The source code should be shipped in the standard formats for transporting directory trees. For Unix and Unix-like operating systems, the convention is to use TAR format, compressed by compress, gzip, bzip or bzip2. For MS Windows, the standard method for distributing directory trees is zip format, which happens to do compression as well, so there is no need to compress the archive after creating it.

The name of the package should consist of the software's name plus the release number, plus the format suffixes appropriate for the archive type. For example, Scanley 2.5.0, packaged for Unix using GNU Zip (gzip) compression, would look like this:

or for Windows using zip compression:

Either of these archives, when unpacked, should create a single new directory tree named scanley-2.5.0 in the current directory. Underneath the new directory, the source code should be arranged in a layout ready for compilation (if compilation is needed) and installation. In the top level of new directory tree, there should be a plain text README file explaining what the software does and what release this is, and giving pointers to other resources, such as the project's web site, other files of interest, etc. Among those other files should be an INSTALL file, sibling to the README file, giving instructions on how to build and install the software for all the operating systems it supports. As mentioned in the section called “How to Apply a License to Your Software” in Chapter 2, Getting Started, there should also be a COPYING or LICENSE file, giving the software's terms of distribution.

There should also be a CHANGES file (sometimes called NEWS), explaining what's new in this release. The CHANGES file accumulates changelists for all releases, in reverse chronological order, so that the list for this release appears at the top of the file. Completing that list is usually the last thing done on a stabilizing release branch; some projects write the list piecemeal as they're developing, others prefer to save it all up for the end and have one person write it, getting information by combing the version control logs. The list looks something like this:

Version 2.5.0
(20 December 2004, from /branches/2.5.x)
http://svn.scanley.org/repos/svn/tags/2.5.0/

 New features, enhancements:
    * Added regular expression queries (issue #53)
    * Added support for UTF-8 and UTF-16 documents
    * Documentation translated into Polish, Russian, Malagasy
    * ...

 Bugfixes:
    * fixed reindexing bug (issue #945)
    * fixed some query bugs (issues #815, #1007, #1008)
    * ...

The list can be as long as necessary, but don't bother to include every little bugfix and feature enhancement. Its purpose is simply to give users an overview of what they would gain by upgrading to the new release. In fact, the changelist is customarily included in the announcement email (see the section called “Testing and Releasing” later in this chapter), so write it with that audience in mind.

The actual layout of the source code inside the tree should be the same as, or as similar as possible to, the source code layout one would get by checking out the project directly from its version control repository. Usually there are a few differences, for example because the package contains some generated files needed for configuration and compilation (see the section called “Compilation and Installation” later in this chapter), or because it includes third-party software that is not maintained by the project, but that is required and that users are not likely to already have. But even if the distributed tree corresponds exactly to some development tree in the version control repository, the distribution itself should not be a working copy (see working copy). The release is supposed to represent a static reference point—a particular, unchangeable configuration of source files. If it were a working copy, the danger would be that the user might update it, and afterward think that he still has the release when in fact he has something different.

Remember that the package is the same regardless of the packaging. The release—that is, the precise entity referred to when someone says "Scanley 2.5.0"—is the tree created by unpacking a zip file or tarball. So the project might offer all of these for download:

...but the source tree created by unpacking them must be the same. That source tree is the distribution; the form in which it is downloaded is merely a matter of convenience. Certain trivial differences between source packages are allowable: for example, in the Windows package, text files should have lines ending with CRLF (Carriage Return and Line Feed), while Unix packages should use just LF. The trees may be arranged slightly differently between source packages destined for different operating systems, too, if those operating systems require different sorts of layouts for compilation. However, these are all basically trivial transformations. The basic source files should be the same across all the packagings of a given release.

For software requiring compilation or installation from source, there are usually standard procedures that experienced users expect to be able to follow. For example, for programs written in C, C++, or certain other compiled languages, the standard under Unix-like systems is for the user to type:

   $ ./configure
   $ make
   # make install

The first command autodetects as much about the environment as it can and prepares for the build process, the second command builds the software in place (but does not install it), and the last command installs it on the system. The first two commands are done as a regular user, the third as root. For more details about setting up this system, see the excellent GNU Autoconf, Automake, and Libtool book by Vaughan, Elliston, Tromey, and Taylor. It is published as treeware by New Riders, and its content is also freely available online at http://sources.redhat.com/autobook/.

This is not the only standard, though it is one of the most widespread. The Ant (http://ant.apache.org/) build system is gaining popularity, especially with projects written in Java, and it has its own standard procedures for building and installing. Also, certain programming languages, such as Perl and Python, recommend that the same method be used for most programs written in that language (for example, Perl modules use the command perl Makefile.PL). If it's not obvious to you what the applicable standards are for your project, ask an experienced developer; you can safely assume that some standard applies, even if you don't know what it is at first.

