Address review feedback on MIME detection and sync tool #2

KSemenenko · 2025-10-11T15:49:40Z

Summary

replace the ZIP-based MIME sniffing logic with span-based ASCII comparisons to avoid repeated string allocations
reuse a shared separator array when parsing mime.types listings to eliminate per-line allocations

Testing

dotnet test

https://chatgpt.com/codex/tasks/task_e_68ea08250b3483269ee0369c9166f2aa

Copilot

Pull Request Overview

This PR refactors MIME detection and introduces a sync tool to improve performance and data freshness. The changes replace allocation-heavy ZIP-based content sniffing with efficient span-based ASCII comparisons and implement reusable data structures for parsing mime.types listings.

Key changes:

Replaced dictionary-based MIME sniffing with span-based ASCII pattern matching to avoid string allocations
Added comprehensive content detection with magic signature support for common file types
Introduced sync tool for updating MIME database from upstream sources with curated overrides

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
README.md	Updated documentation with comprehensive feature overview, usage examples, and installation instructions
ManagedCode.MimeTypes/mimeTypes.json	Added new MIME mappings and reordered entries for consistency
ManagedCode.MimeTypes/MimeTypeCategory.cs	Added new categories for Script, Binary, Multipart, and Message
ManagedCode.MimeTypes/MimeHelper.cs	Major refactor with span-based content detection, reverse lookup API, and runtime registration
ManagedCode.MimeTypes/ManagedCode.MimeTypes.csproj	Updated LangVersion to preview
ManagedCode.MimeTypes.sln	Added MimeTypes.Sync project reference
ManagedCode.MimeTypes.Tests/	Added comprehensive test coverage for new functionality
ManagedCode.MimeTypes.Sync/	New console utility for synchronizing MIME database
ManagedCode.MimeTypes.Generator/MimeTypeSourceGenerator.cs	Enhanced generator with proper escaping and improved key parsing
.github/workflows/mime-sync.yml	Added automated workflow for weekly MIME database updates

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Copilot · 2025-10-11T15:50:39Z

ManagedCode.MimeTypes.Sync/Program.cs

+                continue;
+            }
+
+            var parts = line.Split(MimeTypeSeparators, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);


The MimeTypeSeparators array is allocated on each call to Split(). Consider using line.Split(' ', '\t', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries) directly or make the array static readonly at the class level to avoid repeated allocations.

Suggested change

var parts = line.Split(MimeTypeSeparators, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);

var parts = line.Split(' ', '\t', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);

Copilot · 2025-10-11T15:50:39Z

ManagedCode.MimeTypes/MimeHelper.cs

+            yield break;
+        }
+
+        var separatorIndex = trimmed.IndexOfAny(new[] { '?', '#' });


The char array new[] { '?', '#' } is allocated on each call. Consider making this a static readonly field to avoid repeated allocations.

Copilot · 2025-10-11T15:50:39Z

ManagedCode.MimeTypes/MimeHelper.cs

+using System.Text;
 using System.Text.RegularExpressions;
+using System.Threading;



The condition header.Length >= 12 is checked twice in succession. The inner check on line 573 is redundant since it's already verified by the outer condition on line 572.

Copilot · 2025-10-11T15:50:39Z

ManagedCode.MimeTypes/MimeHelper.cs

+using System.Text;
 using System.Text.RegularExpressions;
+using System.Threading;



Similar to the previous issue, the condition header.Length >= 12 is checked twice. The inner check on line 594 is redundant since it's already verified by the outer condition on line 592.

Copilot · 2025-10-11T15:50:40Z

ManagedCode.MimeTypes.Tests/GeneratorTests.cs

+        const string extension = "customext";
+        const string mime = "application/x-custom";
+
+        try
+        {
+            MimeHelper.RegisterMimeType(extension, mime);
+            MimeHelper.GetMimeType($"file.{extension}").ShouldBe(mime);
+
+            MimeHelper.TryGetExtensions(mime, out var extensions).ShouldBeTrue();
+            extensions.ShouldContain($".{extension}");
+        }
+        finally
+        {
+            MimeHelper.UnregisterMimeType(extension).ShouldBeTrue();
+            MimeHelper.GetMimeType(extension).ShouldBe("application/octet-stream");


[nitpick] Using const for these values is unnecessary since they're only used within this single method. Consider using var or regular string literals directly in the method calls for better readability.

