The Apache HTTP Server is a “heavy-duty” network server that Subversion can leverage. Via a custom module, httpd makes Subversion repositories available to clients via the WebDAV/DeltaV[47] protocol, which is an extension to HTTP 1.1. This protocol takes the ubiquitous HTTP protocol that is the core of the World Wide Web, and adds writing—specifically, versioned writing—capabilities. The result is a standardized, robust system that is conveniently packaged as part of the Apache 2.0 software, supported by numerous operating systems and third-party products, and doesn't require network administrators to open up yet another custom port.[48] While an Apache-Subversion server has more features than svnserve, it's also a bit more difficult to set up. With flexibility often comes more complexity.
Much of the following discussion includes references to Apache configuration directives. While some examples are given of the use of these directives, describing them in full is outside the scope of this chapter. The Apache team maintains excellent documentation, publicly available on their web site at http://httpd.apache.org. For example, a general reference for the configuration directives is located at http://httpd.apache.org/docs-2.0/mod/directives.html.
Also, as you make changes to your Apache setup, it is likely that somewhere
along the way a mistake will be made. If you are not already familiar with
Apache's logging subsystem, you should become aware of it. In your
httpd.conf file are directives that specify the on-disk
locations of the access and error logs generated by Apache (the
CustomLog and ErrorLog directives,
respectively). Subversion's mod_dav_svn uses Apache's
error logging interface as well. You can always browse the contents of
those files for information that might reveal the source of a problem that
is not clearly noticeable otherwise.
To network your repository over HTTP, you basically need four components, available in two packages. You'll need Apache httpd 2.0 or newer, the mod_dav DAV module that comes with it, Subversion, and the mod_dav_svn filesystem provider module distributed with Subversion. Once you have all of those components, the process of networking your repository is as simple as:
-
Getting httpd up and running with the mod_dav module
-
为 mod_dav 安装 mod_dav_svn 后端，它会使用 Subversion 库访问版本库
-
配置你的
httpd.conf来输出(或者说暴露)版本库
You can accomplish the first two items either by compiling
httpd and Subversion from source code or by installing
prebuilt binary packages of them on your system. For the most up-to-date
information on how to compile Subversion for use with the Apache HTTP
Server, as well as how to compile and configure Apache itself for this
purpose, see the INSTALL file in the top level of the
Subversion source code tree.
Once you have all the necessary components installed on your system, all
that remains is the configuration of Apache via its
httpd.conf file. Instruct Apache to load the
mod_dav_svn module using the
LoadModule directive. This directive must precede any
other Subversion-related configuration items. If your Apache was installed
using the default layout, your mod_dav_svn module should
have been installed in the modules subdirectory of the
Apache install location (often /usr/local/apache2).
The LoadModule directive has a simple syntax, mapping a
named module to the location of a shared library on disk:
LoadModule dav_svn_module modules/mod_dav_svn.so
Apache interprets the LoadModule configuration item's
library path as relative to its own server root. If configured as
previously shown, Apache will look for the Subversion DAV module shared
library in its own modules/ subdirectory. Depending on
how Subversion was installed on your system, you might need to specify a
different path for this library altogether, perhaps even an absolute path
such as in the following example:
LoadModule dav_svn_module C:/Subversion/lib/mod_dav_svn.so
Note that if mod_dav was compiled as a shared object
(instead of statically linked directly to the httpd
binary), you'll need a similar LoadModule statement for
it, too. Be sure that it comes before the mod_dav_svn
line:
LoadModule dav_module modules/mod_dav.so LoadModule dav_svn_module modules/mod_dav_svn.so
At a later location in your configuration file, you now need to tell Apache
where you keep your Subversion repository (or repositories). The
Location directive has an XML-like notation, starting
with an opening tag and ending with a closing tag, with various other
configuration directives in the middle. The purpose of the
Location directive is to instruct Apache to do something
special when handling requests that are directed at a given URL or one of
its children. In the case of Subversion, you want Apache to simply hand off
support for URLs that point at versioned resources to the DAV layer. You
can instruct Apache to delegate the handling of all URLs whose path portions
(the part of the URL that follows the server's name and the optional port
number) begin with /repos/ to a DAV provider whose
repository is located at /var/svn/repository using the
following httpd.conf syntax:
<Location /repos> DAV svn SVNPath /var/svn/repository </Location>
If you plan to support multiple Subversion repositories that will reside in
the same parent directory on your local disk, you can use an alternative
directive—SVNParentPath—to indicate that
common parent directory. For example, if you know you will be creating
multiple Subversion repositories in a directory
/var/svn that would be accessed via URLs such as
http://my.server.com/svn/repos1,
http://my.server.com/svn/repos2, and so on, you could use the
httpd.conf configuration syntax in the following
example:
<Location /svn> DAV svn # Automatically map any "/svn/foo" URL to repository /var/svn/foo SVNParentPath /var/svn </Location>
Using this syntax, Apache will delegate the handling of all URLs whose path
portions begin with /svn/ to the Subversion DAV
provider, which will then assume that any items in the directory specified
by the SVNParentPath directive are actually Subversion
repositories. This is a particularly convenient syntax in that, unlike the
use of the SVNPath directive, you don't have to restart
Apache to add or remove hosted repositories.
