API: Fix global URL when external address has no port (#8359)

* API: Fix global URL when external address has no port

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

* Update test

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

* Handle IPv6 correctly.

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

web/api/v1/api.go

@@ -82,7 +82,7 @@ const (
 )
 
 var (
-	LocalhostRepresentations = []string{"127.0.0.1", "localhost"}
+	LocalhostRepresentations = []string{"127.0.0.1", "localhost", "::1"}
 	remoteReadQueries        = prometheus.NewGauge(prometheus.GaugeOpts{
 		Namespace: namespace,
 		Subsystem: subsystem,
@@ -750,8 +750,24 @@ type GlobalURLOptions struct {
 	Scheme        string
 }
 
+// sanitizeSplitHostPort acts like net.SplitHostPort.
+// Additionally, if there is no port in the host passed as input, we return the
+// original host, making sure that IPv6 addresses are not surrounded by square
+// brackets.
+func sanitizeSplitHostPort(input string) (string, string, error) {
+	host, port, err := net.SplitHostPort(input)
+	if err != nil && strings.HasSuffix(err.Error(), "missing port in address") {
+		var errWithPort error
+		host, _, errWithPort = net.SplitHostPort(input + ":80")
+		if errWithPort == nil {
+			err = nil
+		}
+	}
+	return host, port, err
+}
+
 func getGlobalURL(u *url.URL, opts GlobalURLOptions) (*url.URL, error) {
-	host, port, err := net.SplitHostPort(u.Host)
+	host, port, err := sanitizeSplitHostPort(u.Host)
 	if err != nil {
 		return u, err
 	}
@@ -778,11 +794,14 @@ func getGlobalURL(u *url.URL, opts GlobalURLOptions) (*url.URL, error) {
 				// externally, so we replace only the hostname by the one in the
 				// external URL. It could be the wrong hostname for the service on
 				// this port, but it's still the best possible guess.
-				host, _, err := net.SplitHostPort(opts.Host)
+				host, _, err := sanitizeSplitHostPort(opts.Host)
 				if err != nil {
 					return u, err
 				}
-				u.Host = host + ":" + port
+				u.Host = host
+				if port != "" {
+					u.Host = net.JoinHostPort(u.Host, port)
+				}
 			}
 			break
 		}

web/api/v1/api_test.go

@@ -2926,3 +2926,111 @@ func BenchmarkRespond(b *testing.B) {
 		api.respond(&testResponseWriter, response, nil)
 	}
 }
+
+func TestGetGlobalURL(t *testing.T) {
+	mustParseURL := func(t *testing.T, u string) *url.URL {
+		parsed, err := url.Parse(u)
+		require.NoError(t, err)
+		return parsed
+	}
+
+	testcases := []struct {
+		input    *url.URL
+		opts     GlobalURLOptions
+		expected *url.URL
+		errorful bool
+	}{
+		{
+			mustParseURL(t, "http://127.0.0.1:9090"),
+			GlobalURLOptions{
+				ListenAddress: "127.0.0.1:9090",
+				Host:          "127.0.0.1:9090",
+				Scheme:        "http",
+			},
+			mustParseURL(t, "http://127.0.0.1:9090"),
+			false,
+		},
+		{
+			mustParseURL(t, "http://127.0.0.1:9090"),
+			GlobalURLOptions{
+				ListenAddress: "127.0.0.1:9090",
+				Host:          "prometheus.io",
+				Scheme:        "https",
+			},
+			mustParseURL(t, "https://prometheus.io"),
+			false,
+		},
+		{
+			mustParseURL(t, "http://exemple.com"),
+			GlobalURLOptions{
+				ListenAddress: "127.0.0.1:9090",
+				Host:          "prometheus.io",
+				Scheme:        "https",
+			},
+			mustParseURL(t, "http://exemple.com"),
+			false,
+		},
+		{
+			mustParseURL(t, "http://localhost:8080"),
+			GlobalURLOptions{
+				ListenAddress: "127.0.0.1:9090",
+				Host:          "prometheus.io",
+				Scheme:        "https",
+			},
+			mustParseURL(t, "http://prometheus.io:8080"),
+			false,
+		},
+		{
+			mustParseURL(t, "http://[::1]:8080"),
+			GlobalURLOptions{
+				ListenAddress: "127.0.0.1:9090",
+				Host:          "prometheus.io",
+				Scheme:        "https",
+			},
+			mustParseURL(t, "http://prometheus.io:8080"),
+			false,
+		},
+		{
+			mustParseURL(t, "http://localhost"),
+			GlobalURLOptions{
+				ListenAddress: "127.0.0.1:9090",
+				Host:          "prometheus.io",
+				Scheme:        "https",
+			},
+			mustParseURL(t, "http://prometheus.io"),
+			false,
+		},
+		{
+			mustParseURL(t, "http://localhost:9091"),
+			GlobalURLOptions{
+				ListenAddress: "[::1]:9090",
+				Host:          "[::1]",
+				Scheme:        "https",
+			},
+			mustParseURL(t, "http://[::1]:9091"),
+			false,
+		},
+		{
+			mustParseURL(t, "http://localhost:9091"),
+			GlobalURLOptions{
+				ListenAddress: "[::1]:9090",
+				Host:          "[::1]:9090",
+				Scheme:        "https",
+			},
+			mustParseURL(t, "http://[::1]:9091"),
+			false,
+		},
+	}
+
+	for i, tc := range testcases {
+		t.Run(fmt.Sprintf("Test %d", i), func(t *testing.T) {
+			output, err := getGlobalURL(tc.input, tc.opts)
+			if tc.errorful {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			require.Equal(t, tc.expected, output)
+		})
+	}
+}