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diff --git a/src/lexer-source.h b/src/lexer-source.h
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+/*
+ * Copyright 2017 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef WABT_LEXER_SOURCE_H_
+#define WABT_LEXER_SOURCE_H_
+
+#include <cstddef>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "common.h"
+#include "range.h"
+
+namespace wabt {
+
+class LexerSource {
+ public:
+  LexerSource() = default;
+  virtual ~LexerSource() {}
+  virtual std::unique_ptr<LexerSource> Clone() = 0;
+  virtual Result Tell(Offset* out_offset) = 0;
+  virtual size_t Fill(void* dest, size_t size) = 0;
+  virtual Result ReadRange(OffsetRange, std::vector<char>* out_data) = 0;
+
+  WABT_DISALLOW_COPY_AND_ASSIGN(LexerSource);
+};
+
+class LexerSourceFile : public LexerSource {
+ public:
+  explicit LexerSourceFile(const std::string& filename);
+  ~LexerSourceFile();
+
+  bool IsOpen() const { return file_ != nullptr; }
+
+  std::unique_ptr<LexerSource> Clone() override;
+  Result Tell(Offset* out_offset) override;
+  size_t Fill(void* dest, size_t size) override;
+  Result ReadRange(OffsetRange, std::vector<char>* out_data) override;
+
+ private:
+  Result Seek(Offset offset);
+
+  std::string filename_;
+  FILE* file_;
+};
+
+class LexerSourceBuffer : public LexerSource {
+ public:
+  LexerSourceBuffer(const void* data, Offset size);
+
+  std::unique_ptr<LexerSource> Clone() override;
+  Result Tell(Offset* out_offset) override;
+  size_t Fill(void* dest, size_t size) override;
+  Result ReadRange(OffsetRange, std::vector<char>* out_data) override;
+
+ private:
+  const void* data_;
+  Offset size_;
+  Offset read_offset_;
+};
+
+}  // namespace wabt
+
+#endif  // WABT_LEXER_SOURCE_H_