From c7a78ae81e6c0ddcf6937aab5195c284c711dc99 Mon Sep 17 00:00:00 2001
From: Solomon Hykes <solomon@docker.com>
Date: Mon, 2 Jun 2014 09:10:52 +0000
Subject: [PATCH] Simple fork-exec backend

Signed-off-by: Solomon Hykes <solomon@docker.com>
Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
---
 backends/backends.go |   1 +
 backends/exec.go     | 105 +++++++++++++++++++++++++++++++++++++++++++
 swarmd/swarmd.go     |  24 +++++-----
 3 files changed, 118 insertions(+), 12 deletions(-)
 create mode 100644 backends/exec.go

diff --git a/backends/backends.go b/backends/backends.go
index 3358215b94..2f0f6dd7e0 100644
--- a/backends/backends.go
+++ b/backends/backends.go
@@ -16,5 +16,6 @@ func New() *beam.Object {
 	backends.Bind("debug", Debug())
 	backends.Bind("fakeclient", FakeClient())
 	backends.Bind("forward", Forward())
+	backends.Bind("exec", Exec())
 	return beam.Obj(backends)
 }
diff --git a/backends/exec.go b/backends/exec.go
new file mode 100644
index 0000000000..49251a39b3
--- /dev/null
+++ b/backends/exec.go
@@ -0,0 +1,105 @@
+package backends
+
+import (
+	"fmt"
+	"io"
+	"os/exec"
+	"encoding/json"
+	"bufio"
+	"strings"
+	"sync"
+
+	"github.com/docker/libswarm/beam"
+)
+
+func Exec() beam.Sender {
+	e := beam.NewServer()
+	e.OnSpawn(beam.Handler(func(msg *beam.Message) error {
+		if len(msg.Args) < 1 {
+			return fmt.Errorf("usage: SPAWN exec|... <config>")
+		}
+		if msg.Args[0] != "exec" {
+			return fmt.Errorf("invalid command: %s", msg.Args[0])
+		}
+		var config struct {
+			Path	string
+			Args	[]string
+		}
+		if err := json.Unmarshal([]byte(msg.Args[1]), &config); err != nil {
+			config.Path = msg.Args[1]
+			config.Args = msg.Args[2:]
+		}
+		cmd := &command{
+			Cmd:	exec.Command(config.Path, config.Args...),
+			Server: beam.NewServer(),
+		}
+		cmd.OnAttach(beam.Handler(func(msg *beam.Message) error {
+			stdout, err := cmd.StdoutPipe()
+			if err != nil {
+				return err
+			}
+			stdin, err := cmd.StdinPipe()
+			if err != nil {
+				return err
+			}
+			inR, inW := beam.Pipe()
+			if _, err := msg.Ret.Send(&beam.Message{Verb: beam.Ack, Ret: inW}); err != nil {
+				return err
+			}
+			out := beam.Obj(msg.Ret)
+			go func() {
+				defer stdin.Close()
+				for {
+					msg, err := inR.Receive(0)
+					if err != nil {
+						return
+					}
+					if msg.Verb == beam.Log && len(msg.Args) > 0 {
+						fmt.Fprintf(stdin, "%s\n", strings.TrimRight(msg.Args[0], "\r\n"))
+					}
+				}
+			}()
+			cmd.tasks.Add(1)
+			go func() {
+				defer cmd.tasks.Done()
+				scanner := bufio.NewScanner(stdout)
+				for scanner.Scan() {
+					if scanner.Err() != io.EOF && scanner.Err() != nil {
+						return
+					}
+					if err := out.Log(scanner.Text()); err != nil {
+						out.Error("%v", err)
+						return
+					}
+				}
+			}()
+			cmd.tasks.Wait()
+			return nil
+		}))
+		cmd.OnStart(beam.Handler(func(msg *beam.Message) error {
+			cmd.tasks.Add(1)
+			if err := cmd.Cmd.Start(); err != nil {
+				return err
+			}
+			go func() {
+				defer cmd.tasks.Done()
+				if err := cmd.Cmd.Wait(); err != nil {
+					beam.Obj(msg.Ret).Log("%s exited status=%v", cmd.Cmd.Path, err)
+				}
+			}()
+			msg.Ret.Send(&beam.Message{Verb: beam.Ack})
+			return nil
+		}))
+		if _, err := msg.Ret.Send(&beam.Message{Verb: beam.Ack, Ret: cmd}); err != nil {
+			return err
+		}
+		return nil
+	}))
+	return e
+}
+
+type command struct {
+	*exec.Cmd
+	*beam.Server
+	tasks sync.WaitGroup
+}
diff --git a/swarmd/swarmd.go b/swarmd/swarmd.go
index 79099d374c..dccecdb080 100644
--- a/swarmd/swarmd.go
+++ b/swarmd/swarmd.go
@@ -42,37 +42,37 @@ func cmdDaemon(c *cli.Context) {
 		fmt.Println(strings.Join(names, "\n"))
 		return
 	}
-	var previousInstanceIn beam.Receiver
-	for _, backendArg := range c.Args() {
+	var previousInstanceR beam.Receiver
+	// FIXME: refactor into a Pipeline
+	for idx, backendArg := range c.Args() {
 		bName, bArgs, err := parseCmd(backendArg)
 		if err != nil {
 			Fatalf("parse: %v", err)
 		}
-		fmt.Printf("---> Loading backend '%s'\n", strings.Join(append([]string{bName}, bArgs...), " "))
 		_, backend, err := back.Attach(bName)
 		if err != nil {
 			Fatalf("%s: %v\n", bName, err)
 		}
-		fmt.Printf("---> Spawning\n")
 		instance, err := backend.Spawn(bArgs...)
 		if err != nil {
 			Fatalf("spawn %s: %v\n", bName, err)
 		}
-		fmt.Printf("---> Attaching\n")
-		instanceIn, instanceOut, err := instance.Attach("")
+		instanceR, instanceW, err := instance.Attach("")
 		if err != nil {
 			Fatalf("attach: %v", err)
 		}
-		fmt.Printf("---> Starting\n")
+		go func(r beam.Receiver, w beam.Sender, idx int) {
+			if r != nil {
+				beam.Copy(w, r)
+			}
+			w.Close()
+		}(previousInstanceR, instanceW, idx)
 		if err := instance.Start(); err != nil {
 			Fatalf("start: %v", err)
 		}
-		if previousInstanceIn != nil {
-			go beam.Copy(instanceOut, previousInstanceIn)
-		}
-		previousInstanceIn = instanceIn
+		previousInstanceR = instanceR
 	}
-	_, err := beam.Copy(app, previousInstanceIn)
+	_, err := beam.Copy(app, previousInstanceR)
 	if err != nil {
 		Fatalf("copy: %v", err)
 	}