Fix form mapping for file lists and dictionary keys containing brackets

[MohamedHasan3644]

Description

Bug Description

• Collection items containing file-list properties could continue binding nonexistent items until the collection-size limit was reached.
• Root [FromForm] IReadOnlyList<IFormFile> parameters did not respect the parameter name or an explicit [FromForm(Name = "...")] alias.
• Dictionary keys containing ] were truncated, preventing the submitted values from binding correctly.

Description of Code Changes

• Report file lists as found only when uploaded files match the current form prefix.
• Apply equivalent discovery behavior to IReadOnlyList<IFormFile> and IReadOnlyList<IBrowserFile>.
• Use prefix-matching discovery for IFormFileCollection under indexed paths so unrelated uploads do not keep collection probing active.
• Preserve the whole-request file collection returned for a bound IFormFileCollection property.
• Push and pop the form parameter name or alias when mapping a root IReadOnlyList<IFormFile>.
• Recognize structural closing brackets during dictionary-key discovery instead of truncating keys at the first ].
• Add regression coverage for the reported scenarios and the reviewer's unrelated-upload case.

Areas Covered

• File-list discovery and collection termination.
• Collection items with and without matching attachments.
• Unrelated uploads with and without matching model fields.
• Root file-list parameter names and explicit aliases.
• Exclusion of unnamed uploads from named root file lists.
• Dictionary keys containing single or multiple embedded closing brackets.
• Dictionary values containing nested dictionaries, complex objects, and collections.
• Existing parser boundaries, malformed-key handling, and collection overflow detection.

Validation

Endpoint Regression Tests

• SupportsFormFileListInCollectionItem

  • Covers a collection item with and without a matching upload.
  • Verifies exactly one line binds, its label is preserved, and the attachment count is correct.

• SupportsFormFileCollectionInCollectionItem

  • Covers a collection item with and without a matching upload.
  • Verifies exactly one line binds and the whole-request file collection remains available.

• SupportsRootFormFileList

  • Covers the parameter name files and the explicit alias docs.
  • Verifies both matching files bind and an unnamed upload is excluded.

• SupportsDictionaryKeyContainingClosingBracket

  • Verifies HTTP 200 and the exact result a=1, x]y=2.

Both rows were verified independently:

• Without the indexed-prefix discovery fix: both failed with HTTP 400.
• With the fix restored: both passed with HTTP 200 and the expected binding assertions.

Form-Mapping Unit Tests

• Deserialize_Dictionary_KeyContainingClosingBracket

  • Covers keys x]y, x], and x]]y.
  • Verifies exact keys and values without mapping errors.

• Deserialize_Dictionary_KeyContainingClosingBracket_WithNestedDictionary

  • Covers ordinary and bracket-containing keys with nested dictionary values.

• Deserialize_Dictionary_KeyContainingClosingBracket_WithComplexValue

  • Covers ordinary and bracket-containing keys followed by a property path.

• Deserialize_Dictionary_KeyContainingClosingBracket_WithCollectionValue

  • Covers ordinary and bracket-containing keys followed by collection indexes.

• CanDeserialize_ComplexType_IReadOnlyListFormFileWithNoMatches_IsNotFound

  • Verifies an unrelated upload does not mark a named file list as found.

• TryRead_IBrowserFileList_WithNoMatchingFiles_IsNotFound

  • Verifies conversion succeeds with an empty browser-file list and found = false.

Existing parser expectations were updated for embedded brackets while retaining coverage for structural boundaries and malformed inputs.

Build and Test Results

Recorded local validation:

Validation	Result
Focused endpoint regression run	10 passed
Components Endpoints test suite	891 passed, 0 failed, 0 skipped
Http.Extensions test suite	2,302 passed, 0 failed, 0 skipped
Both project builds	0 warnings, 0 errors

Output

Before

After

Fixes #69717

[dotnet-policy-service]

Thanks for your PR, @MohamedHasan3644. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Copilot]

🟢 Approval recommended

The implementation addresses the reported binding failures with consistent behavior and comprehensive regression coverage.

0 open findings

What changed in this PR

Fixes form mapping for file collections and dictionary keys containing closing brackets.

Changes:

• Corrects prefix-aware file discovery and root file-list binding.
• Preserves embedded ] characters in dictionary keys.
• Adds focused unit and endpoint regression coverage.

File	Description
RequestDelegateFactoryTests.FormMapping.cs	Adds endpoint-level regression tests.
RequestDelegateFactory.cs	Applies root file-list parameter prefixes.
BrowserFileFromFormFileTests.cs	Tests unmatched browser-file lists.
FormDataMapperTests.cs	Covers file discovery and bracketed dictionary keys.
FormDataReader.cs	Identifies structural closing brackets.
FileConverter.cs	Makes file-list discovery prefix-aware.

🧠 Review effort: Balanced

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