Make sure to check out our counterpart too: TrueTime, an NTP library for Android.

NTP client for Swift. Calculate the time "now" impervious to manual changes to device clock time.

In certain applications it becomes important to get the real or "true" date and time. On most devices, if the clock has been changed manually, then an NSDate() instance gives you a time impacted by local settings.

Users may do this for a variety of reasons, like being in different timezones, trying to be punctual and setting their clocks 5 – 10 minutes early, etc. Your application or service may want a date that is unaffected by these changes and reliable as a source of truth. TrueTime gives you that.

It's pretty simple actually. We make a request to an NTP server that gives us the actual time. We then establish the delta between device uptime and uptime at the time of the network response. Each time now() is requested subsequently, we account for that offset and return a corrected NSDate value.

import TrueTime

// At an opportune time (e.g. app start):
let client = TrueTimeClient.sharedInstance
client.start()

// You can now use this instead of NSDate():
let now = client.referenceTime?.now()

// To block waiting for fetch, use the following:
client.retrieveReferenceTime { result in
    switch result {
        case let .Success(referenceTime):
            let now = referenceTime.now()
        case let .Failure(error):
            print("Error! \(error)")
    }
}

@import TrueTime;

// At an opportune time (e.g. app start):
TrueTimeClient *client = [TrueTimeClient sharedInstance];
[client startWithHostURLs:@[[NSURL URLWithString:@"time.apple.com"]]];

// You can now use this instead of [NSDate date]:
NSDate *now = [[client referenceTime] now];

// To block waiting for fetch, use the following:
[client retrieveReferenceTimeWithSuccess:^(NTPReferenceTime *referenceTime) {
    NSLog(@"True time: %@", [referenceTime now]);
} failure:^(NSError *error) {
    NSLog(@"Error! %@", error);
}];

TrueTime is currently compatible with iOS 8 and up, macOS 10.9 and tvOS 9.

Add this to your Cartfile:

github "instacart/TrueTime.swift"

Then run:

$ carthage update

• Run git submodule update --init.
• Run carthage bootstrap.
• Open TrueTime.xcodeproj, choose TrueTimeExample and hit run. This will build everything and run the sample app.

• Add TrueTime as a submodule:

$ git submodule add https://github.com/instacart/TrueTime.swift.git

• Navigate to the TrueTime directory and add its dependencies

$ carthage bootstrap

• Install Swift Lint if missing

$ brew install swiftlint

• Drag TrueTime.xcodeproj into the Project Navigator
• Go to Project > Targets > Build Phases > Link Binary With Libraries, click + and select the TrueTime target.

• Since NSDates are just Unix timestamps, it's safe to hold onto values returned by ReferenceTime.now() or persist them to disk without having to adjust them later.
• Reachability events are automatically accounted for to pause/start requests.
• UDP requests are executed in parallel, with a default limit of 5 parallel calls. If one fails, we'll retry up to 3 times by default.
• TrueTime is also available for Android.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.