From f539368a80df93b1851003ba43893eb63d62a9a9 Mon Sep 17 00:00:00 2001
From: Aleksandr Razumov <ar@cydev.ru>
Date: Sun, 29 Apr 2018 14:20:09 +0300
Subject: [PATCH] client: add initialization checks

---
 client.go      | 33 +++++++++++++++++++++------------
 client_test.go | 15 +++++++++++----
 2 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/client.go b/client.go
index 73124b5..a65bd90 100644
--- a/client.go
+++ b/client.go
@@ -182,6 +182,9 @@ var ErrClientClosed = errors.New("client is closed")
 
 // Close stops internal connection and agent, returning CloseErr on error.
 func (c *Client) Close() error {
+	if err := c.checkInit(); err != nil {
+		return err
+	}
 	c.closedMux.Lock()
 	if c.closed {
 		c.closedMux.Unlock()
@@ -189,18 +192,8 @@ func (c *Client) Close() error {
 	}
 	c.closed = true
 	c.closedMux.Unlock()
-	var (
-		agentErr, connErr error
-	)
-	if c.a != nil {
-		agentErr = c.a.Close()
-	}
-	if c.c != nil {
-		connErr = c.c.Close()
-	}
-	if c.close != nil {
-		close(c.close)
-	}
+	agentErr, connErr := c.a.Close(), c.c.Close()
+	close(c.close)
 	c.wg.Wait()
 	if agentErr == nil && connErr == nil {
 		return nil
@@ -263,12 +256,25 @@ var callbackWaitHandlerPool = sync.Pool{
 	},
 }
 
+// ErrClientNotInitialized means that client connection or agent is nil.
+var ErrClientNotInitialized = errors.New("client not initialized")
+
+func (c *Client) checkInit() error {
+	if c == nil || c.c == nil || c.a == nil || c.close == nil {
+		return ErrClientNotInitialized
+	}
+	return nil
+}
+
 // Do is Start wrapper that waits until callback is called. If no callback
 // provided, Indicate is called instead.
 //
 // Do has cpu overhead due to blocking, see BenchmarkClient_Do.
 // Use Start method for less overhead.
 func (c *Client) Do(m *Message, d time.Time, f func(Event)) error {
+	if err := c.checkInit(); err != nil {
+		return err
+	}
 	if f == nil {
 		return c.Indicate(m)
 	}
@@ -288,6 +294,9 @@ func (c *Client) Do(m *Message, d time.Time, f func(Event)) error {
 // Start starts transaction (if f set) and writes message to server, handler
 // is called asynchronously.
 func (c *Client) Start(m *Message, d time.Time, h Handler) error {
+	if err := c.checkInit(); err != nil {
+		return err
+	}
 	c.closedMux.RLock()
 	closed := c.closed
 	c.closedMux.RUnlock()
diff --git a/client_test.go b/client_test.go
index df3c4d0..688fc2f 100644
--- a/client_test.go
+++ b/client_test.go
@@ -447,6 +447,15 @@ func TestClientGC(t *testing.T) {
 	}
 }
 
+func TestClientCheckInit(t *testing.T) {
+	if err := (&Client{}).Indicate(nil); err != ErrClientNotInitialized {
+		t.Error("unexpected error")
+	}
+	if err := (&Client{}).Do(nil, time.Time{}, nil); err != ErrClientNotInitialized {
+		t.Error("unexpected error")
+	}
+}
+
 func TestClientFinalizer(t *testing.T) {
 	var buf bytes.Buffer
 	log.SetOutput(&buf)
@@ -466,9 +475,7 @@ func TestClientFinalizer(t *testing.T) {
 	if err != nil {
 		log.Fatal(err)
 	}
-	if err := c.Close(); err != nil {
-		t.Error(err)
-	}
+	clientFinalizer(c)
 	clientFinalizer(c)
 	response := MustBuild(TransactionID, BindingSuccess)
 	response.Encode()
@@ -497,7 +504,7 @@ func TestClientFinalizer(t *testing.T) {
 	if reader.Err() != nil {
 		t.Error(err)
 	}
-	if lines != 2 {
+	if lines != 3 {
 		t.Error("incorrect count of log lines:", lines)
 	}
 }