Fixes Issue

main PR

Description

TransferEncodingChunked setter only removed the first "chunked" value while the getter returns true if any "chunked" exists. Setting the property to false with multiple "chunked" values left the property returning true.

var headers = new HttpRequestMessage().Headers;
headers.TransferEncoding.Add(new TransferCodingHeaderValue("chunked"));
headers.TransferEncoding.Add(new TransferCodingHeaderValue("chunked"));

headers.TransferEncodingChunked = false;
Console.WriteLine(headers.TransferEncodingChunked); // Was: True, Now: False

Changes:

• Added optional removeAll parameter (default false) to existing RemoveParsedValue method in HttpHeaders.cs
• When removeAll is true, uses an optimized removal strategy: removes first match with RemoveAt, then falls back to List.RemoveAll for remaining matches to maintain O(n) complexity
• When removeAll is false, maintains original behavior (removes first match only)
• Modified HttpGeneralHeaders.TransferEncodingChunked setter to call RemoveParsedValue with removeAll: true
• Removed outdated comment from RemoveParsedValue method
• Added test TransferEncodingChunked_SetToFalse_RemovesAllChunkedValues that validates removal of all "chunked" values while preserving other transfer-encoding values
• Updated test Add_UseSpecialValueWithSpecialAlreadyPresent_AddsDuplicate to reflect corrected behavior

Performance:
The optimized approach maintains O(n) worst-case complexity:

• Common case (0-1 matches): O(n) - single forward pass, breaks after first match
• Multiple matches: O(n) - removes first match, then uses List.RemoveAll (single pass) for remaining items
• Avoids closure allocation in common case by only creating lambda when needed

Customer Impact

Applications adding multiple "chunked" transfer-encoding values cannot reliably disable chunked encoding. Setting TransferEncodingChunked = false fails silently, causing incorrect HTTP headers.

Regression

No. This is a pre-existing bug where RemoveParsedValue only removes the first matching item.

Testing

All 2,666 System.Net.Http unit tests pass. New test validates removing multiple "chunked" values while preserving other transfer-encoding values (e.g., "abc" and "def").

Risk

Low. Change is isolated to TransferEncodingChunked setter and adds an optional parameter to existing RemoveParsedValue method. The parameter maintains backward compatibility with default value false. When set to true, efficiently removes all matching values while maintaining O(n) complexity. Existing single "chunked" value cases unchanged.

• Fixes TransferEncodingChunked may return true after being set to false #116691

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