Alexei Frolov | dea46f7 | 2020-01-07 13:28:24 -0800 | [diff] [blame^] | 1 | // Copyright 2020 The Pigweed Authors |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); you may not |
| 4 | // use this file except in compliance with the License. You may obtain a copy of |
| 5 | // the License at |
| 6 | // |
| 7 | // https://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, WITHOUT |
| 11 | // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| 12 | // License for the specific language governing permissions and limitations under |
| 13 | // the License. |
| 14 | |
| 15 | #include "pw_protobuf/decoder.h" |
| 16 | |
| 17 | #include "pw_varint/varint.h" |
| 18 | |
| 19 | namespace pw::protobuf { |
| 20 | |
| 21 | Status Decoder::Decode(span<const std::byte> proto) { |
| 22 | if (handler_ == nullptr || state_ != kReady) { |
| 23 | return Status::FAILED_PRECONDITION; |
| 24 | } |
| 25 | |
| 26 | state_ = kDecodeInProgress; |
| 27 | proto_ = proto; |
| 28 | |
| 29 | // Iterate over each field in the proto, calling the handler with the field |
| 30 | // key. |
| 31 | while (state_ == kDecodeInProgress && !proto_.empty()) { |
| 32 | const std::byte* original_cursor = proto_.data(); |
| 33 | |
| 34 | uint64_t key; |
| 35 | size_t bytes_read = varint::Decode(proto_, &key); |
| 36 | if (bytes_read == 0) { |
| 37 | state_ = kDecodeFailed; |
| 38 | return Status::DATA_LOSS; |
| 39 | } |
| 40 | |
| 41 | uint32_t field_number = key >> kFieldNumberShift; |
| 42 | Status status = handler_->ProcessField(this, field_number); |
| 43 | if (!status.ok()) { |
| 44 | return status; |
| 45 | } |
| 46 | |
| 47 | // The callback function can modify the decoder's state; check that |
| 48 | // everything is still okay. |
| 49 | if (state_ == kDecodeFailed) { |
| 50 | break; |
| 51 | } |
| 52 | |
| 53 | // If the cursor has not moved, the user has not consumed the field in their |
| 54 | // callback. Skip ahead to the next field. |
| 55 | if (original_cursor == proto_.data()) { |
| 56 | SkipField(); |
| 57 | } |
| 58 | } |
| 59 | |
| 60 | if (state_ != kDecodeInProgress) { |
| 61 | return Status::DATA_LOSS; |
| 62 | } |
| 63 | |
| 64 | state_ = kReady; |
| 65 | return Status::OK; |
| 66 | } |
| 67 | |
| 68 | Status Decoder::ReadVarint(uint32_t field_number, uint64_t* out) { |
| 69 | if (state_ != kDecodeInProgress) { |
| 70 | return Status::FAILED_PRECONDITION; |
| 71 | } |
| 72 | |
| 73 | uint64_t key; |
| 74 | size_t bytes_read = varint::Decode(proto_, &key); |
| 75 | if (bytes_read == 0) { |
| 76 | state_ = kDecodeFailed; |
| 77 | return Status::FAILED_PRECONDITION; |
| 78 | } |
| 79 | |
| 80 | uint32_t field = key >> kFieldNumberShift; |
| 81 | WireType wire_type = static_cast<WireType>(key & kWireTypeMask); |
| 82 | |
| 83 | if (field != field_number || wire_type != WireType::kVarint) { |
| 84 | state_ = kDecodeFailed; |
| 85 | return Status::FAILED_PRECONDITION; |
| 86 | } |
| 87 | |
| 88 | // Advance to the varint value. |
| 89 | proto_ = proto_.subspan(bytes_read); |
| 90 | |
| 91 | bytes_read = varint::Decode(proto_, out); |
| 92 | if (bytes_read == 0) { |
| 93 | state_ = kDecodeFailed; |
| 94 | return Status::DATA_LOSS; |
| 95 | } |
| 96 | |
| 97 | // Advance to the next field. |
| 98 | proto_ = proto_.subspan(bytes_read); |
| 99 | return Status::OK; |
| 100 | } |
| 101 | |
| 102 | void Decoder::SkipField() { |
| 103 | uint64_t key; |
| 104 | proto_ = proto_.subspan(varint::Decode(proto_, &key)); |
| 105 | |
| 106 | WireType wire_type = static_cast<WireType>(key & kWireTypeMask); |
| 107 | size_t bytes_to_skip = 0; |
| 108 | uint64_t value = 0; |
| 109 | |
| 110 | switch (wire_type) { |
| 111 | case WireType::kVarint: |
| 112 | bytes_to_skip = varint::Decode(proto_, &value); |
| 113 | break; |
| 114 | |
| 115 | case WireType::kDelimited: |
| 116 | // Varint at cursor indicates size of the field. |
| 117 | bytes_to_skip += varint::Decode(proto_, &value); |
| 118 | bytes_to_skip += value; |
| 119 | break; |
| 120 | |
| 121 | case WireType::kFixed32: |
| 122 | bytes_to_skip = sizeof(uint32_t); |
| 123 | break; |
| 124 | |
| 125 | case WireType::kFixed64: |
| 126 | bytes_to_skip = sizeof(uint64_t); |
| 127 | break; |
| 128 | } |
| 129 | |
| 130 | if (bytes_to_skip == 0) { |
| 131 | state_ = kDecodeFailed; |
| 132 | } else { |
| 133 | proto_ = proto_.subspan(bytes_to_skip); |
| 134 | } |
| 135 | } |
| 136 | |
| 137 | } // namespace pw::protobuf |