Transport: Prevent DNS lookup if host not provided

[antonyj7]

Currently, if the host is not specified, it defaults to localhost. This can lead to issues if the DNS server does not resolve localhost correctly, potentially resulting in errors such as {"code":14,"message":"dns: A record lookup error: lookup localhost: i/o timeout"}.

I believe that if the host is not provided, the system should skip DNS resolution entirely and directly use the host, which would help prevent these unintended behaviors.

RELEASE NOTES:

• Skip DNS resolution when host not specified

[linux-foundation-easycla]

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• ✅ login: antonyj7 (efbc015, 57aa434, 9b4260a, 28b4f5a, c59868f, 7f2f473, d1fff88)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.14%. Comparing base (bcf9171) to head (28b4f5a).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7665      +/-   ##
==========================================
+ Coverage   81.79%   82.14%   +0.34%     
==========================================
  Files         361      361              
  Lines       27821    27877      +56     
==========================================
+ Hits        22757    22900     +143     
+ Misses       3863     3812      -51     
+ Partials     1201     1165      -36     

Files with missing lines	Coverage Δ
internal/resolver/dns/dns_resolver.go	90.86% <100.00%> (ø)

... and 28 files with indirect coverage changes

[purnesh42H]

@antonyj7 thanks for the change. Though i think hardcoding to only 127.0.0.1 could cause problems in IPv6-preferred or IPv6-only environments. To ensure broader compatibility and future-proof the code, it would be better to handle both IPv4 (127.0.0.1) and IPv6 (::1) loopback addresses when skipping DNS resolution and that would require some more custom logic. Using localhost and relying on the system's DNS resolution to handle the appropriate mapping between IPv4 (127.0.0.1) and IPv6 (::1) might be better in most cases.

Are you facing any specific issues with using localhost? If yes, could you provide more details or logs for that?

[antonyj7]

localhost

Thanks for the review. We have been having issues with some of our VPN servers whereby the DNS does not resolve localhost and spits out {"code":14,"message":"dns: A record lookup error: lookup localhost: i/o timeout"} error.

However, the broader point here was - do we even have to go down the route of resolving DNS in case of localhost ?

grpc.NewClient(endpoint, opts...) fails when we use localhost:$port or :$port (ignoring host) , we have this fixed by passing 127.0.0.1:$port as endpoint

Its not a big deal for us, and we can live with this :-) but if this can be fixed in the library, then we can remove 127.0.0.1 in our code :-)

Meanwhile, I will look at handling both IPv4 and IPv6...

[antonyj7]

closing this, will raise another PR in case we have a generic solution to cater for IPv6 etc..

[purnesh42H]

localhost

Thanks for the review. We have been having issues with some of our VPN servers whereby the DNS does not resolve localhost and spits out {"code":14,"message":"dns: A record lookup error: lookup localhost: i/o timeout"} error.

However, the broader point here was - do we even have to go down the route of resolving DNS in case of localhost ?

grpc.NewClient(endpoint, opts...) fails when we use localhost:$port or :$port (ignoring host) , we have this fixed by passing 127.0.0.1:$port as endpoint

Its not a big deal for us, and we can live with this :-) but if this can be fixed in the library, then we can remove 127.0.0.1 in our code :-)

Meanwhile, I will look at handling both IPv4 and IPv6...

Thanks @antonyj7. There is a similar issue in discussion here #7429