http: fix transport crash when request URL is nil

Fixes #1602

R=rsc, petar-m
CC=golang-dev
https://golang.org/cl/4284043

src/pkg/http/transport.go

@@ -36,6 +36,11 @@ type transport struct {
 }
 
 func (ct *transport) Do(req *Request) (resp *Response, err os.Error) {
+	if req.URL == nil {
+		if req.URL, err = ParseURL(req.RawURL); err != nil {
+			return
+		}
+	}
 	if req.URL.Scheme != "http" && req.URL.Scheme != "https" {
 		return nil, &badStringError{"unsupported protocol scheme", req.URL.Scheme}
 	}

src/pkg/http/transport_test.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Tests for transport.go
+
+package http_test
+
+import (
+	"fmt"
+	. "http"
+	"http/httptest"
+	"io/ioutil"
+	"testing"
+)
+
+func TestTransportNilURL(t *testing.T) {
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		fmt.Fprintf(w, "Hi")
+	}))
+	defer ts.Close()
+
+	req := new(Request)
+	req.URL = nil // what we're actually testing
+	req.Method = "GET"
+	req.RawURL = ts.URL
+	req.Proto = "HTTP/1.1"
+	req.ProtoMajor = 1
+	req.ProtoMinor = 1
+
+	// TODO(bradfitz): test &transport{} and not DefaultTransport
+	// once Transport is exported.
+	res, err := DefaultTransport.Do(req)
+	if err != nil {
+		t.Fatalf("unexpected Do error: %v", err)
+	}
+	body, err := ioutil.ReadAll(res.Body)
+	if g, e := string(body), "Hi"; g != e {
+		t.Fatalf("Expected response body of %q; got %q", e, g)
+	}
+}