SmartREST

Overview

This reference guide walks through the SmartREST protocol, the data format used, as well as the anatomy and registration of SmartREST templates. Built-in messages as well as errors are also discussed. For a step-by-step guide, see the SmartREST guide

The protocol

SmartREST is built upon the well-established HTTP protocol making it work everywhere since most popular platforms provide an HTTP client through which SmartREST can be accessed. SmartREST communicates exclusively through the /s resource using the HTTP POST method for bidirectional communication. The payload data format in CSV (comma-separated values).

The following example shows the communication between a client and the SmartREST endpoint. Note the Authorization header and the custom X-Id header in the request which specifies the SmartREST template to use for this request.

POST /s HTTP/1.0
Authorization: Basic ...
X-Id: ...
Transfer-Encoding: chunked

100,1234456

Each SmartREST request is represented by one row having a unique unsigned integer as its first value determining the action and subsequent values for parameters.

The SmartREST endpoint yields the following response. Note that the HTTP response code is always 200 unless the SmartREST endpoint is not available.

HTTP/1.1 200 OK
Transfer-Encoding: chunked

200,1,123456,Request result

Each row yielded by the SmartREST endpoint represents a set of extracted values from the result of a SmartREST request containing a unique unsigned integer, the SmartREST request line number and the extracted data values, respectively.

Note: If response from Cumulocity REST API would be empty (e.g. like after deleting a Managed Object) then response from SmartREST would be empty as well. Regardless of registered response templates.

Data format

The CSV (comma-separated values) format is used for communication with the SmartREST endpoint. The following rules must be followed to ensure a frictionless communication.

  • Every row must be terminated by the \n character sequence.
  • Values are always separated by a comma (,).
  • If a value contains double-quotes ("), commas (,), leading or trailing whitespace, line-breaks or tab stops, it must be surrounded by quotes ("). Contained double-quotes (") must be escaped by prepending another double-quote ("").

Examples

The following examples illustrate the rules stated above:

100,Hello world!
101," I have leading whitespace!"
102,"I have trailing whitespace!"
103,"I contain a line
break!"
104,"I have ""quotes""!"
105,I also have 'quotes'!

Processing mode

Similar to Cumulocity REST implementation every communication in SmartREST which can lead to data update (i. e., POST, PUT, DELETE) supports two processing modes, PERSISTENT or TRANSIENT. If the data sent to the SmartREST endpoint must be both stored in Cumulocity database and be transferred to real-time processing, then PERSISTENT mode should be set. It is also enabled by default and does not require additional configuration.

In case when it is only needed to communicate data to real-time processing, the TRANSIENT processing mode should be specified by adding it to the header of HTTP request:

POST /s HTTP/1.0
Authorization: Basic ...
X-Id: ...
X-Cumulocity-Processing-Mode: TRANSIENT
Transfer-Encoding: chunked

100,1234456

Please, note that with TRANSIENT mode in the header the body data is not persisted in Cumulocity database.

During real-time processing, the Cumulocity Event Language scripts can be used to define if updates should be stored in the database or not.

Templates

SmartREST templates are a collection of request and response templates used for the conversion of CSV data and Cumulocity REST API calls. Additionally, SmartREST templates contain a template identifier which is compared to the custom X-Id header field to identify the SmartREST template used for processing.

Each request and response template has a unique numeric identifier called the message identifier which is referenced by the first value of each SmartREST request or response row. To avoid collision with one of the default message identifiers, developers are advised to choose message identifiers starting at 100.

Request templates

A request template contains all necessary information to convert a SmartREST request into a corresponding REST API call which is then sent to the platform.

A request template contains the following information:

  • A unique unsigned integer as a message identifier
  • The request method, e.g. GET or POST.
  • The resource URI, for instance /inventory/managedObjects
  • The Content-TYpe and Accept header values of the sent and received data
  • A placeholder such as %%
  • The expected request parameters such as STRINGs, NUMBERs, UNSIGNED integers and DATEs
  • The template string with placeholders for each parameter

Response templates

A response template contains the necessary information to extract data values from a platform REST API call response which are then sent back to the client in the CSV data format.

The following information is contained within a response template:

  • A unique unsigned integer as a message identifier
  • A JSON path referencing a base object or object list to extract data from, e.g. $ or $.managedObjects. If the JSON path points to a list of objects, one row of extracted data for each object in the list is yielded.
  • A JSON path which must exist within the base object or base object list in order to extract values, e.g. $.id. The value is not added to the response.
  • A variable number of JSON paths for each value to extract, e.g. $.id, $.name or $.type. Values are added to the response in the order they were defined in the template.

