Move rewrite /etc/hosts from shell to Go

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")
+}