Access Functions
The first byte of a ThingSet message is either a text-mode identifier (?, =, !, +, -, : and #), a binary request code or a binary status code. Received data with unknown first byte is ignored, so that other text output (e.g. debug print information) can be used in parallel to the ThingSet protocol on the same serial interface.
Requests
The protocol supports the typical CRUD operationsopen in new window. Request codes match with CoAP to allow transparent mapping between ThingSet and HTTP APIs or CoAP devices.
| Code | Text ID | Method | Description |
|---|---|---|---|
| 0x01 | ? | GET | Retrieve all data from a path |
| 0x02 | + or ! | POST | Append data to an object or execute a function |
| 0x04 | - | DELETE | Delete data from an object |
| 0x05 | ? | FETCH | Retrieve a subset of data from a path |
| 0x07 | = | iPATCH | Update (overwrite) data of a path |
The CoAP PUT and PATCH methods are not explicitly implemented. PUT is equivalent to an update of all sub-objects of a resource using a PATCH request. PATCH requests for ThingSet are always idempotent, so only the iPATCH request code is supported. The two different text IDs for POST requests are synonyms. It is decided based on the type of the data object if the request is understood as a function call or a request to create a resource.
Additional request codes may be introduced in the future. Codes 0x0A, 0x0D and 0x20-0x7F are reserved, as they represent the ASCII characters for readable text including LF and CR.
Responses
Response messages in binary format are identified by a first byte greater than or equal to 128 (0x80) containing a status code which shows if the request could be handled successfully. For status codes between 0x80 and 0x9F, the response was successful. If the status code is greater than or equal to 0xA0, an error occured.
The status codes are again aligned with CoAP response codes, but contain an offset so that there is no interference with ASCII characters (less than 0x80).
| Code | CoAP | HTTP | Description | Comment |
|---|---|---|---|---|
| 0x81 | 2.01 | 201 | Created | Answer to POST requests appending data |
| 0x82 | 2.02 | 204 | Deleted | Answer to DELETE request |
| 0x83 | 2.03 | 200 | Valid | Answer to POST requests to exec objects |
| 0x84 | 2.04 | 204 | Changed | Answer to PATCH requests |
| 0x85 | 2.05 | 200 | Content | Answer to GET / FETCH requests |
| 0xA0 | 4.00 | 400 | Bad Request | |
| 0xA1 | 4.01 | 401 | Unauthorized | Authentication needed |
| 0xA3 | 4.03 | 403 | Forbidden | Trying to write read-only value |
| 0xA4 | 4.04 | 404 | Not Found | |
| 0xA5 | 4.05 | 405 | Method Not Allowed | If e.g. DELETE is not allowed for that object |
| 0xA8 | 4.08 | 400 | Request Entity Incomplete | |
| 0xA9 | 4.09 | 409 | Conflict | Configuration conflicts with other settings |
| 0xAD | 4.13 | 413 | Request Entity Too Large | |
| 0xAF | 4.15 | 415 | Unsupported Content-Format | If trying to assign a string to an int |
| 0xC0 | 5.00 | 500 | Internal Server Error | |
| 0xC1 | 5.01 | 501 | Not Implemented |
The text mode converts the the hexadecimal response code into a string without the 0x prefix. The binary mode uses the code directly as the first byte.
Statements
Statements are neither requests nor response messages, as they are sent without expecting a confirmation. Below table lists the message specifier in text and binary mode.
| Code | Text ID | Description |
|---|---|---|
| 0x1F | # | Statement message |
The internal path .pub is used to configure the device to publish certain data items on a regular basis through a defined communication channel (UART, CAN, LoRaWAN, etc.). If implemented in the firmware, the publication interval may be adjustable.
By convention, the object names below the .pub define which data object should be published. This can be an entire group like meas or a subset data object that contains a list of references to other data items like report in the above example.
If a Period_s data object exists, it can be set to 0 to disable publication of this message. For event-based publication, a data object OnChange can be specified, which publishes the message only if one of the data objects has changed.
More details regarding the ThingSet protocol methods for data access will be explained in the next chapter.
GitHub