Write image metadata using json serialisation

Write image metadata using json serialisation

This branch writes outs simplestreams image metadata using
json serialisation instead of a template based approach. It
is a pre-requisit to allow the next step of merging new image
metadata instead of overwriting. This will be used when setting
up private clouds.

https://code.launchpad.net/~wallyworld/juju-core/marshal-image-metadata/+merge/190542

Requires: https://code.launchpad.net/~wallyworld/juju-core/improve-image-metadata-command/+merge/190517

(do not edit description out of merge proposal)

[wallyworld, 2013-10-11 06:48:01]

Please take a look.

[wallyworld, 2013-10-14 09:30:49]

Please take a look.

[thumper, 2013-10-16 01:26:11]

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
File environs/imagemetadata/generate.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
environs/imagemetadata/generate.go:15: metadataInfo, err :=
generateMetadata(series, im, cloudSpec)
This has me queezy.

Surely WriteMetadata would take the metadataInfo as an input parameter?

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
File environs/imagemetadata/generate_test.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
environs/imagemetadata/generate_test.go:17: type generateSuite struct{}
testbase.LoggingSuite

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
environs/imagemetadata/generate_test.go:34: c.Assert(len(metadata), gc.Equals,
1)
gc.HasLen

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/simp...
File environs/imagemetadata/simplestreams.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/simp...
environs/imagemetadata/simplestreams.go:121: Release     string `json:"-"`
What does json:"-" do?

https://codereview.appspot.com/14540055/diff/4001/environs/tools/marshal.go
File environs/tools/marshal.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/tools/marshal.go#n...
environs/tools/marshal.go:69: itemsversion := updated.Format("20060102") //
YYYYMMDD
Some of these changes are the same as the branch I just reviewed.

[wallyworld, 2013-10-16 01:35:16]

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
File environs/imagemetadata/generate.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
environs/imagemetadata/generate.go:15: metadataInfo, err :=
generateMetadata(series, im, cloudSpec)
On 2013/10/16 01:26:11, thumper wrote:
> This has me queezy.
> 
> Surely WriteMetadata would take the metadataInfo as an input parameter?

The sematics of the write function is to take a ImageMetadata struct and write
out the simplestreams metadata. In order to write the metadata, it needs to be
generated from the struct. The method could be called WriteAndGenerate I guess.
But the generation and writing to file is an atomic operation. 

A subsequent branch renames the method anyway and refactors the content to align
with what Andrew did for tools metadata.

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
File environs/imagemetadata/generate_test.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
environs/imagemetadata/generate_test.go:17: type generateSuite struct{}
On 2013/10/16 01:26:11, thumper wrote:
> testbase.LoggingSuite

Will fix

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/gene...
environs/imagemetadata/generate_test.go:34: c.Assert(len(metadata), gc.Equals,
1)
On 2013/10/16 01:26:11, thumper wrote:
> gc.HasLen

Will fix

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/simp...
File environs/imagemetadata/simplestreams.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/imagemetadata/simp...
environs/imagemetadata/simplestreams.go:121: Release     string `json:"-"`
On 2013/10/16 01:26:11, thumper wrote:
> What does json:"-" do?

Tells json not to marshall that attribute. It's there to provide info for other
mthods in the struct to do their thing, but we don't want it serialised to json.

https://codereview.appspot.com/14540055/diff/4001/environs/tools/marshal.go
File environs/tools/marshal.go (right):

https://codereview.appspot.com/14540055/diff/4001/environs/tools/marshal.go#n...
environs/tools/marshal.go:69: itemsversion := updated.Format("20060102") //
YYYYMMDD
On 2013/10/16 01:26:11, thumper wrote:
> Some of these changes are the same as the branch I just reviewed.

I fixed this in a downstream branch - I didn't pump the changes back up the pipe
sorry.

[wallyworld, 2013-10-16 04:12:47]

Please take a look.

[thumper, 2013-10-17 04:04:01]

LGTM