go-gemini/server.go

package gemini

import (
	"crypto/tls"
	"io"
	"net"
	"net/url"
	"strconv"
	"strings"
)

// Status codes.
const (
	StatusInput                     = 10
	StatusSensitiveInput            = 11
	StatusSuccess                   = 20
	StatusRedirectTemporary         = 30
	StatusRedirectPermanent         = 31
	StatusTemporaryFailure          = 40
	StatusServerUnavailable         = 41
	StatusCGIError                  = 42
	StatusProxyError                = 43
	StatusSlowDown                  = 44
	StatusPermanentFailure          = 50
	StatusNotFound                  = 51
	StatusGone                      = 52
	StatusProxyRequestRefused       = 53
	StatusBadRequest                = 59
	StatusClientCertificateRequired = 60
	StatusCertificateNotAuthorised  = 61
	StatusCertificateNotValid       = 62
)

// Status code categories.
const (
	StatusClassInput                     = 1
	StatusClassSuccess                   = 2
	StatusClassRedirect                  = 3
	StatusClassTemporaryFailure          = 4
	StatusClassPermanentFailure          = 5
	StatusClassClientCertificateRequired = 6
)

// Response is a Gemini response.
type Response struct {
	Status int
	Meta   string
	Body   []byte
}

// Write writes the Gemini response header and body to the provided io.Writer.
func (r *Response) Write(w io.Writer) {
	header := strconv.Itoa(r.Status) + " " + r.Meta + "\r\n"
	w.Write([]byte(header))

	// Only write the response body on success
	if r.Status/10 == StatusClassSuccess {
		w.Write(r.Body)
	}
}

// Server is a Gemini server.
type Server struct {
	Addr      string
	TLSConfig *tls.Config
	Handler   Handler
}

// ListenAndServe listens for requests at the server's configured address.
func (s *Server) ListenAndServe() error {
	addr := s.Addr
	if addr == "" {
		addr = ":1965"
	}

	ln, err := net.Listen("tcp", addr)
	if err != nil {
		return err
	}
	defer ln.Close()

	tlsListener := tls.NewListener(ln, s.TLSConfig)
	return s.Serve(tlsListener)
}

// Serve listens for requests on the provided listener.
func (s *Server) Serve(ln net.Listener) error {
	for {
		rw, err := ln.Accept()
		if err != nil {
			return err
		}

		req, err := readLine(rw)
		if err != nil {
			continue
		}
		url, err := url.Parse(req)
		if err != nil {
			continue
		}
		resp := s.Handler.Serve(url)
		resp.Write(rw)
		rw.Close()
	}
}

// Handler handles a url with a response.
type Handler interface {
	// Serve accepts a url, as that is the only information that is provided in
	// a Gemini request.
	Serve(*url.URL) *Response
}

// Mux is a Gemini request multiplexer.
// It matches the URL of each incoming request against a list of registered
// patterns and calls the handler for the pattern that most closesly matches
// the URL.
type Mux struct {
	entries []muxEntry
}

type muxEntry struct {
	scheme  string
	host    string
	path    string
	handler Handler
}

func (m *Mux) match(url *url.URL) Handler {
	for _, e := range m.entries {
		if (e.scheme == "" || url.Scheme == e.scheme) &&
			(e.host == "" || url.Host == e.host) &&
			strings.HasPrefix(url.Path, e.path) {
			return e.handler
		}
	}
	return nil
}

// Handle registers a handler for the given pattern.
func (m *Mux) Handle(pattern string, handler Handler) {
	url, err := url.Parse(pattern)
	if err != nil {
		panic(err)
	}
	m.entries = append(m.entries, muxEntry{
		url.Scheme,
		url.Host,
		url.Path,
		handler,
	})
}

// HandleFunc registers a HandlerFunc for the given pattern.
func (m *Mux) HandleFunc(pattern string, handlerFunc func(url *url.URL) *Response) {
	handler := HandlerFunc(handlerFunc)
	m.Handle(pattern, handler)
}

// Serve responds to the request with the appropriate handler.
func (m *Mux) Serve(url *url.URL) *Response {
	h := m.match(url)
	if h == nil {
		return &Response{
			Status: StatusNotFound,
			Meta:   "Not found",
		}
	}
	return h.Serve(url)
}

// A wrapper around a bare function that implements Handler.
type HandlerFunc func(url *url.URL) *Response

func (f HandlerFunc) Serve(url *url.URL) *Response {
	return f(url)
}