I'm having trouble getting AFNetworking to communicate successfully with a web service. Is there a way to log out (or view in some other way) the exact http request that it is sending?
You should check out AFHTTPRequestOperationLogger, which listens for the notifications sent when operations start and finish, and log them out with configurable verbosity.
I really like Charles for watching network traffic when using the simulator.
Related
I am sure there is little % of iOS developers who haven't used Reachability, directly or via some framework like Alamofire.
What I am interested what it actually does? The best guess I can make is that given host it opens sockets and then listens for said host. But what network protocol does it use, is it simple UDP (it is not http as far as I can observe), where it periodically sends packages to said host and awaits answer?
Reachability sends no packets at all. It doesn't even tell you that a host is actually reachable. It just tells you that if you made a network request, then the system has an active network interface that it would try to use. That's all. There's no promise those packets would arrive (let alone that you'd get a response), just that iOS would try to send them.
Reachability really only has a couple of uses (and most of the time shouldn't be used). It is useful if "no network is available" would cause you to modify your user interface, or to tell you that it might be a good time to re-try a previously failed connection. (Since iOS 12, you should really use NWPathMonitor for this. I don't know any good uses for Reachability since iOS 12.)
The only way that you can know that a request will actually succeed is to try to send it and see if you get a response. That's why it is not recommended that you test Reachability before sending requests. Just send the request and deal with the errors if they come, since it is always possible to have an error, even if Reachability said you could connect.
Is there any configuration like android user-permission in iOS to control access to internet?
I think all new projects access to internet by default, is that correct?
When I send a request to the internet it returns 0 http-error code, it means I can't access to the internet.
yes, it is correct all the new ios project have access to the internet by default.
A status code of 0 in an NSHTTPURLResponse object generally means there was no response and can occur for various reasons. The server will never return a status of 0 as this is not a valid HTTP status code.
Any http request will first be processed by the operating system, and during that phase you can get an error. Getting an error means that your request never got a response from the server (and with the exception of https requests where certificates were not accepted, most likely didn't reach the server).
If this phase succeeds, then you get eventually a reply from the server. This may take time, you may have to wait 60 seconds. Which is why you do all your internet requests on a background thread. That reply will have a status code (status, not error). The status code is NEVER 0.
By default, iOS doesn't allow http requests, and doesn't allow https requests to unsave servers, so you better use only https unless you have a very good reason. You will need a very good reason to convince Apple to let your app on the app store if you want http requests to succeed. But if you get this wrong, you get an error quite early on.
A status of zero most likely means that a background request didn't finish by the time you read the status, a basic programming mistake. You need to learn how background threads and callbacks work. Without that, you won't be able to use http successfully.
Also google for "Reachability" which can tell you if your app currently has internet access (like when WiFi and Mobile Data are turned off, or in Airplane mode).
I'm experiencing slow response times for my first http POST request to my server.
This happens both in Android and iOS networking libraries. (Volley on Android, and Alamofire in iOS).
First response is roughly 0.7s-0.9s, whereas subsequent requests are 0.2s.
I'm guessing this is due to the session being kept-alive by the server, therefore eliminating the need for establishing a new session on each request.
I figure I can make a dummy request when the app starts to start the session, but it doesn't seem very elegant.
I also control the server side (Node.js) so if any configuration needs to be done there I can also try it.
Investigating a little further, I tried sending an https CONNECT request before issuing the first "real" POST request, and the behavior replicates.
After 30 seconds or so, the connection is dropped (probably at the iOS URLSession level, the load balancer is configured to keep connections as 60 seconds).
In theory this makes sense because setting up an https connection takes up several (12 total) packets and I'm on an inter continental connection.
So my solution is to send a CONNECT request when I expect the user to send a regular request.
My iOS app loads images from an nginx HTTP server. After I send 400+ such requests the networking 'gets stuck' and all subsequent HTTP requests result in "The request timed out" error. I can make the images load again only when I restart the app.
Details:
I am using NSURLSession.sharedSession().dataTaskWithURL to send four hundred HTTP GET requests to jpeg files.
Requests are sent sequentially, one after another. The interval between requests is 10 ms.
Each previous unfinished request is cancelled with cancel() method of NSURLSessionDataTask object.
Interestingly:
I can only have this issue with HTTPS requests and when SPDY is enabled on the server.
Non-secure HTTP requests work fine.
Non-SPDY HTTPS requests work fine. I tested it by turning SPDY off on the server side, in the nginx config.
Problem appears both on iOS 8 and 9, on physical device and in the simulator. Both on Wi-Fi and LTE.
When I look at nginx access logs, I can still see the 'stuck' requests coming in. Important nuance: the request log record appears at the exact moment when the iOS app is giving up on it after the time out period ends.
I was hoping to analyze HTTP requests with Charles Proxy but the problem cures itself when requests go through Charles. That is - everything works with Charles, much like effect in quantum mechanics when the fact of looking influences the outcome.
