Skip to content

Fix globstar '**' handling in PrefixedFileProvider.Watch() #47

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
rameel merged 4 commits into from
Mar 29, 2026
Merged

Fix globstar '**' handling in PrefixedFileProvider.Watch() #47

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
21ce1b5
Avoid false negatives when resolving '**' in glob filters
rameel Mar 29, 2026
a073784
Add explanation comment
rameel Mar 29, 2026
5b030e4
Clean up
rameel Mar 29, 2026
c6d2951
Simplify path segment joining
rameel Mar 29, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
79 changes: 67 additions & 12 deletions src/Ramstack.FileProviders/PrefixedFileProvider.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -135,24 +135,77 @@ public void Dispose() =>
var prefixSegments = new PathTokenizer(prefix).GetEnumerator();
var filterSegments = new PathTokenizer(filter).GetEnumerator();

var list = new List<string>();

while (prefixSegments.MoveNext() && filterSegments.MoveNext())
{
var fs = filterSegments.Current;

// The globstar '**' matches any number of remaining segments, including none
if (fs is "**")
{
// Add '**' and all remaining filter segments to the result.
do
{
var segment = filterSegments.Current.ToString();
list.Add(segment);
}
while (filterSegments.MoveNext());

return string.Join("/", list);
// The globstar '**' matches zero or more path segments.
// Once we encounter '**', we lose the ability to deterministically align
// the remaining filter segments with the remaining prefix segments.
//
// Why this matters:
// We are transforming a filter defined over the 'outer' virtual path
// into a filter for the 'inner' provider (mounted at 'prefix').
// To do that precisely, we would need to know how many segments '**' consumes.
//
// However, this is fundamentally ambiguous:
// - '**' may consume 0 segments
// - '**' may consume N segments (including prefix tail segments)
// - or it may match entirely within the underlying provider
//
// Example (false negative if we over-reduce):
// prefix: /modules/profile/assets
// filter: /modules/**/assets/*.js
//
// Underlying provider may contain:
// /src/_build/assets/main.js
//
// Which corresponds to:
// /modules/profile/assets/src/_build/assets/main.js
//
// In this case:
// '**/assets/*.js' --> MUST match
// '*.js' --> would NOT match
//
// Counter-example (false negative if we try to keep prefix tail):
// prefix: /modules/profile/assets
// filter: /modules/**/assets/*.js
//
// Suppose 'assets' in the filter refers to the *prefix itself*,
// and the underlying provider contains only flat files:
// /main.js
//
// (i.e. no nested 'assets/' directory inside the provider)
//
// Then:
// '*.js' --> MUST match
// '**/assets/*.js' --> would NOT match
//
// Conclusion:
// After '**', we cannot know whether subsequent segments belong
// to the prefix or to the underlying provider.
//
// Therefore, any attempt to:
// - consume prefix segments (--> '*.js')
// - or preserve intermediate literals (--> '**/assets/*.js')
// will break valid scenarios.
//
// Strategy:
// - Preserve '**' to allow arbitrary depth
// - Drop ambiguous intermediate segments
// - Keep only the final segment if it is a file pattern (e.g. '*.js')
//
// This guarantees:
// - No false negatives caused by prefix misalignment
// - Possible false positives, which are acceptable for Watch()
while (filterSegments.MoveNext())
fs = filterSegments.Current;

return fs is not "**"
? "**/" + fs.ToString()
: "**";
}

if (fs is "*")
Expand All @@ -174,6 +227,8 @@ public void Dispose() =>

if (!prefixSegments.MoveNext())
{
var list = new List<string>();

// All prefix segments have been matched and consumed successfully.
// Append all remaining filter segments.
while (filterSegments.MoveNext())
Expand Down
6 changes: 6 additions & 0 deletions tests/Ramstack.FileProviders.Tests/PrefixedFileProviderTests.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,12 @@ protected override DirectoryInfo GetDirectoryInfo() =>

[TestCase("/modules/profile/assets", "/modules/**", ExpectedResult = "**")]
[TestCase("/modules/profile/assets", "/modules/**/*.js", ExpectedResult = "**/*.js")]
[TestCase("/modules/profile/assets", "/modules/**/assets/*.js", ExpectedResult = "**/*.js")]
[TestCase("/modules/profile/assets", "/modules/**/profile/assets/*.{js,css}", ExpectedResult = "**/*.{js,css}")]
[TestCase("/modules/profile/assets", "/modules/**/profile/assets/**", ExpectedResult = "**")]
[TestCase("/modules/profile/assets", "/modules/**/profile/assets/**/*", ExpectedResult = "**/*")]
[TestCase("/modules/profile/assets", "/**/*.js", ExpectedResult = "**/*.js")]
[TestCase("/modules/profile/assets", "/**", ExpectedResult = "**")]
[TestCase("/modules/profile/assets", "/modules/profile/*/*.js", ExpectedResult = "*.js")]
[TestCase("/modules/profile/assets", "/modules/profile/{js,css,assets}/*.js", ExpectedResult = "*.js")]
[TestCase("/modules/profile/assets", "/modules/{settings,profile}/{js,css,assets}/*.js", ExpectedResult = "*.js")]
Expand Down
Loading