exec: new API, replace Run with Command

This removes exec.Run and replaces exec.Cmd with a
new implementation. The new exec.Cmd represents
both a currently-running command and also a command
being prepared. It has a good zero value.

You can Start + Wait on a Cmd, or simply Run it.
Start (and Run) deal with copying stdout, stdin,
and stderr between the Cmd's io.Readers and
io.Writers.

There are convenience methods to capture a command's
stdout and/or stderr.

R=r, n13m3y3r, rsc, gustavo, alex.brainman, dsymonds, r, adg, duzy.chan, mike.rosset, kevlar
CC=golang-dev
https://golang.org/cl/4552052

2 files changed, 32 insertions, 35 deletions

diff --git a/src/pkg/http/cgi/host.go b/src/pkg/http/cgi/host.go
index 7e4ccf881d..c283191ef2 100644
--- a/src/pkg/http/cgi/host.go
+++ b/src/pkg/http/cgi/host.go
@@ -156,34 +156,38 @@ func (h *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		cwd = "."
 	}
 
-	args := []string{h.Path}
-	args = append(args, h.Args...)
-
-	cmd, err := exec.Run(
-		pathBase,
-		args,
-		env,
-		cwd,
-		exec.Pipe,        // stdin
-		exec.Pipe,        // stdout
-		exec.PassThrough, // stderr (for now)
-	)
-	if err != nil {
+	internalError := func(err os.Error) {
 		rw.WriteHeader(http.StatusInternalServerError)
 		h.printf("CGI error: %v", err)
+	}
+
+	stdoutRead, stdoutWrite, err := os.Pipe()
+	if err != nil {
+		internalError(err)
 		return
 	}
-	defer func() {
-		cmd.Stdin.Close()
-		cmd.Stdout.Close()
-		cmd.Wait(0) // no zombies
-	}()
 
+	cmd := &exec.Cmd{
+		Path:   pathBase,
+		Args:   append([]string{h.Path}, h.Args...),
+		Dir:    cwd,
+		Env:    env,
+		Stdout: stdoutWrite,
+		Stderr: os.Stderr, // for now
+	}
 	if req.ContentLength != 0 {
-		go io.Copy(cmd.Stdin, req.Body)
+		cmd.Stdin = req.Body
+	}
+
+	err = cmd.Start()
+	if err != nil {
+		internalError(err)
+		return
 	}
+	stdoutWrite.Close()
+	defer cmd.Wait()
 
-	linebody, _ := bufio.NewReaderSize(cmd.Stdout, 1024)
+	linebody, _ := bufio.NewReaderSize(stdoutRead, 1024)
 	headers := make(http.Header)
 	statusCode := 0
 	for {
diff --git a/src/pkg/http/cgi/host_test.go b/src/pkg/http/cgi/host_test.go
index 9ac085f2f3..bbdb715cf9 100644
--- a/src/pkg/http/cgi/host_test.go
+++ b/src/pkg/http/cgi/host_test.go
@@ -17,20 +17,6 @@ import (
 	"testing"
 )
 
-var cgiScriptWorks = canRun("./testdata/test.cgi")
-
-func canRun(s string) bool {
-	c, err := exec.Run(s, []string{s}, nil, ".", exec.DevNull, exec.DevNull, exec.DevNull)
-	if err != nil {
-		return false
-	}
-	w, err := c.Wait(0)
-	if err != nil {
-		return false
-	}
-	return w.Exited() && w.ExitStatus() == 0
-}
-
 func newRequest(httpreq string) *http.Request {
 	buf := bufio.NewReader(strings.NewReader(httpreq))
 	req, err := http.ReadRequest(buf)
@@ -76,8 +62,15 @@ readlines:
 	return rw
 }
 
+var cgiTested = false
+var cgiWorks bool
+
 func skipTest(t *testing.T) bool {
-	if !cgiScriptWorks {
+	if !cgiTested {
+		cgiTested = true
+		cgiWorks = exec.Command("./testdata/test.cgi").Run() == nil
+	}
+	if !cgiWorks {
 		// No Perl on Windows, needed by test.cgi
 		// TODO: make the child process be Go, not Perl.
 		t.Logf("Skipping test: test.cgi failed.")