use a go binary for docker network joining

This gets rid of the brittle bash code that shells out to the docker
cli.

.gitignore

@@ -0,0 +1 @@
+join-networks.tar.gz

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "vendor/github.com/fsouza/go-dockerclient"]
+	path = vendor/github.com/fsouza/go-dockerclient
+	url = https://github.com/codekitchen/go-dockerclient.git
+	branch = add-network-id

Dockerfile

@@ -8,6 +8,10 @@ RUN wget https://github.com/codekitchen/docker-gen/releases/download/v0.6-groupB
  && rm docker-gen-linux-amd64-$DOCKER_GEN_VERSION.tar.gz
 # /XXX
 
+RUN wget https://github.com/codekitchen/dinghy-http-proxy/releases/download/join-networks-v1/join-networks.tar.gz \
+ && tar -C /app -xzvf join-networks.tar.gz \
+ && rm join-networks.tar.gz
+
 # override nginx configs
 COPY *.conf /etc/nginx/conf.d/
 

build.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+set -e
+
+docker run --rm -v "$PWD":/go/src/github.com/codekitchen/dinghy-http-proxy -w /go/src/github.com/codekitchen/dinghy-http-proxy golang:1.6 go build -v -o join-networks
+tar czvf join-networks.tar.gz join-networks
+rm join-networks

join-networks.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"flag"
+
+	docker "github.com/fsouza/go-dockerclient"
+)
+
+var (
+	endpoint = "unix:///tmp/docker.sock"
+)
+
+func main() {
+	var containerName = flag.String("container-name", "", "the name of this docker container")
+	flag.Parse()
+
+	client, err := docker.NewClient(endpoint)
+	if err != nil {
+		panic(err)
+	}
+
+	currentNetworks := getJoinedNetworks(client, *containerName)
+	bridgeNetworks := getBridgeNetworks(client)
+
+	for _, id := range bridgeNetworks {
+		if !currentNetworks[id] {
+			err := client.ConnectNetwork(id, docker.NetworkConnectionOptions{
+				Container: *containerName,
+			})
+			if err != nil {
+				panic(err)
+			}
+		}
+	}
+}
+
+func getJoinedNetworks(client *docker.Client, containerName string) (networks map[string]bool) {
+	networks = make(map[string]bool)
+
+	container, err := client.InspectContainer(containerName)
+	if err != nil {
+		panic(err)
+	}
+
+	for _, net := range container.NetworkSettings.Networks {
+		networks[net.NetworkID] = true
+	}
+
+	return
+}
+
+func getBridgeNetworks(client *docker.Client) (ids []string) {
+	networks, err := client.ListNetworks()
+	if err != nil {
+		panic(err)
+	}
+
+	for _, net := range networks {
+		if net.Driver == "bridge" {
+			ids = append(ids, net.ID)
+		}
+	}
+	return
+}

reload-nginx

@@ -6,17 +6,7 @@ name=${CONTAINER_NAME:-dinghy_http_proxy}
 # Join any networks we haven't joined yet, so that we can talk to containers on
 # those networks. This allows us to talk to containers created with
 # docker-compose v2 configs.
-#
-# This would be better rewritten as a binary that talks directly to the docker
-# API, to avoid the brittle CLI parsing.
-docker inspect -f '{{ range .NetworkSettings.Networks }}{{ .NetworkID }}
-{{ end }}' $name > /tmp/current_networks
-
-for network in `docker network ls | grep bridge | awk '{print $1}'`; do
-  if ! grep -q $network /tmp/current_networks; then
-    docker network connect $network $name
-  fi
-done
+/app/join-networks -container-name $name
 
 # Now that we can reach these other hosts, reload nginx. Order is important
 # here, as nginx errors on startup if it can't resolve any of the specified