9 Configuring and Using mod_oradav

9.1.1 WebDAV

WebDAV is a protocol extension to HTTP 1.1 that supports distributed authoring and versioning. With WebDAV, the Internet becomes a transparent read and write medium, where content can be checked out, edited, and checked in to a URL address.

WebDAV enables collaboration among authors building Web sites. WebDAV also serves as universal read and write access protocol to arbitrary hierarchies of content (not necessarily Web sites). With WebDAV, you can save content to a URL provided by an Internet Service Provider (ISP), and then be able to access and optionally change that content from various devices.

WebDAV was initiated as an Internet Engineering Task Force (IETF) standard. The first phase of WebDAV is specified in RFC 2518, which provides the basic primitives for managing hierarchies of information, locking, reading, writing, and querying properties of a WebDAV document. Subsequent work on WebDAV is ongoing and is focusing on completing issues relating to content management over the Web. This includes WebDAV authentication and authorization (access controls), versioning, bindings, ordered collections, and querying (DAV Advanced Searching and Locating).

Microsoft Web folders is a WebDAV client on Windows 2000, and later versions (using Internet Explorer 5.0 and higher). Office 2000 and Office XP applications and the IIS server support WebDAV, meaning that you can start a Microsoft Office application and specify a URL, edit the content, and save it back to the URL from which it was retrieved. WebDAV also has Java clients (such as DAV Explorer), open source tools (such as Cadaver and Sitecopy), and Apple GUI tools (such as Goliath).

9.1.2 mod_dav

mod_dav is the Apache Software Foundation native implementation of the WebDAV specification.

9.1.3 mod_oradav

mod_oradav is the Oracle module (an OCI application written in C) that is an extended implementation of mod_dav, and is integrated with Oracle HTTP Server. mod_oradav performs read/write activity to local files and to Oracle databases. Oracle databases must have an OraDAV driver (a stored procedure package) that mod_oradav calls to map WebDAV activity to database activity. Essentially, mod_oradav enables WebDAV clients to connect to an Oracle database, read and write content, and query and lock documents in various schemas.

You can configure mod_oradav to use an Oracle database using standard Oracle HTTP Server directives. mod_oradav can immediately leverage other module code (such as mime_magic) in order to perform content management tasks. Most WebDAV processing activity involves streaming content to and from a content provider; and mod_oradav uses OCI streaming logic directly within Oracle HTTP Server.

9.1.4 OraDAV

OraDAV refers to the whole set of capabilities that are available through mod_oradav to Oracle Application Server users. Some OraDAV-specific terms include:

• Apache OraDAV: Code in the Apache HTTP server that supports file-based DAV access and makes calls to Oracle.

• OraDAV driver API: Set of stored procedure calls that are used by the OraDAV driver to manage content in an Oracle database, providing support for the following WebDAV functions over the Internet: reading and writing documents, locking and unlocking documents, managing (creating, populating, deleting) hierarchies of information, retrieving properties associated with documents, and associating properties with specific documents.

• OraDAV driver: Stored procedure implementation of the OraDAV driver API that executes in Oracle and manages a repository.

9.5.1 ORAAllowIndexDetails

In an Oracle HTTP Server environment that is not OraDAV-enabled, mod_dav itself does not respond to HTTP GET requests. Instead, normal Oracle HTTP Server mechanisms are used to respond to GET requests. However, when all your content is in an Oracle database, normal Oracle HTTP Server mechanisms cannot be used to respond to GET requests, and thus OraDAV must respond to GET requests.

The ORAAllowIndexDetails parameter controls how OraDAV responds when a GET request is performed on a DAV collection and no index.html file is found in that collection (directory). In a typical Oracle HTTP Server environment, a separate module takes control, automatically generating and returning to the client HTML that represents an "index" of the resources (files) in that collection.

An OraDAV-enabled Oracle HTTP Server performs similar actions when responding to a GET request on a collection. A Description column (containing links to more detailed information about each resource) is included in the generated index when ORAAllowIndexDetails is set to TRUE.

The default is FALSE, in which case no Description column appears in the generated index, and if ?details is used in a URL, it is ignored and the URL contents are returned.

9.5.2 ORAAltPassword

Specifies the password associated with the user specified by the ORAUser parameter, but the password is a base-64 encoded character string. The ORAAltPassword parameter provides an alternative if you do not want the password to appear in unencoded plain text in that parameter.

