
                    mod_dav Installation and Configuration
                                       
   This page details as much information as possible regarding the
   building, installation, and configuration of the mod_dav Apache
   module. This page does not cover installation of binary distributions
   of mod_dav, although the Apache configuration will still apply.
   
     * [1]Unix Build and Install
     * [2]Windows Build and Install
     * [3]Apache Configuration
     * [4]Setting Up the File Repository
     * [5]Other Notes
     * [6]Expat Build and Install (if necessary)
       
     * [7]What to do if you have a problem
       
     * [8]Configuration for complex setups
       This section explains how to configure mod_dav when other "content
       handlers" such as mod_include, PHP, or CGI scripts are present.
       
   When this page refers to "Unix", it generally means any of the Unix or
   Unix-like platforms (such as Linux, *BSD, Solaris, AIX, HP/UX, etc).
   
   [9][ back to the main mod_dav page ]
     _________________________________________________________________
   
Unix Build and Install

   Step 1: Configuration
          There are two general mechanisms for installing mod_dav into
          your Apache installation. The first method is to create a
          dynamically-loaded module using the "apxs" tool. The second
          method is to statically link mod_dav into the Apache
          executable.
          
          Based on the method you choose, use one of the following
          configure commands:
          
     ./configure --with-apxs=/usr/local/apache/bin/apxs
     
     or
     ./configure --with-apache=/usr/local/apache
     
          Of course, you should use the path to your system's apxs
          executable or Apache build directory.
          
     Note: if you use just --with-apxs (no directory), then configure
     assumes that apxs is in your path.
     
     Note: sometimes, the APXS installation may be broken. If the
     configure process reports this, then please refer to a [10]FAQ
     entry written by the PHP folks. It explains the problem quite well.
     
          The configuration process will do its stuff. One of its tasks
          is to locate the Expat library (an XML parsing library). This
          library is included with Apache 1.3.9 and will automatically be
          found. If you have a previous version of Apache 1.3 (it must be
          at least Apache 1.3.4), then you will need a copy on your
          system. configure will look for it in /usr/{include,lib} and in
          /usr/local/{include,lib}. If it can't find it, then you will
          need to tell configure where it is on your system using the
          --with-expat=<dir> command line option. For example:
          
     ./configure --with-apxs=/usr/local/apache/bin/apxs
     --with-expat=/home/gstein/expat
     
          If you need Expat, then please see [11]the section at the end
          of this document for information on where to get Expat and how
          it must installed on your system.
          
   Step 2: Build and Install
          This is pretty simple. Just use the following two commands:
          
     make
     make install
     
        Dynamic loading
                If you chose to do a dynamically-loaded module using
                APXS, then your module will have been installed into
                Apache's runtime area.
                
                Note: if using APXS and your Apache installation does not
                support loadable modules, then APXS will terminate with
                an error. Typically, we have seen the following error
                when this happens:
                
     apxs:Break: Command failed with rc=16711680
     
                If this happens, then you will need to rebuild and
                reinstall your Apache software with the mod_so module
                included. Note the reinstall part -- we've seen several
                cases where a new Apache was built and installed, but a
                new APXS was not (so the problems continued).
                
                PHP has a [12]FAQ entry about this problem that may help.
                
        Static linking
                If you chose to go with statically linking mod_dav into
                Apache, then mod_dav will have been partially compiled
                and placed into the Apache tree during the make install
                step. You are now ready to (re)configure and build
                Apache. When you configure Apache, there are two methods
                that you can choose. For the APACI-style (./configure
                style), use the following command line option:
                
     --activate-module=src/modules/dav/libdav.a
     
                For the old-style configuration, add the following line
                to your Configuration.tmpl file:
                
     SharedModule modules/dav/libdav.a
     
   Step 3: Configure Apache
          See [13]the Apache configuration section below.
     _________________________________________________________________
   
Win32 Build and Install

   Step 1: Expat installation
          Expat must be installed first. See [14]the Expat section at the
          end of this document for instructions.
          
