SwiftRex / LoggerMiddleware

SwiftRex Logger Middleware

LoggerMiddleware

Usage

Simple usage, logging all actions and state changes for whole app

LoggerMiddleware.default() <> MyOtherMiddleware().lift(...)

Log a single middleware, only actions and state within that middleware field

MyOtherMiddleware().logger().lift(...)

Log a single middleware, but including actions and state changes for the whole app

(same as adding LoggerMiddleware.default() in the chain as seen in the first option)

MyOtherMiddleware().lift(...).logger()

Log a specific group of actions and state tree

IdentityMiddleware<InterestingAction, InterestingAction, InterestingState>()
    .logger()
    .lift(...) // lift InterestingAction and InterestingState to AppAction and AppState
<> MyOtherMiddleware().lift(...)

Parameters

actionTransform

Gives the Input Action and Action Source to be formatted as a string.

Default:

actionTransform: @escaping (InputActionType, ActionSource) -> String = {
    "\n🕹 \($0)\n🎪 \($1.file.split(separator: "/").last ?? ""):\($1.line) \($1.function)"
}

actionPrinter

Gives the action and action source string, formatted from previous parameter, to be logged or saved into a file

Default:

actionPrinter: @escaping (String) -> Void = { os_log(.debug, log: .default, "%{PUBLIC}@", $0) }

stateDiffTransform

Gives the previous state, and the state after the reducers have changed it, so a diff string can be created. Difference struct contains helpers to compare multiline strings, and dumpToString free function is a helper to stringify anything. Alternatively you could stringify using JSONEncoder or any other tool. Be careful with performance, or provide an alternative queue to avoid locking the main queue with heavy log task. Returning nil means that nothing has changed. The default logger will give a "git diff" output, containing + and - for changed lines, including 2 lines of context before and after the change.

Default:

stateDiffTransform: @escaping (StateType?, StateType) -> String? = {
    let stateBefore = dumpToString($0)
    let stateAfter =  dumpToString($1)
    return Difference.diff(old: stateBefore, new: stateAfter, linesOfContext: 2, prefixLines: "🏛 ")
}

stateDiffPrinter

Gives the state diff string, formatted from previous parameter, to be logged or saved into a file. Receiving nil means that the state hasn't changed with this action.

Default:

stateDiffPrinter: @escaping (String?) -> Void = { state in
    if let state = state {
        os_log(.debug, log: .default, "%{PUBLIC}@", state)
    } else {
        os_log(.debug, log: .default, "%{PUBLIC}@", "🏛 No state mutation")
    }
}

queue

The queue to run the string transformation and printer. Use an alternative, low priority, serial queue to avoid locking the UI with logging operations.

Default:

queue: DispatchQueue = .main