Switch over to the google3 unix_file File*.

I also moved macros.h to base/macros.h to ease google3 porting, at
the expense of a larger than necessary change. (I learned my lesson,
though, and didn't make the equivalent base/logging.h change.)

I'm not sure whether we want to keep the unix_file MappedFile given
our existing MemMap, but it's easier to bring it over and then remove
it (and possibly revert the removal) than to bring it over later.

Change-Id: Id50a66faa5ab17b9bc936cc9043dbc26f791f0ca
diff --git a/src/base/unix_file/README b/src/base/unix_file/README
new file mode 100644
index 0000000..e9aec22
--- /dev/null
+++ b/src/base/unix_file/README
@@ -0,0 +1,15 @@
+A simple C++ wrapper for Unix file I/O.
+
+This is intended to be lightweight and easy to use, similar to Java's
+RandomAccessFile and related classes. The usual C++ idioms of RAII and "you
+don't pay for what you don't use" apply.
+
+In particular, the basic RandomAccessFile interface is kept small and simple so
+it's trivial to add new implementations.
+
+This code will not log, because it can't know whether that's appropriate in
+your application.
+
+This code will, in general, return -errno on failure. If an operation consisted
+of multiple sub-operations, it will return the errno corresponding to the most
+relevant operation.
diff --git a/src/base/unix_file/fd_file.cc b/src/base/unix_file/fd_file.cc
new file mode 100644
index 0000000..73130a3
--- /dev/null
+++ b/src/base/unix_file/fd_file.cc
@@ -0,0 +1,134 @@
+/*
+ * Copyright (C) 2009 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 "base/unix_file/fd_file.h"
+#include <errno.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include "logging.h"
+
+namespace unix_file {
+
+FdFile::FdFile() : fd_(-1), auto_close_(true) {
+}
+
+FdFile::FdFile(int fd) : fd_(fd), auto_close_(true) {
+}
+
+FdFile::FdFile(int fd, const std::string& path) : fd_(fd), file_path_(path), auto_close_(true) {
+}
+
+FdFile::~FdFile() {
+  if (auto_close_ && fd_ != -1) {
+    Close();
+  }
+}
+
+void FdFile::DisableAutoClose() {
+  auto_close_ = false;
+}
+
+bool FdFile::Open(const std::string& path, int flags) {
+  return Open(path, flags, 0640);
+}
+
+bool FdFile::Open(const std::string& path, int flags, mode_t mode) {
+  CHECK_EQ(fd_, -1) << path;
+  fd_ = TEMP_FAILURE_RETRY(open(path.c_str(), flags, mode));
+  if (fd_ == -1) {
+    return false;
+  }
+  file_path_ = path;
+  return true;
+}
+
+int FdFile::Close() {
+  int result = TEMP_FAILURE_RETRY(close(fd_));
+  if (result == -1) {
+    return -errno;
+  } else {
+    fd_ = -1;
+    file_path_ = "";
+    return 0;
+  }
+}
+
+int FdFile::Flush() {
+  int rc = TEMP_FAILURE_RETRY(fdatasync(fd_));
+  return (rc == -1) ? -errno : rc;
+}
+
+int64_t FdFile::Read(char* buf, int64_t byte_count, int64_t offset) const {
+  int rc = TEMP_FAILURE_RETRY(pread64(fd_, buf, byte_count, offset));
+  return (rc == -1) ? -errno : rc;
+}
+
+int FdFile::SetLength(int64_t new_length) {
+  int rc = TEMP_FAILURE_RETRY(ftruncate64(fd_, new_length));
+  return (rc == -1) ? -errno : rc;
+}
+
+int64_t FdFile::GetLength() const {
+  struct stat s;
+  int rc = TEMP_FAILURE_RETRY(fstat(fd_, &s));
+  return (rc == -1) ? -errno : s.st_size;
+}
+
+int64_t FdFile::Write(const char* buf, int64_t byte_count, int64_t offset) {
+  int rc = TEMP_FAILURE_RETRY(pwrite64(fd_, buf, byte_count, offset));
+  return (rc == -1) ? -errno : rc;
+}
+
+int FdFile::Fd() const {
+  return fd_;
+}
+
+bool FdFile::IsOpened() const {
+  return fd_ >= 0;
+}
+
+std::string FdFile::GetPath() const {
+  return file_path_;
+}
+
+bool FdFile::ReadFully(void* buffer, int64_t byte_count) {
+  char* ptr = static_cast<char*>(buffer);
+  while (byte_count > 0) {
+    int bytes_read = TEMP_FAILURE_RETRY(read(fd_, ptr, byte_count));
+    if (bytes_read <= 0) {
+      return false;
+    }
+    byte_count -= bytes_read;  // Reduce the number of remaining bytes.
+    ptr += bytes_read;  // Move the buffer forward.
+  }
+  return true;
+}
+
+bool FdFile::WriteFully(const void* buffer, int64_t byte_count) {
+  const char* ptr = static_cast<const char*>(buffer);
+  while (byte_count > 0) {
+    int bytes_read = TEMP_FAILURE_RETRY(write(fd_, ptr, byte_count));
+    if (bytes_read < 0) {
+      return false;
+    }
+    byte_count -= bytes_read;  // Reduce the number of remaining bytes.
+    ptr += bytes_read;  // Move the buffer forward.
+  }
+  return true;
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/fd_file.h b/src/base/unix_file/fd_file.h
new file mode 100644
index 0000000..2b33961
--- /dev/null
+++ b/src/base/unix_file/fd_file.h
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2009 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.
+ */
+
+#ifndef BASE_UNIX_FILE_FD_FILE_H_
+#define BASE_UNIX_FILE_FD_FILE_H_
+
+#include <fcntl.h>
+#include <string>
+#include "base/unix_file/random_access_file.h"
+#include "base/macros.h"
+
+namespace unix_file {
+
+// A RandomAccessFile implementation backed by a file descriptor.
+//
+// Not thread safe.
+class FdFile : public RandomAccessFile {
+ public:
+  FdFile();
+  // Creates an FdFile using the given file descriptor. Takes ownership of the
+  // file descriptor. (Use DisableAutoClose to retain ownership.)