   Step 2: Build
          To build mod_dav using Microsoft Visual C++, simply issue the
          following command line from the directory containing the
          mod_dav files:
          
     nmake /f mod_dav.mak
     
          This builds an optimized version of mod_dav, located in
          Release/mod_dav.dll.
          
          mod_dav can also be built with Microsoft Visual Studio 5.0 or
          later using the supplied .dsp file.
          
   Step 3: Install
          For mod_dav installation, copy the following three files:
          
Release/mod_dav.dll
expat/bin/xmlparse.dll
expat/bin/xmltok.tll

          to the directory where your Apache modules are located
          (ServerRoot). If you use a precompiled binary, then just ensure
          the three DLLs are in the ServerRoot directory.
          
          To add mod_dav to Apache, add the following line to the
          httpd.conf file:
          
     LoadModule dav_module mod_dav.dll
     
   Step 4: Configure Apache
          See [15]the Apache configuration section below.
     _________________________________________________________________
   
Apache Configuration

   See the note on [16]upgrading from 0.9.8 and prior versions.
   
  Loading the DAV Module
  
   Apache must be informed about the mod_dav module through the Addmodule
   and LoadModule directives. LoadModule is used when mod_dav is
   dynamically loaded (i.e. built using APXS or you're on the Win32
   platform). These configuration lines are (normally) inserted
   automatically on the Unix platforms (by APXS or the Apache build
   process), but the Win32 line needs to be added manually for that
   platform.
   (this information is here for reference; if Apache does not recognize
   the mod_dav directives such as DAV or DAVLockDB, then you may be
   missing these configuration lines)
     * Unix platform, dynamic loading:
Loadmodule dav_module libexec/libdav.so
Addmodule mod_dav.c
     * Unix platform, statically linked:
Addmodule mod_dav.c
     * Win32 platform:
Loadmodule dav_module mod_dav.dll
Addmodule mod_dav.c
       
  Enabling DAV
  
   Configuring the mod_dav module is quite simple, actually. Within a
   <Directory> or <Location> directive in your Apache configuration file
   (i.e. httpd.conf), simply insert the following line:
   
     DAV On
     
   If the DAV directive is within a <Directory> directive, then DAV will
   be enabled for that particular directory and its subdirectories. For a
   <Location> directive, then DAV will be enabled for that portion of the
   URL namespace.
   
  The Lock Database
  
   Next, add a DAVLockDB directive at the top-level of your configuration
   file (i.e. outside of a <Directory> or <Location> directive). This
   directive should specify a filename that mod_dav will create. The
   directory should exist and should be writable by the web server
   process.
   
     Note: the directory should not be on an NFS-mounted partition.
     mod_dav uses flock/fcntl to manage access to the database. Some
     operating systems cannot use these operations on an NFS-mounted
     partition.
     
   In the following example, the DAV lock database will be stored in the
   /usr/local/apache/var directory (which must be writable by the server
   process). The file's name will be DAVLock when mod_dav needs to create
   it.
   (actually, mod_dav will create one or more files using this file name
   plus an extension)
   
     DAVLockDB /usr/local/apache/var/DAVLock
     
   The DAVLockDB directive can appear outside of any container or within
   a <VirtualHost>, it only needs to appear once, and a file extension
   should not be supplied.
   
  Lock Timeout Minimums
  
   An optional directive, DAVMinTimeout, specifies the minimum lifetime
   of a lock in seconds. If a client requests a lock timeout less than
   DAVMinTimeout, then the DAVMinTimeout value will be used and returned
   instead. For example, Microsoft's Web Folders defaults to a lock
   timeout of 2 minutes; 10 minutes could be used to reduce network
   traffic and the chance that the client might lose a lock due to
   network latency.
   
   The DAVMinTimeout directive is optional, and may be used on a
   per-server or per-directory/location basis. It takes a single,
   non-negative integer. Since this value represents a minimum allowed,
   setting it to zero (0) will disable this feature. The default value
   for DAVMinTimeout is zero.
   
