mux.go

package httpd

import (
	"errors"
	"net/http"
	"path"
	"sync"
)

//
// What follows is an copy of golang's built in ServeMux with a few modifications:
//  1. An error is returned instead of a panics on registering handlers.
//  2. A delete method has been added to remove handlers.
//  3. Removed 'Helpful Behavior' of adding redirects automatically
//
// ServeMux 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 == "/".
//
// 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/".
//
// ServeMux also takes care of sanitizing the URL request path,
// redirecting any request containing . or .. elements to an
// equivalent .- and ..-free URL.
type ServeMux struct {
	mu    sync.RWMutex
	m     map[string]muxEntry
	hosts bool // whether any patterns contain hostnames
}

type muxEntry struct {
	explicit bool
	h        http.Handler
	pattern  string
}

// NewServeMux allocates and returns a new ServeMux.
func NewServeMux() *ServeMux { return &ServeMux{m: make(map[string]muxEntry)} }

// DefaultServeMux is the default ServeMux used by Serve.
var DefaultServeMux = NewServeMux()

// 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
}

// Find a handler on a handler map given a path string
// Most-specific (longest) pattern wins
func (mux *ServeMux) match(path string) (h http.Handler, pattern string) {
	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
}

// 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.
//
// 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,
// Handler returns a ``page not found'' handler and an empty pattern.
func (mux *ServeMux) Handler(r *http.Request) (h http.Handler, pattern string) {
	if r.Method != "CONNECT" {
		if p := cleanPath(r.URL.Path); p != r.URL.Path {
			_, pattern = mux.handler(r.Host, p)
			url := *r.URL
			url.Path = p
			return http.RedirectHandler(url.String(), http.StatusMovedPermanently), pattern
		}
	}

	return mux.handler(r.Host, r.URL.Path)
}

// handler is the main implementation of Handler.
// The path is known to be in canonical form, except for CONNECT methods.
func (mux *ServeMux) 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 *ServeMux) 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 an error is returned.
func (mux *ServeMux) Handle(pattern string, handler http.Handler) error {
	mux.mu.Lock()
	defer mux.mu.Unlock()

	if pattern == "" {
		return errors.New("http: invalid pattern " + pattern)
	}
	if handler == nil {
		return errors.New("http: nil handler")
	}
	if mux.m[pattern].explicit {
		return errors.New("http: multiple registrations for " + pattern)
	}

	mux.m[pattern] = muxEntry{explicit: true, h: handler, pattern: pattern}

	if pattern[0] != '/' {
		mux.hosts = true
	}

	return nil
}

// HandleFunc registers the handler function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(http.ResponseWriter, *http.Request)) error {
	return mux.Handle(pattern, http.HandlerFunc(handler))
}

func (mux *ServeMux) Deregister(pattern string) {
	mux.mu.Lock()
	defer mux.mu.Unlock()
	delete(mux.m, pattern)
}

func (mux *ServeMux) Patterns() []string {
	mux.mu.Lock()
	defer mux.mu.Unlock()
	patterns := make([]string, len(mux.m))
	i := 0
	for p, _ := range mux.m {
		patterns[i] = p
		i++
	}
	return patterns
}