net/http/cgi: make it work without REQUEST_URI environment variable

Fixes #4367.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7062052

src/pkg/net/http/cgi/child.go

@@ -91,10 +91,19 @@ func RequestFromMap(params map[string]string) (*http.Request, error) {
 
 	// TODO: cookies.  parsing them isn't exported, though.
 
+	uriStr := params["REQUEST_URI"]
+	if uriStr == "" {
+		// Fallback to SCRIPT_NAME, PATH_INFO and QUERY_STRING.
+		uriStr = params["SCRIPT_NAME"] + params["PATH_INFO"]
+		s := params["QUERY_STRING"]
+		if s != "" {
+			uriStr += "?" + s
+		}
+	}
 	if r.Host != "" {
 		// Hostname is provided, so we can reasonably construct a URL,
 		// even if we have to assume 'http' for the scheme.
-		rawurl := "http://" + r.Host + params["REQUEST_URI"]
+		rawurl := "http://" + r.Host + uriStr
 		url, err := url.Parse(rawurl)
 		if err != nil {
 			return nil, errors.New("cgi: failed to parse host and REQUEST_URI into a URL: " + rawurl)
@@ -104,7 +113,6 @@ func RequestFromMap(params map[string]string) (*http.Request, error) {
 	// Fallback logic if we don't have a Host header or the URL
 	// failed to parse
 	if r.URL == nil {
-		uriStr := params["REQUEST_URI"]
 		url, err := url.Parse(uriStr)
 		if err != nil {
 			return nil, errors.New("cgi: failed to parse REQUEST_URI into a URL: " + uriStr)

src/pkg/net/http/cgi/child_test.go

@@ -82,6 +82,28 @@ func TestRequestWithoutHost(t *testing.T) {
 		t.Fatalf("unexpected nil URL")
 	}
 	if g, e := req.URL.String(), "/path?a=b"; e != g {
-		t.Errorf("expected URL %q; got %q", e, g)
+		t.Errorf("URL = %q; want %q", g, e)
+	}
+}
+
+func TestRequestWithoutRequestURI(t *testing.T) {
+	env := map[string]string{
+		"SERVER_PROTOCOL": "HTTP/1.1",
+		"HTTP_HOST":       "example.com",
+		"REQUEST_METHOD":  "GET",
+		"SCRIPT_NAME":     "/dir/scriptname",
+		"PATH_INFO":       "/p1/p2",
+		"QUERY_STRING":    "a=1&b=2",
+		"CONTENT_LENGTH":  "123",
+	}
+	req, err := RequestFromMap(env)
+	if err != nil {
+		t.Fatalf("RequestFromMap: %v", err)
+	}
+	if req.URL == nil {
+		t.Fatalf("unexpected nil URL")
+	}
+	if g, e := req.URL.String(), "http://example.com/dir/scriptname/p1/p2?a=1&b=2"; e != g {
+		t.Errorf("URL = %q; want %q", g, e)
 	}
 }