Support host mounts via COMPLEMENT_HOST_MOUNTS (#312)

* Support host mounts via COMPLEMENT_HOST_MOUNTS

Usage:
```
COMPLEMENT_HOST_MOUNTS='/my/local/dir:/container/dir;/another/local/dir:/container/dir2:ro'

which is:
  - /my/local/dir:/container/dir
  - /another/local/dir:/container/dir2:ro

which is of the form:
  - HOST:CONTAINER[:ro] where :ro makes the mount read-only.
```

* Host mounts are optional

* Add host mounts to README

Author: kegsay

README.md

@@ -77,6 +77,26 @@ If you're looking to run against a custom Dockerfile, it must meet the following
 - The homeserver needs to accept the server name given by the environment variable `SERVER_NAME` at runtime.
 - The homeserver needs to assume dockerfile `CMD` or `ENTRYPOINT` instructions will be run multiple times.
 
+
+### Developing locally
+
+If you want to write Complement tests _and_ hack on a homeserver implementation at the same time it can be very awkward
+to have to `docker build` the image all the time. To resolve this, Complement support "host mounts" which mount a directory
+from the host to the container. This is set via `COMPLEMENT_HOST_MOUNTS`:
+
+```
+COMPLEMENT_HOST_MOUNTS='/my/local/dir:/container/dir;/another/local/dir:/container/dir2:ro'
+
+which is:
+  - /my/local/dir:/container/dir
+  - /another/local/dir:/container/dir2:ro
+
+which is of the form:
+  - HOST:CONTAINER[:ro] where :ro makes the mount read-only.
+```
+
+For example, for Dendrite: `COMPLEMENT_HOST_MOUNTS='/your/local/dendrite:/dendrite:ro;/your/go/path:/go:ro'`.
+
 ### Getting prettier output
 
 The default output isn't particularly nice to read. You can use [gotestfmt](https://github.com/haveyoudebuggedit/gotestfmt)

internal/config/config.go

@@ -15,6 +15,12 @@ import (
 	"time"
 )
 
+type HostMount struct {
+	HostPath      string
+	ContainerPath string
+	ReadOnly      bool
+}
+
 type Complement struct {
 	BaseImageURI          string
 	BaseImageArgs         []string
@@ -23,6 +29,7 @@ type Complement struct {
 	BestEffort            bool
 	SpawnHSTimeout        time.Duration
 	KeepBlueprints        []string
+	HostMounts            []HostMount
 	// The namespace for all complement created blueprints and deployments
 	PackageNamespace string
 	// Certificate Authority generated values for this run of complement. Homeservers will use this
@@ -44,6 +51,14 @@ func NewConfigFromEnvVars() *Complement {
 		cfg.SpawnHSTimeout = time.Duration(50*parseEnvWithDefault("COMPLEMENT_VERSION_CHECK_ITERATIONS", 100)) * time.Millisecond
 	}
 	cfg.KeepBlueprints = strings.Split(os.Getenv("COMPLEMENT_KEEP_BLUEPRINTS"), " ")
+	var err error
+	hostMounts := os.Getenv("COMPLEMENT_HOST_MOUNTS")
+	if hostMounts != "" {
+		cfg.HostMounts, err = newHostMounts(strings.Split(hostMounts, ";"))
+		if err != nil {
+			panic("COMPLEMENT_HOST_MOUNTS parse error: " + err.Error())
+		}
+	}
 	if cfg.BaseImageURI == "" {
 		panic("COMPLEMENT_BASE_IMAGE must be set")
 	}
@@ -95,6 +110,26 @@ func parseEnvWithDefault(key string, def int) int {
 	return def
 }
 
+func newHostMounts(mounts []string) ([]HostMount, error) {
+	var hostMounts []HostMount
+	for _, m := range mounts {
+		segments := strings.Split(m, ":")
+		if len(segments) < 2 {
+			return nil, fmt.Errorf("mount '%s' malformed", m)
+		}
+		var ro string
+		if len(segments) == 3 {
+			ro = segments[2]
+		}
+		hostMounts = append(hostMounts, HostMount{
+			HostPath:      segments[0],
+			ContainerPath: segments[1],
+			ReadOnly:      ro == "ro" || ro == "readonly",
+		})
+	}
+	return hostMounts, nil
+}
+
 // Generate a certificate and private key
 func generateCAValues() (*x509.Certificate, *rsa.PrivateKey, error) {
 	// valid for 10 years

internal/docker/builder.go

@@ -252,13 +252,19 @@ func (d *Builder) construct(bprint b.Blueprint) (errs []error) {
 				// something went wrong, but we have a container which may have interesting logs
 				printLogs(d.Docker, res.containerID, res.contextStr)
 			}
+			if delErr := d.Docker.ContainerRemove(context.Background(), res.containerID, types.ContainerRemoveOptions{
+				Force: true,
+			}); delErr != nil {
+				d.log("%s: failed to remove container which failed to deploy: %s", res.contextStr, delErr)
+			}
 		}
 		// kill the container
 		defer func(r result) {
 			killErr := d.Docker.ContainerKill(context.Background(), r.containerID, "KILL")
 			if killErr != nil {
 				d.log("%s : Failed to kill container %s: %s\n", r.contextStr, r.containerID, killErr)
 			}
+
 		}(res)
 		results[i] = res
 	}

internal/docker/deployer.go

@@ -180,6 +180,18 @@ func deployImage(
 		extraHosts = []string{HostnameRunningComplement + ":172.17.0.1"}
 	}
 
+	for _, m := range cfg.HostMounts {
+		mounts = append(mounts, mount.Mount{
+			Source:   m.HostPath,
+			Target:   m.ContainerPath,
+			ReadOnly: m.ReadOnly,
+			Type:     mount.TypeBind,
+		})
+	}
+	if len(mounts) > 0 {
+		log.Printf("Using host mounts: %+v", mounts)
+	}
+
 	env := []string{
 		"SERVER_NAME=" + hsName,
 	}