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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Using the APIs</title><link rel="stylesheet" href="styles.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /><link rel="start" href="index.html" title="Version Control with Subversion" /><link rel="up" href="svn.developer.html" title="Chapter 8. Embedding Subversion" /><link rel="prev" href="svn.developer.insidewc.html" title="Inside the Working Copy Administration Area" /><link rel="next" href="svn.ref.html" title="Chapter 9. Subversion Complete Reference" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Using the APIs</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="svn.developer.insidewc.html">Prev</a> </td><th width="60%" align="center">Chapter 8. Embedding Subversion</th><td width="20%" align="right"> <a accesskey="n" href="svn.ref.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="svn.developer.usingapi"></a>Using the APIs</h2></div></div></div><p>Developing applications against the Subversion library APIs
is fairly straightforward. Subversion is primarily a set of C
libraries, with header (.h) files that live in the
<code class="filename">subversion/include</code> directory of the source
tree. These headers are copied into your system locations (for
example, <code class="filename">/usr/local/include</code>) when you build
and install Subversion itself from source. These headers
represent the entirety of the functions and types meant to be
accessible by users of the Subversion libraries. The Subversion
developer community is meticulous about ensuring that the public
API is well-documented—refer directly to the header files
for that documentation.</p><p>When examining the public header files, the first thing you
might notice is that Subversion's datatypes and functions are
namespace protected. That is, every public Subversion symbol name begins
with <code class="literal">svn_</code>, followed by a short code for the
library in which the symbol is defined (such as
<code class="literal">wc</code>, <code class="literal">client</code>,
<code class="literal">fs</code>, etc.), followed by a single underscore
(<code class="literal">_</code>) and then the rest of the symbol name.
Semi-public functions (used among source files of a given
library but not by code outside that library, and found inside
the library directories themselves) differ from this naming
scheme in that instead of a single underscore after the library
code, they use a double underscore (<code class="literal">__</code>).
Functions that are private to a given source file have no
special prefixing, and are declared <code class="literal">static</code>.
Of course, a compiler isn't interested in these naming
conventions, but they help to clarify the scope of a given
function or datatype.</p><p>Another good source of information about programming against
the Subversion APIs is the project's own hacking guidelines,
which can be found at <a class="ulink" href="http://subversion.tigris.org/hacking.html" target="_top">http://subversion.tigris.org/hacking.html</a>. This
document contains useful information which, while aimed at
developers and would-be developers of Subversion itself, is
equally applicable to folks developing against Subversion as a
set of third-party libraries.
<sup>[<a id="id410568" href="#ftn.id410568" class="footnote">54</a>]</sup>
</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="svn.developer.usingapi.apr"></a>The Apache Portable Runtime Library</h3></div></div></div><p>Along with Subversion's own datatypes, you will see many
references to datatypes that begin with
<code class="literal">apr_</code>—symbols from the Apache Portable
Runtime (APR) library. APR is Apache's portability library,
originally carved out of its server code as an attempt to
separate the OS-specific bits from the OS-independent portions
of the code. The result was a library that provides a generic
API for performing operations that differ mildly—or
wildly—from OS to OS. While the Apache HTTP Server was
obviously the first user of the APR library, the Subversion
developers immediately recognized the value of using APR as
well. This means that there is practically no OS-specific
code in Subversion itself. Also, it means that the Subversion
client compiles and runs anywhere that Apache HTTP Server
itself does. Currently this list includes all flavors of
Unix, Win32, BeOS, OS/2, and Mac OS X.</p><p>In addition to providing consistent implementations of
system calls that differ across operating systems,
<sup>[<a id="id410601" href="#ftn.id410601" class="footnote">55</a>]</sup>
APR gives Subversion immediate access to many custom
datatypes, such as dynamic arrays and hash tables. Subversion
uses these types extensively. But
perhaps the most pervasive APR datatype, found in nearly every
Subversion API prototype, is the
<span class="structname">apr_pool_t</span>—the APR memory pool.
