Make ResponseWriter an interface

Make ResponseWriter an interface with an unexported method. Implementors
must embed a ResponseWriter from elsewhere. This gives us the
flexibility of an interface while allowing us to add new methods in the
future.

fs.go

@@ -33,7 +33,7 @@ type fileServer struct {
 	fs.FS
 }
 
-func (fs fileServer) ServeGemini(ctx context.Context, w *ResponseWriter, r *Request) {
+func (fs fileServer) ServeGemini(ctx context.Context, w ResponseWriter, r *Request) {
 	serveFile(w, r, fs, path.Clean(r.URL.Path), true)
 }
 
@@ -43,11 +43,11 @@ func (fs fileServer) ServeGemini(ctx context.Context, w *ResponseWriter, r *Requ
 //
 // ServeContent tries to deduce the type from name's file extension.
 // The name is otherwise unused; it is never sent in the response.
-func ServeContent(w *ResponseWriter, r *Request, name string, content io.Reader) {
+func ServeContent(w ResponseWriter, r *Request, name string, content io.Reader) {
 	serveContent(w, name, content)
 }
 
-func serveContent(w *ResponseWriter, name string, content io.Reader) {
+func serveContent(w ResponseWriter, name string, content io.Reader) {
 	// Detect mimetype from file extension
 	ext := path.Ext(name)
 	mimetype := mime.TypeByExtension(ext)
@@ -75,7 +75,7 @@ func serveContent(w *ResponseWriter, name string, content io.Reader) {
 // Outside of those two special cases, ServeFile does not use r.URL.Path for
 // selecting the file or directory to serve; only the file or directory
 // provided in the name argument is used.
-func ServeFile(w *ResponseWriter, r *Request, fsys fs.FS, name string) {
+func ServeFile(w ResponseWriter, r *Request, fsys fs.FS, name string) {
 	if containsDotDot(r.URL.Path) {
 		// Too many programs use r.URL.Path to construct the argument to
 		// serveFile. Reject the request under the assumption that happened
@@ -102,7 +102,7 @@ func containsDotDot(v string) bool {
 
 func isSlashRune(r rune) bool { return r == '/' || r == '\\' }
 
-func serveFile(w *ResponseWriter, r *Request, fsys fs.FS, name string, redirect bool) {
+func serveFile(w ResponseWriter, r *Request, fsys fs.FS, name string, redirect bool) {
 	const indexPage = "/index.gmi"
 
 	// Redirect .../index.gmi to .../
@@ -177,7 +177,7 @@ func serveFile(w *ResponseWriter, r *Request, fsys fs.FS, name string, redirect
 	serveContent(w, name, f)
 }
 
-func dirList(w *ResponseWriter, f fs.File) {
+func dirList(w ResponseWriter, f fs.File) {
 	var entries []fs.DirEntry
 	var err error
 	d, ok := f.(fs.ReadDirFile)

handler.go

@@ -21,23 +21,23 @@ import (
 //
 // Handlers should not modify the provided Request.
 type Handler interface {
-	ServeGemini(context.Context, *ResponseWriter, *Request)
+	ServeGemini(context.Context, ResponseWriter, *Request)
 }
 
 // The HandlerFunc type is an adapter to allow the use of ordinary functions
 // as Gemini handlers. If f is a function with the appropriate signature,
 // HandlerFunc(f) is a Handler that calls f.
-type HandlerFunc func(context.Context, *ResponseWriter, *Request)
+type HandlerFunc func(context.Context, ResponseWriter, *Request)
 
 // ServeGemini calls f(ctx, w, r).
-func (f HandlerFunc) ServeGemini(ctx context.Context, w *ResponseWriter, r *Request) {
+func (f HandlerFunc) ServeGemini(ctx context.Context, w ResponseWriter, r *Request) {
 	f(ctx, w, r)
 }
 
 // StatusHandler returns a request handler that responds to each request
 // with the provided status code and meta.
 func StatusHandler(status Status, meta string) Handler {
-	return HandlerFunc(func(ctx context.Context, w *ResponseWriter, r *Request) {
+	return HandlerFunc(func(ctx context.Context, w ResponseWriter, r *Request) {
 		w.WriteHeader(status, meta)
 	})
 }
@@ -58,7 +58,7 @@ func StripPrefix(prefix string, h Handler) Handler {
 	if prefix == "" {
 		return h
 	}
-	return HandlerFunc(func(ctx context.Context, w *ResponseWriter, r *Request) {
+	return HandlerFunc(func(ctx context.Context, w ResponseWriter, r *Request) {
 		p := strings.TrimPrefix(r.URL.Path, prefix)
 		rp := strings.TrimPrefix(r.URL.RawPath, prefix)
 		if len(p) < len(r.URL.Path) && (r.URL.RawPath == "" || len(rp) < len(r.URL.RawPath)) {
@@ -92,7 +92,7 @@ type timeoutHandler struct {
 	dt time.Duration
 }
 
