1 // Copyright 2021 gRPC authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include "src/core/ext/transport/chttp2/transport/hpack_encoder_table.h"
16
17 #include <grpc/support/port_platform.h>
18
19 #include <algorithm>
20
21 #include "absl/log/check.h"
22
23 namespace grpc_core {
24
AllocateIndex(size_t element_size)25 uint32_t HPackEncoderTable::AllocateIndex(size_t element_size) {
26 DCHECK_GE(element_size, 32u);
27
28 uint32_t new_index = tail_remote_index_ + table_elems_ + 1;
29 DCHECK(element_size <= MaxEntrySize());
30
31 if (element_size > max_table_size_) {
32 while (table_size_ > 0) {
33 EvictOne();
34 }
35 return 0;
36 }
37
38 // Reserve space for this element in the remote table: if this overflows
39 // the current table, drop elements until it fits, matching the decompressor
40 // algorithm.
41 while (table_size_ + element_size > max_table_size_) {
42 EvictOne();
43 }
44 CHECK(table_elems_ < elem_size_.size());
45 elem_size_[new_index % elem_size_.size()] =
46 static_cast<uint16_t>(element_size);
47 table_size_ += element_size;
48 table_elems_++;
49
50 return new_index;
51 }
52
SetMaxSize(uint32_t max_table_size)53 bool HPackEncoderTable::SetMaxSize(uint32_t max_table_size) {
54 if (max_table_size == max_table_size_) {
55 return false;
56 }
57 while (table_size_ > 0 && table_size_ > max_table_size) {
58 EvictOne();
59 }
60 max_table_size_ = max_table_size;
61 const size_t max_table_elems =
62 hpack_constants::EntriesForBytes(max_table_size);
63 // TODO(ctiller): integrate with ResourceQuota to rebuild smaller when we can.
64 if (max_table_elems > elem_size_.size()) {
65 Rebuild(static_cast<uint32_t>(
66 std::max(max_table_elems, 2 * elem_size_.size())));
67 }
68 return true;
69 }
70
EvictOne()71 void HPackEncoderTable::EvictOne() {
72 tail_remote_index_++;
73 CHECK_GT(tail_remote_index_, 0u);
74 CHECK_GT(table_elems_, 0u);
75 auto removing_size = elem_size_[tail_remote_index_ % elem_size_.size()];
76 CHECK(table_size_ >= removing_size);
77 table_size_ -= removing_size;
78 table_elems_--;
79 }
80
Rebuild(uint32_t capacity)81 void HPackEncoderTable::Rebuild(uint32_t capacity) {
82 decltype(elem_size_) new_elem_size(capacity);
83 CHECK_LE(table_elems_, capacity);
84 for (uint32_t i = 0; i < table_elems_; i++) {
85 uint32_t ofs = tail_remote_index_ + i + 1;
86 new_elem_size[ofs % capacity] = elem_size_[ofs % elem_size_.size()];
87 }
88 elem_size_.swap(new_elem_size);
89 }
90
91 } // namespace grpc_core
92