Send inbound TransactionsById requests to the mempool storage service

[hdevalence]

Is your feature request related to a problem? Please describe.

The zebra_network::Request::TransactionsById variant should be handled by the inbound network service.

Describe the solution you'd like

• This page on the Bitcoin wiki https://en.bitcoin.it/wiki/Protocol_documentation#getdata suggests that transaction lookup is only allowed for mempool transactions, to prevent reliance on nodes having transaction indexes. We should check what zcashd does.

• The inbound network service should query the mempool for those transactions and construct a response.

• The response should consist of the found transactions, followed by a list of NotFound hashes

  • zcashd ignores NotFound, but its code says that SPV clients rely on NotFound. Do SPV clients exist on the Zcash network?

Additional context

See:

• https://developer.bitcoin.org/reference/p2p_networking.html#getdata
• https://developer.bitcoin.org/reference/p2p_networking.html#tx
• https://developer.bitcoin.org/reference/p2p_networking.html#notfound

Blocked on actually having a mempool. Part of #889.

[oxarbitrage]

The TransactionsByHash was renamed to TransactionsById in c608260 so i changed the title and the contents of this ticket as it confused me to create a new request but it is not needed.

[teor2345]

The TransactionsByHash was renamed to TransactionsById in c608260 so i changed the title and the contents of this ticket as it confused me to create a new request but it is not needed.

Thanks!

Sorry I missed this ticket, I changed most of the names last week.

[oxarbitrage]

The reply to this message is actually 2 replies. One will have the transactions in the mempool we found but we also need to send a notfound message with a list of not found hashes.

This is what i think we can do and some questions i have:

1- Add code in https://github.com/ZcashFoundation/zebra/blob/main/zebrad/src/components/inbound.rs#L284 that will call https://github.com/ZcashFoundation/zebra/blob/main/zebrad/src/components/mempool.rs#L83 that will call https://github.com/ZcashFoundation/zebra/blob/main/zebrad/src/components/mempool/storage.rs#L100

2- That will get us a collection on what was found in the mempool. We can compare with the hashes in the request we have available here https://github.com/ZcashFoundation/zebra/blob/main/zebrad/src/components/inbound.rs#L284 and construct an additional response with not found hashes.

3- I am not sure on how we can reply with 2 messages in the inbound.rs as all the messages we have just reply with one. Should we wrap the 2 messages in a new response type and send that instead ?

[teor2345]

The reply to this message is actually 2 replies. One will have the transactions in the mempool we found but we also need to send a notfound message with a list of not found hashes.

The minimal scope for this ticket is just the transactions.
(The ticket was opened before we did the mempool scope and design.)

It looks like zcashd and Zebra don't actually need notfound messages:
https://github.com/zcash/zcash/blob/e7b425298f6d9a54810cb7183f00be547e4d9415/src/main.cpp#L5632
https://github.com/ZcashFoundation/zebra/blob/main/zebra-network/src/peer/connection.rs#L115

So can we open another ticket for notfound, and do it later if we have time?

[oxarbitrage]

Ok, cool, that makes this ticket a lot easier to code. Will send a PR.

[teor2345]

It looks like zcashd and Zebra don't actually need notfound messages:
https://github.com/zcash/zcash/blob/e7b425298f6d9a54810cb7183f00be547e4d9415/src/main.cpp#L5632
https://github.com/ZcashFoundation/zebra/blob/main/zebra-network/src/peer/connection.rs#L115

So can we open another ticket for notfound, and do it later if we have time?

I opened ticket #2726 for notfound.