I've been thinking of using Alamofire for my network requests. I've read somewhere that Alamofire does callback caching. What I mean by that is when I do multiple GETs to the same URL, but only 1 does the actual request and both just receive the response. This way I could avoid multiple network calls to same resource, but have the resource in both callbacks
I just cannot find any truth of this concept in their documentation.
So my question is this possible? And if so is this just a behind the scene thing or how do I use it?
I've been testing with the following code from their documentation:
func x() {
Alamofire.request("https://httpbin.org/get").responseJSON { response in
print("Request: \(String(describing: response.request))") // original url request
print("Response: \(String(describing: response.response))") // http url response
print("Result: \(response.result)") // response serialization result
print("Timeline: \(response.timeline)")
if let json = response.result.value {
print("JSON: \(json)") // serialized json response
}
if let data = response.data, let utf8Text = String(data: data, encoding: .utf8) {
print("Data: \(utf8Text)") // original server data as UTF8 string
}
}
}
x()
x()
x()
Method x is called 3 times and 3 GET's are fired over the network.
I'm not sure what you've read, but Alamofire doesn't have any sort of request deduplication. AlamofireImage does, for image requests, but the feature only exists in that library. However, Alamofire does support standard HTTP caching methods, so if you request the same resource twice, and the server properly returned one of the caching headers, Alamofire should accept the locally cached copy. This is done through the standard URLCache class, so you should read its documentation to learn more.
Related
I am in the process of implementing a REST API with Swift. Of course, part of this API is using HTTP requests to retrieve and send data.
Full disclosure, I am inexperienced with Swift and am using this as a learning project to get my feet wet, so to speak. But it's turned into much more of a difficult project than I anticipated.
In implementing the first get method, I have (finally) gotten rid of all the compilation errors. However, when I call the function which utilizes the URLRequest, URLSession, dataTask, etc, it is never entered.
Upon debugging the program, I can watch the program execution reach the CompletionHandler, and skip over it right to "task.resume()."
A similar construction works in a Swift Playground, but does not work in the actual project proper.
So far I have tried a few things, namely making the function access a class instance variable, in hopes that that would force it to execute. But it does not.
I think the issue may be dealing with synchronicity, and perhaps I need to use a Semaphore, but I want to make sure I'm not missing anything obvious first.
import Foundation
/**
A class to wrap all GET and POST requests, to avoid the necessity of repeatedly writing request code in each API method.
*/
class BasicRequest {
private var url: URL
private var header: [String: String]
private var responseType: String
private var jsonResponse: Any?
init(url: URL, header: [String: String], responseType: String) {
self.url = url
self.header = header
self.responseType = responseType
} //END INIT
public func requestJSON() -> Any {
// Create the URLRequest object, and fill the header with the header fields as provided.
var urlRequest = URLRequest(url: self.url)
for (value, key) in self.header {
urlRequest.addValue(value, forHTTPHeaderField: key)
}
let task = URLSession.shared.dataTask(with: urlRequest) { (data, response, error) in
print("Entered the completion handler")
if error != nil {
return
}
guard let httpResponse = response as? HTTPURLResponse, 200 == httpResponse.statusCode else {
print("HTTP Request unsuccessful")
return
}
guard let mime = response?.mimeType, mime == "application/json" else {
print("Not a JSON response")
return
}
do {
let json = try JSONSerialization.jsonObject(with: data!, options: [])
print(json)
self.jsonResponse = json
} catch {
print("Could not transform to JSON")
return
}
}
task.resume()
return "Function has returned"
} //END REQUESTJSON
}
The expected result would be returning a JSON object, however that does not seem to be the case.
With respect to error messages, I get none. The only log I get in the debugger is the boilerplate "process exited with code 0."
To be truthful, I'm at a loss with what is causing this not to work.
It appears you're writing this in a command-line app. In that case the program is terminating before the URLRequest completes.
I think the issue may be dealing with synchronicity, and perhaps I need to use a Semaphore, but I want to make sure I'm not missing anything obvious first.
Exactly.
The typical tool in Swift is DispatchGroup, which is just a higher-level kind of semaphore. Call dispatchGroup.enter() before starting the request, and all dispatchGroup.leave() at the end of the completion handler. In your calling code, include dispatchGroup.wait() to wait for it. (If that's not clear, I can add code for it, but there are also a lot of SO answers you can find that will demonstrate it.)
