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protocol definition
RRDTP version 1 is a data streaming protocol. One host acts as the server, and is the authoritative source for all data values. Multiple clients can connect to the server to send and receive updates to data values. Values can be stored hierarchically in categories. The design of RRDTP draws inspiration from WPI Network Tables, but is designed to be simpler and more easily portable to resource-limited platforms.
Each packet will contain an event type. The currently defined event types are listed below.
- Set value: sent to indicate that a value was updated. Either a client, or the server can send this type of packet.
Values can be one of 7 types.
- int - signed 32-bit integer
- long - signed 64-bit integer
- float - single precision floating point number
- double - double precision floating point number
- boolean - true/false boolean flag
- string - string (ASCII or UTF8)
- unformatted - plain unformatted data. The calling code is responsible for endianness conversion.
Values are identified by a hierarchical naming scheme similar to Java packages. If the value isn't stored in any category, then it can be referred to simply by its name, such as "value1". If the value is stored within a category and any number of subcategories, then it can be referred to by separating the categories with a period ".", for example "category.sub-category.value1". Valid characters that can be used in category and value names are letters, numbers, underscores "_", and hyphens "-". Identifiers are case sensitive ("Value1" != "VALUE1" != "VaLuE1"). Value identifiers are always specified as ASCII format strings ending in a null terminator.
Each RRDTP packet begins with a header containing the 8-bit protocol version number, and the 8-bit event type (see Events section above). The rest of the packet format depends on the event type.
When the client first connects to the server it must send a packet of this type. The client handshake packet contains nothing beyond the header.
Sent by the server in response to the client handshake packet. When the server receives a "client handshake" packet, it will send this packet back along with "create value" packets to synchronize all values to the client.
Sent to set a value entry. The system that sets the value first is considered to own the value, and is the only system allowed to update that value later. A value creation packet contains the value identifier, the data type (1 byte), the size of the data (2 bytes), and the data itself (variable size).