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proxymux.go
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proxymux.go
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package main
import (
"net"
"net/http"
"net/url"
"path"
"strings"
"sync"
)
// ProxyMux is an HTTP 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, ProxyMux 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 ProxyMux
// to redirect a request for "/images" to "/images/", unless "/images" has
// been registered separately.
//
// Patterns may optionally begin with a host name, restricting matches to
// URLs on that host only. Host-specific patterns take precedence over
// general patterns, so that a handler might register for the two patterns
// "/codesearch" and "codesearch.google.com/" without also taking over
// requests for "http://www.google.com/".
//
// ProxyMux also takes care of sanitizing the URL request path,
// redirecting any request containing . or .. elements or repeated slashes
// to an equivalent, cleaner URL.
type ProxyMux struct {
mu sync.RWMutex
m map[string]muxEntry
hosts bool // whether any patterns contain hostnames
}
type muxEntry struct {
h http.Handler
pattern string
}
// NewProxyMux allocates and returns a new ProxyMux.
func NewProxyMux() *ProxyMux { return new(ProxyMux) }
// DefaultProxyMux is the default ProxyMux used by Serve.
var DefaultProxyMux = &defaultProxyMux
var defaultProxyMux ProxyMux
// Does path match pattern?
func pathMatch(pattern, path string) bool {
if len(pattern) == 0 {
// should not happen
return false
}
n := len(pattern)
if pattern[n-1] != '/' {
return pattern == path
}
return len(path) >= n && path[0:n] == pattern
}
// Return 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 != "/" {
np += "/"
}
return np
}
// stripHostPort returns h without any trailing ":<port>".
func stripHostPort(h string) string {
// If no port on host, return unchanged
if strings.IndexByte(h, ':') == -1 {
return h
}
host, _, err := net.SplitHostPort(h)
if err != nil {
return h // on error, return unchanged
}
return host
}
// Find a handler on a handler map given a path string.
// Most-specific (longest) pattern wins.
func (mux *ProxyMux) match(path string) (h http.Handler, pattern string) {
// Check for exact match first.
v, ok := mux.m[path]
if ok {
return v.h, v.pattern
}
// Check for longest valid match.
var n = 0
for k, v := range mux.m {
if !pathMatch(k, path) {
continue
}
if h == nil || len(k) > n {
n = len(k)
h = v.h
pattern = v.pattern
}
}
return
}
// 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 *ProxyMux) redirectToPathSlash(host, path string, u *url.URL) (*url.URL, bool) {
if !mux.shouldRedirect(host, path) {
return u, false
}
path = path + "/"
u = &url.URL{Path: path, RawQuery: u.RawQuery}
return u, true
}
// shouldRedirect 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 ProxyMux.
func (mux *ProxyMux) shouldRedirect(host, path string) bool {
p := []string{path, host + path}
for _, c := range p {
if _, exist := mux.m[c]; exist {
return false
}
}
n := len(path)
if n == 0 {
return false
}
for _, c := range p {
if _, exist := mux.m[c+"/"]; exist {
return path[n-1] != '/'
}
}
return false
}
// http.Handler returns the handler to use for the given request,
// consulting r.Method, r.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.
//
// The path and host are used unchanged for CONNECT requests.
//
// http.Handler also returns the registered pattern that matches the
// request or, in the case of internally-generated redirects,
// the pattern that will match after following the redirect.
//
// If there is no registered handler that applies to the request,
// http.Handler returns a ``page not found'' handler and an empty pattern.
func (mux *ProxyMux) Handler(r *http.Request) (h http.Handler, pattern string) {
// CONNECT requests are not canonicalized.
if r.Method == "CONNECT" {
// If r.URL.Path is /tree and its handler is not registered,
// the /tree -> /tree/ redirect applies to CONNECT requests
// but the path canonicalization does not.
if u, ok := mux.redirectToPathSlash(r.URL.Host, r.URL.Path, r.URL); ok {
return http.RedirectHandler(u.String(), http.StatusMovedPermanently), u.Path
}
return mux.handler(r.Host, r.URL.Path)
}
// All other requests have any port stripped and path cleaned
// before passing to mux.handler.
host := stripHostPort(r.Host)
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(host, path, r.URL); ok {
return http.RedirectHandler(u.String(), http.StatusMovedPermanently), u.Path
}
if path != r.URL.Path {
_, pattern = mux.handler(host, path)
url := *r.URL
url.Path = path
return http.RedirectHandler(url.String(), http.StatusMovedPermanently), pattern
}
return mux.handler(host, r.URL.Path)
}
// handler is the main implementation of http.Handler.
// The path is known to be in canonical form, except for CONNECT methods.
func (mux *ProxyMux) handler(host, path string) (h http.Handler, pattern string) {
mux.mu.RLock()
defer mux.mu.RUnlock()
// Host-specific pattern takes precedence over generic ones
if mux.hosts {
h, pattern = mux.match(host + path)
}
if h == nil {
h, pattern = mux.match(path)
}
if h == nil {
h, pattern = http.NotFoundHandler(), ""
}
return
}
// ServeHTTP dispatches the request to the handler whose
// pattern most closely matches the request URL.
func (mux *ProxyMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
if r.RequestURI == "*" {
if r.ProtoAtLeast(1, 1) {
w.Header().Set("Connection", "close")
}
w.WriteHeader(http.StatusBadRequest)
return
}
h, _ := mux.Handler(r)
h.ServeHTTP(w, r)
}
// Handle registers the handler for the given pattern.
// If a handler already exists for pattern, Handle panics.
func (mux *ProxyMux) Handle(pattern string, handler http.Handler) {
mux.mu.Lock()
defer mux.mu.Unlock()
if pattern == "" {
panic("http: invalid pattern")
}
if handler == nil {
panic("http: nil handler")
}
if _, exist := mux.m[pattern]; exist {
panic("http: multiple registrations for " + pattern)
}
if mux.m == nil {
mux.m = make(map[string]muxEntry)
}
mux.m[pattern] = muxEntry{h: handler, pattern: pattern}
if pattern[0] != '/' {
mux.hosts = true
}
}
// HandleFunc registers the handler function for the given pattern.
func (mux *ProxyMux) HandleFunc(pattern string, handler func(http.ResponseWriter, *http.Request)) {
mux.Handle(pattern, http.HandlerFunc(handler))
}
func (mux *ProxyMux) Deregister(pattern string) error {
mux.mu.Lock()
defer mux.mu.Unlock()
delete(mux.m, pattern)
return nil
}