+  explicit FdFile(int fd);
+  explicit FdFile(int fd, const std::string& path);
+
+  // Destroys an FdFile, closing the file descriptor if Close hasn't already
+  // been called. (If you care about the return value of Close, call it
+  // yourself; this is meant to handle failure cases and read-only accesses.
+  // Note though that calling Close and checking its return value is still no
+  // guarantee that data actually made it to stable storage.)
+  virtual ~FdFile();
+
+  // Opens file 'file_path' using 'flags' and 'mode'.
+  bool Open(const std::string& file_path, int flags);
+  bool Open(const std::string& file_path, int flags, mode_t mode);
+
+  // RandomAccessFile API.
+  virtual int Close();
+  virtual int64_t Read(char* buf, int64_t byte_count, int64_t offset) const;
+  virtual int SetLength(int64_t new_length);
+  virtual int64_t GetLength() const;
+  virtual int64_t Write(const char* buf, int64_t byte_count, int64_t offset);
+  virtual int Flush();
+
+  // Bonus API.
+  int Fd() const;
+  bool IsOpened() const;
+  std::string GetPath() const;
+  void DisableAutoClose();
+  bool ReadFully(void* buffer, int64_t byte_count);
+  bool WriteFully(const void* buffer, int64_t byte_count);
+
+ private:
+  int fd_;
+  std::string file_path_;
+  bool auto_close_;
+
+  DISALLOW_COPY_AND_ASSIGN(FdFile);
+};
+
+}  // namespace unix_file
+
+#endif  // BASE_UNIX_FILE_FD_FILE_H_
diff --git a/src/base/unix_file/fd_file_test.cc b/src/base/unix_file/fd_file_test.cc
new file mode 100644
index 0000000..d620666
--- /dev/null
+++ b/src/base/unix_file/fd_file_test.cc
@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2009 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 "base/unix_file/fd_file.h"
+#include "base/unix_file/random_access_file_test.h"
+#include "gtest/gtest.h"
+
+namespace unix_file {
+
+class FdFileTest : public RandomAccessFileTest {
+ protected:
+  virtual RandomAccessFile* MakeTestFile() {
+    return new FdFile(fileno(tmpfile()));
+  }
+};
+
+TEST_F(FdFileTest, Read) {
+  TestRead();
+}
+
+TEST_F(FdFileTest, SetLength) {
+  TestSetLength();
+}
+
+TEST_F(FdFileTest, Write) {
+  TestWrite();
+}
+
+TEST_F(FdFileTest, UnopenedFile) {
+  FdFile file;
+  EXPECT_EQ(-1, file.Fd());
+  EXPECT_FALSE(file.IsOpened());
+  EXPECT_TRUE(file.GetPath().empty());
+}
+
+TEST_F(FdFileTest, OpenClose) {
+  std::string good_path(GetTmpPath("some-file.txt"));
+  FdFile file;
+  ASSERT_TRUE(file.Open(good_path, O_CREAT | O_WRONLY));
+  EXPECT_GE(file.Fd(), 0);
+  EXPECT_TRUE(file.IsOpened());
+  EXPECT_EQ(0, file.Close());
+  EXPECT_EQ(-1, file.Fd());
+  EXPECT_FALSE(file.IsOpened());
+  EXPECT_TRUE(file.Open(good_path,  O_RDONLY));
+  EXPECT_GE(file.Fd(), 0);
+  EXPECT_TRUE(file.IsOpened());
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/mapped_file.cc b/src/base/unix_file/mapped_file.cc
new file mode 100644
index 0000000..84629b3
--- /dev/null
+++ b/src/base/unix_file/mapped_file.cc
@@ -0,0 +1,162 @@
+/*
+ * Copyright (C) 2008 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 "base/unix_file/mapped_file.h"
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <algorithm>
+#include <string>
+#include "logging.h"
+
+namespace unix_file {
+
+MappedFile::~MappedFile() {
+}
+
+int MappedFile::Close() {
+  if (IsMapped()) {
+    Unmap();
+  }
+  return FdFile::Close();
+}
+
+bool MappedFile::MapReadOnly() {
+  CHECK(IsOpened());
+  CHECK(!IsMapped());
+  struct stat st;
+  int result = TEMP_FAILURE_RETRY(fstat(Fd(), &st));
+  if (result == -1) {
+    PLOG(WARNING) << "Failed to stat file '" << GetPath() << "'";
+    return false;
+  }
+  file_size_ = st.st_size;
+  do {
+    mapped_file_ = mmap(NULL, file_size_, PROT_READ, MAP_PRIVATE, Fd(), 0);
+  } while (mapped_file_ == MAP_FAILED && errno == EINTR);
+  if (mapped_file_ == MAP_FAILED) {
+    PLOG(WARNING) << "Failed to mmap file '" << GetPath() << "' of size "
+                  << file_size_ << " bytes to memory";
+    return false;
+  }
+  map_mode_ = kMapReadOnly;
+  return true;
+}
+
+bool MappedFile::MapReadWrite(int64_t file_size) {
+  CHECK(IsOpened());
+  CHECK(!IsMapped());
+  int result = TEMP_FAILURE_RETRY(ftruncate64(Fd(), file_size));
+  if (result == -1) {
+    PLOG(ERROR) << "Failed to truncate file '" << GetPath()
+                << "' to size " << file_size;
+    return false;
+  }
+  file_size_ = file_size;
+  do {
+    mapped_file_ =
+        mmap(NULL, file_size_, PROT_READ | PROT_WRITE, MAP_SHARED, Fd(), 0);
+  } while (mapped_file_ == MAP_FAILED && errno == EINTR);
+  if (mapped_file_ == MAP_FAILED) {
+    PLOG(WARNING) << "Failed to mmap file '" << GetPath() << "' of size "
+                  << file_size_ << " bytes to memory";
+    return false;
+  }
+  map_mode_ = kMapReadWrite;
+  return true;
+}
