eth/protocols/snap: fix snap sync failure on empty storage range

[rjl493456442]

This pull request addresses an issue in snap sync, specifically when the entire sync process can be halted due to an encountered empty storage range.

Currently, on the snap sync client side, the response to an empty storage range is discarded. However, this response is valid when there are no available storage slots within that range.

For instance, consider a large contract where the entire key space is divided into 16 chunks, and there are no available slots in the last chunk [0xf] -> [end]. When the node receives a request for this particular range, the response includes:

• The proof with origin [0xf]
• A nil storage slot set

If we simply discard this response, the finalization of the last range will be skipped, halting the entire sync process indefinitely. The test case TestSyncWithUnevenStorage can reproduce the scenario described above.

Besides, this pull request also defines the common variables MaxAddress and MaxHash.

[holiman]

FYI, there was no existing test which triggered the chunked-storage-fetch, so I added one here: 2d426e9#diff-25511a64fb71eea2da50f30896725bd1e6f88edd887ee74f7b70bf2685b24059R791 . Might be useful for you too?

[rjl493456442]

@holiman I have something to trigger the chunked-storage https://github.com/ethereum/go-ethereum/pull/28306/files#diff-25511a64fb71eea2da50f30896725bd1e6f88edd887ee74f7b70bf2685b24059R1445

[holiman]

How about something like this?

Suggested change

	for i := 0; i < 3; i++ {
	var n int
	for {
	n = mrand.Intn(15) // the last range is set empty deliberately
	if _, ok := chosen[byte(n)]; ok {
	continue
	}
	chosen[byte(n)] = struct{}{}
	break
	}
	for j := 0; j < slots/3; j++ {
	key := append([]byte{byte(n)}, testutil.RandBytes(31)...)
	val, _ := rlp.EncodeToBytes(testutil.RandBytes(32))
	elem := &kv{key, val}
	tr.MustUpdate(elem.k, elem.v)
	entries = append(entries, elem)
	}
	}
	for i := 0; i < slots; i++ {
	key := testutil.RandBytes(32)
	if key[0] >= 0x80 {
	key[0] -= 0x80
	}
	val, _ := rlp.EncodeToBytes(testutil.RandBytes(32))
	elem := &kv{key, val}
	tr.MustUpdate(elem.k, elem.v)
	entries = append(entries, elem)
	}

[holiman]

Actually, if I do

               if key[0] >= 0x80 {
                       key[0] = 0x00
               }

Then I start to hit the edgecase we want to repro pretty often

[holiman]

The changes looks good to me, but the testcase should be improved: it almost never triggers the condition as far as I can tell.

[holiman]

but the testcase should be improved: it almost never triggers the condition as far as I can tell.

I take that back, it seems ok to me!

[rjl493456442]

Deployed it on 05, and it can finish snap sync.