text: // Copyright 2013 Julien Schmidt. All rights reserved.
  // Based on the path package, Copyright 2009 The Go Authors.
  // Use of this source code is governed by a BSD-style license that can be found
  // at https://github.com/julienschmidt/httprouter/blob/master/LICENSE.
  
  package gin
  
  // cleanPath is the URL version of path.Clean, it returns a canonical URL path
  // for p, eliminating . and .. elements.
  //
  // The following rules are applied iteratively until no further processing can
  // be done:
  //	1. Replace multiple slashes with a single slash.
  //	2. Eliminate each . path name element (the current directory).
  //	3. Eliminate each inner .. path name element (the parent directory)
  //	   along with the non-.. element that precedes it.
  //	4. Eliminate .. elements that begin a rooted path:
  //	   that is, replace "/.." by "/" at the beginning of a path.
  //
  // If the result of this process is an empty string, "/" is returned
  func cleanPath(p string) string {
  	// Turn empty string into "/"
  	if p == "" {
  		return "/"
  	}
  
  	n := len(p)
  	var buf []byte
  
  	// Invariants:
  	//      reading from path; r is index of next byte to process.
  	//      writing to buf; w is index of next byte to write.
  
  	// path must start with '/'
  	r := 1
  	w := 1
  
  	if p[0] != '/' {
  		r = 0
  		buf = make([]byte, n+1)
  		buf[0] = '/'
  	}
  
  	trailing := n > 2 && p[n-1] == '/'
  
  	// A bit more clunky without a 'lazybuf' like the path package, but the loop
  	// gets completely inlined (bufApp). So in contrast to the path package this
  	// loop has no expensive function calls (except 1x make)
  
  	for r < n {
  		switch {
  		case p[r] == '/':
  			// empty path element, trailing slash is added after the end
  			r++
  
  		case p[r] == '.' && r+1 == n:
  			trailing = true
  			r++
  
  		case p[r] == '.' && p[r+1] == '/':
  			// . element
  			r++
  
  		case p[r] == '.' && p[r+1] == '.' && (r+2 == n || p[r+2] == '/'):
  			// .. element: remove to last /
  			r += 2
  
  			if w > 1 {
  				// can backtrack
  				w--
  
  				if buf == nil {
  					for w > 1 && p[w] != '/' {
  						w--
  					}
  				} else {
  					for w > 1 && buf[w] != '/' {
  						w--
  					}
  				}
  			}
  
  		default:
  			// real path element.
  			// add slash if needed
  			if w > 1 {
  				bufApp(&buf, p, w, '/')
  				w++
  			}
  
  			// copy element
  			for r < n && p[r] != '/' {
  				bufApp(&buf, p, w, p[r])
  				w++
  				r++
  			}
  		}
  	}
  
  	// re-append trailing slash
  	if trailing && w > 1 {
  		bufApp(&buf, p, w, '/')
  		w++
  	}
  
  	if buf == nil {
  		return p[:w]
  	}
  	return string(buf[:w])
  }
  
  // internal helper to lazily create a buffer if necessary
  func bufApp(buf *[]byte, s string, w int, c byte) {
  	if *buf == nil {
  		if s[w] == c {
  			return
  		}
  
  		*buf = make([]byte, len(s))
  		copy(*buf, s[:w])
  	}
  	(*buf)[w] = c
  }
  