Merge #76476

76476: sql/pgwire: close cancel request conn as soon as possible r=otan a=rafiss

fixes #76231

Rather than closing in the defer block, do it sooner. This is because
some clients (e.g. PGJDBC) rely on timeout behavior where the connection
is closed as soon as the request data is read.

Release note: None

Co-authored-by: Rafi Shamim <rafi@cockroachlabs.com>

pkg/sql/pgwire/server.go

@@ -747,16 +747,15 @@ func (s *Server) handleCancel(ctx context.Context, conn net.Conn, buf *pgwirebas
 			log.Sessions.Warningf(ctx, "unexpected while handling pgwire cancellation request: %v", err)
 		}
 		telemetry.Inc(sqltelemetry.CancelRequestCounter)
-
-		// The connection that issued the cancel is not a SQL session -- it's an
-		// entirely new connection that's created just to send the cancel. There
-		// isn't anything left for the server to do after it handles the
-		// pgwire cancel request.
-		_ = conn.Close()
 	}()
 
 	var backendKeyDataBits uint64
 	backendKeyDataBits, err = buf.GetUint64()
+	// The connection that issued the cancel is not a SQL session -- it's an
+	// entirely new connection that's created just to send the cancel. We close
+	// the connection as soon as possible after reading the data, since there
+	// is nothing to send back to the client.
+	_ = conn.Close()
 	if err != nil {
 		return
 	}