Implement DnsResolver for Windows by rzikm · Pull Request #129302 · dotnet/runtime

rzikm · 2026-06-11T16:57:33Z

Implements the API approved in #19443:

New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.

Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).

dotnet-policy-service · 2026-06-11T16:59:14Z

Tagging subscribers to this area: @karelz, @dotnet/ncl
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Copilot

Pull request overview

This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.

Changes:

Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.

Show a summary per file

File	Description
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csproj	Adds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs	Adds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.cs	Adds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Adds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs	Adds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.cs	Extends telemetry answer handling to support `string[]`
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.cs	Introduces `DnsResult<T>` envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.cs	Introduces `DnsResponseCode` enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Implements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.cs	Adds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.cs	Adds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs	Adds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.cs	Adds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs	Adds new static `Dns.Resolve*` APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.cs	Makes `Dns` partial to host the new `Dns.Resolve*` partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj	Wires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resx	Adds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs	Adds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.cs	Adds `Libraries.Dnsapi` constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs	Adds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs	Adds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree

MihaZupan

First pass through.

Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?

MihaZupan · 2026-06-11T17:07:10Z

+        public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
+        public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
+        public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
+        public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
+        public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
+        public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
+        public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
+        public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }


Suggested change

public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }

public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }

public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }

public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }

public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }

public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }

public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }

public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }

I think we should talk about this with the team :)

My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.
The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.

I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)

Copilot

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.

MichalPetryka · 2026-06-17T16:29:50Z

I've worked with DNS apis here before so here's what I wanted to note:

This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.

Copilot

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.

+    [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
+    [Collection(nameof(DisableParallelization))]
+    [PlatformSpecific(TestPlatforms.Windows)]
+    public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
+    {
+        private static DnsResolver CreateResolver(LoopbackDnsServer server)
+            => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });


Copilot

Copilot wasn't able to review any files in this pull request.

Replacement for #129302 (thanks, `gh stack submit` 😠) Implements the API approved in #19443: New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records. New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers. Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord. DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl. Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review). --------- Co-authored-by: rzikm <rzikm@users.noreply.github.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings June 11, 2026 16:57

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rzikm closed this Jun 25, 2026

rzikm force-pushed the dns-resolver branch from ed8096c to bc934f2 Compare June 25, 2026 11:15

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rzikm mentioned this pull request Jun 25, 2026

Implement DnsResolver for Windows #129845

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MihuBot mentioned this pull request Jul 14, 2026

[✨ Triage] dotnet/runtime#130541 by MichalPetryka - DnsResolver does not handle misconfigured DNS servers MihuBot/dotnet-triage#211

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MichalPetryka commented Jun 17, 2026 •

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