Docker API can’t apply json filters

Question

According to the https://docs.docker.com/engine/reference/api/docker_remote_api_v1.24/#/list-tasks, filter can be only used to get running containers with a particular service name. For some reason, I am getting a full list of all tasks regardless of their names or desired states. I can't find any proper examples of using curl with JSON requests with Docker API. I'm using the following command:

A)

curl -X GET -H "Content-Type: application/json" -d '{"filters":[{ "service":"demo", "desired-state":"running" }]}' https://HOSTNAME:2376/tasks --cert ~/.docker/cert.pem --key ~/.docker/key.pem --cacert ~/.docker/ca.pem

Returns everything

B) trying to get something working from Docker Remote API Filter Exited

curl https://HOSTNAME:2376/containers/json?all=1&filters={%22status%22:[%22exited%22]} --cert ~/.docker/cert.pem   --key ~/.docker/key.pem   --cacert ~/.docker/ca.pem

This one returns "curl: (60) Peer's Certificate issuer is not recognized.", so I guess that curl request is malformed.

I have asked on Docker forums and they helped a little. I'm amazed that there are no proper documentation anywhere on the internet on how to use Docker API with curl or is it so obvious and I don't understand something?

Answer 1

I should prefix this with the fact that I have never seen curl erroneously report a certificate error when there was some sort of other issue in play, but I will trust your assertion that this is not a certificate problem.

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I thought at first that your argument to filters was incorrect, because according to the API reference, the filters parameter is...

a JSON encoded value of the filters (a map[string][]string) to process on the containers list.

I wasn't exactly sure how to interpret map[string][]string, so I set up a logging proxy (see below) between my Docker client and server and ran docker ps -f status=exited, which produced the following request:

GET /v1.24/containers/json?filters=%7B%22status%22%3A%7B%22exited%22%3Atrue%7D%7D HTTP/1.1\r

If we decode the argument to filters, we see that it is:

{"status":{"exited":true}}

Whereas you are passing:

{"status":["exited"]}

So that's different, obviously, and I was assuming that was the source of the problem...but when trying to verify that, I ran into a curious problem. I can't even run your curl command line as written, because curl tries to perform some globbing behavior due to the braces:

$ curl http://localhost:2376/containers/json'?filters={%22status%22:[%22exited%22]}'
curl: (3) [globbing] nested brace in column 67

If I correctly quote your arguments to filter:

$ python -c 'import urllib; print urllib.quote("""{"status":["exited"]}""")'
%7B%22status%22%3A%5B%22exited%22%5D%7D

It seems to work just fine:

$ curl http://localhost:2376/containers/json'?filters=%7B%22status%22%3A%5B%22exited%22%5D%7D'
[{"Id":...

I can get the same behavior if I use your original expression and pass -g (aka --globoff) to disable the brace expansion:

$ curl -g http://localhost:2376/containers/json'?filters={%22status%22:[%22exited%22]}'
[{"Id":...

One thing I would like to emphasize is the utility of sticking a proxy between the docker client and server. If you ever find yourself asking, "how do I use this API?", an excellent answer is to see exactly what the Docker client is doing in the same situation.

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Setting up a simple logging proxy:

socat -v tcp-listen:2376,fork,reuseaddr unix-connect:/run/docker.sock