The protocol adapter checks the gateway’s authority to publish data on behalf of the device implicitly by means of retrieving a registration assertion for the device from the configured Device Registration service.

Examples

Publish some JSON data for device 4712 using default message type CON (at least once):

coap-client -u gw@DEFAULT_TENANT -k gw-secret -m PUT coaps://hono.eclipseprojects.io/event/DEFAULT_TENANT/4712 -t application/json -e '{"temp": 5}'

Publish some JSON data for device 4712, indicating that the gateway will wait for 10 seconds to receive the response:

coap-client -u gw@DEFAULT_TENANT -k gw-secret -m PUT coaps://hono.eclipseprojects.io/event/DEFAULT_TENANT/4712?hono-ttd=10 -t application/json -e '{"temp": 5}'

{
  "brightness": 87
}

NB The examples above assume that a gateway device has been registered with psk credentials with auth-id gw and secret gw-secret which is authorized to publish data on behalf of device 4712.

Command & Control

The CoAP adapter enables devices to receive commands that have been sent by business applications. Commands are delivered to the device by means of a response message. That means a device first has to send a request, indicating how long it will wait for the response. That request can either be a telemetry or event message, with a hono-ttd query parameter (ttd for time till disconnect) specifying the number of seconds the device will wait for the response. The business application can react on that message by sending a command message, targeted at the device. The CoAP adapter will then send the command message as part of the response message to the device.

Commands handled by gateways

Authenticated gateways will receive commands for devices which do not connect to a protocol adapter directly but instead are connected to the gateway. Corresponding devices have to be configured so that they can be used with a gateway. See Configuring Gateway Devices for details.

A gateway can send a request with the hono-ttd query parameter on the /event or /telemetry URI, indicating its readiness to receive a command for any device it acts on behalf of. Note that in this case, the business application will be notified with the gateway id in the device_id property of the downstream message.

An authenticated gateway can also indicate its readiness to receive a command targeted at a specific device. For that, the /event/${tenantId}/${deviceId} or /telemetry/${tenantId}/${deviceId} URI is to be used, containing the id of the device to receive a command for. The business application will receive a notification with that device id.

If there are multiple concurrent requests with a hono-ttd query parameter, sent by the command target device and/or one or more of its potential gateways, the CoAP adapter will choose the device or gateway to send the command to as follows:

  • A request done by the command target device or by a gateway specifically done for that device, has precedence. If there are multiple, concurrent such requests, the last one will get the command message (if received) in its response. Note that the other requests won’t be answered with a command message in their response event if the business application sent multiple command messages. That means commands for a single device can only be requested sequentially, not in parallel.
  • If the above doesn’t apply, a single hono-ttd request on the /event or /telemetry URI, sent by a gateway that the command target device is configured for, will get the command message in its response.
  • If there are multiple, concurrent such requests by different gateways, all configured for the command target device, the request by the gateway will be chosen, through which the target device has last sent a telemetry or event message. If the target device hasn’t sent a message yet and it is thereby unknown via which gateway the device communicates, then one of the requests will be chosen randomly to set the command in its response.

Sending a Response to a Command (authenticated Device)

  • URI: /command_response/${commandRequestId}
  • Method: POST
  • Type: CON
  • Request Options:
    • (optional) content-type: A media type describing the semantics and format of the payload contained in the request body. This option must be set if the result of processing the command on the device is non-empty. In this case the result data is contained in the request body.
  • Query Parameters:
    • (required) hono-cmd-status: An HTTP status code indicating the outcome of processing the command.
  • Request Body:
    • (optional) Arbitrary data representing the result of processing the command on the device.
  • Response Codes:
    • 2.04 (Changed): The response has been successfully delivered to the application that has sent the command.
    • 4.00 (Bad Request): The request cannot be processed because the command status or command request ID are missing/malformed.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The given tenant is not allowed to use this protocol adapter.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed. Possible reasons for this include:
      • There is no application listening for a reply to the given commandRequestId.
      • The application has already given up on waiting for a response.

This is the preferred way for devices to respond to commands. It is available only if the protocol adapter is configured to require devices to authenticate (which is the default).

Example

Send a response to a previously received command with the command-request-id req-id-uuid for device 4711:

coap-client -u sensor1@DEFAULT_TENANT -k hono-secret coaps://hono.eclipseprojects.io/command_response/req-id-uuid?hono-cmd-status=200

Sending a Response to a Command (unauthenticated Device)

  • URI: /command_response/${tenantId}/${deviceId}/${commandRequestId}
  • Method: PUT
  • Type: CON
  • Request Options:
    • (optional) content-type: A media type describing the semantics and format of the payload contained in the request body. This option must be set if the result of processing the command on the device is non-empty. In this case the result data is contained in the request body.
  • Query Parameters:
    • (required) hono-cmd-status: An HTTP status code indicating the outcome of processing the command.
  • Request Body:
    • (optional) Arbitrary data representing the result of processing the command on the device.
  • Response Codes:
    • 2.04 (Changed): The response has been successfully delivered to the application that has sent the command.
    • 4.00 (Bad Request): The request cannot be processed because the command status or command request ID are missing/malformed.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The given tenant is not allowed to use this protocol adapter.
      • The given device does not belong to the given tenant.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed. Possible reasons for this include:
      • There is no application listening for a reply to the given commandRequestId.
      • The application has already given up on waiting for a response.