-func (t *timeoutHandler) ServeGemini(ctx context.Context, w *ResponseWriter, r *Request) {
+func (t *timeoutHandler) ServeGemini(ctx context.Context, w ResponseWriter, r *Request) {
 	ctx, cancel := context.WithTimeout(ctx, t.dt)
 	defer cancel()
 

mux.go

@@ -212,7 +212,7 @@ func (mux *ServeMux) Handler(r *Request) Handler {
 
 // ServeGemini dispatches the request to the handler whose
 // pattern most closely matches the request URL.
-func (mux *ServeMux) ServeGemini(ctx context.Context, w *ResponseWriter, r *Request) {
+func (mux *ServeMux) ServeGemini(ctx context.Context, w ResponseWriter, r *Request) {
 	h := mux.Handler(r)
 	h.ServeGemini(ctx, w, r)
 }

mux_test.go

@@ -8,7 +8,7 @@ import (
 
 type nopHandler struct{}
 
-func (*nopHandler) ServeGemini(context.Context, *ResponseWriter, *Request) {}
+func (*nopHandler) ServeGemini(context.Context, ResponseWriter, *Request) {}
 
 func TestServeMuxMatch(t *testing.T) {
 	type Match struct {

response.go

@@ -120,7 +120,70 @@ func (r *Response) TLS() *tls.ConnectionState {
 //
 // A ResponseWriter may not be used after the Handler.ServeGemini method
 // has returned.
-type ResponseWriter struct {
+type ResponseWriter interface {
+	// SetMediaType sets the media type that will be sent by Write for a
+	// successful response. If no media type is set, a default of
+	// "text/gemini; charset=utf-8" will be used.
+	//
+	// Setting the media type after a call to Write or WriteHeader has
+	// no effect.
+	SetMediaType(mediatype string)
+
+	// Write writes the data to the connection as part of a Gemini response.
+	//
+	// If WriteHeader has not yet been called, Write calls WriteHeader with
+	// StatusSuccess and the media type set in SetMediaType before writing the data.
+	// If no media type was set, Write uses a default media type of
+	// "text/gemini; charset=utf-8".
+	Write([]byte) (int, error)
+
+	// WriteHeader sends a Gemini response header with the provided
+	// status code and meta.
+	//
+	// If WriteHeader is not called explicitly, the first call to Write
+	// will trigger an implicit call to WriteHeader with a successful
+	// status code and the media type set in SetMediaType.
+	//
+	// The provided code must be a valid Gemini status code.
+	// The provided meta must not be longer than 1024 bytes.
+	// Only one header may be written.
+	WriteHeader(status Status, meta string)
+
+	// Flush sends any buffered data to the client.
+	Flush() error
+
+	// Close closes the connection.
+	// Any blocked Write operations will be unblocked and return errors.
+	Close() error
+
+	// Conn returns the underlying network connection.
+	// To take over the connection, use Hijack.
+	Conn() net.Conn
+
+	// TLS returns information about the underlying TLS connection.
+	TLS() *tls.ConnectionState
+
+	// Hijack lets the caller take over the connection.
+	// After a call to Hijack the Gemini server library
+	// will not do anything else with the connection.
+	// It becomes the caller's responsibility to manage
+	// and close the connection.
+	//
+	// The returned net.Conn may have read or write deadlines
+	// already set, depending on the configuration of the
+	// Server. It is the caller's responsibility to set
+	// or clear those deadlines as needed.
+	Hijack() net.Conn
+
+	reset(io.WriteCloser)
+
+	// unexported method so we can extend this interface over time
+	// without breaking existing code. Implementers must embed a concrete
+	// type from elsewhere.
+	unexported()
+}
+
+type responseWriter struct {
 	bw          *bufio.Writer
 	cl          io.Closer
 	mediatype   string
@@ -130,38 +193,26 @@ type ResponseWriter struct {
 	conn        net.Conn
 }
 
