Avoid extra byte copy inside FileSystemImpl.readFileInternal

Closes #5677

The improvement consists in creating the buffer upfront and using Netty API to read the file channel.

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>

Author: tsegismont

vertx-core/src/main/java/io/vertx/core/file/impl/FileSystemImpl.java

@@ -14,45 +14,21 @@
 import io.vertx.codegen.annotations.Nullable;
 import io.vertx.core.Future;
 import io.vertx.core.buffer.Buffer;
-import io.vertx.core.file.AsyncFile;
-import io.vertx.core.file.CopyOptions;
-import io.vertx.core.file.FileProps;
+import io.vertx.core.file.*;
 import io.vertx.core.file.FileSystem;
 import io.vertx.core.file.FileSystemException;
-import io.vertx.core.file.FileSystemProps;
-import io.vertx.core.file.OpenOptions;
 import io.vertx.core.internal.ContextInternal;
 import io.vertx.core.internal.VertxInternal;
+import io.vertx.core.internal.buffer.BufferInternal;
 
 import java.io.File;
 import java.io.FilenameFilter;
 import java.io.IOException;
 import java.io.RandomAccessFile;
-import java.nio.file.CopyOption;
-import java.nio.file.FileAlreadyExistsException;
-import java.nio.file.FileStore;
-import java.nio.file.FileVisitOption;
-import java.nio.file.FileVisitResult;
-import java.nio.file.Files;
-import java.nio.file.LinkOption;
-import java.nio.file.Path;
-import java.nio.file.Paths;
-import java.nio.file.SimpleFileVisitor;
-import java.nio.file.StandardCopyOption;
-import java.nio.file.attribute.BasicFileAttributes;
-import java.nio.file.attribute.FileAttribute;
-import java.nio.file.attribute.GroupPrincipal;
-import java.nio.file.attribute.PosixFileAttributeView;
-import java.nio.file.attribute.PosixFilePermission;
-import java.nio.file.attribute.PosixFilePermissions;
-import java.nio.file.attribute.UserPrincipal;
-import java.nio.file.attribute.UserPrincipalLookupService;
-import java.util.ArrayList;
-import java.util.EnumSet;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Objects;
-import java.util.Set;
+import java.nio.channels.FileChannel;
+import java.nio.file.*;
+import java.nio.file.attribute.*;
+import java.util.*;
 import java.util.concurrent.Callable;
 import java.util.regex.Pattern;
 
@@ -875,8 +851,16 @@ private BlockingAction<Buffer> readFileInternal(String path) {
       public Buffer perform() {
         try {
           Path target = resolveFile(path).toPath();
-          byte[] bytes = Files.readAllBytes(target);
-          return Buffer.buffer(bytes);
+          try (FileChannel fc = FileChannel.open(target, StandardOpenOption.READ)) {
+            long size = fc.size();
+            if (size > (long) Integer.MAX_VALUE) {
+              throw new OutOfMemoryError("File is too big");
+            }
+            int len = (int) size;
+            BufferInternal res = BufferInternal.buffer(len);
+            res.unwrap().writeBytes(fc, 0, len);
+            return res;
+          }
         } catch (IOException e) {
           throw new FileSystemException(getFileAccessErrorMessage("read", path), e);
         }