If the ORAPassword parameter is not specified, the ORAAltPassword parameter is used for the password.

9.5.3 ORACacheDirectory

Specifies the directory to use for disk caching operations. If you do not use this parameter, disk caching is not performed for OraDAV operations.

The specified directory must exist and be readable by Oracle HTTP Server, but cannot be visible to normal GET requests. (If the directory is visible to normal GET requests, security measures could be bypassed by users accessing the cache directory.)

The directory should not be an NFS-mounted directory, because most UNIX locking mechanisms caution against this. The directory should be located on a file system that supports a "last accessed" time. On Windows systems, this means using NTFS (not FAT) formatted partitions.

Do not use the cache directory for anything other than caching. Any files in the cache directory are subject to deletion.

If you use the ORACacheDirectory parameter, you must also use the ORACacheTotalSize parameter.

9.5.4 ORACacheMaxResourceSize

Specifies a maximum cacheable resource size for disk caching operations.

Example 9-3 shows how to set ORACacheMaxResourceSize.

DAVParam ORACacheMaxResourceSize 1024KB

The setting in Example 9-3 prevents OraDAV from caching any resource larger than one megabyte. The goal is to give Web masters the ability to prevent large media files from dominating the cache. However, be aware that the performance benefit from caching a large file is greater than from caching a small file.

You can specify KB (for kilobytes) or MB (for megabytes) after an integer. If you do not specify a unit after the integer, the default unit is bytes.

9.5.5 ORACachePrunePercent

Specifies the percentage of disk cache usage to be freed up when the cache is full. When the disk cache is full, the oldest files in the cache are deleted (pruned) until the cache disk usage is reduced by the ORACachePrunePercent value.

9.5.6 ORACacheTotalSize

Specifies the size of the cache to use for disk caching operations.

You can specify MB (for megabytes) or GB (for gigabytes) after an integer, as shown in Example 9-4. If you do not specify a unit after the integer, the default unit is bytes.

DAVParam ORACacheTotalSize 1GB

If you use the ORACacheDirectory parameter, you must also use the ORACacheTotalSize parameter.

The ORACacheTotalSize value should be large enough to hold either a significant fraction of your Web site, or all of your most frequently accessed files plus 25 percent more space. If the value is too small, overall performance degrades because of the extra work of writing BLOB data to the file system and quickly deleting files to make room for newer cache requests.

The actual space utilized by the disk cache might sometimes exceed the ORACacheTotalSize value, possibly by as much as the ORACacheMaxResourceSize value. You should also be aware of file system block size issues that could cause the cache to use more disk space than the ORACacheTotalSize value.

9.5.7 ORAConnect

Specifies the Oracle database to which to connect. The value must be in the following format:

database-host:database-port:database-sid

Example 9-5 shows how to use the ORAConnect parameter.

DAVParam ORAConnect my-pc.acme.com:1521:mysid

The ORAConnect parameter lets you connect to a database that is not included in the tnsnames.ora file.

You must specify one, and no more than one, of the following parameters: ORAConnect, ORAService, or ORAConnectSN.

9.5.8 ORAConnectSN

Specifies the Oracle database to which to connect. The value must be in the following format:

database-host:database-port:database-service-name

The ORAConnectSN parameter lets you connect to a database that is not included in the tnsnames.ora file, as shown in Example 9-6.

DAVParam ORAConnectSN my-pc.acme.com:1521:myservice

You must specify one, and no more than one, of the following parameters: ORAService, ORAConnect, or ORAConnectSN.

9.5.9 ORAContainerName

Within the schema specified by the ORAUser parameter, there must exist a container. The ORAContainerName parameter specifies the name of the container to use for the location.

9.5.10 ORAException

Writes PS/SQL stack dumps into the Oracle HTTP Server log file, error_log, in the event of an exception in the PL/SQL package.

9.5.11 ORAGetSource

Applies only to file system access. It specifies one or more file extensions to identify types of files that are not to be executed, but rather opened for editing. Include periods (.) with the file extension and use a comma to separate file extensions. For example:

".htm, .html, .jsp1, .jsp2"

The ORAGetSource parameter lets you open for editing files that are usually executed as a result of a GET operation.

