feat: add test and fix the error of not sending a ServerLost error on server side error (#11930)

Signed-off-by: Manan Gupta <manan@planetscale.com>

Signed-off-by: Manan Gupta <manan@planetscale.com>
Co-authored-by: Manan Gupta <manan@planetscale.com>

go/mysql/conn_flaky_test.go

@@ -1034,6 +1034,15 @@ func (t testRun) ComQuery(c *Conn, query string, callback func(*sqltypes.Result)
 	if strings.Contains(query, "panic") {
 		panic("test panic attack!")
 	}
+	if strings.Contains(query, "close before rows read") {
+		c.writeFields(selectRowsResult)
+		// We want to close the connection after the fields are written
+		// and read on the client. So we sleep for 100 milliseconds
+		time.Sleep(100 * time.Millisecond)
+		c.Close()
+		return nil
+	}
+
 	if strings.Contains(query, "twice") {
 		callback(selectRowsResult)
 	}

go/mysql/query.go

@@ -416,7 +416,7 @@ func (c *Conn) ReadQueryResult(maxrows int, wantfields bool) (*sqltypes.Result,
 	for {
 		data, err := c.readEphemeralPacket()
 		if err != nil {
-			return nil, false, 0, err
+			return nil, false, 0, NewSQLError(CRServerLost, SSUnknownSQLState, "%v", err)
 		}
 
 		if c.isEOFPacket(data) {

go/mysql/query_test.go

@@ -375,6 +375,32 @@ func TestComStmtClose(t *testing.T) {
 	}
 }
 
+// This test has been added to verify that IO errors in a connection lead to SQL Server lost errors
+// So that we end up closing the connection higher up the stack and not reusing it.
+// This test was added in response to a panic that was run into.
+func TestSQLErrorOnServerClose(t *testing.T) {
+	// Create socket pair for the server and client
+	listener, sConn, cConn := createSocketPair(t)
+	defer func() {
+		listener.Close()
+		sConn.Close()
+		cConn.Close()
+	}()
+
+	err := cConn.WriteComQuery("close before rows read")
+	require.NoError(t, err)
+
+	handler := &testRun{t: t}
+	_ = sConn.handleNextCommand(handler)
+
+	// From the server we will receive a field packet which the client will read
+	// At that point, if the server crashes and closes the connection.
+	// We should be getting a Connection lost error.
+	_, _, _, err = cConn.ReadQueryResult(100, true)
+	require.Error(t, err)
+	require.True(t, IsConnLostDuringQuery(err), err.Error())
+}
+
 func TestQueries(t *testing.T) {
 	listener, sConn, cConn := createSocketPair(t)
 	defer func() {