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Copy pathpath.go
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150 lines (127 loc) · 3.6 KB
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Copy pathpath.go
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150 lines (127 loc) · 3.6 KB
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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
}