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| -rw-r--r-- | modules/http2/h2_push.h | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/modules/http2/h2_push.h b/modules/http2/h2_push.h new file mode 100644 index 0000000..947b73b --- /dev/null +++ b/modules/http2/h2_push.h @@ -0,0 +1,158 @@ +/* Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#ifndef __mod_h2__h2_push__ +#define __mod_h2__h2_push__ + +#include <http_protocol.h> + +#include "h2.h" +#include "h2_headers.h" + +struct h2_request; +struct h2_ngheader; +struct h2_session; +struct h2_stream; + +typedef struct h2_push { + const struct h2_request *req; + h2_priority *priority; +} h2_push; + +typedef enum { + H2_PUSH_DIGEST_APR_HASH, + H2_PUSH_DIGEST_SHA256 +} h2_push_digest_type; + +/******************************************************************************* + * push diary + * + * - The push diary keeps track of resources already PUSHed via HTTP/2 on this + * connection. It records a hash value from the absolute URL of the resource + * pushed. + * - Lacking openssl, + * - with openssl, it uses SHA256 to calculate the hash value, otherwise it + * falls back to apr_hashfunc_default() + * - whatever the method to generate the hash, the diary keeps a maximum of 64 + * bits per hash, limiting the memory consumption to about + * H2PushDiarySize * 8 + * bytes. Entries are sorted by most recently used and oldest entries are + * forgotten first. + * - While useful by itself to avoid duplicated PUSHes on the same connection, + * the original idea was that clients provided a 'Cache-Digest' header with + * the values of *their own* cached resources. This was described in + * <https://datatracker.ietf.org/doc/draft-kazuho-h2-cache-digest/> + * and some subsequent revisions that tweaked values but kept the overall idea. + * - The draft was abandoned by the IETF http-wg, as support from major clients, + * e.g. browsers, was lacking for various reasons. + * - For these reasons, mod_h2 abandoned its support for client supplied values + * but keeps the diary. It seems to provide value for applications using PUSH, + * is configurable in size and defaults to a very moderate amount of memory + * used. + * - The cache digest header is a Golomb Coded Set of hash values, but it may + * limit the amount of bits per hash value even further. For a good description + * of GCS, read here: + * <http://giovanni.bajo.it/post/47119962313/golomb-coded-sets-smaller-than-bloom-filters> + ******************************************************************************/ + + +/* + * The push diary is based on the abandoned draft + * <https://datatracker.ietf.org/doc/draft-kazuho-h2-cache-digest/> + * that describes how to use golomb filters. + */ + +typedef struct h2_push_diary h2_push_diary; + +typedef void h2_push_digest_calc(h2_push_diary *diary, apr_uint64_t *phash, h2_push *push); + +struct h2_push_diary { + apr_array_header_t *entries; + int NMax; /* Maximum for N, should size change be necessary */ + int N; /* Current maximum number of entries, power of 2 */ + apr_uint64_t mask; /* mask for relevant bits */ + unsigned int mask_bits; /* number of relevant bits */ + const char *authority; + h2_push_digest_type dtype; + h2_push_digest_calc *dcalc; +}; + +/** + * Determine the list of h2_push'es to send to the client on behalf of + * the given request/response pair. + * + * @param p the pool to use + * @param req the requst from the client + * @param res the response from the server + * @return array of h2_push addresses or NULL + */ +#if AP_HAS_RESPONSE_BUCKETS +apr_array_header_t *h2_push_collect(apr_pool_t *p, + const struct h2_request *req, + apr_uint32_t push_policy, + const ap_bucket_response *res); +#else +apr_array_header_t *h2_push_collect(apr_pool_t *p, + const struct h2_request *req, + apr_uint32_t push_policy, + const struct h2_headers *res); +#endif + +/** + * Create a new push diary for the given maximum number of entries. + * + * @param p the pool to use + * @param N the max number of entries, rounded up to 2^x + * @return the created diary, might be NULL of max_entries is 0 + */ +h2_push_diary *h2_push_diary_create(apr_pool_t *p, int N); + +/** + * Filters the given pushes against the diary and returns only those pushes + * that were newly entered in the diary. + */ +apr_array_header_t *h2_push_diary_update(struct h2_session *session, apr_array_header_t *pushes); + +/** + * Collect pushes for the given request/response pair, enter them into the + * diary and return those pushes newly entered. + */ +#if AP_HAS_RESPONSE_BUCKETS +apr_array_header_t *h2_push_collect_update(struct h2_stream *stream, + const struct h2_request *req, + const ap_bucket_response *res); +#else +apr_array_header_t *h2_push_collect_update(struct h2_stream *stream, + const struct h2_request *req, + const struct h2_headers *res); +#endif + +/** + * Get a cache digest as described in + * https://datatracker.ietf.org/doc/draft-kazuho-h2-cache-digest/ + * from the contents of the push diary. + * + * @param diary the diary to calculdate the digest from + * @param p the pool to use + * @param authority the authority to get the data for, use NULL/"*" for all + * @param pdata on successful return, the binary cache digest + * @param plen on successful return, the length of the binary data + */ +apr_status_t h2_push_diary_digest_get(h2_push_diary *diary, apr_pool_t *p, + int maxP, const char *authority, + const char **pdata, apr_size_t *plen); + +#endif /* defined(__mod_h2__h2_push__) */ |