URL should have an empty Scheme if there is an invalid character (i.e.

not [a-zA-Z0-9+-.]) before there is a ":".

This is particularly helpful in the erroneous-but-relatively-common
case of relative URLs containing an unescaped colon in the query
string--see the added test for an example.

R=rsc
APPROVED=rsc
DELTA=15  (15 added, 0 deleted, 0 changed)
OCL=30354
CL=30356

src/pkg/http/url.go

@@ -180,6 +180,10 @@ func getscheme(rawurl string) (scheme, path string, err os.Error) {
 				return "", "", BadURL{"missing protocol scheme"}
 			}
 			return rawurl[0:i], rawurl[i+1:len(rawurl)], nil
+		default:
+			// we have encountered an invalid character,
+			// so there is no valid scheme
+			return "", rawurl, nil
 		}
 	}
 	return "", rawurl, nil

src/pkg/http/url_test.go

@@ -134,6 +134,17 @@ var urltests = []URLTest {
 		},
 		""
 	},
+	// unescaped :// in query should not create a scheme
+	URLTest{
+		"/foo?query=http://bad",
+		&URL{
+			"/foo?query=http://bad",
+			"", "/foo?query=http://bad",
+			"", "", "",
+			"/foo", "query=http://bad", ""
+		},
+		""
+	},
 }
 
 var urlnofragtests = []URLTest {