+
+bool MappedFile::Unmap() {
+  CHECK(IsMapped());
+  int result = TEMP_FAILURE_RETRY(munmap(mapped_file_, file_size_));
+  if (result == -1) {
+    PLOG(WARNING) << "Failed unmap file '" << GetPath() << "' of size "
+                  << file_size_;
+    return false;
+  } else {
+    mapped_file_ = NULL;
+    file_size_ = -1;
+    return true;
+  }
+}
+
+int64_t MappedFile::Read(char* buf, int64_t byte_count, int64_t offset) const {
+  if (IsMapped()) {
+    if (offset < 0) {
+      errno = EINVAL;
+      return -errno;
+    }
+    int64_t read_size = std::max(0LL, std::min(byte_count, file_size_ - offset));
+    if (read_size > 0) {
+      memcpy(buf, data() + offset, read_size);
+    }
+    return read_size;
+  } else {
+    return FdFile::Read(buf, byte_count, offset);
+  }
+}
+
+int MappedFile::SetLength(int64_t new_length) {
+  CHECK(!IsMapped());
+  return FdFile::SetLength(new_length);
+}
+
+int64_t MappedFile::GetLength() const {
+  if (IsMapped()) {
+    return file_size_;
+  } else {
+    return FdFile::GetLength();
+  }
+}
+
+int MappedFile::Flush() {
+  int rc = IsMapped() ? TEMP_FAILURE_RETRY(msync(mapped_file_, file_size_, 0)) : FdFile::Flush();
+  return rc == -1 ? -errno : 0;
+}
+
+int64_t MappedFile::Write(const char* buf, int64_t byte_count, int64_t offset) {
+  if (IsMapped()) {
+    CHECK_EQ(kMapReadWrite, map_mode_);
+    if (offset < 0) {
+      errno = EINVAL;
+      return -errno;
+    }
+    int64_t write_size = std::max(0LL, std::min(byte_count, file_size_ - offset));
+    if (write_size > 0) {
+      memcpy(data() + offset, buf, write_size);
+    }
+    return write_size;
+  } else {
+    return FdFile::Write(buf, byte_count, offset);
+  }
+}
+
+int64_t MappedFile::size() const {
+  return GetLength();
+}
+
+bool MappedFile::IsMapped() const {
+  return mapped_file_ != NULL && mapped_file_ != MAP_FAILED;
+}
+
+char* MappedFile::data() const {
+  CHECK(IsMapped());
+  return static_cast<char*>(mapped_file_);
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/mapped_file.h b/src/base/unix_file/mapped_file.h
new file mode 100644
index 0000000..161100b
--- /dev/null
+++ b/src/base/unix_file/mapped_file.h
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2008 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.
+ */
+
+#ifndef BASE_UNIX_FILE_MAPPED_FILE_H_
+#define BASE_UNIX_FILE_MAPPED_FILE_H_
+
+#include <fcntl.h>
+#include <string>
+#include "base/unix_file/fd_file.h"
+
+namespace unix_file {
+
+// Random access file which handles an mmap(2), munmap(2) pair in C++
+// RAII style. When a file is mmapped, the random access file
+// interface accesses the mmapped memory directly; otherwise, the
+// standard file I/O is used. Whenever a function fails, it returns
+// false and errno is set to the corresponding error code.
+class MappedFile : public FdFile {
+ public:
+  // File modes used in Open().
+  enum FileMode {
+    kReadOnlyMode = O_RDONLY | O_LARGEFILE,
+    kReadWriteMode = O_CREAT | O_RDWR | O_LARGEFILE,
+  };
+
+  MappedFile() : FdFile(), file_size_(-1), mapped_file_(NULL) {
+  }
+  // Creates a MappedFile using the given file descriptor. Takes ownership of
+  // the file descriptor.
+  explicit MappedFile(int fd) : FdFile(fd), file_size_(-1), mapped_file_(NULL) {
+  }
+
+  // Unmaps and closes the file if needed.
+  virtual ~MappedFile();
+
+  // Maps an opened file to memory in the read-only mode.
+  bool MapReadOnly();
+
+  // Maps an opened file to memory in the read-write mode. Before the
+  // file is mapped, it is truncated to 'file_size' bytes.
+  bool MapReadWrite(int64_t file_size);
+
+  // Unmaps a mapped file so that, e.g., SetLength() may be invoked.
+  bool Unmap();
+
+  // RandomAccessFile API.
+  // The functions below require that the file is open, but it doesn't
+  // have to be mapped.
+  virtual int Close();
+  virtual int64_t Read(char* buf, int64_t byte_count, int64_t offset) const;
+  // SetLength() requires that the file is not mmapped.
+  virtual int SetLength(int64_t new_length);
+  virtual int64_t GetLength() const;
+  virtual int Flush();
+  // Write() requires that, if the file is mmapped, it is mmapped in
+  // the read-write mode. Writes past the end of file are discarded.
+  virtual int64_t Write(const char* buf, int64_t byte_count, int64_t offset);
+
+  // A convenience method equivalent to GetLength().
+  int64_t size() const;
+
+  // Returns true if the file has been mmapped.
+  bool IsMapped() const;
+
+  // Returns a pointer to the start of the memory mapping once the
+  // file is successfully mapped; crashes otherwise.
+  char* data() const;
+
+ private:
+  enum MapMode {
+    kMapReadOnly = 1,
+    kMapReadWrite = 2,
+  };
+
+  mutable int64_t file_size_;  // May be updated in GetLength().