Registration process

This reference guide solely focusses on the registration of SmartREST templates using the SmartREST /s endpoint. Alternatively, templates can also be registered using the platform inventory API.

Before a SmartREST template can be registered, its existence must be checked. If the template already exists, a registration is not necessary and yields an error message.

The existence of a SmartREST template can be checked by making an empty request:

POST /s HTTP/1.0
Authorization: Basic ...
X-Id: ...
Transfer-Encoding: chunked

If the template exists, the following response is yielded where the message identifier 20 indicates that the template exists in the inventory and the parameter 123456 indicates the managed object GId of the template:

HTTP/1.1 200 OK
Transfer-Encoding: chunked

20,12345

If the template does not exist, a response containing an error message is yielded:

HTTP/1.1 200 OK
Transfer-Encoding: chunked

40,"No template for this X-ID."

If the template does not exist, a template registration request can be issued using the previously checked X-Id.

Templates can be registered with one single request containing SmartREST template in the form of CSV data. The difference between a template registration request and a normal SmartREST request is that rows are not processed individually during template registration.

POST /s HTTP/1.0
Authorization: Basic ...
X-Id: ...
Transfer-Encoding: chunked

10,100,POST,/inventory/managedObjects,application/vnd.com.nsn.cumulocity.managedObject+json,application/vnd.com.nsn.cumulocity.managedObject+json,,,"{""name"":""Test Device"",""type"":""com_example_TestDevice"",""c8y_IsDevice"":{}}"
11,201,,"$.c8y_IsDevice","$.id"

Should the template registration be successful, a similar response like above will be returned.

HTTP/1.1 200 OK
Transfer-Encoding: chunked

20,12345

Syntax

Each request and response template is contained within one row of the template data. Request templates are indicated by the message identifier 10 and response templates by the identifier 11. Should one of those message identifiers occour in a SmartREST request, the entire request is treated as a template. Thus any other message identifier besides 10 and 11 will yield an error.

Request templates

Request templates have the following syntax:

10,<ID>,<METHOD>,<URI>,<CONTENT>,<ACCEPT>,<PLACEHOLDER>,<PARAMS>,<TEMPLATE>

Where:

  • <ID> is the message identifier of the request template.
  • <METHOD> is the HTTP method used for the request. GET, POST, PUT and DELETE are supported.
  • <URI> is the resource identifier.
  • <CONTENT> is the Content-Type header field value.
  • <ACCEPT> is the Accept header field value. This is mostly equal to <CONTENT>.
  • <PLACEHOLDER> is the placeholder string which is replaced by parameters in the request URI and template string.
  • <PARAMS> is a space-separated list of parameter types which are required for the template. The number of occourances of the placeholder string in the request URI and template string must be equal to the number of parameters specified.
    • STRING parameters will only yield an error if no value is specified.
    • UNSIGNED parameters will yield an error if the supplied parameter is not an unsigned integer.
    • INTEGER parameters will yield an error if the supplied parameter is not a signed integer.
    • NUMBER parameters will yield an error if the supplied parameter is not a floating-point number.
    • DATE parameters will yield an error if the parameter cannot be parsed as a date.
    • NOW parameters will never yield an error. No request parameter is required.
  • <TEMPLATE> is the actual template string which gets sent as payload to the platform after the placeholders have been replaced with the parameter values.
Example

Create a device:

10,100,POST,/inventory/managedObjects,application/vnd.com.nsn.cumulocity.managedObject+json,application/vnd.com.nsn.cumulocity.managedObject+json,,,"{""name"":""Test Device"",""type"":""com_example_TestDevice"",""c8y_IsDevice"":{}}"

Explanation:

  • 10 describes a request template.
  • 100 is the message identifier of the request template.
  • POST is the HTTP method used.
  • /inventory/managedObjects is the resource identifier.
  • application/vnd.com.nsn.cumulocity.managedObject+json is the content type.
  • application/vnd.com.nsn.cumulocity.managedObject+json is the accept content type.
  • %% is the placeholder string.
  • STRING specifies that the request accepts one parameter which must be a string.

