Motivation:
Currently, if a DNS server returns a non-preferred address type before the preferred one, then both will be returned as the result, and when only taking a single one, this usually ends up being the non-preferred type. However, the JDK requires lookups to only return the preferred type when possible to allow for backwards compatibility.
To allow a client to be able to resolve the appropriate address when running on a machine that does not support IPv6 but the DNS server returns IPv6 addresses before IPv4 addresses when querying.
Modification:
Filter the returned records to the expected type when both types are present.
Result:
Allows a client to run on a machine with IPv6 disabled even when a server returns both IPv4 and IPv6 results. Netty-based code can be a drop-in replacement for JDK-based code in such circumstances.
This PR filters results before returning them to respect JDK expectations.
* Add DnsNameResolver.resolveAll(DnsQuestion)
Motivation:
A user is currently expected to use DnsNameResolver.query() when he or
she wants to look up the full DNS records rather than just InetAddres.
However, query() only performs a single query. It does not handle
/etc/hosts file, redirection, CNAMEs or multiple name servers.
As a result, such a user has to duplicate all the logic in
DnsNameResolverContext.
Modifications:
- Refactor DnsNameResolverContext so that it can send queries for
arbitrary record types.
- Rename DnsNameResolverContext to DnsResolveContext
- Add DnsAddressResolveContext which extends DnsResolveContext for
A/AAAA lookup
- Add DnsRecordResolveContext which extends DnsResolveContext for
arbitrary lookup
- Add DnsNameResolverContext.resolveAll(DnsQuestion) and its variants
- Change DnsNameResolverContext.resolve() delegates the resolve request
to resolveAll() for simplicity
- Move the code that decodes A/AAAA record content to DnsAddressDecoder
Result:
- Fixes#7795
- A user does not have to duplicate DnsNameResolverContext in his or her
own code to implement the usual DNS resolver behavior.
Motivation:
When we do DNS queries we need to ensure we always release the AddressEnvelope.
Modifications:
Also release the AddressEnvelope if the original resolution was done in the meantime and we did not cancel the extra query yet.
Result:
Should fix [#7713]
Motivation:
When following a CNAME response DnsNameResovlerContext may issue a A and AAAA query. However the DnsNameResolverContext would have already issued a A and AAAA query to get the CNAME response, and this may result in 2 additional A/AAAA queries per CNAME response.
Modifications:
- DnsNameResovlerContext#followCname shouldn't issue 2 queries, but instead just a single query with the same record type as the original query
Result:
No more duplicate queries as a result of CNAME responses.
Motivation:
DnsServerAddressStream provides an iterator like interface but maybe expected to start at a specific point upon each new usage. If a DnsServerAddressStream is re-used in multiple independent iterations the order of iteration maybe incorrect. DnsNameResolverContext has a fallback DnsServerAddressStream reference if the cache doesn't contain a hit, but it is shared across multiple independent iterations. This may lead to undesirable DNS query order.
Modifications:
- DnsNameResolverContext#getNameServers should duplicate the default DnsServerAddressStream
Result:
Consistent iteration over the default DnsServerAddressStream in DnsNameResolverContext.
Motivation:
When following a CNAME it is possible there are multiple name servers to query against. However DnsNameResolverContext#followCname explicitly only uses the first name server address when attempting the query. This may lead to resolution failures because we didn't try all the available name servers.
Modifications:
DnsNameResolverContext#followCname should not just try the first name server, but it should try all name servers
Result:
More complete CNAME resolution.
Motivation:
At the moment DefaultDnsCache will expire each record dependong on its own TTL. This may result in unexpected results for the end-user especially if the user for example uses IPV4_PREFERED but the cached AAAA records has a higher TTL then the A records and so the A record was removed. In this case we would only return the AAAA record and not even try to refresh.
Modifications:
Always expire all records for a hostname when one TTL is reached.
Result:
Fixes [#7329]
Motivation:
The usage of DnsCache in DnsNameResolver was racy in general. First of the isEmpty() was not called in a synchronized block while we depended on synchronized. The other problem was that this whole synchronization only worked if the DefaultDnsCache was used and the returned List was not wrapped by the user.
Modifications:
- Rewrite DefaultDnsCache to not depend on synchronization on the returned List by using a CoW approach.
Result:
Fixes [#7583] and other races.
Motivation:
We need to ensure we only call List.* methods in the synchronized block as the returned List may not be thread-safe.
Modifications:
Do not call isEmpty() outside of the synchronized block.
Result:
Fixes [#7583]
Motivation:
DnsNameResolverTest has not been updated in a while.
Modifications:
- Update the DOMAINS definition in DnsNameResolverTest
Result:
More current domain names.
Automatic-Module-Name entry provides a stable JDK9 module name, when Netty is used in a modular JDK9 applications. More info: http://blog.joda.org/2017/05/java-se-9-jpms-automatic-modules.html
When Netty migrates to JDK9 in the future, the entry can be replaced by actual module-info descriptor.
Modification:
The POM-s are configured to put the correct module names to the manifest.
Result:
Fixes#7218.
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.
