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docker.go
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docker.go
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package priv
import (
"context"
"net"
"net/url"
"os"
"sync/atomic"
"github.com/docker/docker/client"
"github.com/pkg/errors"
)
// DockerClient constructs a client that can continue to talk to a root owned docker socket
// * even after the process drops privileges
func DockerClient() (*client.Client, error) {
host := client.DefaultDockerHost
if envHost := os.Getenv("DOCKER_HOST"); envHost != "" {
host = envHost
}
hostURL, err := url.Parse(host)
if err != nil {
return nil, err
}
opts := []client.Opt{
client.FromEnv,
client.WithAPIVersionNegotiation(),
}
if shouldConnectSock(hostURL) {
opt, err := connectSockOpt(hostURL)
if err != nil {
return nil, errors.Wrap(err, "failed to connect to docker socket")
}
opts = append(opts, opt)
}
return client.NewClientWithOpts(opts...)
}
type unclosableConn struct {
net.Conn
inUse int32
}
func (c *unclosableConn) Close() error {
atomic.StoreInt32(&c.inUse, 0)
// don't close a connection we won't have privileges to reopen
return nil
}
// connectSockOpt overrides the client dialer to always return the same socket connection
func connectSockOpt(host *url.URL) (client.Opt, error) {
socketConn, err := net.Dial("unix", host.Path)
if err != nil {
return nil, err
}
c := &unclosableConn{Conn: socketConn, inUse: 0}
return client.WithDialContext(func(ctx context.Context, network, addr string) (conn net.Conn, err error) {
if !atomic.CompareAndSwapInt32(&c.inUse, 0, 1) {
return nil, errors.New("singleton connection already in use")
}
return c, nil
}), nil
}