+  void* mapped_file_;
+  MapMode map_mode_;
+
+  DISALLOW_COPY_AND_ASSIGN(MappedFile);
+};
+
+}  // namespace unix_file
+
+#endif  // BASE_UNIX_FILE_MAPPED_FILE_H_
diff --git a/src/base/unix_file/mapped_file_test.cc b/src/base/unix_file/mapped_file_test.cc
new file mode 100644
index 0000000..f61ed3b
--- /dev/null
+++ b/src/base/unix_file/mapped_file_test.cc
@@ -0,0 +1,265 @@
+/*
+ * Copyright (C) 2008 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 "base/unix_file/mapped_file.h"
+#include "base/unix_file/fd_file.h"
+#include "base/unix_file/random_access_file_test.h"
+#include "base/unix_file/random_access_file_utils.h"
+#include "base/unix_file/string_file.h"
+#include "gtest/gtest.h"
+#include "logging.h"
+
+namespace unix_file {
+
+class MappedFileTest : public RandomAccessFileTest {
+ protected:
+  MappedFileTest() : kContent("some content") {
+  }
+
+  void SetUp() {
+    art::CommonTest::SetEnvironmentVariables(android_data_);
+
+    good_path_ = GetTmpPath("some-file.txt");
+    int fd = TEMP_FAILURE_RETRY(open(good_path_.c_str(), O_CREAT|O_RDWR, 0666));
+    FdFile dst(fd);
+
+    StringFile src;
+    src.Assign(kContent);
+
+    ASSERT_TRUE(CopyFile(src, &dst));
+  }
+
+  virtual RandomAccessFile* MakeTestFile() {
+    TEMP_FAILURE_RETRY(truncate(good_path_.c_str(), 0));
+    MappedFile* f = new MappedFile;
+    CHECK(f->Open(good_path_, MappedFile::kReadWriteMode));
+    return f;
+  }
+
+  const std::string kContent;
+  std::string good_path_;
+};
+
+TEST_F(MappedFileTest, OkayToNotUse) {
+  MappedFile file;
+  EXPECT_EQ(-1, file.Fd());
+  EXPECT_FALSE(file.IsOpened());
+  EXPECT_FALSE(file.IsMapped());
+}
+
+TEST_F(MappedFileTest, OpenClose) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  EXPECT_GE(file.Fd(), 0);
+  EXPECT_TRUE(file.IsOpened());
+  EXPECT_EQ(kContent.size(), file.size());
+  EXPECT_EQ(0, file.Close());
+  EXPECT_EQ(-1, file.Fd());
+  EXPECT_FALSE(file.IsOpened());
+}
+
+TEST_F(MappedFileTest, OpenFdClose) {
+  FILE* f = tmpfile();
+  ASSERT_TRUE(f != NULL);
+  MappedFile file(fileno(f));
+  EXPECT_GE(file.Fd(), 0);
+  EXPECT_TRUE(file.IsOpened());
+  EXPECT_EQ(0, file.Close());
+}
+
+TEST_F(MappedFileTest, CanUseAfterMapReadOnly) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  EXPECT_FALSE(file.IsMapped());
+  EXPECT_TRUE(file.MapReadOnly());
+  EXPECT_TRUE(file.IsMapped());
+  EXPECT_EQ(kContent.size(), file.size());
+  ASSERT_TRUE(file.data());
+  EXPECT_EQ(0, memcmp(kContent.c_str(), file.data(), file.size()));
+  EXPECT_EQ(0, file.Flush());
+}
+
+TEST_F(MappedFileTest, CanUseAfterMapReadWrite) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadWriteMode));
+  EXPECT_FALSE(file.IsMapped());
+  EXPECT_TRUE(file.MapReadWrite(1));
+  EXPECT_TRUE(file.IsMapped());
+  EXPECT_EQ(1, file.size());
+  ASSERT_TRUE(file.data());
+  EXPECT_EQ(kContent[0], *file.data());
+  EXPECT_EQ(0, file.Flush());
+}
+
+TEST_F(MappedFileTest, CanWriteNewData) {
+  const std::string new_path(GetTmpPath("new-file.txt"));
+  ASSERT_EQ(-1, unlink(new_path.c_str()));
+  ASSERT_EQ(ENOENT, errno);
+
+  MappedFile file;
+  ASSERT_TRUE(file.Open(new_path, MappedFile::kReadWriteMode));
+  EXPECT_TRUE(file.MapReadWrite(kContent.size()));
+  EXPECT_TRUE(file.IsMapped());
+  EXPECT_EQ(kContent.size(), file.size());
+  ASSERT_TRUE(file.data());
+  memcpy(file.data(), kContent.c_str(), kContent.size());
+  EXPECT_EQ(0, file.Close());
+  EXPECT_FALSE(file.IsMapped());
+
+  FdFile new_file(TEMP_FAILURE_RETRY(open(new_path.c_str(), O_RDONLY)));
+  StringFile buffer;
+  ASSERT_TRUE(CopyFile(new_file, &buffer));
+  EXPECT_EQ(kContent, buffer.ToStringPiece());
+  EXPECT_EQ(0, unlink(new_path.c_str()));
+}
+
+TEST_F(MappedFileTest, FileMustExist) {
+  const std::string bad_path(GetTmpPath("does-not-exist.txt"));
+  MappedFile file;
+  EXPECT_FALSE(file.Open(bad_path, MappedFile::kReadOnlyMode));
+  EXPECT_EQ(-1, file.Fd());
+}
+
+TEST_F(MappedFileTest, FileMustBeWritable) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  EXPECT_FALSE(file.MapReadWrite(10));
+}
+
+TEST_F(MappedFileTest, RemappingAllowedUntilSuccess) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  EXPECT_FALSE(file.MapReadWrite(10));
+  EXPECT_FALSE(file.MapReadWrite(10));
+}
+
+TEST_F(MappedFileTest, ResizeMappedFile) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadWriteMode));
+  ASSERT_TRUE(file.MapReadWrite(10));
+  EXPECT_EQ(10, file.GetLength());
+  EXPECT_TRUE(file.Unmap());
+  EXPECT_TRUE(file.MapReadWrite(20));
+  EXPECT_EQ(20, file.GetLength());
+  EXPECT_EQ(0, file.Flush());
+  EXPECT_TRUE(file.Unmap());
+  EXPECT_EQ(0, file.Flush());
+  EXPECT_EQ(0, file.SetLength(5));
+  EXPECT_TRUE(file.MapReadOnly());
+  EXPECT_EQ(5, file.GetLength());
+}
+
+TEST_F(MappedFileTest, ReadNotMapped) {
+  TestRead();
+}
+
+TEST_F(MappedFileTest, SetLengthNotMapped) {
+  TestSetLength();
+}
+
+TEST_F(MappedFileTest, WriteNotMapped) {
+  TestWrite();
+}
+
+TEST_F(MappedFileTest, ReadMappedReadOnly) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  ASSERT_TRUE(file.MapReadOnly());
+  TestReadContent(kContent, &file);
+}
+
+TEST_F(MappedFileTest, ReadMappedReadWrite) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadWriteMode));
+  ASSERT_TRUE(file.MapReadWrite(kContent.size()));
+  TestReadContent(kContent, &file);
+}
+
+TEST_F(MappedFileTest, WriteMappedReadWrite) {
+  TEMP_FAILURE_RETRY(unlink(good_path_.c_str()));
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadWriteMode));
+  ASSERT_TRUE(file.MapReadWrite(kContent.size()));
+
+  // Can't write to a negative offset.