I was able to reproduce the issue when the iOS app connected to two different servers with vastly different nginx configurations. This probably means that the issue is not related to a particular nginx setup.
I analyzed the app using "Activity Monitor" instrument. The number of threads it is using during the bulk HTTP requests jumps from 5 to 10. In comparison, when I send just a single HTTP requests the number of threads jumps to 8. CPU load rarely goes above 30%.
What can be the cause of the issue? Can anyone recommend other ways or tools for analysing and debugging it?
Analysing with scheduling instrument
Demo app
This demo app reproduces the issue 100% of the time for me.
https://github.com/exchangegroup/ImageLoadDemo
Versions and settings
My nginx config: http://pastebin.com/pYYjdxfP
OS X: 10.10.4 (14E46), iOS: 8 and 9, Xcode: 7.0 (7A218), nginx: 1.9.4
Not ideal workaround
I managed to keep requests working only if I create a new NSURLSession for each individual request and clear the previous session with finishTasksAndInvalidate or invalidateAndCancel.
// Request 1
let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: configuration)
session.dataTaskWithURL ...
// Request 2
// clear the previous request
session.finishTasksAndInvalidate()
let session2 = NSURLSession(configuration: configuration)
session2.dataTaskWithURL ...
One possibility is that iOS started sending the request, and then packet loss prevented the headers and request body from being fully delivered.
Another possibility that comes to mind is that your server may not be logging the request until it actually finishes trying to deliver it, which would make the time stamps in the server logs line up with when the connection was closed, rather than when it was opened. (IIRC, that's what Apache does; I haven't worked with nginx, so I can't speak for its behavior.) If that's the case, then this is just a simple connection stall. As for why it is stalling, I couldn't guess.
Does the problem occur exclusively for HTTPS traffic? If you can reproduce it with HTTP, you don't need Charles Proxy; just use OS X's "Internet Sharing" feature, and capture the packets with tcpdump or wireshark, listening on the bridge interface. If you can't reproduce it with HTTP, my money would be on a problem with fetching the CRLs or performing the OCSP check while validating the server's certificate.
Is your app ending up with a huge number of threads as a result of excessive async dispatching to new queues, by any chance? Because that could easily cause all sorts of odd misbehavior.
How long is the timeout? If it is too short, your app might simply be running up against performance limitations of the hardware while processing the results of 400 requests delivered in only four seconds.
Also, are you trying to schedule these requests simultaneously? Because I seem to recall reading about a bug that causes NSURLSession to hit a brick wall if you start too many tasks in a single session at the same time. You might try adding tasks only after the number of tasks in a session drops below some threshold and see if that fixes the problem.
I know almost nothing about server/sockets programming. Pardon my ignorance.
I'm making an iOS app that needs to integrate with my web server. The function is analogous to a chat room - multiple clients will be 'connected' and 'listening' to a server session, any one client can send a 'bit', and all clients will receive the 'bit'.
Should I use low-level socket listening and callbacks for this? Is there a better, more power-efficient way? A cool framework I should use?
There are many options for this:
Use a socket to your server and roll your own protocol
Use web sockets and long polling from your app. This means you will fire a HTTP request and your server will keep it open for, let's say, one minute waiting for messages. Take a look here to start: What are Long-Polling, Websockets, Server-Sent Events (SSE) and Comet?
Use a chat server like Openfire or Ejabberd, which use XMPP, and on your client use XMPPFramework (https://github.com/robbiehanson/XMPPFramework)
Depending on the complexity of your app (authentication? blocking contacts? one-to-many and one-to-one chat?) you can decide on any of the above options. With more details I may be able to help you more.
If you want to be able to receive data while the app is not in the foreground, you will need to use Apple's push notification feature, which is implemented in hardware and the only way to make network connections to a device that is in power saving mode.
There's plenty of documentation how it works, basically the device registers with your server (after asking the user for permission), you use the token it gives you to send a ping to Apple's server, which forwards the ping on to the device. The device can then contact your server and download the actual data you want to send to it.
If you're OK with the server only communicating with your app while the app is running, you have a few options. The easiest is "long polling" where the app sends a HTTP request to the server, using something like this:
NSURL *serverUrl = [NSURL URLWithString:#"http://example.com/"];
NSString *response = [NSString stringWithContentsOfURL:serverUrl usedEncoding:NULL error:NULL];
NSLog(#"%#", response);
Instead of the server responding instantly, it can wait around for a long time (for example 45 seconds) until it has something to send to the device, then it responds with the information.
If 45 seconds are reached without having anything to send, it just sends a nothing response and the phone immediately opens up a new URL request to the same URL. This keeps the server from having a bunch of old/abandoned connections open. Typically connections are dropped after 60 seconds, so you want to respond before that time limit is reached. Obviously you'll want to do the request on a background queue with NSOperationQueue.
There are other options, you could use sockets, you could start a web server on a custom HTTP port on the phone (eg: https://github.com/robbiehanson/CocoaHTTPServer). But long polling is often the easiest choice.
Most apps use a combination of push notifications and something else.