http/cgi: pass some default environment variables

This isn't really part of RFC 3875 but matches
the behavior of Apache, et al.

R=iant, iant2
CC=golang-dev
https://golang.org/cl/4435065

src/pkg/http/cgi/host.go

@@ -25,12 +25,21 @@ import (
 	"os"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strconv"
 	"strings"
 )
 
 var trailingPort = regexp.MustCompile(`:([0-9]+)$`)
 
+var osDefaultInheritEnv = map[string][]string{
+	"darwin":  []string{"DYLD_LIBRARY_PATH"},
+	"freebsd": []string{"LD_LIBRARY_PATH"},
+	"hpux":    []string{"LD_LIBRARY_PATH", "SHLIB_PATH"},
+	"linux":   []string{"LD_LIBRARY_PATH"},
+	"windows": []string{"SystemRoot", "COMSPEC", "PATHEXT", "WINDIR"},
+}
+
 // Handler runs an executable in a subprocess with a CGI environment.
 type Handler struct {
 	Path string // path to the CGI executable
@@ -111,12 +120,24 @@ func (h *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		env = append(env, h.Env...)
 	}
 
+	path := os.Getenv("PATH")
+	if path == "" {
+		path = "/bin:/usr/bin:/usr/ucb:/usr/bsd:/usr/local/bin"
+	}
+	env = append(env, "PATH="+path)
+
 	for _, e := range h.InheritEnv {
 		if v := os.Getenv(e); v != "" {
 			env = append(env, e+"="+v)
 		}
 	}
 
+	for _, e := range osDefaultInheritEnv[runtime.GOOS] {
+		if v := os.Getenv(e); v != "" {
+			env = append(env, e+"="+v)
+		}
+	}
+
 	cwd, pathBase := filepath.Split(h.Path)
 	if cwd == "" {
 		cwd = "."

src/pkg/http/cgi/matryoshka_test.go

@@ -22,14 +22,6 @@ func TestHostingOurselves(t *testing.T) {
 		Path: os.Args[0],
 		Root: "/test.go",
 		Args: []string{"-test.run=TestBeChildCGIProcess"},
-		// When using a shared library with gccgo, make sure
-		// we can still find the library when we exec
-		// ourselves.
-		InheritEnv: []string{
-			"LD_LIBRARY_PATH",
-			"SHLIB_PATH",
-			"DYLD_LIBRARY_PATH",
-		},
 	}
 	expectedMap := map[string]string{
 		"test":                  "Hello CGI-in-CGI",