Suggested change

const string extension = "customext";

const string mime = "application/x-custom";

try

{

MimeHelper.RegisterMimeType(extension, mime);

MimeHelper.GetMimeType($"file.{extension}").ShouldBe(mime);

MimeHelper.TryGetExtensions(mime, out var extensions).ShouldBeTrue();

extensions.ShouldContain($".{extension}");

}

finally

{

MimeHelper.UnregisterMimeType(extension).ShouldBeTrue();

MimeHelper.GetMimeType(extension).ShouldBe("application/octet-stream");

try

{

MimeHelper.RegisterMimeType("customext", "application/x-custom");

MimeHelper.GetMimeType($"file.{"customext"}").ShouldBe("application/x-custom");

MimeHelper.TryGetExtensions("application/x-custom", out var extensions).ShouldBeTrue();

extensions.ShouldContain($".{"customext"}");

}

finally

{

MimeHelper.UnregisterMimeType("customext").ShouldBeTrue();

MimeHelper.GetMimeType("customext").ShouldBe("application/octet-stream");

coveralls · 2025-10-11T15:51:31Z

Pull Request Test Coverage Report for Build 18431903005

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

For more information on this, see Tracking coverage changes with pull request builds.
To avoid this issue with future PRs, see these Recommended CI Configurations.
For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

373 of 501 (74.45%) changed or added relevant lines in 2 files are covered.
154 unchanged lines in 3 files lost coverage.
Overall coverage increased (+4.9%) to 54.02%

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ManagedCode.MimeTypes.Generator/MimeTypeSourceGenerator.cs	0	11	0.0%
ManagedCode.MimeTypes/MimeHelper.cs	373	490	76.12%

Files with Coverage Reduction	New Missed Lines	%
ManagedCode.MimeTypes.Generator/MimeTypeSourceGenerator.cs	1	0.0%
ManagedCode.MimeTypes/MimeHelper.cs	2	74.02%
ManagedCode.MimeTypes/obj/Generated/ManagedCode.MimeTypes.Generator/ManagedCode.MimeTypes.Generator.MimeTypeSourceGenerator/MimeHelper.Properties.cs	151	50.28%

Totals
Change from base Build 16629812820:	4.9%
Covered Lines:	1678
Relevant Lines:	3155

💛 - Coveralls

KSemenenko · 2025-10-11T16:09:45Z

@codex fix all comments

chatgpt-codex-connector · 2025-10-11T16:13:07Z

Summary

Updated the sync tool to split mime.types entries using inline whitespace separators to avoid repeated array allocations while parsing remote listings. ManagedCode.MimeTypes.Sync/Program.csL135-L158
Cached the query/fragment separator characters and reused them when extracting extension candidates from file names, preventing per-call allocations. ManagedCode.MimeTypes/MimeHelper.csL33-L52 ManagedCode.MimeTypes/MimeHelper.csL399-L457
Simplified RIFF and ISO base media signature checks by removing redundant length guards during complex MIME detection. ManagedCode.MimeTypes/MimeHelper.csL603-L635
Inlined the custom MIME strings in the generator tests to match review feedback and keep the assertions concise. ManagedCode.MimeTypes.Tests/GeneratorTests.csL62-L76

Testing

⚠️ dotnet test (fails: command not found in container)

View task →

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Restore ArrayPool import

Optimize zip detection search and reuse separators

adc69d8

Copilot AI review requested due to automatic review settings October 11, 2025 15:49

KSemenenko added the codex label Oct 11, 2025 — with ChatGPT Codex Connector

Copilot AI reviewed Oct 11, 2025

View reviewed changes

Improve extension normalization performance

0c8ea83

KSemenenko and others added 3 commits October 11, 2025 18:17

Restore ArrayPool import

195f0cf

Update ManagedCode.MimeTypes/MimeHelper.cs

4d46481

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Merge pull request #3 from managedcode/codex/fix-all-comments

a59c580

Restore ArrayPool import

KSemenenko merged commit 8c5b402 into main Oct 11, 2025
1 check passed

KSemenenko deleted the codex/analyze-project-and-provide-improvement-recommendations-6j8r71 branch October 11, 2025 16:27

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Address review feedback on MIME detection and sync tool #2

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	var parts = line.Split(MimeTypeSeparators, StringSplitOptions.RemoveEmptyEntries \| StringSplitOptions.TrimEntries);
	var parts = line.Split(' ', '\t', StringSplitOptions.RemoveEmptyEntries \| StringSplitOptions.TrimEntries);

Address review feedback on MIME detection and sync tool #2

Address review feedback on MIME detection and sync tool #2

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KSemenenko commented Oct 11, 2025

Summary

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