net/url: fix handling of relative paths in ResolveReference.

Fixes #3560.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6886047

src/pkg/net/url/url.go

@@ -572,23 +572,33 @@ func resolvePath(basepath string, refpath string) string {
 	if len(base) == 0 {
 		base = []string{""}
 	}
+
+	rm := true
 	for idx, ref := range refs {
 		switch {
 		case ref == ".":
-			base[len(base)-1] = ""
+			if idx == 0 {
+				base[len(base)-1] = ""
+				rm = true
+			} else {
+				rm = false
+			}
 		case ref == "..":
 			newLen := len(base) - 1
 			if newLen < 1 {
 				newLen = 1
 			}
 			base = base[0:newLen]
-			base[len(base)-1] = ""
+			if rm {
+				base[len(base)-1] = ""
+			}
 		default:
 			if idx == 0 || base[len(base)-1] == "" {
 				base[len(base)-1] = ref
 			} else {
 				base = append(base, ref)
 			}
+			rm = false
 		}
 	}
 	return strings.Join(base, "/")

src/pkg/net/url/url_test.go

@@ -536,6 +536,15 @@ var resolveReferenceTests = []struct {
 	{"http://foo.com/bar/baz", "../../../../../quux", "http://foo.com/quux"},
 	{"http://foo.com/bar", "..", "http://foo.com/"},
 	{"http://foo.com/bar/baz", "./..", "http://foo.com/"},
+	// ".." in the middle (issue 3560)
+	{"http://foo.com/bar/baz", "quux/dotdot/../tail", "http://foo.com/bar/quux/tail"},
+	{"http://foo.com/bar/baz", "quux/./dotdot/../tail", "http://foo.com/bar/quux/tail"},
+	{"http://foo.com/bar/baz", "quux/./dotdot/.././tail", "http://foo.com/bar/quux/tail"},
+	{"http://foo.com/bar/baz", "quux/./dotdot/./../tail", "http://foo.com/bar/quux/tail"},
+	{"http://foo.com/bar/baz", "quux/./dotdot/dotdot/././../../tail", "http://foo.com/bar/quux/tail"},
+	{"http://foo.com/bar/baz", "quux/./dotdot/dotdot/./.././../tail", "http://foo.com/bar/quux/tail"},
+	{"http://foo.com/bar/baz", "quux/./dotdot/dotdot/dotdot/./../../.././././tail", "http://foo.com/bar/quux/tail"},
+	{"http://foo.com/bar/baz", "quux/./dotdot/../dotdot/../dot/./tail/..", "http://foo.com/bar/quux/dot"},
 
 	// "." and ".." in the base aren't special
 	{"http://foo.com/dot/./dotdot/../foo/bar", "../baz", "http://foo.com/dot/./dotdot/../baz"},