Motivation:
The current DnsNameResolver fails to resolve an A+CNAME answer. For example:
dig moose.rmq.cloudamqp.com
...
;; ANSWER SECTION:
moose.rmq.cloudamqp.com. 1800 IN CNAME ec2-54-152-221-139.compute-1.amazonaws.com.
ec2-54-152-221-139.compute-1.amazonaws.com. 583612 IN A 54.152.221.139
...
The resolver constructs a map of cnames but forgets the trailing "." in the values which lead to not resolve the A record.
Modifications:
Reuse the code of DefaltDnsRecordDecoder which correctly handles the trailing dot.
Result:
Correctly resolve.
Motivation:
JCTools supports both non-unsafe, unsafe versions of queues and JDK6 which allows us to shade the library in netty-common allowing it to stay "zero dependency".
Modifications:
- Remove copy paste JCTools code and shade the library (dependencies that are shaded should be removed from the <dependencies> section of the generated POM).
- Remove usage of OneTimeTask and remove it all together.
Result:
Less code to maintain and easier to update JCTools and less GC pressure as the queue implementation nt creates so much garbage
Motivation:
We use a default of 3 for maxQueriesPerResolve when using the DnsNameResolverBuilder, which is too low if you want to resolve a hostname that uses a lot of CNAME records.
Modifications:
- Use higher default (16)
- Make exception message more clear why it failed.
Result:
Be able to resolve more domains by default and be able to better trouble shoot why a resolver failed.
Motivation:
DnsAddressResolverGroup allows to override the newResolver(...) method to change the settings used by the user. We should better let the user override another method and always apply the InflightNameResolver.
Modifications:
- Mark newResolver(...) method as deprecated, we will make it private soon.
- Add newNameResolver(...) method that user can override.
Result:
Easier to extend DnsAddressResolverGroup
Related issue: #5179
Motivation:
When you attempt to make a lot of connection attempts to the same target
host at the same time and our DNS resolver does not have a record for it
in the cache, the DNS resolver will send as many DNS queries as the
number of connection attempts.
As a result, DNS server will reject or drop the requests, making the
name resolution attempt fail.
Modifications:
- Add InflightNameResolver that keeps the list of name resolution
queries and subscribes to the future of the matching query instead of
sending a duplicate query.
Result:
- The AddressResolvers created by DnsAddressResolverGroup do not send
duplicate DNS queries anymore
Motivation:
Some codecs should be considered unstable as these are relative new. For this purpose we should introduce an annotation which these codecs should us to be marked as unstable in terms of API.
Modifications:
- Add UnstableApi annotation and use it on codecs that are not stable
- Move http2.hpack to http2.internal.hpack as it is internal.
Result:
Better document unstable APIs.
Motivation:
There were some warning in the resolver-dns code base.
Modifications:
- Fix javadocs
- Use the base class to call static method.
Result:
Cleaner code.
Related: #4771
Motivation:
A malicious or misconfigured DNS server can send the CNAME records that
resolve into each other, causing an unexpected infinite loop in
DnsNameResolverContext.onResponseCNAME().
Modifications:
- Remove the dereferenced CNAME from the alias map so that infinite loop
is impossible.
- Fix inspection warnings and typos in DnsNameResolverTest
Result:
Fixes#4771
Motivation:
Current DnsNameResolver api don't allow to define additional records in DNS query.
It can be useful in many cases. For example when we want to query dns server with
real client address (EDNS-CLIENT-SUBNET extension:
http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-02 )
Modifications:
This change add new query methods with list of additional DnsRecord-s for query.
Result:
It is possible to create dns query with EDNS-CLIENT-SUBNET extension for example.
Motivation:
See #3411. A reusable ArrayList in InternalThreadLocalMap can avoid allocations in the following pattern:
```
List<...> list = new ArrayList<...>();
add something to list but never use InternalThreadLocalMap
return list.toArray(new ...[list.size()]);
```
Modifications:
Add a reusable ArrayList to InternalThreadLocalMap and update codes to use it.
Result:
Reuse a thread local ArrayList to avoid allocations.
Motivation:
DnsNameResolverBuilder#nameServerAddresses isn’t initialized with a
default value. In most cases, user will want
DefaultDnsServerAddresses#defaultAddresses.
Modifications:
Initialize DnsNameResolverBuilder#nameServerAddresses with
DefaultDnsServerAddresses#defaultAddresses
Result:
DnsNameResolverBuilder more convenient usage.
Motivation:
As "getHostName" may do a reverse name lookup and return a host name based on the system configured name lookup service, testResolveIp may fail in some special environment. See #4720
Modifications:
Use getHostAddress instead of getHostName
Result:
testResolveIp works in all environments
Motivation:
Caching is currently nested in DnsResolver.
It should also be possible to extend DnsResolver to ba able to pass a different cache on each resolution attemp.
