Persistent Storage API for the Automotive Grade Linux demo¶

The AGL Persistent Storage API is a grpc API for AGL that serves as persistent storage API for the demo. The API is written in Rust and makes use of tonic for grpc functionality as well as RocksDB as a database backend, using rust-rocksdb. Use cases include retaining settings over a system shutdown (e.g. audio, HVAC, profile data, Wifi settings, radio presets, metric vs imperial units).

The most important hardware consideration for this project is that the AGL demo runs on embedded hardware with flash storage, so we want to minimize number of write operations. This impacts the choice of database; we have chosen to work with RocksDB as it is well-suited for embedded computing and tunable with respect to write amplification. In principle the API is flexible with respect to database used (pluggable backends), but only RocksDB is implemented. This API is part of the AGL demo as of release 'Royal Ricefish'.

The AGL Persistent Storage API is constructed using a layered architecture:

• Controller layer: translates proto calls to service calls.
• Service layer: communicates with the controller and facade layers, implements the business logic
• Facade layer: implements RocksDB.

API Specification¶

Namespaces The rpcs described below interact with keys belonging to specific namespaces. This feature enables applications to maintain private namespaces within the same database. Not specifying a namespace when calling the API will result in the default namespace "" being used. Alternatively, a specific namespace (e.g. "AppName") can be chosen. With the exception of DestroyDB, which acts on the entire database, all rpcs can only interact with one namespace at a time.

• DestroyDB() -> StandardResponse(success: boolean, message: string)

• Consumer wants to destroy the entire database.

  DestroyDB() -> //destroys entire database.
  

• Write(key: string, value: string, namespace: string) -> StandardResponse(success: boolean, message: string)

• Consumer wants to save key + value to a given namespace (default is ""), (e.g. 'Vehicle.Infotainment.Radio.CurrentStation':'hr5').

• This overwrites existing value under key.

• An empty string cannot be used as a key.

  Write('Vehicle.Infotainment.Radio.CurrentStation':'wdr 4') -> Response
  
  Write('Vehicle.Infotainment':'yes') -> Response
  
  Write('test':'1') -> Response
  
  Write('':'test') -> Error
  
  Write(key: 'Private.Info', value: 'test', namespace: 'AppName') -> Response
  

• Read(key: string, namespace: string) -> ReadResponse(success: boolean, message: string, value: string)

• Consumer wants to read value of existing key in a given namespace (default is ""), e.g. 'Vehicle.Infotainment.Radio.CurrentStation':

  Read('Vehicle.Infotainment.Radio.CurrentStation') -> 'wdr 4'
  
  Read('Vehicle.doesNotExist') -> ERROR
  
  Read(key: 'Private.Info', namespace: 'AppName') -> 'test'
  

• Delete(key: string, namespace: string) -> StandardResponse(success: boolean, message: string)

• Consumer wants to delete an existing key + value from a given namespace (default is ""), e.g. 'Vehicle.Infotainment.Radio.CurrentStation':

  Delete('Vehicle.Infotainment.Radio.CurrentStation') -> Response
  
  Delete('Vehicle.doesNotExist') -> ERROR
  
  Delete(key: 'Private.Info', namespace: 'AppName') -> Response
  

• Search(key: string, namespace: string) -> ListResponse(success: boolean, message: string, keys: repeated string)

• Consumer wants to list all keys that contain key in a given namespace (default is ""), e.g. 'Radio'

  Search('Radio') -> ('Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Communication.Radio.Volume')
  
  Search('Info') -> ('Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Infotainment.Radio.Volume', 'Vehicle.Infotainment.HVAC.OutdoorTemperature')
  
  Search('nt.Rad') -> ('Vehicle.Infotainment.Radio.CurrentStation')
  
  Search('') -> ('Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Infotainment.Radio.Volume', 'Vehicle.Infotainment.HVAC.OutdoorTemperature', 'Vehicle.Communication.Radio.Volume')
  
  Search(key: '', namespace: 'AppName') -> ('Private.Info')
  

• DeleteNodes(key: string, namespace: string) -> StandardResponse(success: boolean, message: string)

• Consumer wants to delete all keys located in the subtree with root key, within the given namespace (default is ""), e.g. 'Vehicle.Infotainment'

• key = '' returns ERROR

• This rpc assumes that keys follow a VSS-like tree structure.

