A SIMPLE .NET Subversion Trigger

This latest post finds me on my continued Subversion kick. Having checked out the wonderful, yet not quite mature enough Mercurial and the possibly wonderful but completely painful windows experience of GIT, i'm sticking with Subversion as my Visual SourceSafe replacement of choice. This week I have mostly been playing with Subversion hooks- an extremely simple and powerful trigger mechanism used when checking items in or out of a subversion database.

For those who do not know, each subversion database contains a 'hooks' folder in which files exist for pre and post commit/lock/property change/unlock events. Harnessing this hooking mechanism is as simple as creating a file and giving it, for instance the filename 'pre-commit'. The true beauty (i'm sure i mentioned this before) is that the extension doesnt matter - you can use an exe, a batch file, a .pl file etc. etc. and, as long as your filename falls into the pre-defined list, your hook is guaranteed to run on the chosen event. Some templates are created as part of the default database creation, and below is an example of a pre-commit.tmpl script for one of my databases.

<br /><br /><br />#!/bin/sh<br /><br /><br /><br /># PRE-COMMIT HOOK<br /><br />#<br /><br /># The pre-commit hook is invoked before a Subversion txn is<br /><br /># committed. Subversion runs this hook by invoking a program<br /><br /># (script, executable, binary, etc.) named 'pre-commit' (for which<br /><br /># this file is a template), with the following ordered arguments:<br /><br />#<br /><br /># [1] REPOS-PATH (the path to this repository)<br /><br /># [2] TXN-NAME (the name of the txn about to be committed)<br /><br />#<br /><br /># The default working directory for the invocation is undefined, so<br /><br /># the program should set one explicitly if it cares.<br /><br />#<br /><br /># If the hook program exits with success, the txn is committed; but<br /><br /># if it exits with failure (non-zero), the txn is aborted, no commit<br /><br /># takes place, and STDERR is returned to the client. The hook<br /><br /># program can use the 'svnlook' utility to help it examine the txn.<br /><br />#<br /><br /># On a Unix system, the normal procedure is to have 'pre-commit'<br /><br /># invoke other programs to do the real work, though it may do the<br /><br /># work itself too.<br /><br />#<br /><br /># *** NOTE: THE HOOK PROGRAM MUST NOT MODIFY THE TXN, EXCEPT ***<br /><br /># *** FOR REVISION PROPERTIES (like svn:log or svn:author). ***<br /><br />#<br /><br /># This is why we recommend using the read-only 'svnlook' utility.<br /><br /># In the future, Subversion may enforce the rule that pre-commit<br /><br /># hooks should not modify the versioned data in txns, or else come<br /><br /># up with a mechanism to make it safe to do so (by informing the<br /><br /># committing client of the changes). However, right now neither<br /><br /># mechanism is implemented, so hook writers just have to be careful.<br /><br />#<br /><br /># Note that 'pre-commit' must be executable by the user(s) who will<br /><br /># invoke it (typically the user httpd runs as), and that user must<br /><br /># have filesystem-level permission to access the repository.<br /><br />#<br /><br /># On a Windows system, you should name the hook program<br /><br /># 'pre-commit.bat' or 'pre-commit.exe',<br /><br /># but the basic idea is the same.<br /><br />#<br /><br /># The hook program typically does not inherit the environment of<br /><br /># its parent process. For example, a common problem is for the<br /><br /># PATH environment variable to not be set to its usual value, so<br /><br /># that subprograms fail to launch unless invoked via absolute path.<br /><br /># If you're having unexpected problems with a hook program, the<br /><br /># culprit may be unusual (or missing) environment variables.<br /><br /># <br /><br /># Here is an example hook script, for a Unix /bin/sh interpreter.<br /><br /># For more examples and pre-written hooks, see those in<br /><br /># the Subversion repository at<br /><br /># http://svn.collab.net/repos/svn/trunk/tools/hook-scripts/ and<br /><br /># http://svn.collab.net/repos/svn/trunk/contrib/hook-scripts/<br /><br /><br /><br /><br /><br />REPOS="$1"<br /><br />TXN="$2"<br /><br /><br /><br /># Make sure that the log message contains some text.<br /><br />SVNLOOK=/usr/local/bin/svnlook<br /><br />$SVNLOOK log -t "$TXN" "$REPOS" \<br /><br /> grep "[a-zA-Z0-9]" > /dev/null exit 1<br /><br /><br /><br /># Check that the author of this commit has the rights to perform<br /><br /># the commit on the files and directories being modified.<br /><br />commit-access-control.pl "$REPOS" "$TXN" commit-access-control.cfg exit 1<br /><br /><br /><br /># All checks passed, so allow the commit.<br /><br />exit 0<br /><br /><br /><br />

The beauty of this example is that it explains in no uncertain terms the paramaters taken by the hooking procedure:

# [1] REPOS-PATH (the path to this
repository)
# [2] TXN-NAME (the name of the txn
about to be committed)

Using these parameters, it is easy to create triggers in the flavor of your choice. Below, i created a VB.NET console application which (given the repository path and transaction name) uses the external svnlook command to inspect the comment field passed as part of the transaction. If the user has entered comments less than 5 characters (an arbitrary number) the transaction will fail (a la the exit(1) command and will write an error message back to the calling application.

<br /><br /><br /><br />Module Module1<br /><br /><br /><br /><br /><br /> Private repositories As String<br /><br /><br /> Private transaction As String<br /><br /><br /><br /><br /><br /> Sub Main()<br /><br /><br /><br /><br /><br /> Try<br /><br /><br /> repositories = My.Application.CommandLineArgs(0)<br /><br /><br /> transaction = My.Application.CommandLineArgs(1)<br /><br /><br /><br /><br /><br /> Dim processStartInfo As ProcessStartInfo = New ProcessStartInfo()<br /><br /><br /> processStartInfo.WorkingDirectory = "C:\Program Files\CollabNet Subversion Server"<br /><br /><br /> processStartInfo.FileName = "svnlook.exe"<br /><br /><br /> processStartInfo.UseShellExecute = False<br /><br /><br /> processStartInfo.CreateNoWindow = True<br /><br /><br /> processStartInfo.RedirectStandardOutput = True<br /><br /><br /> processStartInfo.RedirectStandardError = True<br /><br /><br /> processStartInfo.Arguments = String.Concat("log -t", " """, transaction, """ """, repositories, """")<br /><br /><br /><br /><br /><br /> Dim p As Process = Process.Start(processStartInfo)<br /><br /><br /> Dim s As String = p.StandardOutput.ReadToEnd()<br /><br /><br /> p.WaitForExit()<br /><br /><br /><br /><br /><br /> If s.Trim.Length() <= 4 Then <br />Console.Error.WriteLine(Space(40)) Console.Error.WriteLine("****************** COMMIT POLICY VIOLATION *******************") <br />Console.Error.WriteLine("The commit policy requires comments to be at least 5 characters in length.") <br />Console.Error.WriteLine("**************************************************************") Environment.Exit(1) <br />Else <br />Environment.Exit(0) <br />End If <br />Catch ex As Exception <br />Console.Error.WriteLine(ex.Message.ToString()) <br />Environment.Exit(1) <br />End Try <br />End Sub <br />End Module <br />



Here's a screenshot of TortoiseSVN when this trigger fires and my limit of 5 characters had not been reached.












I've been working on something a little more substantial for next time, but I hope this serves as a pretty simple introduction to the joys of subversion triggers!