Update operation to EXECUTING:

10,101,PUT,/devicecontrol/operations/%%, application/vnd.com.nsn.cumulocity.operation+json, application/vnd.com.nsn.cumulocity.operation+json,%%,INTEGER,"{""status"":""EXECUTING""}"

Response templates

Response templates have the following syntax:

11,<ID>,<BASE>,<COND>,<VALUE>[,<VALUE>]

Where:

  • <ID> is the message identifier of the response template.
  • <BASE> is the base JSON path pointing to an object or object list from which the values are extracted.
  • <COND> is a conditional JSON path which gets checked for existance. Only if the path exists, values are extracted.
  • <VALUE> is a JSON path pointing to a value to extract within the base object or object in the base object list. An unlimited number of <VALUE>s can be specified.
Example
11,201,,"$.c8y_IsDevice","$.id"

Explanation:

  • 11 describes a response template.
  • 201 is the message identifier of the response template.
  • The base object JSON path is empty, thus $ is assumed.
  • $.c8y_IsDevice specifies that values are only extracted if the object has a fragment called c8y_IsDevice.
  • $.id is the value extracted, namely the device ID.

Using SmartREST with multiple X-Ids

SmartREST supports sending of messages for different X-Ids within the same request. In this case the X-Id header mustn't be used but instead the body will contain additional information about which lines belong to which X-Id.

Sending messages

To indicate the X-Id in the body it is possible to include the following line

15,myxid

All following lines will be handled with the given X-Id until you enter the next X-Id line.

15,myxid1
...
...
15,myxid2
...

Receiving messages

When sending with multiple X-Ids the response also can contain responses from multiple X-Ids. The response will contain an additional line that will indicate which X-Id the following lines are from. The second value in this line indicates how many lines are following from this X-Id.

87,2,myxid1
...
...
87,1,myxid2
...

Checking if templates are registered

You can check if templates are already existing by just include X-Id lines in the body.

15,myxid1
15,myxid2
15,myxid3
15,myxid4

You will get the same response like described in the registration process but for every line.

20,12345
20,12346
40,"No template for this X-ID."
20,12347

Registering templates

Template registration also supports the use of the X-Id in the body. Therefore you can create multiple in a single request.

15,myxid1
10,100,POST,/inventory/managedObjects,application/vnd.com.nsn.cumulocity.managedObject+json,application/vnd.com.nsn.cumulocity.managedObject+json,,,"{""name"":""Test Device"",""type"":""com_example_TestDevice"",""c8y_IsDevice"":{}}"
11,201,,"$.c8y_IsDevice","$.id"
15,myxid2
10,100,POST,/inventory/managedObjects,application/vnd.com.nsn.cumulocity.managedObject+json,application/vnd.com.nsn.cumulocity.managedObject+json,,,"{""name"":""Test Device"",""type"":""com_example_TestDevice"",""c8y_IsDevice"":{}}"
11,201,,"$.c8y_IsDevice","$.id"

SmartREST Real-time Notifications

All available real-time notification endpoints and channels of the Cumulocity platform are also available in a SmartREST syntax. Please have a look at the Real-time notifications reference guide to understand the general functionality of the Bayeux protocol and get an overview of our available endpoints and channels fo real-time notifications.

Using Real-time Notifications with SmartREST

To tell the Cumulocity platform that the real-time notifications should use SmartREST all requests send to the URL must contain the X-Id header.

Message identifiers

Message identifier Message parameters Description
80 None Initial handshake that will return a unique bayeux clientId.
81 clientId,channel Subscribe for the given channel.
82 clientId,channel Unsubscribe for the given channel.
83 clientId Establish conntection for receiving the notifications (long-polling).
84 clientId Disconnect the client from the server.

Handshake

Example request:

80

Example response:

Un1q31d3nt1f13r

Subscribe

Example request:

81,Un1q31d3nt1f13r,/mychannel

Example response:

Unless there is an error there is no specific response for the subscribe

Unsubscribe

Example request:

82,Un1q31d3nt1f13r,/mychannel

Example response:

Unless there is an error there is no specific response for the unsubscribe

Connect

Example request:

83,Un1q31d3nt1f13r

Example response:

The response is formed by the response templates registered via SmartREST for the X-Id. Every received notification via real-time will be parsed with the available templates and every matching template will be returned as response for the connect request.

Keep-Alive:

The Cumulocity platform will send every 10 minutes a space character through an open long-polling connection to detect connection loss. A response for a connect that has been open for a longer time could contain leading space characters in the first line of the response.

