proxy needs to add weavewait to execs as well

Bug came up in a test where we are restarting and doing an exec checking
a network interface right away. weavewait is only added if the container
has a WEAVE_CIDR var set, the same as at container creation.

proxy/start_container_interceptor.go

@@ -2,15 +2,12 @@ package proxy
 
 import (
 	"net/http"
-	"regexp"
 	"strings"
 
 	"github.com/fsouza/go-dockerclient"
 	. "github.com/weaveworks/weave/common"
 )
 
-var containerIDRegexp = regexp.MustCompile("^/v[0-9\\.]*/containers/([^/]*)/.*")
-
 type startContainerInterceptor struct {
 	client  *docker.Client
 	withDNS bool
@@ -21,17 +18,9 @@ func (i *startContainerInterceptor) InterceptRequest(r *http.Request) error {
 }
 
 func (i *startContainerInterceptor) InterceptResponse(r *http.Response) error {
-	subs := containerIDRegexp.FindStringSubmatch(r.Request.URL.Path)
-	if subs == nil {
-		Warning.Printf("No container id found in request with path %s", r.Request.URL.Path)
-		return nil
-	}
-	containerID := subs[1]
-
-	container, err := i.client.InspectContainer(containerID)
+	container, err := inspectContainerInPath(i.client, r.Request.URL.Path)
 	if err != nil {
-		Warning.Printf("Error inspecting container %s: %v", containerID, err)
-		return nil
+		return err
 	}
 
 	cidrs, ok := weaveCIDRsFromConfig(container.Config)
@@ -39,12 +28,12 @@ func (i *startContainerInterceptor) InterceptResponse(r *http.Response) error {
 		Debug.Print("No Weave CIDR, ignoring")
 		return nil
 	}
-	Info.Printf("Container %s was started with CIDR \"%s\"", containerID, strings.Join(cidrs, " "))
+	Info.Printf("Container %s was started with CIDR \"%s\"", container.ID, strings.Join(cidrs, " "))
 	args := []string{"attach"}
 	args = append(args, cidrs...)
-	args = append(args, containerID)
+	args = append(args, container.ID)
 	if _, err := callWeave(args...); err != nil {
-		Warning.Printf("Attaching container %s to weave failed: %v", containerID, err)
+		Warning.Printf("Attaching container %s to weave failed: %v", container.ID, err)
 		return nil
 	}
 	return nil