http/cgi: copy some PATH environment variables to child

R=bradfitz, bradfitzwork, iant2, bradfitzgo
CC=golang-dev
https://golang.org/cl/4444058

src/pkg/http/cgi/host.go

@@ -36,9 +36,10 @@ type Handler struct {
 	Path string // path to the CGI executable
 	Root string // root URI prefix of handler or empty for "/"
 
-	Env    []string    // extra environment variables to set, if any
+	Env        []string    // extra environment variables to set, if any, as "key=value"
-	Logger *log.Logger // optional log for errors or nil to use log.Print
+	InheritEnv []string    // environment variables to inherit from host, as "key"
-	Args   []string    // optional arguments to pass to child process
+	Logger     *log.Logger // optional log for errors or nil to use log.Print
+	Args       []string    // optional arguments to pass to child process
 }
 
 func (h *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
@@ -110,6 +111,12 @@ func (h *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		env = append(env, h.Env...)
 	}
 
+	for _, e := range h.InheritEnv {
+		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

@@ -22,6 +22,14 @@ 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",