diff --git a/pixiecore/booters.go b/pixiecore/booters.go
index da01a43..42bc16c 100644
--- a/pixiecore/booters.go
+++ b/pixiecore/booters.go
@@ -71,22 +71,31 @@ func (s *staticBooter) BootSpec(m Machine) (*Spec, error) {
 	return s.spec, nil
 }
 
-func (s *staticBooter) serveFile(path string) (io.ReadCloser, error) {
+func (s *staticBooter) serveFile(path string) (io.ReadCloser, int64, error) {
 	if strings.HasPrefix(path, "http://") || strings.HasPrefix(path, "https://") {
 		resp, err := http.Get(path)
 		if err != nil {
-			return nil, err
+			return nil, -1, err
 		}
 		if resp.StatusCode != http.StatusOK {
 			resp.Body.Close()
-			return nil, fmt.Errorf("%s: %s", path, http.StatusText(resp.StatusCode))
+			return nil, -1, fmt.Errorf("%s: %s", path, http.StatusText(resp.StatusCode))
 		}
-		return resp.Body, nil
+		return resp.Body, resp.ContentLength, nil
 	}
-	return os.Open(path)
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, -1, err
+	}
+	fi, err := f.Stat()
+	if err != nil {
+		f.Close()
+		return nil, -1, err
+	}
+	return f, fi.Size(), nil
 }
 
-func (s *staticBooter) ReadBootFile(id ID) (io.ReadCloser, error) {
+func (s *staticBooter) ReadBootFile(id ID) (io.ReadCloser, int64, error) {
 	path := string(id)
 	switch {
 	case path == "kernel":
@@ -95,19 +104,19 @@ func (s *staticBooter) ReadBootFile(id ID) (io.ReadCloser, error) {
 	case strings.HasPrefix(path, "initrd-"):
 		i, err := strconv.Atoi(string(path[7:]))
 		if err != nil || i < 0 || i >= len(s.initrd) {
-			return nil, fmt.Errorf("no file with ID %q", id)
+			return nil, -1, fmt.Errorf("no file with ID %q", id)
 		}
 		return s.serveFile(s.initrd[i])
 
 	case strings.HasPrefix(path, "other-"):
 		i, err := strconv.Atoi(string(path[6:]))
 		if err != nil || i < 0 || i >= len(s.otherIDs) {
-			return nil, fmt.Errorf("no file with ID %q", id)
+			return nil, -1, fmt.Errorf("no file with ID %q", id)
 		}
 		return s.serveFile(s.otherIDs[i])
 	}
 
-	return nil, fmt.Errorf("no file with ID %q", id)
+	return nil, -1, fmt.Errorf("no file with ID %q", id)
 }
 
 func (s *staticBooter) WriteBootFile(ID, io.Reader) error {
@@ -229,18 +238,22 @@ func (b *apibooter) BootSpec(m Machine) (*Spec, error) {
 	return &ret, nil
 }
 
-func (b *apibooter) ReadBootFile(id ID) (io.ReadCloser, error) {
+func (b *apibooter) ReadBootFile(id ID) (io.ReadCloser, int64, error) {
 	urlStr, err := getURL(id, &b.key)
 	if err != nil {
-		return nil, err
+		return nil, -1, err
 	}
 
 	u, err := url.Parse(urlStr)
 	if err != nil {
-		return nil, fmt.Errorf("%q is not an URL", urlStr)
+		return nil, -1, fmt.Errorf("%q is not an URL", urlStr)
 	}
-	var ret io.ReadCloser
+	var (
+		ret io.ReadCloser
+		sz  int64 = -1
+	)
 	if u.Scheme == "file" {
+		// TODO serveFile
 		ret, err = os.Open(u.Path)
 	} else {
 		// urlStr will get reparsed by http.Get, which is mildly
@@ -248,18 +261,18 @@ func (b *apibooter) ReadBootFile(id ID) (io.ReadCloser, error) {
 		// Request.
 		resp, err := http.Get(urlStr)
 		if err != nil {
-			return nil, err
+			return nil, -1, err
 		}
 		if resp.StatusCode != 200 {
-			return nil, fmt.Errorf("GET %q failed: %s", urlStr, resp.Status)
+			return nil, -1, fmt.Errorf("GET %q failed: %s", urlStr, resp.Status)
 		}
 
