linter: (1/2) enable errcheck (#5064)

## Description

partially cleanup in preparation for errcheck

i ignored a bunch of defer errors in tests but with the update to go 1.14 we can use `t.Cleanup(func() { if err := <>; err != nil {..}}` to cover those errors, I will do this in pr number two of enabling errcheck.

ref #5059

rpc/client/mock/abci.go

@@ -61,7 +61,7 @@ func (a ABCIApp) BroadcastTxAsync(tx types.Tx) (*ctypes.ResultBroadcastTx, error
 	c := a.App.CheckTx(abci.RequestCheckTx{Tx: tx})
 	// and this gets written in a background thread...
 	if !c.IsErr() {
-		go func() { a.App.DeliverTx(abci.RequestDeliverTx{Tx: tx}) }() // nolint: errcheck
+		go func() { a.App.DeliverTx(abci.RequestDeliverTx{Tx: tx}) }()
 	}
 	return &ctypes.ResultBroadcastTx{
 		Code:      c.Code,
@@ -76,7 +76,7 @@ func (a ABCIApp) BroadcastTxSync(tx types.Tx) (*ctypes.ResultBroadcastTx, error)
 	c := a.App.CheckTx(abci.RequestCheckTx{Tx: tx})
 	// and this gets written in a background thread...
 	if !c.IsErr() {
-		go func() { a.App.DeliverTx(abci.RequestDeliverTx{Tx: tx}) }() // nolint: errcheck
+		go func() { a.App.DeliverTx(abci.RequestDeliverTx{Tx: tx}) }()
 	}
 	return &ctypes.ResultBroadcastTx{
 		Code:      c.Code,

rpc/jsonrpc/client/http_json_client.go

@@ -177,7 +177,7 @@ func (c *Client) Call(method string, params map[string]interface{}, result inter
 	if err != nil {
 		return nil, fmt.Errorf("post failed: %w", err)
 	}
-	defer httpResponse.Body.Close() // nolint: errcheck
+	defer httpResponse.Body.Close()
 
 	responseBytes, err := ioutil.ReadAll(httpResponse.Body)
 	if err != nil {
@@ -221,7 +221,7 @@ func (c *Client) sendBatch(requests []*jsonRPCBufferedRequest) ([]interface{}, e
 	if err != nil {
 		return nil, fmt.Errorf("post failed: %w", err)
 	}
-	defer httpResponse.Body.Close() // nolint: errcheck
+	defer httpResponse.Body.Close()
 
 	responseBytes, err := ioutil.ReadAll(httpResponse.Body)
 	if err != nil {

rpc/jsonrpc/client/http_uri_client.go

@@ -59,7 +59,7 @@ func (c *URIClient) Call(method string, params map[string]interface{}, result in
 	if err != nil {
 		return nil, fmt.Errorf("post form failed: %w", err)
 	}
-	defer resp.Body.Close() // nolint: errcheck
+	defer resp.Body.Close()
 
 	responseBytes, err := ioutil.ReadAll(resp.Body)
 	if err != nil {

rpc/jsonrpc/client/ws_client_test.go

@@ -34,7 +34,7 @@ func (h *myHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		panic(err)
 	}
-	defer conn.Close() // nolint: errcheck
+	defer conn.Close()
 	for {
 		messageType, in, err := conn.ReadMessage()
 		if err != nil {
@@ -72,7 +72,7 @@ func TestWSClientReconnectsAfterReadFailure(t *testing.T) {
 	defer s.Close()
 
 	c := startClient(t, "//"+s.Listener.Addr().String())
-	defer c.Stop()
+	defer c.Stop() // nolint:errcheck // ignore for tests
 
 	wg.Add(1)
 	go callWgDoneOnResult(t, c, &wg)
@@ -104,7 +104,7 @@ func TestWSClientReconnectsAfterWriteFailure(t *testing.T) {
 	s := httptest.NewServer(h)
 
 	c := startClient(t, "//"+s.Listener.Addr().String())
-	defer c.Stop()
+	defer c.Stop() // nolint:errcheck // ignore for tests
 
 	wg.Add(2)
 	go callWgDoneOnResult(t, c, &wg)
@@ -132,7 +132,7 @@ func TestWSClientReconnectFailure(t *testing.T) {
 	s := httptest.NewServer(h)
 
 	c := startClient(t, "//"+s.Listener.Addr().String())
-	defer c.Stop()
+	defer c.Stop() // nolint:errcheck // ignore for tests
 
 	go func() {
 		for {
@@ -181,14 +181,15 @@ func TestNotBlockingOnStop(t *testing.T) {
 	timeout := 2 * time.Second
 	s := httptest.NewServer(&myHandler{})
 	c := startClient(t, "//"+s.Listener.Addr().String())
-	c.Call(context.Background(), "a", make(map[string]interface{}))
+	c.Call(context.Background(), "a", make(map[string]interface{})) // nolint:errcheck // ignore for tests
 	// Let the readRoutine get around to blocking
 	time.Sleep(time.Second)
 	passCh := make(chan struct{})
 	go func() {
 		// Unless we have a non-blocking write to ResponsesCh from readRoutine
 		// this blocks forever ont the waitgroup
-		c.Stop()
+		err := c.Stop()
+		require.NoError(t, err)
 		passCh <- struct{}{}
 	}()
 	select {

rpc/jsonrpc/server/http_server_test.go

@@ -37,7 +37,7 @@ func TestMaxOpenConnections(t *testing.T) {
 	l, err := Listen("tcp://127.0.0.1:0", config)
 	require.NoError(t, err)
 	defer l.Close()
-	go Serve(l, mux, log.TestingLogger(), config)
+	go Serve(l, mux, log.TestingLogger(), config) //nolint:errcheck // ignore for tests
 
 	// Make N GET calls to the server.
 	attempts := max * 2
@@ -55,7 +55,8 @@ func TestMaxOpenConnections(t *testing.T) {
 				return
 			}
 			defer r.Body.Close()
-			io.Copy(ioutil.Discard, r.Body)
+			_, err = io.Copy(ioutil.Discard, r.Body)
+			require.NoError(t, err)
 		}()
 	}
 	wg.Wait()

rpc/jsonrpc/test/main.go

@@ -38,5 +38,8 @@ func main() {
 	if err != nil {
 		tmos.Exit(err.Error())
 	}
-	rpcserver.Serve(listener, mux, logger, config)
+
+	if err = rpcserver.Serve(listener, mux, logger, config); err != nil {
+		tmos.Exit(err.Error())
+	}
 }