  Preventing "Depth Infinity" PROPFINDs
  
   A PROPFIND request with a Depth:&nbspInfinity header can impose a
   large burden on the server. These kinds of requests could "walk" the
   entire repository, returning information about each resource found.
   mod_dav builds the response in memory, so these kinds of requests
   could potentially consume a lot of memory (the memory would be
   released at the end of the request, but the peak can be quite large).
   
   To prevent these kinds of requests, the DAVDepthInfinity directive has
   been provided. It is a simple on/off directive, which can be used on a
   per-server or a per-directory/location basis. The default value for
   this directive is off, meaning these kinds of requests are not
   allowed.
   
   NOTE: the WebDAV Working Group has stated that it is acceptable for
   DAV servers to refuse these kinds of requests. Properly written client
   software should not issue them, and you should not worry about
   disabling them.
   
  Limiting XML Request Body Sizes
  
   mod_dav will parse XML request bodies into memory. It would be a very
   effective "Denial of Service" attach to send a large request body at a
   mod_dav server. Apache defines a directive named LimitRequestBody
   which will limit all methods' request bodies. Unfortunately, this is
   not an effective mechanism for a mod_dav server since large PUT
   operations should be allowed.
   
   To limit just the methods that have an XML request body, mod_dav
   defines the LimitXMLRequestBody directive. The default for this value
   is a compile-time constant, which is set to one million (1000000)
   bytes in the standard distribution. Setting the value to zero (0) will
   disable the size limit.
   
   LimitXMLRequestBody may be set on a per-server or a
   per-directory/location basis, and takes a single non-negative integer
   argument.
   
  Sample Configuration
  
   A sample configuration segment might look like:
   
   ...
   DAVLockDB /usr/local/apache/var/DAVLock
   DAVMinTimeout 600
   <Location /mypages>
       DAV On
   </Location>
   ...
   
  Limiting DAV Access to Authorized Users
  
   The DAV and DAVLockDB directives are the only two configuration
   changes necessary to operate a DAV server. However, it is usually best
   to secure the site to be writable only by specific users. This
   requires the use of the <Limit> directive. Here is an example:
   
   <Location /mypages>
       DAV On
       <Limit PUT POST DELETE PROPFIND PROPPATCH MKCOL COPY MOVE LOCK
   UNLOCK>
           Require user greg
       </Limit>
   </Location>
   
   The above configuration will allow only authorized users to manipulate
   the site. However, it does allow them a bit more freedom than you may
   like. In particular, they may be able to place a .htaccess file into
   the target directory, altering your server configuration. The server
   may have already been configured to not read .htaccess files, but it
   is best to make sure. Also, you may want to disallow other options
   within the DAV-enabled directory -- CGI, symbolic links, server-side
   includes, etc. Here is a modified configuration with the additional
   restrictions placed on it:
   
   <Location /mypages>
       DAV On
       AllowOverride None
       Options None
       <Limit PUT POST DELETE PROPFIND PROPPATCH MKCOL COPY MOVE LOCK
   UNLOCK>
           Require user greg
       </Limit>
   </Location>
   
  Using LimitExcept
  
   Rather than using the <Limit> directive and specifying an exhaustive
   list of HTTP methods to secure, it is also possible to use the
   <LimitExcept> directive. This directive applies the access
   restrictions to all methods except for the methods listed. For
   example, your configuration section might look like:
   
   <Location /mypages>
       DAV On
       AllowOverride None
       Options None
       <LimitExcept GET HEAD OPTIONS>
           require user webadmin
       </LimitExcept>
   </Location>
   
   Choosing to use one or the other is a matter of preference. The
   <Limit> directive is precise and explicit, but the <LimitExcept>
   directive will automatically restrict methods that are added in the
   future.
   
  PROPFIND Security
  
   In the example configurations above, the PROPFIND method was limited,
   even though it is read-only. This is because the PROPFIND method can
   be used to list all the files in the DAV-enabled directory. For
   security purposes, you probably want the exact list of files to be
   hidden.
   
