Rotate the slave log files instead of deleting them.

changelog.html

@@ -79,6 +79,8 @@ Upcoming changes</a>
     (<a href="https://github.com/jenkinsci/jenkins/pull/119">pull request #119</a>)
   <li class=rfe>
     Plugins can now override where jobs are executed.
+  <li class=rfe>
+    Rotate the slave log files instead of deleting them.
   <li class=rfe>
     Added a mechanism to control the XML parser behaviour
     (<a href="https://github.com/jenkinsci/jenkins/pull/67">pull request #67</a>)

core/src/main/java/hudson/slaves/SlaveComputer.java

@@ -24,6 +24,7 @@
 package hudson.slaves;
 
 import hudson.model.*;
+import hudson.util.io.ReopenableRotatingFileOutputStream;
 import jenkins.model.Jenkins.MasterComputer;
 import hudson.remoting.Channel;
 import hudson.remoting.VirtualChannel;
@@ -115,7 +116,7 @@ public class SlaveComputer extends Computer {
 
     public SlaveComputer(Slave slave) {
         super(slave);
-        this.log = new ReopenableFileOutputStream(getLogFile());
+        this.log = new ReopenableRotatingFileOutputStream(getLogFile(),10);
         this.taskListener = new StreamTaskListener(log);
     }
 

core/src/main/java/hudson/util/io/ReopenableFileOutputStream.java

@@ -41,7 +41,7 @@ import java.io.OutputStream;
  * @author Kohsuke Kawaguchi
  */
 public class ReopenableFileOutputStream extends OutputStream {
-    private final File out;
+    protected final File out;
 
     private OutputStream current;
     private boolean appendOnNextOpen = false;

core/src/main/java/hudson/util/io/ReopenableRotatingFileOutputStream.java

+/*
+ * The MIT License
+ *
+ * Copyright (c) 2011, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package hudson.util.io;
+
+import java.io.File;
+import java.io.IOException;
+
+/**
+ * {@link ReopenableFileOutputStream} that does log rotation upon rewind.
+ *
+ * @author Kohsuke Kawaguchi
+ * @since 1.416
+ */
+public class ReopenableRotatingFileOutputStream extends ReopenableFileOutputStream {
+    /**
+     * Number of log files to keep.
+     */
+    private final int size;
+
+    public ReopenableRotatingFileOutputStream(File out, int size) {
+        super(out);
+        this.size = size;
+    }
+
+    protected File getNumberedFileName(int n) {
+        if (n==0)   return out;
+        return new File(out.getPath()+"."+n);
+    }
+
+    @Override
+    public void rewind() throws IOException {
+        super.rewind();
+        for (int i=size-1;i>=0;i--) {
+            File fi = getNumberedFileName(i);
+            if (fi.exists()) {
+                fi.renameTo(getNumberedFileName(i+1));
+            }
+        }
+    }
+
+    /**
+     * Deletes all the log files, including rotated files.
+     */
+    public void deleteAll() {
+        for (int i=0; i<=size; i++) {
+            getNumberedFileName(i).delete();
+        }
+    }
+}

core/src/test/java/hudson/util/io/ReopenableRotatingFileOutputStreamTest.java

+package hudson.util.io;
+
+import hudson.FilePath;
+import junit.framework.TestCase;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.PrintWriter;
+
+/**
+ * @author Kohsuke Kawaguchi
+ */
+public class ReopenableRotatingFileOutputStreamTest extends TestCase {
+    public void testRotation() throws IOException {
+        File base = File.createTempFile("test", "log");
+        ReopenableRotatingFileOutputStream os = new ReopenableRotatingFileOutputStream(base,3);
+        PrintWriter w = new PrintWriter(os,true);
+        for (int i=0; i<=4; i++) {
+            w.println("Content"+i);
+            os.rewind();
+        }
+        w.println("Content5");
+
+        assertEquals("Content5", new FilePath(base).readToString().trim());
+        assertEquals("Content4", new FilePath(new File(base.getPath() + ".1")).readToString().trim());
+        assertEquals("Content3", new FilePath(new File(base.getPath() + ".2")).readToString().trim());
+        assertEquals("Content2", new FilePath(new File(base.getPath() + ".3")).readToString().trim());
+        assertFalse(new File(base.getPath() + ".4").exists());
+
+        os.deleteAll();
+    }
+}