+  EXPECT_EQ(-EINVAL, file.Write(kContent.c_str(), 0, -123));
+
+  // A zero-length write is a no-op.
+  EXPECT_EQ(0, file.Write(kContent.c_str(), 0, 0));
+  // But the file size is as given when mapped.
+  EXPECT_EQ(kContent.size(), file.GetLength());
+
+  // Data written past the end are discarded.
+  EXPECT_EQ(kContent.size() - 1,
+            file.Write(kContent.c_str(), kContent.size(), 1));
+  EXPECT_EQ(0, memcmp(kContent.c_str(), file.data() + 1, kContent.size() - 1));
+
+  // Data can be overwritten.
+  EXPECT_EQ(kContent.size(), file.Write(kContent.c_str(), kContent.size(), 0));
+  EXPECT_EQ(0, memcmp(kContent.c_str(), file.data(), kContent.size()));
+}
+
+#if 0 // death tests don't work on android yet
+
+class MappedFileDeathTest : public MappedFileTest {};
+
+TEST_F(MappedFileDeathTest, MustMapBeforeUse) {
+  MappedFile file;
+  EXPECT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  EXPECT_DEATH(file.data(), "mapped_");
+}
+
+TEST_F(MappedFileDeathTest, RemappingNotAllowedReadOnly) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  ASSERT_TRUE(file.MapReadOnly());
+  EXPECT_DEATH(file.MapReadOnly(), "mapped_");
+}
+
+TEST_F(MappedFileDeathTest, RemappingNotAllowedReadWrite) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadWriteMode));
+  ASSERT_TRUE(file.MapReadWrite(10));
+  EXPECT_DEATH(file.MapReadWrite(10), "mapped_");
+}
+
+TEST_F(MappedFileDeathTest, SetLengthMappedReadWrite) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadWriteMode));
+  ASSERT_TRUE(file.MapReadWrite(10));
+  EXPECT_EQ(10, file.GetLength());
+  EXPECT_DEATH(file.SetLength(0), ".*");
+}
+
+TEST_F(MappedFileDeathTest, SetLengthMappedReadOnly) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  ASSERT_TRUE(file.MapReadOnly());
+  EXPECT_EQ(kContent.size(), file.GetLength());
+  EXPECT_DEATH(file.SetLength(0), ".*");
+}
+
+TEST_F(MappedFileDeathTest, WriteMappedReadOnly) {
+  MappedFile file;
+  ASSERT_TRUE(file.Open(good_path_, MappedFile::kReadOnlyMode));
+  ASSERT_TRUE(file.MapReadOnly());
+  char buf[10];
+  EXPECT_DEATH(file.Write(buf, 0, 0), ".*");
+}
+
+#endif
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/null_file.cc b/src/base/unix_file/null_file.cc
new file mode 100644
index 0000000..050decb
--- /dev/null
+++ b/src/base/unix_file/null_file.cc
@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2009 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 "base/unix_file/null_file.h"
+#include <errno.h>
+
+namespace unix_file {
+
+NullFile::NullFile() {
+}
+
+NullFile::~NullFile() {
+}
+
+int NullFile::Close() {
+  return 0;
+}
+
+int NullFile::Flush() {
+  return 0;
+}
+
+int64_t NullFile::Read(char* buf, int64_t byte_count, int64_t offset) const {
+  if (offset < 0) {
+    return -EINVAL;
+  }
+  return 0;
+}
+
+int NullFile::SetLength(int64_t new_length) {
+  if (new_length < 0) {
+    return -EINVAL;
+  }
+  return 0;
+}
+
+int64_t NullFile::GetLength() const {
+  return 0;
+}
+
+int64_t NullFile::Write(const char* buf, int64_t byte_count, int64_t offset) {
+  if (offset < 0) {
+    return -EINVAL;
+  }
+  return byte_count;
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/null_file.h b/src/base/unix_file/null_file.h
new file mode 100644
index 0000000..e716603
--- /dev/null
+++ b/src/base/unix_file/null_file.h
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2009 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.
+ */
+
+#ifndef BASE_UNIX_FILE_NULL_FILE_H_
+#define BASE_UNIX_FILE_NULL_FILE_H_
+
+#include "base/unix_file/random_access_file.h"
+#include "base/macros.h"
+
+namespace unix_file {
+
+// A RandomAccessFile implementation equivalent to /dev/null. Writes are
+// discarded, and there's no data to be read. Callers could use FdFile in
+// conjunction with /dev/null, but that's not portable and costs a file
+// descriptor. NullFile is "free".
+//
+// Thread safe.
+class NullFile : public RandomAccessFile {
+ public:
+  NullFile();
+  virtual ~NullFile();
+
+  // RandomAccessFile API.
+  virtual int Close();
+  virtual int Flush();
+  virtual int64_t Read(char* buf, int64_t byte_count, int64_t offset) const;
+  virtual int SetLength(int64_t new_length);
+  virtual int64_t GetLength() const;
+  virtual int64_t Write(const char* buf, int64_t byte_count, int64_t offset);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(NullFile);
+};
+
+}  // namespace unix_file
+
+#endif  // BASE_UNIX_FILE_NULL_FILE_H_
diff --git a/src/base/unix_file/null_file_test.cc b/src/base/unix_file/null_file_test.cc
new file mode 100644
index 0000000..0f20acd
--- /dev/null
+++ b/src/base/unix_file/null_file_test.cc
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2009 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 "base/unix_file/null_file.h"
+
+#include <errno.h>
+
+#include "gtest/gtest.h"
+
+namespace unix_file {
+
+class NullFileTest : public testing::Test { };
+
+TEST_F(NullFileTest, Read) {
+  NullFile f;
+  char buf[256];
+  // You can't read a negative number of bytes...
+  ASSERT_EQ(-EINVAL, f.Read(buf, 0, -1));
+  // ...but everything else is fine (though you'll get no data).
