Memory and socket leak of docker daemon when using with rootless docker

[flauschpony]

When using rootless docker every time a client is created with docker.from_env() a UNIX-STREAM socket belonging to the docker daemon is also created. Over time this can lead to hundreds or thousands of sockets and an increased memory usage of the rootless docker process. This happens even when no containers are running.

I noticed this behaviour on our Debian 12 servers, both with the Debian provided version of this library and the latest version installed with pip in a virtual environment.

client.version() output:

{
   "Platform":{
      "Name":"Docker Engine - Community"
   },
   "Components":[
      {
         "Name":"Engine",
         "Version":"26.0.0",
         "Details":{
            "ApiVersion":"1.45",
            "Arch":"amd64",
            "BuildTime":"2024-03-20T15:18:01.000000000+00:00",
            "Experimental":"false",
            "GitCommit":"8b79278",
            "GoVersion":"go1.21.8",
            "KernelVersion":"6.1.0-18-amd64",
            "MinAPIVersion":"1.24",
            "Os":"linux"
         }
      },
      {
         "Name":"containerd",
         "Version":"1.6.31",
         "Details":{
            "GitCommit":"e377cd56a71523140ca6ae87e30244719194a521"
         }
      },
      {
         "Name":"runc",
         "Version":"1.1.12",
         "Details":{
            "GitCommit":"v1.1.12-0-g51d5e94"
         }
      },
      {
         "Name":"docker-init",
         "Version":"0.19.0",
         "Details":{
            "GitCommit":"de40ad0"
         }
      },
      {
         "Name":"rootlesskit",
         "Version":"2.0.2",
         "Details":{
            "ApiVersion":"1.1.1",
            "NetworkDriver":"slirp4netns",
            "PortDriver":"builtin",
            "StateDir":"/run/user/2001/dockerd-rootless"
         }
      },
      {
         "Name":"slirp4netns",
         "Version":"1.2.0",
         "Details":{
            "GitCommit":"656041d45cfca7a4176f6b7eed9e4fe6c11e8383"
         }
      }
   ],
   "Version":"26.0.0",
   "ApiVersion":"1.45",
   "MinAPIVersion":"1.24",
   "GitCommit":"8b79278",
   "GoVersion":"go1.21.8",
   "Os":"linux",
   "Arch":"amd64",
   "KernelVersion":"6.1.0-18-amd64",
   "BuildTime":"2024-03-20T15:18:01.000000000+00:00"
}

How to check the number of sockets belonging to the docker daemon:

lsof -p [PID of docker daemon] | grep UNIX-STREAM | wc -l

Testscript to produce a large amounts of sockets:

import docker

while True:
    client = docker.from_env()