Updated 10/6/06: added @rev argument to svn diff so it works even if the file has moved.

Tools tool tools. Frankly, I’m obsessed with them. I can’t properly embark on a project unless I first set up a decent environment. At my new company, my buddy and I needed a cheap and cheerful way to keep track of our work. We quickly set up a subversion repository on our site5 host, and then I hacked together a subversion post commit hook as described in my previous post.

I added some meat to the commit emails by plugging in a simple diff viewer. The diff viewer is structured as a CGI that can run completely standalone, so you can plug it into just about any server. Here’s a tiny screenshot from Firefox:

There are a few tidbits I’d like to highlight before we get to the install instructions.

The gentle red/blue/green color scheme is copied directly from the Cascade source code control system we created at Marimba. I believe Arthur van Hoff came up with the colors, and I’ve happily recycled them into many similar projects. Red means deleted, blue means changed, green means added.

The diff viewer shows the whole file, not just those terrible contextual diffs that some people seem to like. How can anyone understand a diff without seeing the whole file? I accomplished this amazing feat simply by passing “-U 10000″ to diff.

Also, the diff blocks are connected with up/down arrow links for easy navigation. Click on the arrows to quickly eyeball each of the differences.

To install:

1. Copy the script to your web server and rename it to “diff.cgi” or something appropriate.
2. Make it executable.
3. Set the REPO constant at the top.
4. If you’re using my post commit hook, change the diff links to point to the CGI. Modify this line in the filesToHtml function:

           result << CGI.escapeHTML(file)
   

   to read:

         if revision
           result << "<a href='http://YOUR_HOST/AND_PATH/diff.cgi?file=#{CGI.escape(file)}&rev=#{revision}'>#{CGI.escapeHTML(file)}</a>"
         else
           result << CGI.escapeHTML(file)
         end
   

You can download the script or copy and paste it from below:

#!/usr/bin/ruby -w

# svn-diff : CGI for viewing SVN diffs

require 'cgi'

SVN  = "/usr/bin/svn"
DIFF = "/usr/bin/diff"
REPO = "svn://MODIFY_THIS/TO/POINT/TO/YOUR/REPO"

#
# globals
#

$anchor = 0
$last_op = ' '
$left = []
$right = []

#
# helper for building the next row in the diff
#

def getDiffRow()
  anchor = ""
  result = ""
  if $left.length > 0 or $right.length > 0
    if $last_op != ' '
      if $left.length == 0
        clazz = " class='a'"
      elsif $right.length == 0
        clazz = " class='r'"
      else
        clazz = " class='m'"
      end
      anchor << <<EOF
<a name="#{$anchor}"/><a href="##{$anchor-1}">&uarr;&uarr;</a> <a href="##{$anchor+1}">&darr;&darr;</a>
EOF
      $anchor += 1
    else
      clazz = ""
    end
    result = <<EOF
<tr#{clazz}><td>#{anchor}</td><td>#{$left.join("\n")}</td><td>#{$right.join("\n")}</td></tr>
EOF
  end
  result
end

#
# build the diff
#

def getDiff(repo, file, rev1, rev2)
  result = ""

  diff = `#{SVN} diff -r #{rev1}:#{rev2} #{repo}/#{file}@#{rev1} --diff-cmd #{DIFF} -x '-w -U 10000'`.split("\n")
  raise "svn diff failed" if $? != 0

  index = diff.shift
  equals = diff.shift
  header1 = diff.shift
  if header1 =~ /^---/
    result << "<p><a href='#0' style='text-decoration:none'>&darr;&darr;</a></p>\n"
    result << "<table class='diff' width='80%'>"
    result << "<tr height='2'><td/><td width='48%'/><td width='48%'/></tr>"

    # skip header2 and range
    diff.shift
    diff.shift

    diff.each do |line|
      op = line[0,1]
      line = line[1..-1]

      if (($last_op != ' ' and op == ' ') or ($last_op == ' ' and op != ' '))
        result << getDiffRow
        $left.clear
        $right.clear
      end

      # truncate and escape
      line[62..-1] = "..." if line.length > 65
      line = CGI.escapeHTML(line)

      case op
      when ' '
        $left.push(line)
        $right.push(line)
      when '-' then $left.push(line)
      when '+' then $right.push(line)
      end
      $last_op = op
    end

    result << getDiffRow
    result << "</table>"
  else
    result = "<div class='error'>#{header1}</div>"
  end

  <<EOF
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>#{file}, rev #{rev1}:#{rev2}</title>
        <style type="text/css">
          body {
            font : 11pt verdana;
            background : white;
          }
          .error {
            color : red;
          }
          .diff {
            font-size : 9pt;
            font-family : "lucida console", "courier new", monospace;
            white-space : pre;
            border : 1px solid black;
            border-collapse : collapse;
            line-height : 110%;
          }
          .diff td {
            border : none;
            padding : 0px 10px;
            margin : 0px;
          }
          .diff td a {
            text-decoration: none;
          }
          .a { background : #bbffbb; }
          .r { background : #ffbbbb; }
          .m { background : #bbbbff; }
        </style>
    </head>
    <body>
        <h3>Subversion diff on #{file}, rev #{rev1}:#{rev2}</h3>
#{result}
    </body>
</html>
EOF
end

#
# main - handles either command line or CGI
#

cgi = CGI.new
begin
  if cgi.server_software
    file = cgi.params['file']
    rev = cgi.params['rev']
    raise "bad file param" if !file || file.length == 0
    raise "bad rev param" if !rev || rev.length == 0
    file = file[0]
    rev = rev[0]
  else
    file = ARGV.shift
    rev = ARGV.shift
  end

  raise "bad file param" if file.length == 0
  raise "bad rev param" if rev.length == 0

  rev = rev.to_i
  cgi.out("status" => "OK") {
    getDiff(REPO, file, rev - 1, rev)
  }
rescue StandardError => e
  cgi.out("status" => "SERVER_ERROR") {
    <<EOF
<html>
  <body style="color:red">
    <p>error : #{e.message}</p>
<pre>#{e.backtrace.collect { |x| CGI.escapeHTML(x) }.join("\n")}
</pre>
  </body>
</html>
EOF
  }
end