9.5.12 ORALockExpirationPad

Intended to be used in high-latency network environments, to adjust for the "refresh lock" behavior in Microsoft Office. Microsoft Office attempts to refresh locks on DAV resources just before the lock is set to expire. However, if there is network congestion between the Microsoft Office client and the DAV server, the refresh request might arrive too late, that is, after the lock has expired.

OraDAV periodically looks for locks on resources that have expired and deletes those locks. The ORALockExpirationPad parameter can be used to provide some additional ("pad") time between when a lock expires and when that lock is deleted. For example, if ORALockExpirationPad is set to 120, OraDAV does not actually delete locks until at least two minutes after the expiration time.

9.5.13 ORAPackageName

Identifies the OraDAV driver implementation that is to be called when issuing OraDAV commands. The default is the OraDAV driver, which is the ORDSYS.DAV_API_DRIVER package.

9.5.14 ORAPassword

Specifies the password associated with the user specified by the ORAUser parameter.

If you do not want to specify the password as an unencoded text string with the ORAPassword parameter, you can specify the password as a base-64 encoded string with the ORAAltPassword parameter.

9.5.15 ORARootPrefix

Specifies the directory within the database repository to use as the root. If this parameter is specified, WebDAV clients see this directory as the root and are not be able to see the repository directories that lead up to it.

In Example 9-7, assume that the database repository contains the directory /first/second/third/fourth, and that ORARootPrefix is defined as follows (do not include a trailing slash (/) in the value):

DAVParam ORARootPrefix /first/second

In this case, WebDAV clients will see the /third directory and be able to navigate to the /third/fourth directory, but will not be able to see or navigate to the /first or /first/second directories.

9.5.16 ORAService

Specifies the Oracle database to which to connect. The specified value must match a SID value in the tnsnames.ora file as shown in Example 9-8.

DAVParam ORAService mydbsid.mydomain.com

To connect to a database that is not included in the tnsnames.ora file, use the ORAConnect parameter. You must specify one, and no more than one, of the following parameters: ORAService, ORAConnect, or ORAConnectSN.

9.5.17 ORATraceEvents

Specifies types of events to be recorded in the Apache error log for debugging.

9.5.18 ORATraceLevel

Specifies the level of debugging (trace statements) that will be entered in the Apache error log. The lowest level is 0 (the default), which performs no tracing; the highest level is 4, which performs maximum tracing.

The higher the number you set, the more information is written to the error log file.

9.5.19 ORAUser

Specifies the database user (schema) to use when connecting to the service specified by the ORAService parameter.

This user must have the following privileges:

• CONNECT

• RESOURCE

• CREATE TABLESPACE

• DROP TABLESPACE

• CREATE ANY TRIGGER

  Category	Value
  Applies to	Portal driver and other (non-file system) access
  Required/Optional	Required
  Values	(character string)
  Default	(none)

  
  

9.6.1 DAVDepthInfinity

A PROPFIND request with a Depth: Infinity 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 types of requests can consume a lot of memory. (The memory is released at the end of the request, but the peak memory usage can be high.)

To prevent these types of requests, the DAVDepthInfinity directive is provided. It is a simple on/off directive, which can be used on a per-server, per-directory or location basis. If the value is set to Off, these types of requests are not allowed. A value of On (that is, allowing depth infinity requests) makes it easier for denial of service attacks to occur. However, some clients, such as sitecopy, require a DAVDepthInfinity value of On.

9.6.2 DAVLockDB

Creates a DAV lock database. To create the DAV lock database, add a DAVLockDB directive at the top level of the configuration file (that is, outside a <Directory> or <Location> container directive). The DAVLockDB directive should specify the name of a file that mod_dav creates. The directory in which the file is to be created must exist, and Oracle HTTP Server process must have write permission to it.

In Example 9-9, the DAV lock database is stored in the ORACLE_HOME/Apache/var directory, which must be writable by Oracle HTTP Server process. When mod_dav creates the file, it is named DAVLock. (Actually, mod_dav creates one or more files using this file name plus an extension).

DAVLockDB ORACLE_HOME/Apache/var/DAVLock

The DAVLockDB directive can appear outside any container or within a <VirtualHost> specification. It only needs to appear once, and a file extension should not be supplied.

