Add a parser for messages with a Web Push Protocol-based payload

components/gcm_driver/crypto/message_payload_parser.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/gcm_driver/crypto/message_payload_parser.h"
+
+#include "base/big_endian.h"
+
+namespace gcm {
+
+namespace {
+
+// Size, in bytes, of the salt included in the message header.
+constexpr size_t kSaltSize = 16;
+
+// Size, in bytes, of the uncompressed point included in the message header.
+constexpr size_t kUncompressedPointSize = 65;
+
+// Size, in bytes, of the smallest allowable record_size value.
+constexpr size_t kMinimumRecordSize = 18;
+
+// Size, in bytes, of an empty message with the minimum amount of padding.
+constexpr size_t kMinimumMessageSize =
+    kSaltSize + sizeof(uint32_t) + sizeof(uint8_t) + kUncompressedPointSize +
+    kMinimumRecordSize;
+
+}  // namespace
+
+MessagePayloadParser::MessagePayloadParser(base::StringPiece message) {
+  if (message.size() < kMinimumMessageSize)
+    return;
+
+  salt_ = message.substr(0, kSaltSize).as_string();
+  message.remove_prefix(kSaltSize);
+
+  base::ReadBigEndian(message.data(), &record_size_);
+  message.remove_prefix(sizeof(record_size_));
+
+  if (record_size_ < kMinimumRecordSize)
+    return;
+
+  uint8_t public_key_length;
+  base::ReadBigEndian(message.data(), &public_key_length);
+  message.remove_prefix(sizeof(public_key_length));
+
+  if (public_key_length != kUncompressedPointSize)
+    return;
+
+  if (message[0] != 0x04)
+    return;
+
+  public_key_ = message.substr(0, kUncompressedPointSize).as_string();
+  message.remove_prefix(kUncompressedPointSize);
+
+  ciphertext_ = message.as_string();
+
+  if (ciphertext_.size() < kMinimumRecordSize)
+    return;
+
+  is_valid_ = true;
+}
+
+MessagePayloadParser::~MessagePayloadParser() = default;
+
+}  // namespace gcm