+  ASSERT_EQ(0, f.Read(buf, 128, 0));
+  ASSERT_EQ(0, f.Read(buf, 128, 128));
+}
+
+TEST_F(NullFileTest, SetLength) {
+  NullFile f;
+  // You can't set a negative length...
+  ASSERT_EQ(-EINVAL, f.SetLength(-1));
+  // ...but everything else is fine.
+  ASSERT_EQ(0, f.SetLength(0));
+  ASSERT_EQ(0, f.SetLength(128));
+}
+
+TEST_F(NullFileTest, GetLength) {
+  const std::string content("hello");
+  NullFile f;
+  // The length is always 0.
+  ASSERT_EQ(0, f.GetLength());
+  ASSERT_EQ(content.size(), f.Write(content.data(), content.size(), 0));
+  ASSERT_EQ(0, f.GetLength());
+}
+
+TEST_F(NullFileTest, Write) {
+  const std::string content("hello");
+  NullFile f;
+  // You can't write at a negative offset...
+  ASSERT_EQ(-EINVAL, f.Write(content.data(), content.size(), -128));
+  // But you can write anywhere else...
+  ASSERT_EQ(content.size(), f.Write(content.data(), content.size(), 0));
+  ASSERT_EQ(content.size(), f.Write(content.data(), content.size(), 128));
+  // ...though the file will remain empty.
+  ASSERT_EQ(0, f.GetLength());
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/random_access_file.h b/src/base/unix_file/random_access_file.h
new file mode 100644
index 0000000..22da37f
--- /dev/null
+++ b/src/base/unix_file/random_access_file.h
@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2009 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.
+ */
+
+#ifndef BASE_UNIX_FILE_RANDOM_ACCESS_FILE_H_
+#define BASE_UNIX_FILE_RANDOM_ACCESS_FILE_H_
+
+#include <stdint.h>
+
+namespace unix_file {
+
+// A file interface supporting random-access reading and writing of content,
+// along with the ability to set the length of a file (smaller or greater than
+// its current extent).
+//
+// This interface does not support a stream position (i.e. every read or write
+// must specify an offset). This interface does not imply any buffering policy.
+//
+// All operations return >= 0 on success or -errno on failure.
+//
+// Implementations never return EINTR; callers are spared the need to manually
+// retry interrupted operations.
+//
+// Any concurrent access to files should be externally synchronized.
+class RandomAccessFile {
+ public:
+  virtual ~RandomAccessFile() { }
+
+  virtual int Close() = 0;
+
+  // Reads 'byte_count' bytes into 'buf' starting at offset 'offset' in the
+  // file. Returns the number of bytes actually read.
+  virtual int64_t Read(char* buf, int64_t byte_count, int64_t offset) const = 0;
+
+  // Sets the length of the file to 'new_length'. If this is smaller than the
+  // file's current extent, data is discarded. If this is greater than the
+  // file's current extent, it is as if a write of the relevant number of zero
+  // bytes occurred. Returns 0 on success.
+  virtual int SetLength(int64_t new_length) = 0;
+
+  // Returns the current size of this file.
+  virtual int64_t GetLength() const = 0;
+
+  // Writes 'byte_count' bytes from 'buf' starting at offset 'offset' in the
+  // file. Zero-byte writes are acceptable, and writes past the end are as if
+  // a write of the relevant number of zero bytes also occurred. Returns the
+  // number of bytes actually written.
+  virtual int64_t Write(const char* buf, int64_t byte_count, int64_t offset) = 0;
+
+  // Flushes file data.
+  virtual int Flush() = 0;
+};
+
+}  // namespace unix_file
+
+#endif  // BASE_UNIX_FILE_RANDOM_ACCESS_FILE_H_
diff --git a/src/base/unix_file/random_access_file_test.h b/src/base/unix_file/random_access_file_test.h
new file mode 100644
index 0000000..3baaeae
--- /dev/null
+++ b/src/base/unix_file/random_access_file_test.h
@@ -0,0 +1,172 @@
+/*
+ * Copyright (C) 2009 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.
+ */
+
+#ifndef BASE_UNIX_FILE_RANDOM_ACCESS_FILE_TEST_H_
+#define BASE_UNIX_FILE_RANDOM_ACCESS_FILE_TEST_H_
+
+#include <errno.h>
+
+#include <string>
+
+#include "common_test.h"
+#include "gtest/gtest.h"
+#include "UniquePtr.h"
+
+namespace unix_file {
+
+class RandomAccessFileTest : public testing::Test {
+ protected:
+  virtual ~RandomAccessFileTest() {
+  }
+
+  // Override this to return an instance of the subclass under test that's
+  // backed by a temporary file.
+  virtual RandomAccessFile* MakeTestFile() = 0;
+
+  virtual void SetUp() {
+    art::CommonTest::SetEnvironmentVariables(android_data_);
+  }
+
+  std::string GetTmpPath(const std::string& name) {
+    std::string path;
+    path = android_data_;
+    path += "/";
+    path += name;
+    return path;
+  }
+
+  // TODO(enh): ReadString (and WriteString) might be generally useful.
+  static bool ReadString(RandomAccessFile* f, std::string* s) {
+    s->clear();
+    char buf[256];
+    int64_t n = 0;
+    int64_t offset = 0;
+    while ((n = f->Read(buf, sizeof(buf), offset)) > 0) {
+      s->append(buf, n);
+      offset += n;
+    }
+    return n != -1;
+  }
+
+  void TestRead() {
+    char buf[256];
+    UniquePtr<RandomAccessFile> file(MakeTestFile());
+
+    // Reading from the start of an empty file gets you zero bytes, however many
+    // you ask for.
+    ASSERT_EQ(0, file->Read(buf, 0, 0));
+    ASSERT_EQ(0, file->Read(buf, 123, 0));
+
+    const std::string content("hello");
+    ASSERT_EQ(content.size(), file->Write(content.data(), content.size(), 0));
+
+    TestReadContent(content, file.get());
+  }
+
+  void TestReadContent(const std::string& content, RandomAccessFile* file) {
+    const int buf_size = content.size() + 10;
+    UniquePtr<char> buf(new char[buf_size]);
+    // Can't read from a negative offset.