Whatever the appropriate standards for you project are, don't deviate from them unless you absolutely must. Standard installation procedures are practically spinal reflexes for a lot of system administrators now. If they see familiar invocations documented in your project's INSTALL file, that instantly raises their faith that your project is generally aware of conventions, and that it is likely to have gotten other things right as well. Also, as discussed in the section called “Downloads” in Chapter 2, Getting Started, having a standard build procedure pleases potential developers.

On Windows, the standards for building and installing are a bit less settled. For projects requiring compilation, the general convention seems to be to ship a tree that can fit into the workspace/project model of the standard Microsoft development environments (Developer Studio, Visual Studio, VS.NET, MSVC++, etc.). Depending on the nature of your software, it may be possible to offer a Unix-like build option on Windows via the Cygwin (http://www.cygwin.com/) environment. And of course, if you're using a language or programming framework that comes with its own build and install conventions—e.g., Perl or Python—you should simply use whatever the standard method is for that framework, whether on Windows, Unix, Mac OS X, or any other operating system.

Be willing to put in a lot of extra effort in order to make your project conform to the relevant build or installation standards. Building and installing is an entry point: it's okay for things to get harder after that, if they absolutely must, but it would be a shame for the user's or developer's very first interaction with the software to require unexpected steps.

Although the formal release is a source code package, most users will install from binary packages, either provided by their operating system's software distribution mechanism, or obtained manually from the project web site or from some third party. Here "binary" doesn't necessarily mean "compiled"; it just means any pre-configured form of the package that allows a user to install it on his computer without going through the usual source-based build and install procedures. On RedHat GNU/Linux, it is the RPM system; on Debian GNU/Linux, it is the APT (.deb) system; on MS Windows, it's usually .MSI files or self-installing .exe files.

Whether these binary packages are assembled by people closely associated with the project, or by distant third parties, users are going to treat them as equivalent to the project's official releases, and will file issues in the project's bug tracker based on the behavior of the binary packages. Therefore, it is in the project's interest to provide packagers with clear guidelines, and work closely with them to see to it that what they produce represents the software fairly and accurately.

The main thing packagers need to know is that they should always base their binary packages on an official source release. Sometimes packagers are tempted to pull a later incarnation of the code from the repository, or include selected changes that were committed after the release was made, in order to provide users with certain bug fixes or other improvements. The packager thinks he is doing his users a favor by giving them the more recent code, but actually this practice can cause a great deal of confusion. Projects are prepared to receive reports of bugs found in released versions, and bugs found in recent trunk and major branch code (that is, found by people who deliberately run bleeding edge code). When a bug report comes in from these sources, the responder will often be able to confirm that the bug is known to be present in that snapshot, and perhaps that it has since been fixed and that the user should upgrade or wait for the next release. If it is a previously unknown bug, having the precise release makes it easier to reproduce and easier to categorize in the tracker.

Projects are not prepared, however, to receive bug reports based on unspecified intermediate or hybrid versions. Such bugs can be hard to reproduce; also, they may be due to unexpected interactions in isolated changes pulled in from later development, and thereby cause misbehaviors that the project's developers should not have to take the blame for. I have even seen dismayingly large amounts of time wasted because a bug was absent when it should have been present: someone was running a slightly patched up version, based on (but not identical to) an official release, and when the predicted bug did not happen, everyone had to dig around a lot to figure out why.

Still, there will sometimes be circumstances when a packager insists that modifications to the source release are necessary. Packagers should be encouraged to bring this up with the project's developers and describe their plans. They may get approval, but failing that, they will at least have notified the project of their intentions, so the project can watch out for unusual bug reports. The developers may respond by putting a disclaimer on the project's web site, and may ask that the packager do the same thing in the appropriate place, so that users of that binary package know what they are getting is not exactly the same as what the project officially released. There need be no animosity in such a situation, though unfortunately there often is. It's just that packagers have a slightly different set of goals from developers. The packagers mainly want the best out-of-the-box experience for their users. The developers want that too, of course, but they also need to ensure that they know what versions of the software are out there, so they can receive coherent bug reports and make compatibility guarantees. Sometimes these goals conflict. When they do, it's good to keep in mind that the project has no control over the packagers, and that the bonds of obligation run both ways. It's true that the project is doing the packagers a favor simply by producing the software. But the packagers are also doing the project a favor, by taking on a mostly unglamorous job in order to make the software more widely available, often by orders of magnitude. It's fine to disagree with packagers, but don't flame them; just try to work things out as best you can.