Better error messages

internal/nbconn/nbconn.go

@@ -13,7 +13,6 @@ package nbconn
 import (
 	"crypto/tls"
 	"errors"
-	"fmt"
 	"net"
 	"os"
 	"sync"
@@ -162,11 +161,7 @@ func (c *NetConn) Read(b []byte) (n int, err error) {
 	var readN int
 	if readNonblocking {
 		if setSockModeErr := c.SetBlockingMode(false); setSockModeErr != nil {
-			err = fmt.Errorf("cannot set socket to non-blocking mode: %w", setSockModeErr)
-		}
-
-		if err != nil {
-			return n, err
+			return n, setSockModeErr
 		}
 
 		defer func() {
@@ -298,7 +293,7 @@ func (c *NetConn) flush() error {
 	var errChan chan error
 
 	if err := c.SetBlockingMode(false); err != nil {
-		return fmt.Errorf("cannot set socket to non-blocking mode: %w", err)
+		return err
 	}
 
 	defer func() {
@@ -349,7 +344,7 @@ func (c *NetConn) flush() error {
 
 func (c *NetConn) BufferReadUntilBlock() error {
 	if err := c.SetBlockingMode(false); err != nil {
-		return fmt.Errorf("cannot set socket to non-blocking mode: %w", err)
+		return err
 	}
 
 	defer func() {

internal/nbconn/nbconn_real_non_block_windows.go

@@ -4,6 +4,7 @@ package nbconn
 
 import (
 	"errors"
+	"fmt"
 	"golang.org/x/sys/windows"
 	"io"
 	"syscall"
@@ -154,19 +155,20 @@ func (c *NetConn) SetBlockingMode(blocking bool) error {
 	})
 
 	if ctrlErr != nil || err != nil {
+		retErr := ctrlErr
+		if retErr == nil {
+			retErr = err
+		}
+
 		// Revert counters inc/dec in case of error
 		if blocking {
 			c.nbOperCnt.Add(1)
+
+			return fmt.Errorf("cannot set socket to blocking mode: %w", retErr)
 		} else {
 			c.nbOperCnt.Add(-1)
-		}
 
-		if ctrlErr != nil {
-			return ctrlErr
-		}
-
-		if err != nil {
-			return err
+			return fmt.Errorf("cannot set socket to non-blocking mode: %w", retErr)
 		}
 	}