Wrong Content-Type in response of Remote API to the GET stats request

[hpollinger]

Description of problem:
Using the Remote API, in the response to the GET request for the stats of a container the "Content-Type" is "text/plain; charset=utf-8", but should be "application/json", like it was in earlier versions of the Remote API.
The problem is that parsers rely on the "Content-Type".

docker version:
Client:
Version: 1.8.2
API version: 1.20
Go version: go1.4.2
Git commit: 0a8c2e3
Built: Thu Sep 10 19:19:00 UTC 2015
OS/Arch: linux/amd64

Server:
Version: 1.8.2
API version: 1.20
Go version: go1.4.2
Git commit: 0a8c2e3
Built: Thu Sep 10 19:19:00 UTC 2015
OS/Arch: linux/amd64

docker info:
Containers: 98
Images: 9
Storage Driver: aufs
Root Dir: /var/lib/docker/aufs
Backing Filesystem: extfs
Dirs: 211
Dirperm1 Supported: false
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 3.13.0-63-generic
Operating System: Ubuntu 14.04.3 LTS
CPUs: 4
Total Memory: 7.664 GiB
Name: sirius.mydomain.test
ID: OKAA:4QF6:6QJ4:R4SE:IWFG:YJLY:PFFW:YTEK:URCB:MTCV:QCOY:VP3Y
WARNING: No swap limit support

uname -a:
Linux sirius.mydomain.test 3.13.0-63-generic #103-Ubuntu SMP Fri Aug 14 21:42:59 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Environment details (AWS, VirtualBox, physical, etc.):
Physical

How reproducible:
Always

Steps to Reproduce:

1. Just enter the following command line in terminal:
   $ echo -e "GET /containers/4d50a1065a88/stats HTTP/1.1\r\n" | sudo nc -q -1 -U /var/run/docker.sock

Actual Results:
HTTP/1.1 200 OK
Server: Docker/1.8.2 (linux)
Date: Wed, 23 Sep 2015 08:04:40 GMT
Content-Type: text/plain; charset=utf-8
Transfer-Encoding: chunked
[...]

Expected Results:
HTTP/1.1 200 OK
Server: Docker/1.8.2 (linux)
Date: Wed, 23 Sep 2015 08:04:40 GMT
Content-Type: application/json
Transfer-Encoding: chunked
[...]

Additional info:
I didn't find another response yet that reports the wrong Content-Type, but also didn't check many yet.

[cpuguy83]

Stats never returned application/json to my knowledge, as it's not actually application/json.
It is really new line delimited json.

This is a stream, not a singular response.
Currently all of docker's streaming responses are returned as text/plain.

You can get application/json if you use the stream=0 query param.

[hpollinger]

It responded "application/json" with Remote API 1.17, Docker 1.5.0.

You are right that the stream itself is not really "application/json", but each line (or block) in this stream is. For me its awkward (and it took some time to debug) that the type changes just because its either "one" or "many" of the output. I just want to take the body of the response and put it in the parser that is denoted by the type that is defined in the header of the response - no matter if I do this once or each second.

With the response "text/plain", I have to hard code that the response to the "stats" request has to be handled by the json parser. If this changes, I have to change my code. Thats not how it should be.

[cpuguy83]

Hmmm, you're right. Looks like this probably changed in 1.7 with some big architectural refactorings.
I'll have to take a look and see if some of these changes were intentional.

[thaJeztah]

@cpuguy83 have you had time to look into these changes?

[cpuguy83]

Yes, this is problematic.
We did change to x-json-stream at one point, but this broke some older clients due to versioning issues (ie, certain endpoints weren't properly versioned at one point).

[cpuguy83]

That said, we can probably make the change for the stats endpoint.

[thaJeztah]

It could be versioned to keep the "old" behavior for older clients/api-versions

[cpuguy83]

For stats yes, for other endpoints, no.