KTOR-9559 Add dnsResolver config to Apache5 engine

[fru1tworld]

Subsystem
Client / Apache5 engine

Motivation
KTOR-9559 (umbrella: KTOR-462) / #1678 / #1924

Apache HttpClient 5 has a DnsResolver interface but Apache5EngineConfig does not surface it as a first-class option. Users currently have to drop down to engine { configureConnectionManager { setDnsResolver(...) } } to inject a custom resolver.

Solution
Add Apache5EngineConfig.dnsResolver: DnsResolver? and apply it on the PoolingAsyncClientConnectionManagerBuilder before configureConnectionManager. Defaults to null → Apache's default resolver is used as before.

HttpClient(Apache5) {
    engine {
        dnsResolver = SystemDefaultDnsResolver.INSTANCE
    }
}

Follow-up to the OkHttp dns config PR (#5570); same per-engine pattern. The unified resolver abstraction (KTOR-462) remains out of scope.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: df11505d-c7b8-4d14-b777-e6caa3042f2c

📥 Commits

Reviewing files that changed from the base of the PR and between 7230205 and 5e87237.

📒 Files selected for processing (4)

• ktor-client/ktor-client-apache5/api/ktor-client-apache5.api
• ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5Engine.kt
• ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5EngineConfig.kt
• ktor-client/ktor-client-apache5/jvm/test/io/ktor/client/engine/apache5/Apache5EngineConfigTest.kt

✅ Files skipped from review due to trivial changes (1)

• ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5EngineConfig.kt

🚧 Files skipped from review as they are similar to previous changes (3)

• ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5Engine.kt
• ktor-client/ktor-client-apache5/api/ktor-client-apache5.api
• ktor-client/ktor-client-apache5/jvm/test/io/ktor/client/engine/apache5/Apache5EngineConfigTest.kt

---

📝 Walkthrough

Walkthrough

Adds optional DNS resolver support to the Apache5 engine: new nullable dnsResolver property and public getter/setter on Apache5EngineConfig, wiring to the Apache connection manager when present, and a test verifying resolver invocation.

Changes

DNS resolver support

Layer / File(s)	Summary
Data Shape / Config ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5EngineConfig.kt	Adds public var dnsResolver: DnsResolver? = null and imports org.apache.hc.client5.http.DnsResolver with KDoc describing behavior.
API surface ktor-client/ktor-client-apache5/api/ktor-client-apache5.api	Exports Apache5EngineConfig.getDnsResolver(): DnsResolver and Apache5EngineConfig.setDnsResolver(DnsResolver): void.
Core Implementation / Wiring ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5Engine.kt	Connection manager builder chain now applies setDnsResolver(it) when config.dnsResolver is non-null.
Tests ktor-client/ktor-client-apache5/jvm/test/io/ktor/client/engine/apache5/Apache5EngineConfigTest.kt	New test injects a custom DnsResolver, performs a request, and asserts the resolver was invoked (call counter > 0).

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• ktorio/ktor#5094: Touches PoolingAsyncClientConnectionManagerBuilder configuration in the Apache5 engine and overlaps with connection manager customization discussed here.

Suggested reviewers

• bjhham

🚥 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 accurately summarizes the main change: adding a dnsResolver config option to the Apache5 engine, matching the core objective of the PR.
Description check	✅ Passed	The description follows the template structure with all required sections (Subsystem, Motivation, Solution) properly filled. It provides specific issue references, clear problem statement, and concrete solution with example usage.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@ktor-client/ktor-client-apache5/api/ktor-client-apache5.api`:
- Around line 16-23: The ABI dump lists getDnsResolver and setDnsResolver as
non-nullable, but the source property dnsResolver is nullable; regenerate the
Kotlin ABI for the module so the signatures reflect nullability (getDnsResolver
returns Lorg/apache/hc/client5/http/DnsResolver;? and setDnsResolver accepts a
nullable parameter). Run the project task to update the ABI dump (e.g.,
./gradlew :ktor-client-apache5:updateKotlinAbi) and commit the updated
ktor-client-apache5.api so getDnsResolver, setDnsResolver and the dnsResolver
property signatures match the source nullability.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: cce3911b-2f9f-4b66-87cd-c6195afa3e73

📥 Commits

Reviewing files that changed from the base of the PR and between 295e688 and 7230205.

📒 Files selected for processing (4)

• ktor-client/ktor-client-apache5/api/ktor-client-apache5.api
• ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5Engine.kt
• ktor-client/ktor-client-apache5/jvm/src/io/ktor/client/engine/apache5/Apache5EngineConfig.kt
• ktor-client/ktor-client-apache5/jvm/test/io/ktor/client/engine/apache5/Apache5EngineConfigTest.kt

[bjhham]

Looks good 👍

I've added a new YouTrack issue for tracking KTOR-9559 DNS configuration for the Apache5 client

[fru1tworld]

Thanks for the review! Updated to reference KTOR-9559 in the commit/title 😄