go-gemini/server.go
2020-12-18 00:25:06 -05:00

338 lines
8.7 KiB
Go

package gemini
import (
"bufio"
"crypto/tls"
"errors"
"log"
"net"
"net/url"
"strconv"
"strings"
"time"
)
// Server is a Gemini server.
type Server struct {
// Addr specifies the address that the server should listen on.
// If Addr is empty, the server will listen on the address ":1965".
Addr string
// ReadTimeout is the maximum duration for reading a request.
ReadTimeout time.Duration
// WriteTimeout is the maximum duration before timing out
// writes of the response.
WriteTimeout time.Duration
// Certificates contains the certificates used by the server.
Certificates CertificateDir
// CreateCertificate, if not nil, will be called to create a new certificate
// if the current one is expired or missing.
CreateCertificate func(hostname string) (tls.Certificate, error)
// ErrorLog specifies an optional logger for errors accepting connections
// and file system errors.
// If nil, logging is done via the log package's standard logger.
ErrorLog *log.Logger
// registered responders
responders map[responderKey]Responder
hosts map[string]bool
}
type responderKey struct {
scheme string
hostname string
}
// Register registers a responder for the given pattern.
//
// Patterns must be in the form of "hostname" or "scheme://hostname".
// If no scheme is specified, a scheme of "gemini://" is implied.
// Wildcard patterns are supported (e.g. "*.example.com").
func (s *Server) Register(pattern string, responder Responder) {
if pattern == "" {
panic("gemini: invalid pattern")
}
if responder == nil {
panic("gemini: nil responder")
}
if s.responders == nil {
s.responders = map[responderKey]Responder{}
s.hosts = map[string]bool{}
}
split := strings.SplitN(pattern, "://", 2)
var key responderKey
if len(split) == 2 {
key.scheme = split[0]
key.hostname = split[1]
} else {
key.scheme = "gemini"
key.hostname = split[0]
}
if _, ok := s.responders[key]; ok {
panic("gemini: multiple registrations for " + pattern)
}
s.responders[key] = responder
s.hosts[key.hostname] = true
}
// RegisterFunc registers a responder function for the given pattern.
func (s *Server) RegisterFunc(pattern string, responder func(*ResponseWriter, *Request)) {
s.Register(pattern, ResponderFunc(responder))
}
// 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()
return s.Serve(tls.NewListener(ln, &tls.Config{
ClientAuth: tls.RequestClientCert,
MinVersion: tls.VersionTLS12,
GetCertificate: s.getCertificate,
}))
}
// Serve listens for requests on the provided listener.
func (s *Server) Serve(l net.Listener) error {
var tempDelay time.Duration // how long to sleep on accept failure
for {
rw, err := l.Accept()
if err != nil {
// If this is a temporary error, sleep
if ne, ok := err.(net.Error); ok && ne.Temporary() {
if tempDelay == 0 {
tempDelay = 5 * time.Millisecond
} else {
tempDelay *= 2
}
if max := 1 * time.Second; tempDelay > max {
tempDelay = max
}
s.logf("gemini: Accept error: %v; retrying in %v", err, tempDelay)
time.Sleep(tempDelay)
continue
}
// Otherwise, return the error
return err
}
tempDelay = 0
go s.respond(rw)
}
}
func (s *Server) getCertificate(h *tls.ClientHelloInfo) (*tls.Certificate, error) {
cert, err := s.getCertificateFor(h.ServerName)
if err != nil {
// Try wildcard
wildcard := strings.SplitN(h.ServerName, ".", 2)
if len(wildcard) == 2 {
cert, err = s.getCertificateFor("*." + wildcard[1])
}
}
return cert, err
}
func (s *Server) getCertificateFor(hostname string) (*tls.Certificate, error) {
if _, ok := s.hosts[hostname]; !ok {
return nil, errors.New("hostname not registered")
}
// Generate a new certificate if it is missing or expired
cert, ok := s.Certificates.Lookup(hostname)
if !ok || cert.Leaf != nil && cert.Leaf.NotAfter.Before(time.Now()) {
if s.CreateCertificate != nil {
cert, err := s.CreateCertificate(hostname)
if err == nil {
s.Certificates.Add(hostname, cert)
if err := s.Certificates.Write(hostname, cert); err != nil {
s.logf("gemini: Failed to write new certificate for %s: %s", hostname, err)
}
}
return &cert, err
}
return nil, errors.New("no certificate")
}
return &cert, nil
}
// respond responds to a connection.
