I just added uscan source tar signature validation to a project stored on GitHub. A cookbook approach may be helpful to others.

The uscan man page and wiki watch page both provide a watch file recipe for pointing at GitHub pages:

opts=filenamemangle=s/.+\/v?(\d\S*)\.tar\.gz/<project>-$1\.tar\.gz/ \
  https://github.com/<user>/<project>/tags .*/v?(\d\S*)\.tar\.gz

Here’s what’s going on. You can refer to GitHub repositories as tar.gz files from the tags or releases pages, which list all tags stored on the repository. The problem is, that the naming isn’t right for debian - the tar file name just consists of <version>.tar.gz. The ‘filenamemangle’ option remaps the GitHub tar name to one including the project name, before storing the tar locally.

This is actually not good enough, as it stands, to work in a git-buildpackage environment. The final glob should be more specific, to match only against the branch holding the ‘upstream’ (that is, the non-debian) code branch.

Typical guidance for specifying the signature url, using the pgpsigurlmangle option, tells how to point to the file when it is stored in the same directory as the tar, with an appended “.asc”:

opts=pgpsigurlmangle=s/$/.asc/ ftp://ftp.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-(.+)\.tar\.gz

Unfortunately, it is not practical to store the signature on the GitHub tags/release pages.

I stored the signatures in a dedicated signatures branch, and used a custom ‘pgpsigurlmangle’ definition to point to a raw version of the appropriate signature:

s/$/.asc/ \
 https://github.com/davesteele/splitcpy/tags .+master/(\d[\d\.]*)\.tar\.gz

A couple things to note here:

  • That is a single, continued line.
  • There are two white space occurances in that line, separating the defninition. into an option specification, a tar listing page url, and tar search glob.
  • The two options defined in the ‘opts’ spec are separated by a comma.
  • The multiple rules in the pgpsigurlmangle definition are separated by semicolons.
  • There are four replacement rules defined for the signature url:
    • The first one replaces the url site name with the GitHub ‘raw’ host.
    • The second one points to the right branch.
    • The third one fixes the file name.
    • The fourth one adds the ‘asc’ extension.
  • I’m using ‘master’ as the git-buildpackage ‘upstream’ branch.
  • Occurrences of ‘davesteele’ and ‘splitcpy’ will need to be replaced for other instances.

The key to be used to verify the tar file must be stored under the debian directory. Some older announcements state that the key is stored in debian/upstream-signing-key.pgp. Current documentation says that a binary key can be stored in debian/upstream/signing-key.pgp, or an ascii armored one in debian/upstream/signing-key.asc. All currently work, but support for the first form will be eventually removed.

Also, the key can be replaced with a keyring for team project support.