Fix externalhosts to advertise both IPv4 and IPv6 addresses #10145

wearedood · 2025-08-08T19:27:59Z

When a domain resolves to both IPv4 and IPv6 addresses, the node should advertise both protocols. Previously, only one address was returned due to using ResolveTCPAddr which returns a single address.

This change:

Uses net.LookupHost to get all IP addresses for a domain
Creates addresses for each IP found (both IPv4 and IPv6)
Handles errors gracefully by continuing with other IPs if one fails
Returns error if no valid addresses are found
Updates function signature to return []net.Addr instead of single net.Addr

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Fixes lightningnetwork#8801 When a domain resolves to both IPv4 and IPv6 addresses, the node should advertise both protocols. Previously, only one address was returned due to using ResolveTCPAddr which returns a single address. This change: - Uses net.LookupHost to get all IP addresses for a domain - Creates addresses for each IP found (both IPv4 and IPv6) - Handles errors gracefully by continuing with other IPs if one fails - Returns error if no valid addresses are found - Updates function signature to return []net.Addr instead of single net.Addr

gemini-code-assist

Summary of Changes

Hello @wearedood, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

I've implemented a crucial fix to how external hosts are advertised, specifically addressing an issue where only a single IP address (either IPv4 or IPv6) was being returned, even when a domain resolved to both. My changes ensure that the system now correctly identifies and advertises all available IP addresses for a given host, supporting both IPv4 and IPv6 simultaneously. This was achieved by switching to net.LookupHost to retrieve all IPs and then iterating through them to create and collect all valid network addresses. This enhancement improves network connectivity and robustness for dual-stack environments.

Highlights

Dual-stack address advertisement: Previously, the system would only return a single IP address (either IPv4 or IPv6) when resolving a domain, even if the domain had both types of addresses. This change ensures that if a domain resolves to both IPv4 and IPv6, both are advertised.
Updated function signature: The LookupHost function, which is responsible for resolving hostnames to network addresses, has been updated to return a slice of net.Addr instead of a single net.Addr. This allows it to return all resolved addresses.
Improved IP address resolution: The internal logic for resolving hostnames now uses Go's net.LookupHost function, which provides all IP addresses associated with a given hostname. It then iterates through these addresses, parsing each one and collecting them.
Enhanced error handling: The updated logic includes robust error handling. If parsing a specific IP address fails, it logs the error but continues processing other IPs. An error is only returned if no valid addresses can be found for the host.

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gemini-code-assist

Code Review

This pull request correctly addresses the issue of advertising both IPv4 and IPv6 addresses for external hosts by using net.LookupHost. The overall logic is sound. I've found a few issues, including a critical typo, a missing log statement, and some style guide violations related to line length and comments. Please address these points to improve the code quality and ensure it compiles correctly.

gemini-code-assist · 2025-08-08T19:30:35Z

server.go

-					host, strconv.Itoa(defaultPeerPort),
-					cfg.net.ResolveTCPAddr,
-				)
+			LookuLookupHost: func(host string) ([]net.Addr, error) {


There's a typo in the field name. It should be LookupHost instead of LookuLookupHost for the code to compile correctly.

LookupHost: func(host string) ([]net.Addr, error) {

gemini-code-assist · 2025-08-08T19:30:36Z

server.go

-					cfg.net.ResolveTCPAddr,
-				)
+			LookuLookupHost: func(host string) ([]net.Addr, error) {
+					// Use net.LookupHost to get all IP addresses for the host


This comment, and the ones on lines 1923 and 1937, explain what the code does rather than why. According to the style guide, comments should explain the 'why' if the code isn't self-explanatory. In this case, the code is clear, so these comments can be removed.¹

Style Guide References

Footnotes

Comments should explain the 'why' behind the code, not what the code does, especially if the code is self-documenting. (link) ↩

gemini-code-assist · 2025-08-08T19:30:36Z

server.go

+							// Log the error but continue with other IPs
+							continue


The comment here is inaccurate as no logging is performed. It's good practice to log such errors for debugging purposes. Also, per the style guide, comments should explain the 'why', not the 'what'.¹

// Log the error and continue with other IPs. srvrLog.Warnf("unable to parse address %s for host %s: %v", ip, host, err) continue

Style Guide References

Footnotes

Comments should explain the 'why' behind the code, not what the code does, especially if the code is self-documenting. (link) ↩

gemini-code-assist · 2025-08-08T19:30:36Z

server.go

+
+					// Return error if no valid addresses were found
+					if len(addrs) == 0 {
+						return nil, fmt.Errorf("no valid addresses found for host %s", host)


This line exceeds the 80-character limit specified in the style guide. To adhere to the style guide, you can introduce a variable for the error message string.¹

msg := "no valid addresses found for host %s" return nil, fmt.Errorf(msg, host)

Style Guide References

Footnotes

The line length must not exceed 80 characters. Tabs are counted as 8 spaces. (link) ↩

lightninglabs-deploy · 2025-08-15T20:37:29Z

@wearedood, remember to re-request review from reviewers when ready

gemini-code-assist bot reviewed Aug 8, 2025

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Fix externalhosts to advertise both IPv4 and IPv6 addresses #10145

Fix externalhosts to advertise both IPv4 and IPv6 addresses #10145

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wearedood commented Aug 8, 2025

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lightninglabs-deploy commented Aug 15, 2025

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Fix externalhosts to advertise both IPv4 and IPv6 addresses #10145

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wearedood commented Aug 8, 2025

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