add groupByLabel function

[codekitchen]

This is convenient, but also necessary since the $fieldPath parameter to groupBy can't contain dots in map key names, and labels are typically reverse-domain-name prefixed.

[md5]

This will break if the label actually has a blank value. You may want to check the second return value from container.Labels[label] to see if it is false instead of checking for "". I did this in the whereLabel function.

[codekitchen]

Ah you are right, I misread groupBy as excluding the container if the value is blank, so I went this route for consistency, but it only excludes if the value is nil. I'll change it.

[codekitchen]

Done

[tompson]

I built something specific for grouping by the service name of the docker compose file:

troii@e9eded7

but this pull would make mine obsolete and make it more generic

my vote for this one! ;)

[tompson]

I tried to use groubByLabel like

{{ range $host, $containers := groupByLabel $ "com.docker.compose.service"  }} 

but I always get

function "groupByLabel" not defined

[codekitchen]

@tompson I've successfully used the new function with a binary built by running make with this PR applied, e.g. make && ./docker-gen -only-exposed /path/to/my/tempate.tmpl. It sounds like you're probably not using the right docker-gen binary?

[tompson]

did exactly that, checked multiple times that I got the right binary

do you have an example template file?

[codekitchen]

You probably don't have this PR applied locally then. A simple example template would be:

{{range $project, $containers := groupByLabel $ "com.docker.compose.project"}}{{printf "%s %s\n" $project (first $containers).ID}}{{end}}

[tompson]

wow, that was hard to track down, problem was that in cmd/docker-gen/main.go the import

"github.com/jwilder/docker-gen"

caused that make did not build codekitchen/docker-gen or troii/docker-gen even when I ran make in my repository

[codekitchen]

Ah dang, that's a pain yeah. Glad you got it sorted out.

[md5]

@tompson When I work on this project I add an additional Git remote to my checkout of github.com/jwilder/docker-gen to avoid this problem.

[jwilder]

Thanks @codekitchen!