net/url: support query string without values

Previously, RawQuery was used to indicate the presence of a query
string in url.URL. However, this approach was not able to differentiate
between URLs that have no query string at all (http://foo.bar/) and
those that have a query with no values (http://foo.bar/?).

Add a ForceQuery field to indicate the latter form of URL and use it
in URL.String to create a matching URL with a trailing '?'.

Fixes #13488

Change-Id: Ifac663c73d35759bc6c33a00f84ab116b9b81684
Reviewed-on: https://go-review.googlesource.com/19931Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/url/url.go

@@ -307,14 +307,15 @@ func escape(s string, mode encoding) string {
 // construct a URL struct directly and set the Opaque field instead of Path.
 // These still work as well.
 type URL struct {
-	Scheme   string
-	Opaque   string    // encoded opaque data
-	User     *Userinfo // username and password information
-	Host     string    // host or host:port
-	Path     string
-	RawPath  string // encoded path hint (Go 1.5 and later only; see EscapedPath method)
-	RawQuery string // encoded query values, without '?'
-	Fragment string // fragment for references, without '#'
+	Scheme     string
+	Opaque     string    // encoded opaque data
+	User       *Userinfo // username and password information
+	Host       string    // host or host:port
+	Path       string
+	RawPath    string // encoded path hint (Go 1.5 and later only; see EscapedPath method)
+	ForceQuery bool   // append a query ('?') even if RawQuery is empty
+	RawQuery   string // encoded query values, without '?'
+	Fragment   string // fragment for references, without '#'
 }
 
 // User returns a Userinfo containing the provided username
@@ -459,7 +460,12 @@ func parse(rawurl string, viaRequest bool) (url *URL, err error) {
 	}
 	url.Scheme = strings.ToLower(url.Scheme)
 
-	rest, url.RawQuery = split(rest, "?", true)
+	if strings.HasSuffix(rest, "?") {
+		url.ForceQuery = true
+		rest = rest[:len(rest)-1]
+	} else {
+		rest, url.RawQuery = split(rest, "?", true)
+	}
 
 	if !strings.HasPrefix(rest, "/") {
 		if url.Scheme != "" {
@@ -684,7 +690,7 @@ func (u *URL) String() string {
 		}
 		buf.WriteString(path)
 	}
-	if u.RawQuery != "" {
+	if u.ForceQuery || u.RawQuery != "" {
 		buf.WriteByte('?')
 		buf.WriteString(u.RawQuery)
 	}
@@ -913,7 +919,7 @@ func (u *URL) RequestURI() string {
 			result = u.Scheme + ":" + result
 		}
 	}
-	if u.RawQuery != "" {
+	if u.ForceQuery || u.RawQuery != "" {
 		result += "?" + u.RawQuery
 	}
 	return result

src/net/url/url_test.go

@@ -72,6 +72,17 @@ var urltests = []URLTest{
 		},
 		"ftp://john%20doe@www.google.com/",
 	},
+	// empty query
+	{
+		"http://www.google.com/?",
+		&URL{
+			Scheme:     "http",
+			Host:       "www.google.com",
+			Path:       "/",
+			ForceQuery: true,
+		},
+		"",
+	},
 	// query
 	{
 		"http://www.google.com/?q=go+language",
@@ -874,11 +885,13 @@ var resolveReferenceTests = []struct {
 	// Absolute URL references
 	{"http://foo.com?a=b", "https://bar.com/", "https://bar.com/"},
 	{"http://foo.com/", "https://bar.com/?a=b", "https://bar.com/?a=b"},
+	{"http://foo.com/", "https://bar.com/?", "https://bar.com/?"},
 	{"http://foo.com/bar", "mailto:foo@example.com", "mailto:foo@example.com"},
 
 	// Path-absolute references
 	{"http://foo.com/bar", "/baz", "http://foo.com/baz"},
 	{"http://foo.com/bar?a=b#f", "/baz", "http://foo.com/baz"},
+	{"http://foo.com/bar?a=b", "/baz?", "http://foo.com/baz?"},
 	{"http://foo.com/bar?a=b", "/baz?c=d", "http://foo.com/baz?c=d"},
 
 	// Scheme-relative
@@ -1217,6 +1230,15 @@ var requritests = []RequestURITest{
 		},
 		"//foo",
 	},
+	{
+		&URL{
+			Scheme:     "http",
+			Host:       "example.com",
+			Path:       "/foo",
+			ForceQuery: true,
+		},
+		"/foo?",
+	},
 }
 
 func TestRequestURI(t *testing.T) {