MEDIUM: cache: Add support for 'If-None-Match' request header
Partial support of conditional HTTP requests. This commit adds the
support of the 'If-None-Match' header (see RFC 7232#3.2).
When a client specifies a list of ETags through one or more
'If-None-Match' headers, they are all compared to the one that might have
been stored in the corresponding http cache entry until one of them
matches.
If a match happens, a specific "304 Not Modified" response is
sent instead of the cached data. This response has all the stored
headers but no other data (see RFC 7232#4.1). Otherwise, the whole cached data
is sent.
Although unlikely in a GET/HEAD request, the "If-None-Match: *" syntax is
valid and also receives a "304 Not Modified" response (RFC 7434#4.3.2).
This resolves a part of GitHub issue #821.
diff --git a/src/cache.c b/src/cache.c
index 8faaa44..a5e26c3 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -933,8 +933,14 @@
!htx_cache_add_age_hdr(appctx, res_htx))
goto error;
- /* Skip response body for HEAD requests */
- if (si_strm(si)->txn->meth == HTTP_METH_HEAD)
+ /* In case of a conditional request, we might want to send a
+ * "304 Not Modified" response instead of the stored data. */
+ if (appctx->ctx.cache.send_notmodified)
+ http_replace_res_status(res_htx, ist("304"), ist("Not Modified"));
+
+ /* Skip response body for HEAD requests or in case of "304 Not
+ * Modified" response. */
+ if (si_strm(si)->txn->meth == HTTP_METH_HEAD || appctx->ctx.cache.send_notmodified)
appctx->st0 = HTX_CACHE_EOM;
else
appctx->st0 = HTX_CACHE_DATA;
@@ -1121,6 +1127,61 @@
return 1;
}
+/* Looks for "If-None-Match" headers in the request and compares their value
+ * with the one that might have been stored in the cache_entry. If any of them
+ * matches, a "304 Not Modified" response should be sent instead of the cached
+ * data.
+ * Although unlikely in a GET/HEAD request, the "If-None-Match: *" syntax is
+ * valid and should receive a "304 Not Modified" response (RFC 7434#4.3.2).
+ * Returns 1 if "304 Not Modified" should be sent, 0 otherwise.
+ */
+static int should_send_notmodified_response(struct cache *cache, struct htx *htx,
+ struct cache_entry *entry)
+{
+ int retval = 0;
+
+ struct http_hdr_ctx ctx = { .blk = NULL };
+ struct ist cache_entry_etag = IST_NULL;
+ struct buffer *etag_buffer = NULL;
+
+ if (entry->etag_length == 0)
+ return 0;
+
+ /* If we find a "If-None-Match" header in the request, rebuild the
+ * cache_entry's ETag in order to perform comparisons. */
+ /* There could be multiple "if-none-match" header lines. */
+ while (http_find_header(htx, ist("if-none-match"), &ctx, 0)) {
+
+ /* A '*' matches everything. */
+ if (isteq(ctx.value, ist("*")) != 0) {
+ retval = 1;
+ break;
+ }
+
+ /* Rebuild the stored ETag. */
+ if (etag_buffer == NULL) {
+ etag_buffer = get_trash_chunk();
+
+ if (shctx_row_data_get(shctx_ptr(cache), block_ptr(entry),
+ (unsigned char*)b_orig(etag_buffer),
+ entry->etag_offset, entry->etag_length) == 0) {
+ cache_entry_etag = ist2(b_orig(etag_buffer), entry->etag_length);
+ } else {
+ /* We could not rebuild the ETag in one go, we
+ * won't send a "304 Not Modified" response. */
+ break;
+ }
+ }
+
+ if (http_compare_etags(cache_entry_etag, ctx.value) == 1) {
+ retval = 1;
+ break;
+ }
+ }
+
+ return retval;
+}
+
enum act_return http_action_req_cache_use(struct act_rule *rule, struct proxy *px,
struct session *sess, struct stream *s, int flags)
{
@@ -1165,6 +1226,8 @@
appctx->ctx.cache.entry = res;
appctx->ctx.cache.next = NULL;
appctx->ctx.cache.sent = 0;
+ appctx->ctx.cache.send_notmodified =
+ should_send_notmodified_response(cache, htxbuf(&s->req.buf), res);
if (px == strm_fe(s))
_HA_ATOMIC_ADD(&px->fe_counters.p.http.cache_hits, 1);