Subversion uses pools internally for all its memory allocation
needs (unless an external library requires a different memory
management mechanism for data passed through its API),
<sup>[<a id="id410625" href="#ftn.id410625" class="footnote">56</a>]</sup>
and while a person coding against the Subversion APIs is
not required to do the same, they <span class="emphasis"><em>are</em></span> required to provide
pools to the API functions that need them. This means that
users of the Subversion API must also link against APR, must
call <code class="function">apr_initialize()</code> to initialize the
APR subsystem, and then must create and manage pools for use with
Subversion API calls, typically by using
<code class="function">svn_pool_create()</code>,
<code class="function">svn_pool_clear()</code>, and
<code class="function">svn_pool_destroy()</code>.</p><div class="sidebar"><p class="title"><b>Programming with Memory Pools</b></p><p>Almost every developer who has used the C programming
language has at some point sighed at the daunting task of
managing memory usage. Allocating enough memory to use,
keeping track of those allocations, freeing the memory when
you no longer need it—these tasks can be quite
complex. And of course, failure to do those things properly
can result in a program that crashes itself, or worse,
crashes the computer.</p><p>Higher-level languages, on the other hand, take the job of
memory management away from the developer completely.
<sup>[<a id="id410680" href="#ftn.id410680" class="footnote">57</a>]</sup>
Languages like Java and Python use <em class="firstterm">garbage
collection</em>, allocating memory for
objects when needed, and automatically freeing that memory
when the object is no longer in use.</p><p>APR provides a middle-ground approach called pool-based
memory management. It allows the developer to control
memory usage at a lower resolution—per chunk (or
“<span class="quote">pool</span>”) of memory, instead of per allocated
object. Rather than using <code class="function">malloc()</code> and
friends to allocate enough memory for a given object, you
ask APR to allocate the memory from a memory pool. When
you're finished using the objects you've created in the
pool, you destroy the entire pool, effectively de-allocating the
memory consumed by <span class="emphasis"><em>all</em></span> the objects you allocated from it.
Thus, rather than keeping track of individual objects which need
to be de-allocated, your program simply considers the
general lifetimes of those objects, and allocates the
objects in a pool whose lifetime (the time between the
pool's creation and its deletion) matches the object's
needs.</p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="svn.developer.usingapi.urlpath"></a>URL and Path Requirements</h3></div></div></div><p>With remote version control operation as the whole point
of Subversion's existence, it makes sense that some attention
has been paid to internationalization (i18n) support. After
all, while “<span class="quote">remote</span>” might mean “<span class="quote">across the
office</span>”, it could just as well mean “<span class="quote">across the
globe.</span>” To facilitate this, all of Subversion's public
interfaces that accept path arguments expect those paths to be
canonicalized, and encoded in UTF-8. This means, for example,
that any new client binary that drives the libsvn_client
interface needs to first convert paths from the
locale-specific encoding to UTF-8 before passing those paths
to the Subversion libraries, and then re-convert any resultant
output paths from Subversion back into the locale's encoding
before using those paths for non-Subversion purposes.
Fortunately, Subversion provides a suite of functions (see
<code class="filename">subversion/include/svn_utf.h</code>) that can be
used by any program to do these conversions.</p><p>Also, Subversion APIs require all URL parameters to be
properly URI-encoded. So, instead of passing
<code class="uri">file:///home/username/My File.txt</code> as the URL of a
file named <code class="literal">My File.txt</code>, you need to pass
<code class="uri">file:///home/username/My%20File.txt</code>. Again,
Subversion supplies helper functions that your application can
use—<code class="function">svn_path_uri_encode()</code> and
<code class="function">svn_path_uri_decode()</code>, for URI encoding
and decoding, respectively.</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="svn.developer.usingapi.otherlangs"></a>Using Languages Other than C and C++</h3></div></div></div><p>If you are interested in using the Subversion libraries in
conjunction with something other than a C program—say a
Python or Perl script—Subversion has some support for this
via the Simplified Wrapper and Interface Generator (SWIG). The
SWIG bindings for Subversion are located in
<code class="filename">subversion/bindings/swig</code>. They are still
maturing, but they are usable. These bindings allow you
to call Subversion API functions indirectly, using wrappers that
translate the datatypes native to your scripting language into
the datatypes needed by Subversion's C libraries.</p><p>Significant efforts have been made towards creating
functional SWIG-generated bindings for Python, Perl, and Ruby.
