go-gemini/mux.go
2021-02-23 09:49:20 -05:00

300 lines
9.2 KiB
Go

package gemini
import (
"context"
"net"
"net/url"
"path"
"sort"
"strings"
"sync"
)
// ServeMux 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 closely matches the URL.
//
// Patterns name fixed, rooted paths, like "/favicon.ico",
// or rooted subtrees, like "/images/" (note the trailing slash).
// Longer patterns take precedence over shorter ones, so that
// if there are handlers registered for both "/images/"
// and "/images/thumbnails/", the latter handler will be
// called for paths beginning "/images/thumbnails/" and the
// former will receive requests for any other paths in the
// "/images/" subtree.
//
// Note that since a pattern ending in a slash names a rooted subtree,
// the pattern "/" matches all paths not matched by other registered
// patterns, not just the URL with Path == "/".
//
// Patterns may also contain schemes and hostnames.
// Wildcard patterns can be used to match multiple hostnames (e.g. "*.example.com").
//
// The following are examples of valid patterns, along with the scheme,
// hostname, and path that they match.
//
// Pattern │ Scheme │ Hostname │ Path
// ─────────────────────────────┼────────┼──────────┼─────────────
// /file │ gemini │ * │ /file
// /directory/ │ gemini │ * │ /directory/*
// hostname/file │ gemini │ hostname │ /file
// hostname/directory/ │ gemini │ hostname │ /directory/*
// scheme://hostname/file │ scheme │ hostname │ /file
// scheme://hostname/directory/ │ scheme │ hostname │ /directory/*
// //hostname/file │ * │ hostname │ /file
// //hostname/directory/ │ * │ hostname │ /directory/*
// scheme:///file │ scheme │ * │ /file
// scheme:///directory/ │ scheme │ * │ /directory/*
// ///file │ * │ * │ /file
// ///directory/ │ * │ * │ /directory/*
//
// A pattern without a hostname will match any hostname.
// If a pattern begins with "//", it will match any scheme.
// Otherwise, a pattern with no scheme is treated as though it has a
// scheme of "gemini".
//
// If a subtree has been registered and a request is received naming the
// subtree root without its trailing slash, ServeMux redirects that
// request to the subtree root (adding the trailing slash). This behavior can
// be overridden with a separate registration for the path without
// the trailing slash. For example, registering "/images/" causes ServeMux
// to redirect a request for "/images" to "/images/", unless "/images" has
// been registered separately.
//
// ServeMux also takes care of sanitizing the URL request path and
// redirecting any request containing . or .. elements or repeated slashes
// to an equivalent, cleaner URL.
type ServeMux struct {
mu sync.RWMutex
m map[muxKey]Handler
es []muxEntry // slice of entries sorted from longest to shortest
}
type muxKey struct {
scheme string
host string
path string
}
type muxEntry struct {
handler Handler
key muxKey
}
// cleanPath returns the canonical path for p, eliminating . and .. elements.
func cleanPath(p string) string {
if p == "" {
return "/"
}
if p[0] != '/' {
p = "/" + p
}
np := path.Clean(p)
// path.Clean removes trailing slash except for root;
// put the trailing slash back if necessary.
if p[len(p)-1] == '/' && np != "/" {
// Fast path for common case of p being the string we want:
if len(p) == len(np)+1 && strings.HasPrefix(p, np) {
np = p
} else {
np += "/"
}
}
return np
}
// Find a handler on a handler map given a path string.
// Most-specific (longest) pattern wins.
func (mux *ServeMux) match(key muxKey) Handler {
// Check for exact match first.
if r, ok := mux.m[key]; ok {
return r
} else if r, ok := mux.m[muxKey{"", key.host, key.path}]; ok {
return r
} else if r, ok := mux.m[muxKey{key.scheme, "", key.path}]; ok {
return r
} else if r, ok := mux.m[muxKey{"", "", key.path}]; ok {
return r
}
// Check for longest valid match. mux.es contains all patterns
// that end in / sorted from longest to shortest.
for _, e := range mux.es {
if (e.key.scheme == "" || key.scheme == e.key.scheme) &&
(e.key.host == "" || key.host == e.key.host) &&
strings.HasPrefix(key.path, e.key.path) {
return e.handler
}
}
return nil
}
// redirectToPathSlash determines if the given path needs appending "/" to it.