   An alternative would be to limit the PROPFIND to a group of people, a
   set of domains, or a set of hosts, while the methods that modify
   content are limited to just a few authors. This scenario allows, say,
   your company's employees to browse the files on the server, yet only a
   few people can change them. Anonymous (non-authenticated) visitors
   cannot browse or modify.
   
   Finally, you can simply omit PROPFIND from the limits if your web
   server is intended as a general, read-only repository of files. This
   allows anybody to arbitrarily browse the directories and then to fetch
   the files.
   
  Other Security Issues
  
   Please refer to the [17]security section, on the main mod_dav web
   page, for more information about security issues related to DAV and
   mod_dav in particular.
   
  Upgrading from version 0.9.8 or earlier
  
   Previous versions did not contain a DAVLockDB directive. You will need
   to add that for mod_dav to operate properly.
     _________________________________________________________________
   
Setting Up the File Repository

   mod_dav requires read/write access to the filesystem where the
   documents are stored. The following discussion uses Unix as an
   example; the Win32 platform will have similar concerns when used on an
   NTFS partition (where file/directory security is present).
   
   The need for read/write access means that the owner and group of the
   files will be that of the web server. For discussion, let's say that
   your Apache configuration file contains the following directives
   (among others!):
   
   User nobody
   Group www
   Alias /pages /home/www/davhome
   <Location /pages>
       DAV On
   </Location>
   
   In the above configuration, the web server is running as "nobody" and
   as group "www". mod_dav is going to need to read/write files in the
   /home/www/davhome directory. A directory listing might look like this:
   
drwxr-s---   2 nobody   www          1024 Jul 14 11:28 ./
drwxr-s---  18 nobody   www          1024 Oct 25 17:03 ../
drwxr-s---   2 nobody   www          1024 Oct 11 01:37 .DAV/
-rw-r--r--   1 nobody   www          2976 Jul 14 11:28 acknowledgments.html
-rw-r--r--   1 nobody   www          2755 Jul 14 11:28 demos.html
-rw-r--r--   1 nobody   www          4963 Jul 14 11:28 documentation.html
-rw-r--r--   1 nobody   www          4423 Jul 14 11:28 downloads.html
-rw-r--r--   1 nobody   www          1457 Jul 14 11:28 footnote.html
drwxr-s---   2 nobody   www          1024 Oct 18 11:52 images/
-rw-r--r--   1 nobody   www          5592 Jul 14 11:28 index.html
-rw-r--r--   1 nobody   www          2136 Jul 14 11:28 intro.html
-rw-r--r--   1 nobody   www          5456 Jul 14 11:28 news.html
-rw-r--r--   1 nobody   www          3125 Jul 14 11:28 tutorial.html

   In this example, the web server will have no problem reading and
   writing the files in the /home/www/davhome file repository.
   
   NOTE: the file repository is considered "private" to mod_dav and the
   web server. Modifying files via FTP or through filesystem commands
   should not be allowed. This is for a couple reasons:
    1. External access may create files and directories with ownership or
       privileges that would prevent mod_dav from operating properly.
    2. mod_dav does not use filesystem locking to protect the files from
       modification. Note that filesystem locking isn't even a guarantee
       [against changes] on many operating systems.
     _________________________________________________________________
   
Other Notes

   The DAV spec ([18]RFC 2518) does not incorporate a security model. It
   relies on any web server and file system security that the
   administrator configures.
   
   On Unix machines, the web server process must have permission to write
   to the DAV-enabled directories and any files to be modified.
   
   Local manipulation of files in a DAV-enabled directory is a bad thing.
   Specifically, DAV file locks are implemented by mod_dav, not the file
   system.
     _________________________________________________________________
   
Expat Build and Install

   James Clark's Expat parser is included in the source tree of Apache
   1.3.9 and later. It is only necessary to obtain and build the Expat
   distribution when using an earlier version of Apache.
   
   On Windows precompiled Expat dlls are not shipped with the Apache
   distribution but are available with the mod_dav Win32 distribution.
   