To some extent, the work done preparing the SWIG interface
files for these languages is reusable in efforts to generate
bindings for other languages supported by SWIG (which include
versions of C#, Guile, Java, MzScheme, OCaml, PHP, and Tcl,
among others). However, some extra programming is required to
compensate for complex APIs that SWIG needs some help
translating between languages. For more information on SWIG
itself, see the project's website at <a class="ulink" href="http://www.swig.org/" target="_top">http://www.swig.org/</a>.</p><p>Subversion also has language bindings for Java. The
javahl bindings (located in
<code class="filename">subversion/bindings/java</code> in the
Subversion source tree) aren't SWIG-based, but are instead a
mixture of Java and hand-coded JNI. Javahl covers most
Subversion client-side APIs, and is specifically targeted at
implementors of Java-based Subversion clients and IDE
integrations.</p><p>Subversion's language bindings tend to lack the level of
developer attention given to the core Subversion modules, but
can generally be trusted as production-ready. A number of
scripts and applications, alternative Subversion GUI clients
and other third-party tools are successfully using
Subversion's language bindings today to accomplish their
Subversion integrations.</p><p>It's worth noting here that there are other options for
interfacing with Subversion using other languages: alternative
bindings for Subversion which aren't provided by the
Subversion development community at all. You can find links
to these alternative bindings on the Subversion project's
links page (at <a class="ulink" href="http://subversion.tigris.org/links.html" target="_top">http://subversion.tigris.org/links.html</a>), but there
are a couple of popular ones we feel are especially
noteworthy. First, Barry Scott's PySVN bindings (<a class="ulink" href="http://pysvn.tigris.org/" target="_top">http://pysvn.tigris.org/</a>) are a popular option for
binding with Python. PySVN boasts of a more Pythonic
interface than the more C-like APIs provided by Subversion's
own Python bindings. And if you're looking for a pure Java
implementation of Subversion, check out SVNKit (<a class="ulink" href="http://svnkit.com/" target="_top">http://svnkit.com/</a>), which is Subversion re-written
from the ground up in Java.</p><div class="sidebar"><p class="title"><b>SVNKit vs. javahl</b></p><p>In 2005, a small company called TMate announced the
1.0.0 release of JavaSVN—a pure Java implementation of
Subversion. Since then, the project has been renamed to
SVNKit (available at <a class="ulink" href="http://svnkit.com/" target="_top">http://svnkit.com/</a>)
and has seen great success as a provider of Subversion
functionality to various Subversion clients, IDE
integrations, and other third-party tools.</p><p>The SVNKit library is interesting in that, unlike the
javahl library, it is not merely a wrapper around the
official Subversion core libraries. In fact, it shares no
code with Subversion at all. But while it is easy to
confuse SVNKit with javahl, and easier still to not even
realize which of these libraries you are using, folks should
be aware that SVNKit differs from javahl in some significant
ways. First, SVNKit is not developed as open source
software, and seems to have at any given time only a few
developers working on it. Also, SVNKit's license is more
restrictive than that of Subversion. Finally, by aiming to
be a pure Java Subversion library, SVNKit is limited in
which portions of Subversion can be reasonably cloned while
still keeping up with Subversion's releases. This has
already happened once—SVNKit cannot access
Berkeley-DB-backed Subversion repositories via the
<code class="literal">file://</code> protocol because there's no pure
Java implementation of Berkeley DB that is file format
compatible with the native implementation of that
library.</p><p>That said, SVNKit has a well-established track record of
reliability. And a pure Java solution is much more robust
in the face of programming errors—a bug in SVNKit
might raise an Exception, but a bug in the Subversion core
libraries as accessed via javahl can bring down your entire
Java Runtime Environment. So, weigh the costs when choosing
a Java-based Subversion implementation.</p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="svn.developer.usingapi.codesamples"></a>Code Samples</h3></div></div></div><p><a class="xref" href="svn.developer.usingapi.html#svn.developer.layerlib.repos.ex-1" title="Example 8.1. Using the Repository Layer">Example 8.1, “Using the Repository Layer”</a>
contains a code segment (written in C) that illustrates some
of the concepts we've been discussing. It uses both the
repository and filesystem interfaces (as can be determined by
the prefixes <code class="literal">svn_repos_</code> and
<code class="literal">svn_fs_</code> of the function names,
respectively) to create a new revision in which a directory is
added. You can see the use of an APR pool, which is passed
around for memory allocation purposes. Also, the code reveals
a somewhat obscure fact about Subversion error
handling—all Subversion errors must be explicitly
handled to avoid memory leakage (and in some cases,
application failure).</p><div class="example"><a id="svn.developer.layerlib.repos.ex-1"></a><p class="title"><b>Example 8.1. Using the Repository Layer</b></p><div class="example-contents"><pre class="programlisting">
/* Convert a Subversion error into a simple boolean error code.
