Binary Conversion Language
The goal of the Binary Conversion Language (BCL) is to provide an easy way of defining a schema for decoding freeform third-party binary payloads. A set of mappings in BCL specific to a device type is called a conversion. Conversions are encoded as JSON objects.
More details on the general conversion language available at https://docs.allthingstalk.com/dl/AllThingsTalk_Binary_Conversion_Language_1_0_0.pdf
Structure of a conversion
{
"name": "alarm",
"comment": "Home alarm system",
"version": "1.0.0",
"sense": [
{
"asset": "motion",
"value": {
"byte": 0,
"bytelength": 1,
"type": "boolean"
}
}
]
}
In this example, we declare a data conversion used with a home alarm system device. When the device senses motion it sends one byte to UDP endpoint. This simple template converts that one byte sent by the device into a JSON object with a boolean field called motion.
When the device with enabled binary translation, sends 0x01 the byte gets translated into true resulting in the following object:
{
"motion": true
}
Top-level fields
A conversion MUST have a list field named sense, which contains statements that need to be evaluated during sensing - when de-serializing binary payloads into JSON objects.
A conversion MAY have a string field named comment, provided for a human-readable description of the conversion.
Statements
Statements are JSON objects that describe a single operation that needs to be performed in a conversion. A statement MUST be either a mapping statement, a control statement, or a comment statement. Statements appear in statement blocks.
Statement blocks
Statement blocks are JSON lists whose elements are statements or statement blocks that need to be performed in order to complete the conversion. A statement block MAY contain no elements. Making a statement block empty is the same as omitting it all together - no statements get executed. This can be useful in code generation.
There are two types of statement blocks: sense and do. sense statement blocks are executed when sensing (receiving data), and they are present in the home alarm example. do is used wherever embedding a statement block - usually within control structures - is needed.
Sense block
Sense block MAY contain mapping statements and control statements.
Mapping statements in sense block MUST contain a string field asset, whose value is a string that uses JSON dot-notation to identify the path to the field in the resulting object.
Mapping statements in sense block MUST contain a field value, whose value is a selector that identifies the data that will be stored as the new value of the asset.
Mapping statements in sense block MAY have a string field named comment, provided for human-readable description of the given mapping.
Mapping statements
Mapping statements are used for de-serializing values and metadata from specific parts of binary payloads, special values, variables, and constants into fields in the resulting JSON.
The statement contains two fields:
asset - Path to resulting field using JSON dot notation
value - Constant or payload selector
Examples:
Inject a string field using the constant selector.
{
"sense": [
{
"asset": "sensor",
"value": "motion"
}
]
}
Result:
{
"sensor": "motion"
}
Convert 4 bytes into a 32-bit floating-point number using payload selector. Longitude from GPS beacon
{
"sense": [
{
"asset": "longitude",
"value": {
"byte": 0,
"bytelength": 4,
"byteorder": "big",
"type": "float"
}
}
]
}
Data: - 42 4b bc f9
Result:
{
"longitude": 50.934544
}
Control statements
Control statements MUST have a JSON object field named switch that specifies the payload selector that's going to be evaluated, and its value tested in cases.
Control statements MUST have a JSON array field named on that contains a list of cases that switch value will be tested on.
Control statements are used for executing control logic that MAY lead to executing more statements. The switch is the only available control statement in this version of BCL.
Control statement MAY have a string field named comment, provided for human-readable description of the conversion.
Control statement on list MAY contain zero or more case statements.
The control statement on the list MAY contain a comment statement.
Case statements
The case statement MUST have a JSON object field named case, whose value is a selector whose value is tested with the switch selectors value in the outer switch control statement. If it is equal, do statement block is executed.
Case statement MUST have a JSON list field named do, whose value is a statement block that is executed if case and switch match.
Example:
In this example, payload first byte is an 8-bit integer that defines message type. Message type 0 is positional data about the vehicle and message type 1 is maintenance data. Message type 0 has the following structure:
+-------------------+------------------+-------------+
| 4 bytes | 4 bytes | 2 bytes |
+-------------------+------------------+-------------+
| Longitude (float) | Latitude (float) | Speed (int) |
+-------------------+------------------+-------------+
Let's initialize the switch statement and create the condition for message type 0
{
"sense": [
{
"switch": {
"byte": 0,
"bytelength": 1,
"type": "int"
},
"on": [
{
"case": 0,
"comment": "Positional data",
"do": [
{
"asset": "gps.lat",
"value": {
"byte": 1,
"bytelength": 4,
"byteorder": "big",
"type": "float"
}
},
{
"asset": "gps.lon",
"value": {
"byte": 5,
"bytelength": 4,
"byteorder": "big",
"type": "float"
}
},
{
"asset": "speed",
"value": {
"byte": 9,
"bytelength": 2,
"byteorder": "big",
"type": "int"
}
}
]
}
]
}
]
}
Device sends the following data 00 42 4b bc f9 40 de 98 1c 00 78
First byte 00 determines that this message contains positional data. The message will result in the following object:
{
"gps": {
"lat": 50.934544,
"lon": 6.956068
},
"speed": 120
}
Selectors
Selectors are JSON values. They are used to “select” data from a given location type or “select” data used in a control statement.
Selectors MAY have a string field named comment, provided for human-readable description of the conversion.
Constant selector
The constant selector is a string.
Example:
"foo"
Payload selector
A payload selector is a JSON object.
