Motivation:
At the moment there is not way for the user to know if resolving a domain was failed because the domain was unkown or because of an IO error / timeout. If it was caused by an timeout / IO error the user may want to retry the query. Also if the query was failed because of an IO error / timeout we should not cache it.
Modifications:
- Add DnsNameResolverTimeoutException and include it in the UnkownHostException if the domain could not be resolved because of an timeout. This will allow the user to retry the query when inspecting the cause.
- Do not cache IO errors / timeouts
- Add unit test
Result:
Easier for users to implement retries for DNS querys and not cache IO errors / timeouts.
Motivation:
At the moment there is not way for the user to know if resolving a domain was failed because the domain was unkown or because of an IO error / timeout. If it was caused by an timeout / IO error the user may want to retry the query. Also if the query was failed because of an IO error / timeout we should not cache it.
Modifications:
- Add DnsNameResolverTimeoutException and include it in the UnkownHostException if the domain could not be resolved because of an timeout. This will allow the user to retry the query when inspecting the cause.
- Do not cache IO errors / timeouts
- Add unit test
Result:
Easier for users to implement retries for DNS querys and not cache IO errors / timeouts.
Motivation:
Minor cleanup from 844d804 just to reduce the conditional statements and indentation level.
Modifications:
- combine the else + if into an else if statement
Result:
Code cleaned up.
Motivation:
DN resolution does not fall back to the "original name" lookup after search list is checked. This results in a failure to resolve any name (outside of search list) that has number of dots less than resolv.conf's ndots value (which, for example, is often the case in the context of Kubernetes where kubelet passes on resolv.conf containing "options ndots:5").
It also does not go through the search list in a situation described in resolv.conf man:
"The default for n[dots] is 1, meaning that if there are any dots in a name, the name will be tried first as an absolute name before any search list elements are appended to it."
Modifications:
DnsNameResolverContext::resolve was updated to match Go's https://github.com/golang/go/blob/release-branch.go1.9/src/net/dnsclient_unix.go#L338 logic.
Result:
DnsNameResolverContext::resolve will now try to resolve "original name" if search list yields no results when number of dots in the original name is less than resolv.conf's ndots value. It will also go through the search list in case "origin name" resolution fails and number of dots is equal or larger than resolv.conf's ndots value.
Motivation:
We should not try to use UnixResolverDnsServerAddressStreamProvider when on Windows as it will log some error that will produce noise and may confuse users.
Modifications:
Just use DefaultDnsServerAddressStreamProvider if windows is used.
Result:
Less noise in the logs. This was reported in vert.x: https://github.com/eclipse/vert.x/issues/2204
Motviation:
DnsNameResolverContext#followCname attempts to build a query to follow a CNAME, but puts the original hostname in the DnsQuery instead of the CNAME hostname. This will result in not following CNAME redirects correctly.
Result:
- DnsNameResolverContext#followCname should use the CNAME instead of the original hostname when building the DnsQuery
Result:
More correct handling of redirect queries.
Motivation:
Even if it's a super micro-optimization (most JVM could optimize such
cases in runtime), in theory (and according to some perf tests) it
may help a bit. It also makes a code more clear and allows you to
access such methods in the test scope directly, without instance of
the class.
Modifications:
Add 'static' modifier for all methods, where it possible. Mostly in
test scope.
Result:
Cleaner code with proper 'static' modifiers.
Motivation:
Without a 'serialVersionUID' field, any change to a class will make
previously serialized versions unreadable.
Modifications:
Add missed 'serialVersionUID' field for all Serializable
classes.
Result:
Proper deserialization of previously serialized objects.
Motivation:
DnsCache (an interface) is coupled to DnsCacheEntry (a final class). This means that DnsCache implementations can't implement their own DnsCacheEntry objects if the default behavior isn't appropriate.
Modifications:
- DnsCacheEntry should be moved to DefaultDnsCache as it is an implementation detail
- DnsCache#cache(..) should return a new DnsCacheEntry
- The methods which from DnsCacheEntry that were used outside the scope of DefaultDnsCache should be moved into an interface
Result:
DnsCache is more extensible and not tightly coupled to a default implementation of DnsCacheEntry.
Motivation:
To be able to build with latest java9 release we need to adjust commons-lang version and maven-enforcer-plugin.
Modifications:
- Use commons-lang 2.6.0
- Use maven-enforcer-plugin 3.0.0.M1 when building with java9
Result:
Netty builds again with latest java9 release
Motivation:
We should not use ipv4 google dns servers if the app is configured to run ipv6.
Modifications:
Use either ipv4 or ipv6 dns servers depending on the system config.
Result:
More correct behaviour
Motivation:
When the hostname portion can not be extracted we should just skip the server as otherwise we will produce and exception when trying to create the InetSocketAddress.