Disconnect

Example request:

84,Un1q31d3nt1f13r

Example response:

Unless there is an error there is no specific response for the disconnect

The advice response

The bayeux protocol has a special fragment to tell the client about the recommended settings for timeout of a connection, interval between connect requests and the policy for the follow up after a response for a connect. The advice will be communicated via SmartREST also as a seperate line in the response and can be contained in any response of the above requests.

Response Structure:

86,<timeout>,<interval>,<reconnect policy>

Timeout and interval will be numbers defining the time in millisecons. The reconnect policy can be one of three values:

  • none: do not reconnect after the response from a connect.
  • retry: do reconnect after the response from a connect.
  • handshake: start with a new handshake (e.g. because the clientId is invalid / server has closed session).

An advice response line does not need to have every value filled

Example:

86,,10000,retry

Subscribing with multiple templates

If your device uses multiple templates (e.g. child devices have a different templates than the parent) it is possible to add these templates to your subscribe request. The server will than use all templates (from header and subscribe statement) to parse the responses.

Example request:

POST /devicecontrol/notifications HTTP/1.0
Authorization: Basic ...
X-Id: mytemplate1

81,Un1q31d3nt1f13r,/mychannel,mytemplate2,mytemplate3

In the case multiple templates are used the response will contain an additional line that indicates which lines are parsed with which templates:

87,{number of parsed rows},{X-Id used to parse the following rows}

Example response:

HTTP/1.0 200 OK

 87,2,mytemplate1
100,myvalue
101,myvalue2
87,1,mytemplate3
100,myvalue3

Built-in messages

SmartREST has a variety of built-in messages.

Request messages

Message identifier Message parameters Description
10 Template message identifier
Method
Resource identifier
Content MIME type
Accept MIME type
Placeholder
Request parameters
Template string
Represents a request template. If this message occours in the body, the whole body is treated as a SmartREST template and thus, all messages besides 10 and 11 will yield an error.
11 Template message identifier
Base JSON path
Conditional JSON ath
Value JSON paths
Represents a response template. If this message occours in the body, the whole body is treated as a SmartREST template and thus, all messages besides 10 and 11 will yield an error.
15 X-Id Defines which X-Id to use for the following lines. You must not use the X-Id header when using this line.
61 Device MO GId Poll device credentials during device bootstrapping process. No X-Id header must be present and the device bootstrap authorization must be used.
80 None Initial handshake that will return a unique bayeux clientId. SmartREST real-time notifications.
81 clientId,channel Subscribe for the given channel. SmartREST real-time notifications.
82 clientId,channel Unsubscribe for the given channel. SmartREST real-time notifications.
83 clientId Establish conntection for receiving the notifications (long-polling). SmartREST real-time notifications.
84 clientId Disconnect the client from the server. SmartREST real-time notifications.

Response messages

Message identifier Message parameters Description
20 SmartREST Template MO GId Echo response message. Template was found or has been created and everything is OK.
40 None Template not found.
41 Line number (optional) Template creation error.
42 Line number Malformed request line
43 Line number Invalid message identifier.
45 Line number Invalid message arguments.
50 Line number
HTTP response code
Server error. This message occurs when an error happened between the SmartREST proxy and the platform.
70 Line number
Unique device identifier
Tenant ID
Username
Password
Device bootstrap polling response with credentials.
86 timeout,interval,reconnect policy Settings advice for the client using SmartREST real-time notifications.
87 amount of lines, X-Id Indicates which X-Id was used to create the amount of following response lines.

Error messages

Message identifier Error message
41 Cannot create templates for already existing template object
41 Duplicate message identifiers are not allowed
41 Bad request template definition
41 Bad response template definition
41 Bad value type: ...
41 Bad pattern
41 Not a valid message identifier for template creation
41 Invalid JsonPath
41 Using JsonPath to refer to a list of objects is not allowed for SmartRest
41 Using Filters (?) in JsonPath is not allowed for SmartRest
41 No content type supported for {GET or DELETE} templates.
41 No template string supported for {GET or DELETE} templates.
41 No content type found for {POST or PUT} templates.
41 No template string found for {POST or PUT} templates.
41 Values are only supported for templates with placeholder.
42 Malformed Request
43 Invalid message identifier
45 No arguments supported
45 Wrong number of arguments
45 Value is not a {value type}: {value}