+    ASSERT_EQ(-EINVAL, file->Read(buf.get(), 0, -123));
+
+    // Reading too much gets us just what's in the file.
+    ASSERT_EQ(content.size(), file->Read(buf.get(), buf_size, 0));
+    ASSERT_EQ(std::string(buf.get(), content.size()), content);
+
+    // We only get as much as we ask for.
+    const size_t short_request = 2;
+    ASSERT_LT(short_request, content.size());
+    ASSERT_EQ(short_request, file->Read(buf.get(), short_request, 0));
+    ASSERT_EQ(std::string(buf.get(), short_request),
+              content.substr(0, short_request));
+
+    // We don't have to start at the beginning.
+    const int non_zero_offset = 2;
+    ASSERT_GT(non_zero_offset, 0);
+    ASSERT_EQ(short_request,
+              file->Read(buf.get(), short_request, non_zero_offset));
+    ASSERT_EQ(std::string(buf.get(), short_request),
+              content.substr(non_zero_offset, short_request));
+
+    // Reading past the end gets us nothing.
+    ASSERT_EQ(0, file->Read(buf.get(), buf_size, file->GetLength()));
+    ASSERT_EQ(0, file->Read(buf.get(), buf_size, file->GetLength() + 1));
+  }
+
+  void TestSetLength() {
+    const std::string content("hello");
+    UniquePtr<RandomAccessFile> file(MakeTestFile());
+    ASSERT_EQ(content.size(), file->Write(content.data(), content.size(), 0));
+    ASSERT_EQ(content.size(), file->GetLength());
+
+    // Can't give a file a negative length.
+    ASSERT_EQ(-EINVAL, file->SetLength(-123));
+
+    // Can truncate the file.
+    int64_t new_length = 2;
+    ASSERT_EQ(0, file->SetLength(new_length));
+    ASSERT_EQ(new_length, file->GetLength());
+    std::string new_content;
+    ASSERT_TRUE(ReadString(file.get(), &new_content));
+    ASSERT_EQ(content.substr(0, 2), new_content);
+
+    // Expanding the file appends zero bytes.
+    new_length = file->GetLength() + 1;
+    ASSERT_EQ(0, file->SetLength(new_length));
+    ASSERT_EQ(new_length, file->GetLength());
+    ASSERT_TRUE(ReadString(file.get(), &new_content));
+    ASSERT_EQ('\0', new_content[new_length - 1]);
+  }
+
+  void TestWrite() {
+    const std::string content("hello");
+    UniquePtr<RandomAccessFile> file(MakeTestFile());
+
+    // Can't write to a negative offset.
+    ASSERT_EQ(-EINVAL, file->Write(content.data(), 0, -123));
+
+    // Writing zero bytes of data is a no-op.
+    ASSERT_EQ(0, file->Write(content.data(), 0, 0));
+    ASSERT_EQ(0, file->GetLength());
+
+    // We can write data.
+    ASSERT_EQ(content.size(), file->Write(content.data(), content.size(), 0));
+    ASSERT_EQ(content.size(), file->GetLength());
+    std::string new_content;
+    ASSERT_TRUE(ReadString(file.get(), &new_content));
+    ASSERT_EQ(new_content, content);
+
+    // We can read it back.
+    char buf[256];
+    ASSERT_EQ(content.size(), file->Read(buf, sizeof(buf), 0));
+    ASSERT_EQ(std::string(buf, content.size()), content);
+
+    // We can append data past the end.
+    ASSERT_EQ(content.size(),
+    file->Write(content.data(), content.size(), file->GetLength() + 1));
+    int64_t new_length = 2*content.size() + 1;
+    ASSERT_EQ(file->GetLength(), new_length);
+    ASSERT_TRUE(ReadString(file.get(), &new_content));
+    ASSERT_EQ(std::string("hello\0hello", new_length), new_content);
+  }
+
+ protected:
+  std::string android_data_;
+};
+
+}  // namespace unix_file
+
+#endif  // BASE_UNIX_FILE_RANDOM_ACCESS_FILE_TEST_H_
diff --git a/src/base/unix_file/random_access_file_utils.cc b/src/base/unix_file/random_access_file_utils.cc
new file mode 100644
index 0000000..df3b308
--- /dev/null
+++ b/src/base/unix_file/random_access_file_utils.cc
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2009 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 <vector>
+#include "base/unix_file/random_access_file_utils.h"
+#include "base/unix_file/random_access_file.h"
+
+namespace unix_file {
+
+bool CopyFile(const RandomAccessFile& src, RandomAccessFile* dst) {
+  // We don't call src->GetLength because some files (those in /proc, say)
+  // don't know how long they are. We just read until there's nothing left.
+  std::vector<char> buf(4096);
+  int64_t offset = 0;
+  int64_t n;
+  while ((n = src.Read(&buf[0], buf.size(), offset)) > 0) {
+    if (dst->Write(&buf[0], n, offset) != n) {
+      return false;
+    }
+    offset += n;
+  }
+  return n >= 0;
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/random_access_file_utils.h b/src/base/unix_file/random_access_file_utils.h
new file mode 100644
index 0000000..0535ead
--- /dev/null
+++ b/src/base/unix_file/random_access_file_utils.h
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2009 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.
+ */
+
+#ifndef BASE_UNIX_FILE_RANDOM_ACCESS_FILE_UTILS_H_
+#define BASE_UNIX_FILE_RANDOM_ACCESS_FILE_UTILS_H_
+
+namespace unix_file {
+
+class RandomAccessFile;
+
+// Copies from 'src' to 'dst'. Reads all the data from 'src', and writes it
+// to 'dst'. Not thread-safe. Neither file will be closed.
