version

The version package offers simple helper utilties for tracking and exposing the version information associated with your Go binaries.

Tracking

We use the link tool’s -X option to embed values at build time. The values are:

• Hash: the VCS commit hash the binary was built from
• Branch: the VCS branch the binary was built from
• Tag: the VCS tag the binary was built from
• Timestamp: the date and time the binary was built, in ISO 8601 format.

To populate these values, you need to pass the -ldflags command line argument, with the -X option used to specify variables:

go build -ldflags "-X darlinggo.co/version.Hash={YOUR_HASH_HERE} -X darlinggo.co/version.Tag={YOUR_TAG_HERE} -X darlinggo.co/version.Branch={YOUR_BRANCH_HERE} -X darlinggo.co/version.Timestamp={YOUR_TIMESTAMP_HERE}" .

Obviously, that gets annoying to type out every time you build, so we made it a bit easier with the included ldflags.sh script, which exports the $LDFLAGS environment variable when it’s called, populated wtih all the right information. You can use this on the commandline:

$GOPATH/src/darlinggo.co/version/ldflags.sh
go build -ldflags ${LDFLAGS} .

Or you can include it in your own shell script:

source $GOPATH/src/darlinggo.co/version/ldflags.sh
go build -ldflags ${LDFLAGS} .

Using with vendoring

If you vendor this dependency (and you should!) you need to tell the ldflags.sh script where to look, unfortunately, because your package’s import path becomes part of its import path. Fortunately, you can do this with the PACKAGE_PREFIX variable:

export PACKAGE_PREFIX=my/package/import # e.g., darlinggo.co/version
source vendor/darlinggo.co/version/ldflags.sh
go build -ldflags "${LDFLAGS}" .

Note that we’ll automatically include the vendor part if you have a PACKAGE_PREFIX set, so you don’t have to include that.

Customising for non-Git versioning

Right now, the values supplied by ldflags.sh all rely on the package being tracked with Git to work. While supporting other VCSes is possible, and would be nice, it’s not really a priority at the moment—which is a non-subtle way of saying “pull requests accepted” 😉. However, you can supply your own values to override any or all of the Git values, using environment variables:

• VERSION will override the Git hash.
• TAG will override the Git tag.
• BRANCH will override the Git branch.
• TIMESTAMP will override the date-command generated timestamp.

Exposing

The version information is stored in exported variables, so you can expose it however you want:

• version.Hash has the hash.
• version.Tag has the tag.
• version.Branch has the branch.
• version.Timestamp has the timestamp.

Version also supplies its own http.Handler that writes the version information to the Response. Just associate it with a server:

http.Handle("/version", version.Handler)
err := http.ListenAndServe(":8080", nil)
if err != nil {
	panic(err)
}

The version will be, by default, output in the following format:

VERSION_HASH="{YOUR HASH HERE}"
VERSION_TAG="{YOUR TAG HERE}"
VERSION_BRANCH="{YOUR BRANCH HERE}"
VERSION_TIME="{YOUR TIMESTAMP HERE}"

If the Accept header includes “application/json”, however, the output will be in the following format:

{
	"hash": "{YOUR HASH HERE}",
	"tag": "{YOUR TAG HERE}",
	"branch": "{YOUR BRANCH HERE}",
	"timestamp": "{YOUR TIMESTAMP HERE}"
}