# HTTP/REST The HTTP/REST Module is suitable for either of the following methods: * manual polling of endpoints (*read*) * continuous polling of endpoints (*subscribe*) * publishing data to endpoints (*write*) The HTTP server to be contacted is described by the Cybus::Connection resource. This resource defines hostname, scheme, port, but also additional headers or authentication info. Each REST endpoint is described by a Cybus::Endpoint resource (no pun intended) that defines access to a particular REST path, optionally specifying additional query parameters or headers for this REST path. The currently supported authentication methods are * Username/password for a *basicAuth* scheme * Arbitrary header for e.g. literal *Bearer Tokens* * *Oauth 2.0* Client Credentials Grant ## Commissioning File Specifics The Endpoints for the HTTP connections may either use `subscribe` for subscribing, `read` for event-driven polling, or `write` for publishing, as described above. [Connection Properties](https://docs.cybus.io/1-8-0/documentation/industry-protocol-details/http-rest/httpconnection) [Endpoint Properties](https://docs.cybus.io/1-8-0/documentation/industry-protocol-details/http-rest/httpendpoint) ## Subscribing Data from a REST Server When subscribing, the REST Server is polled at regular intervals according to the `interval` property of the endpoint resource. Each endpoint must contain a path and may contain additional header and query parameters. If the request fails, a warning is logged but no action is taken. Polling is implemented with a best-effort strategy, which means polling will take place *at best* with the desired interval. If the REST server response takes longer than the polling interval, the next request will not be triggered before the previous has been completed. This prevents building up of infinite queues in the event of unfortunate response time / polling interval combinations. However, this serialization is implemented per endpoint (per REST path), so that multiple requests to different paths can actually be in-flight in parallel. #### Response Message Similar to most protocol implementations in the Cybus Connectware, the server response will be wrapped in a JSON structure that follow the convention timestamp/value, like so: {% code lineNumbers="true" %} ```yaml { 'timestamp': 12391238123, ? // ms since epoch "value" : ... // server response } ``` {% endcode %} If the server responds with a *Content-type=application/json*, the response JSON will be embedded to this object as value of the `"value"` property, like so: {% code lineNumbers="true" %} ```yaml // Original server response { "machineState": "okay", "temperature": 23, "logs": [ "message1", "message2" ] } // Resulting protocol module output at MQTT broker { "timestamp": 12391238123, // ms since epoch "value": { "machineState": "okay", "temperature": 23, "logs": [ "message1", "message2" ] } } ``` {% endcode %} If the server response is not parseable as JSON, it will be embedded into the message object as a string, hence {% code lineNumbers="true" %} ```yaml // Original server response protocol // Resulting protocol module output to Cybus broker { "timestamp": 12391238123, // ms since epoch "value": "protocol" } ``` {% endcode %} ### Reading Data from a REST Server Data can also be *read* from the server on certain events. Reading data from the server is triggered by sending a message to the `/req` topic of the endpoint (see also [Operation results](https://docs.cybus.io/1-8-0/services/service-commissioning-files/structure-of-service-commissioning-files/resources/cybus-endpoint#operation-results)). The response from the server is written to the `/res` topic of the endpoint. The message sent on the endpoint’s `/req` topic does not need to have any content to trigger reading of data. #### Dynamic path If the REST endpoint to be called requires a dynamic (changing) *path*, the configured *path* property can be overwritten by the message to the endpoint. This is done by providing a `path` property string in the message payload. Example message with dynamic path overwriting (to be sent on the `/req` topic): {% code lineNumbers="true" %} ```yaml { 'path': '/bar' } ``` {% endcode %} {% code lineNumbers="true" %} ```yaml # Configured path: /foo # Actual path : /bar ``` {% endcode %} It is also possible to append some path suffix to the configured *path* property by the message to the endpoint. Appending requires providing a `pathAppend` property string in the message payload. Example message with dynamic path appended using `pathAppend` (to be sent on the `/req` topic): {% code lineNumbers="true" %} ```yaml { 'pathAppend': '/bar' } ``` {% endcode %} {% code lineNumbers="true" %} ```yaml # Configured path: /foo # Actual path : /foo/bar ``` {% endcode %} #### Dynamic query parameters If the REST endpoint to be called requires dynamic *query* parameters, these can be provided in the message payload as key-value pairs. Example message with dynamic query parameters (to be sent on the `/req` topic): {% code lineNumbers="true" %} ```yaml { 'query': { 'foo': 'bar', 'user': 'cybus' } } ``` {% endcode %} If the endpoint’s configuration already has a `query` property, both provided query parameters are merged. If any parameters are duplicated, the dynamic parameters from the message payload override the ones from the static configuration. ## Publishing Data to a REST Server The HTTP/REST Protocol Mapper also supports the other direction of data flow, namely publishing (pushing) data from MQTT to a REST server using the `write` property in the Cybus::Endpoint resource. Publishing does not work on a regular time interval but will directly forward any new message that is received from the broker on the `/set` topic of the endpoint. The data of the internal MQTT message must be of type object and has to contain a property called `body`, which will be forwarded as the body of the HTTP request. {% code lineNumbers="true" %} ```yaml { 'body': { 'foo': 'bar' } } ``` {% endcode %} The request mime type header of the outgoing HTTP request will be set according to the internal MQTT message value: If the message contains parseable JSON, the mime type of the HTTP request will be set to *application/json*, otherwise it will be set to *application/octet-stream*. Besides that, no further changes are performed on the request. Any additional headers as defined in the endpoint resource will be passed on as given. The result of the HTTP request is returned on the `/res` topic of the endpoint, as explained here: [Operation results](https://docs.cybus.io/1-8-0/services/service-commissioning-files/structure-of-service-commissioning-files/resources/cybus-endpoint#operation-results). The data message on the result topic will have the following format: {% code lineNumbers="true" %} ```yaml { 'id': 29194, 'timestamp': 1629351968526, 'result': { 'value': 0 } } ``` {% endcode %} In this result message, `id` is the request identifier that was sent on the original request, `timestamp` is the Unix timestamp of when the result was received, and `result` is the JSON object with the actual result, but its content depends on the concrete protocol implementation. If there was an error, the resulting JSON object does not contain a property *result* but instead a property `error`. This property is simply a string variable and contains an explanatory message of the error. Hence, in the error case the data message on the result topic will have the following format: {% code lineNumbers="true" %} ```yaml { 'id': 29194, 'timestamp': 1629351968526, 'error': 'POST request on /foo/bar failed with status: 403 Forbidden' } ``` {% endcode %} #### Dynamic path If the REST endpoint to be called requires a dynamic (changing) *path*, the configured *path* property can be overwritten by the message to the endpoint. This is done by providing a `path` property string in the message payload. Example message with dynamic path overwriting (to be sent on the `/set` topic): {% code lineNumbers="true" %} ```yaml { 'path': '/bar', 'body': { 'baz': 'qux' } } ``` {% endcode %} {% code lineNumbers="true" %} ```yaml # Configured path: /foo # Actual path : /bar ``` {% endcode %} It is also possible to append some path suffix to the configured *path* property by the message to the endpoint. Appending requires providing a `pathAppend` property string in the message payload. Example message with dynamic path appended using `pathAppend` (to be sent on the `/set` topic): {% code lineNumbers="true" %} ```yaml { 'pathAppend': '/bar', 'body': { 'baz': 'qux' } } ``` {% endcode %} {% code lineNumbers="true" %} ```yaml # Configured path: /foo # Actual path : /foo/bar ``` {% endcode %} #### Encoded request body If it is required to send binary data as the request body, it is possible to specify the encoding of the message payload body parameter using a flag called `bufferFromBody`. The contend of the body