   If needed, James Clark's Expat parser is available from:
   
     [19]http://www.jclark.com/xml/
     
   For Windows
          Extract the Expat parser .zip into the directory where the
          mod_dav files are located, using the folders stored in the zip.
          Expat will be extracted into the expat/ subdirectory.
          
   For Unix
          Note that the expat Makefile does not automatically build the
          expat library. Add this rule to the Makefile:
          
  libexpat.a: $(OBJS)
        ar -rc $@ $(OBJS)
        ranlib $@
        
          (don't forget to use tabs before the ar and ranlib lines there)
          
          Then type: make libexpat.a
          
          And copy libexpat.a to /usr/local/lib and xmlparse/xmlparse.h
          to /usr/local/include. If you wish to use a different
          directory, then you will need to pass that to ./configure using
          the --with-expat command line option.
     _________________________________________________________________
   
What to do if you have a problem

   Problems with the installation, configuration, or operation of mod_dav
   should be sent to the [20]dav-dev mailing list. There are a number of
   people subscribed to that list who can help, so your chance of a
   speedy reply is much better than sending to Greg's (too-full) email
   inbox.
   
   Information you should include:
     * What versions of mod_dav and Apache are you using?
     * What client are you using to (attempt to) talk to your DAV-enabled
       server?
     * The relevant portions of your httpd.conf
     * The relevant portions of your error_log and access_log
     * Are you attempting to talk to the DAV server through a proxy?
       There are [21]known problems with many proxy servers.
       
   To send mail to the dav-dev mailing list:
   
     [22]dav-dev@lyra.org
     
   Information about subscribing to the mailing list, and a link to the
   list's archive:
   
     [23]http://dav.lyra.org/mailman/listinfo/dav-dev
     _________________________________________________________________
   
Configuration for complex setups

   Apache has a particular design restriction in that only one "content
   handler" is allowed to process a request. There are multiple stages
   involving authorization, access checking, MIME type handling, etc, but
   there is only one content handler.
   
   This content handler is specified with directives such as SetHandler,
   AddHandler, or indirectly by mapping a MIME type to a handler. Apache
   modules may also assert themselves as the handler during the request
   processing. mod_dav asserts itself this way when the DAV directive has
   enabled DAV for a particular directory or location. Content handlers
   may decide to assert themselves based on the request method; for
   example, mod_dav will be the content handler for methods such as PUT,
   DELETE, and PROPPATCH, but not for the GET method (which is left to be
   handled by other modules or Apache itself).
   
   Once a content handler is identified for a request, then it will
   perform the bulk of the processing: it will manage the body of the
   request, and it will construct the response.
   
   The problem that crops up is that many modules will assert themselves
   as the content handler regardless of the request method. When a DAV
   client issues a PROPFIND, it will be intercepted by the other module,
   rather than mod_dav. This is actually reasonable, when you consider
   that a PHP or CGI script is perfectly capable of responding to a
   PROPFIND. It is just that we want mod_dav to do it.
   
   In the sections below, I'll cover some general problems and their
   solutions.
   
  Web Folders fails when copying a dynamic resource
  
   Problem: You are attempting to copy a dynamic resource, such as a CGI
   script, a server-parsed file (.shtml), or a PHP file, and you get an
   error dialog that reads:
   
     An error occurred copying some or all of the selected files.
     
   This is caused by the server-side script not returning a Last-Modified
   header. If the script can support returning headers (e.g. CGI or PHP),
   then it should be modified to ensure that a Last-Modified header is
   returned.
   
   NOTE: the recommendation below has been found to NOT work. It inserts
   a constant Last-Modified time onto a dynamic script. Users' browsers
   and proxies will see the constant time and believe that the output has
   not changed. At this time, there is no specific answer to the problem.
   
   If the script cannot return headers (such as a server-parsed HTML file
   (.shtml)), then you can update your Apache installation to include the
   [24]mod_headers module. Next, add a configuration section to your
   httpd.conf similar to the following:
   
   <Files "*.shtml">
       Header set Last-Modified "Fri, 03 Mar 2000 06:32:31 GMT"
   </Files>
   
   The date that you specify should not be in the future. This will
   pretend that all server-parsed files have a specific, constant
   modification date, but things may be okay.
   
