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