HTTPDNS:Using DoH in iOS clients

Sample code

Create a DataTaskManager to manage NSURLSession.

@interface DataTaskManager : NSObject <NSURLSessionTaskDelegate>

#import "DataTaskManager.h"
@import Network;
@import Foundation;

- (instancetype)init {
    self = [super init];
    if (self) {
        _networkQueue = dispatch_queue_create("com.taskmanager.queue", DISPATCH_QUEUE_SERIAL);
        [self setupDoHConfiguration];
    }
    return self;
}
- (void)setupDoHConfiguration {
    dispatch_async(self.networkQueue, ^{
        NSLog(@"Setting up DoH configuration...");
        
        // Create URL endpoint for HTTPDNS DoH
        const char *dohServerURL = "https://1xxxx3.aliyunhttpdns.com/dns-query";
        nw_endpoint_t urlEndpoint = nw_endpoint_create_url(dohServerURL);
        NSLog(@"Using DoH server: %s", dohServerURL);
        
        nw_resolver_config_t resolverConfig = nw_resolver_config_create_https(urlEndpoint);
        nw_privacy_context_require_encrypted_name_resolution(NW_DEFAULT_PRIVACY_CONTEXT, true, resolverConfig);
        NSLog(@"DoH configuration applied to privacy context");
        
    });
}

Complete the initialization in ViewController.viewDidLoad.

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    ......
    self.dataTaskManager = [[DataTaskManager alloc] init];
    ......
}

Resolution performance instrumentation

You can use NSURLSessionTaskMetrics to instrument the DNS process. This lets you check if DoH resolution is working and monitor the DNS resolution time.

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didFinishCollectingMetrics:(NSURLSessionTaskMetrics *)metrics {
    NSLog(@"\n=== Collecting metrics for request to: %@ ===\n", task.originalRequest.URL);
    
    task.taskDescription = [NSString stringWithFormat:@"%.2f,%@", 
                          metrics.taskInterval.duration,
                          task.originalRequest.URL.absoluteString];
    
    if ([metrics.transactionMetrics count] > 0) {   
        [metrics.transactionMetrics enumerateObjectsUsingBlock:^(NSURLSessionTaskTransactionMetrics *_Nonnull obj, NSUInteger idx, BOOL *_Nonnull stop) {
            NSString *fetchTypeStr = @"Unknown";
            switch (obj.resourceFetchType) {
                case NSURLSessionTaskMetricsResourceFetchTypeNetworkLoad:
                    fetchTypeStr = @"Network Load";
                    break;
                case NSURLSessionTaskMetricsResourceFetchTypeServerPush:
                    fetchTypeStr = @"Server Push";
                    break;
                case NSURLSessionTaskMetricsResourceFetchTypeLocalCache:
                    fetchTypeStr = @"Local Cache";
                    break;
            }
            NSLog(@"Fetch Type: %@", fetchTypeStr);
            
            if (obj.resourceFetchType == NSURLSessionTaskMetricsResourceFetchTypeNetworkLoad) {
                NSURLSessionTaskMetricsDomainResolutionProtocol dnsProtocol = obj.domainResolutionProtocol;
                NSString *dnsProtocolStr = @"Unknown (0)";
                BOOL isDoH = NO;
                
                switch (dnsProtocol) {
                    case NSURLSessionTaskMetricsDomainResolutionProtocolUDP:
                        dnsProtocolStr = @"UDP (1)";
                        break;
                    case NSURLSessionTaskMetricsDomainResolutionProtocolTCP:
                        dnsProtocolStr = @"TCP (2)";
                        break;
                    case NSURLSessionTaskMetricsDomainResolutionProtocolTLS:
                        dnsProtocolStr = @"TLS (3)";
                        break;
                    case NSURLSessionTaskMetricsDomainResolutionProtocolHTTPS:
                        dnsProtocolStr = @"HTTPS/DoH (4)";
                        isDoH = YES;
                        break;
                }
                
                NSLog(@"DNS Protocol: %@", dnsProtocolStr);
                
                #if TARGET_OS_SIMULATOR
                    NSLog(@"Running in simulator - DNS protocol detection not supported");
                #else
                    if (!isDoH) {
                        NSLog(@"DoH not detected");
                    }
                #endif
                
                // Get DNS resolution performance data
                if (obj.domainLookupStartDate && obj.domainLookupEndDate) {
                    int dnsLookupTime = ceil([obj.domainLookupEndDate timeIntervalSinceDate:obj.domainLookupStartDate] * 1000);
                    NSLog(@"DNS Lookup Details:");
                    NSLog(@"  Start: %@", obj.domainLookupStartDate);
                    NSLog(@"  End: %@", obj.domainLookupEndDate);
                    NSLog(@"  Duration: %d ms", dnsLookupTime);
                } else {
                    NSLog(@"No DNS lookup performed (might be cached)");
                }
                
                // Get network request performance data
                if (obj.connectStartDate && obj.connectEndDate) {
                    NSTimeInterval connectionTime = [obj.connectEndDate timeIntervalSinceDate:obj.connectStartDate];
                    NSLog(@"Connection Time: %.3f seconds", connectionTime);
                }
            }
        }];
    } else {
        NSLog(@"No transaction metrics available");
    }
}

Fallback mechanism

1. Configure timeout settings to obtain exception information promptly when DNS resolution fails:

// Set connection timeout
NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
config.waitsForConnectivity = NO;
config.timeoutIntervalForRequest = 5;
config.timeoutIntervalForResource = 10;

2. In the instrumentation chain mentioned above, you can formulate an appropriate fallback strategy. Here is an example of globally falling back to LocalDNS when a DNS exception is detected:

  ......
            
    if (obj.resourceFetchType == NSURLSessionTaskMetricsResourceFetchTypeNetworkLoad) {
        NSURLSessionTaskMetricsDomainResolutionProtocol dnsProtocol = obj.domainResolutionProtocol;
        NSString *dnsProtocolStr = @"Unknown (0)";
        BOOL isDoH = NO;
        
        switch (dnsProtocol) {
            case NSURLSessionTaskMetricsDomainResolutionProtocolUDP:
                dnsProtocolStr = @"UDP (1)";
                break;
            case NSURLSessionTaskMetricsDomainResolutionProtocolTCP:
                dnsProtocolStr = @"TCP (2)";
                break;
            case NSURLSessionTaskMetricsDomainResolutionProtocolTLS:
                dnsProtocolStr = @"TLS (3)";
                break;
            case NSURLSessionTaskMetricsDomainResolutionProtocolHTTPS:
                dnsProtocolStr = @"HTTPS/DoH (4)";
                isDoH = YES;
                break;
        }
        
        NSLog(@"DNS Protocol: %@", dnsProtocolStr);
        
        #if TARGET_OS_SIMULATOR
            NSLog(@"Running in simulator - DNS protocol detection not supported");
        #else
            if (!isDoH) {
                NSLog(@"DoH not detected, falling back to local DNS");
                dispatch_async(dispatch_get_main_queue(), ^{
                    // Disable DoH and use LocalDNS
                    nw_privacy_context_require_encrypted_name_resolution(NW_DEFAULT_PRIVACY_CONTEXT, false, nil);
                });
            }
        #endif  
    }
    
  ......