[dotnet] [bidi] Implement browsing context download events

[nvborisenko]

User description

https://w3c.github.io/webdriver-bidi/#event-browsingContext-downloadWillBegin
https://w3c.github.io/webdriver-bidi/#event-browsingContext-downloadEnd

💥 What does this PR do?

Fix downloadWillBegin event signature, implement downloadEnd event. Adding tests.

🔄 Types of changes

• New feature (non-breaking change which adds functionality and tests!)

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PR Type

Enhancement

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Description

• Fix downloadWillBegin event signature to use proper event args

• Implement new downloadEnd event with polymorphic event args

• Add comprehensive tests for both download events

• Create JSON converters for proper serialization

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Diagram Walkthrough

flowchart LR
  A["BrowsingContext"] --> B["OnDownloadWillBeginAsync"]
  A --> C["OnDownloadEndAsync"]
  B --> D["DownloadWillBeginEventArgs"]
  C --> E["DownloadEndEventArgs"]
  E --> F["DownloadCanceledEventArgs"]
  E --> G["DownloadCompleteEventArgs"]
  H["JSON Converter"] --> E
  I["Tests"] --> B
  I --> C

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File Walkthrough

	Relevant files
Enhancement	BrowsingContext.cs Update download event method signatures                                    dotnet/src/webdriver/BiDi/BrowsingContext/BrowsingContext.cs Fix OnDownloadWillBeginAsync method signatures to use DownloadWillBeginEventArgs Add new OnDownloadEndAsync methods for both sync and async handlers +12/-2    BrowsingContextModule.cs Update module download event subscriptions                              dotnet/src/webdriver/BiDi/BrowsingContext/BrowsingContextModule.cs Fix OnDownloadWillBeginAsync method signatures to use proper event args Add new OnDownloadEndAsync methods subscribing to browsingContext.downloadEnd +12/-2    DownloadEndEventArgs.cs Create download end event args classes                                      dotnet/src/webdriver/BiDi/BrowsingContext/DownloadEndEventArgs.cs Create abstract base class DownloadEndEventArgs Implement DownloadCanceledEventArgs and DownloadCompleteEventArgs derived types Include navigation info and timestamp properties +35/-0    DownloadWillBeginEventArgs.cs Create download will begin event args                                        dotnet/src/webdriver/BiDi/BrowsingContext/DownloadWillBeginEventArgs.cs Create DownloadWillBeginEventArgs record with suggested filename Implement IBaseNavigationInfo interface for navigation context +25/-0    DownloadEndEventArgsConverter.cs Create polymorphic download end converter                                dotnet/src/webdriver/BiDi/Communication/Json/Converters/Polymorphic/DownloadEndEventArgsConverter.cs Implement custom JSON converter for polymorphic DownloadEndEventArgs Handle canceled and complete status discriminators Support deserialization to appropriate derived types +45/-0
Configuration changes	Broker.cs Register download end event converter                                        dotnet/src/webdriver/BiDi/Communication/Broker.cs Register DownloadEndEventArgsConverter for polymorphic JSON serialization +1/-0      BiDiJsonSerializerContext.cs Register download event types for serialization                    dotnet/src/webdriver/BiDi/Communication/Json/BiDiJsonSerializerContext.cs Add JSON serializable attributes for all download event args types Include both base and derived download event classes +4/-0
Tests	BrowsingContextEventsTest.cs Add download events integration tests                                        dotnet/test/common/BiDi/BrowsingContext/BrowsingContextEventsTest.cs Add test for downloadWillBegin event with file download simulation Add test for downloadEnd event verifying completion and filepath Validate event args properties and types +65/-0

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[qodo-merge-pro]

PR Compliance Guide 🔍

Below is a summary of compliance checks for this PR:

Security Compliance
⚪	Unimplemented serialization Description: The custom JSON converter throws NotImplementedException on serialization for DownloadEndEventArgs.Write, which could cause a runtime crash if the type is ever serialized (e.g., logged or echoed back); consider implementing or explicitly preventing serialization paths. DownloadEndEventArgsConverter.cs [41-44] Referred Code public override void Write(Utf8JsonWriter writer, DownloadEndEventArgs value, JsonSerializerOptions options) { throw new NotImplementedException(); }
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[qodo-merge-pro]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
Possible issue	Throw exception on unknown discriminator In the Read method, throw a JsonException for unknown status discriminators instead of returning null to prevent silent failures and improve error handling. dotnet/src/webdriver/BiDi/Communication/Json/Converters/Polymorphic/DownloadEndEventArgsConverter.cs [31-39] public override DownloadEndEventArgs? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) { - return reader.GetDiscriminator("status") switch + var discriminator = reader.GetDiscriminator("status"); + return discriminator switch { "canceled" => JsonSerializer.Deserialize(ref reader, options.GetTypeInfo<DownloadCanceledEventArgs>()), "complete" => JsonSerializer.Deserialize(ref reader, options.GetTypeInfo<DownloadCompleteEventArgs>()), - _ => null, + _ => throw new JsonException($"Unknown 'status' discriminator '{discriminator}' for DownloadEndEventArgs."), }; } Apply / Chat Suggestion importance[1-10]: 7 __ Why: The suggestion correctly identifies that returning null for an unknown discriminator can hide issues. Throwing an exception improves robustness by making failures explicit, which is a good practice for deserialization logic.	Medium
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