Add magic number checks to support image files without an extension #1868
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Implements magic number checks to detect images in files without extensions.
Reviewer's GuideAdds content-based magic number detection to the image viewer plugin so it can handle extension-less image files while preserving existing extension-based behavior and directory checks. Class diagram for Plugin image handling with magic number checksclassDiagram
class Plugin {
+bool CanHandle(string path)
-static bool IsImageByMagicNumber(string path)
}
class WebHandler {
+static bool TryCanHandle(string path)
}
class Directory {
+static bool Exists(string path)
}
class Path {
+static bool HasExtension(string path)
}
class File {
+static bool Exists(string path)
}
class FileStream {
+FileStream(string path, FileMode mode, FileAccess access, FileShare share)
+long Length
+int Read(byte[] buffer, int offset, int count)
+void Dispose()
}
Plugin ..> WebHandler : uses
Plugin ..> Directory : uses
Plugin ..> Path : uses
Plugin ..> File : uses
Plugin ..> FileStream : uses
class FileMode {
}
class FileAccess {
}
class FileShare {
}
FileStream ..> FileMode : uses
FileStream ..> FileAccess : uses
FileStream ..> FileShare : uses
Flow diagram for CanHandle image detection with magic numbersflowchart TD
A[Start CanHandle path] --> B{WebHandler.TryCanHandle path}
B -- true --> Z[Return true]
B -- false --> C{Directory.Exists path}
C -- true --> Y[Return false]
C -- false --> D{Has well known image extension}
D -- true --> Z
D -- false --> E{Path.HasExtension path}
E -- false --> F[Call IsImageByMagicNumber path]
F --> G{IsImageByMagicNumber result}
G -- true --> Z
G -- false --> Y
E -- true --> Y
File-Level Changes
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Hey - I've found 1 issue, and left some high level feedback:
- The
IsImageByMagicNumbermethod catches all exceptions and silently returnsfalse; consider narrowing the exception types or at least logging unexpected exceptions to avoid hiding underlying IO or permission issues. - The magic number comparisons are currently done with repeated index checks; you might improve readability and maintainability by defining static readonly byte signatures (e.g.,
PngSignature,JpegSignature) and using a small helper to compare spans/arrays.
Prompt for AI Agents
Please address the comments from this code review:
## Overall Comments
- The `IsImageByMagicNumber` method catches all exceptions and silently returns `false`; consider narrowing the exception types or at least logging unexpected exceptions to avoid hiding underlying IO or permission issues.
- The magic number comparisons are currently done with repeated index checks; you might improve readability and maintainability by defining static readonly byte signatures (e.g., `PngSignature`, `JpegSignature`) and using a small helper to compare spans/arrays.
## Individual Comments
### Comment 1
<location> `QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Plugin.cs:153-156` </location>
<code_context>
+ if (bytesRead < 4)
+ return false;
+
+ // PNG: 89 50 4E 47 0D 0A 1A 0A
+ if (bytesRead >= 8 &&
+ buffer[0] == 0x89 && buffer[1] == 0x50 && buffer[2] == 0x4E && buffer[3] == 0x47 &&
+ buffer[4] == 0x0D && buffer[5] == 0x0A && buffer[6] == 0x1A && buffer[7] == 0x0A)
+ {
+ return true;
</code_context>
<issue_to_address>
**suggestion:** Consider extracting magic numbers into constants or using spans for cleaner signature checks.
The current chain of `buffer[i] == ...` checks works but is hard to read and extend as you add more formats. Defining each signature as a `ReadOnlySpan<byte>` and comparing via `SequenceEqual` on a slice of `buffer`, or moving each format check into a small helper method, would make the code clearer and easier to maintain while avoiding duplicated index logic.
Suggested implementation:
```csharp
var buffer = new byte[12];
var bytesRead = fs.Read(buffer, 0, buffer.Length);
if (bytesRead < 4)
return false;
ReadOnlySpan<byte> pngSignature = new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A };
// PNG: 89 50 4E 47 0D 0A 1A 0A
if (bytesRead >= pngSignature.Length &&
buffer.AsSpan(0, pngSignature.Length).SequenceEqual(pngSignature))
{
return true;
}
if (Directory.Exists(path))
```
If `System` is not already imported at the top of this file, add `using System;` so that `ReadOnlySpan<byte>` and `AsSpan` are available. You can follow this pattern to add other signatures (e.g., JPEG, GIF, WEBP) by defining additional `ReadOnlySpan<byte>` values and comparing them via `buffer.AsSpan(start, length).SequenceEqual(signature)` to keep all magic numbers centralized and readable.
</issue_to_address>Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.
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Implements magic number checks to detect images in files without extensions.
PR Checklist
I've never built something made with C# before (I only use python and C) so I tried installing Visual Studio to build and test the application, but I couldn't stop getting "Metadata file '.dll' could not be found" errors even after spending an hour attempting various fixes. The changes are simple enough that I hope you will accept them after a quick test on your end.
Not applicable, I would say.
Brief Description of Changes
Please briefly describe the main changes in this PR:
As indicated in the title, the goal is allowing QuickLook to preview image files even when the extension has been removed, which can be useful for example when exploring a browser's cache folders.
This complements the already present support for extension-less video files.
Related Issue (if any)
Please provide related issue numbers:
None.
Additional Notes
Add any extra notes here:
None.
Summary by Sourcery
New Features: