Add a new incremental parsing API

Change-Id: I6b921766836d58df0281fb23b2add3f62a478e14

webm_parser/src/block_header_parser.h

@@ -0,0 +1,63 @@
+// Copyright (c) 2016 The WebM project authors. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS.  All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+#ifndef SRC_BLOCK_HEADER_PARSER_H_
+#define SRC_BLOCK_HEADER_PARSER_H_
+
+#include <cassert>
+#include <cstdint>
+
+#include "src/parser.h"
+#include "src/var_int_parser.h"
+#include "webm/callback.h"
+#include "webm/reader.h"
+#include "webm/status.h"
+
+namespace webm {
+
+struct BlockHeader {
+  std::uint64_t track_number;
+  std::int16_t timecode;
+  std::uint8_t flags;
+
+  bool operator==(const BlockHeader& other) const {
+    return track_number == other.track_number && timecode == other.timecode &&
+           flags == other.flags;
+  }
+};
+
+class BlockHeaderParser : public Parser {
+ public:
+  Status Feed(Callback* callback, Reader* reader,
+              std::uint64_t* num_bytes_read) override;
+
+  // Gets the parsed block header information. This must not be called until the
+  // parse has been successfully completed.
+  const BlockHeader& value() const {
+    assert(state_ == State::kDone);
+    return value_;
+  }
+
+ private:
+  BlockHeader value_;
+
+  VarIntParser uint_parser_;
+
+  int timecode_bytes_remaining_ = 2;
+
+  enum class State {
+    // State                 Transitions to state  When
+    kReadingTrackNumber,  // kReadingTimecode      track parsed
+    kReadingTimecode,     // kReadingFlags         timecode parsed
+    kReadingFlags,        // kDone                 flags parsed
+    kDone,                // No transitions from here (must call Init)
+  } state_ = State::kReadingTrackNumber;
+};
+
+}  // namespace webm
+
+#endif  // SRC_BLOCK_HEADER_PARSER_H_