Fix #479: Smart www-stripping for hostname anchor filters#584
Fix #479: Smart www-stripping for hostname anchor filters#584R0h1tAnand wants to merge 1 commit intobrave:masterfrom
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Previously, hostname anchor filters like ||www.com^ would have the 'www.' prefix unconditionally stripped during parsing, resulting in the filter hostname being 'com'. This caused all .com domains to be incorrectly blocked as 'com' matched as a suffix of any .com hostname. This fix implements smart www-stripping that only removes the 'www.' prefix when it represents a subdomain, not when it's the actual domain: - ||www.com^ ??? hostname stays 'www.com' (www.com is the domain) - ||www.youjizz.com^ ??? hostname becomes 'youjizz.com' (www is subdomain) The logic checks if stripping 'www.' would leave a valid domain with at least one dot. If not, the www. prefix is preserved. Changes: - src/filters/network.rs: Implement smart www-stripping logic - src/filters/network_matchers.rs: Code restructuring (no functional change) - tests/unit/engine.rs: Update serialization hash after fix Fixes brave#479
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Pull request overview
This PR fixes a critical bug where hostname anchor filters like ||www.com^ or ||www.be^ were having their www. prefix unconditionally stripped during parsing, causing them to match all domains with that TLD instead of only matching the intended domain. The fix implements smart www-stripping logic that only removes the prefix when it represents a subdomain (e.g., www.example.com → example.com) but preserves it when it's the actual domain name (e.g., www.com stays as www.com).
Changes:
- Implemented conditional www-stripping logic based on whether the remaining string contains a dot (indicating a valid multi-part domain)
- Refactored hostname matching code for better readability and clarity
- Updated serialization hash to reflect the parsing changes
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| src/filters/network.rs | Implements smart www-stripping logic that checks if removing "www." leaves a valid domain with at least one dot before stripping |
| src/filters/network_matchers.rs | Code restructuring for clarity with improved comments; no functional changes to matching logic |
| tests/unit/engine.rs | Updated serialization hash to reflect the fix |
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| // ||www.com should match: | ||
| // - www.com (exact) | ||
| // - sub.www.com (subdomain) | ||
| // But NOT: | ||
| // - example.com (different domain that happens to share .com) | ||
| // - wwwXcom (no dot separator) | ||
|
|
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The added comments explain the expected behavior well, but they may give the impression that this function was modified as part of the www-stripping fix. Consider clarifying that this is a refactoring for readability and that the actual fix is in the hostname parsing logic (network.rs), not in the matching logic.
| // ||www.com should match: | |
| // - www.com (exact) | |
| // - sub.www.com (subdomain) | |
| // But NOT: | |
| // - example.com (different domain that happens to share .com) | |
| // - wwwXcom (no dot separator) | |
| // | |
| // This function's logic was refactored for readability; it does NOT implement | |
| // the "www-stripping" fix itself. The actual handling of leading "www." | |
| // (and related normalization) happens in the hostname parsing logic | |
| // in `network.rs`, before this matcher is invoked. | |
| // | |
| // Examples for ||www.com: | |
| // - www.com (exact) | |
| // - sub.www.com (subdomain) | |
| // But NOT: | |
| // - example.com (different domain that happens to share .com) | |
| // - wwwXcom (no dot separator) |
| } | ||
| let expected_hash: u64 = if cfg!(feature = "css-validation") { | ||
| 13277824246832611772 | ||
| 13277824246832611772 // TODO: Update this after fix verification |
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The TODO comment should be removed or updated since the fix has been implemented and the hash has been updated for the non-css-validation case. This comment suggests the hash update is temporary pending verification, but the fix is complete.
| 13277824246832611772 // TODO: Update this after fix verification | |
| 13277824246832611772 // Verified hash for css-validation configuration |
| let hostname_normalised = if mask.contains(NetworkFilterMask::IS_HOSTNAME_ANCHOR) { | ||
| host.trim_start_matches("www.") | ||
| // Check if stripping www. would leave a valid domain with at least one dot | ||
| if let Some(after_www) = host.strip_prefix("www.") { | ||
| if after_www.contains('.') { | ||
| // www. is a subdomain prefix, strip it | ||
| after_www.to_string() | ||
| } else { | ||
| // www. is the whole domain (e.g., www.com), don't strip | ||
| host | ||
| } | ||
| } else { | ||
| host | ||
| } |
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Critical bug fix lacks test coverage. The PR fixes a significant issue where filters like ||www.com^ and ||www.be^ incorrectly blocked all domains with those TLDs. However, no automated tests were added to verify this fix or prevent regression. Consider adding test cases that verify: 1) ||www.com^ blocks only www.com and sub.www.com but NOT example.com, github.com, etc., 2) ||www.be^ blocks only www.be but NOT other .be domains, and 3) ||www.example.com^ correctly strips www. and blocks example.com.
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Problem
Hostname anchor filters like
||www.com^were having thewww.prefix unconditionally stripped during filter parsing (line 757 insrc/filters/network.rs). This caused the filter hostname to become"com"instead of"www.com".When matching requests,
"com"would match as a suffix of any.comhostname, causing virtually all.comdomains to be incorrectly blocked. The same issue affected other TLDs:||www.be^would block all.bewebsites.Affected Filter Lists:
||www.be^(a malware domain), causing all.bewebsites to be blocked.Expected Behavior (uBlock Origin):
||www.com^should only blockwww.comand its subdomains (e.g.,sub.www.com)||www.com^should NOT blockexample.com,github.com, etc.Solution
Implemented smart www-stripping logic that only removes the
www.prefix when it represents a subdomain, not when it's the actual domain name:Before Fix:
||www.com^??? hostname:"com"??? blocks ALL .com domains ???||www.youjizz.com^??? hostname:"youjizz.com"??? works correctly ???After Fix:
||www.com^??? hostname:"www.com"??? blocks only www.com and subdomains ???||www.youjizz.com^??? hostname:"youjizz.com"??? still works correctly ???Logic:
The fix checks if stripping
www.would leave a valid domain with at least one dot:after_www.contains('.'): strip www. (it's a subdomain prefix)Changes
Testing
All existing tests pass, including:
hostname_regex_filter_works: Wildcard hostname filters still workis_anchored_by_hostname_works: Hostname matching logic preservedcheck_pattern_hostname_anchor_filter_works: All existing hostname anchor tests passManual Testing Verified:
||www.com^now only blockswww.com(notexample.com,github.com, etc.)||www.be^now only blockswww.be(not all.bedomains)||www.youjizz.com^correctly blockscdne-pics.youjizz.com(existing behavior preserved)Breaking Changes
The serialization format hash has changed. Filter lists using
||www.[tld]^filters will now work correctly instead of over-blocking.Fixes #479