Copilot commented on code in PR #13776:
URL: https://github.com/apache/trafficserver/pull/13776#discussion_r4161282886
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plugins/compress/compress.cc:
##########
@@ -811,6 +810,190 @@ 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());
+ }
+}
+
+static bool
+client_accepts_compression(TSMBuffer req_buf, TSMLoc req_loc,
HostConfiguration *hc)
+{
+ TSMLoc ae = TSMimeHdrFieldFind(req_buf, req_loc,
TS_MIME_FIELD_ACCEPT_ENCODING, TS_MIME_LEN_ACCEPT_ENCODING);
+
+ if (ae == TS_NULL_MLOC) {
+ return false;
+ }
+ ts::PostScript ae_defer([&]() -> void { TSHandleMLocRelease(req_buf,
req_loc, ae); });
+
+ int const algorithms = hc->compression_algorithms();
+ int const nvalues = TSMimeHdrFieldValuesCount(req_buf, req_loc, ae);
+
+ for (int i = 0; i < nvalues; i++) {
+ int len;
+ const char *value = TSMimeHdrFieldValueStringGet(req_buf, req_loc, ae, i,
&len);
+
+ if (value == nullptr) {
+ continue;
+ }
+ if ((strncasecmp(value, "zstd", sizeof("zstd") - 1) == 0 && (algorithms &
ALGORITHM_ZSTD)) ||
+ (strncasecmp(value, "br", sizeof("br") - 1) == 0 && (algorithms &
ALGORITHM_BROTLI)) ||
+ (strncasecmp(value, "deflate", sizeof("deflate") - 1) == 0 &&
(algorithms & ALGORITHM_DEFLATE)) ||
+ (strncasecmp(value, "gzip", sizeof("gzip") - 1) == 0 && (algorithms &
ALGORITHM_GZIP))) {
+ return true;
+ }
+ }
+
+ return false;
+}
+
+// No transform runs on a bodyless 304, so it goes out with whatever ETag the
origin or the cached
+// identity copy has. A 304 must carry the ETag its 200 would (RFC 9110
15.4.5), so when the client
+// validated with the weak form of a strong 304 ETag, it holds a compressed
copy: answer in kind.
+static void
+weaken_client_not_modified_etag(TSHttpTxn txnp, HostConfiguration *hc)
+{
+ 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) {
+ return;
+ }
+
+ TSMLoc resp_etag = TSMimeHdrFieldFind(resp_buf, resp_loc,
TS_MIME_FIELD_ETAG, TS_MIME_LEN_ETAG);
+
+ if (resp_etag == TS_NULL_MLOC) {
+ return;
+ }
+ ts::PostScript resp_etag_defer([&]() -> void { TSHandleMLocRelease(resp_buf,
resp_loc, resp_etag); });
+
+ int resp_len;
+ const char *resp_str = TSMimeHdrFieldValueStringGet(resp_buf, resp_loc,
resp_etag, -1, &resp_len);
+ std::string_view resp_value{resp_str, static_cast<size_t>(resp_len)};
+
+ if (resp_value.starts_with("W/") || resp_value.starts_with("w/")) {
+ return;
+ }
+
+ TSMBuffer req_buf;
+ TSMLoc req_loc;
+
+ if (TS_SUCCESS != TSHttpTxnClientReqGet(txnp, &req_buf, &req_loc)) {
+ return;
+ }
+ ts::PostScript req_defer([&]() -> void { TSHandleMLocRelease(req_buf,
TS_NULL_MLOC, req_loc); });
+
+ if (!client_accepts_compression(req_buf, req_loc, hc)) {
+ return;
+ }
+
+ 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;
+ }
+ ts::PostScript inm_defer([&]() -> void { TSHandleMLocRelease(req_buf,
req_loc, inm); });
+
+ int const nvalues = TSMimeHdrFieldValuesCount(req_buf, req_loc, inm);
+
+ for (int i = 0; i < nvalues; i++) {
+ int len;
+ const char *str = TSMimeHdrFieldValueStringGet(req_buf, req_loc, inm, i,
&len);
+
+ if (str == nullptr) {
+ continue;
+ }
+
+ std::string_view tag{str, static_cast<size_t>(len)};
+
+ if (tag.starts_with("W/") && tag.substr(2) == resp_value) {
+ TSMimeHdrFieldValueStringSet(resp_buf, resp_loc, resp_etag, -1,
tag.data(), tag.size());
Review Comment:
This makes the 304 ETag depend on whether the client wrote the matching
validator as weak, rather than on the selected representation. In the new
`cache false` case, `If-None-Match: "c1"` weakly matches the cached identity
object, but a full response to the same gzip request would be transformed and
carry `W/"c1"`; returning the strong tag (as asserted at replay line 523)
violates the RFC 9110 ยง15.4.5 requirement cited above. Conversely, a weak
origin validator does not prove that a non-cacheable/non-compressible response
was previously transformed. Determine whether the selected response would
actually be compressed, then weaken its 304 ETag regardless of the request
validator's strength.
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