tests added for Top cmd

* doc added for Top
* readme updated
* example Top function added in example/main.go

README.md

@@ -16,6 +16,7 @@ development. [RFC 1939](https://www.ietf.org/rfc/rfc1939.txt) document has been
 * NOOP
 * RSET
 * QUIT
+* TOP
 
 ### Installation
 
@@ -79,6 +80,10 @@ func main() {
 	// LIST <mail-num> command
 	ll, _ := pop.List(1)
 	fmt.Println(ll[0])
+
+	// TOP msgNum n 
+	top, _ := pop.Top(1, 10)
+	fmt.Println(top)
 
 	// DELE command
 	dele, err := pop.Dele("1")

example/main.go

@@ -44,6 +44,9 @@ func main() {
 	list, _ = pop.List(1) // LIST <arg> command
 	fmt.Println(list)     // 1st message size
 
+	top, _ := pop.Top(1, 10) // TOP msgNum n
+	fmt.Println(top)         // Headers, blank line, and top 10 line of the message body in an array
+
 	n, _ := pop.Noop() // NOOP command
 	fmt.Println(n)     // +OK
 

pop3/transaction.go

@@ -397,10 +397,31 @@ func (c *Client) pass(password string) (string, error) {
 	return passResp, nil
 }
 
+// Top is a command which fetches message (msgNum) with n lines. To get messages
+// from mail server, you need to authenticate. The response starts with "+OK"
+// status indicator, and it follows the multiline mail. The server sends header
+// of the message, the blank line separating the headers from the body, and then
+// the number of lines of the message's body. If you request the message line
+// number greater than the number of lines in the body, the mail server sends
+// the entire message.
+// Possible responses:
+// 		+OK message follows
+//		-ERR no such message
+// Example:
+//		C: TOP 1 10
+//		S: +OK message follows
+//		S: <headers of the message, blank line, and the first 10 lines of the body>
+//		S: .
+// 		...
+//		C: TOP 100 10
+//		S: -ERR no such message
+//
+// msgNum indicates message id starts from 1 and n is line of the message's body.
 func (c *Client) Top(msgNum, n int) ([]string, error) {
 	return c.top(msgNum, n)
 }
 
+// top is the implementation function of the Top function.
 func (c *Client) top(msgNum, n int) ([]string, error) {
 	if msgNum < 1 {
 		return nil, fmt.Errorf("%s message number should be greater than 0", e)

pop3/transaction_test.go

@@ -549,3 +549,63 @@ func TestTopNegativeN(t *testing.T) {
 	}
 	log.Println("Connection closed")
 }
+
+func TestTopNotLoggedIn(t *testing.T) {
+	pop, err := Connect(gmailTLSAddr, nil, true)
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+	log.Println("Connection established")
+
+	top, err := pop.Top(1, 20)
+	if err != nil {
+		t.Errorf("err need to be <nil>")
+	}
+	if !strings.HasPrefix(top[0], e) {
+		t.Errorf(top[0])
+	}
+	log.Println(top[0])
+	log.Println(err)
+}
+
+func TestTopPass(t *testing.T) {
+	pop, err := Connect(gmailTLSAddr, nil, true)
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+	log.Println("Connection established")
+
+	username := os.Getenv(userKey)
+	u, err := pop.User(username)
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+	if !strings.HasPrefix(u, ok) {
+		t.Errorf("expected: %s, got: %s", ok, u)
+	}
+
+	password := os.Getenv(passwordKey)
+	p, err := pop.Pass(password)
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+	if !strings.HasPrefix(p, ok) {
+		t.Errorf("expected: %s, got: %s", ok, p)
+	}
+
+	top, err := pop.Top(1, 20)
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+	if !strings.HasPrefix(top[0], ok) {
+		t.Errorf(top[0])
+	}
+	log.Println(top[0])
+
+	quit, err := pop.Quit()
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+	log.Println(quit)
+	log.Println("Connection closed")
+}