*
* NOTE: Subversion errors must be cleared (using svn_error_clear())
* because they are allocated from the global pool, else memory
* leaking occurs.
*/
#define INT_ERR(expr) \
do { \
svn_error_t *__temperr = (expr); \
if (__temperr) \
{ \
svn_error_clear(__temperr); \
return 1; \
} \
return 0; \
} while (0)
/* Create a new directory at the path NEW_DIRECTORY in the Subversion
* repository located at REPOS_PATH. Perform all memory allocation in
* POOL. This function will create a new revision for the addition of
* NEW_DIRECTORY. Return zero if the operation completes
* successfully, non-zero otherwise.
*/
static int
make_new_directory(const char *repos_path,
const char *new_directory,
apr_pool_t *pool)
{
svn_error_t *err;
svn_repos_t *repos;
svn_fs_t *fs;
svn_revnum_t youngest_rev;
svn_fs_txn_t *txn;
svn_fs_root_t *txn_root;
const char *conflict_str;
/* Open the repository located at REPOS_PATH.
*/
INT_ERR(svn_repos_open(&repos, repos_path, pool));
/* Get a pointer to the filesystem object that is stored in REPOS.
*/
fs = svn_repos_fs(repos);
/* Ask the filesystem to tell us the youngest revision that
* currently exists.
*/
INT_ERR(svn_fs_youngest_rev(&youngest_rev, fs, pool));
/* Begin a new transaction that is based on YOUNGEST_REV. We are
* less likely to have our later commit rejected as conflicting if we
* always try to make our changes against a copy of the latest snapshot
* of the filesystem tree.
*/
INT_ERR(svn_repos_fs_begin_txn_for_commit2(&txn, repos, youngest_rev,
apr_hash_make(pool), pool));
/* Now that we have started a new Subversion transaction, get a root
* object that represents that transaction.
*/
INT_ERR(svn_fs_txn_root(&txn_root, txn, pool));
/* Create our new directory under the transaction root, at the path
* NEW_DIRECTORY.
*/
INT_ERR(svn_fs_make_dir(txn_root, new_directory, pool));
/* Commit the transaction, creating a new revision of the filesystem
* which includes our added directory path.
*/
err = svn_repos_fs_commit_txn(&conflict_str, repos,
&youngest_rev, txn, pool);
if (! err)
{
/* No error? Excellent! Print a brief report of our success.
*/
printf("Directory '%s' was successfully added as new revision "
"'%ld'.\n", new_directory, youngest_rev);
}
else if (err->apr_err == SVN_ERR_FS_CONFLICT)
{
/* Uh-oh. Our commit failed as the result of a conflict
* (someone else seems to have made changes to the same area
* of the filesystem that we tried to modify). Print an error
* message.
*/
printf("A conflict occurred at path '%s' while attempting "
"to add directory '%s' to the repository at '%s'.\n",
conflict_str, new_directory, repos_path);
}
else
{
/* Some other error has occurred. Print an error message.
*/
printf("An error occurred while attempting to add directory '%s' "
"to the repository at '%s'.\n",
new_directory, repos_path);
}
INT_ERR(err);
}
</pre></div></div><br class="example-break" /><p>Note that in <a class="xref" href="svn.developer.usingapi.html#svn.developer.layerlib.repos.ex-1" title="Example 8.1. Using the Repository Layer">Example 8.1, “Using the Repository Layer”</a>, the code could
just as easily have committed the transaction using
<code class="function">svn_fs_commit_txn()</code>. But the filesystem
API knows nothing about the repository library's hook
mechanism. If you want your Subversion repository to
automatically perform some set of non-Subversion tasks every
time you commit a transaction (like, for example, sending an
email that describes all the changes made in that transaction
to your developer mailing list), you need to use the
libsvn_repos-wrapped version of that function, which adds the
hook triggering functionality—in this case,
<code class="function">svn_repos_fs_commit_txn()</code>. (For more
information regarding Subversion's repository hooks, see <a class="xref" href="svn.reposadmin.create.html#svn.reposadmin.create.hooks" title="Implementing Repository Hooks">the section called “Implementing Repository Hooks”</a>.)</p><p>Now let's switch languages. <a class="xref" href="svn.developer.usingapi.html#svn.developer.usingapi.otherlangs.ex-1" title="Example 8.2. Using the Repository Layer with Python">Example 8.2, “Using the Repository Layer with Python”</a> is a
sample program that uses Subversion's SWIG Python bindings to
recursively crawl the youngest repository revision, and print
the various paths reached during the crawl.</p><div class="example"><a id="svn.developer.usingapi.otherlangs.ex-1"></a><p class="title"><b>Example 8.2. Using the Repository Layer with Python</b></p><div class="example-contents"><pre class="programlisting">
#!/usr/bin/python
"""Crawl a repository, printing versioned object path names."""