  DeleteNodes('Vehicle.Infotainment') -> Response //deletes ('Vehicle.Infotainment', 'Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Infotainment.Radio.Volume', 'Vehicle.Infotainment.HVAC.OutdoorTemperature')
  
  DeleteNodes('Vehicle') -> Response //deletes ('Vehicle.Infotainment', 'Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Infotainment.Radio.Volume', 'Vehicle.Infotainment.HVAC.OutdoorTemperature', 'Vehicle.Communication.Radio.Volume')
  
  DeleteNodes('') -> ERROR
  
  DeleteNodes('DoesNotExist') -> ERROR
  
  DeleteNodes('Vehic') -> ERROR
  
  DeleteNodes(key: 'Private', namespace: 'AppName') -> Response //deletes ('Private.Info')
  

• ListNodes(node: string, layers: optional int, namespace: string) -> ListResponse(boolean, message, repeated string keys)

• Consumer wants to list all nodes located in the subtree with root node exactly layers layers deep, within the given namespace (default is "") , e.g. 'Vehicle.Infotainment'

  • layers = 0 lists all keys that start in node any number of layers deep
  • layers default value is 1
  • node = '' returns top-level root node(s)
  • This rpc assumes that keys follow a VSS-like tree structure.

  ListNodes('Vehicle.Infotainment', 1) -> ('Vehicle.Infotainment.Radio', 'Vehicle.Infotainment.HVAC')
  
  ListNodes('Vehicle.Infotainment', 2) -> ('Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Infotainment.Radio.Volume', 'Vehicle.Infotainment.HVAC.OutdoorTemperature')
  
  ListNodes('Vehicle', 0) -> ('Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Infotainment.Radio.Volume', 'Vehicle.Infotainment.HVAC.OutdoorTemperature', 'Vehicle.Communication.Radio.Volume', 'Vehicle.Infotainment')
  
  ListNodes('', 0) -> ('Vehicle.Infotainment.Radio.CurrentStation', 'Vehicle.Infotainment.Radio.Volume', 'Vehicle.Infotainment.HVAC.OutdoorTemperature', 'Vehicle.Communication.Radio.Volume', 'Vehicle.Infotainment', 'test')
  
  ListNodes('Vehicle.Infotainment') -> ('Vehicle.Infotainment.Radio', 'Vehicle.Infotainment.HVAC')
  
  ListNodes('', 1) -> ('Vehicle', 'test')
  
  ListNodes('Vehicle.Infotainment.Radio.Volume', 1) -> ()
  
  ListNodes('Vehicle', -1) -> ERROR
  
  ListNodes('Vehicle.DoesNotExist', 1) -> ERROR
  
  ListNodes(key: 'Private', namespace: 'AppName') -> ('Private.Info')
  
  For empty data base:
  ListNodes('', 1) -> ()
  

Example Tree¶

Note: nodes marked by * are keys (and therefore have a value)

Namespace: "" - Vehicle - Infotainment * - Radio - CurrentStation * - Volume * - HVAC - OutdoorTemperature * - Communication - Radio - Volume * - test *

Namespace: "AppName" - Private - Info *

Setup instructions¶

1. Install rust

2. Download or install protobuf (e.g. from here) and set the PROTOC environment variable: echo -n "export PROTOC=/path/to/protoc.exe" >> ~/.bashrc

3. Build application

cargo build

1. Run tests

cargo test

1. Start server

cargo run --release --bin server

rpc Usage¶

Insomnia usage for manual testing is describd in https://konghq.com/blog/engineering/building-grpc-apis-with-rust

DestroyDB: {}

Write: { "key": "foo", "value": "foobar", "namespace": "bar" }

Read: { "key": "foo", "namespace": "bar" }

Delete: { "key": "foo", "namespace": "bar" }

Search: { "key": "foo", "namespace": "bar" }

DeleteNodes: { "key": "foo", "namespace": "bar" }

ListNodes: { "key": "foo", "layers": 1, "namespace": "bar" }