+bool CopyFile(const RandomAccessFile& src, RandomAccessFile* dst);
+
+}  // namespace unix_file
+
+#endif  // BASE_UNIX_FILE_RANDOM_ACCESS_FILE_UTILS_H_
diff --git a/src/base/unix_file/random_access_file_utils_test.cc b/src/base/unix_file/random_access_file_utils_test.cc
new file mode 100644
index 0000000..6317922
--- /dev/null
+++ b/src/base/unix_file/random_access_file_utils_test.cc
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2009 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 "base/unix_file/random_access_file_utils.h"
+#include "base/unix_file/fd_file.h"
+#include "base/unix_file/string_file.h"
+#include "gtest/gtest.h"
+
+namespace unix_file {
+
+class RandomAccessFileUtilsTest : public testing::Test { };
+
+TEST_F(RandomAccessFileUtilsTest, CopyFile) {
+  StringFile src;
+  StringFile dst;
+
+  const std::string content("hello");
+  src.Assign(content);
+  ASSERT_EQ(src.ToStringPiece(), content);
+  ASSERT_EQ(dst.ToStringPiece(), "");
+
+  ASSERT_TRUE(CopyFile(src, &dst));
+  ASSERT_EQ(src.ToStringPiece(), dst.ToStringPiece());
+}
+
+TEST_F(RandomAccessFileUtilsTest, BadSrc) {
+  FdFile src(-1);
+  StringFile dst;
+  ASSERT_FALSE(CopyFile(src, &dst));
+}
+
+TEST_F(RandomAccessFileUtilsTest, BadDst) {
+  StringFile src;
+  FdFile dst(-1);
+
+  // We need some source content to trigger a write.
+  // Copying an empty file is a no-op.
+  src.Assign("hello");
+
+  ASSERT_FALSE(CopyFile(src, &dst));
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/string_file.cc b/src/base/unix_file/string_file.cc
new file mode 100644
index 0000000..5d47b17
--- /dev/null
+++ b/src/base/unix_file/string_file.cc
@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2009 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 "base/unix_file/string_file.h"
+#include <errno.h>
+#include <algorithm>
+#include "logging.h"
+
+namespace unix_file {
+
+StringFile::StringFile() {
+}
+
+StringFile::~StringFile() {
+}
+
+int StringFile::Close() {
+  return 0;
+}
+
+int StringFile::Flush() {
+  return 0;
+}
+
+int64_t StringFile::Read(char *buf, int64_t byte_count, int64_t offset) const {
+  CHECK(buf);
+  CHECK_GE(byte_count, 0);
+
+  if (offset < 0) {
+    return -EINVAL;
+  }
+
+  const int64_t available_bytes = std::min(byte_count, GetLength() - offset);
+  if (available_bytes < 0) {
+    return 0;  // Not an error, but nothing for us to do, either.
+  }
+  memcpy(buf, data_.data() + offset, available_bytes);
+  return available_bytes;
+}
+
+int StringFile::SetLength(int64_t new_length) {
+  if (new_length < 0) {
+    return -EINVAL;
+  }
+  data_.resize(new_length);
+  return 0;
+}
+
+int64_t StringFile::GetLength() const {
+  return data_.size();
+}
+
+int64_t StringFile::Write(const char *buf, int64_t byte_count, int64_t offset) {
+  CHECK(buf);
+  CHECK_GE(byte_count, 0);
+
+  if (offset < 0) {
+    return -EINVAL;
+  }
+
+  if (byte_count == 0) {
+    return 0;
+  }
+
+  // FUSE seems happy to allow writes past the end. (I'd guess it doesn't
+  // synthesize a write of zero bytes so that we're free to implement sparse
+  // files.) GNU as(1) seems to require such writes. Those files are small.
+  const int64_t bytes_past_end = offset - GetLength();
+  if (bytes_past_end > 0) {
+    data_.append(bytes_past_end, '\0');
+  }
+
+  data_.replace(offset, byte_count, buf, byte_count);
+  return byte_count;
+}
+
+void StringFile::Assign(const art::StringPiece &new_data) {
+  data_.assign(new_data.data(), new_data.size());
+}
+
+const art::StringPiece StringFile::ToStringPiece() const {
+  return data_;
+}
+
+}  // namespace unix_file
diff --git a/src/base/unix_file/string_file.h b/src/base/unix_file/string_file.h
new file mode 100644
index 0000000..4277dc2
--- /dev/null
+++ b/src/base/unix_file/string_file.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2009 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.
+ */
+
+#ifndef BASE_UNIX_FILE_STRING_FILE_H_
+#define BASE_UNIX_FILE_STRING_FILE_H_
+
+#include <stdint.h>
+
+#include <string>
+
+#include "base/macros.h"
+#include "base/unix_file/random_access_file.h"
+#include "stringpiece.h"
+
+namespace unix_file {
+
+// A RandomAccessFile implementation backed by a std::string. (That is, all data is
+// kept in memory.)
+//
+// Not thread safe.
+class StringFile : public RandomAccessFile {
+ public:
+  StringFile();
+  virtual ~StringFile();
+
+  // RandomAccessFile API.
+  virtual int Close();
+  virtual int Flush();
+  virtual int64_t Read(char* buf, int64_t byte_count, int64_t offset) const;
+  virtual int SetLength(int64_t new_length);
+  virtual int64_t GetLength() const;
+  virtual int64_t Write(const char* buf, int64_t byte_count, int64_t offset);
+
+  // Bonus API.
+  void Assign(const art::StringPiece& new_data);
+  const art::StringPiece ToStringPiece() const;
+
+ private:
+  std::string data_;
+
+  DISALLOW_COPY_AND_ASSIGN(StringFile);
+};
+
+}  // namespace unix_file
+
+#endif  // BASE_UNIX_FILE_STRING_FILE_H_
diff --git a/src/base/unix_file/string_file_test.cc b/src/base/unix_file/string_file_test.cc
new file mode 100644
index 0000000..8821461
--- /dev/null
+++ b/src/base/unix_file/string_file_test.cc
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2009 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 "base/unix_file/string_file.h"
+#include "base/unix_file/random_access_file_test.h"
+#include "gtest/gtest.h"
+
+namespace unix_file {
+
+class StringFileTest : public RandomAccessFileTest {
+ protected:
+  virtual RandomAccessFile* MakeTestFile() {
+    return new StringFile;
+  }
+};
+
+TEST_F(StringFileTest, Read) {
+  TestRead();
+}
+
+TEST_F(StringFileTest, SetLength) {
+  TestSetLength();
+}
+
+TEST_F(StringFileTest, Write) {
+  TestWrite();
+}
+
+}  // namespace unix_file