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// Copyright 2016 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.
package utils
import (
"strings"
"github.com/juju/errors"
)
// RelativeURLPath returns a relative URL path that is lexically
// equivalent to targpath when interpreted by url.URL.ResolveReference.
// On success, the returned path will always be non-empty and relative
// to basePath, even if basePath and targPath share no elements.
//
// It is assumed that both basePath and targPath are normalized
// (have no . or .. elements).
//
// An error is returned if basePath or targPath are not absolute paths.
func RelativeURLPath(basePath, targPath string) (string, error) {
if !strings.HasPrefix(basePath, "/") {
return "", errors.New("non-absolute base URL")
}
if !strings.HasPrefix(targPath, "/") {
return "", errors.New("non-absolute target URL")
}
baseParts := strings.Split(basePath, "/")
targParts := strings.Split(targPath, "/")
// For the purposes of dotdot, the last element of
// the paths are irrelevant. We save the last part
// of the target path for later.
lastElem := targParts[len(targParts)-1]
baseParts = baseParts[0 : len(baseParts)-1]
targParts = targParts[0 : len(targParts)-1]
// Find the common prefix between the two paths:
var i int
for ; i < len(baseParts); i++ {
if i >= len(targParts) || baseParts[i] != targParts[i] {
break
}
}
dotdotCount := len(baseParts) - i
targOnly := targParts[i:]
result := make([]string, 0, dotdotCount+len(targOnly)+1)
for i := 0; i < dotdotCount; i++ {
result = append(result, "..")
}
result = append(result, targOnly...)
result = append(result, lastElem)
final := strings.Join(result, "/")
if final == "" {
// If the final result is empty, the last element must
// have been empty, so the target was slash terminated
// and there were no previous elements, so "."
// is appropriate.
final = "."
}
return final, nil
}
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