Allow valid SRV hostnames with less than 3 parts

[NathanQingyangXu]

https://jira.mongodb.org/browse/JAVA-5542

[katcharov]

Looking good, just a few comments/questions.

[katcharov]

Does this (user-facing) error message discuss implementation details, for example the number of parts? The spec potentially suggests that this would be described as "...host name ... lacks a subdomain, and the resolved..."? I tried to compare against the other drivers, and I believe this corresponds to the following:

Node: https://github.com/mongodb/node-mongodb-native/pull/4197/files#diff-39b2554fd18da165b59a6351b1aafff3714e2a80c1435f2de9706355b4d32351R1181-R1185
Rust: https://github.com/mongodb/mongo-rust-driver/pull/1211/files#diff-32a39d356e1edde3d94581275b42e994ad1780ce4de8d6935ec5596fe4493ffdR39

However, I am not sure, because the error messages are different. It would have been useful if the spec specified the wording of the error messages.

[NathanQingyangXu]

This exception is mainly for this prose testing case: mongodb/specifications@8e9d768#diff-dfcf948e6a987b880ea85e1907d5b7ce8fb98c9dab752f42ccdaf1e656b8848fR30

[NathanQingyangXu]

thanks for referring to other driver's implementation. will investigate further.

[NathanQingyangXu]

as per the following code snippet, the exception message won't be exposed to end user but end up with a generic exception:

throw new MongoConfigurationException(format("Failed looking up SRV record for '%s'.", resourceName), e);

[NathanQingyangXu]

I changed the logic to accommodate the possibility that 'resolvedHost' could be something like localhost (as in Prosetest case No.3: mongodb/specifications@8e9d768#diff-dfcf948e6a987b880ea85e1907d5b7ce8fb98c9dab752f42ccdaf1e656b8848fR30) which doesn't contain '.' separator and so it has no parent domain. After the code refactoring, no new exception or logic branch is required.

[katcharov]

Were the prose tests passing previously? I thought you were testing against localhost.

exception message won't be exposed to end user

I believe all exception messages are exposed to the user. It may be in "caused by", but this is still visible.

no new exception or logic branch is required

I am not sure I follow the logic well enough to understand this - why is it that the other drivers have introduced 1 or 2 new messages, such as "Server record does not have at least one more domain level than parent URI", but we do not need to?

[NathanQingyangXu]

yeah, you are totally correct in that the exception will be exposed to end user as exception's cause. I missed that. Now after new code change (converging the newly -added logic branch to the existing only flow), we reuse the old same exception mesage as below:

throw new MongoConfigurationException(
                            format("The SRV host name '%s' resolved to a host '%s 'that is not in a sub-domain of the SRV host.",
                                    srvHost, resolvedHost));

It is simply another way to express the same meaning, from my understanding. Maybe it is desirable to maintain backward compatibility so I didn't change it.