9.6.3 DAVMinTimeout

Specifies the minimum lifetime of a lock, in seconds. If a client requests a lock timeout less than the DAVMinTimeout value, then the DAVMinTimeout value is used and returned instead. For example, Microsoft's Web Folders defaults to a lock timeout of 2 minutes (120 seconds); however, you might decide to specify 10 minutes (600 seconds) instead, 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 or location basis. The DAVMinTimeout directive takes a single positive integer. Because this value represents a minimum allowed, setting it to zero (0) disables this feature. The default value for DAVMinTimeout is zero.

9.6.4 DAVOraNLS

Provides globalization support for access to the local file systems. This directive specifies whether or not the file names in the file system need to go through conversion using the NLS_LANG setting. A value of Off, the default, means that no conversion is needed. A value of On means that the character set for the file system provides for conversion of all possible characters in client requests.

9.6.5 DAVOraReadOnly

Specifies whether or not WebDAV should be used in a read-only mode by WebDAV clients. A value of Off, the default, means that WebDAV clients function normally. A value of On prevents WebDAV clients from performing write operations while using WebDAV; however, it does allow read-only activity by Web browsers and WebDAV clients.

9.6.6 DAVOraWebCacheReadOnly

Specifies whether or not OracleAS Web Cache should be used in a read-only mode by WebDAV clients. A value of Off, the default, means that OracleAS Web Cache functions normally. A value of On prevents WebDAV clients from performing write operations while using OracleAS Web Cache; however, it does allow read-only activity by Web browsers and WebDAV clients.

9.6.7 Limit

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 authorized users. This requires the use of the <Limit> directive.

The configuration in Example 9-10 allows 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 an .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, such as CGI, symbolic links or server-side includes.

<Location /mypages>
  DAV On
  <Limit PUT POST DELETE PROPFIND PROPPATCH MKCOL COPY MOVE LOCK UNLOCK>
    Require user greg
  </Limit>
</Location>

Example 9-11 shows a modified configuration with the additional restrictions placed on it through the addition of AllowOverride None and Options None:

<Location /mypages>
  DAV On
  AllowOverride None
  Options None
  <Limit PUT POST DELETE PROPFIND PROPPATCH MKCOL COPY MOVE LOCK UNLOCK>
    Require user greg
  </Limit>
</Location>
<Location /mypages>
  DAV On
  AllowOverride None
  Options None
  <Limit PUT POST DELETE PROPFIND PROPPATCH MKCOL COPY MOVE LOCK UNLOCK>
    Require user greg
  </Limit>
</Location>

9.6.8 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, as shown in Example 9-12. This directive applies the access restrictions to all methods except for the methods listed.

<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 automatically restricts methods that are added in the future.

9.6.9 LimitXMLRequestBody

mod_dav parses XML request bodies into memory. One technique used in denial of service attacks is to send a large request body to a mod_dav server. Oracle HTTP Server defines a directive named LimitRequestBody, which limits all methods' request bodies. Unfortunately, this is not an effective mechanism for a mod_dav server because large PUT operations should be allowed.

To limit just the methods that have an XML request body, mod_dav provides the LimitXMLRequestBody directive. The default for this value is a compile-time constant, which is set to one million (1,000,000) bytes in the standard distribution. Setting the value to zero (0) disables the size limit.

LimitXMLRequestBody may be set on a per-server or a per-directory or location basis, and takes a single non-negative integer argument.

9.8.1 Using Disk Caching with OraDAV

Oracle Application Server can use local file system disk caching with data that is retrieved from an Oracle database. Disk caching is designed to improve the performance of HTTP GET operations on frequently accessed database data. When data is requested from the database, it is retrieved and is stored in a disk cache on the local file system. If a subsequent request is for the same data and if the data is still in the disk cache, Oracle Application Server checks to see if the data has changed in the database (by examining the etag value). If the data has not changed, it is retrieved from the cache, which is more efficient than retrieving a substantial amount of data from the database.

The performance benefit from disk caching is greatest with medium to large-size files (roughly 50 KB and larger). However, with smaller files, the performance benefit is less, and with very small files the performance can be worse with disk caching than without disk caching. For example, if the file myfile.dat is requested and if the file size is only 24 bytes, the time required for copying the file from the database to the local system is very small compared to the time required for accessing the database to check if the file has changed. If disk caching is not used, there is no check of the database to see if the file has changed, and the file is copied from the database in all cases.