import sys
import os.path
import svn.fs, svn.core, svn.repos
def crawl_filesystem_dir(root, directory):
"""Recursively crawl DIRECTORY under ROOT in the filesystem, and return
a list of all the paths at or below DIRECTORY."""
# Print the name of this path.
print directory + "/"
# Get the directory entries for DIRECTORY.
entries = svn.fs.svn_fs_dir_entries(root, directory)
# Loop over the entries.
names = entries.keys()
for name in names:
# Calculate the entry's full path.
full_path = directory + '/' + name
# If the entry is a directory, recurse. The recursion will return
# a list with the entry and all its children, which we will add to
# our running list of paths.
if svn.fs.svn_fs_is_dir(root, full_path):
crawl_filesystem_dir(root, full_path)
else:
# Else it's a file, so print its path here.
print full_path
def crawl_youngest(repos_path):
"""Open the repository at REPOS_PATH, and recursively crawl its
youngest revision."""
# Open the repository at REPOS_PATH, and get a reference to its
# versioning filesystem.
repos_obj = svn.repos.svn_repos_open(repos_path)
fs_obj = svn.repos.svn_repos_fs(repos_obj)
# Query the current youngest revision.
youngest_rev = svn.fs.svn_fs_youngest_rev(fs_obj)
# Open a root object representing the youngest (HEAD) revision.
root_obj = svn.fs.svn_fs_revision_root(fs_obj, youngest_rev)
# Do the recursive crawl.
crawl_filesystem_dir(root_obj, "")
if __name__ == "__main__":
# Check for sane usage.
if len(sys.argv) != 2:
sys.stderr.write("Usage: %s REPOS_PATH\n"
% (os.path.basename(sys.argv[0])))
sys.exit(1)
# Canonicalize the repository path.
repos_path = svn.core.svn_path_canonicalize(sys.argv[1])
# Do the real work.
crawl_youngest(repos_path)
</pre></div></div><br class="example-break" /><p>This same program in C would need to deal with APR's
memory pool system. But Python handles memory usage
automatically, and Subversion's Python bindings adhere to that
convention. In C, you'd be working with custom datatypes
(such as those provided by the APR library) for representing
the hash of entries and the list of paths, but Python has
hashes (called “<span class="quote">dictionaries</span>”) and lists as
built-in datatypes, and provides a rich collection of
functions for operating on those types. So SWIG (with the
help of some customizations in Subversion's language bindings
layer) takes care of mapping those custom datatypes into the
native datatypes of the target language. This provides a more
intuitive interface for users of that language.</p><p>The Subversion Python bindings can be used for working
copy operations, too. In the previous section of this
chapter, we mentioned the <code class="filename">libsvn_client</code>
interface, and how it exists for the sole purpose of
simplifying the process of writing a Subversion client. <a class="xref" href="svn.developer.usingapi.html#svn.developer.usingapi.otherlangs.ex-2" title="Example 8.3. A Python Status Crawler">Example 8.3, “A Python Status Crawler”</a> is a brief
example of how that library can be accessed via the SWIG
Python bindings to recreate a scaled-down version of the
<span class="command"><strong>svn status</strong></span> command.</p><div class="example"><a id="svn.developer.usingapi.otherlangs.ex-2"></a><p class="title"><b>Example 8.3. A Python Status Crawler</b></p><div class="example-contents"><pre class="programlisting">
#!/usr/bin/env python
"""Crawl a working copy directory, printing status information."""
import sys
import os.path
import getopt
import svn.core, svn.client, svn.wc
def generate_status_code(status):
"""Translate a status value into a single-character status code,
using the same logic as the Subversion command-line client."""
