add --format flag to docker version

[phemmer]

This adds the --format flag to docker version.

Closes #14186

Default output:

$ docker version
Client:
 Version:      1.8.0
 API version:  1.20
 Go version:   go1.4.2
 Git commit:   f5bae0a
 Built:        Tue Jun 23 17:56:00 UTC 2015
 OS/Arch:      linux/amd64

Server:
 Version:      1.8.0
 API version:  1.20
 Go version:   go1.4.2
 Git commit:   f5bae0a
 Built:        Tue Jun 23 17:56:00 UTC 2015
 OS/Arch:      linux/amd64

Get server version:

$ docker version --format '{{.Server.Version}}'
1.8.0

Dump raw data:

$ docker version --format '{{json .}}'
{"Client":{"Version":"1.8.0","ApiVersion":"1.20","GitCommit":"f5bae0a","GoVersion":"go1.4.2","Os":"linux","Arch":"amd64","BuildTime":"Tue Jun 23 17:56:00 UTC 2015"},"ServerOK":true,"Server":{"Version":"1.8.0","ApiVersion":"1.20","GitCommit":"f5bae0a","GoVersion":"go1.4.2","Os":"linux","Arch":"amd64","KernelVersion":"3.13.2-gentoo","BuildTime":"Tue Jun 23 17:56:00 UTC 2015"}}

Dead server:

$ docker version
Client:
 Version:      1.8.0-dev
 API version:  1.20
 Go version:   go1.4.1
 Git commit:   2a8293f-dirty
 Built:        Fri Jun 26 01:38:16 UTC 2015
 OS/Arch:      linux/amd64
Get http:///var/run/docker.sock/v1.20/version: dial unix /var/run/docker.sock: no such file or directory. Are you trying to connect to a TLS-enabled daemon without TLS?

(error goes to STDERR, allowing capturing STDOUT to still work if only client data is needed)

[LK4D4]

Is there any drawbacks for using API for such tasks?

[tianon]

I'm a big +1, but I agree with @LK4D4 that it seems like this would be better as a client-side feature -- that way we could even use this to just get the version of the client binary when the server isn't responding or isn't up, which right now looks like this (and is useful):

$ DOCKER_HOST=unix:///not/a/file.sock docker version
Client:
 Version:      1.8.0-dev
 API version:  1.20
 Go version:   go1.4.2
 Git commit:   b96f109-dirty
 Built:        Fri Jun 26 16:26:11 UTC 2015
 OS/Arch:      linux/amd64
Get http:///not/a/file.sock/v1.20/version: dial unix /not/a/file.sock: no such file or directory. Are you trying to connect to a TLS-enabled daemon without TLS?

[tianon]

ie, something like this would happen: (with that warning going to stderr)

$ docker version -f '{{.Client.Version}}'
Get http:///not/a/file.sock/v1.20/version: dial unix /not/a/file.sock: no such file or directory. Are you trying to connect to a TLS-enabled daemon without TLS?
1.8.0-dev

[duglin]

:-) with that format string I kind of wonder why we're even hitting the daemon

[phemmer]

it seems like this would be better as a client-side feature

I'm not quite following. This is a client side feature.

ie, something like this would happen: (with that warning going to stderr)

$ docker version -f '{{.Client.Version}}'
Get http:///not/a/file.sock/v1.20/version: dial unix /not/a/file.sock: no such file or directory. Are you trying to connect to a TLS-enabled daemon without TLS?
1.8.0-dev

That is what happens (except the order of the lines is reversed).

with that format string I kind of wonder why we're even hitting the daemon

Yeah, that is one down side. But the only way I can see to make that happen is to add a function to the template map which fetches the server data. And I think that makes the templating dirty.
And the current behavior is also no change from previous. If you wanted to do docker version | grep "Client version", it still hit the server.

[icecrime]

LGTM

[jessfraz]

LGTM, so sorry needs rebase, we are almost through the tunnel to the end :)

[phemmer]

Rebased.

[jessfraz]

LGTM

[jessfraz]

thanks!

[tiborvass]

@phemmer i just noticed: you shouldn't use #format, that's for old flags, you are introducing a new one here.

[thaJeztah]

ping @phemmer could you take care of this, or want someone else to do so?