Be sure that when you define your new Location, it
doesn't overlap with other exported locations. For example, if your main
DocumentRoot is exported to /www, do
not export a Subversion repository in <Location
/www/repos>. If a request comes in for the URI
/www/repos/foo.c, Apache won't know whether to look for
a file repos/foo.c in the
DocumentRoot, or whether to delegate
mod_dav_svn to return foo.c from the
Subversion repository. The result is often an error from the server of the
form 301 Moved Permanently.
At this stage, you should strongly consider the question of permissions. If you've been running Apache for some time now as your regular web server, you probably already have a collection of content—web pages, scripts, and such. These items have already been configured with a set of permissions that allows them to work with Apache, or more appropriately, that allows Apache to work with those files. Apache, when used as a Subversion server, will also need the correct permissions to read and write to your Subversion repository.
You will need to determine a permission system setup that satisfies
Subversion's requirements without messing up any previously existing web
page or script installations. This might mean changing the permissions on
your Subversion repository to match those in use by other things that Apache
serves for you, or it could mean using the User and
Group directives in httpd.conf to
specify that Apache should run as the user and group that owns your
Subversion repository. There is no single correct way to set up your
permissions, and each administrator will have different reasons for doing
things a certain way. Just be aware that permission-related problems are
perhaps the most common oversight when configuring a Subversion repository
for use with Apache.
此时，如果你配置的 httpd.conf 包含了如下内容：
<Location /svn> DAV svn SVNParentPath /var/svn </Location>
your repository is “anonymously” accessible to the world.
Until you configure some authentication and authorization policies, the
Subversion repositories that you make available via the
Location directive will be generally accessible to
everyone. In other words:
-
任何人可以使用Subversion客户端来从版本库URL取出一个工作副本(或者是它的子目录)。
-
任何人可以在浏览器输入版本库URL交互浏览的方式来查看版本库的最新修订版本。
-
任何人可以提交到版本库。
Of course, you might have already set up a pre-commit
hook script to prevent commits (see 第 3.2 节 “实现版本库钩子”). But as you read on, you'll see
that it's also possible to use Apache's built-in methods to restrict access
in specific ways.
![[提示]](images/tip.png)
|
提示 |
|---|---|
|
Requiring authentication defends against invalid users directly accessing the repository, but does not guard the privacy of valid users' network activity. See 第 4.5 节 “Protecting network traffic with SSL” for how to configure your server to support SSL encryption, which can provide that extra layer of protection. |
The easiest way to authenticate a client is via the HTTP Basic authentication mechanism, which simply uses a username and password to verify a user's identity. Apache provides the htpasswd utility[49] for managing files containing usernames and passwords.
![[警告]](images/warning.png)
|
警告 |
|---|---|
|
Basic authentication is extremely insecure, because it sends passwords over the network in very nearly plain text. See 第 4.3.2 节 “Digest authentication” for details on using the much safer Digest mechanism. |
First, create a password file and grant access to users Harry and Sally:
$ ### First time: use -c to create the file $ ### Use -m to use MD5 encryption of the password, which is more secure $ htpasswd -c -m /etc/svn-auth.htpasswd harry New password: ***** Re-type new password: ***** Adding password for user harry $ htpasswd -m /etc/svn-auth.htpasswd sally New password: ******* Re-type new password: ******* Adding password for user sally $
Next, ensure that Apache has access to the modules which provide the Basic
authentication and related functionality: mod_auth_basic,
mod_authn_file, and mod_authz_user.
In many cases, these modules are compiled into httpd
itself, but if not, you might need to explicitly load one or more of them
using the LoadModule directive:
LoadModule auth_basic_module modules/mod_auth_basic.so LoadModule authn_file_module modules/mod_authn_file.so LoadModule authz_user_module moduels/mod_authz_user.so
After ensuring the Apache has access to the required functionality, you'll
need to add some more directives inside the
<Location> block to tell Apache what type of
authentication you wish to use, and just how to to so:
<Location /svn> DAV svn SVNParentPath /var/svn # Authentication: Basic AuthName "Subversion repository" AuthType Basic AuthBasicProvider file AuthUserFile /etc/svn-auth.htpasswd </Location>
These directives work as follows:
-
AuthNameis an arbitrary name that you choose for the authentication domain. Most browsers display this name in the dialog box when prompting for username and password. -
AuthTypespecifies the type of authentication to use. -
AuthBasicProviderspecifies the Basic authentication provider to use for the location. In our example, we wish to consult a local password file. -
AuthUserFilespecifies the location of the password file to use.