I am trying to access the custom server response body for 500 errors in class HTTPURLResponse (URLResponse) using URLSession.shared.dataTask function. I can only have access to statusCode and allHeaderFields but it doesn't seem to help.
The equivalent in java for ex. is HttpURLConnection.getErrorStream(), but I cannot find something similar in pure swift (I would like to solve this without using 3rd party libs).
How can I get the text response for the 500 error?
let task = session.dataTask(with: urlRequest) { data, response, error in
if let data = data, let response = response as? HTTPURLResponse {
switch response.statusCode {
case 500...599:
let yourErrorResponseString = String(data: data, encoding: .utf8)
default:
break
}
}
}
There is no way you can get the response data out of HTTPURLResponse. It only contains header information.
If you want to retrieve the response data, you need to use something like dataTask(with:completionHandler:) to send your request. That function passes (Data?, URLResponse?, Error?) to your completion handler. The data parameter of the completion handler is the data returned by the server.
For example:
import Foundation
let url = URL(string: "http://httpstat.us/500")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data, let response = response as? HTTPURLResponse else {
return
}
switch response.statusCode {
case 500...599:
print(String(data: data, encoding: .utf8) ?? "No UTF-8 response data")
default:
print("not a 500")
}
}
task.resume()
Edit: Removed force unwrap according to #Rob‘s suggestion
There is no way to get more details about a 500 error from the client side.
500 is "Internal Server Error" and it's intentionally vague and unhelpful since disclosing information about the cause of the error would assist hackers in compromising the site.
However you can get a great deal of information about the error from the server log and the log for whatever was processing your code on the server side (php, etc.).
If you have access to the server logs and don't see enough information, you can increase the level of logging for the server and application.
I have four different requests in my application, three of them requires one call only and the last requires from 1 - 10.
All works fine until the last request when I´m iterating through my data and making the calls. This is my code in Class1:
var data = ...
var points = ...
// I create a new group
let getPointGroup = dispatch_group_create()
// I iterate through my data
for d in data{
// I enter the group
dispatch_group_enter(getPointGroup)
dataService.getPoints(d.point), success: { points -> Void in
points.append(points)
// I leave the group so that I go to the next iteration
dispatch_group_leave(getPointGroup)
}
}
Alamofire request looks like this in Class2:
let headers = [
"Authorization": "Bearer \(token)",
"Content-Type": "application/x-www-form-urlencoded"
]
Alamofire.request(.GET, url, headers:headers)
.responseJSON { response in
switch response.result {
case .Success:
let json = JSON(data: response.data!)
print(json)
success(json)
case .Failure(let error):
print(error)
}
}
But I never hit the GET request, if I remove the iteration completely and just call the Alamofire request once it works perfectly.
Any ideas of how to solve the Alamofire iteration request?
Edit
Not really a duplicate, I have the snippets below in the different classes and the example does not really solve my issue
If this is not running, you could be deadlocking if you use dispatch_group_wait on the main thread, thereby blocking that thread, and preventing Alamofire from running any of its completion handlers (which also require the main thread). This is solved (assuming you are, indeed, using dispatch_group_wait), by replacing that with dispatch_group_notify.
Thus:
let group = dispatch_group_create()
for d in data {
// I enter the group
dispatch_group_enter(group)
dataService.getPoints(d.point)) { additionalPoints, error in
defer { dispatch_group_leave(group) }
guard let let additionalPoints = additionalPoints else {
print(error)
return
}
points.append(additionalPoints)
}
}
dispatch_group_notify(group, dispatch_get_main_queue()) {
// go to the next iteration here
}
Where:
func getPoints(point: WhateverThisIs, completionHandler: (JSON?, NSError?) -> ()) {
let headers = [
"Authorization": "Bearer \(token)"
]
Alamofire.request(.GET, url, headers: headers)
.responseJSON { response in
switch response.result {
case .Success:
let json = JSON(data: response.data!)
completionHandler(json, nil)
case .Failure(let error):
completionHandler(nil, error)
}
}
}
Now, I don't know what your various parameter types were, so I was left to guess, so don't get lost in that. But the key is that (a) you should make sure that all paths within your Alamofire method will call the completion handler; and (b) the caller should use dispatch_group_notify rather than dispatch_group_wait, avoiding the blocking of any threads.