// This occurs when a handler for path + "/" was already registered, but
// not for path itself. If the path needs appending to, it creates a new
// URL, setting the path to u.Path + "/" and returning true to indicate so.
func (mux *ServeMux) redirectToPathSlash(key muxKey, u *url.URL) (*url.URL, bool) {
mux.mu.RLock()
shouldRedirect := mux.shouldRedirectRLocked(key)
mux.mu.RUnlock()
if !shouldRedirect {
return u, false
}
return u.ResolveReference(&url.URL{Path: key.path + "/"}), true
}
// shouldRedirectRLocked reports whether the given path and host should be redirected to
// path+"/". This should happen if a handler is registered for path+"/" but
// not path -- see comments at ServeMux.
func (mux *ServeMux) shouldRedirectRLocked(key muxKey) bool {
if _, exist := mux.m[key]; exist {
return false
}
n := len(key.path)
if n == 0 {
return false
}
if _, exist := mux.m[muxKey{key.scheme, key.host, key.path + "/"}]; exist {
return key.path[n-1] != '/'
}
return false
}
func getWildcard(hostname string) (string, bool) {
if net.ParseIP(hostname) == nil {
split := strings.SplitN(hostname, ".", 2)
if len(split) == 2 {
return "*." + split[1], true
}
}
return "", false
}
// Handler returns the handler to use for the given request, consulting
// r.URL.Scheme, r.URL.Host, and r.URL.Path. It always returns a non-nil handler. If
// the path is not in its canonical form, the handler will be an
// internally-generated handler that redirects to the canonical path. If the
// host contains a port, it is ignored when matching handlers.
func (mux *ServeMux) Handler(r *Request) Handler {
scheme := r.URL.Scheme
host := r.URL.Hostname()
path := cleanPath(r.URL.Path)
// If the given path is /tree and its handler is not registered,
// redirect for /tree/.
if u, ok := mux.redirectToPathSlash(muxKey{scheme, host, path}, r.URL); ok {
return StatusHandler(StatusPermanentRedirect, u.String())
}
if path != r.URL.Path {
u := *r.URL
u.Path = path
return StatusHandler(StatusPermanentRedirect, u.String())
}
mux.mu.RLock()
defer mux.mu.RUnlock()
h := mux.match(muxKey{scheme, host, path})
if h == nil {
// Try wildcard
if wildcard, ok := getWildcard(host); ok {
h = mux.match(muxKey{scheme, wildcard, path})
}
}
if h == nil {
h = NotFoundHandler()
}
return h
}
// 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) {
h := mux.Handler(r)
h.ServeGemini(ctx, w, r)
}
// Handle registers the handler for the given pattern.
// If a handler already exists for pattern, Handle panics.
func (mux *ServeMux) Handle(pattern string, handler Handler) {
if pattern == "" {
panic("gemini: invalid pattern")
}
if handler == nil {
panic("gemini: nil handler")
}
mux.mu.Lock()
defer mux.mu.Unlock()
var key muxKey
if strings.HasPrefix(pattern, "//") {
// match any scheme
key.scheme = ""
pattern = pattern[2:]
} else {
// extract scheme
cut := strings.Index(pattern, "://")
if cut == -1 {
// default scheme of gemini
key.scheme = "gemini"
} else {
key.scheme = pattern[:cut]
pattern = pattern[cut+3:]
}
}
// extract hostname and path
cut := strings.Index(pattern, "/")
if cut == -1 {
key.host = pattern
key.path = "/"
} else {
key.host = pattern[:cut]
key.path = pattern[cut:]
}
// strip port from hostname
if hostname, _, err := net.SplitHostPort(key.host); err == nil {
key.host = hostname
}
if _, exist := mux.m[key]; exist {
panic("gemini: multiple registrations for " + pattern)
}
if mux.m == nil {
mux.m = make(map[muxKey]Handler)
}
mux.m[key] = handler
e := muxEntry{handler, key}
if key.path[len(key.path)-1] == '/' {
mux.es = appendSorted(mux.es, e)
}
}
func appendSorted(es []muxEntry, e muxEntry) []muxEntry {
n := len(es)
i := sort.Search(n, func(i int) bool {
return len(es[i].key.scheme) < len(e.key.scheme) ||
len(es[i].key.host) < len(es[i].key.host) ||
len(es[i].key.path) < len(e.key.path)
})
if i == n {
return append(es, e)
}
// we now know that i points at where we want to insert
es = append(es, muxEntry{}) // try to grow the slice in place, any entry works.
copy(es[i+1:], es[i:]) // move shorter entries down
es[i] = e
return es
}
// HandleFunc registers the handler function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler HandlerFunc) {
mux.Handle(pattern, handler)
}