Add port binding utility

Author: lippserd

utils/port.go

@@ -0,0 +1,117 @@
+package utils
+
+import (
+	"context"
+	"fmt"
+	"github.com/docker/docker/client"
+	"github.com/docker/go-connections/nat"
+	"github.com/pkg/errors"
+	"net"
+	"strconv"
+)
+
+type PortDecision struct {
+	dockerHost string
+	exposed    string
+	port       string
+	remote     bool
+}
+
+func NewPortDecision(c *client.Client, port string) *PortDecision {
+	url, err := client.ParseHostURL(c.DaemonHost())
+	if err != nil {
+		panic(err)
+	}
+	p := &PortDecision{port: port}
+	if url.Scheme != "unix" {
+		portNumber, err := GetFreePort()
+		if err != nil {
+			panic(err)
+		}
+		p.dockerHost = url.Hostname()
+		p.exposed = strconv.Itoa(portNumber)
+		p.remote = true
+	} else {
+		p.exposed = port
+	}
+
+	return p
+}
+
+func (p *PortDecision) Address(ctx context.Context, c *client.Client, id string) string {
+	if p.remote {
+		return p.dockerHost
+	}
+
+	return MustString(DockerContainerAddress(ctx, c, id))
+}
+
+func (p *PortDecision) Binding(ctx context.Context, c *client.Client, id string) (*PortBinding, error) {
+	var port string
+	host := p.Address(ctx, c, id)
+	if p.remote {
+		r, err := c.ContainerInspect(context.Background(), id)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to inspect container")
+		}
+
+		defaultPort, err := nat.NewPort(nat.SplitProtoPort(p.port))
+		if err != nil {
+			return nil, errors.Wrap(err, "can't parse default port")
+		}
+
+		p, ok := r.NetworkSettings.Ports[defaultPort]
+		if !ok {
+			return nil, errors.New(fmt.Sprintf("default port %s not exposed", defaultPort))
+		}
+		port = p[0].HostPort
+	}
+
+	return &PortBinding{
+		Host: host,
+		Port: port,
+	}, nil
+}
+
+func (p *PortDecision) Map() nat.PortMap {
+	if p.remote {
+		return nat.PortMap{
+			nat.Port(fmt.Sprintf("%s/tcp", p.port)): []nat.PortBinding{
+				{
+					HostIP:   "0.0.0.0",
+					HostPort: p.exposed,
+				},
+			},
+		}
+	}
+
+	return nil
+}
+
+func (p *PortDecision) Port() string {
+	return p.exposed
+}
+
+func (p *PortDecision) Remote() bool {
+	return p.remote
+}
+
+func GetFreePort() (int, error) {
+	addr, err := net.ResolveTCPAddr("tcp", ":0")
+	if err != nil {
+		return 0, err
+	}
+
+	l, err := net.ListenTCP("tcp", addr)
+	if err != nil {
+		return 0, err
+	}
+	defer l.Close()
+
+	return l.Addr().(*net.TCPAddr).Port, nil
+}
+
+type PortBinding struct {
+	Host string
+	Port string
+}