support running multiple DoH/DoT DNSTT tunnels

[garmr-ulfr]

This pull request introduces support for multiple DNS-over-HTTPS (DoH) and DNS-over-TLS (DoT) resolvers in the common/httpclient.go file, replacing the previous single-resolver approach. It also includes a new test suite to validate the functionality of these resolvers.

Enhancements to DNS Resolver Functionality:

• Support for Multiple Resolvers: Added lists of predefined DoH and DoT resolvers (dohResolvers and dotResolvers) to enable the creation of multiple DNS tunnels. (common/httpclient.go, common/httpclient.goR43-R64)
• Refactored newDNSTT to newDNSTTs: The function now initializes multiple DNSTT instances using all resolvers in the lists, instead of a single instance based on a single resolver. (common/httpclient.go, [1] [2]
• Updated HTTP Client Initialization: Modified GetHTTPClient to integrate multiple DNS tunnels into the HTTP client configuration. (common/httpclient.go, common/httpclient.goL100-R128)

Testing Improvements:

• New Test Suite: Added TestDNSResolvers in common/httpclient_test.go to validate each DoH/DoT provider.

[Copilot]

Pull Request Overview

This PR enhances the DNS tunneling functionality by introducing support for multiple DNS-over-HTTPS (DoH) and DNS-over-TLS (DoT) resolvers, replacing the previous single-resolver approach with predefined resolver lists to enable creation of multiple DNS tunnels.

• Adds predefined lists of DoH and DoT resolvers for redundancy and load distribution
• Refactors newDNSTT to newDNSTTs to create multiple DNSTT instances
• Updates HTTP client initialization to integrate multiple DNS tunnels

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
common/httpclient.go	Adds resolver lists, refactors DNS tunnel creation to support multiple instances, and updates HTTP client configuration
common/httpclient_test.go	Introduces test suite to validate DoH/DoT resolver functionality

Comments suppressed due to low confidence (1)

common/httpclient_test.go:36

• The error message incorrectly states 'DNS over TLS resolvers' when this is testing DoH resolvers. It should say 'All DNS over HTTPS resolvers failed'.

		assert.Empty(t, failed, "All DNS over TLS resolvers failed")

[WendelHime]

@garmr-ulfr sorry, I just noticed that I forgot to review this PR! Do we still want to merge it? Kindling already receives a list of DNS servers that should be used by the smart dialer, shouldn't we use the same list here?

[garmr-ulfr]

@WendelHime, honestly, I forgot about this too 😆.

Kindling already receives a list of DNS servers that should be used by the smart dialer, shouldn't we use the same list here?

I'm not sure, but, since we'll be moving away from flashlight completely soon, I don't think it really matters.