Fix edge-case Uri debug assert failure #123054
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Pull request overview
This PR fixes a debug assertion failure in Uri path canonicalization that occurs when the Compress method removes an entire path that was missing a leading slash. The fix adds a bounds check before accessing the character at the start position.
- Adds bounds check (
dest.Length > start) before accessingdest[start]to prevent reading past buffer length - Adds braces for consistency with coding style
- Includes a test case that reproduces the edge case scenario
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/libraries/System.Private.Uri/src/System/Uri.cs | Adds bounds check and braces to prevent out-of-bounds access when path compression removes entire path |
| src/libraries/System.Private.Uri/tests/FunctionalTests/UriRelativeResolutionTest.cs | Adds test case for FTP URI where entire path can be removed by compression |
This was referenced Jan 13, 2026
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If
Compressremoves the entire path, and that path was otherwise missing a leading slash, we can get into the case wheredest.Length == startafter theCompresscall.This triggers a debug assert in the
ValueStringBuilder'sthis[]accessor since we're reading past the length, but it's actually harmless in practice in this case since the underlying buffer will always have at least 1 available character afterstarton this path (note thedest.Length - offset > 0condition before compression).