src/webapps/datanode/tail.jsp

<%
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file 
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
%>
<%@ page
  contentType="text/html; charset=UTF-8"
  import="javax.servlet.*"
  import="javax.servlet.http.*"
  import="java.io.*"
  import="java.util.*"
  import="java.net.*"
  import="org.apache.hadoop.hdfs.*"
  import="org.apache.hadoop.hdfs.server.namenode.*"
  import="org.apache.hadoop.hdfs.server.datanode.*"
  import="org.apache.hadoop.hdfs.protocol.*"
  import="org.apache.hadoop.io.*"
  import="org.apache.hadoop.conf.*"
  import="org.apache.hadoop.net.DNS"
  import="org.apache.hadoop.util.*"
  import="org.apache.hadoop.net.NetUtils"
  import="java.text.DateFormat"
%>

<%!
  static final DataNode datanode = DataNode.getDataNode();

  public void generateFileChunks(JspWriter out, HttpServletRequest req) 
    throws IOException {
    String referrer = req.getParameter("referrer");
    boolean noLink = false;
    if (referrer == null) {
      noLink = true;
    }

    String filename = req.getParameter("filename");
    if (filename == null) {
      out.print("Invalid input (file name absent)");
      return;
    }

    String namenodeInfoPortStr = req.getParameter("namenodeInfoPort");
    int namenodeInfoPort = -1;
    if (namenodeInfoPortStr != null)
      namenodeInfoPort = Integer.parseInt(namenodeInfoPortStr);
    
    final int chunkSizeToView = JspHelper.string2ChunkSizeToView(req.getParameter("chunkSizeToView"));

    if (!noLink) {
      out.print("<h3>Tail of File: ");
      JspHelper.printPathWithLinks(filename, out, namenodeInfoPort);
	    out.print("</h3><hr>");
      out.print("<a href=\"" + referrer + "\">Go Back to File View</a><hr>");
    }
    else {
      out.print("<h3>" + filename + "</h3>");
    }
    out.print("<b>Chunk size to view (in bytes, up to file's DFS block size): </b>");
    out.print("<input type=\"text\" name=\"chunkSizeToView\" value=" +
              chunkSizeToView + " size=10 maxlength=10>");
    out.print("&nbsp;&nbsp;<input type=\"submit\" name=\"submit\" value=\"Refresh\"><hr>");
    out.print("<input type=\"hidden\" name=\"filename\" value=\"" + filename +
              "\">");
    out.print("<input type=\"hidden\" name=\"namenodeInfoPort\" value=\"" + namenodeInfoPort +
    "\">");
    if (!noLink)
      out.print("<input type=\"hidden\" name=\"referrer\" value=\"" + 
                referrer+ "\">");

    //fetch the block from the datanode that has the last block for this file
    final DFSClient dfs = new DFSClient(datanode.getNameNodeAddr(), JspHelper.conf);
    List<LocatedBlock> blocks = 
      dfs.namenode.getBlockLocations(filename, 0, Long.MAX_VALUE).getLocatedBlocks();
    if (blocks == null || blocks.size() == 0) {
      out.print("No datanodes contain blocks of file "+filename);
      dfs.close();
      return;
    }
    LocatedBlock lastBlk = blocks.get(blocks.size() - 1);
    long blockSize = lastBlk.getBlock().getNumBytes();
    long blockId = lastBlk.getBlock().getBlockId();
    long genStamp = lastBlk.getBlock().getGenerationStamp();
    DatanodeInfo chosenNode;
    try {
      chosenNode = JspHelper.bestNode(lastBlk);
    } catch (IOException e) {
      out.print(e.toString());
      dfs.close();
      return;
    }      
    InetSocketAddress addr = NetUtils.createSocketAddr(chosenNode.getName());
    //view the last chunkSizeToView bytes while Tailing
    final long startOffset = blockSize >= chunkSizeToView? blockSize - chunkSizeToView: 0;

    out.print("<textarea cols=\"100\" rows=\"25\" wrap=\"virtual\" style=\"width:100%\" READONLY>");
    JspHelper.streamBlockInAscii(addr, blockId, genStamp, blockSize, startOffset, chunkSizeToView, out);
    out.print("</textarea>");
    dfs.close();
  }

%>



<html>
<head>
<%JspHelper.createTitle(out, request, request.getParameter("filename")); %>
</head>
<body>
<form action="/tail.jsp" method="GET">
<% 
   generateFileChunks(out,request);
%>
</form>
<hr>

<h2>Local logs</h2>
<a href="/logs/">Log</a> directory

<%
out.println(ServletUtil.htmlFooter());
%>