However, this <Location> block doesn't yet do
anything useful. It merely tells Apache that if
authorization were required, it should challenge the Subversion client for a
username and password. (When authorization is required, Apache requires
authentication as well.) What's missing here, however, are directives that
tell Apache which sorts of client requests require
authorization; currently, none do. The simplest thing is to specify that
all requests require authorization by adding
Require valid-user to the block:
<Location /svn> DAV svn SVNParentPath /var/svn # Authentication: Basic AuthName "Subversion repository" AuthType Basic AuthBasicProvider file AuthUserFile /etc/svn-auth.htpasswd # Authorization: Authenticated users only Require valid-user </Location>
Refer to 第 4.4 节 “授权选项” for more detail on
the Require directive and other ways to set authorization
policies.
![[注意]](images/note.png)
|
注意 |
|---|---|
|
The default value of the |
Digest authentication is an improvement on Basic authentication which allows the server to verify a client's identity without sending the password over the network unprotected. Both client and server create a non-reversible MD5 hash of the username, password, requested URI, and a nonce (number used once) provided by the server and changed each time authentication is required. The client sends its hash to the server, and the server then verifies that the hashes match.
Configuring Apache to use Digest authentication is straightforward. You'll
need to ensure that the mod_auth_digest module is
available (instead of mod_auth_basic), and then make a
few small variations on our prior example:
<Location /svn> DAV svn SVNParentPath /var/svn # Authentication: Digest AuthName "Subversion repository" AuthType Digest AuthDigestProvider file AuthUserFile /etc/svn-auth.htdigest # Authorization: Authenticated users only Require valid-user </Location>
Notice that AuthType is now set to
Digest, and we specify a different path for
AuthUserFile. Digest authentication uses a different
file format than Basic authentication, created and managed using Apache's
htdigest utility[50]
rather than htpasswd. Digest authentication also has the
additional concept of a “realm”, which must match the value of
the AuthName directive.
|
|
注意 |
|---|---|
|
For digest authentication, the authentication provider is selected using the
|
The password file can be created as follows:
$ ### First time: use -c to create the file $ htdigest -c /etc/svn-auth.htdigest "Subversion repository" harry Adding password for harry in realm Subversion repository. New password: ***** Re-type new password: ***** $ htdigest /etc/svn-auth.htdigest "Subversion repository" sally Adding user sally in realm Subversion repository New password: ******* Re-type new password: ******* $
At this point, you've configured authentication, but not authorization. Apache is able to challenge clients and confirm identities, but it has not been told how to allow or restrict access to the clients bearing those identities. This section describes two strategies for controlling access to your repositories.
最简单的访问控制形式是授权特定用户为只读版本库访问或者是读/写访问版本库。
You can restrict access on all repository operations by adding
Require valid-user directly inside the
<Location> block. The example from 第 4.3.2 节 “Digest authentication” allows only clients that
successfully authenticate to do anything with the Subversion repository:
<Location /svn> DAV svn SVNParentPath /var/svn # Authentication: Digest AuthName "Subversion repository" AuthType Digest AuthUserFile /etc/svn-auth.htdigest # Authorization: Authenticated users only Require valid-user </Location>
Sometimes you don't need to run such a tight ship. For example,
Subversion's own source code repository at http://svn.collab.net/repos/svn allows anyone in the world to
perform read-only repository tasks (such as checking out working copies and
browsing the repository), but restricts write operations to authenticated
users. The Limit and LimitExcept
directives allow for this type of selective restriction. Like the
Location directive, these blocks have starting and ending
tags, and you would nest them inside your
<Location> block.
The parameters present on the Limit and
LimitExcept directives are HTTP request types that are
affected by that block. For example, to allow anonymous read-only
operations, you would use the LimitExcept directive
(passing the GET, PROPFIND,
OPTIONS, and REPORT request type
parameters) and place the previously mentioned Require
valid-user directive inside the
<LimitExcept> block instead of just inside the
<Location> block.
<Location /svn>
DAV svn
SVNParentPath /var/svn
# Authentication: Digest
AuthName "Subversion repository"
AuthType Digest
AuthUserFile /etc/svn-auth.htdigest
# Authorization: Authenticated users only for non-read-only
# (write) operations; allow anonymous reads
<LimitExcept GET PROPFIND OPTIONS REPORT>
Require valid-user
</LimitExcept>
</Location>
These are only a few simple examples. For more in-depth information about
Apache access control and the Require directive, take a
look at the Security section of the Apache
documentation's tutorials collection at http://httpd.apache.org/docs-2.0/misc/tutorials.html.
It's possible to set up finer-grained permissions using mod_authz_svn. This Apache module grabs the various opaque URLs passing from client to server, asks mod_dav_svn to decode them, and then possibly vetoes requests based on access policies defined in a configuration file.
If you've built Subversion from source code,
mod_authz_svn is automatically built and installed
alongside mod_dav_svn. Many binary distributions install
it automatically as well. To verify that it's installed correctly, make
sure it comes right after mod_dav_svn's
LoadModule directive in httpd.conf:
LoadModule dav_module modules/mod_dav.so LoadModule dav_svn_module modules/mod_dav_svn.so LoadModule authz_svn_module modules/mod_authz_svn.so
To activate this module, you need to configure your
<Location> block to use the
AuthzSVNAccessFile directive, which specifies a file
containing the permissions policy for paths within your repositories. (In a
moment, we'll discuss the format of that file.)
