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

components/gcm_driver/crypto/message_payload_parser.h

Index: components/gcm_driver/crypto/message_payload_parser.h
diff --git a/components/gcm_driver/crypto/message_payload_parser.h b/components/gcm_driver/crypto/message_payload_parser.h
new file mode 100644
index 0000000000000000000000000000000000000000..7c6e1eedb353cb6cb0e8e13a84a8bdd38328925a
--- /dev/null
+++ b/components/gcm_driver/crypto/message_payload_parser.h
@@ -0,0 +1,85 @@
+// 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.
+
+#ifndef COMPONENTS_GCM_DRIVER_CRYPTO_MESSAGE_PAYLOAD_PARSER_H_
+#define COMPONENTS_GCM_DRIVER_CRYPTO_MESSAGE_PAYLOAD_PARSER_H_
+
+#include <stdint.h>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/strings/string_piece.h"
+
+namespace gcm {
+
+// Parses and validates the binary message payload included in messages that
+// are encrypted per draft-ietf-webpush-encryption-08:
+//
+// https://tools.ietf.org/html/draft-ietf-httpbis-encryption-encoding-08#section-2.1
+//
+// In summary, such messages start with a binary header block that includes the
+// parameters needed to decrypt the content, other than the key. All content
+// following this binary header is considered the ciphertext.
+//
+// +-----------+--------+-----------+-----------------+
+// | salt (16) | rs (4) | idlen (1) | public_key (65) |
+// +-----------+--------+-----------+-----------------+
+//
+// Specific to Web Push encryption, the `public_key` parameter of this header
+// must be set to the ECDH public key of the sender. This is a point on the
+// P-256 elliptic curve in uncompressed form, 65 bytes long starting with 0x04.
+//
+// https://tools.ietf.org/html/draft-ietf-webpush-encryption-08#section-3.1
+class MessagePayloadParser {
+ public:
+  explicit MessagePayloadParser(base::StringPiece message);
+  ~MessagePayloadParser();
+
+  // Returns whether the parser represents a valid message.
+  bool IsValid() const { return is_valid_; }
+
+  // Returns the 16-byte long salt for the message. Must only be called after
+  // validity of the message has been verified.
+  const std::string& salt() const {
+    CHECK(is_valid_);
+    return salt_;
+  }
+
+  // Returns the record size for the message. Must only be called after validity
+  // of the message has been verified.
+  uint32_t record_size() const {
+    CHECK(is_valid_);
+    return record_size_;
+  }
+
+  // Returns the sender's ECDH public key for the message. This will be a point
+  // on the P-256 elliptic curve in uncompressed form. Must only be called after
+  // validity of the message has been verified.
+  const std::string& public_key() const {
+    CHECK(is_valid_);
+    return public_key_;
+  }
+
+  // Returns the ciphertext for the message. This will be at least the size of
+  // a single record, which is 18 octets. Must only be called after validity of
+  // the message has been verified.
+  const std::string& ciphertext() const {
+    CHECK(is_valid_);
+    return ciphertext_;
+  }
+
+ private:
+  bool is_valid_ = false;
+
+  std::string salt_;
+  uint32_t record_size_ = 0;
+  std::string public_key_;
+  std::string ciphertext_;
+
+  DISALLOW_COPY_AND_ASSIGN(MessagePayloadParser);
+};
+
+}  // namespace gcm
+
+#endif  // COMPONENTS_GCM_DRIVER_CRYPTO_MESSAGE_PAYLOAD_PARSER_H_