-		ret, err = resp.Body, nil
+		ret, sz, err = resp.Body, resp.ContentLength, nil
 	}
 	if err != nil {
-		return nil, err
+		return nil, -1, err
 	}
-	return ret, nil
+	return ret, sz, nil
 }
 
 func (b *apibooter) WriteBootFile(id ID, body io.Reader) error {
diff --git a/pixiecore/booters_test.go b/pixiecore/booters_test.go
index 74ddf64..f8a4dfb 100644
--- a/pixiecore/booters_test.go
+++ b/pixiecore/booters_test.go
@@ -43,7 +43,7 @@ func mustWrite(dir, path, contents string) {
 	}
 }
 
-func mustRead(f io.ReadCloser, err error) string {
+func mustRead(f io.ReadCloser, sz int64, err error) string {
 	if err != nil {
 		panic(err)
 	}
@@ -52,6 +52,9 @@ func mustRead(f io.ReadCloser, err error) string {
 	if err != nil {
 		panic(err)
 	}
+	if sz >= 0 && int64(len(bs)) != sz {
+		panic(fmt.Errorf("sz = %d, but ReadCloser has %d bytes", sz, len(bs)))
+	}
 	return string(bs)
 }
 
diff --git a/pixiecore/cli/cli.go b/pixiecore/cli/cli.go
index 5a47a3b..072eeb4 100644
--- a/pixiecore/cli/cli.go
+++ b/pixiecore/cli/cli.go
@@ -18,7 +18,6 @@ package cli // import "go.universe.tf/netboot/pixiecore/cli"
 import (
 	"fmt"
 	"io/ioutil"
-	"net"
 	"os"
 
 	"github.com/spf13/cobra"
@@ -71,7 +70,7 @@ func todo(msg string, args ...interface{}) {
 func serverConfigFlags(cmd *cobra.Command) {
 	cmd.Flags().BoolP("debug", "d", false, "Log more things that aren't directly related to booting a recognized client")
 	cmd.Flags().BoolP("log-timestamps", "t", false, "Add a timestamp to each log line")
-	cmd.Flags().IPP("listen-addr", "l", net.IPv4zero, "IPv4 address to listen on")
+	cmd.Flags().StringP("listen-addr", "l", "", "IPv4 address to listen on")
 	cmd.Flags().IntP("port", "p", 80, "Port to listen on for HTTP")
 	cmd.Flags().Bool("dhcp-no-bind", false, "Handle DHCP traffic without binding to the DHCP server port")
 	cmd.Flags().String("ipxe-bios", "", "Path to an iPXE binary for BIOS/UNDI")
@@ -97,7 +96,7 @@ func serverFromFlags(cmd *cobra.Command) *pixiecore.Server {
 	if err != nil {
 		fatalf("Error reading flag: %s", err)
 	}
-	addr, err := cmd.Flags().GetIP("listen-addr")
+	addr, err := cmd.Flags().GetString("listen-addr")
 	if err != nil {
 		fatalf("Error reading flag: %s", err)
 	}
@@ -122,9 +121,6 @@ func serverFromFlags(cmd *cobra.Command) *pixiecore.Server {
 		fatalf("Error reading flag: %s", err)
 	}
 
-	if addr != nil && addr.To4() == nil {
-		fatalf("Listen address must be IPv4")
-	}
 	if httpPort <= 0 {
 		fatalf("HTTP port must be >0")
 	}
@@ -154,8 +150,8 @@ func serverFromFlags(cmd *cobra.Command) *pixiecore.Server {
 	if debug {
 		ret.Debug = ret.Log
 	}
-	if addr != nil {
-		ret.Address = addr.String()
+	if addr != "" {
+		ret.Address = addr
 	}
 
 	return ret
diff --git a/pixiecore/http.go b/pixiecore/http.go
index e1730eb..0397447 100644
--- a/pixiecore/http.go
+++ b/pixiecore/http.go
@@ -108,13 +108,16 @@ func (s *Server) handleFile(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "missing filename", http.StatusBadRequest)
 	}
 
