Slices and memory leaks

Slicing an existing slice can lead to memory leaks under certain conditions.

Leaking capacity

Mistake

func getMessageType(msg []byte) []byte {
  return msg[:5] // This makes a slice with the same capacity as msg
}

Fix

func getMessageType(msg []byte) []byte {
  msgType := make([]byte, 5)
  copy(msgType, msg)
  return msgType
}

Slices and pointers

When working with slices, if the element is a pointer or a struct with pointer fields, it will not be collected by the garbage collector.

Either make a copy of the slice to remove unwanted elements or set the remaining slices to nil.

References

• 100 Go Mistakes