net/url: allow Parse, ParseRequestURI to parse ipv6 zone identifiers in URIs

Using IPv6 link-local addresses to make connections between on-link
nodes is useful for small distributed applications but it requires zone
identifiers to distinguish a correct IP link. It's the same for
transports using URI for destination discovery such as HTTP, WebSocket.

This change allows Parse, ParseRequestURI functions and String method of
URL to parse/return a literal IPv6 address followed by a zone identifier
within a URI as described in RFC 6874.

Fixes #6530.

Change-Id: I2936ea65c1446994770cf2ee2c28a1c73faaa0ca
Reviewed-on: https://go-review.googlesource.com/2431
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/url/url.go

@@ -51,6 +51,7 @@ type encoding int
 
 const (
 	encodePath encoding = 1 + iota
+	encodeHost
 	encodeUserPassword
 	encodeQueryComponent
 	encodeFragment
@@ -64,6 +65,9 @@ func (e EscapeError) Error() string {
 
 // Return true if the specified character should be escaped when
 // appearing in a URL string, according to RFC 3986.
+//
+// Please be informed that for now shouldEscape does not check all
+// reserved characters correctly. See golang.org/issue/5684.
 func shouldEscape(c byte, mode encoding) bool {
 	// §2.3 Unreserved characters (alphanum)
 	if 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' {
@@ -92,6 +96,10 @@ func shouldEscape(c byte, mode encoding) bool {
 			// that too.
 			return c == '@' || c == '/' || c == '?' || c == ':'
 
+		case encodeHost: // §3.2.1
+			// The RFC allows ':'.
+			return c != ':'
+
 		case encodeQueryComponent: // §3.4
 			// The RFC reserves (so we must escape) everything.
 			return true
@@ -101,6 +109,13 @@ func shouldEscape(c byte, mode encoding) bool {
 			// everything, so escape nothing.
 			return false
 		}
+
+	case '[', ']': // §2.2 Reserved characters (reserved)
+		switch mode {
+		case encodeHost: // §3.2.1
+			// The RFC allows '[', ']'.
+			return false
+		}
 	}
 
 	// Everything else must be escaped.
@@ -401,10 +416,6 @@ func parse(rawurl string, viaRequest bool) (url *URL, err error) {
 		if err != nil {
 			goto Error
 		}
-		if strings.Contains(url.Host, "%") {
-			err = errors.New("hexadecimal escape in host")
-			goto Error
-		}
 	}
 	if url.Path, err = unescape(rest, encodePath); err != nil {
 		goto Error
@@ -418,26 +429,76 @@ Error:
 func parseAuthority(authority string) (user *Userinfo, host string, err error) {
 	i := strings.LastIndex(authority, "@")
 	if i < 0 {
-		host = authority
+		host, err = parseHost(authority)
-		return
+	} else {
+		host, err = parseHost(authority[i+1:])
 	}
-	userinfo, host := authority[:i], authority[i+1:]
+	if err != nil {
+		return nil, "", err
+	}
+	if i < 0 {
+		return nil, host, nil
+	}
+	userinfo := authority[:i]
 	if strings.Index(userinfo, ":") < 0 {
 		if userinfo, err = unescape(userinfo, encodeUserPassword); err != nil {
-			return
+			return nil, "", err
 		}
 		user = User(userinfo)
 	} else {
 		username, password := split(userinfo, ":", true)
 		if username, err = unescape(username, encodeUserPassword); err != nil {
-			return
+			return nil, "", err
 		}
 		if password, err = unescape(password, encodeUserPassword); err != nil {
-			return
+			return nil, "", err
 		}
 		user = UserPassword(username, password)
 	}
-	return
+	return user, host, nil
+}
+
+// parseHost parses host as an authority without user information.
+func parseHost(host string) (string, error) {
+	litOrName := host
+	if strings.HasPrefix(host, "[") {
+		// Parse an IP-Literal in RFC 3986 and RFC 6874.
+		// E.g., "[fe80::1], "[fe80::1%25en0]"
+		//
+		// RFC 4007 defines "%" as a delimiter character in
+		// the textual representation of IPv6 addresses.
+		// Per RFC 6874, in URIs that "%" is encoded as "%25".
+		i := strings.LastIndex(host[1:], "]")
+		if i < 0 {
+			return "", errors.New("missing ']' in host")
+		}
+		// Parse a host subcomponent without a ZoneID in RFC
+		// 6874 because the ZoneID is allowed to use the
+		// percent encoded form.
+		j := strings.Index(host[1:1+i], "%25")
+		if j < 0 {
+			litOrName = host[1 : 1+i]
+		} else {
+			litOrName = host[1 : 1+j]
+		}
+	}
+	// A URI containing an IP-Literal without a ZoneID or
+	// IPv4address in RFC 3986 and RFC 6847 must not be
+	// percent-encoded.
+	//
+	// A URI containing a DNS registered name in RFC 3986 is
+	// allowed to be percent-encoded, though we don't use it for
+	// now to avoid messing up with the gap between allowed
+	// characters in URI and allowed characters in DNS.
+	// See golang.org/issue/7991.
+	if strings.Contains(litOrName, "%") {
+		return "", errors.New("percent-encoded characters in host")
+	}
+	var err error
+	if host, err = unescape(host, encodeHost); err != nil {
+		return "", err
+	}
+	return host, nil
 }
 
