Add configurable SSE parser buffer limit

[Copilot]

SSE parsing now supports a caller-configured buffer limit through SseParserOptions<T>.

API

• Adds SseParserOptions<T> with ItemParser and MaxBufferSize.
• Sets MaxBufferSize to -1 by default, preserving the internal default limit.
• Uses the options-based SseParser.Create overload as the parser creation path.

var parser = SseParser.Create(stream, new SseParserOptions<string>(
    static (_, bytes) => Encoding.UTF8.GetString(bytes))
{
    MaxBufferSize = 1024 * 1024
});

Coverage

• Replaces reflection-based buffer-limit test setup with the public API.
• Updates parser and formatter tests for the options-based construction path.

Note

This description was generated by GitHub Copilot.

• Fixes [API Proposal]: Option to limit SseParser's internal buffer size #129168

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Suppressed comments (2)

src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/SseParserOptions.cs:28

• SseParserOptions<T>.MaxBufferSize is documented as "-1 to use the default limit", but values < -1 currently flow through and (because of the _maxBufferSize >= 0 guard) effectively disable the limit. It would be safer to validate that MaxBufferSize is either -1 or >= 0 and throw ArgumentOutOfRangeException otherwise.

        /// <summary>Gets the parser to use to transform each payload of bytes into a data element.</summary>
        public SseItemParser<T> ItemParser { get; }

        /// <summary>Gets or sets the maximum buffer size, or -1 to use the default limit.</summary>
        public int MaxBufferSize { get; set; } = -1;

src/libraries/System.Net.ServerSentEvents/tests/SseParserTests.cs:34

• There’s no test coverage for invalid MaxBufferSize values (e.g., < -1). Adding a focused test would ensure the new option can’t be used to silently disable buffer limiting via negative values.

        [Fact]
        public void Options_DefaultMaxBufferSize()
        {
            var options = new SseParserOptions<string>(delegate { return ""; });

            Assert.Equal(-1, options.MaxBufferSize);
        }

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