Document and cleanup

example.go

@@ -16,31 +16,44 @@ type Example struct {
 	Next plugin.Handler
 }
 
-// ServeDNS implements the plugin.Handler interface.
+// ServeDNS implements the plugin.Handler interface. This method gets called when example is used
+// in a Server.
 func (e Example) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
-	// Somewhat convoluted, as we could have printed "example" here and just call
-	// the next plugin - but as an example, show how to wrap a ResponseWriter might be
-	// educational.
+	// This function could be simpler. I.e. just fmt.Println("example") here, but we want to show
+	// a slightly more complex example as to make this more interesting.
+	// Here we wrap the dns.ResponseWriter in a new ResponseWriter and call the next plugin, when the
+	// answer comes back, it will print "example".
+
+	// Wrap.
 	pw := NewResponsePrinter(w)
+
+	// Call next plugin (if any).
 	return plugin.NextOrFailure(e.Name(), e.Next, ctx, pw, r)
 }
 
 // Name implements the Handler interface.
 func (e Example) Name() string { return "example" }
 
+// ResponsePrinter wrap a dns.ResponseWriter and will write example to standard output when
+// WriteMsg is called.
 type ResponsePrinter struct {
 	dns.ResponseWriter
 }
 
-// NewResponsePrinter returns a dns.Msg modifier that print example when a query is received.
+// NewResponsePrinter returns ResponseWriter.
 func NewResponsePrinter(w dns.ResponseWriter) *ResponsePrinter {
 	return &ResponsePrinter{ResponseWriter: w}
 }
 
-// WriteMsg records the status code and calls the underlying ResponseWriter's WriteMsg method.
+// WriteMsg calls the underlying ResponseWriter's WriteMsg method and prints "example" to standard
+// output.
 func (r *ResponsePrinter) WriteMsg(res *dns.Msg) error {
-	fmt.Fprintf(out, "example")
+	fmt.Fprintln(out, ex)
 	return r.ResponseWriter.WriteMsg(res)
 }
 
+// Make out a reference to os.Stdout so we can easily overwrite it for testing.
 var out io.Writer = os.Stdout
+
+// What we will print.
+const ex = "example"

example_test.go

@@ -12,18 +12,24 @@ import (
 )
 
 func TestExample(t *testing.T) {
-	ex := Example{Next: test.ErrorHandler()}
+	// Create a new Example Plugin. Use the test.ErrorHandler as the next plugin.
+	x := Example{Next: test.ErrorHandler()}
 
+	// Setup a new output buffer that is *not* standard output, so we can check if
+	// example is really being printed.
 	b := &bytes.Buffer{}
 	out = b
 
 	ctx := context.TODO()
 	r := new(dns.Msg)
 	r.SetQuestion("example.org.", dns.TypeA)
+	// Create a new Recorder that captures the result, this isn't actually used in this test
+	// as it just serves as something that implements the dns.ResponseWriter interface.
 	rec := dnstest.NewRecorder(&test.ResponseWriter{})
 
-	ex.ServeDNS(ctx, rec, r)
-	if x := b.String(); x != "example" {
-		t.Errorf("Failed to print 'example', got %s", x)
+	// Call our plugin directly, and check the result.
+	x.ServeDNS(ctx, rec, r)
+	if a := b.String(); a != ex+"\n" {
+		t.Errorf("Failed to print '%s', got %s", ex, a)
 	}
 }

setup.go

@@ -7,6 +7,8 @@ import (
 	"github.com/mholt/caddy"
 )
 
+// init registers this plugin within the Caddy plugin framework. It uses "example" as the
+// name, and couples it to the Action "setup".
 func init() {
 	caddy.RegisterPlugin("example", caddy.Plugin{
 		ServerType: "dns",
@@ -14,15 +16,22 @@ func init() {
 	})
 }
 
+// setup is the function that gets called when the config parser see the token "example". Setup is responsible
+// for parsing any extra options the example plugin may have. The first token this function sees is "example".
 func setup(c *caddy.Controller) error {
-	c.Next()
+	c.Next() // Ignore "example" and give us the next token.
 	if c.NextArg() {
+		// If there was another token, return an error, because we don't have any configuration.
+		// Any errors returned from this setup function should be wrapped with plugin.Error, so we
+		// can present a slightly nicer error message to the user.
 		return plugin.Error("example", c.ArgErr())
 	}
 
+	// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
 		return Example{Next: next}
 	})
 
+	// All OK, return a nil error.
 	return nil
 }

setup_test.go

@@ -6,7 +6,9 @@ import (
 	"github.com/mholt/caddy"
 )
 
-func TestSetupWhoami(t *testing.T) {
+// TestSetup tests the various things that should be parsed by setup.
+// Make sure you also test for parse errors.
+func TestSetup(t *testing.T) {
 	c := caddy.NewTestController("dns", `example`)
 	if err := setup(c); err != nil {
 		t.Fatalf("Expected no errors, but got: %v", err)