code_map = { svn.wc.svn_wc_status_none : ' ',
svn.wc.svn_wc_status_normal : ' ',
svn.wc.svn_wc_status_added : 'A',
svn.wc.svn_wc_status_missing : '!',
svn.wc.svn_wc_status_incomplete : '!',
svn.wc.svn_wc_status_deleted : 'D',
svn.wc.svn_wc_status_replaced : 'R',
svn.wc.svn_wc_status_modified : 'M',
svn.wc.svn_wc_status_merged : 'G',
svn.wc.svn_wc_status_conflicted : 'C',
svn.wc.svn_wc_status_obstructed : '~',
svn.wc.svn_wc_status_ignored : 'I',
svn.wc.svn_wc_status_external : 'X',
svn.wc.svn_wc_status_unversioned : '?',
}
return code_map.get(status, '?')
def do_status(wc_path, verbose):
# Calculate the length of the input working copy path.
wc_path_len = len(wc_path)
# Build a client context baton.
ctx = svn.client.svn_client_ctx_t()
def _status_callback(path, status, root_path_len=wc_path_len):
"""A callback function for svn_client_status."""
# Print the path, minus the bit that overlaps with the root of
# the status crawl
text_status = generate_status_code(status.text_status)
prop_status = generate_status_code(status.prop_status)
print '%s%s %s' % (text_status, prop_status, path)
# Do the status crawl, using _status_callback() as our callback function.
revision = svn.core.svn_opt_revision_t()
revision.type = svn.core.svn_opt_revision_head
svn.client.svn_client_status2(wc_path, revision, _status_callback,
svn.core.svn_depth_infinity, verbose,
0, 0, 1, ctx)
def usage_and_exit(errorcode):
"""Print usage message, and exit with ERRORCODE."""
stream = errorcode and sys.stderr or sys.stdout
stream.write("""Usage: %s OPTIONS WC-PATH
Options:
--help, -h : Show this usage message
--verbose, -v : Show all statuses, even uninteresting ones
""" % (os.path.basename(sys.argv[0])))
sys.exit(errorcode)
if __name__ == '__main__':
# Parse command-line options.
try:
opts, args = getopt.getopt(sys.argv[1:], "hv", ["help", "verbose"])
except getopt.GetoptError:
usage_and_exit(1)
verbose = 0
for opt, arg in opts:
if opt in ("-h", "--help"):
usage_and_exit(0)
if opt in ("-v", "--verbose"):
verbose = 1
if len(args) != 1:
usage_and_exit(2)
# Canonicalize the repository path.
wc_path = svn.core.svn_path_canonicalize(args[0])
# Do the real work.
try:
do_status(wc_path, verbose)
except svn.core.SubversionException, e:
sys.stderr.write("Error (%d): %s\n" % (e.apr_err, e.message))
sys.exit(1)
</pre></div></div><br class="example-break" /><p>As was the case in <a class="xref" href="svn.developer.usingapi.html#svn.developer.usingapi.otherlangs.ex-1" title="Example 8.2. Using the Repository Layer with Python">Example 8.2, “Using the Repository Layer with Python”</a>, this
program is pool-free and uses, for the most part, normal
Python data types. The call to
<code class="function">svn_client_ctx_t()</code> is deceiving because
the public Subversion API has no such function—this just
happens to be a case where SWIG's automatic language
generation bleeds through a little bit (the function is a sort
of factory function for Python's version of the corresponding
complex C structure). Also note that the path passed to this
program (like the last one) gets run through
<code class="function">svn_path_canonicalize()</code>, because to
<span class="emphasis"><em>not</em></span> do so runs the risk of triggering the
underlying Subversion C library's assertions about such
things, which translate into rather immediate and
unceremonious program abortion.</p></div><div class="footnotes"><br /><hr width="100" align="left" /><div class="footnote"><p><sup>[<a id="ftn.id410568" href="#id410568" class="para">54</a>] </sup>After all, Subversion uses Subversion's APIs,
too.</p></div><div class="footnote"><p><sup>[<a id="ftn.id410601" href="#id410601" class="para">55</a>] </sup>Subversion uses ANSI system calls and datatypes as much
as possible.</p></div><div class="footnote"><p><sup>[<a id="ftn.id410625" href="#id410625" class="para">56</a>] </sup>Neon and Berkeley DB are examples of such libraries.</p></div><div class="footnote"><p><sup>[<a id="ftn.id410680" href="#id410680" class="para">57</a>] </sup>Or at least make it something you only toy with when
doing extremely tight program optimization.</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="svn.developer.insidewc.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="svn.developer.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="svn.ref.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Inside the Working Copy Administration Area </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 9. Subversion Complete Reference</td></tr></table></div></body></html>
