extract docker-bridge-ip fetching from proxy into bash script

proxy/create_container_interceptor.go

@@ -3,17 +3,16 @@ package proxy
 import (
 	"bytes"
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
-	"strings"
 
 	"github.com/fsouza/go-dockerclient"
 )
 
 type createContainerInterceptor struct {
-	client  *docker.Client
-	withDNS bool
+	client         *docker.Client
+	withDNS        bool
+	dockerBridgeIP string
 }
 
 type createContainerRequestBody struct {
@@ -97,11 +96,7 @@ func (i *createContainerInterceptor) setWeaveDNS(container *createContainerReque
 		return nil
 	}
 
-	dockerBridgeIP, err := getDockerBridgeIP()
-	if err != nil {
-		return err
-	}
-	container.HostConfig.DNS = append(container.HostConfig.DNS, dockerBridgeIP)
+	container.HostConfig.DNS = append(container.HostConfig.DNS, i.dockerBridgeIP)
 
 	if len(container.HostConfig.DNSSearch) == 0 {
 		container.HostConfig.DNSSearch = []string{"."}
@@ -109,26 +104,6 @@ func (i *createContainerInterceptor) setWeaveDNS(container *createContainerReque
 	return nil
 }
 
-func getDockerBridgeIP() (string, error) {
-	out, err := callWeave("dns-args")
-	if err != nil {
-		return "", fmt.Errorf("Error fetching weave dns-args: %s", err)
-	}
-
-	var dockerBridgeIP string
-	segments := strings.Split(string(out), " ")
-	for i := 0; i < len(segments)-1; i++ {
-		if segments[i] == "--dns" {
-			dockerBridgeIP = segments[i+1]
-		}
-	}
-
-	if dockerBridgeIP == "" {
-		return "", fmt.Errorf("Docker bridge IP not found in weave output: %s", string(out))
-	}
-	return dockerBridgeIP, nil
-}
-
 func (i *createContainerInterceptor) InterceptResponse(res *http.Response) (*http.Response, error) {
 	return res, nil
 }

proxy/proxy.go

@@ -12,9 +12,10 @@ import (
 )
 
 type Proxy struct {
-	Dial    func() (net.Conn, error)
-	client  *docker.Client
-	withDNS bool
+	Dial           func() (net.Conn, error)
+	client         *docker.Client
+	withDNS        bool
+	dockerBridgeIP string
 }
 
 func NewProxy(targetURL string, withDNS bool) (*Proxy, error) {
@@ -22,6 +23,15 @@ func NewProxy(targetURL string, withDNS bool) (*Proxy, error) {
 	if err != nil {
 		return nil, err
 	}
+
+	var dockerBridgeIP []byte
+	if withDNS {
+		dockerBridgeIP, err = callWeave("docker-bridge-ip")
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	client, err := docker.NewClient(targetURL)
 	if err != nil {
 		return nil, err
@@ -30,8 +40,9 @@ func NewProxy(targetURL string, withDNS bool) (*Proxy, error) {
 		Dial: func() (net.Conn, error) {
 			return net.Dial(targetNetwork(u), targetAddress(u))
 		},
-		client:  client,
-		withDNS: withDNS,
+		client:         client,
+		withDNS:        withDNS,
+		dockerBridgeIP: string(dockerBridgeIP),
 	}, nil
 }
 
@@ -82,7 +93,7 @@ func (proxy *Proxy) weaveStatus(w http.ResponseWriter, r *http.Request) {
 }
 
 func (proxy *Proxy) createContainer(w http.ResponseWriter, r *http.Request) {
-	newClient(proxy.Dial, &createContainerInterceptor{proxy.client, proxy.withDNS}).ServeHTTP(w, r)
+	newClient(proxy.Dial, &createContainerInterceptor{proxy.client, proxy.withDNS, proxy.dockerBridgeIP}).ServeHTTP(w, r)
 }
 
 func (proxy *Proxy) startContainer(w http.ResponseWriter, r *http.Request) {

weave

@@ -921,6 +921,10 @@ case "$COMMAND" in
         dns_args "$@"
         echo -n $DNS_ARGS
         ;;
+    docker-bridge-ip)
+        docker_bridge_ip
+        echo -n $DOCKER_BRIDGE_IP
+        ;;
     start)
         collect_cidr_args "$@"
         shift $CIDR_COUNT