Initial commit

vendor/github.com/gin-gonic/gin/path.go

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+// 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 {
+	const stackBufSize = 128
+	// Turn empty string into "/"
+	if p == "" {
+		return "/"
+	}
+
+	// Reasonably sized buffer on stack to avoid allocations in the common case.
+	// If a larger buffer is required, it gets allocated dynamically.
+	buf := make([]byte, 0, stackBufSize)
+
+	n := len(p)
+
+	// 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
+
+		if n+1 > stackBufSize {
+			buf = make([]byte, n+1)
+		} else {
+			buf = buf[:n+1]
+		}
+		buf[0] = '/'
+	}
+
+	trailing := n > 1 && p[n-1] == '/'
+
+	// A bit more clunky without a 'lazybuf' like the path package, but the loop
+	// gets completely inlined (bufApp calls).
+	// loop has no expensive function calls (except 1x make)		// So in contrast to the path package this loop has no expensive function
+	// calls (except make, if needed).
+
+	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 += 2
+
+		case p[r] == '.' && p[r+1] == '.' && (r+2 == n || p[r+2] == '/'):
+			// .. element: remove to last /
+			r += 3
+
+			if w > 1 {
+				// can backtrack
+				w--
+
+				if len(buf) == 0 {
+					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 the original string was not modified (or only shortened at the end),
+	// return the respective substring of the original string.
+	// Otherwise return a new string from the buffer.
+	if len(buf) == 0 {
+		return p[:w]
+	}
+	return string(buf[:w])
+}
+
+// Internal helper to lazily create a buffer if necessary.
+// Calls to this function get inlined.
+func bufApp(buf *[]byte, s string, w int, c byte) {
+	b := *buf
+	if len(b) == 0 {
+		// No modification of the original string so far.
+		// If the next character is the same as in the original string, we do
+		// not yet have to allocate a buffer.
+		if s[w] == c {
+			return
+		}
+
+		// Otherwise use either the stack buffer, if it is large enough, or
+		// allocate a new buffer on the heap, and copy all previous characters.
+		length := len(s)
+		if length > cap(b) {
+			*buf = make([]byte, length)
+		} else {
+			*buf = (*buf)[:length]
+		}
+		b = *buf
+
+		copy(b, s[:w])
+	}
+	b[w] = c
+}