Copilot commented on code in PR #13776:
URL: https://github.com/apache/trafficserver/pull/13776#discussion_r4160288577
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plugins/compress/compress.cc:
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@@ -811,6 +810,57 @@ add_vary_header_to_client_response(TSHttpTxn txnp)
TSHandleMLocRelease(resp_buf, TS_NULL_MLOC, resp_loc);
}
+// A 304 carries the origin's strong ETag, which the cache would merge over
the weakened ETag of a
+// stored compressed copy. Keep it weak when both name the same entity.
+static void
+keep_cached_etag_weak(TSHttpTxn txnp)
+{
+ TSMBuffer srv_buf;
+ TSMLoc srv_loc;
+
+ if (TS_SUCCESS != TSHttpTxnServerRespGet(txnp, &srv_buf, &srv_loc)) {
+ return;
+ }
+ ts::PostScript srv_defer([&]() -> void { TSHandleMLocRelease(srv_buf,
TS_NULL_MLOC, srv_loc); });
+
+ if (TSHttpHdrStatusGet(srv_buf, srv_loc) != TS_HTTP_STATUS_NOT_MODIFIED) {
+ return;
+ }
+
+ TSMBuffer cached_buf;
+ TSMLoc cached_loc;
+
+ if (TS_SUCCESS != TSHttpTxnCachedRespGet(txnp, &cached_buf, &cached_loc)) {
+ return;
+ }
+ ts::PostScript cached_defer([&]() -> void { TSHandleMLocRelease(cached_buf,
TS_NULL_MLOC, cached_loc); });
+
+ TSMLoc srv_etag = TSMimeHdrFieldFind(srv_buf, srv_loc, TS_MIME_FIELD_ETAG,
TS_MIME_LEN_ETAG);
+
+ if (srv_etag == TS_NULL_MLOC) {
+ return;
+ }
+ ts::PostScript srv_etag_defer([&]() -> void { TSHandleMLocRelease(srv_buf,
srv_loc, srv_etag); });
+
+ TSMLoc cached_etag = TSMimeHdrFieldFind(cached_buf, cached_loc,
TS_MIME_FIELD_ETAG, TS_MIME_LEN_ETAG);
+
+ if (cached_etag == TS_NULL_MLOC) {
+ return;
+ }
+ ts::PostScript cached_etag_defer([&]() -> void {
TSHandleMLocRelease(cached_buf, cached_loc, cached_etag); });
+
+ int srv_len;
+ const char *srv_str = TSMimeHdrFieldValueStringGet(srv_buf, srv_loc,
srv_etag, -1, &srv_len);
+ int cached_len;
+ const char *cached_str = TSMimeHdrFieldValueStringGet(cached_buf,
cached_loc, cached_etag, -1, &cached_len);
+ std::string_view srv_value{srv_str, static_cast<size_t>(srv_len)};
+ std::string_view cached_value{cached_str, static_cast<size_t>(cached_len)};
+
+ if (cached_value.starts_with("W/") && cached_value.substr(2) == srv_value) {
+ TSMimeHdrFieldValueStringSet(srv_buf, srv_loc, srv_etag, -1,
cached_value.data(), cached_value.size());
Review Comment:
This condition is not scoped to cache entries transformed by `compress`. An
uncompressed response can legitimately be cached with `W/"v1"`; if a later 304
upgrades that validator to `"v1"`, this hook rewrites it back to weak merely
because the opaque tags match. That discards origin metadata and prevents
subsequent strong `If-Range` validation even though the body was never
transformed. Please preserve weakness only when the cached representation is
known to have been produced by this transform, and cover weak-to-strong
revalidation of an uncompressed response.
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