This resource MUST be used by devices that have not authenticated to the protocol adapter. Note that this requires the HONO_COAP_AUTHENTICATION_REQUIRED configuration property to be explicitly set to false.

Examples

Send a response to a previously received command with the command-request-id req-id-uuid for the unauthenticated device 4711:

coap-client -u sensor1@DEFAULT_TENANT -k hono-secret coaps://hono.eclipseprojects.io/command_response/DEFAULT_TENANT/4711/req-id-uuid?hono-cmd-status=200 -e '{"brightness-changed": true}'

Sending a Response to a Command (authenticated Gateway)

  • URI: /command_response/${tenantId}/${deviceId}/${commandRequestId}
  • Method: PUT
  • Type: CON
  • Request Options:
    • (optional) content-type: A media type describing the semantics and format of the payload contained in the request body. This option must be set if the result of processing the command on the device is non-empty. In this case the result data is contained in the request body.
  • Query Parameters:
    • (required) hono-cmd-status: An HTTP status code indicating the outcome of processing the command.
  • Request Body:
    • (optional) Arbitrary data representing the result of processing the command on the device.
  • Response Codes:
    • 2.04 (Changed): The response has been successfully delivered to the application that has sent the command.
    • 4.00 (Bad Request): The request cannot be processed because the command status or command request ID are missing/malformed.
    • 4.03 (Forbidden): The request cannot be processed because the device’s registration status cannot be asserted. Possible reasons for this include:
      • The given tenant is not allowed to use this protocol adapter.
      • The given device does not belong to the given tenant.
      • The gateway is not authorized to act on behalf of the device.
      • The gateway associated with the device is not registered or disabled.
    • 4.04 (Not Found): The request cannot be processed because the device is disabled or does not exist.
    • 4.13 (Request Entity Too Large): The request cannot be processed because the request body exceeds the maximum supported size.
    • 4.29 (Too Many Requests): The request cannot be processed because the tenant’s message limit for the current period is exceeded.
    • 5.03 (Service Unavailable): The request cannot be processed. Possible reasons for this include:
      • There is no application listening for a reply to the given commandRequestId.
      • The application has already given up on waiting for a response.

This resource can be used by gateway components to send the response to a command on behalf of other devices which do not connect to a protocol adapter directly but instead are connected to the gateway, e.g. using some low-bandwidth radio based technology like SigFox or LoRa. In this case the credentials provided by the gateway during connection establishment with the protocol adapter are used to authenticate the gateway whereas the parameters from the URI are used to identify the device that the gateway publishes data for.

The protocol adapter checks the gateway’s authority to send responses to a command on behalf of the device implicitly by means of retrieving a registration assertion for the device from the configured Device Registration service.

Examples

Send a response to a previously received command with the command-request-id req-id-uuid for device 4712:

coap-client -u gw@DEFAULT_TENANT -k gw-secret coaps://hono.eclipseprojects.io/command_response/DEFAULT_TENANT/4712/req-id-uuid?hono-cmd-status=200 -e '{"brightness-changed": true}'

NB The example above assumes that a gateway device has been registered with psk credentials with auth-id gw and secret gw-secret which is authorized to publish data on behalf of device 4712.

Downstream Meta Data

The adapter includes the following meta data in messages being sent downstream:

Name Type Description
device_id string The identifier of the device that the message originates from.
orig_adapter string Contains the adapter’s type name which can be used by downstream consumers to determine the protocol adapter that the message has been received over. The CoAP adapter’s type name is hono-coap.
orig_address string Contains the (relative) URI that the device has originally posted the data to.
ttd integer Contains the effective number of seconds that the device will wait for a response. This property is only set if the request contains the hono-ttd URI-query option.

The adapter also considers defaults registered for the device at either the tenant or the device level. The values of the default properties are determined as follows:

  1. If the message already contains a non-empty property of the same name, the value if unchanged.
  2. Otherwise, if a default property of the same name is defined in the device’s registration information, that value is used.
  3. Otherwise, if a default property of the same name is defined for the tenant that the device belongs to, that value is used.

Note that of the standard AMQP 1.0 message properties only the content-type and ttl can be set this way to a default value.

Event Message Time-to-live

Events published by devices will usually be persisted by the messaging infrastructure in order to support deferred delivery to downstream consumers.

In most cases, the messaging infrastructure can be configured with a maximum time-to-live to apply to the events so that the events will be removed from the persistent store if no consumer has attached to receive the event before the message expires.

In order to support environments where the messaging infrastructure cannot be configured accordingly, the protocol adapter supports setting a downstream event message’s ttl property based on the default ttl and max-ttl values configured for a tenant/device as described in the Tenant API.

Tenant specific Configuration

The adapter uses the Tenant API to retrieve tenant specific configuration for adapter type hono-coap. The following properties are (currently) supported:

Name Type Default Value Description
enabled boolean true If set to false the adapter will reject all data from devices belonging to the tenant.
max-ttd integer 60 Defines a tenant specific upper limit for the time until disconnect property that devices may include in requests for uploading telemetry data or events. Please refer to the Command & Control concept page for a discussion of this parameter’s purpose and usage.
This property can be set for the hono-coap adapter type as an extension property in the adapter section of the tenant configuration.
If it is not set, then the default value of 60 seconds is used.
timeoutToAck integer - This property has the same semantics as the corresponding property at the adapter level. However, any (non-null) value configured for a tenant takes precedence over the adapter level value for all devices of the particular tenant.