Fix for base path copying bug

url/parser.go

@@ -223,7 +223,7 @@ func (p *parser) BasicParser(urlOrRef string, base *Url, url *Url, stateOverride
 				}
 			} else if base.path.isOpaque() && r == '#' {
 				url.scheme = base.scheme
-				url.path = base.path // TODO: Ensure copy????
+				url.path = base.path.copy()
 				url.query = base.query
 				url.fragment = new(string)
 				state = StateFragment
@@ -267,7 +267,7 @@ func (p *parser) BasicParser(urlOrRef string, base *Url, url *Url, stateOverride
 				url.host = base.host
 				url.port = base.port
 				url.decodedPort = base.decodedPort
-				url.path = base.path // TODO: Ensure copy????
+				url.path = base.path.copy()
 				url.query = base.query
 				if r == '?' {
 					url.query = new(string)
@@ -456,7 +456,7 @@ func (p *parser) BasicParser(urlOrRef string, base *Url, url *Url, stateOverride
 				state = StateFileSlash
 			} else if base != nil && base.scheme == "file" {
 				url.host = base.host
-				url.path = base.path // TODO: Ensure copy????
+				url.path = base.path.copy()
 				url.query = base.query
 				if r == '?' {
 					url.query = new(string)

url/path.go

@@ -48,6 +48,10 @@ func (p *path) stripTrailingSpacesIfOpaque() {
 	}
 }
 
+func (p *path) copy() *path {
+	return &path{p: append([]string{}, p.p...), opaque: p.opaque}
+}
+
 func (p *path) String() string {
 	if p.opaque {
 		return p.p[0]

url/url_test.go

@@ -481,3 +481,30 @@ func Test_DecodedPort(t *testing.T) {
 		t.Errorf("DecodedPort() = %v, want %v", u.DecodedPort(), defaultPort)
 	}
 }
+
+func TestURL_BasePathShouldNotChange(t *testing.T) {
+
+	// Test for behaviour described in issue #32
+	//
+	// Base URL path erroneously changes during Parse(),
+	// due to path struct being shared between both
+	// base Url and newly minted Url.
+	//
+	// https://github.com/nlnwa/whatwg-url/issues/32
+
+	baseURL := "http://example.org/ns/foo"
+	p := NewParser()
+	base, _ := p.Parse(baseURL)
+
+	expected := "http://example.org/ns/bar#"
+	u, _ := base.Parse("bar#")
+	// Sanity check expected behaviour
+	if u.String() != expected {
+		t.Errorf("Parse() = %v, want %v", u, expected)
+	}
+
+	// Ensure the base path has not changed during Parse()
+	if base.String() != baseURL {
+		t.Errorf("base URL = %v, want %v", base.String(), baseURL)
+	}
+}