src/webapps/datanode/tail.jsp

<%@ 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.server.common.*"
  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.security.token.Token"
  import="org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier"
  import="org.apache.hadoop.util.*"
  import="org.apache.hadoop.net.NetUtils"
  import="org.apache.hadoop.security.UserGroupInformation"
  import="java.text.DateFormat"
%>

<%!
  static JspHelper jspHelper = new JspHelper();

  public void generateFileChunks(JspWriter out, HttpServletRequest req,
                                 Configuration conf
                                ) throws IOException, InterruptedException {
    long startOffset = 0;
    
    int chunkSizeToView = 0;
    String tokenString = req.getParameter(JspHelper.DELEGATION_PARAMETER_NAME);
    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);
    
    String chunkSizeToViewStr = req.getParameter("chunkSizeToView");
    if (chunkSizeToViewStr != null && Integer.parseInt(chunkSizeToViewStr) > 0)
      chunkSizeToView = Integer.parseInt(chunkSizeToViewStr);
    else chunkSizeToView = JspHelper.getDefaultChunkSize(conf);

    if (!noLink) {
      out.print("<h3>Tail of File: ");
      JspHelper.printPathWithLinks(filename, out, namenodeInfoPort, 
                                   tokenString);
	    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
    UserGroupInformation ugi = JspHelper.getUGI(req, conf);
    DFSClient dfs = JspHelper.getDFSClient(ugi, jspHelper.nameNodeAddr, 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();
    Token<BlockTokenIdentifier> accessToken = lastBlk.getBlockToken();
    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
    if (blockSize >= chunkSizeToView)
      startOffset = blockSize - chunkSizeToView;
    else startOffset = 0;

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

%>



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

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

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