[client] Fix IPv6 address formatting in DNS address construction by mango766 · Pull Request #5603 · netbirdio/netbird

mango766 · 2026-03-16T14:00:04Z

Summary

Fixes #5601
Related to #4074

Several places in the DNS client code construct server addresses using fmt.Sprintf("%s:%d", ip, port). This produces malformed addresses when the IP is IPv6, since IPv6 addresses contain colons and need brackets when combined with a port (e.g., [2606:4700:4700::1111]:53 instead of 2606:4700:4700::1111:53).

This causes DNS resolution to fail with dial udp: address 2606:4700:4700::1111:53: too many colons in address when IPv6 nameservers are configured.

Changes

Replaced fmt.Sprintf("%s:%d", ip, port) with net.JoinHostPort() in:

client/internal/routemanager/dnsinterceptor/handler.go — upstream DNS address for the DNS interceptor (most critical, directly causes query failures)
client/internal/dns/service_listener.go — DNS listener address and port binding probes
client/internal/routemanager/client/client.go — DNS address for dynamic route handlers

net.JoinHostPort() is the standard Go idiom for this — it automatically wraps IPv6 addresses in brackets. The rest of the codebase already uses this function in many places (e.g., peer/worker_ice.go, ssh/detection/detection.go).

Test plan

Verify existing DNS tests still pass (go test ./client/internal/dns/...)
Verify route manager tests pass (go test ./client/internal/routemanager/...)
Configure an IPv6 nameserver (e.g., Cloudflare 2606:4700:4700::1111) and verify DNS queries succeed
Verify IPv4 nameserver behavior is unchanged

Summary by CodeRabbit

Refactor
- Enhanced internal DNS address handling with standardized formatting utilities, improving code consistency and maintainability across core networking components.

Replace fmt.Sprintf("%s:%d", ip, port) with net.JoinHostPort() to properly handle IPv6 addresses that need bracket wrapping (e.g., [2606:4700:4700::1111]:53 instead of 2606:4700:4700::1111:53). Without this fix, configuring IPv6 nameservers causes "too many colons in address" errors because Go's net.Dial cannot parse the malformed address string. Fixes netbirdio#5601 Related to netbirdio#4074 Co-Authored-By: Claude (claude-opus-4-6) <noreply@anthropic.com>

coderabbitai · 2026-03-16T14:00:21Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 41b5c730-99d1-4fda-8908-792ff324f962

📥 Commits

Reviewing files that changed from the base of the PR and between 3e6baea and e9474f9.

📒 Files selected for processing (3)

client/internal/dns/service_listener.go
client/internal/routemanager/client/client.go
client/internal/routemanager/dnsinterceptor/handler.go

📝 Walkthrough

Walkthrough

This PR fixes IPv6 address formatting in DNS address construction by replacing fmt.Sprintf with net.JoinHostPort across three DNS-related files. The fix ensures IPv6 addresses are properly bracketed when combined with ports.

Changes

Cohort / File(s)	Summary
DNS Service Listener `client/internal/dns/service_listener.go`	Replaced `fmt.Sprintf("%s:%d", ip, port)` with `net.JoinHostPort(ip.String(), strconv.Itoa(port))` in DNS listener address construction to support IPv6 addresses.
Route Manager DNS Handling `client/internal/routemanager/client/client.go`, `client/internal/routemanager/dnsinterceptor/handler.go`	Replaced DNS address string formatting with `net.JoinHostPort()` for dynamic route handlers and upstream DNS interceptor to properly format IPv6 addresses with bracketed notation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested reviewers

pappz

Poem

🐰 IPv6 brackets now in place,
No more colons in the space,
DNS queries flow with grace,
Addresses formatted just right! 🌐

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing IPv6 address formatting in DNS address construction across the client code.
Description check	✅ Passed	The description provides a comprehensive summary of the problem, lists all changed files, explains the rationale, and includes a test plan. However, the PR description template sections are not formally filled out per the repository template.
Linked Issues check	✅ Passed	All four locations identified in issue `#5601` have been addressed: dnsinterceptor/handler.go, service_listener.go (two locations), and client/client.go. The changes replace fmt.Sprintf with net.JoinHostPort, correctly fixing IPv6 address formatting.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing IPv6 address formatting in DNS address construction across the three files. No unrelated modifications are present.

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sonarqubecloud · 2026-03-16T14:00:47Z

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

CLAassistant · 2026-03-16T14:00:58Z

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

easonysliu seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
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lixmal · 2026-03-16T14:25:14Z

Can you please stick to the PR template?
Thanks for the contribution!

lixmal approved these changes Mar 16, 2026

View reviewed changes

lixmal merged commit a590c38 into netbirdio:main Mar 17, 2026
37 of 42 checks passed

This was referenced Mar 26, 2026

[client] Add IPv6 routing, fake IPs, and DNS bind selection #5706

Merged

[client] Add IPv6 support to ACL manager, USP filter, and forwarder #5688

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[client] Fix IPv6 address formatting in DNS address construction#5603

[client] Fix IPv6 address formatting in DNS address construction#5603
lixmal merged 1 commit intonetbirdio:mainfrom
mango766:fix/ipv6-address-formatting-dns

mango766 commented Mar 16, 2026 •

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mango766 commented Mar 16, 2026 •

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