devcam: exec child binaries when possible

Change-Id: I56d56d9f7416e3d5958e736762063a48dcd8e9f9

dev/devcam/appengine.go

@@ -95,15 +95,7 @@ func (c *gaeCmd) RunCommand(args []string) error {
 	}
 	cmdArgs = append(cmdArgs, args...)
 	cmdArgs = append(cmdArgs, c.applicationDir)
-	cmd := exec.Command(devAppServerBin, cmdArgs...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	if err := cmd.Start(); err != nil {
-		return fmt.Errorf("Could not start dev_appserver.py: %v", err)
-	}
-	go handleSignals(cmd.Process)
-	cmd.Wait()
-	return nil
+	return runExec(devAppServerBin, cmdArgs)
 }
 
 func (c *gaeCmd) checkFlags(args []string) error {

dev/devcam/camget.go

@@ -99,14 +99,7 @@ func (c *getCmd) RunCommand(args []string) error {
 		cmdArgs = append(cmdArgs, "-server="+blobserver)
 	}
 	cmdArgs = append(cmdArgs, args...)
-	cmd := exec.Command(cmdBin, cmdArgs...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	if err := cmd.Start(); err != nil {
-		return fmt.Errorf("Could not run camget: %v", err)
-	}
-	go handleSignals(cmd.Process)
-	return cmd.Wait()
+	return runExec(cmdBin, cmdArgs)
 }
 
 func (c *getCmd) checkFlags(args []string) error {

dev/devcam/camput.go

@@ -98,14 +98,7 @@ func (c *putCmd) RunCommand(args []string) error {
 		"-server=" + blobserver,
 	}
 	cmdArgs = append(cmdArgs, args...)
-	cmd := exec.Command(cmdBin, cmdArgs...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	if err := cmd.Start(); err != nil {
-		return fmt.Errorf("Could not run camput: %v", err)
-	}
-	go handleSignals(cmd.Process)
-	return cmd.Wait()
+	return runExec(cmdBin, cmdArgs)
 }
 
 func (c *putCmd) checkFlags(args []string) error {

dev/devcam/devcam.go

@@ -21,6 +21,7 @@ import (
 	"io"
 	"log"
 	"os"
+	"os/exec"
 	"os/signal"
 	"path/filepath"
 	"strings"
@@ -29,6 +30,26 @@ import (
 	"camlistore.org/pkg/cmdmain"
 )
 
+// sysExec is set to syscall.Exec on platforms that support it.
+var sysExec func(argv0 string, argv []string, envv []string) (err error)
+
+// runExec execs bin. If the platform doesn't support exec, it runs it and waits
+// for it to finish.
+func runExec(bin string, args []string) error {
+	if sysExec != nil {
+		sysExec(bin, append([]string{filepath.Base(bin)}, args...), os.Environ())
+	}
+
+	cmd := exec.Command(bin, args...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("Could not run camput: %v", err)
+	}
+	go handleSignals(cmd.Process)
+	return cmd.Wait()
+}
+
 func setenv(key, value string) {
 	err := os.Setenv(key, value)
 	if err != nil {

dev/devcam/exec.go

@@ -0,0 +1,27 @@
+// +build !windows
+
+/*
+Copyright 2013 The Camlistore Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"syscall"
+)
+
+func init() {
+	sysExec = syscall.Exec
+}

dev/devcam/server.go

@@ -383,13 +383,7 @@ func (c *serverCmd) RunCommand(args []string) error {
 	cmdArgs := []string{
 		"-configfile=" + filepath.Join(c.camliSrcRoot, "config", "dev-server-config.json"),
 		"-listen=" + c.listen,
-		"-openbrowser=" + strconv.FormatBool(c.openBrowser)}
-	cmd := exec.Command(camliBin, cmdArgs...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	if err := cmd.Start(); err != nil {
-		return fmt.Errorf("Could not start camlistored: %v", err)
+		"-openbrowser=" + strconv.FormatBool(c.openBrowser),
 	}
-	go handleSignals(cmd.Process)
-	return cmd.Wait()
+	return runExec(camliBin, cmdArgs)
 }