Modifications:
* Introduce DnsCache, NoopDnsCache and DefaultDnsCache. The latter contains all the current caching logic that was extracted.
* Introduce protected versions of doResolve and doResolveAll that can be used as extension points to build resolvers that bypass the main cache and use a different one on each resolution.
Result:
Isolated caching logic. Better extensibility.
Motivation:
There are some wrong links and tags in javadoc.
Modifications:
Fix the wrong links and tags in javadoc.
Result:
These links will work correctly in javadoc.
Motivation:
On contrary to `DefaultNameResolver`, `DnsNameResolver` doesn't currently honor hosts file.
Modifications:
* Introduce `HostsFileParser` that parses `/etc/hosts` or `C:\Windows\system32\drivers\etc\hosts` depending on the platform
* Introduce `HostsFileEntriesResolver` that uses the former to resolve host names
* Make `DnsNameResolver` check his `HostsFileEntriesResolver` prior to trying to resolve names against the DNS server
* Introduce `DnsNameResolverBuilder` so we now have a builder for `DnsNameResolver`s
* Additionally introduce a `CompositeNameResolver` that takes several `NameResolver`s and tries to resolve names by delegating sequentially
* Change `DnsNameResolver.asAddressResolver` to return a composite and honor hosts file
Result:
Hosts file support when using `DnsNameResolver`.
Consistent behavior with JDK implementation.
Motivation:
As discussed in #4529, NameResolver design shouldn't be resolving SocketAddresses (or String name + port) and return InetSocketAddresses. It should resolve String names and return InetAddresses.
This SocketAddress to InetSocketAddresses resolution is actually a different concern, used by Bootstrap.
Modifications:
Extract SocketAddress to InetSocketAddresses resolution concern to a new class hierarchy named AddressResolver.
These AddressResolvers delegate to NameResolvers.
Result:
Better separation of concerns.
Note that new AddressResolvers generate a bit more allocations because of the intermediate Promise and List<InetAddress>.
Motivation:
There's no way to override the default settings of the DnsNameResolvers
created by DnsNameResolverGroup because DnsNameResolverGroup is final.
Modifications:
- Make DnsNameResolverGroup non-final
- Add a new overridable protected method 'newResolver()' so that a user
can override it to create an alternative DnsNameResolver instance or
set the non-default properties
Result:
A user can configure the DnsNameResolver.
Motivation:
Each server should be checked for every record type. Currently, if there
are only two configured servers and the first is down, it is impossible
to query for IPv4 addresses because the second server is only ever
queried for type AAAA.
Modifications:
Do not cycle DNS servers while cycling DNS record types (A and AAAA)
Result:
Name resolution is less fragile when the number of available DNS servers
is 2.
Related: #3972
Motivation:
DnsNameResolver limits the number of concurrent in-progress DNS queries
to 65536 regardless the number of DNS servers it communicates with. When
the number of available DNS servers are more than just one, we end up
using much less (65536 / numDnsServers) query IDs per DNS server, which
is non-optimal.
Modifications:
- Replace the query ID and context management with
DnsQueryContextManager
- Eash DNS server gets its own query ID space
Result:
Much bigger query ID space, and thus there's less chance of getting the
'query ID space exhaustion' error
Motivation:
When DnsNameResolverContext succeeds to get the address(es), it cancels
the promise of other queries in progress.
Unlike expectation, DnsNameResolverContext.query() attempts to retry
even when the query has failed due to cancellation.
As a result, the resolver sends unnecessary extra queries to a DNS
server and then tries to mark the promised that's been fulfilled
already, leading to unnecessarily verbose 'failed to notify success to a
promise' messages.
Modifications:
Do not perform an extra query when the previous query has failed due to
cancellation
Result:
DnsNameResolver does not send unnecessary extra queries and thus does
not log the 'failed to notify success to a promise' message.
Motivation:
As relaying on external DNS Server can result to test-failures we should better use a mock DNS Server for the dns tests.
Modifications:
- Refactor the DnsNameResolverTest to use a mock DNS Server which is using apacheds.
- Allow to disable adding an opt resources as some servers not support it.
Result:
More stable testsuite.
Motivation:
Some DNS servers in DnsNameResolverTest are outdated and some of them
returns NoError for non-existent domains.
Modifications:
- Update the DNS server list from http://meo.ws/dnsrec.php again
- Update the web-scraper script
Result:
DnsNameResolverTest.testNegativeTtl() should not fail anymore.
Motivation:
DNS lookups in DnsNameResolverTest can take longer than expected due to
retries. The hard limit of 5 seconds is being applied to
testNegativeTtl(), making the first uncached lookup cause a timeout.
Modifications:
Do not use JUnit's Timeout annotation but implement simple timeout
mechanism that apples only to cached lookups.
Result:
testNegativeTtl() should not fail when an initial negative lookup
requires a retry.
