fix: crash when favicon endpoint returns non-image response - #173
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The favicon fetcher now rejects non-image responses at two levels: 1. Content-Type header check — rejects responses that are clearly not images (e.g. text/html served by misconfigured servers) 2. Magic byte validation — verifies the response body starts with recognized image format signatures (PNG, JPEG, GIF, ICO, BMP, WebP, SVG) Previously, servers returning HTML error pages (like nginx default pages) for /favicon.ico would pass raw HTML to Fyne's image renderer, causing XML parse errors and potential crashes. The cache reader also validates stored data on read, automatically evicting entries that don't pass the image format check (protecting against previously cached invalid responses).
The fetchAndUpdateFavicon goroutine was updating img.Resource and calling img.Refresh() directly from a background goroutine without synchronization. This could cause a nil pointer dereference when Fyne's renderer accessed the image concurrently. Wrap the UI update in fyne.Do() to ensure it runs on the main thread. Also rename the static resource from "favicon.png" to "favicon" to avoid Fyne making incorrect format assumptions from the file extension.
Update existing test servers to set Content-Type: image/* headers, matching the new validation requirements. Add new test cases: - TestFetcher_RejectsHTMLResponse: verifies HTML content-type is rejected - TestFetcher_RejectsNonImageData: verifies non-image bytes are rejected even when server claims image content-type - TestFetcher_CacheEvictsInvalidData: verifies invalid cached entries are evicted and fresh data is fetched - TestIsImageData: table-driven tests for magic byte detection - TestIsImageContentType: table-driven tests for content-type parsing
- Reduce cyclomatic complexity by using a table-driven magic byte check with bytes.HasPrefix instead of individual if-statements (gocyclo) - Extract GIF magic strings into the imageMagic table (goconst) - Use direct return of strings.Contains for SVG check (staticcheck S1008)
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Summary
Fixes a crash (
nil pointer dereference) when the favicon fetcher receives non-image content (e.g. HTML error pages) from servers that don't serve a proper favicon.Reproducible with:
linkquisition "https://console.mistral.ai"(their/favicon.icoreturns an nginx HTML page).Changes
Validate favicon responses (
internal/favicon/favicon.go)image/*Content-Type headersFix thread-safety in UI update (
cmd/browser_picker.go)img.Resource/img.Refresh()infyne.Do()to prevent concurrent access from the favicon goroutine"favicon.png"to"favicon"to avoid format assumption from extensionTests (
internal/favicon/favicon_test.go)Content-Typeheaders on test serversTesting
linkquisition "https://console.mistral.ai"no longer crashes (favicon gracefully falls back to placeholder)