Inspect remote images

[miminar]

Added new flag to docker inspect command:

$ docker inspect --remote <imageName>[:<tag>]...

Which inspects remote images. If a short name is given, all additional registries will be queried until a match is found. Additional [:TAG] suffix may further specify desired <image>.

This allows for remote inspection without downloading image layers.

[miminar]

@llunved Could you please take a look? I'll make a scratch build for you to try.

[llunved]

An initial smoke test shows that this appears to be generally working as intended. Two possible issues:
"docker inspect --remote docker.io/tomcat" vs the "docker inspect docker.io/tomcat" shows a slightly different output:

<     "VirtualSize": 0,
<     "Registry": "docker.io",
<     "Digest": "sha256:3ab045cce1bc1a73516596474bee0073206ce4843a85fccf8f1329a35625543b",
<     "Tag": "latest"
---
>     "VirtualSize": 347798454

Also there is error output on local inspect:

# docker inspect docker.io/tomcat 1> /dev/null
INFO[0658] GET /v1.19/containers/docker.io/tomcat/json  
ERRO[0658] Handler for GET /containers/{name:.*}/json returned error: no such id: docker.io/tomcat 
ERRO[0658] HTTP Error                                    err=no such id: docker.io/tomcat statusCode=404
INFO[0658] GET /v1.19/images/docker.io/tomcat/json     

I don't see that with earlier versions of docker.

[miminar]

@llunved Thanks for checking it out.
VirtualSize needs to be computed locally like this:

VirtualSize = img.Size + sum([img.getNthParent(n).Size for n in range(1, img.numParents + 1)])

So we could:

• pull all the parent json files and make this computation - could make it time consuming
• remove this attribute completely from output
• leave it as it is

Must the output of remote inspect match the local one? I've added Registry, Digest and Tag attributes because they may be interesting to the user. If he has several additional registries and inspects image identified by a short name, he should get at least the source registry information. But perhaps it could be logged as INFO messages to stderr. WDYT?

As for the error messages, they aren't shown in the latest version. However, they will appear in Docker daemon's journal -- and the same applies to older versions without these patches.

[llunved]

@miminar I looked at it again.

• The error is gone
• On vritual size does the server simply return size of 0 or is the field not returned but the client just shows 0? We should probably filter out fields that are not returned by the server, but conversely we should keep all the fields the server does actually return, even if they are 0.
• The other thing that confused me was the Digest and Tag missing... But again, if the data isn't there (locally in this case), we shouldn't make it up...

Overall LGTM

[miminar]

On 12.6.2015 16:51, llunved wrote:

@miminar https://github.com/miminar I looked at it again.

• The error is gone
• On vritual size does the server simply return size of 0 or is the field not returned but the client just shows 0? We
  should probably filter out fields that are not returned by the server, but conversely we should keep all the fields
  the server does actually return, even if they are 0.
  Registry doesn't return it. It's created and computed by client. I'll filter it out.
• The other thing that confused me was the Digest and Tag missing... But again, if the data isn't there (locally in
  this case), we shouldn't make it up...
  Ok, I'll remove them. I'll at least make this information appear in debug messages on stderr.

Overall LGTM

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