1 /*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "src/ipc/buffered_frame_deserializer.h"
18
19 #include <inttypes.h>
20
21 #include <algorithm>
22 #include <type_traits>
23 #include <utility>
24
25 #include "google/protobuf/io/zero_copy_stream_impl_lite.h"
26 #include "perfetto/base/logging.h"
27 #include "perfetto/base/utils.h"
28
29 #include "src/ipc/wire_protocol.pb.h"
30
31 namespace perfetto {
32 namespace ipc {
33
34 namespace {
35
36 // The header is just the number of bytes of the Frame protobuf message.
37 constexpr size_t kHeaderSize = sizeof(uint32_t);
38 } // namespace
39
BufferedFrameDeserializer(size_t max_capacity)40 BufferedFrameDeserializer::BufferedFrameDeserializer(size_t max_capacity)
41 : capacity_(max_capacity) {
42 PERFETTO_CHECK(max_capacity % base::kPageSize == 0);
43 PERFETTO_CHECK(max_capacity > base::kPageSize);
44 }
45
46 BufferedFrameDeserializer::~BufferedFrameDeserializer() = default;
47
48 BufferedFrameDeserializer::ReceiveBuffer
BeginReceive()49 BufferedFrameDeserializer::BeginReceive() {
50 // Upon the first recv initialize the buffer to the max message size but
51 // release the physical memory for all but the first page. The kernel will
52 // automatically give us physical pages back as soon as we page-fault on them.
53 if (!buf_.IsValid()) {
54 PERFETTO_DCHECK(size_ == 0);
55 // TODO(eseckler): Don't commit all of the buffer at once on Windows.
56 buf_ = base::PagedMemory::Allocate(capacity_);
57
58 // Surely we are going to use at least the first page, but we may not need
59 // the rest for a bit.
60 buf_.AdviseDontNeed(buf() + base::kPageSize, capacity_ - base::kPageSize);
61 }
62
63 PERFETTO_CHECK(capacity_ > size_);
64 return ReceiveBuffer{buf() + size_, capacity_ - size_};
65 }
66
EndReceive(size_t recv_size)67 bool BufferedFrameDeserializer::EndReceive(size_t recv_size) {
68 PERFETTO_CHECK(recv_size + size_ <= capacity_);
69 size_ += recv_size;
70
71 // At this point the contents buf_ can contain:
72 // A) Only a fragment of the header (the size of the frame). E.g.,
73 // 03 00 00 (the header is 4 bytes, one is missing).
74 //
75 // B) A header and a part of the frame. E.g.,
76 // 05 00 00 00 11 22 33
77 // [ header, size=5 ] [ Partial frame ]
78 //
79 // C) One or more complete header+frame. E.g.,
80 // 05 00 00 00 11 22 33 44 55 03 00 00 00 AA BB CC
81 // [ header, size=5 ] [ Whole frame ] [ header, size=3 ] [ Whole frame ]
82 //
83 // D) Some complete header+frame(s) and a partial header or frame (C + A/B).
84 //
85 // C Is the more likely case and the one we are optimizing for. A, B, D can
86 // happen because of the streaming nature of the socket.
87 // The invariant of this function is that, when it returns, buf_ is either
88 // empty (we drained all the complete frames) or starts with the header of the
89 // next, still incomplete, frame.
90
91 size_t consumed_size = 0;
92 for (;;) {
93 if (size_ < consumed_size + kHeaderSize)
94 break; // Case A, not enough data to read even the header.
95
96 // Read the header into |payload_size|.
97 uint32_t payload_size = 0;
98 const char* rd_ptr = buf() + consumed_size;
99 memcpy(base::AssumeLittleEndian(&payload_size), rd_ptr, kHeaderSize);
100
101 // Saturate the |payload_size| to prevent overflows. The > capacity_ check
102 // below will abort the parsing.
103 size_t next_frame_size =
104 std::min(static_cast<size_t>(payload_size), capacity_);
105 next_frame_size += kHeaderSize;
106 rd_ptr += kHeaderSize;
107
108 if (size_ < consumed_size + next_frame_size) {
109 // Case B. We got the header but not the whole frame.
