net/http/cookiejar: increase test coverage

The jarKey function handles broken PublicSuffixList implementations but
no test verified it.

Change-Id: Ifb76de9e8c3941f3b08d3e43970056e023013457
Reviewed-on: https://go-review.googlesource.com/38357Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/cookiejar/jar.go

@@ -345,6 +345,9 @@ func jarKey(host string, psl PublicSuffixList) string {
 			// Storing cookies under host is a safe stopgap.
 			return host
 		}
+		// Only len(suffix) is used to determine the jar key from
+		// here on, so it is okay if psl.PublicSuffix("www.buggy.psl")
+		// returns "com" as the jar key is generated from host.
 	}
 	prevDot := strings.LastIndex(host[:i-1], ".")
 	return host[prevDot+1:]

src/net/http/cookiejar/jar_test.go

@@ -19,6 +19,9 @@ var tNow = time.Date(2013, 1, 1, 12, 0, 0, 0, time.UTC)
 
 // testPSL implements PublicSuffixList with just two rules: "co.uk"
 // and the default rule "*".
+// The implementation has two intentional bugs:
+//    PublicSuffix("www.buggy.psl") == "xy"
+//    PublicSuffix("www2.buggy.psl") == "com"
 type testPSL struct{}
 
 func (testPSL) String() string {
@@ -28,6 +31,12 @@ func (testPSL) PublicSuffix(d string) string {
 	if d == "co.uk" || strings.HasSuffix(d, ".co.uk") {
 		return "co.uk"
 	}
+	if d == "www.buggy.psl" {
+		return "xy"
+	}
+	if d == "www2.buggy.psl" {
+		return "com"
+	}
 	return d[strings.LastIndex(d, ".")+1:]
 }
 
@@ -187,6 +196,8 @@ var jarKeyTests = map[string]string{
 	"co.uk":               "co.uk",
 	"uk":                  "uk",
 	"192.168.0.5":         "192.168.0.5",
+	"www.buggy.psl":       "www.buggy.psl",
+	"www2.buggy.psl":      "buggy.psl",
 	// The following are actual outputs of canonicalHost for
 	// malformed inputs to canonicalHost (see above).
 	"":              "",