Allow mocking of preprocessed file read

Bug: 17415692
Test: Clean build of AOSP succeeds.

Change-Id: I723031e9847b589909825736f1094e6bba039f7a
diff --git a/line_reader.cpp b/line_reader.cpp
new file mode 100644
index 0000000..82e2ace
--- /dev/null
+++ b/line_reader.cpp
@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2015, The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include "line_reader.h"
+
+#include <fstream>
+#include <sstream>
+
+using std::istringstream;
+using std::ifstream;
+using std::string;
+using std::unique_ptr;
+
+namespace android {
+namespace aidl {
+
+class FileLineReader : public LineReader {
+ public:
+  FileLineReader() = default;
+  virtual ~FileLineReader() {
+    input_stream_.close();
+  }
+
+  bool Init(const std::string& file_path) {
+    input_stream_.open(file_path, ifstream::in | ifstream::binary);
+    return input_stream_.is_open() && input_stream_.good();
+  }
+
+  bool ReadLine(string* line) override {
+    if (!input_stream_.good()) {
+      return false;
+    }
+    line->clear();
+    std::getline(input_stream_, *line);
+    return true;
+  }
+
+ private:
+  ifstream input_stream_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileLineReader);
+};  // class FileLineReader
+
+class MemoryLineReader : public LineReader {
+ public:
+  MemoryLineReader(const string& contents) : input_stream_(contents) {}
+  virtual ~MemoryLineReader() = default;
+
+  bool ReadLine(string* line) override {
+    if (!input_stream_.good()) {
+      return false;
+    }
+    line->clear();
+    std::getline(input_stream_, *line);
+    return true;
+  }
+
+ private:
+  istringstream input_stream_;
+
+  DISALLOW_COPY_AND_ASSIGN(MemoryLineReader);
+};  // class MemoryLineReader
+
+unique_ptr<LineReader> LineReader::ReadFromFile(const string& file_path) {
+  unique_ptr<FileLineReader> file_reader(new FileLineReader());
+  unique_ptr<LineReader> ret;
+  if (file_reader->Init(file_path)) {
+    ret.reset(file_reader.release());
+  }
+  return ret;
+}
+
+unique_ptr<LineReader> LineReader::ReadFromMemory(const string& contents) {
+  return unique_ptr<LineReader>(new MemoryLineReader(contents));
+}
+
+}  // namespace android
+}  // namespace aidl