Add support for DOCKER_HOST env var

If DOCKER_HOST is set, docker-gen will use that as the address
and default back to unix:///var/run/docker.sock if not specified.

Author: jwilder

docker-gen.go

@@ -172,6 +172,9 @@ func generateFromEvents(client *docker.Client, configs ConfigFile) {
 	eventChan := getEvents()
 	for {
 		event := <-eventChan
+		if event == nil {
+			return
+		}
 		if event.Status == "start" || event.Status == "stop" || event.Status == "die" {
 			generateFromContainers(client)
 		}
@@ -211,10 +214,13 @@ func main() {
 	}
 
 	endpoint := "unix:///var/run/docker.sock"
+	if os.Getenv("DOCKER_HOST") != "" {
+		endpoint = os.Getenv("DOCKER_HOST")
+	}
 	client, err := docker.NewClient(endpoint)
 
 	if err != nil {
-		panic(err)
+		log.Fatalf("Unable to parse %s: %s", endpoint, err)
 	}
 
 	generateFromContainers(client)

docker_client.go

@@ -2,13 +2,15 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
 	"io"
 	"log"
 	"net"
 	"net/http"
 	"net/http/httputil"
 	"os"
 	"os/signal"
+	"strconv"
 	"strings"
 	"syscall"
 
@@ -18,6 +20,68 @@ import (
 type DockerContainer struct {
 }
 
+// based off of https://github.com/dotcloud/docker/blob/2a711d16e05b69328f2636f88f8eac035477f7e4/utils/utils.go
+func parseHost(addr string) (string, string, error) {
+
+	var (
+		proto string
+		host  string
+		port  int
+	)
+	addr = strings.TrimSpace(addr)
+	switch {
+	case addr == "tcp://":
+		return "", "", fmt.Errorf("Invalid bind address format: %s", addr)
+	case strings.HasPrefix(addr, "unix://"):
+		proto = "unix"
+		addr = strings.TrimPrefix(addr, "unix://")
+		if addr == "" {
+			addr = "/var/run/docker.sock"
+		}
+	case strings.HasPrefix(addr, "tcp://"):
+		proto = "tcp"
+		addr = strings.TrimPrefix(addr, "tcp://")
+	case strings.HasPrefix(addr, "fd://"):
+		return "fd", addr, nil
+	case addr == "":
+		proto = "unix"
+		addr = "/var/run/docker.sock"
+	default:
+		if strings.Contains(addr, "://") {
+			return "", "", fmt.Errorf("Invalid bind address protocol: %s", addr)
+		}
+		proto = "tcp"
+	}
+
+	if proto != "unix" && strings.Contains(addr, ":") {
+		hostParts := strings.Split(addr, ":")
+		if len(hostParts) != 2 {
+			return "", "", fmt.Errorf("Invalid bind address format: %s", addr)
+		}
+		if hostParts[0] != "" {
+			host = hostParts[0]
+		} else {
+			host = "127.0.0.1"
+		}
+
+		if p, err := strconv.Atoi(hostParts[1]); err == nil && p != 0 {
+			port = p
+		} else {
+			return "", "", fmt.Errorf("Invalid bind address format: %s", addr)
+		}
+
+	} else if proto == "tcp" && !strings.Contains(addr, ":") {
+		return "", "", fmt.Errorf("Invalid bind address format: %s", addr)
+	} else {
+		host = addr
+	}
+	if proto == "unix" {
+		return proto, host, nil
+
+	}
+	return proto, fmt.Sprintf("%s:%d", host, port), nil
+}
+
 func splitDockerImage(img string) (string, string, string) {
 	index := 0
 	repository := img
@@ -39,7 +103,12 @@ func splitDockerImage(img string) (string, string, string) {
 }
 
 func newConn() (*httputil.ClientConn, error) {
-	conn, err := net.Dial("unix", "/var/run/docker.sock")
+	proto, addr, err := parseHost(os.Getenv("DOCKER_HOST"))
+	if err != nil {
+		return nil, err
+	}
+
+	conn, err := net.Dial(proto, addr)
 	if err != nil {
 		return nil, err
 	}

docker_client_test.go

@@ -122,3 +122,53 @@ func TestSplitDockerImageWithLocalRepositoryAndTag(t *testing.T) {
 	}
 
 }
+
+func TestParseHostUnix(t *testing.T) {
+	proto, addr, err := parseHost("unix:///var/run/docker.sock")
+	if err != nil {
+		t.Fatalf("%s", err)
+	}
+	if proto != "unix" || addr != "/var/run/docker.sock" {
+		t.Fatal("failed to parse unix:///var/run/docker.sock")
+	}
+}
+
+func TestParseHostUnixDefault(t *testing.T) {
+	proto, addr, err := parseHost("")
+	if err != nil {
+		t.Fatalf("%s", err)
+	}
+	if proto != "unix" || addr != "/var/run/docker.sock" {
+		t.Fatal("failed to parse ''")
+	}
+}
+
+func TestParseHostUnixDefaultNoPath(t *testing.T) {
+	proto, addr, err := parseHost("unix://")
+	if err != nil {
+		t.Fatalf("%s", err)
+	}
+	if proto != "unix" || addr != "/var/run/docker.sock" {
+		t.Fatal("failed to parse unix://")
+	}
+}
+
+func TestParseHostTCP(t *testing.T) {
+	proto, addr, err := parseHost("tcp://127.0.0.1:4243")
+	if err != nil {
+		t.Fatalf("%s", err)
+	}
+	if proto != "tcp" || addr != "127.0.0.1:4243" {
+		t.Fatal("failed to parse tcp://127.0.0.1:4243")
+	}
+}
+
+func TestParseHostTCPDefault(t *testing.T) {
+	proto, addr, err := parseHost("tcp://:4243")
+	if err != nil {
+		t.Fatalf("%s", err)
+	}
+	if proto != "tcp" || addr != "127.0.0.1:4243" {
+		t.Fatal("failed to parse unix:///var/run/docker.sock")
+	}
+}