Beam messages can attach arbitrary file descriptors.

Each transport is responsible for implementing file passing using the
best available method.

Current state of implementation:

* inmem: full
* unix: not yet implemented

beam.go

@@ -2,6 +2,7 @@ package beam
 
 import (
 	"errors"
+	"os"
 )
 
 type Sender interface {
@@ -16,6 +17,7 @@ type Receiver interface {
 type Message struct {
 	Name string
 	Args []string
+	Att  *os.File
 }
 
 const (

inmem/inmem_test.go

@@ -1,8 +1,11 @@
 package inmem
 
 import (
+	"fmt"
 	"github.com/docker/beam"
 	"github.com/dotcloud/docker/pkg/testutils"
+	"io/ioutil"
+	"os"
 	"testing"
 )
 
@@ -141,3 +144,42 @@ func TestSendNested(t *testing.T) {
 		}
 	})
 }
+
+func TestSendFile(t *testing.T) {
+	r, w := Pipe()
+	defer r.Close()
+	defer w.Close()
+	tmp, err := ioutil.TempFile("", "beam-test-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmp.Name())
+	fmt.Fprintf(tmp, "hello world\n")
+	tmp.Sync()
+	tmp.Seek(0, 0)
+	testutils.Timeout(t, func() {
+		go func() {
+			_, _, err := w.Send(&beam.Message{"file", []string{"path=" + tmp.Name()}, tmp}, 0)
+			if err != nil {
+				t.Fatal(err)
+			}
+		}()
+		msg, _, _, err := r.Receive(0)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if msg.Name != "file" {
+			t.Fatalf("%#v", msg)
+		}
+		if msg.Args[0] != "path="+tmp.Name() {
+			t.Fatalf("%#v", msg)
+		}
+		txt, err := ioutil.ReadAll(msg.Att)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if string(txt) != "hello world\n" {
+			t.Fatalf("%s\n", txt)
+		}
+	})
+}

unix/conn.go

@@ -51,6 +51,9 @@ func (c *Conn) Close() error {
 }
 
 func (c *Conn) Send(msg *beam.Message, mode int) (beam.Receiver, beam.Sender, error) {
+	if msg.Att != nil {
+		return nil, nil, fmt.Errorf("file attachment not yet implemented in unix transport")
+	}
 	parts := []string{msg.Name}
 	parts = append(parts, msg.Args...)
 	b := []byte(data.EncodeList(parts))