feat(dsn): add example

dsn/example_test.go

@@ -0,0 +1,39 @@
+package dsn_test
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/jhillyerd/enmime"
+	"github.com/jhillyerd/enmime/dsn"
+)
+
+// ExampleParseReport shows how to parse message as Delivery Status Notification (DSN).
+func ExampleParseReport() {
+	f, err := os.Open("testdata/simple_dsn.raw")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	defer f.Close()
+
+	env, err := enmime.ReadEnvelope(f)
+	if err != nil {
+		fmt.Print(err)
+		return
+	}
+
+	rep, err := dsn.ParseReport(env.Root)
+	if err != nil {
+		fmt.Print(err)
+		return
+	}
+
+	fmt.Printf("Original message: %s", rep.OriginalMessage)
+	fmt.Printf("Failed?: %t\n", dsn.IsFailed(rep.DeliveryStatus.RecipientDSNs[0]))
+	fmt.Printf("Why?: %s", rep.Explanation.Text)
+	// Output:
+	// Original message: [original message goes here]
+	// Failed?: true
+	// Why?: [human-readable explanation goes here]
+}