rpc: expose CBlockIndex::nTx in getblock(header) #13451

1. 
   instagibbs commented at 8:47 pm on June 12, 2018: member

   Recent publication of a weakness in Bitcoin’s merkle tree construction demonstrates many SPV applications vulnerable to an expensive to pull off yet still plausible attack: https://bitslog.wordpress.com/2018/06/09/leaf-node-weakness-in-bitcoin-merkle-tree-design/

   Including the coinbase in the txoutproof seems the most effective fix, however results in a significant efficiency downgrade. Transactors will not even know a priori what the size of their proof will be within a couple orders of magnitude, unless they use the mid-state of SHA2 as detailed in the blog post.

   Some applications, like Elements blockchain platform that take SPV-style proofs have optional access to a bitcoind to verify these proofs of inclusion and check depth in the chain. Returning CBlockIndex::nTx would allow an extremely easy and compact way of checking the depth of the tree, with no additional overhead to the codebase, and works with pruned nodes.

   getblockheader is arguably not the place for it, but as mentioned before, is a natural workflow for us checking depth of a block in a possibly pruned node.

   We should also ensure that verifytxoutproof ends up validating this depth fact as well, but left this for another PR.

2. in src/rpc/blockchain.cpp:698 in f9eda3e14e outdated

   694@@ -694,6 +695,7 @@ static UniValue getblockheader(const JSONRPCRequest& request)
   695             "  \"bits\" : \"1d00ffff\", (string) The bits\n"
   696             "  \"difficulty\" : x.xxx,  (numeric) The difficulty\n"
   697             "  \"chainwork\" : \"0000...1f3\"     (string) Expected number of hashes required to produce the current chain (in hex)\n"
   698+            "  \"nTx\" : n,             (numeric) The number of transactions in the block. This result can also be returned for pruned blocks, as it's stored in the block index.\n"
   

   ---

   ---

   

   MarcoFalke commented at 10:22 pm on June 12, 2018:

   This result can also be returned for pruned blocks, as it’s stored in the block index

   Should be a comment in the source code instead?

   I believe we have a pruning test, so it would make sense to add an assert_equal(nTx, whatever) there?

3. MarcoFalke added the label RPC/REST/ZMQ on Jun 12, 2018
4. MarcoFalke renamed this:
   expose CBlockIndex::nTx in getblockheader
   rpc: expose CBlockIndex::nTx in getblockheader
   on Jun 12, 2018
5. 
   MarcoFalke commented at 10:27 pm on June 12, 2018: member

   Similar to mediantime, this should also be exposed in getblock
6. expose CBlockIndex::nTx in getblock(header) 86edf4a2a5
7. instagibbs force-pushed on Jun 13, 2018
8. 
   instagibbs commented at 2:21 pm on June 13, 2018: member

   more tests, exposure and rewording as per @MarcoFalke suggestions
9. 
   instagibbs commented at 2:22 pm on June 13, 2018: member

   If it’s not too much trouble I’d also like this backported for 0.16.2
10. instagibbs renamed this:
    rpc: expose CBlockIndex::nTx in getblockheader
    rpc: expose CBlockIndex::nTx in getblock(header)
    on Jun 13, 2018
11. 
    MarcoFalke commented at 2:38 pm on June 13, 2018: member

    utACK 86edf4a2a502416ba8d6cebbce61030992f7ff6f

    Also, tagged for backport, since it is a rather trivial rpc change with tests already included.

12. MarcoFalke added this to the milestone 0.16.2 on Jun 13, 2018
13. MarcoFalke added the label Needs backport on Jun 13, 2018
14. 
    promag commented at 5:34 pm on June 13, 2018: member

    utACK 86edf4a.
15. 
    jtimon commented at 3:11 pm on June 14, 2018: contributor

    utACK 86edf4a2a502416ba8d6cebbce61030992f7ff6f
16. 
    laanwj commented at 5:39 pm on June 14, 2018: member

    utACK 86edf4a2a502416ba8d6cebbce61030992f7ff6f
17. laanwj merged this on Jun 14, 2018
18. laanwj closed this on Jun 14, 2018

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19. laanwj referenced this in commit cc7cbd756a on Jun 14, 2018
20. fanquake referenced this in commit cbd2f70b75 on Jun 15, 2018
21. 
    fanquake commented at 0:03 am on June 26, 2018: member

    Added to #13455 for backport.
22. fanquake removed the label Needs backport on Jun 26, 2018
23. laanwj referenced this in commit 7e74c54fed on Jul 9, 2018
24. laanwj referenced this in commit dac5374cce on Jul 9, 2018
25. HashUnlimited referenced this in commit 6f9ba098aa on Jan 11, 2019
26. jasonbcox referenced this in commit b209ed30d6 on Dec 20, 2019
27. PastaPastaPasta referenced this in commit 046b5b09e4 on Apr 7, 2020
28. PastaPastaPasta referenced this in commit f7d5e538df on Apr 8, 2020
29. jonspock referenced this in commit 38ba78b205 on Oct 2, 2020
30. jonspock referenced this in commit 8aa103bfe2 on Oct 5, 2020
31. jonspock referenced this in commit 682550b52a on Oct 10, 2020
32. PastaPastaPasta referenced this in commit 300572e4f1 on Dec 16, 2020
33. PastaPastaPasta referenced this in commit 46b08dada0 on Dec 18, 2020
34. PastaPastaPasta referenced this in commit 0da4f596bb on Dec 18, 2020
35. ckti referenced this in commit 381e268d45 on Mar 28, 2021
36. MarcoFalke locked this on Sep 8, 2021

Contributors
instagibbs MarcoFalke promag jtimon laanwj fanquake

Labels
RPC/REST/ZMQ

Milestone
0.16.2