Apache is flexible, so you have the option to configure your block in one of three general patterns. To begin, choose one of these basic configuration patterns. (The following examples are very simple; look at Apache's own documentation for much more detail on Apache authentication and authorization options.)
The most open approach is to allow access to everyone. This means Apache never sends authentication challenges, and all users are treated as “anonymous”. (See 例 6.2 “匿名访问的配置样例”.)
例 6.2. 匿名访问的配置样例
<Location /repos> DAV svn SVNParentPath /var/svn # Authentication: None # Authorization: Path-based access control AuthzSVNAccessFile /path/to/access/file </Location>
On the opposite end of the paranoia scale, you can configure Apache to
authenticate all clients. This block unconditionally requires
authentication via the Require valid-user directive, and
defines a means to authenticate valid users. (See 例 6.3 “认证访问的配置样例”.)
例 6.3. 认证访问的配置样例
<Location /repos> DAV svn SVNParentPath /var/svn # Authentication: Digest AuthName "Subversion repository" AuthType Digest AuthUserFile /etc/svn-auth.htdigest # Authorization: Path-based access control; authenticated users only AuthzSVNAccessFile /path/to/access/file Require valid-user </Location>
A third very popular pattern is to allow a combination of authenticated and
anonymous access. For example, many administrators want to allow anonymous
users to read certain repository directories, but restrict access to more
sensitive areas to authenticated users. In this setup, all users start out
accessing the repository anonymously. If your access control policy demands
a real username at any point, Apache will demand authentication from the
client. To do this, use both the Satisfy Any and
Require valid-user directives. (See 例 6.4 “混合认证/匿名访问的配置样例”.)
例 6.4. 混合认证/匿名访问的配置样例
<Location /repos> DAV svn SVNParentPath /var/svn # Authentication: Digest AuthName "Subversion repository" AuthType Digest AuthUserFile /etc/svn-auth.htdigest # Authorization: Path-based access control; try anonymous access # first, but authenticate if necessary AuthzSVNAccessFile /path/to/access/file Satisfy Any Require valid-user </Location>
The next step is to create the authorization file containing access rules for particular paths within the repository. We describe how later in this chapter, in 第 5 节 “基于路径的授权”.
The mod_dav_svn module goes through a lot of work to make
sure that data you've marked “unreadable” doesn't get
accidentally leaked. This means it needs to closely monitor all of the
paths and file-contents returned by commands such as svn
checkout and svn update. If these commands
encounter a path that isn't readable according to some authorization policy,
the path is typically omitted altogether. In the case of history or rename
tracing—for example, running a command such as svn cat -r
OLD foo.c on a file that was renamed long ago—the rename
tracking will simply halt if one of the object's former names is determined
to be read-restricted.
All of this path checking can sometimes be quite expensive, especially in
the case of svn log. When retrieving a list of
revisions, the server looks at every changed path in each revision and
checks it for readability. If an unreadable path is discovered, it's
omitted from the list of the revision's changed paths (normally seen with
the --verbose (-v) option), and the whole
log message is suppressed. Needless to say, this can be time-consuming on
revisions that affect a large number of files. This is the cost of
security: even if you haven't configured a module such as
mod_authz_svn at all, the mod_dav_svn
module is still asking Apache httpd to run authorization
checks on every path. The mod_dav_svn module has no idea
what authorization modules have been installed, so all it can do is ask
Apache to invoke whatever might be present.
On the other hand, there's also an escape hatch of sorts, which allows you
to trade security features for speed. If you're not enforcing any sort of
per-directory authorization (i.e., not using
mod_authz_svn or similar module), you can disable all of
this path checking. In your httpd.conf file, use the
SVNPathAuthz directive as shown in 例 6.5 “禁用所有的路径检查”.
The SVNPathAuthz directive is “on” by
default. When set to “off,” all path-based authorization
checking is disabled; mod_dav_svn stops invoking
authorization checks on every path it discovers.
Connecting to a repository via http:// means that all
Subversion activity is sent across the network in the clear. This means
that actions such as checkouts, commits, and updates could potentially be
intercepted by an unauthorized party “sniffing” network
traffic. Encrypting traffic using SSL is a good way to protect potentially
sensitive information over the network.
If a Subversion client is compiled to use OpenSSL, it gains the ability to
speak to an Apache server via https:// URLs, so all
traffic is encrypted with a per-connection session key. The WebDAV library
used by the Subversion client is not only able to verify server
certificates, but can also supply client certificates when challenged by the
server.
