Add ReadFully and WriteFully to libbase.

Change-Id: I6b7aa2a93398e7acdd1d74c71d9abed08a72b3c4
diff --git a/file_test.cpp b/file_test.cpp
index fc48b32..e5cf696 100644
--- a/file_test.cpp
+++ b/file_test.cpp
@@ -79,3 +79,28 @@
   ASSERT_TRUE(android::base::ReadFdToString(tf.fd, &s)) << errno;
   EXPECT_EQ("abc", s);
 }
+
+TEST(file, ReadFully) {
+  int fd = open("/proc/version", O_RDONLY);
+  ASSERT_NE(-1, fd) << strerror(errno);
+
+  char buf[1024];
+  memset(buf, 0, sizeof(buf));
+  ASSERT_TRUE(android::base::ReadFully(fd, buf, 5));
+  ASSERT_STREQ("Linux", buf);
+
+  ASSERT_EQ(0, lseek(fd, 0, SEEK_SET)) << strerror(errno);
+
+  ASSERT_FALSE(android::base::ReadFully(fd, buf, sizeof(buf)));
+
+  close(fd);
+}
+
+TEST(file, WriteFully) {
+  TemporaryFile tf;
+  ASSERT_TRUE(tf.fd != -1);
+  ASSERT_TRUE(android::base::WriteFully(tf.fd, "abc", 3));
+  std::string s;
+  ASSERT_TRUE(android::base::ReadFileToString(tf.filename, &s)) << errno;
+  EXPECT_EQ("abc", s);
+}