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diff --git a/src/error-handler.h b/src/error-handler.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_ERROR_HANDLER_H_
+#define WABT_ERROR_HANDLER_H_
+
+#include <string>
+
+#include "color.h"
+#include "common.h"
+
+namespace wabt {
+
+class ErrorHandler {
+ public:
+  explicit ErrorHandler(Location::Type);
+
+  virtual ~ErrorHandler() {}
+
+  // Returns true if the error was handled.
+  virtual bool OnError(const Location&,
+                       const std::string& error,
+                       const std::string& source_line,
+                       size_t source_line_column_offset) = 0;
+
+  // Helper function for binary locations.
+  bool OnError(size_t offset, const std::string& error) {
+    return OnError(Location(offset), error, std::string(), 0);
+  }
+
+  // OnError will be called with with source_line trimmed to this length.
+  virtual size_t source_line_max_length() const = 0;
+
+  std::string DefaultErrorMessage(const Color&,
+                                  const Location&,
+                                  const std::string& error,
+                                  const std::string& source_line,
+                                  size_t source_line_column_offset,
+                                  int indent);
+
+ protected:
+  Location::Type location_type_;
+};
+
+class ErrorHandlerNop : public ErrorHandler {
+ public:
+  ErrorHandlerNop();
+
+  bool OnError(const Location&,
+               const std::string& error,
+               const std::string& source_line,
+               size_t source_line_column_offset) override {
+    return false;
+  }
+
+  size_t source_line_max_length() const override { return 80; }
+};
+
+class ErrorHandlerFile : public ErrorHandler {
+ public:
+  enum class PrintHeader {
+    Never,
+    Once,
+    Always,
+  };
+
+  explicit ErrorHandlerFile(Location::Type,
+                            FILE* file = stderr,
+                            const std::string& header = std::string(),
+                            PrintHeader print_header = PrintHeader::Never,
+                            size_t source_line_max_length = 80);
+
+  bool OnError(const Location&,
+               const std::string& error,
+               const std::string& source_line,
+               size_t source_line_column_offset) override;
+
+  size_t source_line_max_length() const override {
+    return source_line_max_length_;
+  }
+
+ private:
+  void PrintErrorHeader();
+
+  FILE* file_;
+  std::string header_;
+  PrintHeader print_header_;
+  size_t source_line_max_length_;
+  Color color_;
+};
+
+class ErrorHandlerBuffer : public ErrorHandler {
+ public:
+  explicit ErrorHandlerBuffer(Location::Type,
+                              size_t source_line_max_length = 80);
+
+  bool OnError(const Location&,
+               const std::string& error,
+               const std::string& source_line,
+               size_t source_line_column_offset) override;
+
+  size_t source_line_max_length() const override {
+    return source_line_max_length_;
+  }
+
+  const std::string& buffer() const { return buffer_; }
+
+ private:
+  size_t source_line_max_length_;
+  std::string buffer_;
+  Color color_;
+};
+
+}  // namespace wabt
+
+#endif // WABT_ERROR_HANDLER_H_