   Note: I have not performed exhaustive tests to discover the
   ramifications of forcing a Last-Modified header to a fixed time. In my
   tests, this allows Web Folders to perform the copy successfully, and
   Internet Explorer seems to be fine with it.
   
  I'm getting PHP output rather than the source
  
   This is caused by the simple fact that a GET is always going to run
   the script. There is no way to distinguish a "GET for the result" and
   a "GET for authoring."
   Note: this problem applies to any server-side scripting solution. It
   is not specific to PHP. For demonstrations sake, I will use PHP as an
   example.
   
   PHP and mod_dav will also conflict when they each attempt to handle
   the different HTTP request methods. This is caused by the simple fact
   that both modules are configured for the same location or directory,
   and are competing for acting as the content handler.
   
   There are several ways to fix this. They all solve the problem by
   providing a separate URL to access the PHP source. In one scenario,
   you can provide a simple "source" URL:
   
   Alias /phparea /home/gstein/php_files
   Alias /php-source /home/gstein/php_files
   <Location /php-source>
       DAV On
       ForceType text/plain
   </Location>
   
   A different alternative is to present the source through another
   virtual server:
   
   <VirtualHost 12.34.56.78>
       DocumentRoot /home/gstein/php_files
   </VirtualHost>
   <VirtualHost 12.34.56.78:81>
       DocumentRoot /home/gstein/php_files
       DAV On
       ForceType text/plain
   </VirtualHost>
   
   There are probably a few, similar ways to accomplish the same kind of
   setup. I have used the first form (a secondary URL space)
   successfully, but have not tried the second virtual host. Other people
   have reported success with it, however.
   
   In each of these ways to fix the problem, we are taking advantage of
   the fact that there are different URL namespaces that map to the same,
   underlying filesystem space. By attaching different processing to the
   URL spaces, we can create different behaviors during the translation
   to the filesystem space.
   
   Finally, I believe that it may be possible to ensure that mod_dav
   occurs later in the AddModule directives, thus making mod_dav be the
   content handler for methods besides GET. If PHP is later in the list,
   then it will end up handling all methods. This trickery does not solve
   the authoring problem, however.
     _________________________________________________________________
   
   
    [25]Greg Stein
    
   Last modified: Wed Jun 28 00:18:59 PDT 2000

References

   1. http://www.webdav.org/mod_dav/install.html#unix
   2. http://www.webdav.org/mod_dav/install.html#win32
   3. http://www.webdav.org/mod_dav/install.html#apache
   4. http://www.webdav.org/mod_dav/install.html#repository
   5. http://www.webdav.org/mod_dav/install.html#notes
   6. http://www.webdav.org/mod_dav/install.html#expat
   7. http://www.webdav.org/mod_dav/install.html#problem
   8. http://www.webdav.org/mod_dav/install.html#complex
   9. http://www.webdav.org/mod_dav/
  10. http://www.php.net/FAQ.php#6.11
  11. http://www.webdav.org/mod_dav/install.html#expat
  12. http://www.php.net/FAQ.php#6.11
  13. http://www.webdav.org/mod_dav/install.html#apache
  14. http://www.webdav.org/mod_dav/install.html#expat
  15. http://www.webdav.org/mod_dav/install.html#apache
  16. http://www.webdav.org/mod_dav/install.html#add-lockdb
  17. http://www.webdav.org/mod_dav/index.html#security
  18. http://www.webdav.org/specs/index.html#dav
  19. http://www.jclark.com/xml/
  20. http://dav.lyra.org/mailman/listinfo/dav-dev
  21. http://www.webdav.org/other/proxy.html
  22. mailto:dav-dev@lyra.org
  23. http://dav.lyra.org/mailman/listinfo/dav-dev
  24. http://www.apache.org/docs/mod/mod_headers.html
  25. mailto:gstein@lyra.org
