The first byte of a ThingSet message is either a text-mode identifier (
#), 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.
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.
|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
0x7F are reserved, as they represent the ASCII characters for readable text including
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
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).
|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|
|0xA3||4.03||403||Forbidden||Trying to write read-only value|
|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|
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 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.
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
Bat or a subset data object that contains a list of references to other data items like
eChange in the above example.
More details regarding the ThingSet protocol methods for data access will be explained in the next chapter.
Idea for evaluation
Publication of a statement can be manually triggered by sending the statement with empty payload to that device.