async: ensure connection close error is set (#180)

The previous implementation had a couple of issues that could cause
closeWithError() to not propagate the passed error properly.

1. c.error.Store() is only called after c.close(), which could cause the
   channel returned by CloseChannel() to be closed before the error is
   set. Callers that that block on the channel may attempt to read the
   error before it is set.
2. If c.close() fails, closeError is returned, but not set to
   c.error.Store(), causing callers to miss it. Additionally, the
   original error is ignored and not made available to callers at all.

To fix these issues, closeWithError() is updated to set c.error before
calling c.close() and all errors are returned and set to c.error by
using errors.Join().

In order to support different kinds of concrete error types, the type of
the error field had to be changed from atomic.Value to error.

Signed-off-by: Luiz Aoqui <[email protected]>

async.go

@@ -37,7 +37,8 @@ type Async struct {
 	stale              []*packet.Packet
 	logger             types.Logger
 	wg                 sync.WaitGroup
-	error              atomic.Value
+	errorMu            sync.RWMutex
+	error              error
 	streamsMu          sync.Mutex
 	streams            map[uint16]*Stream
 	newStreamHandlerMu sync.Mutex
@@ -241,11 +242,9 @@ func (c *Async) Logger() types.Logger {
 
 // Error returns the error that caused the frisbee.Async connection to close
 func (c *Async) Error() error {
-	err := c.error.Load()
-	if err == nil {
-		return nil
-	}
-	return err.(error)
+	c.errorMu.RLock()
+	defer c.errorMu.RUnlock()
+	return c.error
 }
 
 // Closed returns whether the frisbee.Async connection is closed
@@ -424,12 +423,16 @@ func (c *Async) close() error {
 }
 
 func (c *Async) closeWithError(err error) error {
+	c.errorMu.Lock()
+	defer c.errorMu.Unlock()
+
+	c.error = err
 	closeError := c.close()
 	if closeError != nil {
 		c.Logger().Debug().Err(closeError).Msgf("attempted to close connection with error `%s`, but got error while closing", err)
-		return closeError
+		c.error = errors.Join(closeError, err)
+		return c.error
 	}
-	c.error.Store(err)
 	_ = c.conn.Close()
 	return err
 }