Add reverse DNS resolution support to resolver

[sgerbino]

Implement reverse DNS lookup capability for the resolver class, enabling hostname lookups from IP addresses using getnameinfo() on POSIX and GetNameInfoW() on Windows.

New API:

• resolve(endpoint) - reverse resolve with default flags
• resolve(endpoint, reverse_flags) - reverse resolve with custom flags
• reverse_flags enum (numeric_host, numeric_service, name_required, datagram_service)
• reverse_resolver_result class with endpoint(), host_name(), service_name()

Implementation uses worker threads on both platforms since the underlying APIs (getnameinfo/GetNameInfoW) are synchronous. Thread lifetime is managed via shared_ptr to prevent use-after-free during shutdown.

Resolves #64.

Summary by CodeRabbit

• New Features

  • Reverse DNS resolution: resolve endpoints to host and service names.
  • Configurable reverse-resolution flags for fine-grained lookup behavior.
  • Async/await-compatible reverse lookups on Windows and POSIX platforms.

• Chores

  • Improved resolver lifetime, thread tracking, and graceful shutdown so in-flight lookups complete or cancel cleanly.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds endpoint-based reverse DNS resolution: new public reverse_flags, reverse_resolver_result, resolver overloads resolve(endpoint[, reverse_flags]), a reverse_resolve_awaitable, and a resolver_impl::reverse_resolve API; POSIX and IOCP services implement worker-thread getnameinfo/GetNameInfoW paths and thread/shutdown tracking.

Changes

Cohort / File(s)	Summary
Public API include/boost/corosio/resolver.hpp, include/boost/corosio/resolver_results.hpp	Adds reverse_flags enum + bitwise operators, reverse_resolver_result type (endpoint, host, service), reverse_resolve_awaitable, and resolver::resolve(endpoint[, reverse_flags]) overloads.
POSIX resolver implementation src/corosio/src/detail/posix/resolver_service.cpp	Adds reverse_resolve_op, reverse_op_ member, posix_resolver_impl::reverse_resolve(...) using getnameinfo, flags_to_ni_flags() helper, worker-thread execution, and shutdown/wait-for-threads integration.
IOCP (Windows) resolver implementation src/corosio/src/detail/iocp/resolver_service.cpp, src/corosio/src/detail/iocp/resolver_service.hpp	Adds reverse_resolve_op, win_resolver_impl::reverse_resolve(...) using GetNameInfoW on worker thread, wide→UTF‑8 conversion, thread lifecycle tracking (thread_started/thread_finished/is_shutting_down), and changes to resolver ownership tracking (shared_ptr / resolver_ptrs_).
Service lifecycle / shutdown src/corosio/src/detail/*/resolver_service.{cpp,hpp}	Service now tracks active worker threads, always posts completion ops for draining, waits for worker threads during shutdown, and updates cancel/destroy flows to cover reverse operations.

Sequence Diagram(s)

sequenceDiagram
    participant Client as Client
    participant Resolver as Resolver
    participant Impl as ResolverImpl
    participant Worker as WorkerThread
    participant Scheduler as Scheduler

    Client->>Resolver: co_await resolve(endpoint, flags)
    Resolver->>Impl: reverse_resolve(coro, executor, endpoint, flags, stop_token, ec*, result*)
    Impl->>Worker: spawn worker thread (getnameinfo / GetNameInfoW)
    Worker->>Worker: perform lookup, convert strings
    Worker->>Impl: populate op (host/service, error)
    Worker->>Scheduler: post completion op
    Scheduler->>Impl: invoke op() -> resume coroutine
    Impl->>Client: coroutine resumes with reverse_resolver_result

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related PRs

• Implement POSIX resolver and refactor services for runtime backend se… #58: Refactors resolver/service and scheduler work-tracking that this reverse-resolution implementation builds upon and extends.

Poem

🐰 I nibble PTRs in moonlit code,
Hopping threads down network road,
From IP back to name I peep,
Worker hums while coroutines sleep,
A carrot-host returned to keep.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main objective of the changeset: adding reverse DNS resolution support to the resolver class.
Linked Issues check	✅ Passed	The pull request implements all primary coding objectives from issue #64: reverse DNS API, flags support, platform-specific implementations, worker threads, endpoint conversion, and new result types.
Out of Scope Changes check	✅ Passed	All changes are directly aligned with issue #64 objectives: resolver headers/implementation updates, platform-specific resolver services, new result types, and reverse resolution infrastructure.

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

✨ Finishing touches

• 📝 Generate docstrings

---

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

[cppalliance-bot]

An automated preview of the documentation is available at https://85.corosio.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-01-26 22:33:15 UTC

[coderabbitai]

Actionable comments posted: 3

🤖 Fix all issues with AI agents

In `@src/corosio/src/detail/iocp/resolver_service.cpp`:
- Around line 19-23: The file using std::memcpy (resolver_service.cpp) is
missing the <cstring> include; add `#include` <cstring> near the other includes
(alongside <thread> and boost headers) so std::memcpy is provided directly
rather than relying on transitive includes used by functions like memcpy in the
reverse path.

In `@src/corosio/src/detail/iocp/resolver_service.hpp`:
- Around line 269-286: Update the file-level overview comment to reflect that
reverse DNS resolution now spawns worker threads and that shutdown is tracked;
explicitly mention the presence of thread bookkeeping methods (thread_started,
thread_finished, is_shutting_down) and state members (shutting_down_,
active_threads_) as part of the shutdown protocol, and note that resolver
instances are tracked via resolver_list_ and resolver_ptrs_. Keep the summary
concise, remove the outdated claim that this path avoids worker threads, and add
a short sentence describing the purpose of the condition variable cv_ and
win_mutex mutex_ in coordinating thread shutdown.

In `@src/corosio/src/detail/posix/resolver_service.cpp`:
- Around line 703-794: The file uses std::memcpy inside
posix_resolver_impl::reverse_resolve (in resolver_service.cpp) but does not
include <cstring>; add an explicit `#include` <cstring> at the top of the file so
std::memcpy is available without relying on transitive includes (this touches
resolver_service.cpp where reverse_resolve and std::memcpy are used).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.58%. Comparing base (a700836) to head (332b97d).
⚠️ Report is 6 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #85      +/-   ##
===========================================
+ Coverage    84.19%   84.58%   +0.38%     
===========================================
  Files           43       43              
  Lines         2822     2951     +129     
===========================================
+ Hits          2376     2496     +120     
- Misses         446      455       +9     

see 5 files with indirect coverage changes

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/corosio/src/detail/iocp/resolver_service.cpp`:
- Around line 435-452: GetNameInfoW's return value should be stored directly
into reverse_op_.gai_error instead of calling ::WSAGetLastError(); in the block
after calling GetNameInfoW (use the GetNameInfoW call and reverse_op_ locals to
find the spot), set reverse_op_.gai_error = result when result != 0 and set
reverse_op_.gai_error = 0 when result == 0 (while still populating
reverse_op_.stored_host and reverse_op_.stored_service via from_wide as
currently done).