基本上，我们确实有一个APIHelper类，其中GET&实现了POST方法，可以从任何视图控制器调用，我们将在标头中发送一个访问令牌以确保安全，一旦访问令牌过期，我们需要调用API来获取访问令牌，并需要在标头中发送更新的令牌。
class func postMethod(methodName: String, success: @escaping (AnyObject?, String?)->Void, Failure:@escaping (NSError)->Void)
{
do {
if ReachabilityManager.shared.isConnectedToNetwork() == false
{
PageNavigation.moveToInternet()
} else {
let session = URLSession.shared
let urlPath = URL(string: "(AppConstants.BaseUrl)" + "(methodName)")
var request = URLRequest(url: urlPath! as URL)
print( "JSON request is (urlPath!)")
request.httpMethod = "POST"
request = WebAPIHelper.headers(methodType: "POST", methodName: methodName, request: request, isAddUserAuthorization: false)
let jsonBody = try JSONEncoder().encode(CommonDBHelper.getActiveUserRefreshToken())
request.httpBody = jsonBody
let task = session.dataTask(with: request, completionHandler: {(data, response, error) in
if(error == nil)
{
do
{
if let httpResponse = response as? HTTPURLResponse
{
let headers = httpResponse.allHeaderFields
let statusCode = httpResponse.statusCode
if (statusCode == 200)
{
let JSON = try JSONSerialization.jsonObject(with: data!, options:JSONSerialization.ReadingOptions.allowFragments)
if let currentServerTime = headers["Date"] as? String
{
success(JSON as AnyObject?, currentServerTime)
}
else{
success(JSON as AnyObject?, nil) // Closure being called as a function
}
}
else
{
GenericMethods.showAlert(alertMessage: "Some error occured. Please try again later")
}
}
else
{
GenericMethods.showAlert(alertMessage: "Some error occured. Please try again later")
}
}
catch let JSONError as NSError
{
Failure(JSONError as NSError)
print("JSON Error (JSONError)")
GenericMethods.showAlert(alertMessage: "Some error occured. Please try again later")
}
}
else
{
Failure(error! as NSError)
GenericMethods.showAlert(alertMessage: "Some error occured. Please try again later")
}
})
task.resume()
}
}
catch {
print("Error in catch (error.localizedDescription)")
}
}
所以GET&POST一次将被多个线程调用，那么如何将所有调用保持在等待模式，直到我收到Access Token API的响应，对于这种类型的场景有什么解决方案吗？
class func headers(methodType:String, methodName:String, request:URLRequest, isAddUserAuthorization : Bool) -> URLRequest
{
let methodName = methodName
var request = request
if isTokenExpired(){
//how to keep waiting all other api calling in waiting mode here until i get response
RefreshTokenAPI(completed: { (accesstoken) ->Void in
request.addValue(accesstoken, forHTTPHeaderField: "AccessToken")
})
}
else{
request.addValue(getAccessTokenFromDefaults(), forHTTPHeaderField: "AccessToken")
}
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("application/json", forHTTPHeaderField: "Accept")
print(request.allHTTPHeaderFields!)
return request as URLRequest
}
这里的目标是在收到访问令牌后启动后续请求。人们通常会采用一种完成处理程序模式，例如只有在检索到访问请求后才调用的闭包：
class func headers(methodType: String, methodName: String, request: URLRequest, isAddUserAuthorization: Bool, completion: @escaping (URLRequest) -> Void) {
var request = request
// presumably you have code that is using methodType and methodName, too ...
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("application/json", forHTTPHeaderField: "Accept")
if isTokenExpired() {
refreshTokenAPI { accesstoken in
request.addValue(accesstoken, forHTTPHeaderField: "AccessToken")
completion(request)
}
} else {
request.addValue(getAccessTokenFromDefaults(), forHTTPHeaderField: "AccessToken")
completion(request)
}
}
然后不是：
request = WebAPIHelper.headers(methodType: "POST", methodName: methodName, request: request, isAddUserAuthorization: false)
...
// currently issuing request here
调用方将根据headers完成处理程序中的request移动所有内容：
WebAPIHelper.headers(methodType: "POST", methodName: methodName, request: request, isAddUserAuthorization: false) { request in
// issue request here
...
}
// but not here
这是一个简单的"一旦检索到访问令牌就启动请求"模式。
你也可以追求其他模式。例如，您可以为授权请求创建一个队列，该队列将挂起，直到RefreshTokenApi恢复该队列。然后，所有需要令牌的请求都将添加到该队列中。或者，您可以使用自定义Operation模式，其中isReady是在成功检索令牌时设置的。有很多方法可以剥猫皮，但希望这能说明我们采用异步模式而不是"停止"或"等待"的想法。
如果你想确保允许并发请求调用refreshTokenAPI，那么你可以让它等待，但只能在一些后台队列上这样做，并避免阻塞调用线程：
private var queue = DispatchQueue(label: "com.domain.app.token") // custom serial queue to avoid blocking calling thread
func headers(methodType: String, methodName: String, request: URLRequest, isAddUserAuthorization: Bool, completion: @escaping (URLRequest) -> Void) {
queue.async { [self] in
var request = request
// presumably you have code that is using methodType and methodName, too ...
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("application/json", forHTTPHeaderField: "Accept")
if isTokenExpired() {
let semaphore = DispatchSemaphore(value: 0)
refreshTokenAPI { token in
request.addValue(token, forHTTPHeaderField: "AccessToken")
DispatchQueue.main.async { completion(request) }
semaphore.signal()
}
semaphore.wait()
} else {
request.addValue(getAccessTokenFromDefaults(), forHTTPHeaderField: "AccessToken")
DispatchQueue.main.async { completion(request) }
}
}
}
坦率地说，我可能会考虑将这些网络请求封装在Operation的自定义异步子类中(或使用Combine(，但这超出了这个问题的范围。