Move rewrite /etc/hosts from shell to Go

prog/weaveutil/attach.go

@@ -3,13 +3,16 @@ package main
 import (
 	"fmt"
 	"net"
+	"os"
 	"strconv"
+	"strings"
 	"syscall"
 
 	docker "github.com/fsouza/go-dockerclient"
 	"github.com/vishvananda/netns"
 
 	weavenet "github.com/weaveworks/weave/net"
+	"github.com/weaveworks/weave/proxy"
 )
 
 func attach(args []string) error {
@@ -110,3 +113,30 @@ func detach(args []string) error {
 	}
 	return weavenet.DetachContainer(weavenet.NSPathByPid(pid), args[0], weavenet.VethName, cidrs)
 }
+
+func rewriteEtcHosts(args []string) error {
+	if len(args) < 4 {
+		cmdUsage("rewrite-etc-hosts", "<hosts-path> <fqdn> <image> <cidr>... [name:addr...]")
+	}
+	hostsPath := args[0]
+	fqdn := args[1]
+	image := args[2]
+	var ips []*net.IPNet
+	for _, cidr := range strings.Fields(args[3]) {
+		_, ipnet, err := net.ParseCIDR(cidr)
+		if err != nil {
+			return err
+		}
+		ips = append(ips, ipnet)
+	}
+	extraHosts := args[4:]
+	docker := os.Getenv("DOCKER_HOST")
+	if docker == "" {
+		docker = "unix:///var/run/docker.sock"
+	}
+	p, err := proxy.StubProxy(proxy.Config{DockerHost: docker, Image: image})
+	if err != nil {
+		return err
+	}
+	return p.RewriteEtcHosts(hostsPath, fqdn, ips, extraHosts)
+}

prog/weaveutil/main.go

@@ -40,6 +40,7 @@ func init() {
 		"unique-id":                uniqueID,
 		"swarm-manager-peers":      swarmManagerPeers,
 		"is-docker-plugin-enabled": isDockerPluginEnabled,
+		"rewrite-etc-hosts":        rewriteEtcHosts,
 	}
 }
 

proxy/hosts.go

@@ -0,0 +1,65 @@
+package proxy
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"path"
+	"strings"
+)
+
+// rewrite /etc/hosts, unlinking the file (so Docker does not modify it again) but
+// leaving it with valid contents...
+func (proxy *Proxy) RewriteEtcHosts(hostsPath, fqdn string, ips []*net.IPNet, extraHosts []string) error {
+	hostsPathDir := path.Dir(hostsPath)
+	mnt := "/container"
+	mntHosts := path.Join(mnt, path.Base(hostsPath))
+	var buf bytes.Buffer
+	writeEtcHostsContents(&buf, fqdn, ips, extraHosts)
+	contents := buf.String()
+	cmdLine := fmt.Sprintf("echo '%s' > %s && rm -f %s && echo '%s' > %s", contents, mntHosts, mntHosts, contents, mntHosts)
+	mounts := []string{hostsPathDir + ":" + mnt}
+	proxy.runTransientContainer([]string{"sh"}, []string{"-c", cmdLine}, mounts)
+	return nil
+}
+
+// we assume (for compatibility with the weave script) that fqdn has a dot
+// between hostname and domain. domain may be blank.
+func writeEtcHostsContents(w io.Writer, fqdn string, cidrs []*net.IPNet, extraHosts []string) {
+	index := strings.Index(fqdn, ".")
+	name := fqdn[:index]
+	var hostnames string
+	if index == len(fqdn)-1 { // dot comes at the end - no domain
+		hostnames = name
+	} else {
+		if fqdn[len(fqdn)-1] == '.' { // strip a final trailing dot
+			fqdn = fqdn[:len(fqdn)-1]
+		}
+		hostnames = fqdn + " " + name
+	}
+
+	fmt.Fprintln(w, "# created by Weave - BEGIN")
+	fmt.Fprintln(w, "# container hostname")
+	for _, cidr := range cidrs {
+		fmt.Fprintf(w, "%-15s %s\n", cidr.IP, hostnames)
+	}
+	fmt.Fprintln(w)
+	fmt.Fprintln(w, "# static names added with --add-host")
+	for _, eh := range extraHosts {
+		parts := strings.SplitN(eh, ":", 2)
+		if len(parts) != 2 {
+			continue
+		}
+		fmt.Fprintf(w, "%-15s %s\n", parts[1], parts[0])
+	}
+	fmt.Fprintln(w)
+	fmt.Fprintln(w, "# default localhost entries")
+	fmt.Fprintln(w, "127.0.0.1       localhost")
+	fmt.Fprintln(w, "::1             ip6-localhost ip6-loopback")
+	fmt.Fprintln(w, "fe00::0         ip6-localnet")
+	fmt.Fprintln(w, "ff00::0         ip6-mcastprefix")
+	fmt.Fprintln(w, "ff02::1         ip6-allnodes")
+	fmt.Fprintln(w, "ff02::2         ip6-allrouters")
+	fmt.Fprintln(w, "# created by Weave - END")
+}

weave

@@ -851,52 +851,13 @@ dns_args() {
     fi
 }
 
-etc_hosts_contents() {
-    FQDN=$1
-    shift
-    NAME=${FQDN%%.*}
-    HOSTNAMES="$NAME"
-    [ "$NAME" = "$FQDN" -o "$NAME." = "$FQDN" ] || HOSTNAMES="${FQDN%.} $HOSTNAMES"
-
-    echo "# created by Weave - BEGIN"
-    echo "# container hostname"
-    for CIDR in $ALL_CIDRS ; do
-        echo "${CIDR%/*}    $HOSTNAMES"
-    done
-    echo
-    echo "# static names added with --add-host"
-    for EXTRA_HOST in "$@" ; do
-        echo "${EXTRA_HOST#*:}     ${EXTRA_HOST%:*}"
-    done
-
-    cat <<-EOF
-
-# default localhost entries
-127.0.0.1       localhost
-::1             ip6-localhost ip6-loopback
-fe00::0         ip6-localnet
-ff00::0         ip6-mcastprefix
-ff02::1         ip6-allnodes
-ff02::2         ip6-allrouters
-EOF
-
-    echo "# created by Weave - END"
-}
-
 rewrite_etc_hosts() {
     HOSTS_PATH_AND_FQDN=$(docker inspect -f '{{.HostsPath}} {{.Config.Hostname}}.{{.Config.Domainname}}' $CONTAINER) || return 1
     HOSTS=${HOSTS_PATH_AND_FQDN% *}
     FQDN=${HOSTS_PATH_AND_FQDN#* }
-    CONTAINERS_PATH=$(dirname $HOSTS)
-    MNT=/container
-    MNT_HOSTS=$MNT/$(basename $HOSTS)
-    CONTENTS="$(etc_hosts_contents $FQDN "$@")"
     # rewrite /etc/hosts, unlinking the file (so Docker does not modify it again) but
     # leaving it with valid contents...
-    docker run --rm --net=none -e WEAVE_CIDR=none \
-        -v $CONTAINERS_PATH:$MNT \
-        --entrypoint=sh \
-        $EXEC_IMAGE -c "echo '$CONTENTS' > $MNT_HOSTS && rm -f $MNT_HOSTS && echo '$CONTENTS' > $MNT_HOSTS"
+    util_op rewrite-etc-hosts "$HOSTS" "$FQDN" "$EXEC_IMAGE" "$ALL_CIDRS" "$@"
 }
 
 # Print an error to stderr and return with an indicative exit status