public final class DnsOptions extends Object

A class configuring Cronet's host resolution functionality. Note that while we refer to DNS as the most common mechanism being used for brevity, settings apply to other means of resolving hostnames like hosts file resolution.

Cronet resolve hostnames in two ways - either by using the system resolver (using getaddrinfo provided by system libraries), or by using a custom resolver which is built into the networking stack Cronet uses.

The built-in stack provides several advantages over using the system resolver:

  • It has been tailored to the needs of the networking stack, particularly speed and stability.
  • getaddrinfo is a blocking call which requires dedicating worker threads and makes cancellation impossible (we need to abandon the thread until the call completes)
  • The getaddrinfo interface gives no insight into the root cause of failures
  • struct addrinfo provides no TTL (Time To Live) of the returned addresses. This restricts flexibility of handling caching (e.g. allowing the use of stale DNS records) and requires us to either rely on OS DNS caches, or be extremely conservative with the TTL.
  • As part of the OS, getaddrinfo evolves slowly. Using a custom stack enables Cronet to introduce features like encrypted DNS faster.

Most configuration in this class is only applicable if the built-in DNS resolver is used.

Nested Class Summary

class DnsOptions.Builder Builder for DnsOptions
@interface DnsOptions.Experimental An annotation for APIs which are not considered stable yet. 
class DnsOptions.StaleDnsOptions A class configuring Cronet's stale DNS functionality. 

Public Method Summary

static DnsOptions.Builder

Inherited Method Summary

Public Methods

public static DnsOptions.Builder builder ()

public Boolean getEnableStaleDns ()

public Boolean getPersistHostCache ()

public Long getPersistHostCachePeriodMillis ()

public Boolean getPreestablishConnectionsToStaleDnsResults ()

public DnsOptions.StaleDnsOptions getStaleDnsOptions ()

public Boolean getUseBuiltInDnsResolver ()