Can not distinguish between "does not exist" and "has no value"

[ceving]

I wrote the pwned passwords into a bucket. Because I only need to know if the hash exists, I wrote an empty value into the bucket.

err := hashes.Put(hash, []byte{})

Now I tried to find a hash, but I had to realize that Go does not distinguish between an empty array and nil. The problem is: Bolt returns nil to indicate that a key does not exist. This is a problem because of Go's limitation.

How to store keys without values in order to check just for existence?

I think Bucket.Get needs to return an additional boolean or Bucket needs an additional function to check just for existence.

Go itself also indicates the existence of a key in a map by an additional boolean:

i, ok := m["route"]

[Elbehery]

@ceving Get returns nil if the key does not exist, or the value is a nested bucket

this could be a feature cc @ahrtr @fuweid @tjungblu @ivanvc

[ahrtr]

For the case of "does not exist", bucket.Get returns nil.

For the case "has no value", bucket.Get returns []byte{}, which is obviously not nil.

The only known minor problem is that even you write a nil value for a key, when you read it back in a separate transaction, it still returns []byte{}.

[ahrtr]

For example,

func TestBucket_Get_NonExistent(t *testing.T) {
	db := btesting.MustCreateDB(t)

	if err := db.Update(func(tx *bolt.Tx) error {
		b, err := tx.CreateBucket([]byte("widgets"))
		if err != nil {
			t.Fatal(err)
		}
		return b.Put([]byte("foo"), nil)
	}); err != nil {
		t.Fatal(err)
	}

	db.View(func(tx *bolt.Tx) error {
		b := tx.Bucket([]byte("widgets"))
		if v := b.Get([]byte("foo")); v != nil {
			t.Fatal("expected nil value")  // The test case will fail here.
		}
		return nil
	})
}

[ahrtr]

In short, no matter what value you write into bbolt, when you read it back, you will always get []byte{} as long as len(value) == 0 is true.

The only exception is that when you write a nil value, and you will still get a nil value when you read it back in the same transaction.

Will raise a PR to add a known issue.

[ahrtr]

Completed in #730