net/http/cgi: allow CGI host to configure where child's stderr goes

Patch originally from Steven Hartland. Tweaked a bit & added a test.

Fixes #7197

Change-Id: I09012b4674e7c641dba31a24e9758cedb898d3ee
Reviewed-on: https://go-review.googlesource.com/21196
Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/net/http/cgi/host.go b/src/net/http/cgi/host.go
index b2657b13a8..2eea64334b 100644
--- a/src/net/http/cgi/host.go
+++ b/src/net/http/cgi/host.go
@@ -58,6 +58,7 @@ type Handler struct {
 	InheritEnv []string    // environment variables to inherit from host, as "key"
 	Logger     *log.Logger // optional log for errors or nil to use log.Print
 	Args       []string    // optional arguments to pass to child process
+	Stderr     io.Writer   // optional stderr for the child process; nil means os.Stderr
 
 	// PathLocationHandler specifies the root http Handler that
 	// should handle internal redirects when the CGI process
@@ -70,6 +71,13 @@ type Handler struct {
 	PathLocationHandler http.Handler
 }
 
+func (h *Handler) stderr() io.Writer {
+	if h.Stderr != nil {
+		return h.Stderr
+	}
+	return os.Stderr
+}
+
 // removeLeadingDuplicates remove leading duplicate in environments.
 // It's possible to override environment like following.
 //    cgi.Handler{
@@ -204,7 +212,7 @@ func (h *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		Args:   append([]string{h.Path}, h.Args...),
 		Dir:    cwd,
 		Env:    env,
-		Stderr: os.Stderr, // for now
+		Stderr: h.stderr(),
 	}
 	if req.ContentLength != 0 {
 		cmd.Stdin = req.Body