Note, in order to make the completion handler callable even if the network request failed, I had to make the parameter to that closure optional. And while I was there, I added an optional error parameter, too.
A few unrelated changes included in the above sample:
I'd suggest using a different variable name for the parameter of your closure. The points.append(points) in your original code snippet suggests some confusion between your points array and the points that is passed back in the closure.
You don't have to set the Content-Type header, as Alamofire does that for you.
I didn't change it above, but it is inefficient to use responseJSON (which uses NSJSONSerialization to parse the JSON) and then use SwiftyJSON to parse the raw data with NSJSONSerialization again. Personally, I don't bother with SwiftyJSON, but if you want to use it, I'd suggest use Alamofire's response method rather responseJSON. There's no point in parsing the JSON twice.
I am using Alamofire in swift to send http request/post to server. Below is the code I used in swift.
Alamofire.request(.POST, "http://localhost:8080/hello", headers: [ACCESS_TOKEN:token, "Content-Type":"application/x-www-form-urlencoded" ],
parameters:["friend_id" : friendId, "skill_id" : skillId]).response(completionHandler: {
(request, response, data, error) in
print(request)
print(response)
print(data)
print(error)
})
Below is the code defined in server side:
#POST
#Path("/hello")
#Produces(MediaType.APPLICATION_JSON)
public Response nominateSkill(#Context HttpServletRequest request, #FormParam("friend_id") long friendId, #FormParam("skill_id") int skillId) {
// ...
}
When I run the swift code, I always got below error message in server side:
A servlet request to the URI http://localhost:8080/hello contains form parameters in the request body but the request body has been consumed by the servlet or a servlet filter accessing the request parameters. Only resource methods using #FormParam will work as expected. Resource methods consuming the request body by other means will not work as expected.
I think the problem would be coursed by the swift code which didn't set the parameter correctly. But I don't know how to set them correctly?
I found the solution after some search. I need to add "encoding: .URL" on the request method like below:
Alamofire.request(.POST, "http://localhost:8080/hello", headers: [ACCESS_TOKEN:token, "Content-Type":"application/x-www-form-urlencoded" ],
parameters:["friend_id" : friendId, "skill_id" : skillId],
encoding: .URL).response(completionHandler: {
(request, response, data, error) in
print(request)
print(response)
print(data)
print(error)
})
Your swift code seems fine. Make sure on which side problem is occur. You can try https://chrome.google.com/webstore/detail/postman/fhbjgbiflinjbdggehcddcbncdddomop?hl=en to test the api and make sure api doen't have any issues.
You may also try to change data type of friend_id and skill_id to string in server side and run again.
The server that I am using returns error messages in the HTTP status message. For example, it will return "400 User already exists" rather than "400 Bad Request".
I would like to access the string "User already exists" in the response method called by Alamofire. However, I cannot find any way to access this string.
I found this question on StackOverflow already: Swift Alamofire: How to get the HTTP response status code
Unfortunately, no one gives an answer to the question. :(
Here is where Chrome shows where the error is:
I would suggest trying to print out all the possible data fields that you are given and see what you can find. Please try the following example and see if that sheds any light.
let URL = NSURL(string: "your/url/to/somewhere")!
let parameters = ["foo": "bar"]
Alamofire.request(.POST, URL, parameters: parameters)
.response { request, response, data, error in
println("Request: \(request)")
println("Response: \(response)")
println("Error: \(error)")
if let data = data as? NSData {
println("Data: \(NSString(data: data, encoding: NSUTF8StringEncoding)!)")
}
}
Return response in json format from the server and then i think you'll be able to get the appropriate status.
I've implemented that thing using php codeigniter..from where my response is like
$response['status'] = 'user_already_exists';
$this->response($response, 400);
Now in swift you can go with this
Alamofire.request(.POST,URL, parameters:parameters) .responseJSON
{
(request, response, data, error) in
var json = JSON(data!) //I've used swiftyJSON for reading json response
let status = json["status"].stringValue
println("Status : \(status)")
}
Hope this may help you.