This was happing when trying to run the test-suite on a system and using java7:
java.lang.IllegalArgumentException: hostname can't be null
at java.net.InetSocketAddress.checkHost(InetSocketAddress.java:149)
at java.net.InetSocketAddress.<init>(InetSocketAddress.java:216)
at io.netty.util.internal.SocketUtils$10.run(SocketUtils.java:171)
at io.netty.util.internal.SocketUtils$10.run(SocketUtils.java:168)
at java.security.AccessController.doPrivileged(Native Method)
at io.netty.util.internal.SocketUtils.socketAddress(SocketUtils.java:168)
at io.netty.resolver.dns.DefaultDnsServerAddressStreamProvider.<clinit>(DefaultDnsServerAddressStreamProvider.java:74)
at io.netty.resolver.dns.DnsServerAddressesTest.testDefaultAddresses(DnsServerAddressesTest.java:39)
Modifications:
Skip if hostname can not be extracted.
Result:
No more java.lang.ExceptionInInitializerError.
Motivation:
JNDI allows to specify an port so we should respect it.
Modifications:
Use the specified port and if none is specifed use 53.
Result:
Correct handling of JNDI configured DNS.
Motivation:
DnsNameResolverTest has been observed to timeout on the CI servers. We should increase the timeout from 5 seconds to 30 seconds.
Modifications:
- Increase timeout from 5 to 30 seconds.
Result:
Less false failures due to slower CI machines.
Motivation:
The DNS resolver may use default configuration inherited from the environment. This means the ndots value may change and result in test failure if the tests don't explicitly set the assumed value.
Modifications:
- Explicitly set ndots in resolver-dns unit tests so we don't fail if the environment overrides the search domain and ndots
Result:
Unit tests are less dependent upon the enviroment they run in.
Fixes https://github.com/netty/netty/issues/6966.
Motivation:
UnixResolverDnsServerAddressStreamProvider currently throws an exception if /etc/resolver exists but it empty. This shouldn't be an exception and can be tolerated as if there is no contribution from /etc/resolver.
Modifications:
- Treat /etc/resolver as present and empty the same as not being present
Result:
UnixResolverDnsServerAddressStreamProvider initialization can tolerate empty /etc/resolver directory.
Motivation:
InetSocketAddress#getHostName() may attempt a reverse lookup which may lead to test failures because the expected address will not match.
Modifications:
- Use InetSocketAddress#getHostString() which will not attempt any lookups and instead return the original String
Result:
UnixResolverDnsServerAddressStreamProviderTest is more reliable.
Motivation:
If there are multiple DNS servers to query Java's DNS resolver will attempt to resolve A and AAAA records in sequential order and will terminate with a failure once all DNS servers have been exhausted. Netty's DNS server will share the same DnsServerAddressStream for the different record types which may send the A question to the first host and the AAAA question to the second host. Netty's DNS resolution also may not progress to the next DNS server in all situations and doesn't have a means to know when resolution has completed.
Modifications:
- DnsServerAddressStream should support new methods to allow the same stream to be used to issue multiple queries (e.g. A and AAAA) against the same host.
- DnsServerAddressStream should support a method to determine when the stream will start to repeat, and therefore a failure can be returned.
- Introduce SequentialDnsServerAddressStreamProvider for sequential use cases
Result:
Fixes https://github.com/netty/netty/issues/6926.
Motivation:
ba80fbbe05 modified the UnknownHostException to not include the search domain if the DNS query failed, but this masks what DNS query actually failed. Have the full hostname (including the search domain) provides more visibility and may help diagnose a configuration error if queries are unexpectedly failing.
Modifications:
- Remove DnsNameResolverContext#pristineHostname
Result:
UnknownHostException is more accurate and reflect what hostname actually resulted in failure.
Motivation:
DnsQueryLifecycleObserver is designed to capture the life cycle of every query. DnsNameResolverContext has a custom trace mechanism which consists of a StringBuilder and manual calls throughout the class. We can remove some special case code in DnsNameResolverContext and instead use a special implementation of DnsQueryLifecycleObserver when trace is enabled.
Modifications:
- Remove all references to the boolean trace variables in DnsNameResolverContext and DnsNameResolver
- Introduce TraceDnsQueryLifecycleObserver which will be used when trace is enabled and will log similar data as what trace currently provides
Result:
Less special case code in DnsNameResolverContext and instead delegate to TraceDnsQueryLifecycleObserver to capture trace information.
Motivation:
The DNS resolver supports search domains. However the ndots are not correctly enforced. The search domain should only be appended under the following scenario [1]:
> Resolver queries having fewer than ndots dots (default is 1) in them will be attempted using each component of the search path in turn until a match is found.
The DNS resolver current appends the search domains if ndots is 0 which should never happen (because no domain can have less than 0 dots).
[1] https://linux.die.net/man/5/resolv.conf
Modifications:
- Parse /etc/resolv.conf to get the default value for ndots on Unix platforms
- The search domain shouldn't be used if ndots is 0
- Avoid failing a promise to trigger the search domain queries in DnsNameResolverContext#resolve
Result:
More correct usage of search domains in the DNS resolver.
