[dotnet] Serialize command parameters directly to UTF-8

[RenderMichael]

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Description

Serialize command parameters directly into UTF-8 bytes, and pass the array around.

Motivation and Context

System.Text.Json operates natively in UTF-8, and it is much more efficient to serialize to a byte[] rather than materializing a string.

The HTTP request contents are in the form of a byte[] anyway, so we are avoiding a lot of back and forth between formats here.

Old Flow: Dictionary<string, object> -> UTF-8 inside STJ -> string returned by STJ -> Encoded to byte[]
New Flow: Dictionary<string, object> -> UTF-8 returned by STJ

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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PR Type

Enhancement, Tests

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Description

• Introduced UTF-8 byte serialization for command parameters.

• Updated HTTP request handling to use byte arrays directly.

• Enhanced event arguments to support UTF-8 request bodies.

• Added unit tests to validate new serialization logic.

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Changes walkthrough 📝

	Relevant files
Enhancement	Command.cs Add UTF-8 serialization for command parameters                      dotnet/src/webdriver/Command.cs Added GetParametersAsUtf8Bytes method for UTF-8 serialization. Updated ToString method for improved parameter representation. +17/-1    HttpCommandExecutor.cs Use byte arrays for HTTP request bodies                                    dotnet/src/webdriver/Remote/HttpCommandExecutor.cs Replaced string-based request body with byte array. Updated HTTP request content handling to use byte arrays. +3/-3      SendingRemoteHttpRequestEventArgs.cs Support UTF-8 byte arrays in event arguments                          dotnet/src/webdriver/Remote/SendingRemoteHttpRequestEventArgs.cs Added support for UTF-8 byte arrays in request body. Enhanced RequestBody property to handle string and byte arrays. +30/-2
Tests	CommandTests.cs Add tests for UTF-8 serialization of parameters                    dotnet/test/common/CommandTests.cs Added tests for null and empty parameter serialization. Updated existing tests to validate UTF-8 byte serialization. +17/-1

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PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Memory Allocation The empty JSON object "{}" is allocated as a new array on each call to GetParametersAsUtf8Bytes() for null/empty parameters. Consider caching this as a static readonly field to avoid repeated allocations. return "{}"u8.ToArray(); Potential Race Condition The lazy initialization of _requestBody field is not thread-safe. Multiple threads accessing the RequestBody property could result in the string being decoded multiple times. if (_requestBody is not null) { return _requestBody; } return _requestBody = _utf8RequestBody is null ? null : Encoding.UTF8.GetString(_utf8RequestBody); }

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PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Score
Possible issue	Prevent null reference exception Add null check for SessionId in ToString() method to prevent potential NullReferenceException when SessionId is null. dotnet/src/webdriver/Command.cs [126] -return $"[{this.SessionId}]: {this.Name} Parameters: {this.ParametersAsJsonString}"; +return $"[{this.SessionId?.ToString() ?? "null"}]: {this.Name} Parameters: {this.ParametersAsJsonString}"; Apply this suggestion Suggestion importance[1-10]: 8 Why: The suggestion addresses a potential NullReferenceException that could occur in production when SessionId is null, making the code more robust and preventing runtime crashes.	8
General	Improve performance through caching Cache the UTF-8 bytes result in GetParametersAsUtf8Bytes() to avoid repeated serialization of the same parameters. dotnet/src/webdriver/Command.cs [108-118] +private byte[]? _cachedUtf8Bytes; public byte[] GetParametersAsUtf8Bytes() { - if (this.Parameters != null && this.Parameters.Count > 0) + if (_cachedUtf8Bytes == null) { - return JsonSerializer.SerializeToUtf8Bytes(this.Parameters, s_jsonSerializerOptions); + _cachedUtf8Bytes = this.Parameters != null && this.Parameters.Count > 0 + ? JsonSerializer.SerializeToUtf8Bytes(this.Parameters, s_jsonSerializerOptions) + : "{}"u8.ToArray(); } - else - { - return "{}"u8.ToArray(); - } + return _cachedUtf8Bytes; } Apply this suggestion Suggestion importance[1-10]: 6 Why: The suggestion introduces caching for serialized UTF-8 bytes, which can improve performance by avoiding repeated serialization operations, especially useful when the same command is executed multiple times.	6

[RenderMichael]

Old constructor kept around for backwards compatibility, but unused by our code.

[RenderMichael]

This event args seems to be an obscure mechanism to add headers to requests. I don't know how many people are accessing the SendingRemoteHttpRequestEventArgs.RequestBody property in the world.

For this reason, I feel that the added complexity is warranted: We will not decode our data into a string unless the user requests it (and we cache it here so users do not have to worry about it).

[RenderMichael]

Sidenote: ParametersAsJsonString does JSON serialization, here inside the ToString() method. I missed this as part of #14741. Do we want to change this? (Follow-up PR either way)

[nvborisenko]

This is interesting. I propose to create simple benchmark to measure how much memory is allocated before/after.

Let's say user wants to get WebElement.Displayed property - most memory consuming command.

[nvborisenko]

Command is an abstraction. Command to bytes... we should mention json in method name. Like GetParametersAsJsoonUtf8Bytes()

[RenderMichael]

Per offline discussion, this change is not worth the added complexity and maintenance burden. Closing this PR.