You can set the following OraDAV parameters to control disk caching for OraDAV operations:

• ORACacheDirectory

• ORACacheTotalSize

• ORACacheMaxResourceSize

• ORACachePrunePercent

If you specify ORACacheDirectory, disk caching for OraDAV operations is enabled. In this case, you must also specify a value for ORACacheTotalSize, and you can specify values for ORACacheMaxResourceSize and ORACachePrunePercent parameters. If you do not specify ORACacheDirectory, disk caching for OraDAV operations is not enabled, and other disk cache-related parameters are not relevant.

9.8.2 Bypassing Oracle Application Server Web Cache for WebDAV Activities

Oracle Application Server Web Cache enhances performance for most Web activity, which involves client read-only operations of data on the Web server system. However, OracleAS Web Cache does not cache OraDAV operations, which are designed for read/write capability. Thus, for better performance, WebDAV clients can connect directly to Oracle HTTP Server.

To bypass OracleAS Web Cache for WebDAV clients, you can use port 7778, which is the standard port for Oracle HTTP Server. If you do this, WebDAV clients connect directly to the Web server, resulting in better performance than if OracleAS Web Cache was used.

9.8.3 Using Oracle Application Server Web Cache for Browsing Activities

If your WebDAV clients always bypass OracleAS Web Cache, you may want to tune OracleAS Web Cache for read-only clients such as Web browsers. To do so, add the DAVOraWebCacheReadOnly On setting for an OraDAV-enabled location in the httpd.conf file, as shown in Example 9-14.

<Location /dav_public>
  DAV On
  DAVOraWebCacheReadOnly On
</Location>

9.9.1 Mapping Containers Under the Root Location

Note the following when mapping containers under the root location:

• Do not map the root itself. That is, do not specify <Location />.

• Do not map a container as a subelement in the hierarchy to another container. For example, do not specify the following two containers: <Location /project1> and <Location /project1/project2>. However, it is acceptable to specify <Location /project1> and <Location /project2>.

• Do not create any symbolic links to the container or any location under the container in the hierarchy.

9.9.2 Globalization Support Considerations with OraDAV

For access to database data, the character set used for client requests, such as in URLs and file names, must be compatible with the character set used for the database. Specifically, if the character set for the database is not the same as for the client requests, the character set for the database must provide for conversion of all possible characters in client requests (and thus must be a superset of the character set for client requests). That is, the character set for the database must not cause replacement characters during the conversion.

When you start Oracle HTTP Server, the NLS_LANG environment variable must reflect the character set for client requests. For example, if file names and URLs contain Kanji characters, you can specify NLS_LANG=JAPANESE_JAPAN.JA16SJIS (for ShiftJIS characters). In this case, the database character set must be one that accommodates SJIS characters, for example, UTF8.

For access to the local file system, as opposed to database access, the character set for the file system must be the same as, or compatible with, the character set for URLs embedded in client requests. The character set for the file system must provide for conversion of all possible characters in client requests. The NLS_LANG parameter value must represent the character set of both the client and the OraDAV server. You must also specify a value of On for the parameter DAVOraNLS.

For example, assume that you are using Web folders on a system where the files have ShiftJIS characters and that the file system under dav_public is represented by the operating system in the JAPANESE_JAPAN.JA16SJIS character sets shown in Figure 9-2.

Figure 9-2 OraDAV Access to File System with ShiftJIS Characters

Description of "Figure 9-2 OraDAV Access to File System with ShiftJIS Characters"

In this case, you must do the following:

1. Set the NLS_LANG value to JAPANESE_JAPAN.JA16SJIS.

2. Include the following in the httpd.conf file:

   <Location /dav_public>
     DAV On
     DAVOraNLS On
   </Location>
   
   

   
   

   Note: If you use Microsoft Internet Explorer with OraDAV and a multibyte character set, you must disable (uncheck) the Internet option (Internet Options, Advanced tab) Always send URLs as UTF-8. (By default, this option is enabled.) The requirement to disable this option applies to both database access and file system access.

   
   

9.9.3 PROPFIND Security

In the example configurations in the preceding sections on the <Limit> and <LimitExcept> directives, 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 reasons, it is probably best to protect the list of files from general read access.

An alternative is 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, for example, 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.