func (s *Server) respond(conn net.Conn) {
if d := s.ReadTimeout; d != 0 {
conn.SetReadDeadline(time.Now().Add(d))
}
if d := s.WriteTimeout; d != 0 {
conn.SetWriteDeadline(time.Now().Add(d))
}
r := bufio.NewReader(conn)
w := newResponseWriter(conn)
// Read requested URL
rawurl, err := r.ReadString('\r')
if err != nil {
return
}
// Read terminating line feed
if b, err := r.ReadByte(); err != nil {
return
} else if b != '\n' {
w.WriteStatus(StatusBadRequest)
}
// Trim carriage return
rawurl = rawurl[:len(rawurl)-1]
// Ensure URL is valid
if len(rawurl) > 1024 {
w.WriteStatus(StatusBadRequest)
} else if url, err := url.Parse(rawurl); err != nil || url.User != nil {
// Note that we return an error status if User is specified in the URL
w.WriteStatus(StatusBadRequest)
} else {
// Store information about the TLS connection
connState := conn.(*tls.Conn).ConnectionState()
var cert *tls.Certificate
if len(connState.PeerCertificates) > 0 {
peerCert := connState.PeerCertificates[0]
// Store the TLS certificate
cert = &tls.Certificate{
Certificate: [][]byte{peerCert.Raw},
Leaf: peerCert,
}
}
req := &Request{
URL: url,
RemoteAddr: conn.RemoteAddr(),
TLS: connState,
Certificate: cert,
}
resp := s.responder(req)
if resp != nil {
resp.Respond(w, req)
} else {
w.WriteStatus(StatusNotFound)
}
}
w.b.Flush()
conn.Close()
}
func (s *Server) responder(r *Request) Responder {
if h, ok := s.responders[responderKey{r.URL.Scheme, r.URL.Hostname()}]; ok {
return h
}
wildcard := strings.SplitN(r.URL.Hostname(), ".", 2)
if len(wildcard) == 2 {
if h, ok := s.responders[responderKey{r.URL.Scheme, "*." + wildcard[1]}]; ok {
return h
}
}
return nil
}
func (s *Server) logf(format string, args ...interface{}) {
if s.ErrorLog != nil {
s.ErrorLog.Printf(format, args...)
} else {
log.Printf(format, args...)
}
}
// ResponseWriter is used by a Gemini handler to construct a Gemini response.
type ResponseWriter struct {
b *bufio.Writer
bodyAllowed bool
wroteHeader bool
mediatype string
}
func newResponseWriter(conn net.Conn) *ResponseWriter {
return &ResponseWriter{
b: bufio.NewWriter(conn),
}
}
// WriteHeader writes the response header.
// If the header has already been written, WriteHeader does nothing.
//
// Meta contains more information related to the response status.
// For successful responses, Meta should contain the mimetype of the response.
// For failure responses, Meta should contain a short description of the failure.
// Meta should not be longer than 1024 bytes.
func (w *ResponseWriter) WriteHeader(status Status, meta string) {
if w.wroteHeader {
return
}
w.b.WriteString(strconv.Itoa(int(status)))
w.b.WriteByte(' ')
w.b.WriteString(meta)
w.b.Write(crlf)
// Only allow body to be written on successful status codes.
if status.Class() == StatusClassSuccess {
w.bodyAllowed = true
}
w.wroteHeader = true
}
// WriteStatus writes the response header with the given status code.
//
// WriteStatus is equivalent to WriteHeader(status, status.Message())
func (w *ResponseWriter) WriteStatus(status Status) {
w.WriteHeader(status, status.Message())
}
// SetMediaType sets the media type that will be written for a successful response.
// If the mimetype is not set, it will default to "text/gemini".
func (w *ResponseWriter) SetMediaType(mediatype string) {
w.mediatype = mediatype
}
// Write writes the response body.
// If the response status does not allow for a response body, Write returns
// ErrBodyNotAllowed.
//
// If the response header has not yet been written, Write calls WriteHeader
// with StatusSuccess and the mimetype set in SetMimetype.
func (w *ResponseWriter) Write(b []byte) (int, error) {
if !w.wroteHeader {
mediatype := w.mediatype
if mediatype == "" {
mediatype = "text/gemini"
}
w.WriteHeader(StatusSuccess, mediatype)
}
if !w.bodyAllowed {
return 0, ErrBodyNotAllowed
}
return w.b.Write(b)
}
// A Responder responds to a Gemini request.
type Responder interface {
// Respond accepts a Request and constructs a Response.
Respond(*ResponseWriter, *Request)
}
// ResponderFunc is a wrapper around a bare function that implements Responder.
type ResponderFunc func(*ResponseWriter, *Request)
func (f ResponderFunc) Respond(w *ResponseWriter, r *Request) {
f(w, r)
}