Add hostname template action

This adds the ability to display the remote hostname
of the visitors IP with template actions.

caddyhttp/httpserver/context.go

@@ -63,6 +63,18 @@ func (c Context) Header(name string) string {
 	return c.Req.Header.Get(name)
 }
 
+// Hostname gets the (remote) hostname of the client making the request.
+func (c Context) Hostname() string {
+	ip := c.IP()
+
+	hostnameList, err := net.LookupAddr(ip)
+	if err != nil || len(hostnameList) == 0 {
+		return c.Req.RemoteAddr
+	}
+
+	return hostnameList[0]
+}
+
 // Env gets a map of the environment variables.
 func (c Context) Env() map[string]string {
 	osEnv := os.Environ()

caddyhttp/httpserver/context_test.go

@@ -244,6 +244,37 @@ func TestHeader(t *testing.T) {
 	}
 }
 
+func TestHostname(t *testing.T) {
+	context := getContextOrFail(t)
+
+	tests := []struct {
+		inputRemoteAddr  string
+		expectedHostname string
+	}{
+		// Test 0 - ipv4 with port
+		{"8.8.8.8:1111", "google-public-dns-a.google.com."},
+		// Test 1 - ipv4 without port
+		{"8.8.8.8", "google-public-dns-a.google.com."},
+		// Test 2 - ipv6 with port
+		{"[2001:4860:4860::8888]:11", "google-public-dns-a.google.com."},
+		// Test 3 - ipv6 without port and brackets
+		{"2001:4860:4860::8888", "google-public-dns-a.google.com."},
+		// Test 4 - no hostname available
+		{"1.1.1.1", "1.1.1.1"},
+	}
+
+	for i, test := range tests {
+		testPrefix := getTestPrefix(i)
+
+		context.Req.RemoteAddr = test.inputRemoteAddr
+		actualHostname := context.Hostname()
+
+		if actualHostname != test.expectedHostname {
+			t.Errorf(testPrefix+"Expected hostname %s, found %s", test.expectedHostname, actualHostname)
+		}
+	}
+}
+
 func TestEnv(t *testing.T) {
 	context := getContextOrFail(t)