openOBD function composition

It is possible to construct complex openOBD functions by combining several functional building blocks. Every building block can be seen on its own as a separate function. Every function is executed within its own context. A function call in openOBD means that the control over the openOBD session is temporarily handed over from one function to another. Once the latter function finishes its execution, the calling function regains control over the openOBD session. These separate functions (or functional blocks) do not necessarily need to be hosted at the same location. It is possible to combine functions from third parties that are hosted at different locations.

Here we will illustrate how this technically works.

sequenceDiagram
    autonumber
    participant DEFAULT as Default function
    participant F1 as Function x<br/>Towbar coding
    participant F2 as Function y<br/>Unlock ECU
box lightgray
    participant OS as openOBD session
end

 note over OS: default context<br/>available
 DEFAULT->>OS: createFunctionContext(x)
 note over OS: context x<br/>available 
 OS->>DEFAULT: sessionInfo_x
 DEFAULT->>F1: runFunction(x, sessionInfo_x)
 F1->>OS: createFunctionContext(y)
 note over OS: context y<br/>available
 OS->>F1: sessionInfo_y
 F1->>F2: runFunction(y, sessionInfo_y)
 F2->>OS: authenticate(y)
 activate OS
 note over OS: context y<br/>active
 OS-->>F2: session_token
        activate F2
        rect rgb(200, 150, 255)
        Note right of F2: OBD communication<br/>to unlock ECU
        F2-->OS: OBD communication
        end
        F2->>OS: finish(y)
        deactivate OS
        deactivate F2
        OS-->>F1: authentication_token
        note over OS: context x<br/>available
    F1->>OS: authenticate(x)
    activate OS
    note over OS: context x<br/>active    
    OS-->>F1: session_token
    activate F1
    rect rgb(200, 150, 255)
    Note right of F1: OBD communication<br/>to code towbar
    F1-->OS: OBD communication
    end
    F1->>OS: finish()
    deactivate OS
    deactivate F1
    OS-->>DEFAULT: authentication_token
    note over OS: default context<br/>available
    Note right of DEFAULT: Evaluate results<br/>and finish session
    DEFAULT->>OS: finish()