It's beyond the scope of this book to describe how to generate client and server SSL certificates and how to configure Apache to use them. Many other references, including Apache's own documentation, describe the process.
|
|
提示 |
|---|---|
|
SSL certificates from well-known entities generally cost money, but at a bare minimum, you can configure Apache to use a self-signed certificate generated with a tool such as OpenSSL (http://openssl.org).[51] |
When connecting to Apache via https://, a Subversion
client can receive two different types of responses:
-
一个服务器证书
-
A challenge for a client certificate
When the client receives a server certificate, it needs to verify that the server is who it claims to be. OpenSSL does this by examining the signer of the server certificate, or certificate authority (CA). If OpenSSL is unable to automatically trust the CA, or if some other problem occurs (such as an expired certificate or hostname mismatch), the Subversion command-line client will ask you whether you want to trust the server certificate anyway:
$ svn list https://host.example.com/repos/project Error validating server certificate for 'https://host.example.com:443': - The certificate is not issued by a trusted authority. Use the fingerprint to validate the certificate manually! Certificate information: - Hostname: host.example.com - Valid: from Jan 30 19:23:56 2004 GMT until Jan 30 19:23:56 2006 GMT - Issuer: CA, example.com, Sometown, California, US - Fingerprint: 7d:e1:a9:34:33:39:ba:6a:e9:a5:c4:22:98:7b:76:5c:92:a0:9c:7b (R)eject, accept (t)emporarily or accept (p)ermanently?
This dialogue is essentially the same question you may have seen coming from
your web browser (which is just another HTTP client like Subversion). If
you choose the (p)ermanent option, Subversion will cache
the server certificate in your private runtime auth/
area, just as your username and password are cached (see 第 11.2.1 节 “缓存凭证”), and will automatically
trust the certificate in the future.
Your runtime servers file also gives you the ability to
make your Subversion client automatically trust specific CAs, either
globally or on a per-host basis. Simply set the
ssl-authority-files variable to a semicolon-separated
list of PEM-encoded CA certificates:
[global] ssl-authority-files = /path/to/CAcert1.pem;/path/to/CAcert2.pem
Many OpenSSL installations also have a predefined set of
“default” CAs that are nearly universally trusted. To make the
Subversion client automatically trust these standard authorities, set the
ssl-trust-default-ca variable to true.
If the client receives a challenge for a certificate, the server is asking the client to prove its identity. The client must send back a certificate signed by a CA that the server trusts, along with a challenge response which proves that the client owns the private key associated with the certificate. The private key and certificate are usually stored in an encrypted format on disk, protected by a passphrase. When Subversion receives this challenge, it will ask you for the path to the encrypted file and the passphrase that protects it:
$ svn list https://host.example.com/repos/project Authentication realm: https://host.example.com:443 Client certificate filename: /path/to/my/cert.p12 Passphrase for '/path/to/my/cert.p12': ********
Notice that the client credentials are stored in a .p12
file. To use a client certificate with Subversion, it must be in PKCS#12
format, which is a portable standard. Most web browsers are able to import
and export certificates in that format. Another option is to use the
OpenSSL command-line tools to convert existing certificates into PKCS#12.
The runtime servers file also allows you to automate
this challenge on a per-host basis. If you set the
ssl-client-cert-file and
ssl-client-cert-password variables, Subversion can
automatically respond to a client certificate challenge without prompting
you:
[groups] examplehost = host.example.com [examplehost] ssl-client-cert-file = /path/to/my/cert.p12 ssl-client-cert-password = somepassword
More security-conscious folk might want to exclude
ssl-client-cert-password to avoid storing the passphrase
in the clear on disk.
We've covered most of the authentication and authorization options for Apache and mod_dav_svn. But there are a few other nice features that Apache provides.
One of the most useful benefits of an Apache/WebDAV configuration for your
Subversion repository is that your versioned files and directories are
immediately available for viewing via a regular web browser. Since
Subversion uses URLs to identify versioned resources, those URLs used for
HTTP-based repository access can be typed directly into a web browser. Your
browser will issue an HTTP GET request for that URL;
based on whether that URL represents a versioned directory or file,
mod_dav_svn will respond with a directory listing or with
file contents.
If the URLs do not contain any information about which version of the resource you wish to see, mod_dav_svn will answer with the youngest version. This functionality has the wonderful side effect that you can pass around Subversion URLs to your peers as references to documents, and those URLs will always point at the latest manifestation of that document. Of course, you can even use the URLs as hyperlinks from other web sites, too.
As of Subversion 1.6, mod_dav_svn supports a public URI
syntax for examining older revisions of both files and directories. The
syntax uses the query string portion of the URL to specify either or both of
a peg revision and operative revision, which Subversion will then use to
determine which version of the file or directory to display to your web
browser. Add the query string name/value pair
p=, where
PEGREVPEGREV is a revision number, to specify the peg
revision you wish to apply to the request. Use
r=, where
REVREV is a revision number, to specify an operative
revision.
For example, if you wish to see the latest version of a
README.txt file located in your project's
/trunk, point your web browser to that file's
repository URL, which might look something like the following:
http://host.example.com/repos/project/trunk/README.txt
If you now wish to see some older version of that file, add an operative revision to the URL's query string:
http://host.example.com/repos/project/trunk/README.txt?r=1234
What if the thing you're trying to view no longer exists in the youngest revision of the repository? That's where a peg revision is handy:
http://host.example.com/repos/project/trunk/deleted-thing.txt?p=321
And of course, you can combine peg revision and operative revision specifiers to fine-tune the exact item you wish to view:
http://host.example.com/repos/project/trunk/renamed-thing.txt?p=123&r=21
The previous URL would display revision 21 of the object which, in revision
123, was located at /trunk/renamed-thing.txt in the
repository. See 第 2 节 “Peg 和实施修订版本” for a detailed
explanation of these “peg revision” and “operative
revision” concepts. They can be a bit tricky to wrap your head
around.