-func newResponseWriter(w io.WriteCloser) *ResponseWriter {
-	return &ResponseWriter{
+func newResponseWriter(w io.WriteCloser) *responseWriter {
+	return &responseWriter{
 		bw: bufio.NewWriter(w),
 		cl: w,
 	}
 }
 
-func (w *ResponseWriter) reset(wc io.WriteCloser) {
+func (w *responseWriter) reset(wc io.WriteCloser) {
 	w.bw.Reset(wc)
-	*w = ResponseWriter{
+	*w = responseWriter{
 		bw: w.bw,
 		cl: wc,
 	}
 }
 
-// SetMediaType sets the media type that will be sent by Write for a
-// successful response. If no media type is set, a default of
-// "text/gemini; charset=utf-8" will be used.
-//
-// Setting the media type after a call to Write or WriteHeader has
-// no effect.
-func (w *ResponseWriter) SetMediaType(mediatype string) {
+func (w *responseWriter) SetMediaType(mediatype string) {
 	w.mediatype = mediatype
 }
 
-// Write writes the data to the connection as part of a Gemini response.
-//
-// If WriteHeader has not yet been called, Write calls WriteHeader with
-// StatusSuccess and the media type set in SetMediaType before writing the data.
-// If no media type was set, Write uses a default media type of
-// "text/gemini; charset=utf-8".
-func (w *ResponseWriter) Write(b []byte) (int, error) {
+func (w *responseWriter) Write(b []byte) (int, error) {
 	if w.hijacked {
 		return 0, ErrHijacked
 	}
@@ -179,17 +230,7 @@ func (w *ResponseWriter) Write(b []byte) (int, error) {
 	return w.bw.Write(b)
 }
 
-// WriteHeader sends a Gemini response header with the provided
-// status code and meta.
-//
-// If WriteHeader is not called explicitly, the first call to Write
-// will trigger an implicit call to WriteHeader with a successful
-// status code and the media type set in SetMediaType.
-//
-// The provided code must be a valid Gemini status code.
-// The provided meta must not be longer than 1024 bytes.
-// Only one header may be written.
-func (w *ResponseWriter) WriteHeader(status Status, meta string) {
+func (w *responseWriter) WriteHeader(status Status, meta string) {
 	if w.hijacked {
 		return
 	}
@@ -208,8 +249,7 @@ func (w *ResponseWriter) WriteHeader(status Status, meta string) {
 	w.wroteHeader = true
 }
 
-// Flush sends any buffered data to the client.
-func (w *ResponseWriter) Flush() error {
+func (w *responseWriter) Flush() error {
 	if w.hijacked {
 		return ErrHijacked
 	}
@@ -220,23 +260,18 @@ func (w *ResponseWriter) Flush() error {
 	return w.bw.Flush()
 }
 
-// Close closes the connection.
-// Any blocked Write operations will be unblocked and return errors.
-func (w *ResponseWriter) Close() error {
+func (w *responseWriter) Close() error {
 	if w.hijacked {
 		return ErrHijacked
 	}
 	return w.cl.Close()
 }
 
-// Conn returns the underlying network connection.
-// To take over the connection, use Hijack.
-func (w *ResponseWriter) Conn() net.Conn {
+func (w *responseWriter) Conn() net.Conn {
 	return w.conn
 }
 
-// TLS returns information about the underlying TLS connection.
-func (w *ResponseWriter) TLS() *tls.ConnectionState {
+func (w *responseWriter) TLS() *tls.ConnectionState {
 	if tlsConn, ok := w.conn.(*tls.Conn); ok {
 		state := tlsConn.ConnectionState()
 		return &state
@@ -244,17 +279,9 @@ func (w *ResponseWriter) TLS() *tls.ConnectionState {
 	return nil
 }
 
-// Hijack lets the caller take over the connection.
-// After a call to Hijack the Gemini server library
-// will not do anything else with the connection.
-// It becomes the caller's responsibility to manage
-// and close the connection.
-//
-// The returned net.Conn may have read or write deadlines
-// already set, depending on the configuration of the
-// Server. It is the caller's responsibility to set
-// or clear those deadlines as needed.
-func (w *ResponseWriter) Hijack() net.Conn {
+func (w *responseWriter) Hijack() net.Conn {
 	w.hijacked = true
 	return w.conn
 }
+
+func (w *responseWriter) unexported() {}