Fixes https://github.com/netty/netty/issues/6844.
Motivation:
It’s currently complicated to extend `DnsNameResolver` as the default
value for `searchDomain` is package private.
Modifications:
* let `DnsNameResolver` accept a null `searchDomains` and then default
to `DEFAULT_SEARCH_DOMAINS`, just like it’s being done with
`resolvedAddressTypes`.
* set default `DnsNameResolverBuilder#searchDomains` value to null to
avoid cloning internal `DnsNameResolver.DEFAULT_SEARCH_DOMAINS` in
`DnsNameResolver` constructor.
Result:
More versatile `DnsNameResolver` constructor.
No array copy when using default search domains.
Motivation:
UnixResolverDnsServerAddressStreamProvider allows the default name server address stream to be null, but there should always be a default stream to fall back to ([1] Search Strategy).
UnixResolverDnsServerAddressStreamProvider currently shuffles the names servers are multiple are present, but the defined behavior is to try them sequentially [2].
[1] Search Strategy Section - https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/resolver.5.html
[2] DESCRIPTION/nameserver Section - https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/resolver.5.html
Modifications:
- UnixResolverDnsServerAddressStreamProvider should always use the first file provided to derive the default domain server address stream. Currently if there are multiple domain names in the file identified by the first argument of the constructor then one will be selected at random.
- UnixResolverDnsServerAddressStreamProvider should return name servers sequentially.
- Reduce access level on some methods which don't have known use-cases externally.
Result:
Fixes https://github.com/netty/netty/issues/6736
Motivation:
IDN.toUnicode(...) removes trailing dots when used in Java7 while it not does on java8.
Modifications:
Check if we should test with the trailing dot removed or not.
Result:
Test pass on Java7 as well.
Motivation:
A single DNS query may follow many different paths through resolver-dns. The query may fail for various reasons related to the DNS protocol, general IO errors, it may be cancelled due to the query count being exceeded, or other reasons. A query may also result in other queries as we follow the DNS protocol (e.g. redirects, CNAME, etc...). It is currently impossible to collect information about the life cycle of an individual query though resolver-dns. This information may be valuable when considering which DNS servers are preferred over others.
Modifications:
- Introduce an interface which can provide visibility into all the potential outcomes of an individual DNS query
Result:
resolver-dns provides visibility into individual DNS queries which can be used to avoid poorly performing DNS servers.
Motivation:
1. The use of InternetProtocolFamily is not consistent:
the DnsNameResolverContext and DnsNameResolver contains switches
instead of appropriate methods usage.
2. The InternetProtocolFamily class contains redundant switches in the
constructor.
Modifications:
1. Replacing switches to the use of an appropriate methods.
2. Simplifying the InternetProtocolFamily constructor.
Result:
Code is cleaner and simpler.
Motivation:
Using reflection to obtain the default name servers may fail in Java9 and also in previous Java versions if a SecurityManager is present.
Modifications:
Try using jndi-dns to obtain default name servers and only try using reflection if this fails.
Result:
Be able to detect default name servers in all cases. Fixes [#6347].
Motivation:
DnsServerAddresses loads the default DNS servers used for DNS resolution in a static initialization block. This is subject to blocking and may cause unexpected delays. We can move this initialization to DefaultDnsServerAddressStreamProvider where it is more expected to load the JDK's default configuration.
Modifications:
- Move all the static initialization from DnsServerAddresses to DefaultDnsServerAddressStreamProvider
- Deprecate static methods in DnsServerAddresses which have moved to DefaultDnsServerAddressStreamProvider
- Remove usage of deprecated methods in DnsServerAddresses
Result:
Usage of JDK's blocking DNS resolver is not required to use resolver-dns.
Motivation:
DnsNameResolverContext completes its DNS query promise automatically
when no queries are in progress, which means there's no need to fail the
promise explicitly.
Modifications:
- Do not fail a DNS query promise explicitly but add an informational
trace
Result:
- Fixes#6600
- Unexpected exception on one question type does not fail the promise
too soon. If the other question succeeds, the query will succeed,
making the resolver more robust.
Motivation:
Recently DnsServerAddressStreamProvider was introduced to allow control for each query as to which DNS server should be used for resolution to respect the local host's default DNS server configuration. However resolver-dns also accepts a stream of DNS servers to use by default, but this stream is not host name aware. This creates an ambiguity as to which method is used to determine the DNS server to user during resolution, and in which order. We can remove this ambiguity and provide a more general API by just supporting DnsServerAddressStreamProvider.
Modifications:
- Remove the fixed DnsServerAddresses and instead only accept a DnsServerAddressStreamProvider.
- Add utility methods to help use DnsServerAddressStreamProvider for a single entry, a list of entries, and get the default for the current machine.
Result:
Fixes https://github.com/netty/netty/issues/6573.
