Return 404 when Active Storage image variants cannot be processed - #172
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thibaudgg
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September 1, 2026 11:57
Blobs can be stored as PNG/JPEG while the bytes are not a format libvips can load. Variant generation then raised Vips::Error from the representations redirect, turning newsletter/Trix image URLs into 500s (AppSignal #458). Rescue that like an unusable blob. Co-authored-by: Thibaud Guillaume-Gentil <thibaud@thibaud.gg>
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Why
Production AppSignal exception incident #458 is a
Vips::ErrorfromActiveStorage::Representations::RedirectController#show:Recent traces (tenant
ragedevert, blobs ~9548 and ~9549) 500 while transforming the blob to the newsletter/Trix JPEG variant (resize_to_limit: [1024, 768], matchingapp/views/active_storage/blobs/_blob.html.erb).The blob is stored/named as an image, so Active Storage treats it as representable, but the bytes are not a format libvips can load (corrupt, truncated, or not actually an image). Rails already returns 404 for an invalid variation signature; this extends that to failed image processing.
Upload-time validation alone would not stop the 500s: these blobs already exist, Trix only checks the browser-reported MIME type, and org logos already validate bytes with Vips. This keeps the existing images in place and makes their representation URLs fail closed.
What
ActiveStorage::Representations::BaseController#set_representationafter boot and rescueVips::Error/ImageProcessing::Errornext to the existingInvalidSignaturehandler (head :not_found).after_initialize(notto_prepare+ prepend): the gem controller is not loaded while initializers run, and gem controllers do not reload.Do not merge or deploy from this PR. Leave the AppSignal incident open.