From 22efbad9450fc95748e0bc3bee04ec49702d7ed2 Mon Sep 17 00:00:00 2001
From: Baptiste Mathus <batmat@batmat.net>
Date: Fri, 1 Dec 2017 23:17:18 +0100
Subject: [PATCH] [JENKINS-34855] Create a FileChannelWriter

---
 .../java/hudson/util/FileChannelWriter.java   | 57 +++++++++++++++++
 .../hudson/util/FileChannelWriterTest.java    | 63 +++++++++++++++++++
 2 files changed, 120 insertions(+)
 create mode 100644 core/src/main/java/hudson/util/FileChannelWriter.java
 create mode 100644 core/src/test/java/hudson/util/FileChannelWriterTest.java

diff --git a/core/src/main/java/hudson/util/FileChannelWriter.java b/core/src/main/java/hudson/util/FileChannelWriter.java
new file mode 100644
index 0000000000..fd28d73427
--- /dev/null
+++ b/core/src/main/java/hudson/util/FileChannelWriter.java
@@ -0,0 +1,57 @@
+package hudson.util;
+
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
+import java.io.IOException;
+import java.io.Writer;
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.charset.Charset;
+import java.nio.file.OpenOption;
+import java.nio.file.Path;
+
+/**
+ * This class has been created to help make {@link AtomicFileWriter} hopefully more reliable in some corner cases.
+ * We created this wrapper to be able to access {@link FileChannel#force(boolean)} which seems to be one of the rare
+ * ways to actually have a guarantee that data be flushed to the physical device (only guaranteed for local, not for
+ * remote obviously though).
+ *
+ * <p>The goal using this is to reduce as much as we can the likeliness to see zero-length files be created in place
+ * of the original ones.</p>
+ *
+ * @see <a href="https://issues.jenkins-ci.org/browse/JENKINS-34855">JENKINS-34855</a>
+ * @see <a href="https://github.com/jenkinsci/jenkins/pull/2548">PR-2548</a>
+ */
+@Restricted(NoExternalUse.class)
+public class FileChannelWriter extends Writer {
+
+    private final Charset charset;
+    private final FileChannel channel;
+
+    FileChannelWriter(Path filePath, Charset charset, OpenOption... options) throws IOException {
+        this.charset = charset;
+        channel = FileChannel.open(filePath, options);
+    }
+
+    @Override
+    public void write(char cbuf[], int off, int len) throws IOException {
+        final CharBuffer charBuffer = CharBuffer.wrap(cbuf, off, len);
+        ByteBuffer byteBuffer = charset.encode(charBuffer);
+        channel.write(byteBuffer);
+    }
+
+    @Override
+    public void flush() throws IOException {
+        channel.force(true);
+    }
+
+    @Override
+    public void close() throws IOException {
+        if(channel.isOpen()) {
+            channel.force(true);
+            channel.close();
+        }
+    }
+}
diff --git a/core/src/test/java/hudson/util/FileChannelWriterTest.java b/core/src/test/java/hudson/util/FileChannelWriterTest.java
new file mode 100644
index 0000000000..c8aaf4c35d
--- /dev/null
+++ b/core/src/test/java/hudson/util/FileChannelWriterTest.java
@@ -0,0 +1,63 @@
+package hudson.util;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.channels.ClosedChannelException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.StandardOpenOption;
+
+import static org.hamcrest.CoreMatchers.not;
+import static org.hamcrest.core.IsEqual.equalTo;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.fail;
+
+public class FileChannelWriterTest {
+    @Rule
+    public TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+    File file;
+    FileChannelWriter writer;
+
+    @Before
+    public void setUp() throws Exception {
+        file = temporaryFolder.newFile();
+        writer = new FileChannelWriter(file.toPath(), StandardCharsets.UTF_8, StandardOpenOption.WRITE);
+    }
+
+    @Test
+    public void write() throws Exception {
+        writer.write("helloooo");
+        writer.close();
+
+        assertContent("helloooo");
+    }
+
+
+    @Test
+    public void flush() throws Exception {
+        writer.write("hello é è à".toCharArray());
+
+        writer.flush();
+        assertContent("hello é è à");
+    }
+
+    @Test(expected = ClosedChannelException.class)
+    public void close() throws Exception {
+        writer.write("helloooo");
+        writer.close();
+
+        writer.write("helloooo");
+        fail("Should have failed the line above");
+    }
+
+
+    private void assertContent(String string) throws IOException {
+        assertThat(FileUtils.readFileToString(file, StandardCharsets.UTF_8), equalTo(string));
+    }
+}