 // String reassembles the URL into a valid URL string.
@@ -475,7 +536,7 @@ func (u *URL) String() string {
 				buf.WriteByte('@')
 			}
 			if h := u.Host; h != "" {
-				buf.WriteString(h)
+				buf.WriteString(escape(h, encodeHost))
 			}
 		}
 		if u.Path != "" && u.Path[0] != '/' && u.Host != "" {

src/net/url/url_test.go

@@ -289,6 +289,86 @@ var urltests = []URLTest{
 		},
 		"",
 	},
+	// host subcomponent; IPv4 address in RFC 3986
+	{
+		"http://192.168.0.1/",
+		&URL{
+			Scheme: "http",
+			Host:   "192.168.0.1",
+			Path:   "/",
+		},
+		"",
+	},
+	// host and port subcomponents; IPv4 address in RFC 3986
+	{
+		"http://192.168.0.1:8080/",
+		&URL{
+			Scheme: "http",
+			Host:   "192.168.0.1:8080",
+			Path:   "/",
+		},
+		"",
+	},
+	// host subcomponent; IPv6 address in RFC 3986
+	{
+		"http://[fe80::1]/",
+		&URL{
+			Scheme: "http",
+			Host:   "[fe80::1]",
+			Path:   "/",
+		},
+		"",
+	},
+	// host and port subcomponents; IPv6 address in RFC 3986
+	{
+		"http://[fe80::1]:8080/",
+		&URL{
+			Scheme: "http",
+			Host:   "[fe80::1]:8080",
+			Path:   "/",
+		},
+		"",
+	},
+	// host subcomponent; IPv6 address with zone identifier in RFC 6847
+	{
+		"http://[fe80::1%25en0]/", // alphanum zone identifier
+		&URL{
+			Scheme: "http",
+			Host:   "[fe80::1%en0]",
+			Path:   "/",
+		},
+		"",
+	},
+	// host and port subcomponents; IPv6 address with zone identifier in RFC 6847
+	{
+		"http://[fe80::1%25en0]:8080/", // alphanum zone identifier
+		&URL{
+			Scheme: "http",
+			Host:   "[fe80::1%en0]:8080",
+			Path:   "/",
+		},
+		"",
+	},
+	// host subcomponent; IPv6 address with zone identifier in RFC 6847
+	{
+		"http://[fe80::1%25%65%6e%301-._~]/", // percent-encoded+unreserved zone identifier
+		&URL{
+			Scheme: "http",
+			Host:   "[fe80::1%en01-._~]",
+			Path:   "/",
+		},
+		"http://[fe80::1%25en01-._~]/",
+	},
+	// host and port subcomponents; IPv6 address with zone identifier in RFC 6847
+	{
+		"http://[fe80::1%25%65%6e%301-._~]:8080/", // percent-encoded+unreserved zone identifier
+		&URL{
+			Scheme: "http",
+			Host:   "[fe80::1%en01-._~]:8080",
+			Path:   "/",
+		},
+		"http://[fe80::1%25en01-._~]:8080/",
+	},
 }
 
 // more useful string for debugging than fmt's struct printer
@@ -358,9 +438,33 @@ var parseRequestURLTests = []struct {
 	{"/", true},
 	{pathThatLooksSchemeRelative, true},
 	{"//not.a.user@%66%6f%6f.com/just/a/path/also", true},
+	{"*", true},
+	{"http://192.168.0.1/", true},
+	{"http://192.168.0.1:8080/", true},
+	{"http://[fe80::1]/", true},
+	{"http://[fe80::1]:8080/", true},
+
+	// Tests exercising RFC 6874 compliance:
+	{"http://[fe80::1%25en0]/", true},                 // with alphanum zone identifier
+	{"http://[fe80::1%25en0]:8080/", true},            // with alphanum zone identifier
+	{"http://[fe80::1%25%65%6e%301-._~]/", true},      // with percent-encoded+unreserved zone identifier
+	{"http://[fe80::1%25%65%6e%301-._~]:8080/", true}, // with percent-encoded+unreserved zone identifier
+
 	{"foo.html", false},
 	{"../dir/", false},
-	{"*", true},
+	{"http://192.168.0.%31/", false},
+	{"http://192.168.0.%31:8080/", false},
+	{"http://[fe80::%31]/", false},
+	{"http://[fe80::%31]:8080/", false},
+	{"http://[fe80::%31%25en0]/", false},
+	{"http://[fe80::%31%25en0]:8080/", false},
+
+	// These two cases are valid as textual representations as
+	// described in RFC 4007, but are not valid as address
+	// literals with IPv6 zone identifiers in URIs as described in
+	// RFC 6874.
+	{"http://[fe80::1%en0]/", false},
+	{"http://[fe80::1%en0]:8080/", false},
 }
 
 func TestParseRequestURI(t *testing.T) {