Reading from a Proxy Cache While the Network Is Down
Prepare the actual set of reusable responses needed for offline reading, including dependencies and freshness behavior.
A page opens while the network is available, then loses its styles and pictures offline. The HTML was only one of the objects the reading session needed.
A forward cache retains eligible responses that pass through it. It does not discover every future link, fetch resources merely mentioned in HTML or reproduce the application running at the origin.
Prepare the reading set
List the documents readers need, their images, stylesheets and other dependencies. Then distinguish three cases:
| Response state | Offline consequence |
|---|---|
| Stored and reusable | The cache can potentially satisfy the request |
| Stored but requiring validation | The missing origin can prevent reuse |
| Never stored or absent from the cache | There are no response bytes to serve |
Opening one page before disconnecting does not establish that every dependency reached this shared cache. A browser might have served some resources from its own local cache instead.
Freshness survives the cable being unplugged
Offline operation needs an explicit policy for stale content. A request for only-if-cached is a separate way to ask a cooperating cache for an already stored reply. HTTP has restrictions on when stale responses may be used, including applicable revalidation requirements. A saved object is not an unconditional permission to serve it indefinitely.
Squid 7's offline_mode is a particular deployment option that stops ordinary validation attempts. It changes validation behavior; it cannot manufacture missing objects or reconstruct a live login workflow. The directive is not available in Squid 8.
Ordinary HTTPS CONNECT also keeps page contents inside TLS. A tunneling proxy does not obtain reusable HTML and image objects from those encrypted bytes.
For a defined public reading collection, plan and check the complete working set and its update policy. For arbitrary interactive browsing, a cache alone cannot promise a complete offline copy of what the user might request next.