zookeeper: allow CreateServer to work in an existing directory.

It only succeeds if the directory is empty, for instance
when it's created by ioutil.TempDir.

Also add Server.Addr method and change the NotRunning
error to ErrNotRunning.

https://code.launchpad.net/~rogpeppe/gozk/allow-existing-server-dir/+merge/96778

(do not edit description out of merge proposal)

[rog, 2012-03-09 15:19:45]

Please take a look.

[fwereade, 2012-03-12 10:34:46]

LGTM

https://codereview.appspot.com/5787068/diff/5/runserver.go
File runserver.go (right):

https://codereview.appspot.com/5787068/diff/5/runserver.go#newcode20
runserver.go:20: var ErrNotRunning = errors.New("process not running")
I'm not really *against* this change, but I don't understand the motivation --
is the Err-ness not always clear from context?

[rog, 2012-03-13 11:27:14]

forgot to publish this.

https://codereview.appspot.com/5787068/diff/5/runserver.go
File runserver.go (right):

https://codereview.appspot.com/5787068/diff/5/runserver.go#newcode20
runserver.go:20: var ErrNotRunning = errors.New("process not running")
On 2012/03/12 10:34:46, fwereade wrote:
> I'm not really *against* this change, but I don't understand the motivation --
> is the Err-ness not always clear from context?

it's conventional. try a recursive grep in $GOROOT for '^var.*errors\.New'

there are one or two exceptions, but they're not exported, except for io.EOF and
filepath.SkipDir, neither of which are "proper" errors.

[niemeyer, 2012-03-13 21:02:36]

LGTM

https://codereview.appspot.com/5787068/diff/5/runserver.go
File runserver.go (right):

https://codereview.appspot.com/5787068/diff/5/runserver.go#newcode20
runserver.go:20: var ErrNotRunning = errors.New("process not running")
On 2012/03/13 11:27:14, rog wrote:
> it's conventional. try a recursive grep in $GOROOT for '^var.*errors\.New'

Just to be fair with William, this wasn't a well established convention until
very recently.

https://codereview.appspot.com/5787068/diff/5/server_test.go
File server_test.go (right):

https://codereview.appspot.com/5787068/diff/5/server_test.go#newcode207
server_test.go:207: dir, err := ioutil.TempDir("", "zktest-")
dir := c.MkDir()

[rog, 2012-03-14 09:43:54]

*** Submitted:

zookeeper: allow CreateServer to work in an existing directory.

It only succeeds if the directory is empty, for instance
when it's created by ioutil.TempDir.

Also add Server.Addr method and change the NotRunning
error to ErrNotRunning.

R=fwereade, niemeyer
CC=
https://codereview.appspot.com/5787068