Minor File interface changes.

These are intended to make the sample file writing easier.

src/filesystem.cc

@@ -79,18 +79,23 @@ class RealFile : public File {
     return 0;
   }
 
-  int Write(re2::StringPiece *data) final {
+  int Sync() final { return (fsync(fd_) < 0) ? errno : 0; }
+
+  int Truncate(off_t length) final {
+    return (ftruncate(fd_, length) < 0) ? errno : 0;
+  }
+
+  int Write(re2::StringPiece data, size_t *bytes_written) final {
     if (fd_ < 0) {
       return EBADF;
     }
     ssize_t ret;
-    while ((ret = write(fd_, data->data(), data->size())) == -1 &&
-           errno == EINTR)
+    while ((ret = write(fd_, data.data(), data.size())) == -1 && errno == EINTR)
       ;
     if (ret < 0) {
       return errno;
     }
-    data->remove_prefix(ret);
+    *bytes_written = static_cast<size_t>(ret);
     return 0;
   }
 

src/filesystem.h

@@ -65,9 +65,15 @@ class File {
   // Already closed is considered a success.
   virtual int Close() = 0;
 
+  // fsync(), returning 0 on success or errno>0 on failure.
+  virtual int Sync() = 0;
+
+  // ftruncate(), returning 0 on success or errno>0 on failure.
+  virtual int Truncate(off_t length) = 0;
+
   // Write to the file, returning 0 on success or errno>0 on failure.
-  // On success, data->remove_prefix will be called with the written bytes.
-  virtual int Write(re2::StringPiece *data) = 0;
+  // On success, |bytes_written| will be updated.
+  virtual int Write(re2::StringPiece data, size_t *bytes_written) = 0;
 };
 
 // Interface to the local filesystem. There's typically one per program,

src/testutil.cc

@@ -109,8 +109,10 @@ void WriteFileOrDie(const std::string &path, re2::StringPiece contents) {
                                       O_WRONLY | O_CREAT | O_TRUNC, 0600, &f);
   CHECK_EQ(ret, 0) << "open " << path << ": " << strerror(ret);
   while (!contents.empty()) {
-    ret = f->Write(&contents);
+    size_t written;
+    ret = f->Write(contents, &written);
     CHECK_EQ(ret, 0) << "write " << path << ": " << strerror(ret);
+    contents.remove_prefix(written);
   }
   ret = f->Close();
   CHECK_EQ(ret, 0) << "close " << path << ": " << strerror(ret);