URI.Parse should never change it's input

Decode the URI in place, but use the bytes of the URI instead of the
bytes of the input parameter.

uri.go

@@ -305,11 +305,12 @@ func (u *URI) parse(host, uri []byte, isTLS bool) error {
 		}
 	}
 
-	host, err := parseHost(host)
-	if err != nil {
+	u.host = append(u.host, host...)
+	if parsedHost, err := parseHost(u.host); err != nil {
 		return err
+	} else {
+		u.host = parsedHost
 	}
-	u.host = append(u.host, host...)
 	lowercaseBytes(u.host)
 
 	b := uri
@@ -353,6 +354,8 @@ func (u *URI) parse(host, uri []byte, isTLS bool) error {
 // information. That is, as host[:port].
 //
 // Based on https://github.com/golang/go/blob/8ac5cbe05d61df0a7a7c9a38ff33305d4dcfea32/src/net/url/url.go#L619
+//
+// The host is parsed and unescaped in place overwriting the contents of the host parameter.
 func parseHost(host []byte) ([]byte, error) {
 	if len(host) > 0 && host[0] == '[' {
 		// Parse an IP-Literal in RFC 3986 and RFC 6874.
@@ -425,6 +428,8 @@ func (e InvalidHostError) Error() string {
 // which section of the URL string is being unescaped.
 //
 // Based on https://github.com/golang/go/blob/8ac5cbe05d61df0a7a7c9a38ff33305d4dcfea32/src/net/url/url.go#L199
+//
+// Unescapes in place overwriting the contents of s and returning it.
 func unescape(s []byte, mode encoding) ([]byte, error) {
 	// Count %, check that they're well-formed.
 	n := 0

uri_test.go

@@ -427,3 +427,23 @@ func TestInvalidUrl(t *testing.T) {
 		t.Fail()
 	}
 }
+
+func TestNoOverwriteInput(t *testing.T) {
+	str := `//%AA`
+	url := []byte(str)
+
+	u := AcquireURI()
+	defer ReleaseURI(u)
+
+	if err := u.Parse(nil, url); err != nil {
+		t.Error(err)
+	}
+
+	if string(url) != str {
+		t.Error()
+	}
+
+	if u.String() != "http://\xaa/" {
+		t.Errorf("%q", u.String())
+	}
+}