Google登录：出现故障时如何重试？

Question

Issue: I need to refresh the Google token used for signing into my server. Most of the time this works well, but sometimes the call to Google to get a fresh token (with a TTL of ~1hr) fails for a variety of reasons.

Desired solution: some means of retrying the call to Google that will actually work.

I have code like the following in my app:

private val googleSignInClient: GoogleSignInClient by lazy {
    // This takes a measurable amount of time to compute, so do it lazily
    val gso = GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestIdToken(WEB_CLIENT_ID) // need this to get user ID token later
            .requestEmail()
            .build()
    GoogleSignIn.getClient(appContext, gso)
}

override fun getToken() = getRefreshedGoogleInfo()?.googleToken()

/**
 * Here we "silently sign in" to get a refreshed Google ID Token.
 *
 * This method might block, so do not call it from the main thread.
 */
private fun getRefreshedGoogleInfo(): GoogleUserInfo? {
    val task = googleSignInClient.silentSignIn()

    // If the task is already complete, return the result immediately
    if (task.isComplete) {
        val info = task.result.toGoogleUserInfo()
        Logger.v(TAG, "silentSignIn result from already-completed task = %s", info.toString())
        return info
    }

    // If the task is not complete, await up to 5s and return result, or null
    return try {
        val info = task.await().toGoogleUserInfo()
        Logger.v(TAG, "silentSignIn result from await task = %s", info.toString())
        info
    } catch (e: Exception) {
        Logger.e(TAG, e, "silentSignIn result from await task = null\nerror = ${e.localizedMessage}")
        null
    }
}

private fun Task<GoogleSignInAccount>.await() = Tasks.await(this, 5, TimeUnit.SECONDS)

Sometimes, the call task.await() will fail because it timed out. In such a case, what is the best strategy to try again? I have tried a naive strategy of just trying again immediately up to some arbitrary numerical limit, but I have observed that if it fails the first time, it always fails on subsequent attempts. The Google docs aren't very helpful with respect to this scenario.

Answer 1

Instead of waiting the task up to 5 seconds, why not try again with requests and intents ? Let me show you in your code with edits.

private fun getRefreshedGoogleInfo(): GoogleUserInfo? {
        val task = googleSignInClient.silentSignIn()

    // If the task is already complete, return the result immediately
    if (task.isComplete) {
        val info = task.result.toGoogleUserInfo()
        Logger.v(TAG, "silentSignIn result from already-completed task = %s", info.toString())
        return info
    }
    else{ //Else is not necessary, but it will somehow increase readability.
        // There's no immediate result ready, displays some progress indicator and waits for the async callback.
        task.addOnCompleteListener(this){ signInTask -> 
            //We repeat the same task control again, but this time it is async.
            if(signInTask.isComplete){
                val info = task.result.toGoogleUserInfo() //Redone the same things in first task.isComplete scope.
                Logger.v(TAG, "silentSignIn result from already-completed task = %s", info.toString())
                return info
            }
            else{ //Again, not necessary but still.
                //This is where we are gonna try again.
                signInToGoogle() //Go below to see the trick.
            }
        }
    }
}

With the code above alone, you do not have to wait for 5 seconds, but it will not try again. To try again with more persistant way ( I assume you use these functions on an activity ) :

    private fun signInToGoogle(){
        val signInIntent = googleSignInClient!!.signInIntent
        startActivityForResult(signInIntent, RC_SIGN_IN) //You might consider checking for internet connection before calling this
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if(requestCode == RC_SIGN_IN){
            val task = GoogleSignIn.getSignedInAccountFromIntent(data)
            /* your code with task handle goes here */
            //task.result carries the same object as above. But since this is a listener, it can not be returned with a value. So it is up to you how to handle again. I handle this with a class-wide variable which contains GoogleUserInfo?
        }
    }

RC_SIGN_IN is just a number for request. You could add it to your companion objects like this or use it as it is :

companion object {
    private const val RC_SIGN_IN = 9001
}

Note : You could use intents for the first try too. Or if intents are too much hassle for you, you could Make function sleep for 5 seconds and call the function again.

But i strongly recommend you to use intent.