[DWDS] Fixes hot reload/restart crashes after closing browser tab on web-server device #2699

jyameo · 2025-10-15T18:25:00Z

This PR introduces graceful handling for scenarios where no browser clients are connected to DWDS during hot reload and hot restart operations. Previously, DWDS threw generic StateError exceptions that required Flutter Tools to parse error messages using brittle string matching. Now, a custom NoClientsAvailableException is thrown and caught, with structured error responses that include a noClientsAvailable boolean field in the JSON output. This enables type-safe error handling and eliminates the need for error string parsing. The changes affect the reloadSources and hotRestart methods in WebSocketProxyService, which now return success responses with metadata when no clients are available, treating this as a recoverable scenario rather than a fatal error.

Related to flutter/flutter#174791

Changes in Flutter tools (Child PR): flutter/flutter#177026

Follow up bug: dart-lang/sdk#61757

bkonyi · 2025-10-15T19:18:19Z

dwds/lib/src/services/web_socket_proxy_service.dart

+      _logger.info('No clients available for hot restart');
+      return {
+        'result': {
+          'type': 'Success',


This doesn't feel right as this isn't a Success.

Realistically, we should be doing something like throwing an RPCError with an error code that package:vm_service forwards without modification. Right now, package:vm_service catches all exceptions and wraps them in RPCErrors with a kServerError code, but maybe we should update it to rethrow RPCError instances.

Another option would be to update the hotRestart extension to return ReloadReport as well so we can be consistent between hotReload and hotRestart.

Good catch! This shouldn’t be treated as a success. I think returning a ReloadReport would be the better approach to keep things consistent and also add the field noClientsAvailable. For now, I’ve removed the type field since it’s not being used for this operation.

In another PR, we can refactor this to return a ReloadReport instead, that would also involve updating the Chrome path and Flutter tools as well, as they currently expect the existing format.

How does that sound? @bkonyi

I actually don't think we can remove the type property in the result without consequence. package:vm_service checks for this and, if it can't find the type, returns a Response by default. While I don't think anyone is checking for the Success object explicitly since there's no useful information attached to it, this could break things.

I think it's just worth updating the return type to be ReloadReport now and then updating Flutter to return the same when we roll this change.

Following our discussion I have made the changes to throw an RPC Error for this scenario which we catch in Flutter tools. PTAL

@bkonyi @srujzs

Hmm, I feel like this resurrects the original issue we had where we can't distinguish what the kServerError corresponds to, whereas if we had hot restart return a ReloadReport, we have that metadata in the report.

(also I'll be OOO tomorrow, so if you decide this is the right approach anyways, feel free to land it)

Hey Srujan, Ben sand I discussed this and decided that this approach to throw an RPCError would work better since changing hot restart to return a ReloadReport would also require modifying the Chrome path, which could introduce some breakage.

In Flutter tools, I check for the calling method and kServerError to distinguish that this is the specific scenario. We could technically add a new RPCErrorKind for this, but I’m not sure it’s really necessary.

Thoughts? @bkonyi

If we'd like to avoid using the generic kServerError, I think we can go ahead and use kIsolateCannotReload to indicate that the reload has failed.

FYI: dart-lang/sdk#61757

dwds/lib/src/services/web_socket_proxy_service.dart

srujzs

Looks good, thanks Jessy! I'm guessing we can't add a test in DWDS as it requires closing the browser or somehow disrupting the connection which is going to be manual and therefore requires something like the Flutter test runner.

dwds/lib/src/services/web_socket_proxy_service.dart

jyameo · 2025-10-15T20:24:27Z

Looks good, thanks Jessy! I'm guessing we can't add a test in DWDS as it requires closing the browser or somehow disrupting the connection which is going to be manual and therefore requires something like the Flutter test runner.

yes that's correct I have added a test in flutter tools for this scenario

dwds/lib/src/services/web_socket_proxy_service.dart

bkonyi

LGTM with one nit.

dwds/lib/src/services/web_socket_proxy_service.dart

…ver device (#177026) This PR fixes crashes during hot reload/restart operations on web-server devices that occur when browser tabs are closed. Previously, the VM service would throw "Bad state: No element" errors when attempting operations with no connected clients. The fix introduces graceful handling on both sides: DWDS now catches NoClientsAvailableException in its hot reload/restart operations and returns structured JSON responses with a noClientsAvailable boolean flag instead of throwing exceptions. Flutter Tools reads this flag via a helper method _checkNoClientsAvailable() and handles the scenario gracefully by displaying "Recompile complete. No client connected." while preserving the DWDS connection to automatically support browser reconnections without requiring a full restart of the Flutter tools. Fixes: #174791 Changes in DWDS (Parent PR): dart-lang/webdev#2699 Follow up bug: dart-lang/sdk#61757

Revisions updated by `dart tools/rev_sdk_deps.dart`. protobuf (https://github.com/dart-lang/protobuf/compare/14bbd0b..78cf743): 78cf743 2025-10-20 Ömer Sinan Ağacan Fix a few extension field bugs (google/protobuf.dart#1062) tools (https://github.com/dart-lang/tools/compare/f5920a2..d0941a3): d0941a35 2025-10-17 Morgan :) Unify watcher tests (dart-lang/tools#2211) fa978cd2 2025-10-17 Morgan :) Remove backup expectations (dart-lang/tools#2209) web (https://github.com/dart-lang/web/compare/816abcc..5a7d0be): 5a7d0be 2025-10-16 Srujan Gaddam Initial commit of package:js_interop 0.1.0-beta (dart-lang/web#476) webdev (https://github.com/dart-lang/webdev/compare/2517aa9..82b3855): 82b38557 2025-10-20 Jessy Yameogo [DWDS] Fixes hot reload/restart crashes after closing browser tab on web-server device (dart-lang/webdev#2699) Change-Id: I98c840892d243f3dc34f9409956d8726ff84238a Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/456040 Commit-Queue: Konstantin Shcheglov <scheglov@google.com> Auto-Submit: Devon Carew <devoncarew@google.com> Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

added NoClientsAvailableException logic

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github-actions bot added the package:dwds label Oct 15, 2025

jyameo requested review from bkonyi and srujzs October 15, 2025 18:25

updated version to prepare for release

77b297e

jyameo added the prepare-release label Oct 15, 2025

jyameo mentioned this pull request Oct 15, 2025

Fixed hot reload/restart crashes after closing browser tab on web-server device flutter/flutter#177026

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jyameo added 2 commits October 15, 2025 16:18

addressed comments

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remove duplicate logging

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jyameo requested a review from bkonyi October 15, 2025 20:27

jyameo added 3 commits October 16, 2025 16:18

updated to throw RpcError

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reverted chnages to _ReloadReportWithMetadata

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updated changelog

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jyameo requested a review from srujzs October 16, 2025 20:40

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refactored string No clients available for ....

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jyameo requested a review from bkonyi October 17, 2025 14:18

updated to use kIsolateCannotReload

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jyameo merged commit 82b3855 into dart-lang:main Oct 20, 2025
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This was referenced Oct 22, 2025

[DWDS] Creating hotfix release for https://github.com/dart-lang/webdev/pull/2699 #2702

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[beta] CP: Fixes hot reload/restart crashes after closing browser tab on web-server device flutter/flutter#177456

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[DWDS] Fixes hot reload/restart crashes after closing browser tab on web-server device #2699

[DWDS] Fixes hot reload/restart crashes after closing browser tab on web-server device #2699

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