Payload selector MUST have an integer field named byte AND/OR an integer field named endbyte. The value of byte field represents the starting byte from which the chunk is going to be selected (counting from the beginning of the payload). The value of endbyte represents a byte counting from the end of the payload and is described as a value that is less or equal to zero. If both byte and endbyte are present in the payload selector, they are representing a range selector "from byte to endbyte".
Payload selector MAY have an integer field named bytelength, whose value represents the length of the chunk in bytes, starting from and including the byte indexed by byte field. It defaults to 1. The field bytelength MUST NOT be present if the payload selector contains both byte and endbyte.
Payload selector MAY have a string field named byteorder, whose value represents the byte order of the chunk of bytes. Values for this field can be big (Big Endian) or little (Little Endian). This value defaults to the big.
Payload selector MUST have an integer field named type, which defined the data type to which bytes should be converted.
Examples:
Select 16-bit integer with little endian:
{
"byte": 1,
"bytelength": 2,
"type": "int",
"byteorder": "little"
}
Select whole payload as a hex string:
{
"byte": 0,
"endbyte": 0,
"type": "hex"
}
Select the last 4 bytes of the payload as a 32-bit unsigned integer (Big Endian by default):
{
"endbyte": -4,
"bytelength": 4,
"type": "uint"
}
Supported data types
Numeric
bytelength is required. A fix was provided to use the default value of 1 byte if bytelength field is not provided inside selectors.
int - signed integer. Can have bytelength 1, 2, 4, 8 which are 8-bit to 64-bit integers respectively. Defaults to 1
uint - unsigned integer. Same constraints as int.
int and uint value ranges
uint8 : 0 to 255
uint16 : 0 to 65535
uint32 : 0 to 4294967295
uint64 : 0 to 18446744073709551615
int8 : -128 to 127
int16 : -32768 to 32767
int32 : -2147483648 to 2147483647
int64 : -9223372036854775808 to 9223372036854775807
float - floating-point number. Can have bytelength 4 and 8 which are 32-bit floating-point number and 64-bit double precision floating-point number.
Boolean
boolean - boolean. 0x00 will be treated as false.
String
string - UTF-8 encoded string.
Hex
hex - output as hex string.
Nested structure
Dot notation can be used to create JSON with a nested structure.
{
"sense": [
{
"asset": "simple_key",
"value": "value1"
},
{
"asset": "level1.level2.level3.level4",
"value": "value2"
}
]
}
{
"message": {
"level1": {
"level2": {
"level3": {
"level4": "value2"
}
}
},
"simple_key": "value1"
}
}
Full Example
Let's now fully expand all the pieces that we've talked about in this document.
{
"sense": [
{
"asset": "message_code",
"value": {
"byte": 0,
"bytelength": 1,
"type": "uint"
}
},
{
"switch": {
"byte": 0,
"bytelength": 1,
"type": "int"
},
"on": [
{
"case": 0,
"comment": "Positional data",
"do": [
{
"asset": "data_type",
"value": "Position"
},
{
"asset": "gps.lat",
"value": {
"byte": 1,
"bytelength": 4,
"type": "float"
}
},
{
"asset": "gps.lon",
"value": {
"byte": 4,
"bytelength": 4,
"type": "float"
}
},
{
"asset": "speed",
"value": {
"byte": 8,
"bytelength": 2,
"type": "int"
}
}
]
},
{
"case": 1,
"comment": "Maintenance data",
"do": [
{
"asset": "data_type",
"value": "Maintenance"
},
{
"asset": "on",
"value": {
"byte": 1,
"type": "boolean"
}
},
{
"asset": "fuel",
"value": {
"byte": 2,
"bytelength": 4,
"type": "uint"
}
},
{
"asset": "driver",
"value": {
"byte": 6,
"bytelength": 4,
"type": "string"
}
},
{
"asset": "driver_hex",
"value": {
"byte": 6,
"bytelength": 4,
"type": "hex"
}
}
]
}
]
},
{
"asset": "full_payload",
"value": {
"byte": 0,
"endbyte": 0,
"type": "hex"
}
}
]
}
As before, this template parses two types of messages indicated by the first byte. In the beginning, though there is a new mapping statement that adds message type to the resulting JSON. In the switch block, a new statement is added to parse maintenance data.
Data: 01 01 00 00 05 8c 6f 6c 65 67
The first byte is always mapped to message_code.
Field data_type is a constant selector that will be evaluated to Maintenance.
0x01 -> 1
The message therefore should be parsed as maintenance data. We have already tried parsing Positional data, the example can be found above.
Let's explore how the switch statement will work in this case.
The byte at position 1 is parsed as a boolean and mapped to on, which determines if the vehicle is powered on.
0x01 -> true
Next, fuel level is parsed from four bytes starting at position 2 and mapped to field fuel. Fuel will be parsed as unit, which is an unsigned integer because fuel can't drop below 0. Since 4 bytes is selected, the number will be parsed into 32-bit uint.
0x0000058c -> 1420
Driver name is then parsed as a string. Name is parsed from 4 bytes starting from position 6.
0x6f6c6567 -> "oleg"
Driver name is also outputted as hex string and mapped to field driver_hex.
0x6f6c6567 -> 6f6c6567
We also are adding the whole original payload to the output as hex in the field called full_payload. We are selecting the whole payload by defining the start of the selector as byte: 0 and the end as endbyte: 0.
We get the following result for our Translated Binary Payload.
{
"message_code": 1,
"data_type": "Maintenance",
"on": true,
"fuel": 1420,
"driver": "oleg",
"driver_hex": "6f6c6567",
"full_payload": "01010000058c6f6c6567"
}
Updated 3 months ago