110 if (next_frame_size > capacity_) {
111 // The caller is expected to shut down the socket and give up at this
112 // point. If it doesn't do that and insists going on at some point it
113 // will hit the capacity check in BeginReceive().
114 PERFETTO_DLOG("Frame too large (size %zu)", next_frame_size);
115 return false;
116 }
117 break;
118 }
119
120 // Case C. We got at least one header and whole frame.
121 DecodeFrame(rd_ptr, payload_size);
122 consumed_size += next_frame_size;
123 }
124
125 PERFETTO_DCHECK(consumed_size <= size_);
126 if (consumed_size > 0) {
127 // Shift out the consumed data from the buffer. In the typical case (C)
128 // there is nothing to shift really, just setting size_ = 0 is enough.
129 // Shifting is only for the (unlikely) case D.
130 size_ -= consumed_size;
131 if (size_ > 0) {
132 // Case D. We consumed some frames but there is a leftover at the end of
133 // the buffer. Shift out the consumed bytes, so that on the next round
134 // |buf_| starts with the header of the next unconsumed frame.
135 const char* move_begin = buf() + consumed_size;
136 PERFETTO_CHECK(move_begin > buf());
137 PERFETTO_CHECK(move_begin + size_ <= buf() + capacity_);
138 memmove(buf(), move_begin, size_);
139 }
140 // If we just finished decoding a large frame that used more than one page,
141 // release the extra memory in the buffer. Large frames should be quite
142 // rare.
143 if (consumed_size > base::kPageSize) {
144 size_t size_rounded_up = (size_ / base::kPageSize + 1) * base::kPageSize;
145 if (size_rounded_up < capacity_) {
146 char* madvise_begin = buf() + size_rounded_up;
147 const size_t madvise_size = capacity_ - size_rounded_up;
148 PERFETTO_CHECK(madvise_begin > buf() + size_);
149 PERFETTO_CHECK(madvise_begin + madvise_size <= buf() + capacity_);
150 buf_.AdviseDontNeed(madvise_begin, madvise_size);
151 }
152 }
153 }
154 // At this point |size_| == 0 for case C, > 0 for cases A, B, D.
155 return true;
156 }
157
PopNextFrame()158 std::unique_ptr<Frame> BufferedFrameDeserializer::PopNextFrame() {
159 if (decoded_frames_.empty())
160 return nullptr;
161 std::unique_ptr<Frame> frame = std::move(decoded_frames_.front());
162 decoded_frames_.pop_front();
163 return frame;
164 }
165
DecodeFrame(const char * data,size_t size)166 void BufferedFrameDeserializer::DecodeFrame(const char* data, size_t size) {
167 if (size == 0)
168 return;
169 std::unique_ptr<Frame> frame(new Frame);
170 const int sz = static_cast<int>(size);
171 ::google::protobuf::io::ArrayInputStream stream(data, sz);
172 if (frame->ParseFromBoundedZeroCopyStream(&stream, sz))
173 decoded_frames_.push_back(std::move(frame));
174 }
175
176 // static
Serialize(const Frame & frame)177 std::string BufferedFrameDeserializer::Serialize(const Frame& frame) {
178 std::string buf;
179 buf.reserve(1024); // Just an educated guess to avoid trivial expansions.
180 buf.insert(0, kHeaderSize, 0); // Reserve the space for the header.
181 frame.AppendToString(&buf);
182 const uint32_t payload_size = static_cast<uint32_t>(buf.size() - kHeaderSize);
183 PERFETTO_DCHECK(payload_size == static_cast<uint32_t>(frame.GetCachedSize()));
184 // Don't send messages larger than what the receiver can handle.
185 PERFETTO_DCHECK(kHeaderSize + payload_size <= kIPCBufferSize);
186 char header[kHeaderSize];
187 memcpy(header, base::AssumeLittleEndian(&payload_size), kHeaderSize);
188 buf.replace(0, kHeaderSize, header, kHeaderSize);
189 return buf;
190 }
191
192 } // namespace ipc
193 } // namespace perfetto
194