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