Added split test buffer that shows the subject overwritte

With this test, and with previous cloneArg() code, the parsing
will cause subject to become "fff" because c.pa.subject points
to somewhere in the underlying buffer that is now overwritten
with the body payload. With proper cloneArg(), the c.pa.subject
(and other) point to the copy of argBuf.

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

server/split_test.go

@@ -515,3 +515,53 @@ func TestSplitBufferMsgOp(t *testing.T) {
 		t.Fatalf("Expected MSG_END_N state vs %d\n", c.state)
 	}
 }
+
+func TestSplitBufferLeafMsgArg(t *testing.T) {
+	c := &client{msubs: -1, mpay: -1, mcl: 1024, subs: make(map[string]*subscription), kind: LEAF}
+	msg := []byte("LMSG foo + bar baz 11\r\n")
+	if err := c.parse(msg); err != nil {
+		t.Fatalf("Unexpected parse error: %v\n", err)
+	}
+	if c.state != MSG_PAYLOAD {
+		t.Fatalf("Expected MSG_PAYLOAD state vs %d\n", c.state)
+	}
+	checkPA := func(t *testing.T) {
+		t.Helper()
+		if !bytes.Equal(c.pa.subject, []byte("foo")) {
+			t.Fatalf("Expected subject to be %q, got %q", "foo", c.pa.subject)
+		}
+		if !bytes.Equal(c.pa.reply, []byte("bar")) {
+			t.Fatalf("Expected reply to be %q, got %q", "bar", c.pa.reply)
+		}
+		if n := len(c.pa.queues); n != 1 {
+			t.Fatalf("Expected 1 queue, got %v", n)
+		}
+		if !bytes.Equal(c.pa.queues[0], []byte("baz")) {
+			t.Fatalf("Expected queues to be %q, got %q", "baz", c.pa.queues)
+		}
+	}
+	checkPA(t)
+
+	// overwrite msg with payload
+	n := copy(msg, []byte("fffffffffff"))
+	if err := c.parse(msg[:n]); err != nil {
+		t.Fatalf("Unexpected parse error: %v\n", err)
+	}
+	if c.state != MSG_END_R {
+		t.Fatalf("Expected MSG_END_R state vs %d\n", c.state)
+	}
+	checkPA(t)
+
+	// Finish processing
+	copy(msg, []byte("\r\n"))
+	if err := c.parse(msg[:2]); err != nil {
+		t.Fatalf("Unexpected parse error: %v\n", err)
+	}
+	if c.state != OP_START {
+		t.Fatalf("Expected OP_START state vs %d\n", c.state)
+	}
+	if c.pa.subject != nil || c.pa.reply != nil || c.pa.queues != nil || c.pa.size != 0 ||
+		c.pa.szb != nil || c.pa.arg != nil {
+		t.Fatalf("parser state not cleaned-up properly: %+v", c.pa)
+	}
+}