As a reminder, this feature of mod_dav_svn offers only a limited repository browsing experience. You can see directory listings and file contents, but no revision properties (such as commit log messages) or file/directory properties. For folks who require more extensive browsing of repositories and their history, there are several third-party software packages which offer this. Some examples include ViewVC (http://viewvc.tigris.org), Trac (http://trac.edgewall.org) and WebSVN (http://websvn.info). These third-party tools don't affect mod_dav_svn's built-in “browseability”, and generally offer a much wider set of features, including the display of the aforementioned property sets, display of content differences between file revisions, and so on.
When browsing a Subversion repository, the web browser gets a clue about how
to render a file's contents by looking at the
Content-Type: header returned in Apache's response to the
HTTP GET request. The value of this header is some sort
of MIME type. By default, Apache will tell the web browsers that all
repository files are of the “default” MIME type, typically
text/plain. This can be frustrating, however, if a user
wishes repository files to render as something more meaningful—for
example, it might be nice to have a foo.html file in
the repository actually render as HTML when browsing.
To make this happen, you need only to make sure that your files have the
proper svn:mime-type set. We discuss this in more detail
in 第 4.1 节 “文件内容类型”, and you can even
configure your client to automatically attach proper
svn:mime-type properties to files entering the repository
for the first time; see 第 3.4 节 “自动设置属性”.
Continuing our example, if one were to set the
svn:mime-type property to text/html on
file foo.html, Apache would properly tell your web
browser to render the file as HTML. One could also attach proper
image/* MIME-type properties to image files and
ultimately get an entire web site to be viewable directly from a repository!
There's generally no problem with this, as long as the web site doesn't
contain any dynamically generated content.
You generally will get more use out of URLs to versioned files—after
all, that's where the interesting content tends to lie. But you might have
occasion to browse a Subversion directory listing, where you'll quickly note
that the generated HTML used to display that listing is very basic, and
certainly not intended to be aesthetically pleasing (or even interesting).
To enable customization of these directory displays, Subversion provides an
XML index feature. A single SVNIndexXSLT directive in
your repository's Location block of
httpd.conf will instruct mod_dav_svn
to generate XML output when displaying a directory listing, and to reference
the XSLT stylesheet of your choice:
<Location /svn> DAV svn SVNParentPath /var/svn SVNIndexXSLT "/svnindex.xsl" … </Location>
Using the SVNIndexXSLT directive and a creative XSLT
stylesheet, you can make your directory listings match the color schemes and
imagery used in other parts of your web site. Or, if you'd prefer, you can
use the sample stylesheets provided in the Subversion source distribution's
tools/xslt/ directory. Keep in mind that the path
provided to the SVNIndexXSLT directory is actually a URL
path—browsers need to be able to read your stylesheets to make use of
them!
If you're serving a collection of repositories from a single URL via the
SVNParentPath directive, then it's also possible to have
Apache display all available repositories to a web browser. Just activate
the SVNListParentPath directive:
<Location /svn> DAV svn SVNParentPath /var/svn SVNListParentPath on … </Location>
If a user now points her web browser to the URL
http://host.example.com/svn/, she'll see a list of all
Subversion repositories sitting in /var/svn.
Obviously, this can be a security problem, so this feature is turned off by
default.
Because Apache is an HTTP server at heart, it contains fantastically
flexible logging features. It's beyond the scope of this book to discuss
all of the ways logging can be configured, but we should point out that even
the most generic httpd.conf file will cause Apache to
produce two logs: error_log and
access_log. These logs may appear in different places,
but are typically created in the logging area of your Apache installation.
(On Unix, they often live in /usr/local/apache2/logs/.)
The error_log describes any internal errors that Apache
runs into as it works. The access_log file records
every incoming HTTP request received by Apache. This makes it easy to see,
for example, which IP addresses Subversion clients are coming from, how
often particular clients use the server, which users are authenticating
properly, and which requests succeed or fail.
Unfortunately, because HTTP is a stateless protocol, even the simplest
Subversion client operation generates multiple network requests. It's very
difficult to look at the access_log and deduce what the
client was doing—most operations look like a series of cryptic
PROPPATCH, GET,
PUT, and REPORT requests. To make
things worse, many client operations send nearly identical series of
requests, so it's even harder to tell them apart.
mod_dav_svn, however, can come to your aid. By activating an “operational logging” feature, you can ask mod_dav_svn to create a separate log file describing what sort of high-level operations your clients are performing.