parameter will then be converted into a buffer, respecting the encoding. Allowed encodings can be found here . {% code lineNumbers="true" %} ```yaml { 'bufferFromBody': 'base64', 'body': 'YmFy' } ``` {% endcode %} ## Connection Probing While HTTP by itself doesn’t require a continuous connection, the HTTP protocol implementation in the Connectware is monitoring the connection state for up-to-date connectivity information. The connection state is estimated by monitoring each successful read and write, and additionally by a probing function scheduled to run if no read or write operation is in progress. The additional probing function is run after the time interval from the property `probeInterval` (default: 10 seconds). By default the probing is performed by sending an *OPTIONS* request against the endpoint server. If this request fails with network error (e.g. ECONNRESET, ETIMEOUT, EUNREACHABLE), the connection state is assumed to be disconnected. If it succeeds, or if it at least gets a HTTP response from the endpoint, the connection is assumed to be connected. Additionally the properties `probePath` and `probeMethod` allow configuring a custom HTTP path and HTTP method to be used by the probing function. See the section *Connection Properties* for more details on these properties. ## Oauth 2.0 Client Credentials Grant This module supports the *Oauth 2.0 Client Credentials Grant* flow for authenticating requests (see [rfc6749 Section-4.4](https://datatracker.ietf.org/doc/html/rfc6749#section-4.4)). Tokens are automatically refreshed when they expire. To use this authentication method the property *oauthClientCredentials* needs to be configured in the connection object providing *client\_id*, *client\_secret*, *auth\_url* and, optionally, as some Oauth 2.0 implementations do not require it, *audience* and *grant\_type* (which defaults to *client\_credentials*). Example configuration: {% code lineNumbers="true" %} ```yaml httpConnection: type: Cybus::Connection properties: protocol: Http targetState: connected connection: scheme: https host: one.host.io oauthClientCredentials: client_id: your_client_id client_secret: your_client_secret auth_url: oauth2.token.server ``` {% endcode %} ## Sample Commissioning File Download: {% file src="" %} {% code lineNumbers="true" %} ```yaml --- # ----------------------------------------------------------------------------# # Commissioning File # ----------------------------------------------------------------------------# # Copyright: Cybus GmbH (2020) # Contact: support@cybus.io # ----------------------------------------------------------------------------# # Source Interface Definition - HTTP/REST endpoint # ----------------------------------------------------------------------------# description: > Sample commissioning file for communicating with HTTP/REST endpoint metadata: name: Http Connectivity icon: https://www.cybus.io/wp-content/uploads/2017/10/for-whom1.svg provider: cybus homepage: https://www.cybus.io version: 0.0.1 parameters: httpHost: description: IP address of the HTTP Server type: string default: 192.168.0.1 httpPort: description: HTTP port of the Server type: number default: 80 initialReconnectDelay: type: integer default: 1000 maxReconnectDelay: type: integer default: 30000 factorReconnectDelay: type: integer default: 2 resources: httpConnection: type: Cybus::Connection properties: protocol: Http connection: scheme: https host: !ref httpHost port: !ref httpPort connectionStrategy: initialDelay: !ref initialReconnectDelay maxDelay: !ref maxReconnectDelay incrementFactor: !ref factorReconnectDelay base: type: Cybus::Endpoint properties: protocol: Http connection: !ref httpConnection subscribe: path: / counter: type: Cybus::Endpoint properties: protocol: Http connection: !ref httpConnection subscribe: path: /counter getPost: type: Cybus::Endpoint properties: protocol: Http connection: !ref httpConnection subscribe: path: /post writePost: type: Cybus::Endpoint properties: protocol: Http connection: !ref httpConnection write: path: /post httpMapping: type: Cybus::Mapping properties: mappings: - subscribe: endpoint: !ref base publish: topic: !sub '${Cybus::MqttRoot}/server/base' - subscribe: endpoint: !ref counter publish: topic: !sub '${Cybus::MqttRoot}/server/counter' - subscribe: endpoint: !ref getPost publish: topic: !sub '${Cybus::MqttRoot}/server/post' - subscribe: endpoint: !ref counter publish: endpoint: !ref writePost ``` {% endcode %}