net/url: add URL.Hostname and URL.Port accessors

Fixes #16142

Change-Id: I7609faaf00c69646b0bd44a60a63a22d9265feb0
Reviewed-on: https://go-review.googlesource.com/28933Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Reviewed-by: Francesc Campoy Flores <campoy@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/url/url.go

@@ -872,6 +872,7 @@ func resolvePath(base, ref string) string {
 }
 
 // IsAbs reports whether the URL is absolute.
+// Absolute means that it has a non-empty scheme.
 func (u *URL) IsAbs() bool {
 	return u.Scheme != ""
 }
@@ -951,3 +952,43 @@ func (u *URL) RequestURI() string {
 	}
 	return result
 }
+
+// Hostname returns u.Host, without any port number.
+//
+// If Host is an IPv6 literal with a port number, Hostname returns the
+// IPv6 literal without the square brackets. IPv6 literals may include
+// a zone identifier.
+func (u *URL) Hostname() string {
+	return stripPort(u.Host)
+}
+
+// Port returns the port part of u.Host, without the leading colon.
+// If u.Host doesn't contain a port, Port returns an empty string.
+func (u *URL) Port() string {
+	return portOnly(u.Host)
+}
+
+func stripPort(hostport string) string {
+	colon := strings.IndexByte(hostport, ':')
+	if colon == -1 {
+		return hostport
+	}
+	if i := strings.IndexByte(hostport, ']'); i != -1 {
+		return strings.TrimPrefix(hostport[:i], "[")
+	}
+	return hostport[:colon]
+}
+
+func portOnly(hostport string) string {
+	colon := strings.IndexByte(hostport, ':')
+	if colon == -1 {
+		return ""
+	}
+	if i := strings.Index(hostport, "]:"); i != -1 {
+		return hostport[i+len("]:"):]
+	}
+	if strings.Contains(hostport, "]") {
+		return ""
+	}
+	return hostport[colon+len(":"):]
+}

src/net/url/url_test.go

@@ -1479,3 +1479,47 @@ func TestURLErrorImplementsNetError(t *testing.T) {
 		}
 	}
 }
+
+func TestURLHostname(t *testing.T) {
+	tests := []struct {
+		host string // URL.Host field
+		want string
+	}{
+		{"foo.com:80", "foo.com"},
+		{"foo.com", "foo.com"},
+		{"FOO.COM", "FOO.COM"}, // no canonicalization (yet?)
+		{"1.2.3.4", "1.2.3.4"},
+		{"1.2.3.4:80", "1.2.3.4"},
+		{"[1:2:3:4]", "1:2:3:4"},
+		{"[1:2:3:4]:80", "1:2:3:4"},
+		{"[::1]:80", "::1"},
+	}
+	for _, tt := range tests {
+		u := &URL{Host: tt.host}
+		got := u.Hostname()
+		if got != tt.want {
+			t.Errorf("Hostname for Host %q = %q; want %q", tt.host, got, tt.want)
+		}
+	}
+}
+
+func TestURLPort(t *testing.T) {
+	tests := []struct {
+		host string // URL.Host field
+		want string
+	}{
+		{"foo.com", ""},
+		{"foo.com:80", "80"},
+		{"1.2.3.4", ""},
+		{"1.2.3.4:80", "80"},
+		{"[1:2:3:4]", ""},
+		{"[1:2:3:4]:80", "80"},
+	}
+	for _, tt := range tests {
+		u := &URL{Host: tt.host}
+		got := u.Port()
+		if got != tt.want {
+			t.Errorf("Port for Host %q = %q; want %q", tt.host, got, tt.want)
+		}
+	}
+}