To do this, you need to make use of Apache's CustomLog
directive (which is explained in more detail in Apache's own
documentation). Be sure to invoke this directive
outside your Subversion Location
block:
<Location /svn>
DAV svn
…
</Location>
CustomLog logs/svn_logfile "%t %u %{SVN-ACTION}e" env=SVN-ACTION
In this example, we're asking Apache to create a special logfile,
svn_logfile, in the standard Apache
logs directory. The %t and
%u variables are replaced by the time and username of the
request, respectively. The really important parts are the two instances of
SVN-ACTION. When Apache sees that variable, it
substitutes the value of the SVN-ACTION environment
variable, which is automatically set by mod_dav_svn
whenever it detects a high-level client action.
So, instead of having to interpret a traditional
access_log like this:
[26/Jan/2007:22:25:29 -0600] "PROPFIND /svn/calc/!svn/vcc/default HTTP/1.1" 207 398 [26/Jan/2007:22:25:29 -0600] "PROPFIND /svn/calc/!svn/bln/59 HTTP/1.1" 207 449 [26/Jan/2007:22:25:29 -0600] "PROPFIND /svn/calc HTTP/1.1" 207 647 [26/Jan/2007:22:25:29 -0600] "REPORT /svn/calc/!svn/vcc/default HTTP/1.1" 200 607 [26/Jan/2007:22:25:31 -0600] "OPTIONS /svn/calc HTTP/1.1" 200 188 [26/Jan/2007:22:25:31 -0600] "MKACTIVITY /svn/calc/!svn/act/e6035ef7-5df0-4ac0-b811-4be7c823f998 HTTP/1.1" 201 227 …
你可以细读一个更加智能的 svn_logfile 文件：
[26/Jan/2007:22:24:20 -0600] - get-dir /tags r1729 props [26/Jan/2007:22:24:27 -0600] - update /trunk r1729 depth=infinity [26/Jan/2007:22:25:29 -0600] - status /trunk/foo r1729 depth=infinity [26/Jan/2007:22:25:31 -0600] sally commit r1730
In addition to the SVN-ACTION environment variable,
mod_dav_svn also populates the
SVN-REPOS and SVN-REPOS-NAME
variables, which carry the filesystem path to the repository and the
basename thereof, respectively. You might wish to include references to one
or both of these variables in your CustomLog format
string, too, especially if you are combining usage information from multiple
repositories into a single log file.
For an exhaustive list of all actions logged, see 第 6 节 “High-level Logging”.
One of the nice advantages of using Apache as a Subversion server is that it can be set up for simple replication. For example, suppose that your team is distributed across four offices around the globe. The Subversion repository can exist only in one of those offices, which means the other three offices will not enjoy accessing it—they're likely to experience significantly slower traffic and response times when updating and committing code. A powerful solution is to set up a system consisting of one master Apache server and several slave Apache servers. If you place a slave server in each office, users can check out a working copy from whichever slave is closest to them. All read requests go to their local slave. Write requests get automatically routed to the single master server. When the commit completes, the master then automatically “pushes” the new revision to each slave server using the svnsync replication tool.
This configuration creates a huge perceptual speed increase for your users, because Subversion client traffic is typically 80–90% read requests. And if those requests are coming from a local server, it's a huge win.
In this section, we'll walk you through a standard setup of this single-master/multiple-slave system. However, keep in mind that your servers must be running at least Apache 2.2.0 (with mod_proxy loaded) and Subversion 1.5 (mod_dav_svn).
First, configure your master server's httpd.conf file
in the usual way. Make the repository available at a certain URI location,
and configure authentication and authorization however you'd like. After
that's done, configure each of your “slave” servers in the
exact same way, but add the special SVNMasterURI
directive to the block:
<Location /svn> DAV svn SVNPath /var/svn/repos SVNMasterURI http://master.example.com/svn … </Location>
This new directive tells a slave server to redirect all write requests to the master. (This is done automatically via Apache's mod_proxy module.) Ordinary read requests, however, are still serviced by the slaves. Be sure that your master and slave servers all have matching authentication and authorization configurations; if they fall out of sync, it can lead to big headaches.
Next, we need to deal with the problem of infinite recursion. With the current configuration, imagine what will happen when a Subversion client performs a commit to the master server. After the commit completes, the server uses svnsync to replicate the new revision to each slave. But because svnsync appears to be just another Subversion client performing a commit, the slave will immediately attempt to proxy the incoming write request back to the master! Hilarity ensues.
The solution to this problem is to have the master push revisions to a
different <Location> on the slaves. This location
is configured to not proxy write requests at all, but
to accept normal commits from (and only from) the master's IP address:
<Location /svn-proxy-sync> DAV svn SVNPath /var/svn/repos Order deny,allow Deny from all # Only let the server's IP address access this Location: Allow from 10.20.30.40 … </Location>
Now that you've configured your Location blocks on master
and slaves, you need to configure the master to replicate to the slaves.
This is done the usual way— using svnsync. If
you're not familiar with this tool, see 第 4.7 节 “版本库复制” for details.
