How do I tell Subversion to treat a file as a binary file?

Question

How do I tell Subversion (svn) to treat a file as a binary file?

Answer 1

It is possible to manually identify a file located within a repository as binary by using:

svn propset svn:mime-type application/octet-stream <filename> 

This is generally not necessary, as Subversion will attempt to determine whether a file is binary when the file is first added. If Subversion is incorrectly tagging a certain type as "text" when it should be treated as binary, it is possible to configure Subversion's auto-props feature to automatically tag that file with a non-text MIME type. Regardless of the properties configured on the file, Subversion still stores the file in a binary format within the repository.

If Subversion identifies the MIME type as a "text" type, it enables certain features which are not available on binary files, such as svn diff and svn blame. It also allows for automatic line ending conversion, which is configurable on a client-by-client basis.

For more information, see How does Subversion handle binary files?

Answer 2

From page 367 of the Subversion book

In the most general sense, Subversion handles binary files more gracefully than CVS does. Because CVS uses RCS, it can only store successive full copies of a changing binary file. Subversion, however, expresses differences between files using a binary differencing algorithm, regardless of whether they contain textual or binary data. That means all files are stored differentially (compressed) in the repository.

CVS users have to mark binary files with -kb flags to prevent data from being garbled (due to keyword expansion and line-ending translations). They sometimes forget to do this.

Subversion takes the more paranoid route. First, it never performs any kind of keyword or line-ending translation unless you explicitly ask it to do so (see the section called “Keyword Substitution” and the section called “End-of-Line Character Sequences” for more details). By default, Subversion treats all file data as literal byte strings, and files are always stored in the repository in an untranslated state.

Second, Subversion maintains an internal notion of whether a file is “text” or “binary” data, but this notion is only extant in the working copy. During an svn update, Subversion will perform contextual merges on locally modified text files, but will not attempt to do so for binary files.

To determine whether a contextual merge is possible, Subversion examines the svn:mime-type property. If the file has no svn:mime-type property, or has a MIME type that is textual (e.g., text/*), Subversion assumes it is text. Otherwise, Subversion assumes the file is binary. Subversion also helps users by running a binary-detection algorithm in the svn import and svn add commands. These commands will make a good guess and then (possibly) set a binary svn:mime-type property on the file being added. (If Subversion guesses wrong, the user can always remove or hand-edit the property.)

Hand editing would be done by

svn propset svn:mime-type some/type filename.extension