-	f, err := s.Booter.ReadBootFile(ID(name))
+	f, sz, err := s.Booter.ReadBootFile(ID(name))
 	if err != nil {
 		s.log("HTTP", "Error getting file %q (query %q from %s): %s", name, r.URL, r.RemoteAddr, err)
 		http.Error(w, "couldn't get file", http.StatusInternalServerError)
 		return
 	}
 	defer f.Close()
+	if sz >= 0 {
+		w.Header().Set("Content-Length", strconv.FormatInt(sz, 10))
+	}
 	if _, err = io.Copy(w, f); err != nil {
 		s.log("HTTP", "Copy of %q to %s (query %q) failed: %s", name, r.RemoteAddr, r.URL, err)
 		return
diff --git a/pixiecore/http_test.go b/pixiecore/http_test.go
index e5e94d9..7b99d05 100644
--- a/pixiecore/http_test.go
+++ b/pixiecore/http_test.go
@@ -28,9 +28,11 @@ import (
 
 type booterFunc func(Machine) (*Spec, error)
 
-func (b booterFunc) BootSpec(m Machine) (*Spec, error)         { return b(m) }
-func (b booterFunc) ReadBootFile(id ID) (io.ReadCloser, error) { return nil, errors.New("no") }
-func (b booterFunc) WriteBootFile(id ID, r io.Reader) error    { return errors.New("no") }
+func (b booterFunc) BootSpec(m Machine) (*Spec, error) { return b(m) }
+func (b booterFunc) ReadBootFile(id ID) (io.ReadCloser, int64, error) {
+	return nil, -1, errors.New("no")
+}
+func (b booterFunc) WriteBootFile(id ID, r io.Reader) error { return errors.New("no") }
 
 var logSync sync.Mutex
 
@@ -149,8 +151,9 @@ boot kernel initrd=initrd0 initrd=initrd1 thing=http://localhost:1234/_/file?nam
 type readBootFile string
 
 func (b readBootFile) BootSpec(m Machine) (*Spec, error) { return nil, nil }
-func (b readBootFile) ReadBootFile(id ID) (io.ReadCloser, error) {
-	return ioutil.NopCloser(bytes.NewBuffer([]byte(fmt.Sprintf("%s %s", id, b)))), nil
+func (b readBootFile) ReadBootFile(id ID) (io.ReadCloser, int64, error) {
+	d := fmt.Sprintf("%s %s", id, b)
+	return ioutil.NopCloser(bytes.NewBuffer([]byte(d))), int64(len(d)), nil
 }
 func (b readBootFile) WriteBootFile(id ID, r io.Reader) error { return errors.New("no") }
 
diff --git a/pixiecore/pixiecore.go b/pixiecore/pixiecore.go
index 510da8b..854759c 100644
--- a/pixiecore/pixiecore.go
+++ b/pixiecore/pixiecore.go
@@ -102,7 +102,12 @@ type Booter interface {
 	// the client machine's request.
 	BootSpec(m Machine) (*Spec, error)
 	// Get the bytes corresponding to an ID given in Spec.
-	ReadBootFile(id ID) (io.ReadCloser, error)
+	//
+	// Additionally returns the total number of bytes in the
+	// ReadCloser, or -1 if the size is unknown. Be warned, returning
+	// -1 will make the boot process orders of magnitude slower due to
+	// poor ipxe behavior.
+	ReadBootFile(id ID) (io.ReadCloser, int64, error)
 	// Write the given Reader to an ID given in Spec.
 	WriteBootFile(id ID, body io.Reader) error
 }
@@ -214,6 +219,8 @@ func (s *Server) Serve() error {
 	// blocking.
 	s.errs = make(chan error, 5)
 
+	s.debug("Init", "Starting Pixiecore goroutines")
+
 	go func() { s.errs <- s.serveDHCP(dhcp) }()
 	go func() { s.errs <- s.servePXE(pxe) }()
 	go func() { s.errs <- s.serveTFTP(tftp) }()