First, make sure that each slave repository has a
pre-revprop-change hook script which allows remote
revision property changes. (This is standard procedure for being on the
receiving end of svnsync.) Then log into the master
server and configure each of the slave repository URIs to receive data from
the master repository on the local disk:
$ svnsync init http://slave1.example.com/svn-proxy-sync file:///var/svn/repos Copied properties for revision 0. $ svnsync init http://slave2.example.com/svn-proxy-sync file:///var/svn/repos Copied properties for revision 0. $ svnsync init http://slave3.example.com/svn-proxy-sync file:///var/svn/repos Copied properties for revision 0. # Perform the initial replication $ svnsync sync http://slave1.example.com/svn-proxy-sync Transmitting file data .... Committed revision 1. Copied properties for revision 1. Transmitting file data ....... Committed revision 2. Copied properties for revision 2. … $ svnsync sync http://slave2.example.com/svn-proxy-sync Transmitting file data .... Committed revision 1. Copied properties for revision 1. Transmitting file data ....... Committed revision 2. Copied properties for revision 2. … $ svnsync sync http://slave3.example.com/svn-proxy-sync Transmitting file data .... Committed revision 1. Copied properties for revision 1. Transmitting file data ....... Committed revision 2. Copied properties for revision 2. …
After this is done, we configure the master server's
post-commit hook script to invoke
svnsync on each slave server:
#!/bin/sh # Post-commit script to replicate newly committed revision to slaves svnsync sync http://slave1.example.com/svn-proxy-sync > /dev/null 2>&1 & svnsync sync http://slave2.example.com/svn-proxy-sync > /dev/null 2>&1 & svnsync sync http://slave3.example.com/svn-proxy-sync > /dev/null 2>&1 &
The extra bits on the end of each line aren't necessary, but they're a
sneaky way to allow the sync commands to run in the background so that the
Subversion client isn't left waiting forever for the commit to finish. In
addition to this post-commit hook, you'll need a
post-revprop-change hook as well so that when a user,
say, modifies a log message, the slave servers get that change also:
#!/bin/sh
# Post-revprop-change script to replicate revprop-changes to slaves
REV=${2}
svnsync copy-revprops http://slave1.example.com/svn-proxy-sync ${REV} > /dev/null 2>&1 &
svnsync copy-revprops http://slave2.example.com/svn-proxy-sync ${REV} > /dev/null 2>&1 &
svnsync copy-revprops http://slave3.example.com/svn-proxy-sync ${REV} > /dev/null 2>&1 &
The only thing we've left out here is what to do about user-level locks (of the svn lock variety). Locks are enforced by the master server during commit operations; but all the information about locks is distributed during read operations such as svn update and svn status by the slave server. As such, a fully functioning proxy setup needs to perfectly replicate lock information from the master server to the slave servers. Unfortunately, most of the mechanisms that one might employ to accomplish this replication fall short in one way or another[52]. Many teams don't use Subversion's locking features at all, so this may be a nonissue for you. Sadly, for those teams which do use locks, we have no recommendations on how to gracefully work around this shortcoming.
Your master/slave replication system should now be ready to use. A couple of words of warning are in order, however. Remember that this replication isn't entirely robust in the face of computer or network crashes. For example, if one of the automated svnsync commands fails to complete for some reason, the slaves will begin to fall behind. For example, your remote users will see that they've committed revision 100, but then when they run svn update, their local server will tell them that revision 100 doesn't yet exist! Of course, the problem will be automatically fixed the next time another commit happens and the subsequent svnsync is successful—the sync will replicate all waiting revisions. But still, you may want to set up some sort of out-of-band monitoring to notice synchronization failures and force svnsync to run when things go wrong.
Several of the features already provided by Apache in its role as a robust
web server can be leveraged for increased functionality or security in
Subversion as well. The Subversion client is able to use SSL (the Secure
Sockets Layer, discussed earlier). If your Subversion client is built to
support SSL, it can access your Apache server using
https:// and enjoy a high-quality encrypted network
session.
同样有用的是Apache和Subversion关系的一些特性，像可以指定自定义的端口(而不是缺省的HTTP的80)或者是一个Subversion可以被访问的虚拟主机名，或者是通过HTTP代理服务器访问的能力，这些特性都是Neon所支持的，所以Subversion轻易得到这些支持。
Finally, because mod_dav_svn is speaking a subset of the WebDAV/DeltaV protocol, it's possible to access the repository via third-party DAV clients. Most modern operating systems (Win32, OS X, and Linux) have the built-in ability to mount a DAV server as a standard network “shared folder.” This is a complicated topic, but also wondrous when implemented. For details, read 附录 C, WebDAV 和自动版本.
Note that there are a number of other small tweaks one can make to
mod_dav_svn that are too obscure to mention in this
chapter. For a complete list of all httpd.conf
directives that mod_dav_svn responds to, see “指令”一节.
[47] See http://www.webdav.org/.
[48] 他们讨厌这样做。
[51] While self-signed certificates are still vulnerable to a “man-in-the-middle” attack, such an attack is much more difficult for a casual observer to pull off, compared to sniffing unprotected passwords.
[52] http://subversion.tigris.org/issues/show_bug.cgi?id=3457 tracks these problems.