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# Description `NodeBrowser` was synchronous end to end, so a node manager whose browse result depends on I/O had nowhere to `await`. The aggregation server sample is the concrete case: its browser has to browse the aggregated server, and the only way to write it was `Next() => NextAsync().GetAwaiter().GetResult()`, which holds a request worker for the full remote round trip on every browse. This is option (1) from the issue, the small non-breaking step: - `INodeBrowser` and `NodeBrowser` gain `ValueTask<IReference?> NextAsync(CancellationToken cancellationToken = default)`. The default completes synchronously with the result of `Next()`, so every existing browser that only overrides `Next()` keeps working unchanged (the samples' `MemoryBufferBrowser` and the migration-analyzer test snippets compile untouched). - `AsyncCustomNodeManager.BrowseAsync` and `TranslateBrowsePathAsync` iterate browsers through `NextAsync` with the request's cancellation token. The loop bodies already awaited; only the iteration could not. - `DirectoryBrowser` was the one browser the stack ships that blocked on async I/O. It now awaits the file-system provider enumeration in `NextAsync` and keeps `Next()` as the bridge for the remaining synchronous consumers (`UANodeSetHelpers` export, `CustomNodeManager2`). Cancellation now propagates instead of being reported as an empty directory. - The synchronous paths (`CustomNodeManager2`, `CoreNodeManager` diagnostics, nodeset export) are unchanged on purpose; they have no place to await. **Not done, by design.** Browser creation stays synchronous. `OnCreateBrowser` runs under the node's browse lock, so the documented contract is that a browser fetches lazily on its first `NextAsync`. The issue itself notes the async creation seam is not needed for the aggregation case. `IAsyncEnumerable` (option 3) is not attempted. **Compatibility note.** A type that implements `INodeBrowser` directly without deriving from `NodeBrowser` has to add the member. Nothing in this repo or the samples does that; derived browsers are unaffected. **Docs** updated in `NodeManagers.md`, `AsyncServerSupport.md`, `MigrationGuide.md` and `migrate/2.0.x/node-states.md`, with a was/now example for a browser that previously bridged sync-over-async. **Tests** - `NodeBrowserTests` (new): default wrapper completes synchronously and yields the same sequence as `Next()`, push-back through `NextAsync`, a `Next`-only override observed through `NextAsync`, an awaited `NextAsync` override with cancellation. - `AsyncCustomNodeManagerTests`: a browser whose `Next()` throws is driven entirely through `NextAsync` by browse, by the continuation-point round trip (push-back on the async path), and by translate-path. - `DirectoryObjectStateTests`: the async path of the directory browser, including the throwing provider and cancellation. Verified locally: `Opc.Ua.Server` builds on net10.0 and net48 with 0 errors; the browser-related server suites (1342 tests) and the new unit tests pass on net10.0; `dotnet format whitespace --verify-no-changes` is clean on the changed files. ## Related Issues - Fixes #4415 ## Checklist - [x] I have signed the [CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf) and read the [CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md) doc. - [x] I have added tests that prove my fix is effective or that my feature works and increased code coverage. - [x] I have added all necessary documentation. - [x] I have verified that my changes do not introduce (new) build or analyzer warnings. - [ ] I ran **all** tests locally using the **UA.slnx** solution against at least .net **framework** and .net **10**, and all passed. - [ ] I fixed **all** failing and flaky tests in the CI pipelines and **all** CodeQL warnings. - [ ] I have addressed **all** PR feedback received. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>