Implement GetManifest , Manifest, GetUtxoSnapshotChunk, UtxoSnapshotChunk p2p messages

[kushti]

Implement following new messages on top of #1514

• GetManifest - send manifest (BatchAVLProverManifest) identifier
• Manifest - do SnapshotsDb.readManifestBytes and send manifest bytes over wire
• GetUtxoSnapshotChunk - send utxo subtree (BatchAVLProverSubtree) identifier
• UtxoSnapshotChunk - do SnapshotsDb.readSubtreeBytes and send subtree bytes over wire

• tests

[knizhnik]

I wonder why SnapshotsDb.readSubtreeBytes and SnapshotsDb.readManifestBytes methods are called read*Bytes while them are actually returning deserialized BatchAVLProverManifest and BatchAVLProverSubtree?
Should I serialize them in array of bytes?
And is there any sense in serializing data fetched from the database to immediately serialize it back to send through network?

[kushti]

I wonder why SnapshotsDb.readSubtreeBytes and SnapshotsDb.readManifestBytes methods are called read*Bytes while them are actually returning deserialized BatchAVLProverManifest and BatchAVLProverSubtree? Should I serialize them in array of bytes? And is there any sense in serializing data fetched from the database to immediately serialize it back to send through network?

No sense in serialization round-trip just to send bytes over the wire.

Thus I think it is better to have SnapshotsDb.readSubtreeBytes / SnapshotsDb.readManifestBytes methods (reading bytes) along with SnapshotsDb.readSubtree / SnapshotsDb.readManifest (reading entities) , and use former for p2p messaging