go-gemini/mux.go

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2020-10-28 12:59:45 -06:00
package gemini
import (
"net/url"
"path"
"sort"
"strings"
"sync"
)
// The following code is modified from the net/http package.
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// 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 == "/".
//
// 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[string]muxEntry
es []muxEntry // slice of entries sorted from longest to shortest.
}
type muxEntry struct {
r Responder
pattern string
}
// 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(path string) Responder {
// Check for exact match first.
v, ok := mux.m[path]
if ok {
return v.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 strings.HasPrefix(path, e.pattern) {
return e.r
}
}
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(path string, u *url.URL) (*url.URL, bool) {
mux.mu.RLock()
shouldRedirect := mux.shouldRedirectRLocked(path)
mux.mu.RUnlock()
if !shouldRedirect {
return u, false
}
path = path + "/"
u = &url.URL{Path: path, RawQuery: u.RawQuery}
return u, 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(path string) bool {
if _, exist := mux.m[path]; exist {
return false
}
n := len(path)
if n == 0 {
return false
}
if _, exist := mux.m[path+"/"]; exist {
return path[n-1] != '/'
}
return false
}
// Respond dispatches the request to the responder whose
// pattern most closely matches the request URL.
func (mux *ServeMux) Respond(w *ResponseWriter, r *Request) {
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(path, r.URL); ok {
w.WriteHeader(StatusRedirect, u.String())
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return
}
if path != r.URL.Path {
u := *r.URL
u.Path = path
w.WriteHeader(StatusRedirect, u.String())
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return
}
mux.mu.RLock()
defer mux.mu.RUnlock()
resp := mux.match(path)
if resp == nil {
w.WriteStatus(StatusNotFound)
return
}
resp.Respond(w, r)
}
// Handle registers the responder for the given pattern.
// If a responder already exists for pattern, Handle panics.
func (mux *ServeMux) Handle(pattern string, responder Responder) {
mux.mu.Lock()
defer mux.mu.Unlock()
if pattern == "" {
panic("gemini: invalid pattern")
}
if responder == nil {
panic("gemini: nil responder")
}
if _, exist := mux.m[pattern]; exist {
panic("gemini: multiple registrations for " + pattern)
}
if mux.m == nil {
mux.m = make(map[string]muxEntry)
}
e := muxEntry{responder, pattern}
mux.m[pattern] = e
if pattern[len(pattern)-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].pattern) < len(e.pattern)
})
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 responder function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, responder func(*ResponseWriter, *Request)) {
if responder == nil {
panic("gemini: nil responder")
}
mux.Handle(pattern, ResponderFunc(responder))
}