ezelkow1 commented on code in PR #13776:
URL: https://github.com/apache/trafficserver/pull/13776#discussion_r4162603969
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plugins/compress/compress.cc:
##########
@@ -811,6 +810,167 @@ 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 and the
stored copy is
+// encoded; an identity copy's ETag is the origin's own, so it may
legitimately become strong.
+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 cached_ce = TSMimeHdrFieldFind(cached_buf, cached_loc,
TS_MIME_FIELD_CONTENT_ENCODING, TS_MIME_LEN_CONTENT_ENCODING);
+
+ if (cached_ce == TS_NULL_MLOC) {
+ return;
+ }
+ TSHandleMLocRelease(cached_buf, cached_loc, cached_ce);
+
+ 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());
+ }
+}
+
+// No transform runs on a bodyless 304, so it goes out with the origin's or
the cached identity
+// copy's strong ETag. A 304 must carry the ETag its 200 would (RFC 9110
15.4.5), and this
+// request's 200 would have been compressed, so weaken it to match.
+static void
+weaken_client_not_modified_etag(TSHttpTxn txnp)
+{
+ TSMBuffer resp_buf;
+ TSMLoc resp_loc;
+
+ if (TS_SUCCESS != TSHttpTxnClientRespGet(txnp, &resp_buf, &resp_loc)) {
+ return;
+ }
+ ts::PostScript resp_defer([&]() -> void { TSHandleMLocRelease(resp_buf,
TS_NULL_MLOC, resp_loc); });
+
+ if (TSHttpHdrStatusGet(resp_buf, resp_loc) == TS_HTTP_STATUS_NOT_MODIFIED) {
+ etag_header(resp_buf, resp_loc);
+ }
+}
+
+static int
+not_modified_etag_plugin(TSCont contp, TSEvent event, void *edata)
+{
+ TSHttpTxn txnp = static_cast<TSHttpTxn>(edata);
+
+ switch (event) {
+ case TS_EVENT_HTTP_SEND_RESPONSE_HDR:
+ weaken_client_not_modified_etag(txnp);
+ break;
+
+ case TS_EVENT_HTTP_TXN_CLOSE:
+ TSContDestroy(contp);
+ break;
+
+ default:
+ fatal("compress 304 ETag unknown event");
+ }
+
+ TSHttpTxnReenable(txnp, TS_EVENT_HTTP_CONTINUE);
+
+ return 0;
+}
+
+static void
+remove_field_with_dups(TSMBuffer bufp, TSMLoc hdr_loc, const char *name, int
name_len)
+{
+ TSMLoc field = TSMimeHdrFieldFind(bufp, hdr_loc, name, name_len);
+
+ while (field != TS_NULL_MLOC) {
+ TSMLoc next_dup = TSMimeHdrFieldNextDup(bufp, hdr_loc, field);
+
+ TSMimeHdrFieldDestroy(bufp, hdr_loc, field);
+ TSHandleMLocRelease(bufp, hdr_loc, field);
+ field = next_dup;
+ }
+}
+
+// With nothing stored, an origin 304 leaves no representation to tell whether
this request's 200
+// would have been compressed. A weak validator likely came from a compressed
copy, so fetch the 200
+// instead; ATS still answers the client's conditional from it, and the 304 is
weakened if needed.
+static void
+unconditionalize_weak_validation(TSHttpTxn txnp)
+{
+ TSMBuffer cached_buf;
+ TSMLoc cached_loc;
+
+ if (TS_SUCCESS == TSHttpTxnCachedRespGet(txnp, &cached_buf, &cached_loc)) {
+ TSHandleMLocRelease(cached_buf, TS_NULL_MLOC, cached_loc);
+ return;
+ }
+
+ TSMBuffer req_buf;
+ TSMLoc req_loc;
+
+ if (TS_SUCCESS != TSHttpTxnServerReqGet(txnp, &req_buf, &req_loc)) {
+ return;
+ }
+ ts::PostScript req_defer([&]() -> void { TSHandleMLocRelease(req_buf,
TS_NULL_MLOC, req_loc); });
+
+ TSMLoc inm = TSMimeHdrFieldFind(req_buf, req_loc,
TS_MIME_FIELD_IF_NONE_MATCH, TS_MIME_LEN_IF_NONE_MATCH);
+
+ if (inm == TS_NULL_MLOC) {
+ return;
+ }
+
+ bool has_weak = false;
+ int const nvalues = TSMimeHdrFieldValuesCount(req_buf, req_loc, inm);
+
+ for (int i = 0; i < nvalues && !has_weak; i++) {
+ int len;
+ const char *str = TSMimeHdrFieldValueStringGet(req_buf, req_loc, inm, i,
&len);
+
+ has_weak = str != nullptr && std::string_view{str,
static_cast<size_t>(len)}.starts_with("W/");
+ }
+ TSHandleMLocRelease(req_buf, req_loc, inm);
+
+ if (has_weak) {
+ debug("no stored response to judge a weak validator against, fetching
unconditionally");
+ remove_field_with_dups(req_buf, req_loc, TS_MIME_FIELD_IF_NONE_MATCH,
TS_MIME_LEN_IF_NONE_MATCH);
+ remove_field_with_dups(req_buf, req_loc, TS_MIME_FIELD_IF_MODIFIED_SINCE,
TS_MIME_LEN_IF_MODIFIED_SINCE);
+ }
Review Comment:
Good catch. It was broader than POST, since the strip had no method check at
all, and it also forced full fetches from origins that issue weak ETags
themselves. Removed the upstream strip entirely: conditionals now always reach
the origin as sent. For an origin 304 with nothing stored to judge by, the
plugin weakens its ETag only for GET/HEAD and only when the client's
`If-None-Match` holds the weak form of the 304's strong ETag. Added regression
cases for a conditional POST (precondition reaches the origin, 412 passes
through) and a weak-ETag origin (304 passes through unchanged).
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